strength and higher hardness values in comparison to the part near the external surface and bottom section, where relatively low hardness values were noticed.

<figure><img src="image_2638.png" /><figcaption>Fig.4: True stress-strain curves for top, middle and bottom slices of AA2011 FSC billet and comparision with hardness [16]</figcaption></figure>

Influence of materials by analyzing strength of single step FSC AA7075 billet

To assess the impact of materials, upsetting tests were conducted on miniaturized samples extracted from the center of each from AA7075 FSC billet section.

The trend for strength profiles of AA7075 FSC billets was found similar to AA2011. The highest strength was observed for the specimen at the top section followed by the sample at the middle slice. Concerning the bottom section of AA7075, the lowest strength value could be expected but due to poor chips bonding and the existence of defects such as air cavities, it was not possible to extract the upsetting sample Fig. 5. These issues are primarily attributed to the difficulty in consolidating AA7075 material. Comparing to AA2011 FSC billets for the specimen of top slice (Fig. 6) extracted from center, AA7075 upsetting sample showed higher strength but lower plastic deformation under the same manufacturing process and upsetting conditions. This trend can be attributed to the fact that AA7075 presents the class of aluminum alloys with the highest strength and relatively lower ductility compared to the other series of aluminum alloys.

On comparing the true stress-strain curves of the single-step FSC billet AA7075, extracted from the center of the top slice, with the as-received AA7075 sheet, the FSC billet exhibited lower strength. However, it is evident that this decrease in strength can be attributed to the premature
strength and higher hardness values in comparison to the part near the external surface and bottom section, where relatively low hardness values were noticed.

<figure><img src="image_2634.png" /><figcaption>Fig.4: True stress-strain curves for top, middle and bottom slices of AA2011 FSC billet and comparision with hardness [16]</figcaption></figure>

Influence of materials by analyzing strength of single step FSC AA7075 billet

To assess the impact of materials, upsetting tests were conducted on miniaturized samples extracted from the center of each from AA7075 FSC billet section.

The trend for strength profiles of AA7075 FSC billets was found similar to AA2011. The highest strength was observed for the specimen at the top section followed by the sample at the middle slice. Concerning the bottom section of AA7075, the lowest strength value could be expected but due to poor chips bonding and the existence of defects such as air cavities, it was not possible to extract the upsetting sample Fig. 5. These issues are primarily attributed to the difficulty in consolidating AA7075 material. Comparing to AA2011 FSC billets for the specimen of top slice (Fig. 6) extracted from center, AA7075 upsetting sample showed higher strength but lower plastic deformation under the same manufacturing process and upsetting conditions. This trend can be attributed to the fact that AA7075 presents the class of aluminum alloys with the highest strength and relatively lower ductility compared to the other series of aluminum alloys.

On comparing the true stress-strain curves of the single-step FSC billet AA7075, extracted from the center of the top slice, with the as-received AA7075 sheet, the FSC billet exhibited lower strength. However, it is evident that this decrease in strength can be attributed to the premature
failure of the specimen, as all samples extracted from the FSC billet AA7075 failed during upsetting tests.

<figure><img src="image_2639.png" /><figcaption>Fig. 5 True stress-strain curves of AA7075 for single step FSC billet samples x1 and y1</figcaption></figure>

<figure><img src="image_2640.png" /><figcaption>Fig. 6 True stress-strain curves for AA7075 and AA2011 as-received materials and single step FSC billets sample x1</figcaption></figure>

## Effect of Process variants

An improvement was noticed for hardness values and grain size distribution with minimal defects at the bottom of the billet in the case of multi-step FSC methods [14]. Therefore, the same upsetting testing method was also applied to the billets of multi-step FSC approach to compare results with the single-step approach. Employing advanced characterization techniques to assess the billet quality will allow to draw a better conclusion regarding the adoption of a more suitable FSC process variant.

**Double sided method:** This FSC approach was primarily introduced to enhance the mechanical properties especially at the bottom zone of the FSC billet. It is clear from Fig. 7 and Fig. 8 that an improvement occurred at bottom zone's strength compared to the middle zone for both AA2011 and AA7075. A similar enhancement was also noted in previous studies [14] during hardness measurements for AA2024-O. In the case of ductile material (AA2011), upsetting tests were successfully conducted for samples from all zones (top, middle, and bottom). However, for AA7075, premature failure occurred, possibly due to its less ductile nature inherited from the as-received material. In addition, highest plastic deformation was shown by specimens at top zone, followed by specimen at bottom zone and the lowest strength and plastic deformation shown by the upsetting specimen at the middle zone of the double sided FSC AA7075 billet.
failure of the specimen, as all samples extracted from the FSC billet AA7075 failed during upsetting tests.

<figure><img src="image_2635.png" /><figcaption>Fig. 5 True stress-strain curves of AA7075 for single step FSC billet samples x1 and y1</figcaption></figure>

<figure><img src="image_2636.png" /><figcaption>Fig. 6 True stress-strain curves for AA7075 and AA2011 as-received materials and single step FSC billets sample x1</figcaption></figure>

## Effect of Process variants

An improvement was noticed for hardness values and grain size distribution with minimal defects at the bottom of the billet in the case of multi-step FSC methods [14]. Therefore, the same upsetting testing method was also applied to the billets of multi-step FSC approach to compare results with the single-step approach. Employing advanced characterization techniques to assess the billet quality will allow to draw a better conclusion regarding the adoption of a more suitable FSC process variant.

**Double sided method:** This FSC approach was primarily introduced to enhance the mechanical properties especially at the bottom zone of the FSC billet. It is clear from Fig. 7 and Fig. 8 that an improvement occurred at bottom zone's strength compared to the middle zone for both AA2011 and AA7075. A similar enhancement was also noted in previous studies [14] during hardness measurements for AA2024-O. In the case of ductile material (AA2011), upsetting tests were successfully conducted for samples from all zones (top, middle, and bottom). However, for AA7075, premature failure occurred, possibly due to its less ductile nature inherited from the as-received material. In addition, highest plastic deformation was shown by specimens at top zone, followed by specimen at bottom zone and the lowest strength and plastic deformation shown by the upsetting specimen at the middle zone of the double sided FSC AA7075 billet.
<figure><img src="image_2641.png" /><figcaption>Fig. 7 True stress-strain curves for FSC AA2011 billet obtained double sided approach (Exp 3)</figcaption></figure>

<figure><img src="image_2642.png" /><figcaption>Fig. 8 True stress-strain curves for FSC AA7075 billet obtained double sided approach (Exp 4)</figcaption></figure>

**Mass addition method:** The mass addition approach involves recycling the desired input mass in a stepwise manner, typically in two steps. Primarily this method was also introduced to enhance the mechanical properties, especially in the bottom zone of the FSC billet.

Likewise double sided approach, mass addition also led to increase the strength of the bottom zone of the billet compared to the strength of middle section especially in the case of ductile material AA2011 (Fig. 9). On the other hand, the middle section was affected by air cavities and several other defects possibly indicating that favorable bonding conditions were not achieved between the billet of step 1 and step 2 during the mass addition approach for AA7075. Comparing to single-step approach, the defective zone with air cavities moved from bottom to middle section (Fig. 10).

However, both the top and bottom specimens exhibited the highest plastic deformation when compared to the single-step and double-sided approaches.

<figure><img src="image_2643.png" /><figcaption>Fig. 9 True stress-strain curves for FSC AA2011 billet obtained through mass addition approach (Exp 5)</figcaption></figure>

<figure><img src="image_2644.png" /><figcaption>Fig. 10 True stress-strain curves for FSC AA7075 billet obtained through mass addition approach (Exp 6).</figcaption></figure>

Overall, the local strength of the FSC billet depends on various factors, including the input material, process variant, and process conditions. The double-sided approach of the FSC process exhibited the highest strength, followed by mass addition and single-step methods, respectively.
<figure><img src="image_2637.png" /><figcaption>Fig. 7 True stress-strain curves for FSC AA2011 billet obtained double sided approach (Exp 3)</figcaption></figure>

<figure><img src="image_2638.png" /><figcaption>Fig. 8 True stress-strain curves for FSC AA7075 billet obtained double sided approach (Exp 4)</figcaption></figure>

**Mass addition method:** The mass addition approach involves recycling the desired input mass in a stepwise manner, typically in two steps. Primarily this method was also introduced to enhance the mechanical properties, especially in the bottom zone of the FSC billet.

Likewise double sided approach, mass addition also led to increase the strength of the bottom zone of the billet compared to the strength of middle section especially in the case of ductile material AA2011 (Fig. 9). On the other hand, the middle section was affected by air cavities and several other defects possibly indicating that favorable bonding conditions were not achieved between the billet of step 1 and step 2 during the mass addition approach for AA7075. Comparing to single-step approach, the defective zone with air cavities moved from bottom to middle section (Fig. 10).

However, both the top and bottom specimens exhibited the highest plastic deformation when compared to the single-step and double-sided approaches.

<figure><img src="image_2639.png" /><figcaption>Fig. 9 True stress-strain curves for FSC AA2011 billet obtained through mass addition approach (Exp 5)</figcaption></figure>

<figure><img src="image_2640.png" /><figcaption>Fig. 10 True stress-strain curves for FSC AA7075 billet obtained through mass addition approach (Exp 6).</figcaption></figure>

Overall, the local strength of the FSC billet depends on various factors, including the input material, process variant, and process conditions. The double-sided approach of the FSC process exhibited the highest strength, followed by mass addition and single-step methods, respectively.
In the context of material, the performance of the FSC billet improved with the ductility of the material. For the sake of better understanding the top zone was selected as no FSC billet was found defective at this zone (Fig. 11). The top zone exhibited significantly higher strength than the as-received strength in the case of AA2011 for all process variants. For AA7075, the strength of FSC multi-step approach billet was comparable to as-received while single step approach billet strength was relatively very low. Further, the bottom zone was found defective in single step, which then moved to the middle section in the case of mass-addition method. This suggests that the double-sided approach is the only potential FSC process variant for recycling very high or low ductile aluminum alloy chips.

<figure><img src="image_2645.png" /><figcaption>Fig. 11 Comparison of true stress-strain curves for as received material and top slice (x1 sample) of different FSC billets for AA2011 (on left), and AA7075 (on right)</figcaption></figure>

**Conclusion**

Overall, the performance of upsetting tests on miniaturized samples of FSC billet proved effective in obtaining local mechanical properties. This study also provides supportive results in confirming the gradation in the properties of FSC billet.

The flow curves were found in good agreement with the hardness trend across the billet section. A higher hardness value in a specific zone corresponds to increased strength, and conversely, a lower hardness value in another zone corresponds to reduced strength.

Further, this study highlighted the unique feature of the mass addition approach during recycling AA7075 chips. In particular, the failure of upsetting samples was noticed at the mid-zone, due to porosity and defects. This aspect was not possible to analyze during hardness measurement.

Concerning the process variants, double sided approach proved effective for producing FSC billets and offering relatively better consolidation to the FSCed billet and therefore outperformed single-step and mass addition methods.

Regarding the material aspect, upsetting samples were successfully performed on billets of AA2011 while failures occurred during AA7075 billet for all FSC process variants, highlighting the positive influence of material ductility on upsetting test outcomes.

The future work can be dedicated to assessing the formability of recycled billets through forgeability tests. Additionally, new possibilities should be explored for developing more advanced materials using the FSC process.

**Acknowledgement**

This study was funded by Italian MUR funds through European Union-NEXT Generation EU scheme; title of the project: "Finalizing processes for multi-material based Functionally Graded billets and wires obtained through solid state recycling operations of aluminum alloy chips - FULL RECYCLE", PRIN 2022.
In the context of material, the performance of the FSC billet improved with the ductility of the material. For the sake of better understanding the top zone was selected as no FSC billet was found defective at this zone (Fig. 11). The top zone exhibited significantly higher strength than the as-received strength in the case of AA2011 for all process variants. For AA7075, the strength of FSC multi-step approach billet was comparable to as-received while single step approach billet strength was relatively very low. Further, the bottom zone was found defective in single step, which then moved to the middle section in the case of mass-addition method. This suggests that the double-sided approach is the only potential FSC process variant for recycling very high or low ductile aluminum alloy chips.

<figure><img src="image_2641.png" /><figcaption>Fig. 11 Comparison of true stress-strain curves for as received material and top slice (x1 sample) of different FSC billets for AA2011 (on left), and AA7075 (on right)</figcaption></figure>

## Conclusion

Overall, the performance of upsetting tests on miniaturized samples of FSC billet proved effective in obtaining local mechanical properties. This study also provides supportive results in confirming the gradation in the properties of FSC billet.

The flow curves were found in good agreement with the hardness trend across the billet section. A higher hardness value in a specific zone corresponds to increased strength, and conversely, a lower hardness value in another zone corresponds to reduced strength.

Further, this study highlighted the unique feature of the mass addition approach during recycling AA7075 chips. In particular, the failure of upsetting samples was noticed at the mid-zone, due to porosity and defects. This aspect was not possible to analyze during hardness measurement.

Concerning the process variants, double sided approach proved effective for producing FSC billets and offering relatively better consolidation to the FSCed billet and therefore outperformed single-step and mass addition methods.

Regarding the material aspect, upsetting samples were successfully performed on billets of AA2011 while failures occurred during AA7075 billet for all FSC process variants, highlighting the positive influence of material ductility on upsetting test outcomes.

The future work can be dedicated to assessing the formability of recycled billets through forgeability tests. Additionally, new possibilities should be explored for developing more advanced materials using the FSC process.

## Acknowledgement

This study was funded by Italian MUR funds through European Union-NEXT Generation EU scheme; title of the project: "Finalizing processes for multi-material based Functionally Graded billets and wires obtained through solid state recycling operations of aluminum alloy chips - FULL RECYCLE", PRIN 2022.
## References

[1] Information on https://alucycle.international-aluminium.org/public-access/

[2] T.G. Gutowski, S. Sahni, J.M. Allwood, M.F. Ashby, E. Worrell, The energy required to produce materials: constraints on energy-intensity improvements, parameters of demand, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 371.1986 (2013): 20120003. https://doi.org/10.1098/rsta.2012.0003

[3] D. Raabe et al., Making sustainable aluminum by recycling scrap: The science of “dirty” alloys, Progress in Materials Science. (2022): 100947. https://doi.org/10.1016/j.pmatsci.2022.100947

[4] Information on https://www.iea.org/reports/material-efficiency-in-clean-energy-transitions

[5] J.R. Duflou, A.E. Tekkaya, M. Haase, T. Welo, K. Vanmeensel, K Kellens, W Dewulf, D. Paraskevas, Environmental assessment of solid state recycling routes for aluminium alloys: can solid state processes significantly reduce the environmental impact of aluminium recycling?. CIRP Annals (2015) 64(1) pp 37-40. https://doi.org/10.1016/j.cirp.2015.04.051

[6] U.M.J. Boin and M. Bertram. Melting standardized aluminum scrap: A mass balance model for Europe. Jom, 57(8), pp.26-33. https://doi.org/10.1007/s11837-005-0164-4

[7] B. Wan, W. Chen, T. Lu, F. Liu, Z. Jiang, M. Mao, Review of solid state recycling of aluminum chips, Resources, Conservation and Recycling.125 (2017):37-47. https://doi.org/10.1016/j.resconrec.2017.06.004

[8] M. Haase, N.B. Khalifa, A.E. Tekkaya, W.Z. Misiolek, Improving mechanical properties of chip-based aluminum extrudates by integrated extrusion and equal channel angular pressing (iECAP) Materials Science and Engineering A (2012) 539 pp 194-204. https://doi.org/10.1016/j.msea.2012.01.081

[9] F. Widerøe, T. Welo, Using contrast material techniques to determine metal flow in screw extrusion of aluminium. Journal of Materials Processing Technology (2013) 213(7) pp 1007-18. https://doi.org/10.1016/j.jmatprotec.2012.11.013

[10] D. Paraskevas, S. Dadbakhsh, J. Vleugels, K Vanmeensel, W Dewulf, J Duflou, Solid state recycling of pure Mg and AZ31 Mg machining chips via spark plasma sintering Materials & Design (2016) 109 520-29. https://doi.org/10.1016/j.matdes.2016.07.082

[11] G. Buffa, D. Baffari, G. Ingarao, L. Fratini. Uncovering technological and environmental potentials of aluminum alloy scraps recycling through friction stir consolidation, International Journal of Precision Engineering and Manufacturing-Green Technology (2020) 7/5 pp 955-64. https://doi.org/10.1007/s40684-019-00159-5

[12] A. Latif, G. Ingarao and L. Fratini. Multi-material based functionally graded billets manufacturing through friction stir consolidation of aluminium alloys chips. CIRP Annals.

[13] W. Tang, A.P. Reynolds, Friction consolidation of aluminum chips, Friction Stir Welding and Processing VI. 289 (2011). https://doi.org/10.1002/9781118062302.ch34

[14] A. Latif, G. Ingarao, M. Gucciardi, L. Fratini, A novel approach to enhance mechanical properties during recycling of aluminum alloy scrap through friction stir consolidation The International Journal of Advanced Manufacturing Technology (2022) 119(3) pp 1989-2005]. https://doi.org/10.1007/s00170-021-08346-y

[15] P. Hetz, P, M. Kraus and M. Merklein. Characterization of sheet metal components by using an upsetting test with miniaturized cylindrical specimen. CIRP Annals.

[16] LATIF, A., INGARAO, G., FRATINI, L., HETZ, P., & MERKLEIN, M. (2023). Characterization of friction stir consolidated recycled billet by uniaxial compression tests with miniaturized cylindrical specimen. MATERIALS RESEARCH PROCEEDINGS, 28, 1997-2004. https://doi.org/10.21741/9781644902479-215

[17] Puleo, R., Latif, A., Ingarao, G., Di Lorenzo, R., & Fratini, L. (2023). Solid bonding criteria design for aluminum chips recycling through Friction Stir Consolidation. Journal of Materials Processing Technology, 319, 118080. https://doi.org/10.1016/j.jmatprotec.2023.118080
## References

[1] Information on https://alucycle.international-aluminium.org/public-access/

[2] T.G. Gutowski, S. Sahni, J.M. Allwood, M.F. Ashby, E. Worrell, The energy required to produce materials: constraints on energy-intensity improvements, parameters of demand, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 371.1986 (2013): 20120003. https://doi.org/10.1098/rsta.2012.0003

[3] D. Raabe et al., Making sustainable aluminum by recycling scrap: The science of “dirty” alloys, Progress in Materials Science. (2022): 100947. https://doi.org/10.1016/j.pmatsci.2022.100947

[4] Information on https://www.iea.org/reports/material-efficiency-in-clean-energy-transitions

[5] J.R. Duflou, A.E. Tekkaya, M. Haase, T. Welo, K. Vanmeensel, K Kellens, W Dewulf, D. Paraskevas, Environmental assessment of solid state recycling routes for aluminium alloys: can solid state processes significantly reduce the environmental impact of aluminium recycling?. CIRP Annals (2015) 64(1) pp 37-40. https://doi.org/10.1016/j.cirp.2015.04.051

[6] U.M.J. Boin and M. Bertram. Melting standardized aluminum scrap: A mass balance model for Europe. Jom, 57(8), pp.26-33. https://doi.org/10.1007/s11837-005-0164-4

[7] B. Wan, W. Chen, T. Lu, F. Liu, Z. Jiang, M. Mao, Review of solid state recycling of aluminum chips, Resources, Conservation and Recycling.125 (2017):37-47. https://doi.org/10.1016/j.resconrec.2017.06.004

[8] M. Haase, N.B. Khalifa, A.E. Tekkaya, W.Z. Misiolek, Improving mechanical properties of chip-based aluminum extrudates by integrated extrusion and equal channel angular pressing (iECAP) Materials Science and Engineering A (2012) 539 pp 194-204. https://doi.org/10.1016/j.msea.2012.01.081

[9] F. Widerøe, T. Welo, Using contrast material techniques to determine metal flow in screw extrusion of aluminium. Journal of Materials Processing Technology (2013) 213(7) pp 1007-18. https://doi.org/10.1016/j.jmatprotec.2012.11.013

[10] D. Paraskevas, S. Dadbakhsh, J. Vleugels, K Vanmeensel, W Dewulf, J Duflou, Solid state recycling of pure Mg and AZ31 Mg machining chips via spark plasma sintering Materials & Design (2016) 109 520-29. https://doi.org/10.1016/j.matdes.2016.07.082

[11] G. Buffa, D. Baffari, G. Ingarao, L. Fratini. Uncovering technological and environmental potentials of aluminum alloy scraps recycling through friction stir consolidation, International Journal of Precision Engineering and Manufacturing-Green Technology (2020) 7/5 pp 955-64. https://doi.org/10.1007/s40684-019-00159-5

[12] A. Latif, G. Ingarao and L. Fratini. Multi-material based functionally graded billets manufacturing through friction stir consolidation of aluminium alloys chips. CIRP Annals.

[13] W. Tang, A.P. Reynolds, Friction consolidation of aluminum chips, Friction Stir Welding and Processing VI. 289 (2011). https://doi.org/10.1002/9781118062302.ch34

[14] A. Latif, G. Ingarao, M. Gucciardi, L. Fratini, A novel approach to enhance mechanical properties during recycling of aluminum alloy scrap through friction stir consolidation The International Journal of Advanced Manufacturing Technology (2022) 119(3) pp 1989-2005]. https://doi.org/10.1007/s00170-021-08346-y

[15] P. Hetz, P, M. Kraus and M. Merklein. Characterization of sheet metal components by using an upsetting test with miniaturized cylindrical specimen. CIRP Annals.

[16] LATIF, A., INGARAO, G., FRATINI, L., HETZ, P., & MERKLEIN, M. (2023). Characterization of friction stir consolidated recycled billet by uniaxial compression tests with miniaturized cylindrical specimen. MATERIALS RESEARCH PROCEEDINGS, 28, 1997-2004. https://doi.org/10.21741/9781644902479-215

[17] Puleo, R., Latif, A., Ingarao, G., Di Lorenzo, R., & Fratini, L. (2023). Solid bonding criteria design for aluminum chips recycling through Friction Stir Consolidation. Journal of Materials Processing Technology, 319, 118080. https://doi.org/10.1016/j.jmatprotec.2023.118080
# Investigation of the reshaping process by hydroforming using magnetorheological fluids

PICCININNI Antonio¹,ᵃ*, CUSANNO Angela¹,ᵇ, INGARAO Giuseppe²,ᶜ, PALUMBO Gianfranco¹,ᵈ and FRATINI Livan²,ᵉ

¹Dept. of Mechanics, Mathematics and Management, Politecnico di Bari, Via Orabona 4, 70125 Bari

²Department of Engineering, University of Palermo, Viale delle Scienze, Palermo, 90128, Italy

ᵃantonio.piccininni@poliba.it, ᵇangela.cusanno@poliba.it, ᶜgiuseppe.ingarao@unipa.it,

ᵈgianfranco.palumbo@poliba.it, ᶜlivan.fratini@unipa.it

**Keywords:** Aluminium, Reshaping, Hydroforming, Magnetorheological Fluids

**Abstract.** The reshaping of End-of-Life (EoL) components is considered a promising approach to put in practice one of the virtuous strategies of the Circular Economy. The heterogeneity in a EoL part, the alternation of deformed/undeformed regions resulting from the manufacturing process, may hinder an effective reshaping into a brand new geometry. Therefore, the proper selection among the sheet metal forming processes to overcome such a limitation is of utmost importance. The present work, based on a full numerical approach, investigates the reshaping process of a disc-shaped EoL by hydroforming using a Magneto Rheological Fluid (MRF) as the forming medium. The basic idea is to combine the advantages coming from the flexibility of the hydroforming process with those from the MRF whose behavior (i.e. its viscosity affecting the shear stresses at the contact with the blank) can be tailored by adjusting the applied magnetic field. The reshaping approach is investigated according to two separate routes, differentiated by a different target geometry. A factorial plan of numerical simulations allowed to investigate the effect of the MRF behaviour as well as the geometry of the EoL component on the quality of the reshaped part, expressed in terms of accuracy in the final shape and thickness distribution.

**Introduction**

The production of the five key materials (aluminum, steel, cement, paper, and plastic) is responsible for more than 50% of emitted greenhouse gases (GHG) each year [1]. Primary aluminum production is the most energy and emissions intensive among the aforementioned materials [2]. The main approach for reducing the primary production and decoupling the resource depletion from the economic growth is the implementation of Circular Economy Strategies [3]. Turning End-of-Life (EoL) products/components directly into new products/components is considered a promising route to be investigated. Remanufacturing and Reshaping are considered two strategies, among the five enlisted by Cooper and Allwood [4], to reuse EoL in line with the pillars of the Circular Economy. At the same time, it should be pointed out that a successful application of the Remanufacturing/Reshaping strategies needs the choice of innovative processes or, alternatively, the re-design of the conventional ones. Moreover, sheet metal based accounts for a large share of the semi-finished product: thus, investigating new reuse solution for sheet metal based EoL components would be of utmost importance. As it is documented in the scientific literature, flexible sheet metal forming processes are ideal candidate to put in practice the principle of the Reshaping, being also able to overcome the limitation coming from an already deformed EoL component. As an example, Brosius et al. [5] describe the reshaping of a car hood into a rectangular sheet metal component by the hydroforming process. Takano et al. [6], once flattened a bent sheet, applied the Single Point Incremental Forming (SPIF) to reshape the blank into a new

<figure><img src="image_2646.png" /></figure>
# Investigation of the reshaping process by hydroforming using magnetorheological fluids

PICCININNI Antonio¹,ᵃ*, CUSANNO Angela¹,ᵇ, INGARAO Giuseppe²,ᶜ, PALUMBO Gianfranco¹,ᵈ and FRATINI Livan²,ᵉ

¹Dept. of Mechanics, Mathematics and Management, Politecnico di Bari, Via Orabona 4, 70125 Bari

²Department of Engineering, University of Palermo, Viale delle Scienze, Palermo, 90128, Italy

ᵃantonio.piccininni@poliba.it, ᵇangela.cusanno@poliba.it, ᶜgiuseppe.ingarao@unipa.it,

ᵈgianfranco.palumbo@poliba.it, ᶜlivan.fratini@unipa.it

**Keywords:** Aluminium, Reshaping, Hydroforming, Magnetorheological Fluids

**Abstract.** The reshaping of End-of-Life (EoL) components is considered a promising approach to put in practice one of the virtuous strategies of the Circular Economy. The heterogeneity in a EoL part, the alternation of deformed/undeformed regions resulting from the manufacturing process, may hinder an effective reshaping into a brand new geometry. Therefore, the proper selection among the sheet metal forming processes to overcome such a limitation is of utmost importance. The present work, based on a full numerical approach, investigates the reshaping process of a disc-shaped EoL by hydroforming using a Magneto Rheological Fluid (MRF) as the forming medium. The basic idea is to combine the advantages coming from the flexibility of the hydroforming process with those from the MRF whose behavior (i.e. its viscosity affecting the shear stresses at the contact with the blank) can be tailored by adjusting the applied magnetic field. The reshaping approach is investigated according to two separate routes, differentiated by a different target geometry. A factorial plan of numerical simulations allowed to investigate the effect of the MRF behaviour as well as the geometry of the EoL component on the quality of the reshaped part, expressed in terms of accuracy in the final shape and thickness distribution.

**Introduction**

The production of the five key materials (aluminum, steel, cement, paper, and plastic) is responsible for more than 50% of emitted greenhouse gases (GHG) each year [1]. Primary aluminum production is the most energy and emissions intensive among the aforementioned materials [2]. The main approach for reducing the primary production and decoupling the resource depletion from the economic growth is the implementation of Circular Economy Strategies [3]. Turning End-of-Life (EoL) products/components directly into new products/components is considered a promising route to be investigated. Remanufacturing and Reshaping are considered two strategies, among the five enlisted by Cooper and Allwood [4], to reuse EoL in line with the pillars of the Circular Economy. At the same time, it should be pointed out that a successful application of the Remanufacturing/Reshaping strategies needs the choice of innovative processes or, alternatively, the re-design of the conventional ones. Moreover, sheet metal based accounts for a large share of the semi-finished product: thus, investigating new reuse solution for sheet metal based EoL components would be of utmost importance. As it is documented in the scientific literature, flexible sheet metal forming processes are ideal candidate to put in practice the principle of the Reshaping, being also able to overcome the limitation coming from an already deformed EoL component. As an example, Brosius et al. [5] describe the reshaping of a car hood into a rectangular sheet metal component by the hydroforming process. Takano et al. [6], once flattened a bent sheet, applied the Single Point Incremental Forming (SPIF) to reshape the blank into a new

<figure><img src="image_2642.png" /></figure>
geometry. Recently, the authors of the present paper proposed a new Reshaping approach based on the Sheet Hydroforming (SHF) process: blanks with a square deep drawn feature located in different positions was successfully reshaped according to a new brand benchmark geometry [7]. Nevertheless, the research for process variants allowing to further improve the performance of the SHF process is still an open question: as an example, MagnetoRheological Pressure Forming (MRPF) is gaining interest since the thickness and the strain distribution on the formed part can be affected by properly changing the properties of the forming medium [8]. In the case of MRPF, the forming medium is a MagnetoRheological Fluid (MRF), that is based on a suspension of magnetically responsive particles in a liquid carrier, whose rheological behaviour (e.g., its viscosity) can be changed quickly and reversibly if subjected to a magnetic field [9]. MRFs are currently used in the automotive field for brakes [10] and clutches [11], but also in sheet metal forming applications [12]. In the present work the adoption of a MRF as the forming medium in a reshaping approach by sheet hydroforming was numerically simulated. The aim is to evaluate to what extent the variation in the MRF behaviour (due to the change in the applied magnetic field) allows to effectively reshape an EoL component represented by a circular blank with a deep drawn feature. The main influencing parameters (those related to the geometrical properties of the deep drawing feature and those related to the MRF behaviour) were changed according to a factorial plan to evaluate how they affected the final shape and thickness distribution of the reshaped part. In order to make the approach more general, the reshaping was simulated according to two different targets, a frustum-shaped geometry and a hemispherical one.

## Methodology

The reshaping approach by SHF adopting a MRF as the forming media was simulated according to two different routes: (i) the first one, indicated as ROUTE#1, is based on an initial deep drawing step to obtain the EoL component that is subsequently forced to copy a truncated cone die (see Fig. 1a); (ii) in the second one (indicated as ROUTE#2), the same EoL by deep drawing is deformed by the MRF in a free-bulging-like condition up to a target height (see Fig. 1b).

<figure><img src="image_2647.png" /><figcaption>Fig. 1 The reshaping approach: a) target die for the ROUTE#1, b) target shape for the ROUTE#2 (dimensions are in mm)</figcaption></figure>

**FE model of the reshaping routes.** The whole process was simulated using the FE commercial code Abaqus (v2017) and was based on two consecutive steps (both were solved using the dynamic implicit solver). By taking advantages from a 2D axisymmetric approach, the circular blank was initially deformed by deep drawing (to obtain the EoL component) and subsequently reshaped by the action of the MRF. The two investigated approaches are resumed in Fig. 2.
geometry. Recently, the authors of the present paper proposed a new Reshaping approach based on the Sheet Hydroforming (SHF) process: blanks with a square deep drawn feature located in different positions was successfully reshaped according to a new brand benchmark geometry [7]. Nevertheless, the research for process variants allowing to further improve the performance of the SHF process is still an open question: as an example, MagnetoRheological Pressure Forming (MRPF) is gaining interest since the thickness and the strain distribution on the formed part can be affected by properly changing the properties of the forming medium [8]. In the case of MRPF, the forming medium is a MagnetoRheological Fluid (MRF), that is based on a suspension of magnetically responsive particles in a liquid carrier, whose rheological behaviour (e.g., its viscosity) can be changed quickly and reversibly if subjected to a magnetic field [9]. MRFs are currently used in the automotive field for brakes [10] and clutches [11], but also in sheet metal forming applications [12]. In the present work the adoption of a MRF as the forming medium in a reshaping approach by sheet hydroforming was numerically simulated. The aim is to evaluate to what extent the variation in the MRF behaviour (due to the change in the applied magnetic field) allows to effectively reshape an EoL component represented by a circular blank with a deep drawn feature. The main influencing parameters (those related to the geometrical properties of the deep drawing feature and those related to the MRF behaviour) were changed according to a factorial plan to evaluate how they affected the final shape and thickness distribution of the reshaped part. In order to make the approach more general, the reshaping was simulated according to two different targets, a frustum-shaped geometry and a hemispherical one.

## Methodology

The reshaping approach by SHF adopting a MRF as the forming media was simulated according to two different routes: (i) the first one, indicated as ROUTE#1, is based on an initial deep drawing step to obtain the EoL component that is subsequently forced to copy a truncated cone die (see Fig. 1a); (ii) in the second one (indicated as ROUTE#2), the same EoL by deep drawing is deformed by the MRF in a free-bulging-like condition up to a target height (see Fig. 1b).

<figure><img src="image_2643.png" /><figcaption>Fig. 1 The reshaping approach: a) target die for the ROUTE#1, b) target shape for the ROUTE#2 (dimensions are in mm)</figcaption></figure>

**FE model of the reshaping routes.** The whole process was simulated using the FE commercial code Abaqus (v2017) and was based on two consecutive steps (both were solved using the dynamic implicit solver). By taking advantages from a 2D axisymmetric approach, the circular blank was initially deformed by deep drawing (to obtain the EoL component) and subsequently reshaped by the action of the MRF. The two investigated approaches are resumed in Fig. 2.
<figure><img src="image_2648.png" /><figcaption>Fig. 2 Overview of the two investigated Reshaping routes</figcaption></figure>

Regardless of the investigated route, the first step to obtain the EoL component was simulated by modelling the tools (punch, blankholder and die) as analytical rigid wire-based bodies and the blank as a shell deformable body (initial diameter of 66 mm and thickness of 0.5 mm). The blank was discretized by means of 0.1 mm SAX1 (2 nodes, one-point integration) elements. Contacts pairs between the blank and the tools were modelled as surface-to-surface component, setting the friction coefficient of 0.1 (penalty formulation). Material data of the blank (flow curve and limit forming curve) were taken from literature [7]. As for the reshaping step, the MRF was modelled as a solid axisymmetric body and discretized by means of 3300 CAX4H (4-node bilinear, hybrid with constant pressure) elements whose size was progressively refined (from 1 to 0.25 mm) in proximity of the contact with the EoL. The MRF was modelled as purely elastic body and material data (Young's modulus and Poisson's ratio) expressed as a function of the applied magnetic field (the determination of the elastic properties is detailed in [13]). The MRF exerted its action on the blank because of the vertical displacement of a punch (indicated as *Punch-MRF* in Fig. 1) modelled as an analytical rigid body (as the other tools). During the reshaping step, the blank peripheral node was completely constrained (thus mainly inducing a stretching-based deformation mechanism).

**FE simulation of different reshaping scenarios.** The effectiveness of the reshaping step, in terms of overall quality of the final component, was judged to be mainly dependent on the value of the applied magnetic field (that, in turns, affects the MRF behaviour) and on the geometry of EoL part (basically, the geometric properties of the deep drawn feature). Therefore, a factorial plan of 25 simulations was created based on a Central Composite Design by varying the following set of parameters: (i) the radial position of punch during the deep drawn (indicated by *r* in Fig. 3), (ii) the diameter of the punch (indicated by *d*<sub>p</sub> in Fig. 3), (iii) the punch stroke during the deep drawing step (*h*) and (iv) the applied magnetic field (*B*).
<figure><img src="image_2644.png" /><figcaption>Fig. 2 Overview of the two investigated Reshaping routes</figcaption></figure>

Regardless of the investigated route, the first step to obtain the EoL component was simulated by modelling the tools (punch, blankholder and die) as analytical rigid wire-based bodies and the blank as a shell deformable body (initial diameter of 66 mm and thickness of 0.5 mm). The blank was discretized by means of 0.1 mm SAX1 (2 nodes, one-point integration) elements. Contacts pairs between the blank and the tools were modelled as surface-to-surface component, setting the friction coefficient of 0.1 (penalty formulation). Material data of the blank (flow curve and limit forming curve) were taken from literature [7]. As for the reshaping step, the MRF was modelled as a solid axisymmetric body and discretized by means of 3300 CAX4H (4-node bilinear, hybrid with constant pressure) elements whose size was progressively refined (from 1 to 0.25 mm) in proximity of the contact with the EoL. The MRF was modelled as purely elastic body and material data (Young's modulus and Poisson's ratio) expressed as a function of the applied magnetic field (the determination of the elastic properties is detailed in [13]). The MRF exerted its action on the blank because of the vertical displacement of a punch (indicated as *Punch-MRF* in Fig. 1) modelled as an analytical rigid body (as the other tools). During the reshaping step, the blank peripheral node was completely constrained (thus mainly inducing a stretching-based deformation mechanism).

**FE simulation of different reshaping scenarios.** The effectiveness of the reshaping step, in terms of overall quality of the final component, was judged to be mainly dependent on the value of the applied magnetic field (that, in turns, affects the MRF behaviour) and on the geometry of EoL part (basically, the geometric properties of the deep drawn feature). Therefore, a factorial plan of 25 simulations was created based on a Central Composite Design by varying the following set of parameters: (i) the radial position of punch during the deep drawn (indicated by *r* in Fig. 3), (ii) the diameter of the punch (indicated by *d*<sub>p</sub> in Fig. 3), (iii) the punch stroke during the deep drawing step (*h*) and (iv) the applied magnetic field (*B*).
<figure><img src="image_2649.png" /><figcaption>Fig. 3 Geometrical parameters affecting the deep drawn feature.</figcaption></figure>

The mentioned quantities were varied within their relative variation ranges, listed in Table 1.

<table><caption>Table 1 Intervals range of the input parameters</caption><thead><tr><td>Input parameter</td><td>Lower Bound</td><td>Upper Bound</td></tr></thead><tbody><tr><td>r</td><td>0 mm</td><td>15 mm</td></tr><tr><td>d<sub>p</sub></td><td>4 mm</td><td>6 mm</td></tr><tr><td>h</td><td>1 mm</td><td>1.8 mm</td></tr><tr><td>B</td><td>0 mT</td><td>3.8 mT</td></tr></tbody></table>

The results of each simulation were analyzed in terms of error-based response outputs to evaluate the effectiveness of the reshaping step. More in details, the two error functions were meant to quantify the average percentage deviation in terms of thickness distribution (Eq. 1) and final shape (Eq. 2). The reference case, against which the two error functions were calculated, was: (i) the deformed blank only by the action the MRF (in absence of applied magnetic field) for the ROUTE#1 and (ii) the target geometry shown in Fig. 1b for the ROUTE#2.

$$Err_{avg,th}[\%] = \frac{1}{N} \sum_{i=1}^{N} \left( \frac{t_{i,ref} - t_{i,comp}}{t_{i,ref}} \cdot 100 \right) \qquad (1)$$

$$Err_{avg,sh}[\%] = \frac{1}{N} \sum_{i=1}^{N} \left( \frac{u_{i,ref} - u_{i,comp}}{u_{i,ref}} \cdot 100 \right) \qquad (2)$$

The subscripts *ref* and *comp* refer to the quantities (nodal thickness *t* and displacement *u*) extracted from the reference case and from each simulated condition, respectively; *N* is the total number of nodes discretizing the blank. The plan of 25 simulations was simulated for both the reshaping routes.

## Results and discussion

**Reshaping ROUTE#1.** The table containing the input and the response values from each of the simulated conditions was imported into the working environment of the integration platform modeFRONTIER (v 2023R3). The values of the two response variables were fitted by means of interpolating Response Surfaces (RS) trained by means of Radial Basis Functions (RBF). In order to choose the most effective kernel (among Hardy's MultiQuadrics, Inverse MultiQuadrics, Gaussians, Duchon's Polyharmonic Splines and Wendland's Compactly Supported), data were split into two subgroups: the training set (generally containing between 80% and 90% of the whole
<figure><img src="image_2645.png" /><figcaption>Fig. 3 Geometrical parameters affecting the deep drawn feature.</figcaption></figure>

The mentioned quantities were varied within their relative variation ranges, listed in Table 1.

<table><caption>Table 1 Intervals range of the input parameters</caption><thead><tr><td>Input parameter</td><td>Lower Bound</td><td>Upper Bound</td></tr></thead><tbody><tr><td>r</td><td>0 mm</td><td>15 mm</td></tr><tr><td>d<sub>p</sub></td><td>4 mm</td><td>6 mm</td></tr><tr><td>h</td><td>1 mm</td><td>1.8 mm</td></tr><tr><td>B</td><td>0 mT</td><td>3.8 mT</td></tr></tbody></table>

The results of each simulation were analyzed in terms of error-based response outputs to evaluate the effectiveness of the reshaping step. More in details, the two error functions were meant to quantify the average percentage deviation in terms of thickness distribution (Eq. 1) and final shape (Eq. 2). The reference case, against which the two error functions were calculated, was: (i) the deformed blank only by the action the MRF (in absence of applied magnetic field) for the ROUTE#1 and (ii) the target geometry shown in Fig. 1b for the ROUTE#2.

$$Err_{avg,th}[\%] = \frac{1}{N} \sum_{i=1}^{N} \left( \frac{t_{i,ref} - t_{i,comp}}{t_{i,ref}} \cdot 100 \right) \qquad (1)$$

$$Err_{avg,sh}[\%] = \frac{1}{N} \sum_{i=1}^{N} \left( \frac{u_{i,ref} - u_{i,comp}}{u_{i,ref}} \cdot 100 \right) \qquad (2)$$

The subscripts *ref* and *comp* refer to the quantities (nodal thickness *t* and displacement *u*) extracted from the reference case and from each simulated condition, respectively; *N* is the total number of nodes discretizing the blank. The plan of 25 simulations was simulated for both the reshaping routes.

## Results and discussion

**Reshaping ROUTE#1.** The table containing the input and the response values from each of the simulated conditions was imported into the working environment of the integration platform modeFRONTIER (v 2023R3). The values of the two response variables were fitted by means of interpolating Response Surfaces (RS) trained by means of Radial Basis Functions (RBF). In order to choose the most effective kernel (among Hardy's MultiQuadrics, Inverse MultiQuadrics, Gaussians, Duchon's Polyharmonic Splines and Wendland's Compactly Supported), data were split into two subgroups: the training set (generally containing between 80% and 90% of the whole
set) that is used to actually train the RS and the validation set (containing the remaining part of the data table) used to evaluate the predictive capability of the trained model. The Err<sub>avg,sh</sub> and Err<sub>avg,th</sub> were accurately fitted by the RBF Gaussian and Hardy's MultiQuadrics kernels, respectively.

<figure><img src="image_2650.png" /><figcaption>Fig. 4 Reshaping ROUTE#1: RS on the response variable Err<sub>avg,sh</sub> (a, b) and on the response variable Err<sub>avg,th</sub> (c, d).</figcaption></figure>

The 3D visualization of the regression model in Fig. 4a suggests that the final geometry of the reshaped part was slightly influenced by the punch diameter used during the deep drawing step: setting, in fact, the $d_p$ at 4 mm the error variable is weakly influenced. Similarly, the applied magnetic field showed an almost negligible influence as well. On the other hand, as shown by the RS in Fig. 4b, the final shape got less accurate when increasing the punch stroke and/or moving the deep drawn feature far from the rotation axis ($r$ equal to 15 mm). Such a consideration was justified by the fact that blank's region far from the rotation axis were subjected to lower strain levels since almost immediately in contact with the inclined segment of the die. As an example, the final shape of the ID6 and ID7 was compared with the reference target: if the deep drawn feature is located at the center of the blank, the reshaped part shows only small variation in its flat part (see the detailed plot Fig. 5a). Moving the strain inhomogeneity far from the rotation axis, on the other hand, affects the shape of the whole tapered surface of the reshaped part (the green and black curves are not completely overlapped (see Fig. 5b).
set) that is used to actually train the RS and the validation set (containing the remaining part of the data table) used to evaluate the predictive capability of the trained model. The Err<sub>avg,sh</sub> and Err<sub>avg,th</sub> were accurately fitted by the RBF Gaussian and Hardy's MultiQuadrics kernels, respectively.

<figure><img src="image_2646.png" /><figcaption>Fig. 4 Reshaping ROUTE#1: RS on the response variable Err<sub>avg,sh</sub> (a, b) and on the response variable Err<sub>avg,th</sub> (c, d).</figcaption></figure>

The 3D visualization of the regression model in Fig. 4a suggests that the final geometry of the reshaped part was slightly influenced by the punch diameter used during the deep drawing step: setting, in fact, the $d_p$ at 4 mm the error variable is weakly influenced. Similarly, the applied magnetic field showed an almost negligible influence as well. On the other hand, as shown by the RS in Fig. 4b, the final shape got less accurate when increasing the punch stroke and/or moving the deep drawn feature far from the rotation axis ($r$ equal to 15 mm). Such a consideration was justified by the fact that blank's region far from the rotation axis were subjected to lower strain levels since almost immediately in contact with the inclined segment of the die. As an example, the final shape of the ID6 and ID7 was compared with the reference target: if the deep drawn feature is located at the center of the blank, the reshaped part shows only small variation in its flat part (see the detailed plot Fig. 5a). Moving the strain inhomogeneity far from the rotation axis, on the other hand, affects the shape of the whole tapered surface of the reshaped part (the green and black curves are not completely overlapped (see Fig. 5b).
<figure><img src="image_2651.png" /><figcaption>Fig. 5 Influence of the parameter “r” on the final geometry of the reshaped part</figcaption></figure>

On the other hand, when looking at the deviation of the final thickness distribution in the reshaped part from the target one (see Fig. 4c and Fig. 4d), similar conclusions could be drawn. In fact, the heterogeneity resulting from the deep drawing could not be completely eliminated during the reshaping even if the deep drawn feature was located close to the center of the blank (see Fig. 6a); as expected, by moving the feature close to the peripheral region of the blank, the residual heterogeneity in the thickness distribution of the reshaped part was even more evident (see Fig. 6b).

<figure><img src="image_2652.png" /><figcaption>Fig. 6 Influence of the parameter “r” on the final thickness distribution of the reshaped part</figcaption></figure>

Eventually, by looking at the main effect plots in Fig. 7 (a and b), it could be concluded that, when reshaping the EoL component in a closed die, the depth (h) and the radial position (r) of the deep drawn feature showed a much larger influence on the final shape and thickness distribution (in accordance with what reported in [7]).
<figure><img src="image_2647.png" /><figcaption>Fig. 5 Influence of the parameter “r” on the final geometry of the reshaped part</figcaption></figure>

On the other hand, when looking at the deviation of the final thickness distribution in the reshaped part from the target one (see Fig. 4c and Fig. 4d), similar conclusions could be drawn. In fact, the heterogeneity resulting from the deep drawing could not be completely eliminated during the reshaping even if the deep drawn feature was located close to the center of the blank (see Fig. 6a); as expected, by moving the feature close to the peripheral region of the blank, the residual heterogeneity in the thickness distribution of the reshaped part was even more evident (see Fig. 6b).

<figure><img src="image_2648.png" /><figcaption>Fig. 6 Influence of the parameter “r” on the final thickness distribution of the reshaped part</figcaption></figure>

Eventually, by looking at the main effect plots in Fig. 7 (a and b), it could be concluded that, when reshaping the EoL component in a closed die, the depth (h) and the radial position (r) of the deep drawn feature showed a much larger influence on the final shape and thickness distribution (in accordance with what reported in [7]).
<figure><img src="image_2653.png" /><figcaption>Fig. 7 Reshaping ROUTE#1: main effect plots on Err<sub>avg,sh</sub> (a) and Err<sub>avg,th</sub> (b)</figcaption></figure>

**Reshaping ROUTE#2.** The same approach was used also to analyze the results from the second DoE plan. The 3D visualization of the regression models (Hardy's MultiQuadrics kernel on the Err<sub>avg,sh</sub> variable and Inverse MultiQuadrics kernel on the Err<sub>avg,th</sub> variable) suggests that the successful reshaping of the EoL into the target geometry was strictly related to the applied magnetic field (Fig. 8a). Also in this case, the radial position of the deep drawn feature influences the final geometry of the reshaped component (Fig. 8a).

<figure><img src="image_2654.png" /></figure>
<figure><img src="image_2649.png" /><figcaption>Fig. 7 Reshaping ROUTE#1: main effect plots on Err<sub>avg,sh</sub> (a) and Err<sub>avg,th</sub> (b)</figcaption></figure>

**Reshaping ROUTE#2.** The same approach was used also to analyze the results from the second DoE plan. The 3D visualization of the regression models (Hardy's MultiQuadrics kernel on the Err<sub>avg,sh</sub> variable and Inverse MultiQuadrics kernel on the Err<sub>avg,th</sub> variable) suggests that the successful reshaping of the EoL into the target geometry was strictly related to the applied magnetic field (Fig. 8a). Also in this case, the radial position of the deep drawn feature influences the final geometry of the reshaped component (Fig. 8a).

<figure><img src="image_2650.png" /></figure>
<figure><img src="image_2655.png" /><figcaption>Fig. 8 Reshaping ROUTE#2: RS on the response variable Err<sub>avg,sh</sub> (a, b) and on the response variable Err<sub>avg,th</sub> (c, d).</figcaption></figure>

In order to deepen more the effect of the applied magnetic field (B), ID6 and ID14 were compared with the target geometry: the comparison in Fig. 9a clearly suggest that, for the same displacement of the plate moving the MRF (Punch-MRF in Fig. 2), the reshaping step was less effective if no magnetic field was applied (B equal to 0 mT). On the contrary, the increased fluid viscosity resulting from the increase of the magnetic field B allowed to obtain a final shape almost completely overlapped to the target one (Fig. 9b).

<figure><img src="image_2656.png" /><figcaption>Fig. 9 Influence of the parameter “B” on the final geometry of the reshaped part</figcaption></figure>

In the case of the final thickness distribution (the RS are shown in Fig. 8, c and d), an expected reduction of the discrepancy with the target distribution was achieved when increasing the magnetic field. The comparison of the curve demonstrates that, despite the difference close to the rotation axis (strictly related to the heterogeneously cold-worked regions after the deep drawing), the thickness distribution approximated better the target one thanks to the increased MRF viscosity (Fig. 10a). On the other hand, as a consequence of the lower final bulging height reached in absence of magnetic field, the final distribution was much less accurate (Fig. 10b).
<figure><img src="image_2651.png" /><figcaption>Fig. 8 Reshaping ROUTE#2: RS on the response variable Err<sub>avg,sh</sub> (a, b) and on the response variable Err<sub>avg,th</sub> (c, d).</figcaption></figure>

In order to deepen more the effect of the applied magnetic field (B), ID6 and ID14 were compared with the target geometry: the comparison in Fig. 9a clearly suggest that, for the same displacement of the plate moving the MRF (Punch-MRF in Fig. 2), the reshaping step was less effective if no magnetic field was applied (B equal to 0 mT). On the contrary, the increased fluid viscosity resulting from the increase of the magnetic field B allowed to obtain a final shape almost completely overlapped to the target one (Fig. 9b).

<figure><img src="image_2652.png" /><figcaption>Fig. 9 Influence of the parameter “B” on the final geometry of the reshaped part</figcaption></figure>

In the case of the final thickness distribution (the RS are shown in Fig. 8, c and d), an expected reduction of the discrepancy with the target distribution was achieved when increasing the magnetic field. The comparison of the curve demonstrates that, despite the difference close to the rotation axis (strictly related to the heterogeneously cold-worked regions after the deep drawing), the thickness distribution approximated better the target one thanks to the increased MRF viscosity (Fig. 10a). On the other hand, as a consequence of the lower final bulging height reached in absence of magnetic field, the final distribution was much less accurate (Fig. 10b).
<figure><img src="image_2657.png" /><figcaption>Fig. 10 Influence of the parameter “B” on the final thickness distribution of the reshaped part</figcaption></figure>

The analysis of the main effect plot (Fig. 11a) allowed to conclude that the parameter B remarkably influenced the two response variables. In particular, when dealing with deviation in the final thickness distribution, also the radial position of the deep drawn feature showed a non-negligible effect (Fig. 11a).

<figure><img src="image_2658.png" /><figcaption>Fig. 11 Reshaping ROUTE#2: main effect plot</figcaption></figure>

## Conclusions

In the present work, the reshaping by hydroforming was studied including the investigation of the advantages coming from the adoption of a MRF as the forming medium. The key findings of the presented methodology as it follows: (i) a simple 2D axisymmetric model made possible to easily simulate the sequence of two manufacturing step: an initial deep drawing step to obtain the EoL component and the subsequent reshaping by MRF hydroforming; (ii) Taking into account two reshaping routes allowed to evaluate to what extent the process parameter of the deep drawing step
<figure><img src="image_2653.png" /><figcaption>Fig. 10 Influence of the parameter “B” on the final thickness distribution of the reshaped part</figcaption></figure>

The analysis of the main effect plot (Fig. 11a) allowed to conclude that the parameter B remarkably influenced the two response variables. In particular, when dealing with deviation in the final thickness distribution, also the radial position of the deep drawn feature showed a non-negligible effect (Fig. 11a).

<figure><img src="image_2654.png" /><figcaption>Fig. 11 Reshaping ROUTE#2: main effect plot</figcaption></figure>

## Conclusions

In the present work, the reshaping by hydroforming was studied including the investigation of the advantages coming from the adoption of a MRF as the forming medium. The key findings of the presented methodology as it follows: (i) a simple 2D axisymmetric model made possible to easily simulate the sequence of two manufacturing step: an initial deep drawing step to obtain the EoL component and the subsequent reshaping by MRF hydroforming; (ii) Taking into account two reshaping routes allowed to evaluate to what extent the process parameter of the deep drawing step
as well as the MRF behavior could have an influence according to the final target shape; (iii) in the case of the reshaping adopting a closed die (ROUTE#1), the *B* parameter had a negligible influence on the final quality of the reshaped part that, on the contrary, was much more dependent on the geometry of the EoL component (radial position and depth of the deep drawn feature); (iv) when changing the target geometry (ROUTE#2), the influence of the parameters changed completely: only an increase in the MRF viscosity (i.e. an increase in the applied magnetic field) allowed to obtain a reshaped part with a very accurate final shape and a thickness distribution close to the target values.

## Acknowledgments

Financed by the European Union - NextGenerationEU (National Sustainable Mobility Center CN00000023, Italian Ministry of University and Research Decree n. 1033 - 17/06/2022, Spoke 11 - Innovative Materials & Lightweighting). The opinions expressed are those of the authors only and should not be considered as representative of the European Union or the European Commission's official position. Neither the European Union nor the European Commission can be held responsible for them.

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[6] Takano, H., Kitazawa, K., and Goto, T., 2008, “Incremental Forming of Nonuniform Sheet Metal: Possibility of Cold Recycling Process of Sheet Metal Waste,” Int. J. Mach. Tools Manuf., **48**(3), pp. 477–482. https://doi.org/10.1016/j.ijmachtools.2007.10.009

[7] Piccininni, A., Cusanno, A., Palumbo, G., Zaheer, O., Ingarao, G., and Fratini, L., 2022, “Reshaping End-of-Life Components by Sheet Hydroforming: An Experimental and Numerical Analysis,” J. Mater. Process. Technol., **306**(June), p. 117650. https://doi.org/10.1016/j.jmatprotec.2022.117650

[8] Wang, P. yi, Zhang, W. zhuo, Wang, Z. jin, and Yi, J., 2016, “Effect of Viscosity of Viscous Medium on Formability of Al1060-O Sheet in Viscous Pressure Forming (VPF): An Experimental Study,” Int. J. Adv. Manuf. Technol., pp. 1–10. https://doi.org/10.1007/s00170-016-8429-3

[9] Zhu, X., Jing, X., and Cheng, L., 2012, “Magnetorheological Fluid Dampers: A Review on Structure Design and Analysis,” J. Intell. Mater. Syst. Struct., **23**(8), pp. 839–873. https://doi.org/10.1177/1045389X12436735

[10] Kumbhar, B. K., Patil, S. R., and Sawant, S. M., 2015, “Synthesis and Characterization of
as well as the MRF behavior could have an influence according to the final target shape; (iii) in the case of the reshaping adopting a closed die (ROUTE#1), the *B* parameter had a negligible influence on the final quality of the reshaped part that, on the contrary, was much more dependent on the geometry of the EoL component (radial position and depth of the deep drawn feature); (iv) when changing the target geometry (ROUTE#2), the influence of the parameters changed completely: only an increase in the MRF viscosity (i.e. an increase in the applied magnetic field) allowed to obtain a reshaped part with a very accurate final shape and a thickness distribution close to the target values.

## Acknowledgments

Financed by the European Union - NextGenerationEU (National Sustainable Mobility Center CN00000023, Italian Ministry of University and Research Decree n. 1033 - 17/06/2022, Spoke 11 - Innovative Materials & Lightweighting). The opinions expressed are those of the authors only and should not be considered as representative of the European Union or the European Commission's official position. Neither the European Union nor the European Commission can be held responsible for them.

## References

[1] Oberhausen, G., Zhu, Y., and Cooper, D. R., 2022, “Reducing the Environmental Impacts of Aluminum Extrusion,” Resour. Conserv. Recycl., **179**(December 2021), p. 106120.
https://doi.org/10.1016/j.resconrec.2021.106120

[2] Ashby, M. F., 2021, “Materials and Environment,” M.F.B.T.-M. and the E. (Third E. Ashby, ed., Butterworth-Heinemann, pp. 41–64. https://doi.org/10.1016/B978-0-12-821521-0.00003-7

[3] Tolio, T., Bernard, A., Colledani, M., Kara, S., Seliger, G., Duflou, J., Battaia, O., and Takata, S., 2017, “Design, Management and Control of Demanufacturing and Remanufacturing Systems,” CIRP Ann., **66**(2), pp. 585–609. https://doi.org/10.1016/j.cirp.2017.05.001

[4] Cooper, D. R., and Allwood, J. M., 2012, “Reusing Steel and Aluminum Components at End of Product Life,” Environ. Sci. Technol., **46**(18), pp. 10334–10340.
https://doi.org/10.1021/es301093a

[5] Brosius, A., Hermes, M., Khalifa, N. Ben, Trompeter, M., and Tekkaya, A. E., 2009, “Innovation by Forming Technology: Motivation for Research,” Int. J. Mater. Form., **2**(1), pp. 29–38.
https://doi.org/10.1007/s12289-009-0656-9

[6] Takano, H., Kitazawa, K., and Goto, T., 2008, “Incremental Forming of Nonuniform Sheet Metal: Possibility of Cold Recycling Process of Sheet Metal Waste,” Int. J. Mach. Tools Manuf., **48**(3), pp. 477–482.
https://doi.org/10.1016/j.ijmachtools.2007.10.009

[7] Piccininni, A., Cusanno, A., Palumbo, G., Zaheer, O., Ingarao, G., and Fratini, L., 2022, “Reshaping End-of-Life Components by Sheet Hydroforming: An Experimental and Numerical Analysis,” J. Mater. Process. Technol., **306**(June), p. 117650.
https://doi.org/10.1016/j.jmatprotec.2022.117650

[8] Wang, P. yi, Zhang, W. zhuo, Wang, Z. jin, and Yi, J., 2016, “Effect of Viscosity of Viscous Medium on Formability of Al1060-O Sheet in Viscous Pressure Forming (VPF): An Experimental Study,” Int. J. Adv. Manuf. Technol., pp. 1–10.
https://doi.org/10.1007/s00170-016-8429-3

[9] Zhu, X., Jing, X., and Cheng, L., 2012, “Magnetorheological Fluid Dampers: A Review on Structure Design and Analysis,” J. Intell. Mater. Syst. Struct., **23**(8), pp. 839–873.
https://doi.org/10.1177/1045389X12436735

[10] Kumbhar, B. K., Patil, S. R., and Sawant, S. M., 2015, “Synthesis and Characterization of
Magneto-Rheological (MR) Fluids for MR Brake Application,” Eng. Sci. Technol. an Int. J., **18**(3), pp. 432–438. https://doi.org/10.1016/j.jestch.2015.03.002

[11] Bucchi, F., Forte, P., and Frendo, F., 2012, “Experimental Characterization of a Permanent Magnet Magnetorheological Clutch for Automotive Applications,” ASME 2012 11th Bienn. Conf. Eng. Syst. Des. Anal. ESDA 2012, **4**, pp. 345–355. https://doi.org/10.1115/ESDA2012-82284

[12] Li, F., Zhou, F. J., Wang, M. N., Zhu, S. Y., and Jin, C. C., 2017, “New Processing Research on Sheet Metal Bidirectional Pressure Forming Using a Magnetorheological Fluid,” Int. J. Adv. Manuf. Technol., **88**(1–4), pp. 923–929. https://doi.org/10.1007/s00170-016-8831-x

[13] Cusanno, A., Piccininni, A., Guglielmi, P., and Palumbo, G., 2022, “Evaluation of the Rheological Behaviour of Magnetorheological Fluids Combining Bulge Tests and Inverse Analysis,” *Key Engineering Materials*, Trans Tech Publications Ltd, pp. 1778–1785. https://doi.org/10.4028/p-4irh1n
Magneto-Rheological (MR) Fluids for MR Brake Application,” Eng. Sci. Technol. an Int. J., **18**(3), pp. 432–438. https://doi.org/10.1016/j.jestch.2015.03.002

[11] Bucchi, F., Forte, P., and Frendo, F., 2012, “Experimental Characterization of a Permanent Magnet Magnetorheological Clutch for Automotive Applications,” ASME 2012 11th Bienn. Conf. Eng. Syst. Des. Anal. ESDA 2012, **4**, pp. 345–355. https://doi.org/10.1115/ESDA2012-82284

[12] Li, F., Zhou, F. J., Wang, M. N., Zhu, S. Y., and Jin, C. C., 2017, “New Processing Research on Sheet Metal Bidirectional Pressure Forming Using a Magnetorheological Fluid,” Int. J. Adv. Manuf. Technol., **88**(1–4), pp. 923–929. https://doi.org/10.1007/s00170-016-8831-x

[13] Cusanno, A., Piccininni, A., Guglielmi, P., and Palumbo, G., 2022, “Evaluation of the Rheological Behaviour of Magnetorheological Fluids Combining Bulge Tests and Inverse Analysis,” *Key Engineering Materials*, Trans Tech Publications Ltd, pp. 1778–1785. https://doi.org/10.4028/p-4irh1n
# Remanufacturing process chain for end-of-life aluminium car body parts: Technical and economic analysis

FARIOLI Daniele¹,ᵃ*, MURGESE Luca¹,ᵇ, PINARDI Camilla¹,ᶜ, KAYA Ertuğrul¹,ᵈ and STRANO Matteo¹ᵉ

¹Politecnico di Milano, Department of Mechanical Engineering, Via La Masa 1, 20156 Milano, Italy

ᵃdaniele.farioli@polimi.it, ᵇluca.murgese@mail.polimi.it, ᶜcamilla.pinardi@mail.polimi.it, ᵈertugrul.kaya@polimi.it, ᵉmatteo.strano@polimi.it

**Keywords:** Remanufacturing, Dismantling, Aluminium Sheets, Flattening, Circular Economy

**Abstract.** This paper investigates the potential for remanufacturing aluminium sheets from end-of-life vehicles (ELVs), specifically focusing on car hoods. The study explores various pre-flattening procedures and reshaping techniques, with warm flattening showing promise despite challenges such as paint degradation. A Design of Experiment (DoE) was used to assess the impact of various factors on the flattening process, and Finite Element (FE) simulations were used to validate the experimental findings. An economic feasibility analysis was also conducted, which revealed that while technically feasible, the economic viability of this remanufacturing process is currently challenging due to the high costs compared to purchasing new sheets. However, with the increasing use of aluminium in automotive body panels and potential market shifts, these remanufacturing initiatives could become economically viable in the future, contributing to sustainability goals in the automotive sector.

**Introduction.**

Traditional business models follow a “make-use-dispose” approach, but the concept of circulating materials and products, which offers environmental and economic benefits, is gaining popularity. This can be achieved through open-loop or closed-loop supply chains where materials or products are reused, recycled, repurposed, or remanufactured. This paper focuses on the remanufacturing of automotive panels to enable a circular economy of car body panels. Specifically, it analyses the use of a flattening technique on Al-alloy automotive panels as an alternative to conventional recycling by melting. Aluminium, a high-value material, is increasingly used in the automotive sector due to its lightweight and corrosion-resistant properties. Unlike recycling, flattening allows for the reuse of material without remelting, preserving the chemical composition of a specific alloy. There is growing interest in recycling aluminium scrap at temperatures below solidus, known as “melt-less” or solid-state recycling, which offers significant environmental benefits in terms of energy and material savings. The paper provides a comprehensive analysis of flattening as a remanufacturing process, including a technical, economic, and environmental assessment of a case study related to End-of-Life Vehicles (ELVs) aluminium hoods [1], [2].

**Circular Economy in the automotive sector.**

The concept of circular economy aims to minimize waste and promote sustainable resource usage by designing products, materials, and systems to maximize their value and longevity. With energy and material consumption rising rapidly, resource constraints have become increasingly critical. Developing closed-loop manufacturing systems is crucial for economic and environmental sustainability, meeting consumer needs, and creating high-skill jobs. In the automotive sector, implementing a circular economy requires adopting Closed-Loop Supply Chain (CLSC) practices,

<figure><img src="image_2659.png" /></figure>
# Remanufacturing process chain for end-of-life aluminium car body parts: Technical and economic analysis

FARIOLI Daniele¹,ᵃ*, MURGESE Luca¹,ᵇ, PINARDI Camilla¹,ᶜ, KAYA Ertuğrul¹,ᵈ and STRANO Matteo¹ᵉ

¹Politecnico di Milano, Department of Mechanical Engineering, Via La Masa 1, 20156 Milano, Italy

ᵃdaniele.farioli@polimi.it, ᵇluca.murgese@mail.polimi.it, ᶜcamilla.pinardi@mail.polimi.it, ᵈertugrul.kaya@polimi.it, ᵉmatteo.strano@polimi.it

**Keywords:** Remanufacturing, Dismantling, Aluminium Sheets, Flattening, Circular Economy

**Abstract.** This paper investigates the potential for remanufacturing aluminium sheets from end-of-life vehicles (ELVs), specifically focusing on car hoods. The study explores various pre-flattening procedures and reshaping techniques, with warm flattening showing promise despite challenges such as paint degradation. A Design of Experiment (DoE) was used to assess the impact of various factors on the flattening process, and Finite Element (FE) simulations were used to validate the experimental findings. An economic feasibility analysis was also conducted, which revealed that while technically feasible, the economic viability of this remanufacturing process is currently challenging due to the high costs compared to purchasing new sheets. However, with the increasing use of aluminium in automotive body panels and potential market shifts, these remanufacturing initiatives could become economically viable in the future, contributing to sustainability goals in the automotive sector.

**Introduction.**

Traditional business models follow a “make-use-dispose” approach, but the concept of circulating materials and products, which offers environmental and economic benefits, is gaining popularity. This can be achieved through open-loop or closed-loop supply chains where materials or products are reused, recycled, repurposed, or remanufactured. This paper focuses on the remanufacturing of automotive panels to enable a circular economy of car body panels. Specifically, it analyses the use of a flattening technique on Al-alloy automotive panels as an alternative to conventional recycling by melting. Aluminium, a high-value material, is increasingly used in the automotive sector due to its lightweight and corrosion-resistant properties. Unlike recycling, flattening allows for the reuse of material without remelting, preserving the chemical composition of a specific alloy. There is growing interest in recycling aluminium scrap at temperatures below solidus, known as “melt-less” or solid-state recycling, which offers significant environmental benefits in terms of energy and material savings. The paper provides a comprehensive analysis of flattening as a remanufacturing process, including a technical, economic, and environmental assessment of a case study related to End-of-Life Vehicles (ELVs) aluminium hoods [1], [2].

**Circular Economy in the automotive sector.**

The concept of circular economy aims to minimize waste and promote sustainable resource usage by designing products, materials, and systems to maximize their value and longevity. With energy and material consumption rising rapidly, resource constraints have become increasingly critical. Developing closed-loop manufacturing systems is crucial for economic and environmental sustainability, meeting consumer needs, and creating high-skill jobs. In the automotive sector, implementing a circular economy requires adopting Closed-Loop Supply Chain (CLSC) practices,

<figure><img src="image_2655.png" /></figure>
which include reverse logistics. Unlike traditional open-loop supply chains, CLSC incorporates cradle-to-cradle principles, involving gatekeeping, collection, sorting, and disposal or recovery (e.g., reuse, recycle, refurbish, remanufacture). Implementing CLSC faces challenges, grouped into environmental, cultural, economic, manufacturing and technological, information-related, regulations, managerial, and organizational barriers. However, various facilitating drivers, such as economic, environmental, technical, and political factors, also exist [3]. In the automotive sector, implementing a circular economy relies on adopting Closed-Loop Supply Chain (CLSC) practices, which differ from traditional open-loop supply chains by incorporating reverse logistics. This shift moves from a cradle-to-grave approach to a cradle-to-cradle model. Reverse logistics consists of gatekeeping, collection, sorting, and disposal or recovery (e.g., reuse, recycle, refurbish, remanufacture). However, implementing CLSC faces challenges, including environmental, cultural, economic, manufacturing and technological, information-related, regulations, managerial, and organizational barriers. Despite these challenges, facilitating drivers such as economic, environmental, technical, and political factors exist. In the automotive sector, achieving a perfect CLSC is unlikely due to the complexity of the network and involvement of various actors. Nevertheless, the CLSC in the automotive field mainly involves the forward supply chain network (suppliers, manufacturers, customer clusters) and the reverse chain network (collection centers, recyclers, remanufacturers, dismantlers, shredders, landfills) [4].

The reverse logistics network starts with the collection of ELVs from customer clusters. The owner of a used vehicle who wants to sell it has many opportunities. If the vehicle is in good condition, he/she can decide to sell it to another person, or to a collection centre such as a dealership. If the vehicle is not in good condition, that means it is an ELV, the owner can decide to take it directly to a dismantler or to a collection centre that is in contact with a dismantler. In dismantling centres, cars are depolluted and disassembled, it is decided which parts and materials can be recovered and which must be sent to landfills. In general, the outputs of the dismantling process are used components and hulk, composed of ELV body, chassis, and other structural parts. The hulk is sent to a shredding facility where it is possible to divide all the different materials composing it. Usually, the ferrous and non-ferrous fractions obtained are recycled while the Automotive Shredder Residue (ASR), that is the non-metal fraction obtained, is sent to the landfills.

The objective of the sheet remanufacturing through flattening, the focus of this paper, is to avoid the transfer of ELV aluminium sheets from the dismantlers to the shredders and recyclers. For this reason, it has been necessary to evaluate deeply the existing relations between dismantlers and shredders. These last are complementary figures, the shredder is particularly sensitive to the dismantler's aggressiveness in disassembling the ELV. When only a small percentage of the vehicle is sold as parts, it considerably limits the dismantler's profitability and increases the shredder's profitability. This is particularly true for Al components that have a high economic value. Aluminium, being obtained from bauxite, is a Critical Raw Material (CRM), whose recovery is very important. This is the reason why emphasis is placed on the flattening technique that can be applied to Al-alloy sheets, by either cold or warm reshaping. It consists of using a used metal sheet, cutting out a preform, and forming the sheet again [5]. Remanufacturing activities offer a distinct advantage as they embody the ideal compromise between recycling efforts and the preservation of inherent value.

## Experimental feasibility study.

A case study from the automotive sector was selected. It was decided to focus the analysis on car hoods since they are often characterized by extended Al panels. Aluminium hoods are built with inner and outer Al alloy panels, polyurethane foams, and structural tapes. To start the experimental process, three hoods produced in different years and belonging to different car models (Peugeot 407 SW of 2004, Jeep Renegade of 2014, BMW series 5 G30 of 2017) were collected from dismantling
which include reverse logistics. Unlike traditional open-loop supply chains, CLSC incorporates cradle-to-cradle principles, involving gatekeeping, collection, sorting, and disposal or recovery (e.g., reuse, recycle, refurbish, remanufacture). Implementing CLSC faces challenges, grouped into environmental, cultural, economic, manufacturing and technological, information-related, regulations, managerial, and organizational barriers. However, various facilitating drivers, such as economic, environmental, technical, and political factors, also exist [3]. In the automotive sector, implementing a circular economy relies on adopting Closed-Loop Supply Chain (CLSC) practices, which differ from traditional open-loop supply chains by incorporating reverse logistics. This shift moves from a cradle-to-grave approach to a cradle-to-cradle model. Reverse logistics consists of gatekeeping, collection, sorting, and disposal or recovery (e.g., reuse, recycle, refurbish, remanufacture). However, implementing CLSC faces challenges, including environmental, cultural, economic, manufacturing and technological, information-related, regulations, managerial, and organizational barriers. Despite these challenges, facilitating drivers such as economic, environmental, technical, and political factors exist. In the automotive sector, achieving a perfect CLSC is unlikely due to the complexity of the network and involvement of various actors. Nevertheless, the CLSC in the automotive field mainly involves the forward supply chain network (suppliers, manufacturers, customer clusters) and the reverse chain network (collection centers, recyclers, remanufacturers, dismantlers, shredders, landfills) [4].

The reverse logistics network starts with the collection of ELVs from customer clusters. The owner of a used vehicle who wants to sell it has many opportunities. If the vehicle is in good condition, he/she can decide to sell it to another person, or to a collection centre such as a dealership. If the vehicle is not in good condition, that means it is an ELV, the owner can decide to take it directly to a dismantler or to a collection centre that is in contact with a dismantler. In dismantling centres, cars are depolluted and disassembled, it is decided which parts and materials can be recovered and which must be sent to landfills. In general, the outputs of the dismantling process are used components and hulk, composed of ELV body, chassis, and other structural parts. The hulk is sent to a shredding facility where it is possible to divide all the different materials composing it. Usually, the ferrous and non-ferrous fractions obtained are recycled while the Automotive Shredder Residue (ASR), that is the non-metal fraction obtained, is sent to the landfills.

The objective of the sheet remanufacturing through flattening, the focus of this paper, is to avoid the transfer of ELV aluminium sheets from the dismantlers to the shredders and recyclers. For this reason, it has been necessary to evaluate deeply the existing relations between dismantlers and shredders. These last are complementary figures, the shredder is particularly sensitive to the dismantler's aggressiveness in disassembling the ELV. When only a small percentage of the vehicle is sold as parts, it considerably limits the dismantler's profitability and increases the shredder's profitability. This is particularly true for Al components that have a high economic value. Aluminium, being obtained from bauxite, is a Critical Raw Material (CRM), whose recovery is very important. This is the reason why emphasis is placed on the flattening technique that can be applied to Al-alloy sheets, by either cold or warm reshaping. It consists of using a used metal sheet, cutting out a preform, and forming the sheet again [5]. Remanufacturing activities offer a distinct advantage as they embody the ideal compromise between recycling efforts and the preservation of inherent value.

**Experimental feasibility study.**

A case study from the automotive sector was selected. It was decided to focus the analysis on car hoods since they are often characterized by extended Al panels. Aluminium hoods are built with inner and outer Al alloy panels, polyurethane foams, and structural tapes. To start the experimental process, three hoods produced in different years and belonging to different car models (Peugeot 407 SW of 2004, Jeep Renegade of 2014, BMW series 5 G30 of 2017) were collected from dismantling
facilities. Disassembling the hoods and cutting them into various sections to generate representative samples were the first operations carried out. The three Al-hoods employed were cut according to Figure 1, which represents only one of the three end-of-life part from which samples were extracted. In total 18 samples made of three different 6000 series Al hoods were obtained. Some of the samples present a mild initial curvature (labelled with “B” in Figure 1); some other included a sharp design line (labelled with “D” in Figure 1, where a change in concavity can be appreciated). The trimming process was performed with an angle grinder because of its precision and reduced energy consumption compared to other methods.

Then, it was necessary to remove the polyurethane foams through a mechanical action. In addition to that, a significant issue arose during the removal of structural tapes, leading to various attempts, including mechanical methods and solvents. The subsequent steps included the paint removal from certain samples: various techniques were taken into consideration. Sandblasting removed the paint but led to deformation issues, attributed to the interaction between residual stresses from the original forming process and the one introduced by this process. Chemical solvents were then employed, demonstrating good efficacy in stripping the paint from the specimen surface.

Later, the specimens were geometrically characterized using a 3D scanner (Artec EVA) and a 2D laser profilometer system (Wenglor MLWI 131), described in Figure 2. Both systems provide as output either an .stl file or a .csv file containing a cloud of data point. Such data were analysed through MATLAB: the software allowed generating a script for automatically determining the local radius of curvature and the maximum height of each specimen profile. After scanning, a 400 tons hydraulic press was employed to reshape the aluminium samples. Such process is meant to cancel out the original curved shape of the samples and providing a flat sheet by applying a pressure through two flat dies.

<figure><img src="image_2660.png" /><figcaption>Figure 1. Drawn pattern followed during the cutting.</figcaption></figure>

<figure><img src="image_2661.png" /><figcaption>Figure 2. Laser-based profilometer used for 3D scanning the samples.</figcaption></figure>

<figure><img src="image_2662.png" /><figcaption>Figure 3. Exploded view of the modular flattening dies.</figcaption></figure>

Flattened panels, once reshaped, can be reused for another purpose, in a circular economy perspective. A modular tooling set has been designed, made of steel 1.2842, divided into four parts as shown in Figure 3. The flattening plates can be heated up to T=300 °C to perform warm reshaping. The lower plate is stationary while the upper plate descends and presses the samples with different speeds, with the following sequence:

1) First, a rapid descent of the top die occurs, at 80 mm/min;

2) Then, the speed is reduced to 25 mm/min until contact with the sample and onset of flattening. This speed is maintained up to a target tonnage is reached;

3) Lastly, once reached the target tonnage (i.e. the dwell force, DwF), the position of the upper plate is maintained to press at a constant force onto the sample for a pre-determined time called dwell time ($\tau$).

The temperature of the upper and lower plate can be set and maintained constant by means of 18 electrical resistances (9 for each plate). Knowing the surface area of each specimen, an average dwelling pressure P is calculated for each operation as the ratio between the tonnage (DwF) and the surface area. A Design of Experiment (DoE) was established to understand the influence of
facilities. Disassembling the hoods and cutting them into various sections to generate representative samples were the first operations carried out. The three Al-hoods employed were cut according to Figure 1, which represents only one of the three end-of-life part from which samples were extracted. In total 18 samples made of three different 6000 series Al hoods were obtained. Some of the samples present a mild initial curvature (labelled with “B” in Figure 1); some other included a sharp design line (labelled with “D” in Figure 1, where a change in concavity can be appreciated). The trimming process was performed with an angle grinder because of its precision and reduced energy consumption compared to other methods.

Then, it was necessary to remove the polyurethane foams through a mechanical action. In addition to that, a significant issue arose during the removal of structural tapes, leading to various attempts, including mechanical methods and solvents. The subsequent steps included the paint removal from certain samples: various techniques were taken into consideration. Sandblasting removed the paint but led to deformation issues, attributed to the interaction between residual stresses from the original forming process and the one introduced by this process. Chemical solvents were then employed, demonstrating good efficacy in stripping the paint from the specimen surface.

Later, the specimens were geometrically characterized using a 3D scanner (Artec EVA) and a 2D laser profilometer system (Wenglor MLWI 131), described in Figure 2. Both systems provide as output either an .stl file or a .csv file containing a cloud of data point. Such data were analysed through MATLAB: the software allowed generating a script for automatically determining the local radius of curvature and the maximum height of each specimen profile. After scanning, a 400 tons hydraulic press was employed to reshape the aluminium samples. Such process is meant to cancel out the original curved shape of the samples and providing a flat sheet by applying a pressure through two flat dies.

<figure><img src="image_2656.png" /><figcaption>Figure 1. Drawn pattern followed during the cutting.</figcaption></figure>

<figure><img src="image_2657.png" /><figcaption>Figure 2. Laser-based profilometer used for 3D scanning the samples.</figcaption></figure>

<figure><img src="image_2658.png" /><figcaption>Figure 3. Exploded view of the modular flattening dies.</figcaption></figure>

Flattened panels, once reshaped, can be reused for another purpose, in a circular economy perspective. A modular tooling set has been designed, made of steel 1.2842, divided into four parts as shown in Figure 3. The flattening plates can be heated up to T=300 °C to perform warm reshaping. The lower plate is stationary while the upper plate descends and presses the samples with different speeds, with the following sequence:

1) First, a rapid descent of the top die occurs, at 80 mm/min;

2) Then, the speed is reduced to 25 mm/min until contact with the sample and onset of flattening. This speed is maintained up to a target tonnage is reached;

3) Lastly, once reached the target tonnage (i.e. the dwell force, DwF), the position of the upper plate is maintained to press at a constant force onto the sample for a pre-determined time called dwell time ($\tau$).

The temperature of the upper and lower plate can be set and maintained constant by means of 18 electrical resistances (9 for each plate). Knowing the surface area of each specimen, an average dwelling pressure P is calculated for each operation as the ratio between the tonnage (DwF) and the surface area. A Design of Experiment (DoE) was established to understand the influence of
temperature (T), pressure (P), dwell time (τ), and presence of folds on the flattening process. These parameters were chosen based on their expected influence on the re-forming operation [6]. As previously mentioned, from ELVs parts 18 specimens with initial different geometry have been selected for testing. The selected variables for the analysis included two values of temperature T (25-250 °C), two values of pressure P for the dwelling stage (30-40 MPa), two values of dwell time τ (10-20 s, with longer time exclusively for hot-flattened specimens), and the presence of design line as a categorical factor (see Figure 1, samples type “D”). Such values of temperature, pressure, and dwell time were selected after a preliminary experimental campaign not described for sake of simplicity. In fact, such values guaranteed observing significantly different responses and spring-back, allowing capturing the effect of the process parameters, which is the aim of this DoE.

After flattening, specimens were geometrically measured again. Preliminary observations after the hydraulic press operation revealed that cold flattening was less effective, particularly for components with significant curvature. This might be attributed to the spring-back phenomenon and to the fact that being the curvature “large”, not effective plastic deformation is applied while reshaping. A noteworthy observation was made regarding the role of paint in the flattening process. Some painted samples revealed issues during hot flattening, including paint melting, bubbles formation, and generation of gaseous substances as shown in Figure 4. This phenomenon was attributed to pyrolysis, a thermochemical decomposition reaction in a reducing atmosphere. Despite the challenges posed by paint degradation, it was observed that warm flattening allowed for easy removal of the superficial layer of paint without chemical action (Figure 5). This added value to the component, as the E-coating (substrate protective layer) remained unaffected.

To investigate the influence of process parameters, the relationships between independent and dependent variables were examined.

<figure><img src="image_2663.png" /><figcaption>Figure 4. Specimen after warm flattening.</figcaption></figure>

<figure><img src="image_2664.png" /><figcaption>Figure 5. Easier paint detachment if flattening is performed at 250°C.</figcaption></figure>

The beneficial effect of temperature is shown in Figure 6, where the boxplot of the difference between the initial curvature radius and the final curvature radius after flattening is reported. Larger differences imply a more effective flattening operation. The specimens flattened at 250 °C exhibit significantly higher curvature radius differences than those flattened at room temperature. This is clearly due to lowered strength of Al at elevated temperatures. For specimens with a design lines, a significant influence of pressure was also observed, as shown in Figure 7. Samples subjected to higher pressure, surprisingly, exhibit a smaller difference in height, i.e. larger springback. Sometimes the difference is even negative, with a final part which is less flat than the initial part.
temperature (T), pressure (P), dwell time (τ), and presence of folds on the flattening process. These parameters were chosen based on their expected influence on the re-forming operation [6]. As previously mentioned, from ELVs parts 18 specimens with initial different geometry have been selected for testing. The selected variables for the analysis included two values of temperature T (25-250 °C), two values of pressure P for the dwelling stage (30-40 MPa), two values of dwell time τ (10-20 s, with longer time exclusively for hot-flattened specimens), and the presence of design line as a categorical factor (see Figure 1, samples type “D”). Such values of temperature, pressure, and dwell time were selected after a preliminary experimental campaign not described for sake of simplicity. In fact, such values guaranteed observing significantly different responses and spring-back, allowing capturing the effect of the process parameters, which is the aim of this DoE.

After flattening, specimens were geometrically measured again. Preliminary observations after the hydraulic press operation revealed that cold flattening was less effective, particularly for components with significant curvature. This might be attributed to the spring-back phenomenon and to the fact that being the curvature “large”, not effective plastic deformation is applied while reshaping. A noteworthy observation was made regarding the role of paint in the flattening process. Some painted samples revealed issues during hot flattening, including paint melting, bubbles formation, and generation of gaseous substances as shown in Figure 4. This phenomenon was attributed to pyrolysis, a thermochemical decomposition reaction in a reducing atmosphere. Despite the challenges posed by paint degradation, it was observed that warm flattening allowed for easy removal of the superficial layer of paint without chemical action (Figure 5). This added value to the component, as the E-coating (substrate protective layer) remained unaffected.

To investigate the influence of process parameters, the relationships between independent and dependent variables were examined.

<figure><img src="image_2659.png" /><figcaption>Figure 4. Specimen after warm flattening.</figcaption></figure>

<figure><img src="image_2660.png" /><figcaption>Figure 5. Easier paint detachment if flattening is performed at 250°C.</figcaption></figure>

The beneficial effect of temperature is shown in Figure 6, where the boxplot of the difference between the initial curvature radius and the final curvature radius after flattening is reported. Larger differences imply a more effective flattening operation. The specimens flattened at 250 °C exhibit significantly higher curvature radius differences than those flattened at room temperature. This is clearly due to lowered strength of Al at elevated temperatures. For specimens with a design lines, a significant influence of pressure was also observed, as shown in Figure 7. Samples subjected to higher pressure, surprisingly, exhibit a smaller difference in height, i.e. larger springback. Sometimes the difference is even negative, with a final part which is less flat than the initial part.
<figure><img src="image_2665.png" /><figcaption>Figure 6. Box-plot of the variation in radius vs. T with specimens featuring a design line.</figcaption></figure>

<figure><img src="image_2666.png" /><figcaption>Figure 7. Box-plot of the variation in height vs. P with specimens featuring a design line.</figcaption></figure>

This is because flattening may induce a U-shaped deformation, or a spring-forward effect, as visible in Figure 8. The spring-forward effect is a consequence of the initial geometry of the sample (Figure 8-a) which is characterized by a design line (not touching the lower plate) and a change in concavity: the red area has a concavity pointing upwards while the green area (where the design line is present) downwards. Furthermore, the curvature radius of the red zone is larger than the green one, making more difficult to enter in the plastic field simply with flat dies, which during flattening are basically applying counter-bending to the material. After dwelling, the central portion of the sample, where the design line was present (Figure 8-c), can deform plastically because of the flattening plates which firstly un-bend and then compress the material through the thickness. The red portion instead, having a larger curvature radius, unbends mainly elastically. Therefore, that portion does not get completely flat and still a curvature pointing upwards exists, leading to a lateral raise of the flange which might be bigger than the initial maximum height pre-flattening. Experimental observations highlighted that the spring-forward phenomenon is typical in parts exhibiting a design line once pressed at higher pressures and warm conditions since temperature can facilitate plastic deformation at the contact to the design lines. Besides, a higher contact pressure ensures a better heat transfer between the warm dies and the part, making the unbending of the central fold easier. Lastly, dwell time τ could ensure a longer or shorter heat transfer by contact directly from dies to the part, emphasizing or not the spring-forward effect. As for τ, distinct behaviours were observed in specimens with and without design lines (Figure 9).

<figure><img src="image_2667.png" /><figcaption>Figure 8. a) Positioning of the part. b) Flattening. c) Spring-forward effect. d) Residual “U” shape effect, or spring-forward.</figcaption></figure>
<figure><img src="image_2661.png" /><figcaption>Figure 6. Box-plot of the variation in radius vs. T with specimens featuring a design line.</figcaption></figure>

<figure><img src="image_2662.png" /><figcaption>Figure 7. Box-plot of the variation in height vs. P with specimens featuring a design line.</figcaption></figure>

This is because flattening may induce a U-shaped deformation, or a spring-forward effect, as visible in Figure 8. The spring-forward effect is a consequence of the initial geometry of the sample (Figure 8-a) which is characterized by a design line (not touching the lower plate) and a change in concavity: the red area has a concavity pointing upwards while the green area (where the design line is present) downwards. Furthermore, the curvature radius of the red zone is larger than the green one, making more difficult to enter in the plastic field simply with flat dies, which during flattening are basically applying counter-bending to the material. After dwelling, the central portion of the sample, where the design line was present (Figure 8-c), can deform plastically because of the flattening plates which firstly un-bend and then compress the material through the thickness. The red portion instead, having a larger curvature radius, unbends mainly elastically. Therefore, that portion does not get completely flat and still a curvature pointing upwards exists, leading to a lateral raise of the flange which might be bigger than the initial maximum height pre-flattening. Experimental observations highlighted that the spring-forward phenomenon is typical in parts exhibiting a design line once pressed at higher pressures and warm conditions since temperature can facilitate plastic deformation at the contact to the design lines. Besides, a higher contact pressure ensures a better heat transfer between the warm dies and the part, making the unbending of the central fold easier. Lastly, dwell time τ could ensure a longer or shorter heat transfer by contact directly from dies to the part, emphasizing or not the spring-forward effect. As for τ, distinct behaviours were observed in specimens with and without design lines (Figure 9).

<figure><img src="image_2663.png" /><figcaption>Figure 8. a) Positioning of the part. b) Flattening. c) Spring-forward effect. d) Residual “U” shape effect, or spring-forward.</figcaption></figure>
<figure><img src="image_2668.png" /><figcaption>Figure 9. Box-plot of the variation in height vs. t for specimens with (up) and without (down) a design line.</figcaption></figure>

For long dwell times, specimens with design lines exhibit improvements in curvature radius but deterioration in terms of maximum height. When flattening is performed at high temperature with a long dwelling time, thermal distortions are induced. In conclusion, the mechanism of flattening is complex because of several factors, which might interact with each other (Figure 10): geometry, residual stresses, thermal distortions and process parameters are fundamental actors.

<figure><img src="image_2669.png" /><figcaption>Figure 10. Interaction plots between factors (P, T, τ) onto the response variables $\Delta H_{max}\%$ (top) and $\Delta R_{mean}\%$ (bottom) for specimens with a design line.</figcaption></figure>

Because of the intrinsic complexity of this process, in the next section of this article it is presented a Finite Element (FE) simulation of one case study tested, with the aim of understanding if flattening, spring-back and part shape can be predicted digitally.

## Simulation of the flattening process.

This section presents the results obtained from an FE simulation that digitally replicates the entire remanufacturing process chain. Altair Inspire Form software was employed for this activity. The material employed in the simulation is the Al 6016 (as in the real case). It was modelled with elastoplastic behaviour. The software adopts a yielding criterion according to a three-parameter Barlatt model (R00=0,686, R45=0,5, R90=0,666) with exponent m=8. The plastic field of the material follows a power law model with coefficient K=400 MPa and hardening exponent n=0,213. Altair Inspire Form uses an explicit FE solver and all the forming stages were modelled: initial cold forming of the hood, trimming of the specimen, cold flattening, and spring-back (Figure 12). Prior to the final simulation (Figure 13), a convergence analysis of the mesh size was carried out. In the end, the initial flat blank was modelled with quadrilateral shell elements with edge size equal to 4 mm. No remeshing or adaptive algorithms were implemented. The flattening simulation
<figure><img src="image_2664.png" /><figcaption>Figure 9. Box-plot of the variation in height vs. t for specimens with (up) and without (down) a design line.</figcaption></figure>

For long dwell times, specimens with design lines exhibit improvements in curvature radius but deterioration in terms of maximum height. When flattening is performed at high temperature with a long dwelling time, thermal distortions are induced. In conclusion, the mechanism of flattening is complex because of several factors, which might interact with each other (Figure 10): geometry, residual stresses, thermal distortions and process parameters are fundamental actors.

<figure><img src="image_2665.png" /><figcaption>Figure 10. Interaction plots between factors (P, T, τ) onto the response variables $\Delta H_{max}\%$ (top) and $\Delta R_{mean}\%$ (bottom) for specimens with a design line.</figcaption></figure>

Because of the intrinsic complexity of this process, in the next section of this article it is presented a Finite Element (FE) simulation of one case study tested, with the aim of understanding if flattening, spring-back and part shape can be predicted digitally.

## Simulation of the flattening process.

This section presents the results obtained from an FE simulation that digitally replicates the entire remanufacturing process chain. Altair Inspire Form software was employed for this activity. The material employed in the simulation is the Al 6016 (as in the real case). It was modelled with elastoplastic behaviour. The software adopts a yielding criterion according to a three-parameter Barlatt model (R00=0,686, R45=0,5, R90=0,666) with exponent m=8. The plastic field of the material follows a power law model with coefficient K=400 MPa and hardening exponent n=0,213. Altair Inspire Form uses an explicit FE solver and all the forming stages were modelled: initial cold forming of the hood, trimming of the specimen, cold flattening, and spring-back (Figure 12). Prior to the final simulation (Figure 13), a convergence analysis of the mesh size was carried out. In the end, the initial flat blank was modelled with quadrilateral shell elements with edge size equal to 4 mm. No remeshing or adaptive algorithms were implemented. The flattening simulation
revealed low plastic strain near the design line (Figure 13), suggesting that the mechanical properties of the component were only partially affected. The values of the elastic springback obtained from the FE simulation (i.e. the nodal coordinates of the meshed part) were imported in MATLAB and then compared to the ones measured onto the real specimen. Despite minor deviations, there was notable correspondence between actual and virtual profiles (Figure 11). This result validates the use of FE simulation as a tool for predicting accurately the component final morphology.

<figure><img src="image_2670.png" /><figcaption>Figure 12. From left to right: output of the forming process; output of the trimming operation of one part extracted from Figure 1; 3D scan with Artec EVA of the real sample pre-flattening.</figcaption></figure>

<figure><img src="image_2671.png" /><figcaption>Figure 13. From left to right: simulative setup for flattening; plastic strain distribution of the part after flattening and spring-back.</figcaption></figure>

<figure><img src="image_2672.png" /><figcaption>Figure 11. Up: Height profile of the scanned portion from the real specimen. Down: Height profile of the simulated specimen. The dashed rectangle corresponds to the same regions.</figcaption></figure>

## Economic feasibility.

To perform an economic analysis, it is necessary to evaluate which will be the future aluminium sheet quantity recoverable from ELVs. Analysing UNRAE (Unione Nazionale Rappresentati Autoveicoli Esteri) data from 1990 to 2022, the values of car registrations and car radiations were forecasted for future years (Figure 14). The data collected showed that reasonably the newest car models (last 5/10 years), after an average of 18 years of usage are dismantled. Therefore, it was assumed for simplicity, that 2022 car registrations are related to 2040 car radiations, and 2025 car registrations to 2043 car radiations. The missing point is knowing the car registered in 2025. For that a “scenario-based” analysis was employed allowing the forecast of car registrations of 2025. It was then possible to compare car radiations of 2040 and 2043 and the number of cars dismantled in 2040 and 2043 was obtained.

The data resulting from the forecasts allowed to understand the values of the sales volumes and of the dismantling volumes, however, they had to be transformed into Al sheet fluxes. To do that, the 59 best-selling cars of 2022 were considered as reference, classified according to their segment, and analysed to determine which bodywork components they have in aluminium. Such 59 best-selling car models represent the 72.9% of the entire market share in Italy of sold cars in 2022. For sake of simplicity, the first 20 top sold car models are reported in Table 1.
revealed low plastic strain near the design line (Figure 13), suggesting that the mechanical properties of the component were only partially affected. The values of the elastic springback obtained from the FE simulation (i.e. the nodal coordinates of the meshed part) were imported in MATLAB and then compared to the ones measured onto the real specimen. Despite minor deviations, there was notable correspondence between actual and virtual profiles (Figure 11). This result validates the use of FE simulation as a tool for predicting accurately the component final morphology.

<figure><img src="image_2666.png" /><figcaption>Figure 12. From left to right: output of the forming process; output of the trimming operation of one part extracted from Figure 1; 3D scan with Artec EVA of the real sample pre-flattening.</figcaption></figure>

<figure><img src="image_2667.png" /><figcaption>Figure 13. From left to right: simulative setup for flattening; plastic strain distribution of the part after flattening and spring-back.</figcaption></figure>

<figure><img src="image_2668.png" /><figcaption>Figure 11. Up: Height profile of the scanned portion from the real specimen. Down: Height profile of the simulated specimen. The dashed rectangle corresponds to the same regions.</figcaption></figure>

## Economic feasibility.

To perform an economic analysis, it is necessary to evaluate which will be the future aluminium sheet quantity recoverable from ELVs. Analysing UNRAE (Unione Nazionale Rappresentati Autoveicoli Esteri) data from 1990 to 2022, the values of car registrations and car radiations were forecasted for future years (Figure 14). The data collected showed that reasonably the newest car models (last 5/10 years), after an average of 18 years of usage are dismantled. Therefore, it was assumed for simplicity, that 2022 car registrations are related to 2040 car radiations, and 2025 car registrations to 2043 car radiations. The missing point is knowing the car registered in 2025. For that a “scenario-based” analysis was employed allowing the forecast of car registrations of 2025. It was then possible to compare car radiations of 2040 and 2043 and the number of cars dismantled in 2040 and 2043 was obtained.

The data resulting from the forecasts allowed to understand the values of the sales volumes and of the dismantling volumes, however, they had to be transformed into Al sheet fluxes. To do that, the 59 best-selling cars of 2022 were considered as reference, classified according to their segment, and analysed to determine which bodywork components they have in aluminium. Such 59 best-selling car models represent the 72.9% of the entire market share in Italy of sold cars in 2022. For sake of simplicity, the first 20 top sold car models are reported in Table 1.
<figure><img src="image_2673.png" /><figcaption>Figure 14. Analysis of the Italian car registration and radiations in the last 30 years from UNRAE.</figcaption></figure>

<table><caption>Table 1. First top 20 sold car models in Italy (2022).</caption><thead><tr><th>Number</th><th>Brand</th><th>Model</th><th>Segment</th><th>2022 Sales</th></tr></thead><tbody><tr><td>1</td><td>Fiat</td><td>Panda</td><td>A</td><td>105,384</td></tr><tr><td>2</td><td>Lancia</td><td>Ypsilon</td><td>B</td><td>40,970</td></tr><tr><td>3</td><td>Fiat</td><td>500</td><td>A</td><td>33,996</td></tr><tr><td>4</td><td>Dacia</td><td>Sandero</td><td>B</td><td>33,922</td></tr><tr><td>5</td><td>Citroen</td><td>C3</td><td>B</td><td>31,879</td></tr><tr><td>6</td><td>Jeep</td><td>Renegade</td><td>C</td><td>29,954</td></tr><tr><td>7</td><td>Ford</td><td>Puma</td><td>B</td><td>29,479</td></tr><tr><td>8</td><td>Toyota</td><td>Yaris</td><td>B</td><td>27,813</td></tr><tr><td>9</td><td>Toyota</td><td>Yaris Cross</td><td>B</td><td>26,023</td></tr><tr><td>10</td><td>Peugeot</td><td>208</td><td>B</td><td>25,827</td></tr><tr><td>11</td><td>Renault</td><td>Captur</td><td>B</td><td>25,456</td></tr><tr><td>12</td><td>Dacia</td><td>Duster</td><td>C</td><td>25,245</td></tr><tr><td>13</td><td>Volkswagen</td><td>T-Roc</td><td>C</td><td>25,053</td></tr><tr><td>14</td><td>Fiat</td><td>500X</td><td>C</td><td>22,244</td></tr><tr><td>15</td><td>Jeep</td><td>Compass</td><td>C</td><td>22,151</td></tr><tr><td>16</td><td>Volkswagen</td><td>T-Cross</td><td>B</td><td>20,851</td></tr><tr><td>17</td><td>Opel</td><td>Corsa</td><td>B</td><td>17,839</td></tr><tr><td>18</td><td>Renault</td><td>Clio</td><td>B</td><td>17,839</td></tr><tr><td>19</td><td>Peugeot</td><td>3008</td><td>C</td><td>17,138</td></tr><tr><td>20</td><td>Peugeot</td><td>2008</td><td>B</td><td>16,449</td></tr></tbody></table>

<figure><img src="image_2674.png" /><figcaption>Table 2. Car model considered as “reference” for the automotive market in Italy. Courtesy of Volkswagen.</figcaption></figure>

<figure><img src="image_2675.png" /><figcaption>Figure 15. Example of maximum inscribable rectangle in Volkswagen Polo car body.</figcaption></figure>

<table><caption>Table 3. Al sheet percentage with respect to the total sheet used in the automotive field to produce external car body components.</caption><thead><tr><th>Segment</th><th>2022 sales</th><th>Tot. Area sheet used (10³ m²)</th><th>Tot. Area Al-sheet used (10³ m²)</th><th>Tot. Area steel-sheet used (10³ m²)</th><th>Al-sheet percentage (%)</th></tr></thead><tbody><tr><td>A</td><td>199647</td><td>715,1</td><td>3,0</td><td>712,1</td><td>0,4</td></tr><tr><td>B</td><td>410767</td><td>2335,9</td><td>54,6</td><td>2301,4</td><td>2,3</td></tr><tr><td>C</td><td>255049</td><td>1385,3</td><td>89,4</td><td>1295,9</td><td>6,5</td></tr><tr><td>D</td><td>94038</td><td>657,8</td><td>119,3</td><td>538,5</td><td>18,1</td></tr></tbody></table>

<table><caption>Table 4. Area of rectangular panels potentially recoverable by Volkswagen car models, representative of “common” and most-sold car designs in the Italian market.</caption><thead><tr><th>Representative car model</th><th>Tot. Area from doors (m²)</th><th>Tot. Area from hood (m²)</th><th>Tot. Area from roof (m²)</th></tr></thead><tbody><tr><td>UP (segment A)</td><td>1,03</td><td>0,24</td><td>0,86</td></tr><tr><td>T-Cross (segment B)</td><td>0,95</td><td>0,69</td><td>1,07</td></tr><tr><td>T-Roc (segment C)</td><td>1,33</td><td>0,49</td><td>0,71</td></tr><tr><td>Tiguan (segment D)</td><td>1,29</td><td>0,83</td><td>1,45</td></tr></tbody></table>

By observing the data collected, it emerged that the most common Al component is the hood. This is because, as reported in [7], the transition from a steel hood to an aluminium one offers significant advantages.

Then, considering the Volkswagen brand as a representative brand (Table 2), for each segment, the average panel area present in the bodywork components (i.e. hood, roof, and doors) was calculated. Combining the data obtained from 2022 reference cars and the Volkswagen reference brand, the Al sheet percentage present in the car bodies of each segment (Table 3) is estimated. Making some assumptions on the likely gradual increase in the use of aluminium car body panels, the percentage of Al was calculated also for 2025. Finally, using again the Volkswagen brand as a
<figure><img src="image_2669.png" /><figcaption>Figure 14. Analysis of the Italian car registration and radiations in the last 30 years from UNRAE.</figcaption></figure>

<table><caption>Table 1. First top 20 sold car models in Italy (2022).</caption><thead><tr><th>Number</th><th>Brand</th><th>Model</th><th>Segment</th><th>2022 Sales</th></tr></thead><tbody><tr><td>1</td><td>Fiat</td><td>Panda</td><td>A</td><td>105,384</td></tr><tr><td>2</td><td>Lancia</td><td>Ypsilon</td><td>B</td><td>40,970</td></tr><tr><td>3</td><td>Fiat</td><td>500</td><td>A</td><td>33,996</td></tr><tr><td>4</td><td>Dacia</td><td>Sandero</td><td>B</td><td>33,922</td></tr><tr><td>5</td><td>Citroen</td><td>C3</td><td>B</td><td>31,879</td></tr><tr><td>6</td><td>Jeep</td><td>Renegade</td><td>C</td><td>29,954</td></tr><tr><td>7</td><td>Ford</td><td>Puma</td><td>B</td><td>29,479</td></tr><tr><td>8</td><td>Toyota</td><td>Yaris</td><td>B</td><td>27,813</td></tr><tr><td>9</td><td>Toyota</td><td>Yaris Cross</td><td>B</td><td>26,023</td></tr><tr><td>10</td><td>Peugeot</td><td>208</td><td>B</td><td>25,827</td></tr><tr><td>11</td><td>Renault</td><td>Captur</td><td>B</td><td>25,456</td></tr><tr><td>12</td><td>Dacia</td><td>Duster</td><td>C</td><td>25,245</td></tr><tr><td>13</td><td>Volkswagen</td><td>T-Roc</td><td>C</td><td>25,053</td></tr><tr><td>14</td><td>Fiat</td><td>500X</td><td>C</td><td>22,244</td></tr><tr><td>15</td><td>Jeep</td><td>Compass</td><td>C</td><td>22,151</td></tr><tr><td>16</td><td>Volkswagen</td><td>T-Cross</td><td>B</td><td>20,851</td></tr><tr><td>17</td><td>Opel</td><td>Corsa</td><td>B</td><td>17,839</td></tr><tr><td>18</td><td>Renault</td><td>Clio</td><td>B</td><td>17,839</td></tr><tr><td>19</td><td>Peugeot</td><td>3008</td><td>C</td><td>17,138</td></tr><tr><td>20</td><td>Peugeot</td><td>2008</td><td>B</td><td>16,449</td></tr></tbody></table>

<table><caption>Table 2. Car model considered as “reference” for the automotive market in Italy. Courtesy of Volkswagen.</caption><thead><tr><th>Segment A</th><th>Segment B</th><th>Segment C</th><th>Segment D</th></tr></thead><tbody><tr><td>UP</td><td>Polo</td><td>Golf</td><td>Tiguan</td></tr><tr><td></td><td>T-cross</td><td>T-roc</td><td>Passat</td></tr></tbody></table>

<figure><img src="image_2670.png" /><figcaption>Figure 15. Example of maximum inscribable rectangle in Volkswagen Polo car body.</figcaption></figure>

<table><caption>Table 3. Al sheet percentage with respect to the total sheet used in the automotive field to produce external car body components.</caption><thead><tr><th>Segment</th><th>2022 sales</th><th>Tot. Area sheet used (10³ m²)</th><th>Tot. Area Al-sheet used (10³ m²)</th><th>Tot. Area steel-sheet used (10³ m²)</th><th>Al-sheet percentage (%)</th></tr></thead><tbody><tr><td>A</td><td>199647</td><td>715,1</td><td>3,0</td><td>712,1</td><td>0,4</td></tr><tr><td>B</td><td>410767</td><td>2335,9</td><td>54,6</td><td>2301,4</td><td>2,3</td></tr><tr><td>C</td><td>255049</td><td>1385,3</td><td>89,4</td><td>1295,9</td><td>6,5</td></tr><tr><td>D</td><td>94038</td><td>657,8</td><td>119,3</td><td>538,5</td><td>18,1</td></tr></tbody></table>

<table><caption>Table 4. Area of rectangular panels potentially recoverable by Volkswagen car models, representative of “common” and most-sold car designs in the Italian market.</caption><thead><tr><th>Representative car model</th><th>Tot. Area from doors (m²)</th><th>Tot. Area from hood (m²)</th><th>Tot. Area from roof (m²)</th></tr></thead><tbody><tr><td>UP (segment A)</td><td>1,03</td><td>0,24</td><td>0,86</td></tr><tr><td>T-Cross (segment B)</td><td>0,95</td><td>0,69</td><td>1,07</td></tr><tr><td>T-Roc (segment C)</td><td>1,33</td><td>0,49</td><td>0,71</td></tr><tr><td>Tiguan (segment D)</td><td>1,29</td><td>0,83</td><td>1,45</td></tr></tbody></table>

By observing the data collected, it emerged that the most common Al component is the hood. This is because, as reported in [7], the transition from a steel hood to an aluminium one offers significant advantages.

Then, considering the Volkswagen brand as a representative brand (Table 2), for each segment, the average panel area present in the bodywork components (i.e. hood, roof, and doors) was calculated. Combining the data obtained from 2022 reference cars and the Volkswagen reference brand, the Al sheet percentage present in the car bodies of each segment (Table 3) is estimated. Making some assumptions on the likely gradual increase in the use of aluminium car body panels, the percentage of Al was calculated also for 2025. Finally, using again the Volkswagen brand as a
reference, for each segment, it was calculated the average surface achievable from each bodywork component (i.e. hood, roof, and doors) by determining the maximum inscribable rectangle in the car body (Figure 15). The achievable surface (Table 4) is intended as the sheet area that can be recovered from an ELV considering that in car bodies some obstacles to reworking such as handles, roof bars, cleaning systems for windscreen, etc. can be encountered.

Following this procedure, the aluminium output fluxes in 2040 can be calculated. The same route can be followed to calculate 2043 Al output fluxes with the expected 2025 aluminium percentage. A comparison between 2040 and 2043 Al sheet output fluxes was performed and the expected areas recoverable from the car body panels of ELVs are reported for three different market scenarios in Figure 16. It is worth noting that the quantity of recoverable Al sheets from ELVs is expected to increase exponentially, the figure proves that in only three years a growth of 81% might occur. The economic feasibility study was performed to evaluate if the remanufacturing of aluminium car body panels is a viable alternative to recycling from an economic perspective. Since remanufacturing through flattening is a novel recovery technique [1], different business scenarios were considered for the sake of completeness.

<figure><img src="image_2676.png" /><figcaption>Figure 16. Predicted amounts of Al sheet from ELVs under three market scenarios.</figcaption></figure>

A cost was calculated for each of the pre-flattening procedures, namely disassembly, cutting, polyurethane foam removal, paint stripping, and flattening costs. Other costs included in the analysis are opportunity costs. It is worth highlighting that the costs related to pre-flattening are unvaried for all the different scenarios. They have been calculated considering, for each different pre-flattening step, the contribution of three cost items: labour, equipment, and energy. The results obtained are 2.75 €/hood for the disassembly phase, 2.11 €/hood for the cutting operation, 2.50 €/hood for the polyurethane foam removal, and 7.80 €/hood for the paint stripping procedure performed with a chemical solvent. The total amounts to 15.16 €/hood. On the other hand, the costs related to the flattening operation vary depending on the business scenario considered and the expected Al sheet flux. For the first business scenario, it is assumed that the flattening is conducted by dismantlers who execute flattening on a rented press. In this case, the main cost items are the ones related to hoods transport and press renting, in addition to manpower and energy consumed by the press. The value of the energy consumed during each flattening cycle was obtained from the value of the instantaneous power consumed by the press. In a second business scenario, the possibility of integrating into the automotive market an emerging entity in charge of automotive sheet remanufacturing is assumed. Many assumptions were made, as having 20 sheet remanufacturers in the whole Italian area collaborating with the 1505 Italian authorized dismantlers. The costs to be calculated refer to hoods purchase, transport, manpower, energy, equipment, and facility. Summing up the pre-flattening costs to all the cost items generated by the flattening operation, the total costs of the remanufacturing procedure are obtained. The results are reported in Table 5 for 2040 and 2043,
reference, for each segment, it was calculated the average surface achievable from each bodywork component (i.e. hood, roof, and doors) by determining the maximum inscribable rectangle in the car body (Figure 15). The achievable surface (Table 4) is intended as the sheet area that can be recovered from an ELV considering that in car bodies some obstacles to reworking such as handles, roof bars, cleaning systems for windscreen, etc. can be encountered.

Following this procedure, the aluminium output fluxes in 2040 can be calculated. The same route can be followed to calculate 2043 Al output fluxes with the expected 2025 aluminium percentage. A comparison between 2040 and 2043 Al sheet output fluxes was performed and the expected areas recoverable from the car body panels of ELVs are reported for three different market scenarios in Figure 16. It is worth noting that the quantity of recoverable Al sheets from ELVs is expected to increase exponentially, the figure proves that in only three years a growth of 81% might occur. The economic feasibility study was performed to evaluate if the remanufacturing of aluminium car body panels is a viable alternative to recycling from an economic perspective. Since remanufacturing through flattening is a novel recovery technique [1], different business scenarios were considered for the sake of completeness.

<figure><img src="image_2671.png" /><figcaption>Figure 16. Predicted amounts of Al sheet from ELVs under three market scenarios.</figcaption></figure>

A cost was calculated for each of the pre-flattening procedures, namely disassembly, cutting, polyurethane foam removal, paint stripping, and flattening costs. Other costs included in the analysis are opportunity costs. It is worth highlighting that the costs related to pre-flattening are unvaried for all the different scenarios. They have been calculated considering, for each different pre-flattening step, the contribution of three cost items: labour, equipment, and energy. The results obtained are 2.75 €/hood for the disassembly phase, 2.11 €/hood for the cutting operation, 2.50 €/hood for the polyurethane foam removal, and 7.80 €/hood for the paint stripping procedure performed with a chemical solvent. The total amounts to 15.16 €/hood. On the other hand, the costs related to the flattening operation vary depending on the business scenario considered and the expected Al sheet flux. For the first business scenario, it is assumed that the flattening is conducted by dismantlers who execute flattening on a rented press. In this case, the main cost items are the ones related to hoods transport and press renting, in addition to manpower and energy consumed by the press. The value of the energy consumed during each flattening cycle was obtained from the value of the instantaneous power consumed by the press. In a second business scenario, the possibility of integrating into the automotive market an emerging entity in charge of automotive sheet remanufacturing is assumed. Many assumptions were made, as having 20 sheet remanufacturers in the whole Italian area collaborating with the 1505 Italian authorized dismantlers. The costs to be calculated refer to hoods purchase, transport, manpower, energy, equipment, and facility. Summing up the pre-flattening costs to all the cost items generated by the flattening operation, the total costs of the remanufacturing procedure are obtained. The results are reported in Table 5 for 2040 and 2043,
crossing the business scenarios with the 3 above mentioned scenarios concerning to material fluxes. Another business scenario might consider that the flattening operations are performed by the Original Equipment Manufacturers (OEMs) or the Independent Remanufacturers (IRs). Recently, many automotive brands have introduced remanufacturing centres, however, they are all intended to remanufacture components that can be reused in car productions, not metal sheets [8]. For this reason, this scenario has not been further investigated.

<table><caption>Table 5. Results of the cost analysis.</caption><thead><tr><th rowspan="3">Business scenarios</th><th colspan="3">2040</th><th colspan="3">2043</th></tr><tr><th colspan="3">market scenarios</th><th colspan="3">market scenarios</th></tr><tr><th>1</th><th>2</th><th>3</th><th>1</th><th>2</th><th>3</th></tr></thead><tbody><tr><th>1</th><td>26.88 €</td><td>25.90 €</td><td>30.68 €</td><td>26.37 €</td><td>29.94 €</td><td>26.56 €</td></tr><tr><th>2</th><td>32.75 €</td><td>32.35 €</td><td>31.44 €</td><td>30.60 €</td><td>30.43 €</td><td>29.99 €</td></tr></tbody></table>

It is evident that the hood remanufacturing costs are bigger than the cost of a primary Al sheet of area equal to the one that can be obtained from an ELV hood, which is about 4 €. However, the remanufacturing costs are lower in 2043 than in 2040, this means that higher volumes of aluminium hoods incentivize this practice through a better cost amortization. Besides, we can expect, at least in Europe, increasing costs of critical raw materials; while at the moment the proposed process seems anti-economic, it provides a dramatic reduction of environmental impact, and it might economically benefit from future variation of the market and business conditions.

## Conclusions

In conclusion, the dies design phase allowed to create a re-forming instrument considering a multitude of design constraints. The technical feasibility allowed to define the best flattening parameters to achieve a uniform flattening. It is advisable to use high temperatures (250 °C), moderate pressures (30 MPa), and not excessively prolonged dwell times (10 s). Interrelationships between independent variables were also discovered, specifically between temperature and pressure, and between pressure and dwell time (Figure 10). Experimental observations also showed the complex deformation behaviour of sheets once flattened, showing an interesting spring-forward phenomenon. Moreover, the simulation on Altair Inspire Form proved that the flattening process does not highly compromise the material formability (Figure 13) and that digital tools can be used for predicting the final part geometry (Figure 11). The economic feasibility analysis enabled to evaluate the costs related to five different remanufacturing business scenarios. The most viable scenarios emerged: flattening performed by dismantlers who rent the press and flattening executed by new remanufacturing figures. However, the costs associated with Al hoods remanufacturing are high (Table 5), surpassing the costs of purchasing new aluminium sheets of the same area amounting to 4 €. Therefore, only a significant growth in Al hood volumes and the introduction of governmental incentives can make aluminium hoods remanufacturing become advantageous. From the analysis performed on the possible future Al fluxes generated by ELVs, it can be stated that, if aluminium will be introduced in bodywork components more massively, as stated by many car brands, an exponential growth in Al sheet volumes is expected. By simply assuming that, in 2025, aluminium hoods will be introduced in some of the best-selling car models of 2022, the volumes of Al achievable from ELVs would nearly duplicate passing from 2040 to 2043.

## References

[1] D. Farioli, M. Fabrizio, E. Kaya, M. Strano, and V. Mussi, "Reshaping of thin steel parts by cold and warm flattening," *Int. J. Mater. Form.*, vol. 16, no. 4, 2023. https://doi.org/10.1007/s12289-023-01759-y
crossing the business scenarios with the 3 above mentioned scenarios concerning to material fluxes. Another business scenario might consider that the flattening operations are performed by the Original Equipment Manufacturers (OEMs) or the Independent Remanufacturers (IRs). Recently, many automotive brands have introduced remanufacturing centres, however, they are all intended to remanufacture components that can be reused in car productions, not metal sheets [8]. For this reason, this scenario has not been further investigated.

<table><caption>Table 5. Results of the cost analysis.</caption><thead><tr><th rowspan="3">Business scenarios</th><th colspan="3">2040</th><th colspan="3">2043</th></tr><tr><th colspan="3">market scenarios</th><th colspan="3">market scenarios</th></tr><tr><th>1</th><th>2</th><th>3</th><th>1</th><th>2</th><th>3</th></tr></thead><tbody><tr><th>1</th><td>26.88 €</td><td>25.90 €</td><td>30.68 €</td><td>26.37 €</td><td>29.94 €</td><td>26.56 €</td></tr><tr><th>2</th><td>32.75 €</td><td>32.35 €</td><td>31.44 €</td><td>30.60 €</td><td>30.43 €</td><td>29.99 €</td></tr></tbody></table>

It is evident that the hood remanufacturing costs are bigger than the cost of a primary Al sheet of area equal to the one that can be obtained from an ELV hood, which is about 4 €. However, the remanufacturing costs are lower in 2043 than in 2040, this means that higher volumes of aluminium hoods incentivize this practice through a better cost amortization. Besides, we can expect, at least in Europe, increasing costs of critical raw materials; while at the moment the proposed process seems anti-economic, it provides a dramatic reduction of environmental impact, and it might economically benefit from future variation of the market and business conditions.

## Conclusions

In conclusion, the dies design phase allowed to create a re-forming instrument considering a multitude of design constraints. The technical feasibility allowed to define the best flattening parameters to achieve a uniform flattening. It is advisable to use high temperatures (250 °C), moderate pressures (30 MPa), and not excessively prolonged dwell times (10 s). Interrelationships between independent variables were also discovered, specifically between temperature and pressure, and between pressure and dwell time (Figure 10). Experimental observations also showed the complex deformation behaviour of sheets once flattened, showing an interesting spring-forward phenomenon. Moreover, the simulation on Altair Inspire Form proved that the flattening process does not highly compromise the material formability (Figure 13) and that digital tools can be used for predicting the final part geometry (Figure 11). The economic feasibility analysis enabled to evaluate the costs related to five different remanufacturing business scenarios. The most viable scenarios emerged: flattening performed by dismantlers who rent the press and flattening executed by new remanufacturing figures. However, the costs associated with Al hoods remanufacturing are high (Table 5), surpassing the costs of purchasing new aluminium sheets of the same area amounting to 4 €. Therefore, only a significant growth in Al hood volumes and the introduction of governmental incentives can make aluminium hoods remanufacturing become advantageous. From the analysis performed on the possible future Al fluxes generated by ELVs, it can be stated that, if aluminium will be introduced in bodywork components more massively, as stated by many car brands, an exponential growth in Al sheet volumes is expected. By simply assuming that, in 2025, aluminium hoods will be introduced in some of the best-selling car models of 2022, the volumes of Al achievable from ELVs would nearly duplicate passing from 2040 to 2043.

## References

[1] D. Farioli, M. Fabrizio, E. Kaya, M. Strano, and V. Mussi, "Reshaping of thin steel parts by cold and warm flattening," *Int. J. Mater. Form.*, vol. 16, no. 4, 2023. https://doi.org/10.1007/s12289-023-01759-y
[2] J. R. Duflou et al., "Environmental assessment of solid state recycling routes for aluminium alloys: Can solid state processes significantly reduce the environmental impact of aluminium recycling?," *CIRP Ann. - Manuf. Technol.*, vol. 64, no. 1, pp. 37-40, 2015. https://doi.org/10.1016/j.cirp.2015.04.051

[3] D. Parker et al., "Remanufacturing Market Study," 2015.

[4] A. Shahedi, M. M. Nasiri, M. S. Sangari, F. Werner, and F. Jolai, "A Stochastic Multi-Objective Model for a Sustainable Closed-Loop Supply Chain Network Design in the Automotive Industry," *Process Integr. Optim. Sustain.*, vol. 6, no. 1, pp. 189-209, Mar. 2022. https://doi.org/10.1007/s41660-021-00204-4

[5] G. Copani, P. Shafinejad, T. Hipke, R. Haase, and T. Paizs, "New metals remanufacturing business models in automotive industry," *Procedia CIRP*, vol. 112, pp. 436-441, 2022. https://doi.org/10.1016/j.procir.2022.09.033

[6] F. Grimaldi, "Erase & Rewind," Politecnico di Milano, 2022.

[7] M. A. Omar, *The Automotive Body Manufacturing Systems and Processes*. Wiley, 2011. doi: 10.1002/9781119990888

[8] M. Kalverkamp and T. Raabe, "Automotive Remanufacturing in the Circular Economy in Europe," *J. Macromarketing*, vol. 38, no. 1, pp. 112-130, Mar. 2018. https://doi.org/10.1177/0276146717739066
[2] J. R. Duflou et al., "Environmental assessment of solid state recycling routes for aluminium alloys: Can solid state processes significantly reduce the environmental impact of aluminium recycling?," *CIRP Ann. - Manuf. Technol.*, vol. 64, no. 1, pp. 37-40, 2015. https://doi.org/10.1016/j.cirp.2015.04.051

[3] D. Parker et al., "Remanufacturing Market Study," 2015.

[4] A. Shahedi, M. M. Nasiri, M. S. Sangari, F. Werner, and F. Jolai, "A Stochastic Multi-Objective Model for a Sustainable Closed-Loop Supply Chain Network Design in the Automotive Industry," *Process Integr. Optim. Sustain.*, vol. 6, no. 1, pp. 189-209, Mar. 2022. https://doi.org/10.1007/s41660-021-00204-4

[5] G. Copani, P. Shafinejad, T. Hipke, R. Haase, and T. Paizs, "New metals remanufacturing business models in automotive industry," *Procedia CIRP*, vol. 112, pp. 436-441, 2022. https://doi.org/10.1016/j.procir.2022.09.033

[6] F. Grimaldi, "Erase & Rewind," Politecnico di Milano, 2022.

[7] M. A. Omar, *The Automotive Body Manufacturing Systems and Processes*. Wiley, 2011. doi: 10.1002/9781119990888

[8] M. Kalverkamp and T. Raabe, "Automotive Remanufacturing in the Circular Economy in Europe," *J. Macromarketing*, vol. 38, no. 1, pp. 112-130, Mar. 2018. https://doi.org/10.1177/0276146717739066
# Sustainability and economic assessment of an innovative automated filament winding process

BIANCHI Iacopo<fnref n="1" />,ª, DE PRISCO Nello<fnref n="2" />,ᵇ, MANCIA Tommaso<fnref n="1" />,ᶜ,
MARTONE Alfonso<fnref n="2" />,ᵈ, PALMIERI Barbara<fnref n="2" />,ᵉ, SIMONCINI Michela<fnref n="1" />,>f,
VERDINI Tommaso<fnref n="1" />,<fnref n="9" />*

**Keywords:** Filament Winding, CFRP, LCA, LCC

**Abstract.** The present paper aims at studying the environmental and economic impacts of an innovative Filament Winding (FW) process used to realize a tubular shape structural component in Carbon Fiber Reinforced Polymer (CFRP). To this purpose, the Life Cycle Assessment (LCA) and Life Cycle Costing (LCC) methodologies were applied using a “from cradle to grave” approach. Specifically, a towbar used for aircraft pushback was considered as case study. All phases of the life cycle of the analyzed component were included (from the raw materials extraction to the disposal phase). The comparison between the CFRP towbar investigated and a traditional one in aluminum alloy was performed. The LCC analysis was conducted by considering all costs associated with the automated filament winding process, from the initial investment costs. For all the considered impact categories, the CFRP towbar showed the lowest environmental impacts, mainly due to both the reduced weight and service life fuel consumption. The cost and carbon footprint of the innovative component were associated with raw materials use.

**Introduction**

Carbon Fiber Reinforced Polymers (CFRP) are gaining an increasing interest in many industrial fields, such as aerospace, automotive, biomedical, nautical and construction. Such materials are highly indicated for applications in which low weights and high mechanical performances are required. As a matter of fact, due to the higher specific properties of composites, weight reduction can be achieved while maintaining the same performance of traditional material components. Among the processes carried out in CFRPs, Filament Winding (FW) represents a valuable solution for automated production of axisymmetric components. FW is a technology based on the winding of impregnated continuous fibers on a rotating mandrel [1]. By winding several layers of material at defined angles and following precise paths, high performance structures, such as pipes, tubes, pressure vessels, shafts and rotor blades, can be produced [2,3]. This technology can help overcome the issues related to labour intensive and expensive phases of traditional composite manufacturing techniques by completely automating the lay-up phase. In fact, high labour costs and long production time are common issue in different composite manufacturing technologies such as autoclave and vacuum bag molding [4]. These aspects are critical on an industrial level and can limit the spread of composite material use. Hence, FW can represent a relevant improvement with respect to other composite manufacturing techniques; as a matter of fact, automated fiber deposition methods could help to reduce the costs of composite parts, making them more competitive market alternatives.

<figure><img src="image_2677.png" /></figure>

<footnote n="1">¹Università Politecnica delle Marche, Via Brecce Bianche 12, 60123 Ancona, Italy</footnote>

<footnote n="2">²Advanced Tools and Moulds, A.T.M. srl, Via San Pasquale a Chiaia, 83, 80121 Napoli, Italy</footnote>

<footnote>ªi.bianchi@pm.univpm.it, ᵇnellodeprisco@atmsrl.com, ᶜt.mancia@staff.univpm.it,</footnote>

<footnote>ᵈalfmartone@gmail.com, ᶜbarbara.palmieri@atmsrl.com, ᵈm.simoncini@staff.univpm.it,</footnote>

<footnote n="9">⁹t.verdini@pm.univpm.it</footnote>
# Sustainability and economic assessment of an innovative automated filament winding process

BIANCHI Iacopo<fnref n="1" />,ª, DE PRISCO Nello<fnref n="2" />,ᵇ, MANCIA Tommaso<fnref n="1" />,ᶜ,
MARTONE Alfonso<fnref n="2" />,ᵈ, PALMIERI Barbara<fnref n="2" />,ᵉ, SIMONCINI Michela<fnref n="1" />,*f,
VERDINI Tommaso<fnref n="1" />,<fnref n="9" />*

**Keywords:** Filament Winding, CFRP, LCA, LCC

**Abstract.** The present paper aims at studying the environmental and economic impacts of an innovative Filament Winding (FW) process used to realize a tubular shape structural component in Carbon Fiber Reinforced Polymer (CFRP). To this purpose, the Life Cycle Assessment (LCA) and Life Cycle Costing (LCC) methodologies were applied using a “from cradle to grave” approach. Specifically, a towbar used for aircraft pushback was considered as case study. All phases of the life cycle of the analyzed component were included (from the raw materials extraction to the disposal phase). The comparison between the CFRP towbar investigated and a traditional one in aluminum alloy was performed. The LCC analysis was conducted by considering all costs associated with the automated filament winding process, from the initial investment costs. For all the considered impact categories, the CFRP towbar showed the lowest environmental impacts, mainly due to both the reduced weight and service life fuel consumption. The cost and carbon footprint of the innovative component were associated with raw materials use.

**Introduction**

Carbon Fiber Reinforced Polymers (CFRP) are gaining an increasing interest in many industrial fields, such as aerospace, automotive, biomedical, nautical and construction. Such materials are highly indicated for applications in which low weights and high mechanical performances are required. As a matter of fact, due to the higher specific properties of composites, weight reduction can be achieved while maintaining the same performance of traditional material components. Among the processes carried out in CFRPs, Filament Winding (FW) represents a valuable solution for automated production of axisymmetric components. FW is a technology based on the winding of impregnated continuous fibers on a rotating mandrel [1]. By winding several layers of material at defined angles and following precise paths, high performance structures, such as pipes, tubes, pressure vessels, shafts and rotor blades, can be produced [2,3]. This technology can help overcome the issues related to labour intensive and expensive phases of traditional composite manufacturing techniques by completely automating the lay-up phase. In fact, high labour costs and long production time are common issue in different composite manufacturing technologies such as autoclave and vacuum bag molding [4]. These aspects are critical on an industrial level and can limit the spread of composite material use. Hence, FW can represent a relevant improvement with respect to other composite manufacturing techniques; as a matter of fact, automated fiber deposition methods could help to reduce the costs of composite parts, making them more competitive market alternatives.

<figure><img src="image_2672.png" /></figure>

<footnote n="1">¹Università Politecnica delle Marche, Via Brecce Bianche 12, 60123 Ancona, Italy</footnote>

<footnote n="2">²Advanced Tools and Moulds, A.T.M. srl, Via San Pasquale a Chiaia, 83, 80121 Napoli, Italy</footnote>

<footnote>ªi.bianchi@pm.univpm.it, ᵇnellodeprisco@atmsrl.com, ᶜt.mancia@staff.univpm.it,</footnote>

<footnote>ᵈalfmartone@gmail.com, ᶜbarbara.palmieri@atmsrl.com, ᵈm.simoncini@staff.univpm.it,</footnote>

<footnote n="9">⁹t.verdini@pm.univpm.it</footnote>
In this contest, MIUR (Ministry of Education, University and Research) is funding the research project titled "Smart Tow Winding", involving the Marche Polytechnic University and ATM srl, concerning the development of an innovative process for the fabrication of composite components through filament winding technology characterized by increased performances and improved sustainability and cost with respect to traditional metal parts. The main outcome of the project is the development of an innovative CFRPs towbar for airplanes and helicopters pushback. Towbars are designed to connect a pushback vehicle to the front landing gear of aircrafts in order to safely maneuver them on the ground and prepare them for takeoff or push them back to the gates. They are traditionally realized in metals (e.g. low-carbon steels and aluminum alloys) but composite materials such as CFRPs produced via filament winding can be a valuable alternative to provide weight reduction while maintaining the same stiffness and safety factor [5].

From an environmental sustainability perspective, the weight reduction provided by CFRPs can help reduce fuel consumption and emissions associated with the service life of transport sectors components. However, composite parts manufacturing is typically characterized by high carbon footprint due to energy intensive processes for raw materials production (i.e. resin and carbon fibers) and molding processes [6]. These processes could counterbalance the benefits associated with weight reduction in terms of emissions reduction. For this reason, a Design for Environment approach is required to ensure that innovative composite parts are not only a valuable solution from a mechanical performance point of view but also in terms of sustainability. For the present case study, a detailed analysis of the economic and environmental impacts of composites and FW is crucial to ensure a sustainable development of the innovative towbar.

At present, several literature analyses investigated the possibilities in FW processes by considering, for example, sustainable materials, improved deposition trajectories and designs [7–9]. Few sustainability assessments concerning filament wound products can be found in literature; Schneider et al assessed the environmental impacts of CFRPs preform for ceramic matrix composites production via FW [10]. Rasheed et al compared FW and pultrusion processes for the production of glass-fiber composites from both economic and environmental perspectives [11]. Mindermann et al investigated the structural performances and sustainability of different natural fibers composites realized via FW [12]. However, literature lacks of studies concerning the design and life cycle analyses of high performance composite wound components employed as substitutes for traditional metal parts. Detailed evaluations of innovative production processes and comparison with traditional systems are required to determine possible criticalities and improvements of new products. In addition, cost analyses for CFRPs are required to provide industrial decision-making tools.

In this framework, the present paper concerns the design and environmental and economic sustainability of a CFRP towbar for aircraft pushback produced using an automated FW system and comparison with traditional metal towbar. An initial design phase was conducted on the composite part using different simulation software and the obtained data were employed in comparative Life Cycle Assessment and Life Cycle Costing analyses

## Materials and Method

The first phase of this work concerned the design phase of an innovative composite towbar for aircraft pushback. The considered towbar has a length equal to 3000 mm and a circular cross section with a constant diameter of 80 mm. This component can be used to maneuver a 6000 kg helicopter. The part is essentially subjected to two possible load conditions: tensile loads related to the aircraft acceleration and compressive load associated with the braking phase. The maximum load value is equal to 177 kN and it can be calculated considering the aircraft weight, an impact load factor equal to 2 and a safety factor equal to 1.5. Data related to the components dimensions and structural requirements were provided by the industrial experts. The traditional steel towbar has a wall thickness equal to 3.6 mm and a total weight of 28.92 kg. The goal of the design phase
In this contest, MIUR (Ministry of Education, University and Research) is funding the research project titled "Smart Tow Winding", involving the Marche Polytechnic University and ATM srl, concerning the development of an innovative process for the fabrication of composite components through filament winding technology characterized by increased performances and improved sustainability and cost with respect to traditional metal parts. The main outcome of the project is the development of an innovative CFRPs towbar for airplanes and helicopters pushback. Towbars are designed to connect a pushback vehicle to the front landing gear of aircrafts in order to safely maneuver them on the ground and prepare them for takeoff or push them back to the gates. They are traditionally realized in metals (e.g. low-carbon steels and aluminum alloys) but composite materials such as CFRPs produced via filament winding can be a valuable alternative to provide weight reduction while maintaining the same stiffness and safety factor [5].

From an environmental sustainability perspective, the weight reduction provided by CFRPs can help reduce fuel consumption and emissions associated with the service life of transport sectors components. However, composite parts manufacturing is typically characterized by high carbon footprint due to energy intensive processes for raw materials production (i.e. resin and carbon fibers) and molding processes [6]. These processes could counterbalance the benefits associated with weight reduction in terms of emissions reduction. For this reason, a Design for Environment approach is required to ensure that innovative composite parts are not only a valuable solution from a mechanical performance point of view but also in terms of sustainability. For the present case study, a detailed analysis of the economic and environmental impacts of composites and FW is crucial to ensure a sustainable development of the innovative towbar.

At present, several literature analyses investigated the possibilities in FW processes by considering, for example, sustainable materials, improved deposition trajectories and designs [7–9]. Few sustainability assessments concerning filament wound products can be found in literature; Schneider et al assessed the environmental impacts of CFRPs preform for ceramic matrix composites production via FW [10]. Rasheed et al compared FW and pultrusion processes for the production of glass-fiber composites from both economic and environmental perspectives [11]. Mindermann et al investigated the structural performances and sustainability of different natural fibers composites realized via FW [12]. However, literature lacks of studies concerning the design and life cycle analyses of high performance composite wound components employed as substitutes for traditional metal parts. Detailed evaluations of innovative production processes and comparison with traditional systems are required to determine possible criticalities and improvements of new products. In addition, cost analyses for CFRPs are required to provide industrial decision-making tools.

In this framework, the present paper concerns the design and environmental and economic sustainability of a CFRP towbar for aircraft pushback produced using an automated FW system and comparison with traditional metal towbar. An initial design phase was conducted on the composite part using different simulation software and the obtained data were employed in comparative Life Cycle Assessment and Life Cycle Costing analyses

## Materials and Method

The first phase of this work concerned the design phase of an innovative composite towbar for aircraft pushback. The considered towbar has a length equal to 3000 mm and a circular cross section with a constant diameter of 80 mm. This component can be used to maneuver a 6000 kg helicopter. The part is essentially subjected to two possible load conditions: tensile loads related to the aircraft acceleration and compressive load associated with the braking phase. The maximum load value is equal to 177 kN and it can be calculated considering the aircraft weight, an impact load factor equal to 2 and a safety factor equal to 1.5. Data related to the components dimensions and structural requirements were provided by the industrial experts. The traditional steel towbar has a wall thickness equal to 3.6 mm and a total weight of 28.92 kg. The goal of the design phase
is to determine a composite material layering for the towbar able to withstand the defined load and with a reduced weight with respect to the traditional component. To this purpose, an iterative design phase similar to that presented in previous literature was followed [13].

The composite part is produced by filament winding using a towpreg constituted by carbon fibers (68%wt) and an epoxy resin matrix (32%wt); starting from the constituents datasheets, the composite material mechanical properties were calculated using mixture rules (Table 1).

<table><caption>Table 1 Mechanical properties of the considered materials</caption><thead><tr><th></th><th>Carbon fiber</th><th>Epoxy resin</th><th>Composite material</th></tr></thead><tbody><tr><td>Elastic modulus (E)</td><td>230 GPa</td><td>3500 MPa</td><td>75 GPa</td></tr><tr><td>Ultimate Tensile Strength (t)</td><td>4900 MPa</td><td>73 MPa</td><td>750 MPa</td></tr><tr><td>Density (ρ)</td><td>1.8 g/cm³</td><td>1.1 g/cm³</td><td>1.5 g/cm³</td></tr></tbody></table>

In accordance with previous literature, an iterative procedure based on the use two software was followed to define the composite layers number and orientation [13]. CADWIND was employed to create virtual models of composite layers with different winding angles. The software allows to simulate the filament winding process and calculate fiber paths and winding patterns. This also allows to create meshed models that represent the composite part and can be simulated in Finite Element Method (FEM) software considering parameters such as winding angles, bandwidth and number of layers [14]. The models created in CADWIND were imported in Siemens NX FEM software to simulate their structural response in a static structural solution (SOL 101). The previously defined compressive and tensile loads were applied to the structure and the stress and strain in each composite layer were obtained. Maximum stress and strain criteria (i.e. max strain equal to 0.007) were employed to determine whether or not the layering satisfied the structural requirements. In addition, buckling and fatigue resistance verifications were conducted. The final part configuration was obtained iteratively, by analyzing the output of the FEM simulations and changing the layer number (and therefore the part thickness) and orientation consequently. The design phase was also crucial for the Life Cycle Analyses as it provided primary data regarding the component material use and production phases.

## Life Cycle Assessment

In order to evaluate the environmental effects of the CFRP towbar and to compare them to those of the traditional aluminium component, the standardized methodology outlined in the UNI EN ISO 14040-44 standard was applied.

## Goal and scope definition

The present LCA analysis aims at quantifying the environmental impact of a composite materials towbar and comparing them to a commercial aluminium towbars. The functional unit (FU) is defined as the production and use of a towbar used to transport helicopters for 100000 pushback operations, with an average operation length of 1 km and an average speed of 9 km/h. The present analysis can be classified as “from cradle to grave” as it includes input and output from the extraction of raw materials to the final use of the components. Figure 1 shows all the cycle phases included in the study.

Hence, two scenarios were considered: Scenario 1 concerns the production of the CFRP towbar by means of a FW process; it includes raw materials production (carbon fibers and resin), prepregging phases, aluminium mandrel production, FW, curing and use phase. On the other hand, Scenario 2 deals with the production of an aluminum towbar; this scenario includes the extrusion of an aluminium circular tube, sandblasting, surface cleaning, powder coating to provide corrosion resistance and service life emission.
is to determine a composite material layering for the towbar able to withstand the defined load and with a reduced weight with respect to the traditional component. To this purpose, an iterative design phase similar to that presented in previous literature was followed [13].

The composite part is produced by filament winding using a towpreg constituted by carbon fibers (68%wt) and an epoxy resin matrix (32%wt); starting from the constituents datasheets, the composite material mechanical properties were calculated using mixture rules (Table 1).

<table><caption>Table 1 Mechanical properties of the considered materials</caption><thead><tr><th></th><th>Carbon fiber</th><th>Epoxy resin</th><th>Composite material</th></tr></thead><tbody><tr><td>Elastic modulus (E)</td><td>230 GPa</td><td>3500 MPa</td><td>75 GPa</td></tr><tr><td>Ultimate Tensile Strength (t)</td><td>4900 MPa</td><td>73 MPa</td><td>750 MPa</td></tr><tr><td>Density (ρ)</td><td>1.8 g/cm³</td><td>1.1 g/cm³</td><td>1.5 g/cm³</td></tr></tbody></table>

In accordance with previous literature, an iterative procedure based on the use two software was followed to define the composite layers number and orientation [13]. CADWIND was employed to create virtual models of composite layers with different winding angles. The software allows to simulate the filament winding process and calculate fiber paths and winding patterns. This also allows to create meshed models that represent the composite part and can be simulated in Finite Element Method (FEM) software considering parameters such as winding angles, bandwidth and number of layers [14]. The models created in CADWIND were imported in Siemens NX FEM software to simulate their structural response in a static structural solution (SOL 101). The previously defined compressive and tensile loads were applied to the structure and the stress and strain in each composite layer were obtained. Maximum stress and strain criteria (i.e. max strain equal to 0.007) were employed to determine whether or not the layering satisfied the structural requirements. In addition, buckling and fatigue resistance verifications were conducted. The final part configuration was obtained iteratively, by analyzing the output of the FEM simulations and changing the layer number (and therefore the part thickness) and orientation consequently. The design phase was also crucial for the Life Cycle Analyses as it provided primary data regarding the component material use and production phases.

## Life Cycle Assessment

In order to evaluate the environmental effects of the CFRP towbar and to compare them to those of the traditional aluminium component, the standardized methodology outlined in the UNI EN ISO 14040-44 standard was applied.

## Goal and scope definition

The present LCA analysis aims at quantifying the environmental impact of a composite materials towbar and comparing them to a commercial aluminium towbars. The functional unit (FU) is defined as the production and use of a towbar used to transport helicopters for 100000 pushback operations, with an average operation length of 1 km and an average speed of 9 km/h. The present analysis can be classified as “from cradle to grave” as it includes input and output from the extraction of raw materials to the final use of the components. Figure 1 shows all the cycle phases included in the study.

Hence, two scenarios were considered: Scenario 1 concerns the production of the CFRP towbar by means of a FW process; it includes raw materials production (carbon fibers and resin), prepregging phases, aluminium mandrel production, FW, curing and use phase. On the other hand, Scenario 2 deals with the production of an aluminium towbar; this scenario includes the extrusion of an aluminium circular tube, sandblasting, surface cleaning, powder coating to provide corrosion resistance and service life emission.
<figure><img src="image_2678.png" /><figcaption>Figure 1 System boundaries of the LCA analysis of a CRFP towbar</figcaption></figure>

## Life Cycle Inventory (LCI)

Both primary and secondary data were employed for the LCI phase. Previous literature analyses and commercial database were used as secondary data source.

* Transport of fiber and epoxy resin was retrieved by the study conducted by Forcellese et al. [15];

* CF production was modelled according to Forcellese et al. [15]; towpreg was considered to be constituted by 60%wt (in weight) by CF and 40%wt by epoxy resin;

* Preimpregnation process energy and material use (electric energy, raw materials use, consumables, release paper) was modelled according to Postacchini et al. [16];

* Energy consumption for the filament winding process for towbar production was taken from literature [17];

* “Curing phase” was modelled according to Forcellese et al. [15].

* The quantity of aluminium used for the mandrel construction was estimated considering its final dimensions and the amount of material removed by chipping operations; the data regarding the mandrel (e.g. weight and volume) were obtained from the part CAD model. It was assumed that it has a service life of 100 cycles;

* Starting from a commercial extruded bar in aluminium alloy, the mandrel was produced by means of turning operation. In addition, threading for attachment to the winding machine was considered. Machining operations were modelled considering the Ecoinvent database.

* The amount of material removed during threading of the aluminium mandrel was 50% of the chip previously produced during turning;

The defined service life of the FU and the average consumption value of a tug were used for the use phase modelling. The fuel consumption emissions were allocated to the functional unit considering its weight in each scenario.

## Life cycle impact assessment (LCIA)

The impact categories used in this LCA analysis are ReCiPe and Global Warming Potential (GWP). ReCiPe provides a complete overview of environmental effects of products or processes, by considering 18 midpoint impact categories, whilst GWP quantifies the GreenHouse Gases (GHG) emission in the atmosphere and evaluates how they effect to global warming and climate change.
<figure><img src="image_2673.png" /><figcaption>Figure 1 System boundaries of the LCA analysis of a CRFP towbar</figcaption></figure>

## Life Cycle Inventory (LCI)

Both primary and secondary data were employed for the LCI phase. Previous literature analyses and commercial database were used as secondary data source.

* Transport of fiber and epoxy resin was retrieved by the study conducted by Forcellese et al. [15];

* CF production was modelled according to Forcellese et al. [15]; towpreg was considered to be constituted by 60%wt (in weight) by CF and 40%wt by epoxy resin;

* Preimpregnation process energy and material use (electric energy, raw materials use, consumables, release paper) was modelled according to Postacchini et al. [16];

* Energy consumption for the filament winding process for towbar production was taken from literature [17];

* “Curing phase” was modelled according to Forcellese et al. [15].

* The quantity of aluminium used for the mandrel construction was estimated considering its final dimensions and the amount of material removed by chipping operations; the data regarding the mandrel (e.g. weight and volume) were obtained from the part CAD model. It was assumed that it has a service life of 100 cycles;

* Starting from a commercial extruded bar in aluminium alloy, the mandrel was produced by means of turning operation. In addition, threading for attachment to the winding machine was considered. Machining operations were modelled considering the Ecoinvent database.

* The amount of material removed during threading of the aluminium mandrel was 50% of the chip previously produced during turning;

The defined service life of the FU and the average consumption value of a tug were used for the use phase modelling. The fuel consumption emissions were allocated to the functional unit considering its weight in each scenario.

## Life cycle impact assessment (LCIA)

The impact categories used in this LCA analysis are ReCiPe and Global Warming Potential (GWP). ReCiPe provides a complete overview of environmental effects of products or processes, by considering 18 midpoint impact categories, whilst GWP quantifies the GreenHouse Gases (GHG) emission in the atmosphere and evaluates how they effect to global warming and climate change.
<table><caption>Table 2 Relevant LCI data</caption><tbody><tr><td colspan="3"><strong>Mandrel production phase</strong></td></tr><tr><td>Aluminium quantity</td><td>31.60</td><td>kg</td></tr><tr><td>Aluminium removed by turning</td><td>0.07</td><td>kg</td></tr><tr><td>Aluminium removed by threading</td><td>0.03</td><td>kg</td></tr><tr><td colspan="3"><strong>Preimpregnation phase</strong></td></tr><tr><td>Towpreg meter</td><td>5874.70</td><td>m</td></tr><tr><td>Carbon fiber quantity</td><td>1.02</td><td>g/m</td></tr><tr><td>Epoxy resin quantity</td><td>0.48</td><td>g/m</td></tr><tr><td>Acetone (polishing)</td><td>0.02</td><td>g/m</td></tr><tr><td>Polypropylene (release paper)</td><td>0.55</td><td>g/m</td></tr><tr><td colspan="3"><strong>Freezer storage towpreg</strong></td></tr><tr><td>Electricity</td><td>7.50</td><td>kWh</td></tr><tr><td colspan="3"><strong>Filament winding</strong></td></tr><tr><td>Kg CFRP</td><td>8.81</td><td>kg</td></tr><tr><td>Electricity</td><td>3.50</td><td>Wh/kg</td></tr><tr><td colspan="3"><strong>Curing phase</strong></td></tr><tr><td>Electricity</td><td>9.54</td><td>KWh</td></tr><tr><td>Nylon 66 (vacuum bag)</td><td>0.28</td><td>kg</td></tr><tr><td>PET (breather)</td><td>0.21</td><td>kg</td></tr><tr><td>PTFE (release film)</td><td>0.031</td><td>kg</td></tr><tr><td>Organic solvent (release agent)</td><td>0.17</td><td>kg</td></tr><tr><td colspan="3"><strong>Use Phase</strong></td></tr><tr><td>Electricity</td><td>36.3</td><td>kWh</td></tr><tr><td colspan="3"><strong>Transport phase</strong></td></tr><tr><td>CF transport, ferry</td><td>1010</td><td>kgkm</td></tr><tr><td>CF transport, truck</td><td>899</td><td>kgkm</td></tr><tr><td>ER transport, truck</td><td>3830</td><td>kgkm</td></tr><tr><td>Mandrel transport, truck</td><td>2530</td><td>kgkm</td></tr><tr><td>Towbar transport, truck</td><td>204</td><td>kgkm</td></tr></tbody></table>

## Life Cycle Costing

LCC summarizes the costs associated with all the life cycle phases of a product that are directly calculated starting from one are more cost factors in that life cycle. LCC follows a methodology similar to LCA, involving the establishment of FU and system boundaries [18].

The present LCC analysis aims at quantifying the costs associated with a CFRP towbar life cycle. In this case, FU and system boundaries are same as those used in previous LCA analysis.

Both primary and secondary data were employed for the cost evaluation. Lean Cost software was used for the evaluation of the mandrel costs and literature analyses were used for all other phases. Towpreg commercial cost per kg was considered in this analysis. For the filament winding phase, energy, material, labour, machine depreciation and maintenance, mandrel production costs were included. A service life of 100 cycle was considered for the mandrel in order to allocate its production cost to the FU [4]. The curing phase included energy, material, labour and autoclave costs [19]. Finally, in the refrigerated storage phase and use phase only include cost resulting from energy consumption (the depreciation costs of the freezer attributable to the material needed for the towbar construction are negligible).

## Results and discussion

Preliminary FEM analyses were conducted considering single layers with different winding angles (from 20° to 85°) subjected to tensile load. Lower winding angles provide higher tensile stiffness and strength while lower structure weight. In fact, due to anisotropic properties of towpregs, it is better to align the fibers along the load direction to improve the structural response of the composite part. Hence, focus was given to layering with the majority of low winding angle layers. Layers with angle close to 90° were also used as they provide high layers compaction during the production process. After several iterations, the final symmetrical layering was defined as follows:
<table><caption>Table 2 Relevant LCI data</caption><tbody><tr><td colspan="3"><strong>Mandrel production phase</strong></td></tr><tr><td>Aluminium quantity</td><td>31.60</td><td>kg</td></tr><tr><td>Aluminium removed by turning</td><td>0.07</td><td>kg</td></tr><tr><td>Aluminium removed by threading</td><td>0.03</td><td>kg</td></tr><tr><td colspan="3"><strong>Preimpregnation phase</strong></td></tr><tr><td>Towpreg meter</td><td>5874.70</td><td>m</td></tr><tr><td>Carbon fiber quantity</td><td>1.02</td><td>g/m</td></tr><tr><td>Epoxy resin quantity</td><td>0.48</td><td>g/m</td></tr><tr><td>Acetone (polishing)</td><td>0.02</td><td>g/m</td></tr><tr><td>Polypropylene (release paper)</td><td>0.55</td><td>g/m</td></tr><tr><td colspan="3"><strong>Freezer storage towpreg</strong></td></tr><tr><td>Electricity</td><td>7.50</td><td>kWh</td></tr><tr><td colspan="3"><strong>Filament winding</strong></td></tr><tr><td>Kg CFRP</td><td>8.81</td><td>kg</td></tr><tr><td>Electricity</td><td>3.50</td><td>Wh/kg</td></tr><tr><td colspan="3"><strong>Curing phase</strong></td></tr><tr><td>Electricity</td><td>9.54</td><td>KWh</td></tr><tr><td>Nylon 66 (vacuum bag)</td><td>0.28</td><td>kg</td></tr><tr><td>PET (breather)</td><td>0.21</td><td>kg</td></tr><tr><td>PTFE (release film)</td><td>0.031</td><td>kg</td></tr><tr><td>Organic solvent (release agent)</td><td>0.17</td><td>kg</td></tr><tr><td colspan="3"><strong>Use Phase</strong></td></tr><tr><td>Electricity</td><td>36.3</td><td>kWh</td></tr><tr><td colspan="3"><strong>Transport phase</strong></td></tr><tr><td>CF transport, ferry</td><td>1010</td><td>kgkm</td></tr><tr><td>CF transport, truck</td><td>899</td><td>kgkm</td></tr><tr><td>ER transport, truck</td><td>3830</td><td>kgkm</td></tr><tr><td>Mandrel transport, truck</td><td>2530</td><td>kgkm</td></tr><tr><td>Towbar transport, truck</td><td>204</td><td>kgkm</td></tr></tbody></table>

## Life Cycle Costing

LCC summarizes the costs associated with all the life cycle phases of a product that are directly calculated starting from one are more cost factors in that life cycle. LCC follows a methodology similar to LCA, involving the establishment of FU and system boundaries [18].

The present LCC analysis aims at quantifying the costs associated with a CFRP towbar life cycle. In this case, FU and system boundaries are same as those used in previous LCA analysis.

Both primary and secondary data were employed for the cost evaluation. Lean Cost software was used for the evaluation of the mandrel costs and literature analyses were used for all other phases. Towpreg commercial cost per kg was considered in this analysis. For the filament winding phase, energy, material, labour, machine depreciation and maintenance, mandrel production costs were included. A service life of 100 cycle was considered for the mandrel in order to allocate its production cost to the FU [4]. The curing phase included energy, material, labour and autoclave costs [19]. Finally, in the refrigerated storage phase and use phase only include cost resulting from energy consumption (the depreciation costs of the freezer attributable to the material needed for the towbar construction are negligible).

## Results and discussion

Preliminary FEM analyses were conducted considering single layers with different winding angles (from 20° to 85°) subjected to tensile load. Lower winding angles provide higher tensile stiffness and strength while lower structure weight. In fact, due to anisotropic properties of towpregs, it is better to align the fibers along the load direction to improve the structural response of the composite part. Hence, focus was given to layering with the majority of low winding angle layers. Layers with angle close to 90° were also used as they provide high layers compaction during the production process. After several iterations, the final symmetrical layering was defined as follows:
$$[85/20/20/20/30/30/20/20/30/30/\overline{85}]_s$$

For this configuration, the maximum stress registered in the static structural simulation is equal to 193 MPa and it is lower than the ultimate tensile strength of the composite material (750 MPa). For what concerns the buckling simulation, the load the triggers the elastic instability is about 1.7 times higher than the applied load; hence, compressive loads do not result critical for the component. Similarly, the obtained maximum stress is below the fatigue limit of the material hence infinite life is expected. The obtained configuration leads to a towbar total weight equal to 9 kg, about a quarter of the equivalent components realized in aluminum alloy.

## Sustainability assessment results

Figure 2 shows the LCIA results in terms of GWP for the considered scenarios. The CFRP towbar resulted the most sustainable solution, with total impacts about 65% lower than those of the commercial aluminium towbar (i.e. 318 kg CO2 eq vs 915 kg CO2 eq). The most impactful phase for the CFRP towbar is the prepregging phase (i.e. 261 kg CO2 eq, about 82% of the total). This is mainly due to the production process of the carbon fiber PAN-precursor required for the prepreg, as it includes the time consuming and energy intensive stabilization process. To reduce the environmental impacts in this phase bio-precursors like cellulose or lignin can be used. To increase the sustainability of CFRP recyclable thermoplastic resins could be employed as substitution for thermosetting epoxy resin. FW process is associated with negligible impacts, making this highly automated technology recommended to produce tubular components or vessel. Similarly, the materials used for the vacuum bag and the energy required for the polymerization of the towbar in the curing phase have low impacts. Towpreg refrigerated storage has negligible influence on the total impacts.

The most relevant phase in the Al towbar scenario is the extrusion process, which includes the extraction and production of raw aluminium and the extrusion process. Due to the energy consumption required for Al extraction, this phase accounts for about 90% of the total scenario impacts. The use phase of the Al towbar is associated with higher emissions if compared to CFRP towbar (i.e. 57 kg CO2 eq vs 13 kg CO2 eq). In fact, the weight reduction provided by the composite part leads to a decrease in energy consumption required for aircraft transport.

Figure 3 shows the comparison between impacts of the CFRP and Al towbars according to 18 ReCiPe midpoint categories. Data were normalized (i.e. divided for a reference impact value) and made dimensionless. As for GWP, CFRP towbar has the lowest life cycle impact in most of the midpoint categories. The CFRP towbar has a high impact in the Marine Ecotoxicity category due to air emissions of chemicals (particularly hydrogen cyanide) associated with carbon fibers production. The aluminium towbar has high impact on climate change due to the production of the raw material, which requires large amounts of energy for the electrolysis of alumina. In addition, it emits greenhouse gases contributing to global warming and may be associated with forest destruction for bauxite extraction. Since the energy for aluminium production comes from fossil sources, such as coal or oil, aluminium production also has a significant impact on the category “fossil depletion”, referring to the consumption of fossil resources with resulting economic and environmental consequences. To reduce environmental impacts is important to promote the adoption of renewable sources and aluminium recycling for secondary aluminium production.
$$[85/20/20/20/30/30/20/20/30/30/\overline{85}]_s$$

For this configuration, the maximum stress registered in the static structural simulation is equal to 193 MPa and it is lower than the ultimate tensile strength of the composite material (750 MPa). For what concerns the buckling simulation, the load the triggers the elastic instability is about 1.7 times higher than the applied load; hence, compressive loads do not result critical for the component. Similarly, the obtained maximum stress is below the fatigue limit of the material hence infinite life is expected. The obtained configuration leads to a towbar total weight equal to 9 kg, about a quarter of the equivalent components realized in aluminum alloy.

## Sustainability assessment results

Figure 2 shows the LCIA results in terms of GWP for the considered scenarios. The CFRP towbar resulted the most sustainable solution, with total impacts about 65% lower than those of the commercial aluminium towbar (i.e. 318 kg CO2 eq vs 915 kg CO2 eq). The most impactful phase for the CFRP towbar is the prepregging phase (i.e. 261 kg CO2 eq, about 82% of the total). This is mainly due to the production process of the carbon fiber PAN-precursor required for the prepreg, as it includes the time consuming and energy intensive stabilization process. To reduce the environmental impacts in this phase bio-precursors like cellulose or lignin can be used. To increase the sustainability of CFRP recyclable thermoplastic resins could be employed as substitution for thermosetting epoxy resin. FW process is associated with negligible impacts, making this highly automated technology recommended to produce tubular components or vessel. Similarly, the materials used for the vacuum bag and the energy required for the polymerization of the towbar in the curing phase have low impacts. Towpreg refrigerated storage has negligible influence on the total impacts.

The most relevant phase in the Al towbar scenario is the extrusion process, which includes the extraction and production of raw aluminium and the extrusion process. Due to the energy consumption required for Al extraction, this phase accounts for about 90% of the total scenario impacts. The use phase of the Al towbar is associated with higher emissions if compared to CFRP towbar (i.e. 57 kg CO2 eq vs 13 kg CO2 eq). In fact, the weight reduction provided by the composite part leads to a decrease in energy consumption required for aircraft transport.

Figure 3 shows the comparison between impacts of the CFRP and Al towbars according to 18 ReCiPe midpoint categories. Data were normalized (i.e. divided for a reference impact value) and made dimensionless. As for GWP, CFRP towbar has the lowest life cycle impact in most of the midpoint categories. The CFRP towbar has a high impact in the Marine Ecotoxicity category due to air emissions of chemicals (particularly hydrogen cyanide) associated with carbon fibers production. The aluminium towbar has high impact on climate change due to the production of the raw material, which requires large amounts of energy for the electrolysis of alumina. In addition, it emits greenhouse gases contributing to global warming and may be associated with forest destruction for bauxite extraction. Since the energy for aluminium production comes from fossil sources, such as coal or oil, aluminium production also has a significant impact on the category “fossil depletion”, referring to the consumption of fossil resources with resulting economic and environmental consequences. To reduce environmental impacts is important to promote the adoption of renewable sources and aluminium recycling for secondary aluminium production.
<figure><img src="image_2679.png" /><figcaption>Figure 2 results and phases impact contributions for the two towbars</figcaption></figure>

<figure><img src="image_2680.png" /><figcaption>Figure 3 comparison between impacts of the CFRP and Al towbar according to ReCiPe midpoint categories</figcaption></figure>

Life Cycle Costing results

LCC results are presented in Table 3 and Figure 4. As can be observed in Figure 4, the highest cost contribution is attributed to material purchase (i.e. 344€); specifically, around 90% of this category is due to the cost of the towpreg (i.e. 326 €). Another significant cost factor is labor (125€), which requires a high level of expertise for the filament winding process and molding and demolding phases of autoclave curing. Energy cost and machinery cost are similar; the latter includes maintenance and depreciation cost of machines over their service life. These costs were allocated
<figure><img src="image_2674.png" /><figcaption>Figure 2 results and phases impact contributions for the two towbars</figcaption></figure>

<figure><img src="image_2675.png" /><figcaption>Figure 3 comparison between impacts of the CFRP and Al towbar according to ReCiPe midpoint categories</figcaption></figure>

Life Cycle Costing results

LCC results are presented in Table 3 and Figure 4. As can be observed in Figure 4, the highest cost contribution is attributed to material purchase (i.e. 344€); specifically, around 90% of this category is due to the cost of the towpreg (i.e. 326 €). Another significant cost factor is labor (125€), which requires a high level of expertise for the filament winding process and molding and demolding phases of autoclave curing. Energy cost and machinery cost are similar; the latter includes maintenance and depreciation cost of machines over their service life. These costs were allocated
to the functional unit considering the required production time and the machines service life. The total cost is the sum of all cost factor and amounts to 522.70€.

<figure><img src="image_2681.png" /><figcaption>Figure 4 cost breakdown of CFRP towbar</figcaption></figure>

<table><caption>Table 3 Cost evaluation</caption><tbody><tr><td><strong>Mandrel</strong></td><td></td></tr><tr><td>Mandrel cost (calculated by Lean Cost)</td><td>431.69 €</td></tr><tr><td><strong>Filament Winding Phase</strong></td><td></td></tr><tr><td>Energy cost</td><td>8.20 €</td></tr><tr><td>CFRP towpreg cost</td><td>326.05 €</td></tr><tr><td>Labour cost</td><td>80.00 €</td></tr><tr><td>Machining (machine cost + maintenance)</td><td>24.63 €</td></tr><tr><td>Mandrel (for each cycle of service life)</td><td>4.32 €</td></tr><tr><td><strong>Freezer Storage Towpreg Phase</strong></td><td></td></tr><tr><td>Energy cost</td><td>1.57 €</td></tr><tr><td>Freezer (machine + maintenance)</td><td>0.04 €</td></tr><tr><td><strong>Curing phase</strong></td><td></td></tr><tr><td>Energy cost</td><td>4.30 €</td></tr><tr><td>Labour cost</td><td>45.00 €</td></tr><tr><td>Ny 66 cost (vacuum bag)</td><td>2.04 €</td></tr><tr><td>PET cost (breather)</td><td>2.81 €</td></tr><tr><td>PTFE cost (release film)</td><td>0.13 €</td></tr><tr><td>Organic solvent cost (release agent)</td><td>13.20 €</td></tr><tr><td>Autoclave</td><td>3.39 €</td></tr><tr><td><strong>Use Phase</strong></td><td></td></tr><tr><td>Energy cost</td><td>7.06 €</td></tr></tbody></table>

## Conclusions and further developments

This paper presents the design and life cycle analyses of a CFRP towbar and comparison with traditional component. FEM software, LCA and LCC methodologies were employed to conduct the study. The main findings of the analysis are reported as follows:

* Overall, the final composite layering as defined as:

$$[85/20/20/20/30/30/30/20/20/30/30/85]_s$$

* This leads to a composite part that weighs 9 kg, about a quarter of the traditional aluminum component (36 kg). This layering has stress value within material limits and has sufficient fatigue and buckling resistance.

* The CFRP towbar resulted in lower impacts with respect to the aluminum one in terms of both GWP and ReCiPe midpoint categories (e.g. 318 kg CO2 eq vs 915 kg CO2 eq). In
to the functional unit considering the required production time and the machines service life. The total cost is the sum of all cost factor and amounts to 522.70€.

<figure><img src="image_2676.png" /><figcaption>Figure 4 cost breakdown of CFRP towbar</figcaption></figure>

<table><caption>Table 3 Cost evaluation</caption><tbody><tr><td><strong>Mandrel</strong></td><td></td></tr><tr><td>Mandrel cost (calculated by Lean Cost)</td><td>431.69 €</td></tr><tr><td><strong>Filament Winding Phase</strong></td><td></td></tr><tr><td>Energy cost</td><td>8.20 €</td></tr><tr><td>CFRP towpreg cost</td><td>326.05 €</td></tr><tr><td>Labour cost</td><td>80.00 €</td></tr><tr><td>Machining (machine cost + maintenance)</td><td>24.63 €</td></tr><tr><td>Mandrel (for each cycle of service life)</td><td>4.32 €</td></tr><tr><td><strong>Freezer Storage Towpreg Phase</strong></td><td></td></tr><tr><td>Energy cost</td><td>1.57 €</td></tr><tr><td>Freezer (machine + maintenance)</td><td>0.04 €</td></tr><tr><td><strong>Curing phase</strong></td><td></td></tr><tr><td>Energy cost</td><td>4.30 €</td></tr><tr><td>Labour cost</td><td>45.00 €</td></tr><tr><td>Ny 66 cost (vacuum bag)</td><td>2.04 €</td></tr><tr><td>PET cost (breather)</td><td>2.81 €</td></tr><tr><td>PTFE cost (release film)</td><td>0.13 €</td></tr><tr><td>Organic solvent cost (release agent)</td><td>13.20 €</td></tr><tr><td>Autoclave</td><td>3.39 €</td></tr><tr><td><strong>Use Phase</strong></td><td></td></tr><tr><td>Energy cost</td><td>7.06 €</td></tr></tbody></table>

## Conclusions and further developments

This paper presents the design and life cycle analyses of a CFRP towbar and comparison with traditional component. FEM software, LCA and LCC methodologies were employed to conduct the study. The main findings of the analysis are reported as follows:

* Overall, the final composite layering as defined as:

$$[85/20/20/20/30/30/30/20/20/30/30/85]_s$$

* This leads to a composite part that weighs 9 kg, about a quarter of the traditional aluminum component (36 kg). This layering has stress value within material limits and has sufficient fatigue and buckling resistance.

* The CFRP towbar resulted in lower impacts with respect to the aluminum one in terms of both GWP and ReCiPe midpoint categories (e.g. 318 kg CO2 eq vs 915 kg CO2 eq). In
both cases, raw materials production resulted the most relevant contributor to the total impacts.

* The total CFRP towbar cost is equal to 522.70€; the largest cost factor is attributed to materials purhcase (344€).

* In future studies, different polymeric matrixes and reinforcement (i.e. thermoplastic polymers and natural fibers), could be considered as possible sustainable alternatives to reduce the environmental and economic impacts of the filament wound CFRP towbar. In addition, economic comparison with traditional alternatives could also be included.

## Acknowledgements

This research was supported by the Italian Ministry of University and Research (MUR, Ministero dell'Università e della Ricerca) within the National Operational Programme on Research and Innovation 2014-2022 (Programma Operativo Nazionale "Ricerca e Innovazione" 2014-2020 (PON "R&I" 2014-2020) - area di specializzazione "Fabbrica Intelligente") project "SMART TOW WINDING Nuove soluzioni ad elevata automazione per l'impregnazione e avvolgimento di Tow" (CUP: B19C20000340005, ARS01_00871).

## References

[1] M.A. Mateen, D.V. Ravi Shankar, M. Manzoor Hussain, Design and development of low cost two axis filament winding machine, Journal of Advanced Manufacturing Technology. 12 (2018) 117-126.

[2] M. Azeem, H.H. Ya, M. Kumar, P. Stabla, M. Smolnicki, L. Gemi, R. Khan, T. Ahmed, Q. Ma, M.R. Sadique, A.A. Mokhtar, M. Mustapha, Application of Filament Winding Technology in Composite Pressure Vessels and Challenges: A Review, J Energy Storage. 49 (2022) 103468. https://doi.org/10.1016/J.EST.2021.103468

[3] Ö.S. Sahin, A. Akdemir, A. Avci, L. Gemi, Fatigue crack growth behavior of filament wound composite pipes in corrosive environment, Journal of Reinforced Plastics and Composites. 28 (2009) 2957-2970. https://doi.org/10.1177/0731684408094068

[4] A. Vita, V. Castorani, M. Germani, M. Marconi, Comparative life cycle assessment and cost analysis of autoclave and pressure bag molding for producing CFRP components, International Journal of Advanced Manufacturing Technology. 105 (2019) 1967-1982. https://doi.org/10.1007/S00170-019-04384-9/FIGURES/12

[5] S. wen Chen, H. Liu, F. hai Li, Analysis of Boeing 737 aircraft towing accidents, Eng Fail Anal. 80 (2017) 234-240. https://doi.org/10.1016/J.ENGFAILANAL.2017.06.024

[6] S. Das, Life cycle assessment of carbon fiber-reinforced polymer composites, International Journal of Life Cycle Assessment. 16 (2011) 268-282. https://doi.org/10.1007/s11367-011-0264-z

[7] G.D. Shrigandhi, B.S. Kothavale, Biodegradable composites for filament winding process, in: Mater Today Proc, 2021: pp. 2762-2768. https://doi.org/10.1016/j.matpr.2020.12.718

[8] W. Polini, L. Sorrentino, Design of winding with two rovings for cost efficiency and quality in robotized filament winding, in: Proceedings of the ASME Design Engineering Technical Conference, 2003: pp. 177-186. https://doi.org/10.1115/detc2003/dfm-48151

[9] E. Wilson, C. Karr, S. Messimer, Genetic algorithm optimization of a filament winding process modeled in WITNESS, Materials and Manufacturing Processes. 18 (2003) 509-521. https://doi.org/10.1081/AMP-120022025
both cases, raw materials production resulted the most relevant contributor to the total impacts.

* The total CFRP towbar cost is equal to 522.70€; the largest cost factor is attributed to materials purhcase (344€).

* In future studies, different polymeric matrixes and reinforcement (i.e. thermoplastic polymers and natural fibers), could be considered as possible sustainable alternatives to reduce the environmental and economic impacts of the filament wound CFRP towbar. In addition, economic comparison with traditional alternatives could also be included.

## Acknowledgements

This research was supported by the Italian Ministry of University and Research (MUR, Ministero dell'Università e della Ricerca) within the National Operational Programme on Research and Innovation 2014-2022 (Programma Operativo Nazionale "Ricerca e Innovazione" 2014-2020 (PON "R&I" 2014-2020) - area di specializzazione "Fabbrica Intelligente") project "SMART TOW WINDING Nuove soluzioni ad elevata automazione per l'impregnazione e avvolgimento di Tow" (CUP: B19C20000340005, ARS01_00871).

## References

[1] M.A. Mateen, D.V. Ravi Shankar, M. Manzoor Hussain, Design and development of low cost two axis filament winding machine, Journal of Advanced Manufacturing Technology. 12 (2018) 117-126.

[2] M. Azeem, H.H. Ya, M. Kumar, P. Stabla, M. Smolnicki, L. Gemi, R. Khan, T. Ahmed, Q. Ma, M.R. Sadique, A.A. Mokhtar, M. Mustapha, Application of Filament Winding Technology in Composite Pressure Vessels and Challenges: A Review, J Energy Storage. 49 (2022) 103468. https://doi.org/10.1016/J.EST.2021.103468

[3] Ö.S. Sahin, A. Akdemir, A. Avci, L. Gemi, Fatigue crack growth behavior of filament wound composite pipes in corrosive environment, Journal of Reinforced Plastics and Composites. 28 (2009) 2957-2970. https://doi.org/10.1177/0731684408094068

[4] A. Vita, V. Castorani, M. Germani, M. Marconi, Comparative life cycle assessment and cost analysis of autoclave and pressure bag molding for producing CFRP components, International Journal of Advanced Manufacturing Technology. 105 (2019) 1967-1982. https://doi.org/10.1007/S00170-019-04384-9/FIGURES/12

[5] S. wen Chen, H. Liu, F. hai Li, Analysis of Boeing 737 aircraft towing accidents, Eng Fail Anal. 80 (2017) 234-240. https://doi.org/10.1016/J.ENGFAILANAL.2017.06.024

[6] S. Das, Life cycle assessment of carbon fiber-reinforced polymer composites, International Journal of Life Cycle Assessment. 16 (2011) 268-282. https://doi.org/10.1007/s11367-011-0264-z

[7] G.D. Shrigandhi, B.S. Kothavale, Biodegradable composites for filament winding process, in: Mater Today Proc, 2021: pp. 2762-2768. https://doi.org/10.1016/j.matpr.2020.12.718

[8] W. Polini, L. Sorrentino, Design of winding with two rovings for cost efficiency and quality in robotized filament winding, in: Proceedings of the ASME Design Engineering Technical Conference, 2003: pp. 177-186. https://doi.org/10.1115/detc2003/dfm-48151

[9] E. Wilson, C. Karr, S. Messimer, Genetic algorithm optimization of a filament winding process modeled in WITNESS, Materials and Manufacturing Processes. 18 (2003) 509-521. https://doi.org/10.1081/AMP-120022025