bluuebunny/crossref_metadata_2025 huggingface dataset:
The mediating effects of cost estimates reliability on BIM adoption: SEM model analysis
Authors: Adillah Ismail Noor Akmal , Maisham Mysarah , Mohd Zaki Zulkhairy Affandy , Muhammad Rooshdi Raja Rafidah Raja , Sahamir Shaza Rina
Published: November 2019

This paper presents the Structural Equation Modelling (SEM) analysis to evaluate the mediating effects of cost estimates reliability towards the Building Information Modelling (BIM) technology adoption. Using results from a survey by questionnaire, SEM analysis employing SPSS-AMOS application is to assess the relationships amongst the studied constructs (Improved Information, Perceived Benefits, BIM Adoption and Cost Estimates Reliability) by testing three hypotheses. The SEM model was established with its validation through the assessment on its uni-dimensionality, validity, reliability, and fitness index, prior to the hypotheses testing. There are two effects possibly involved in the constructs’ relationships, namely direct and indirect effects, in which were examined using Sobel Mediation Test. The results showed that from all mediating relationships developed amongst the constructs, only Cost Estimates Reliability construct demonstrates its role as partial mediator in the direct relationship between Improved Information and BIM adoption constructs. Whilst the other two hypotheses failed the test, indicating no mediation is possible in between the related constructs relationships. The analysis confirmed that the BIM capabilities could provide better mechanism in understanding project information to establish more reliable cost estimates. It could then improve the estimators’ skills and knowledge throughout the whole cost estimating process, hence potentially motivating them towards adopting the BIM technology.
Fundamental Valuation of Construction Stocks: A Content Analysis from Property Developers
Authors: Nordin M S A , Rahim N Ab , Adnan H
Published: November 2019

The expansion of the Malaysian Construction Companies requires a holistic understanding on the intrinsic values as well as the nature of growth and value features of stocks in order to effectively invest in this sector. The paper aims to assess the intrinsic values of the Malaysia construction companies using fundamental methods of valuation. Content Analysis has been employed to the 10 property developers that has been listed under the top 10 Malaysian property developers in year 2018 identified as Company A to J. Based on the data derived from the companies’ annual report, Bursa Malaysia and stock-related websites, intrinsic value of the construction stock is assessed using three fundamental methods of valuation comprising Price Earning Multiple, Relative Price Earning as well as the Dividend Growth Model. The results suggested that there is a huge inconsistencies of intrinsic values across the first two methods of valuation where most of the stocks are in the state of undervalued while valuation derived from the Dividend Growth Model signifies the overvaluation state of all stocks’ opening prices. This research is expected to provide a preliminary evidence on the intrinsic values of Malaysian Construction Companies as similar analysis and indicators can be used in reviewing the characteristics as well as fundamentally valuing the construction stock in both small and larger investment portfolios.
Friction and lubrication in sheet metal forming simulations: Application to the Renault Talisman trunk lid inner part
Authors: Lacues J. , Pan C. , Franconville J.-C. , Guillot P. , Capellaere M. , Chezan T. , Hol J. , Wiebenga J.H. , Souchet A. , Ferragu V.
Published: November 2019

More and more automotive companies realize that controlling the tribological conditions in stamping production enables prevention of production issues, increasing overall production stability, and therewith achieving higher quality parts. Therefore, increasing effort is spent in accurately accounting for friction and lubrication conditions in sheet metal forming simulations. In this work, a selection of results for a Groupe Renault case is presented whereby forming simulations are utilized to simulate issues, including splits and wrinkles, observed in stamping production for the Renault Talisman trunk lid inner part. A comparison between simulation results and experimental measurements on parts taken from production is made. This comparison shows that the respective issues can only be simulated accurately when accounting for the actual tribological conditions in stamping production. By doing so, simulation accuracy is increased, now enabling Renault to improve part quality by controlling, adjusting and optimizing the tribological conditions in both in simulations and production.
Modelling the surface roughness influence on the hole expansion ratio of multiphase steel
Authors: Münstermann S , Wechsuwanmanee P , Lian J
Published: November 2019

There exist both extrinsic manufacturing process-related and intrinsic material-immanent effects on the edge crack sensitivity of dualphase steels. Extrinsic influences can be further divided into effects of residual damage as well as roughness-induced effects. A new simulation framework is applied to quantitatively assess the surface roughness-induced influences on the edge crack sensitivity of cold rolled dualphase steel of grade DP1000. Hole expansion ratios are numerically predicted for four different edge manufacturing processes, including drilling, milling, waterjet cutting, and wire cutting. The simulation framework applies the idea to make use of a ductile damage mechanics model. It employs realistic material parameters for all elements situated in the bulk, whereas those elements situated at the edge to be expanded during the test apply artificial model parameters. These are identified with the help of sub-models with geometrical surface representation. For the sub-model construction, roughness profiles are experimentally characterized by white light confocal microscopy. With the new simulation framework, numerical predictions of hole expansion ratios can be significantly improved, even though a remarkable overestimation still remains. Among others, this general overestimation can be attributed to local strain hardening, residual stresses, and microstructural modifications.
Experimental and numerical analysis of damage and fracture mechanisms in metal sheets under non-proportional loading paths
Authors: Brünig Michael , Gerke Steffen , Zistl Moritz
Published: November 2019

New biaxial experiments and corresponding numerical simulations with specimens taken from metal sheets are discussed. Inelastic deformation behavior as well as damage and fracture mechanisms are examined in detail under different biaxial loading conditions with special focus on non-proportional loading paths. In this context, a continuum damage model is presented based on a yield condition and a damage criterion as well as evolution equations for plastic and damage strain rates. The damage criterion takes into account the effect of different processes on the micro-scale depending on the stress state. Experiments with biaxially loaded specimens with newly developed geometries have been performed using proportional and non-proportional loading histories. Strain fields are monitored by digital image correlation technique and fracture surfaces are analyzed with scanning electron microscopy. Numerical simulations of the experiments have been performed and numerical results are compared with available experimental data. In addition, based on the numerical calculations stress distributions in critical specimen’s areas are detected allowing prediction of damage and fracture modes. The results demonstrate the efficiency of the new geometries of the specimens covering a wide range of stress states as well as the effect of the loading paths on damage and fracture behavior in ductile metal sheets.
Design and Validation of 3D-Printed Tools for Stamping of DP600
Authors: Asnafi Nader , Rajalampi Jukka , Aspenberg David
Published: November 2019

This paper is focused on automotive stamping tools & dies and the impact of 3D metal printing on design and production of such tools & dies. Forming (U-bend) and trimming/cutting/blanking tools & dies designed both conventionally and by topology optimization were 3D-printed, using Laser-based Powder Bed Fusion (LPBF), in the maraging steel DIN 1.2709. These 3D-printed tools were then used to form (U-bend) and trim/cut/blank 2-mm thick hot-dip galvanized DP600. An approval of the forming tool required that 50,000 U-bends were formed in 2-mm thick DP600 without any surface scratches on the sheet metal part. An approval of the trimming/cutting/blanking tool required 100,000 trimming strokes with this tool, where the maximum (sheet metal) burr height was lower than 0.2 mm (lower than 10% of the sheet thickness (2 mm in this study)). The 3D-printed forming and trimming/cutting/blanking tools & dies - both the conventionally designed and the topology optimized versions – managed the criteria mentioned above and were therefore approved. The approval means that these concepts can now be used to make production stamping tools and dies. This paper describes the topology optimization, the forming & trimming/cutting/blanking testing, the results yielding an approval of the 3D-printed tool concepts, and the 3D-printed production tools for stamping of DP600.
Bridging the gap between engineering and tryout of sheet metal forming parts by a smart solution
Authors: Stippak Michael , Carleer Bart
Published: November 2019

When a good simulation solution is found by an engineering department the challenge is to transfer this knowledge properly to the tryout process, because in an ideal process, the tryout would reproduce engineered results in a minimum time. But very often this knowledge transfer exists only of handing over printed simulation reports to the tryout team and then it depends on the interpretation of such a document to reproduce all important information to get similar results in reality. A solution to improve this situation would be to connect engineering and tryout with a smart digital solution, which supports tryout to reproduce the results from simulation fast and easy. The draw-in from simulation solution can be used as target to reproduce the same draw-in at tryout, because if draw-in is matching, then also the material flow is matching and the strain distribution too. To do so a sensitivity analysis based on the found simulation solution should be calculated by variation of the drawbead restraining and binder force and then exported to a smart digital tryout solution. Finally this smart digital tryout solution would provide all required information to tryout that they are able to reproduce the draw-in like engineered as fast as possible to speed up the process by avoiding unnecessary tool modifications. Based on this the gap between engineering and tryout can be bridged in a more efficient way.
Influence of varying sheet material properties on dry deep drawing process
Authors: Krachenfels K , Rothammer B , Zhao R , Tremmel S , Merklein M
Published: November 2019

Deep drawing is one of the most important processes in sheet metal forming. Conventionally, lubricants are used to reduce friction and wear. Demands for increased sustainability, environmental protection and resource efficiency motivate the realization of lubricant-free forming processes. The direct contact between tool and workpiece during dry deep drawing results in challenging tribological conditions, which cause an increase in friction and wear. Friction-reducing surface modifications of the tool such as carbon based coatings are being developed for the adaptation of the tribological conditions. The aim of this work is the simulation-based analysis of the stress spectrum for varying sheet properties for the qualification of wear-reducing surface modifications for a wide range of applications. By a simulation model for a rectangular cup, the influence of different batches of steel and aluminum materials with varying friction coefficients and mechanical properties is investigated within the framework of variant simulations. The tribological conditions in the simulation are described on the basis of friction coefficients from the strip drawing test. From the simulation results, the applicability of surface modifications for dry deep drawing is being evaluated depending on the sheet specific properties.
Characterizing axial crash foldability of AHSS & UHSS sheets by means of L-profile compression tests
Authors: Wagner L. , Larour P. , Lackner J. , Schauer H. , Berger E.
Published: November 2019

Small-scale crash tests of crash boxes have established themselves as an assessment tool for high strength materials for their application in crash-relevant structures in the automotive body. However, when investigating UHSS grades it can be seen that the performance outcome is highly susceptible to details of the crash box geometry, e.g. shape of cross section or position of spot welds, and the test setup. This may even lead to opposing crash performance ratings for the same grade if different setups are compared. In order to rule out any side effects of specimen geometry and test setup, a simpler test method is desired. If a crash box sustains plastic folding in its first fold it often also sustains the subsequent plastic folding events. Accordingly, the L-profile compression test is presented where a specimen, mimicking a quarter of the crash box cross-section, is compressed, forming a single plastic fold. The crash performance assessment is carried out by means of the so called crash index, a weighted relative measure of crack and fracture lengths within the sample, and correlated to the results of corresponding small scale tests, i.e. bending, notched tensile and hole expansion tests.
Multi-Coefficient Optimization of Homogeneous Anisotropic Hardening Model for Ahss
Authors: Lee Shinyeong , Kim Jin-Hwan , Barlat Frédéric
Published: November 2019

The goal of this research is to find out which test is best to predict the hardening of advanced high strength steel (AHSS) sheets and what kind of optimization method is most efficient. In this work, tension-compression and cyclic simple shear tests were conducted on AHSS sheets. Both experiments were carried out in the format of several cycles. Based on the experimental results, the distortional plasticity model (HAH) coefficients were optimized through the Nelder-Mead simplex algorithm and a genetic algorithm. The results were discussed to assess which test is best for the prediction of the stress-strain curve during forward-reverse loading and which method leads for lower computing time and higher accuracy.
Improved bendability characterization of UHSS sheets
Authors: Wagner L. , Schauer H. , Pauli H. , Hinterdorfer J.
Published: November 2019

Bendability characterization of UHSS sheets is often limited by punch-sheet-liftoff during standardized bending tests. This phenomenon is characterized by a smaller radius on the bent sheet than the desired tool radius and might lead to a misinterpretation of the admissible bending radii from such tests. An alternative bending setup is proposed suppressing punch-sheet-liftoff. The proposed setup aims at imitating bending in multistage stamping processes and to some extent also roll forming. The target bending radius to sheet thickness ratios of the investigated UHSS sheets were chosen to be 2.0. Alternative tool geometries are investigated as well. Short segments of an Euler spiral between the tool parts exhibiting the target curvature and the linear neighbor regions are used to avoid triggering strain localizations at these curvature discontinuities, further decreasing the admissible bending ratios. Finite element simulations of the proposed bending test were conducted in order to identify the optimal tool shape. All results were compared to corresponding results from standardized bending tests of the respective UHSS sheets. The proposed setup succeeded in suppressing punch-sheet-liftoff for the desired bending ratios and was able to provide smaller bending ratios for the investigated UHSS sheets as compared to the ratios from standardized bending tests.
Investigation of non-proportional load paths by using a cruciform specimen in a conventional Nakajima test
Authors: Norz R. , Volk W.
Published: November 2019

The prediction of necking in sheet-metal forming is one of the most important tasks in the simulation of forming processes. The most common way to predict the necking for linear load paths is the Forming Limit Diagram (FLD) according to ISO 12004-2. This criterion is valid only for linear load paths. For non-proportional loading paths, Volk introduced a Generalized Forming Limit Concept (GFLC). This model enables the prediction of the formability for any non-proportional loading paths. The experimental investigation of those loading paths is still very challenging and complex. It involves a wide range of testing equipment for the pre- and post-strain of specimens. Jocham introduced a new method that allows the investigation of various non-proportional loading paths by using a cruciform specimen and a draw bead tool in a conventional Nakajima test setup. The height of the draw beads can be varied to create different load paths in the specimen centre. Nevertheless it is necessary for the thinnest part of the specimen to be in the middle of the specimen. This is achieved by milling an indentation into the centre. This mechanical procedure affects the formability of the material. In this paper, the cruciform specimens are laser weld from three single metal sheets in order to minimize the influence of the manufacturing process on the specimen. With this procedure, it is possible to test unmanufactured sheets. However, the crack still occurs in the centre of the specimen. With the new cruciform specimen, we are able to create arbitrary non-proportional strain paths.
Influence of single hat crash box flange triggering and impactor top plate welding strategy on axial crash foldability of AHSS & UHSS sheets
Authors: Larour P , Lackner J , Wagner L
Published: November 2019

Axial crash tests are usually performed in order to assess the crash foldability of AHSS & UHSS sheets in the framework of a material homologation process. With a real component like single hat column geometry with RSW flange welded and MAG welded top/down head plates crash box design, it is getting more and more difficult to assess properly the crash performance of AHSS & UHSS steel grades with tensile strength Rm ⩾ 1000 MPa (RSW: resistance spot welded, MAG: metal active gas welded). The crash box flange is namely excessively stiff and prevents the initiation of a proper crash-folding pattern, resulting in a high amount of material failure, which makes some judgement about material crash ability difficult. Therefore the present experimental investigation focuses on the one hand on the triggering strategy in the top flange area to break the excessive stiffness of the spot-welded flange. On the other hand some effort has been put in the improved joining strategy of the top impactor head plate to the crash box itself. The top head plate is usually necessary in real components for load transfer to the crash box and fixation to the surrounding body in white structure. Some excessive welding of the top impactor plate, especially in the already largely stiffened spot-welded flange region, has however a strong detrimental effect on crash fold initiation. The welding of the top head plate in the flange and back crash box areas is avoided, thus increasing the degrees of freedom between top impactor plate and crash box column along with an effective reduction of the initial crash box bending stiffness. Some minimized welding of impactor plate to the crash box column, especially avoiding flange areas, allows a successful initiation of the crash folding process but only in combination with pressed round triggers in the flange area near the first spot weld. With these modifications it is first possible to assess and rank the intrinsic axial crash foldability of the material with Rm ⩾ 1000 MPa by means of a crack length based crash index.
Digital process support in toolmaking by using optical metrology
Authors: Essig Peter , Liewald Mathias , Bolay Christian , Schubert Thomas
Published: November 2019

Increasing demands on the quality of outer skin car body panels, shortening product development processes of new car models in the future fundamentally challenge manufacturing companies in international competition. Such challenges emerge, for example, in the field of toolmaking, which plays a decisive role in the valueadded chain due to its high time and costs share. Here, the high proportion of manual, experiencebased operations in tool tryout often leads to unstable processes requiring many iteration steps until approval. Blue, non-dry colour is applied on sheet metal which creates a spotting image that makes the contact areas between the forming die surface visible. In die tryout, spotting images provide a visual indication of the current phase and also serve as quality criteria of sheet metal components. For this reason, research work reported about in this paper deals with the development of a procedure for generating digital spotting images by using optical 3D coordinate-measuring technology to keep the spotting image permanently available during die tryout phase, for example on smart devices. In fundamental investigations, different influences on the spotting image due to light conditions and STL-mesh size of the scanned geometry are initially examined in order to quantify both the physical and the digital spotting image. The knowledge gained is subsequently validated and further improved by means of test with series press tools. The results demonstrate how digital and physical spotting images are generated and quantified for a reduced time in sheet metal simulation and die tryout phase of large press tools. This is achieved by the systematic provision of process parameters from the series production, such as the force transmission between the forming die surfaces, the local sheet thicknesses and the documentation of process variation in the blank holder by using digital spotting images.
Prediction of flow curves of very thin brass sheets incorporating size effect in hardening model
Authors: Anand Dhruv , Kumar D Ravi
Published: November 2019

Due to the size effect, the plastic deformation behavior of very thin sheets is dependent on the ratio of specimen thickness to grain size. The general hardening models used for bulk materials and thick sheets are not applicable for representing the plastic flow behavior of very thin sheets accurately. In the present work, the grain size effect (ratio of sheet thickness to grain size t/d) on flow behavior in uni-axial tension has been studied. Very thin sheet specimens of CuZn36 brass of thickness 50μm, 100μm, 150μm and 200μm have been used in this study. The brass sheets were annealed with different combinations of annealing temperature and time to achieve a large range of t/d ratio (1 to 17). A new hardening model has been developed incorporating the grain size effect on flow stress by determination of strength coefficient as a function of t/d. The predicted curves using the developed hardening model agreed well with the experimental results.
Investigation of the influence of forming parameters on the springback of hot-stamped hat-shaped parts
Authors: ChiuHuang Cheng-Kai , Wang Shi-Wei , Lee Ping-Kun
Published: November 2019

The application of hot stamping parts has become a dominant approach to achieve lightweight design and increase crashworthiness performance in the automotive industry. Compared to the cold stamping parts, the main feature of the hot stamped component is its high strength and good size stability. However, recent studies have shown that the springback or size deviation of hot stamped parts caused some assembly problems. This paper aims to investigate the influence of forming parameters on the part’s springback via a hot stamping hat-shaped die. Three different forming parameters with the same blank heating temperature (930°C) were conducted in the study: (1) transfer time 8 sec/die quenching 15 sec (2) transfer time 8 sec/die quenching 8 sec and (3) transfer time 18 sec/die quenching 15 sec. The selected forming parameters are used to evaluate the effect of the before-forming blank temperature and die-opening blank temperature on the springback of the hot stamping parts. The results show that the case 3 with a prolonged transfer time causes a small portion of ferrite phase formation in the hot-stamped part, resulting in the decrease of the tensile strength and a more significant springback is observed.
On the Failure Prediction of Dual-Phase Steel and Aluminium Alloys Exposed to Combined Tension and Bending
Authors: Barlo Alexander , Sigvant Mats , Endelt Benny
Published: November 2019

The interest in accurate prediction of failure of sheet metals in the automotive industry has increased significantly over the last two decades. This paper aims to evaluate two failure prediction approaches implemented in the commercial Finite Element code AutoFormplus R7.04; (i) the standard Forming Limit Diagram (FLD), and (ii) the Non-linear Forming Limit Diagram. The evaluation will be testing the two approaches accuracy on predicting failure of both an AA6016 aluminium alloy and a CR440Y780T-DP dual-phase steel alloy specimen exposed to combined tension and bending. Based on the findings of this study, it is concluded that neither of the evaluated approaches is able to accurately predict failure in both cases presented.
Sensitivity analysis of process and tube parameters in free-bending processes
Authors: Beulich N , Spoerer J , Volk W
Published: November 2019

Free-bending processes are used to manufacture highly-complex profile shapes for different kinds of industry sectors. This paper focuses on the enhanced version of the MOS bending technique (6DOF), which is used by BMW to produce semi-finished products for the tube hydroforming process. In order to achieve a better process understanding, the bending process was analyzed with regard to process and tube parameters. In the first experimental bending series, the process precision was measured and evaluated by standard deviation and process capability. In the second bending series, the analysis focuses on the weld seam position and the wrinkling behavior of the tube. The correlations shown between process parameters and the resulting bending geometry are the basis for the validation of a process simulation model developed in LS-Dyna. Therefore, the comparison of experimental data and data measured numerically represents a good agreement. The FEM model was used to perform a numerical based sensitivity analysis of the bending process in relation to process and tube parameters. The result identifies the main factors contributing to the free-bending process.
Crystal plasticity based predictions of mechanical properties from heterogeneous steel microstructures
Authors: Kok P.J.J. , Spanjer W. , Korver F. , An Y. , Aarnts M.
Published: November 2019

An accurate understanding of the influence of the microstructure on mechanical properties as well as how the material behaves in forming tests is vital for product development and process improvement. The heterogeneity of the microstructure is very different for the various families of steel grades. As a consequence spatial stress and strain distributions on the micro scale will also differ a lot in these materials during forming operations. In the important family of Dual Phase (DP) steel grades. the combination of ductile ferrite phase and hard martensite particles enables an excellent hardening behaviour. However these micro constituents also result in a strong locally heterogeneous behaviour caused by the high material property contrast. To enable an accurate prediction of the materials response in forming processes advanced microstructure models as well as fast crystal plasticity code is essential. Within Tata Steel both are available. A Multi-Level Voronoi microstructure generator, capable of generating very complex Representative Volume Elements, is directly connected to the DAMASK code of the Max Planck Institüt für Eisenforschung. This crystal plasticity software is based on an ultrafast Fourier Spectral Solver. Crystal plasticity simulations with different loading cases (e.g. uni-axial, plane strain, simple shear) study various effects of microstructure heterogeneity on stress and strain distributions as well as on global hardening behaviour. Outcome is that not only the volume fraction but also the spatial distribution of the martensite particles has a large impact on local stresses and strains as well as on average hardening behaviour. Another important heterogeneity parameter is the carbon content, which influences strongly the hardness and hardenability of the martensite particles. An attempt is made to incorporate also this effect in crystal plasticity simulations.
Warm Forming Simulation of a ZEK100 Magnesium Door Panel
Authors: Omer Kaab , Butcher Clifford , Worswick Michael , Skszek Tim
Published: November 2019

The warm forming of a door panel made of commercial grade ZEK100 magnesium alloy sheet was modelled using finite element techniques (Autoform). The operation consisted of a heating step, a forming step and a cooling/springback step. The material properties of the ZEK100 blank were modelled using a set of temperature- and strain rate-dependent stress-strain curves, which were derived based on a Zerilli-Armstrong constitutive model. In order to simplify the material model to enable its complex response to be represented within a commercial finite element code, the anisotropy of the magnesium sheet was approximated using a Banabic-2005 yield surface and yield asymmetry was neglected, a reasonable approach for warm forming. Necking was predicted using a set of forming limit curves obtained at different isothermal temperatures. The entire forming model was run at a punch speed of 160 mm/s, and two initial blank temperatures: 215 and 230 °C. The tooling was initially at room temperature. The model predicted that the blank cracked when its initial temperature was 215 °C due to excessive cooling. The best formability (lack of wrinkling and necking) was predicted when the blank was heated to 230 °C. These predictions agree well with the forming trial outcomes.
Improved Spring-Back Compensation Strategy through Location Optimized Part Position in the Dies
Authors: Birkert A , Hartmann B , Lepple F , Straub M , Zimmermann P
Published: November 2019

Further increasing requirements to the quality of car body components represent a huge challenge for the process planner. As the elastic energy is changing in each stamping operation, it is quite challenging to decide how to compensate which stamping operation. The belonging process definition is known as the compensation strategy. A key prerequisite of an appropriate compensation strategy is a proper location of the part in all stamping operations along the process chain. Proper means that the distance of the part to the die must be minimal to prevent any undefined shift of the part in the die and thus unwanted deformations when closing the dies. Both shifting and deformations would cause dimensional deviations and surface defects. Today different strategies are applied to meet these requirements at least approximately. Strategies, which are published in different papers yet, can only provide suboptimal results. Here a new compensation strategy is being presented, which fulfils the requirement to a proper part location not only in the trimming dies, which corresponds to the so-called Drawshell Strategy, but also in the restriking dies. An important advantage of the respective strategy is that it generally can be applied on all multistage car body stamping operations.
Numerical simulation of hydraulic bulging using uniaxial and biaxial flow curves and different yield criteria
Authors: Prakash Ved , Kumar D. Ravi , Merklein Marion , Hagenah Hinnerk
Published: November 2019

In sheet metal forming industry, finite element analysis has become a necessary step before actual production of the parts. It helps in the improvement of part quality as well reduces the effort applied in experimental trials. However, the success of finite element simulation mainly depends on the constitutive model used for defining the plastic deformation behaviour of the sheet material. Material characterization in biaxial stress state helps in selecting advanced constitutive models in numerical simulations. In this work, aluminium alloy AA5083 sheet material is characterized in uniaxial and biaxial tension conditions. Hydraulic bulge tests are performed to obtain the flow curves and material properties which are then used to find the coefficients in different yield criteria. These coefficients and the flow curves, fitted using different work hardening laws, are used in finite element simulation of the hydraulic bulge test and the results are validated by experiments.
Prediction of residual stresses in biaxial stretching of tailor welded blanks by finite element analysis
Authors: Kumar Amit , Kumar D Ravi , Gautam Vijay
Published: November 2019

Residual stresses in sheet metal components play an important role in determining the life of parts especially in automotive industry. In this work, residual stresses have been predicted numerically in biaxial stretching of laser welded interstitial free (IF) steel blanks of different thickness combinations. The effective stress-effective strain curves of the parent sheets obtained from uniaxial tensile tests have been used as an input in finite element (FE) simulations to define the flow behavior of the materials. It has been found out that the residual stresses are tensile and similar on both sides of the weld zone in tailor welded blanks (TWB) of same thickness combination. In TWBs of different thickness combinations, the residual stresses on both sides are tensile and almost equal in the central region of the cup and they became compressive as the distance from the pole increases. The effect of thickness ratio on residual stresses has also been predicted in FE simulations of biaxial stretching of TWBs. It has been found out that with increase in the thickness ratio, the residual stress has slightly increased. Residual stresses have also been determined experimentally by using x-ray diffraction technique and it has been found out that the predicted values agreed well with the experimental results.
Sliding characteristics of hot-dip galvanized steel sheets depending on aging time after production
Authors: Hoshino K , Yamasaki Y , Taira S
Published: November 2019

The effect of aging time after production on the frictional characteristics of hot-dip galvanized steel sheets (HDG) was examined in this study to stabilize and improve the press formability of HDG. Conventional HDG with the Zn coating weight of 67 g/m2 including 0.36 mass% Al were used as test specimens. The specimens were aged for a predetermined period, after which their friction coefficients were measured with a flat sliding test. It was found that an Al-based oxide grew on the HDG surface and the friction coefficient tended to decrease with increased aging time. This suggests that the Al-based oxide reduced the friction coefficient. To understand how the Al-based oxide affects the friction coefficient, surface observation and analysis of both the test specimens and the tools after sliding were carried out. Although the Al-based oxide was not detected on the HDG surface in the area of contact with the sliding tool, the oxide was detected as adhering material on the tool surface after sliding, suggesting that the adhering material on the tool reduced the adhesion force between the metallic Zn of the HDG and the tool. This could lead to a lower friction coefficient because shearing resistance was decreased.
Press formability of newly developed high lubricity hot-dip galvanized steel sheets
Authors: Furuya S , Hoshino K , Ogihara Y , Yamasaki Y , Taira S
Published: November 2019

Surface modification technology was applied to hot-dip galvanized steel sheets (HDG) in order to improve their press formability. The frictional behavior and press formability of surface modified HDG were investigated in comparison with those of conventional HDG, conventional electrogalvanized steel sheets (EG) and pre-phosphate treated EG (EG pre-phos). Specimens of these coated mild steel sheets with various mechanical properties were used as test materials. The friction coefficient was measured by a flat sliding test, and press formability was evaluated by a deep drawing test and a stretch forming test. As a result, surface modified HDG showed a lower friction coefficient and higher press formability than conventional HDG and conventional EG. The friction coefficient and press formability of surface modified HDG were similar to those of EG pre-phos. In deep drawing, the inflow of material from the flange area to the cracking area becomes easier due to the lower friction coefficient of surface modified HDG, which leads to improvement of deep drawability. In stretch forming, the outflows of material from the sheet/punch contact area to the cracking area become easier due to the lower friction coefficient of surface modified HDG, leading to improvement of stretch formability. These results indicate that surface modified HDG is a promising material for automotive use.
Thermomechanical forming and crash simulations
Authors: Abspoel M , Scholting M E , Lansbergen M
Published: November 2019

With increasing possibilities and demands for FEM predictions, there is a need to get each input right. For example friction modelling, press kinematics, tool deformations are issues that are addressed more and more. FEM simulations including these advanced models require that each piece of the puzzle must be right. Description of the accurate thermomechanical plasticity behaviour is important for these simulations because press and tool deformations, friction behaviour and crashworthiness are depending on having the right forces and temperatures in your system. This thermomechanical plasticity behaviour consists of strain rate and temperature dependent hardening curves and a yield locus to scale these hardening curves for the different deformation modes. An accurate and easy to use yield locus which can be determined from only three tensile tests is Vegter 2017. The hardening behaviour consists of a static part and a strain rate and temperature dependent dynamic part. The static hardening behaviour can be determined with a tensile test and a biaxial test for the extrapolation to higher strains. The dynamic hardening behaviour can be determined with high strain rate tensile tests. An additive strain rate – temperature model is used to correct the necessary plasticity tests and prepare them for hardening fitting. With a strain rate jump test the validity of the additive model is proven. Comparison between FEM simulations and measurements for several practical deformation processes show a good prediction of the forces and temperatures of the thermomechanical plasticity model.
Augmented Reality for Forming Technology – Visualisation of Simulation Results and Component Measurement
Authors: Lechner M , Schulte R , Merklein M
Published: November 2019

In sheet and bulk forming, numerical simulation has become established over the last 20 years as an indispensable tool for research and industrial practice. The numerical calculation of forming processes supports a time- and cost-efficient development in the context of a virtual product evaluation. Currently, simulation and measurement results are mainly displayed on conventional screens. However, this approach has several disadvantages. On the one hand, only cut-outs can be displayed, especially in the case of large components. A visualisation of entire components in real size is often not possible. On the other hand, no direct comparison with the real components is possible. Augmented Reality is a promising approach to solve the challenges outlined above. As part of the contribution, an innovative approach for component validation based on Augmented Reality technology will be introduced. Thereby, the visualisation using different Augmented Reality devices and the feasibility of a measurement task with Augmented Reality devices will be presented.
A knowledge-based surrogate modeling approach for cup drawing with limited data
Authors: Morand L , Helm D , Iza-Teran R , Garcke J
Published: November 2019

To predict the quality of a process outcome with given process parameters in real-time, surrogate models are often adopted. A surrogate model is a statistical model that interpolates between data points obtained either by process measurements or deterministic models of the process. However, in manufacturing processes the amount of useful data is often limited, and therefore setting up a sufficiently accurate surrogate model is challenging. The present contribution shows how to handle limited data in a surrogate modeling approach using the example of a cup drawing process. The purpose of the surrogate model is to classify the quality of the drawn cup and to predict its final geometry. These classification and regression tasks are solved via machine learning methods. The training data is sampled on a relatively wide range varying three parameters of a finite element simulation, namely sheet metal thickness, blank holder force, and friction. The geometrical features of the cup are extracted using domain knowledge. Besides this knowledge-based approach, an outlook is given for a data-driven surrogate modeling approach.
Effect of novel impact hydroforming technology on the formability of Al alloys
Authors: Xu Y , El-Aty A Abd , Zhang S H , Ma Y , Chen D Y
Published: November 2019

Currently, Aluminium (Al) alloys are increasingly used in the aerospace and automobile industries because of their outstanding properties such as lightweight and corrosion resistance properties. On the other hand, the applications of these materials are limited due to their poor formability especially at room temperature. Although hydroforming technology is one of the technique used to improve the formability of Al alloys, it still cannot fulfil the requirements of designers and manufacturers to form thin-walled complex shaped components. It has been found that high-speed forming is able to improve the formability of lightweight metals at room temperature. Thus, this investigation aims at investigating the effect of the novel technology called impact hydroforming (high-strain-rate forming) on the formability of Al alloys. Impact hydroforming (IHF) technology is proposed by combining the advantages of high-speed forming and hydroforming, and it was used to address the issues of quasi-static hydroforming. A high strain rate uniaxial tensile test was accomplished using Hopkinson tensile bar to investigate the effect of high strain rate on the formability of Al alloys. Thereafter, an IHF bulge experiment setup was developed by making use of a light gas gun which can accelerate the projectile up to 300m/s. The results show that the ductility and the formability of the Al alloy increased under high strain rate conditions, which means that the high-speed forming which is the basics of IHF technology is an appropriate method to improve the formability of Al alloys and form complex shape components.
Investigation of Crack Prediction Method Using Limiting Surface Strain in High-Strength Steel Sheets
Authors: Shinmiya T , Fujii Y , Yamasaki Y , Tamai Y
Published: November 2019

To study cracks, which are affected by bending forming, a hat-shape forming experiment was conducted. Then, a prediction method using limiting surface strain for bending crack was investigated. In the case of high bendability steel, breakage occurred after necking, which grew from the front and rear surface with obvious thickness reduction. In this type of breakage, it was found that the forming limit could be predicted by using a conventional forming limit diagram (FLD), which means that there is a limiting strain at the middle of the thickness direction. On the other hand, in the case of low bendability steel, cracks outside the bending surface occurred and grew, followed by breaking without the necking with obvious thickness reduction. In this case, the forming limit could not be predicted by using FLD, and it was found that the forming limit could be predicted by using limiting surface strain for bending crack, which could be obtained by finite element analysis (FEA) and an experiment by a V-shape bending test.
Identification of process limits for punching with a slant angle
Authors: Schenek Adrian , Liewald Mathias , Senn Sergei
Published: November 2019

In order to experimentally identify process limits during punching with slant angle, a test tool was manufactured at the Institute for Metal Forming Technology (IFU) for in-situ measuring the horizontal punch deflection. The modular design of a test tool enabled the variation of numerous cutting parameters such as the “cutting clearance”, the “punch length” or the “slant angle”. Considering current lightweight construction trends in automotive industry, sheet metal materials HC340LA, DP600 and DP1000 were investigated, since these high-strength steel materials allow the use of relatively thin sheets in modern car body designs. As a result of investigations carried out in single stroke testings, a cutting parameter-dependent overview of maximum possible slant angles could be obtained, which was not yet available according to the current state of the art. Based on gained results, design guidelines for tools for punching with slant angles were derived, which were subsequently validated by endurance tests performed under lab conditions. In summary, the research work carried out does not only show a list of the maximum possible slant angles. Rather, it was possible to work out the insight that the process limits for punching with slant angle are assumed to be too conservative in industrial practice. For example even the high-strength sheet material DP1000 was punched reliably with a punch diameter of d=5mm up to a slant angle of 17.5°. In industrial practice, a cost-intensive cam solution would have been used from a slant angle of approx. 5°.
Assessment of solutions to reduce wear with the warm forming of aluminum
Authors: Maillard A , Piat C , Chen YM
Published: November 2019

Aluminum warm forming can be used to form very hard sheet materials and reduce the weight of the parts produced, helping to lighten cars. While many studies have focused on the aluminum warm forming technique, few examine the effects of temperature on sheet - tool contact conditions during repetitive parts making. The purpose of this study is to focus on the different sheet/tool contact configurations with the warm forming of aluminum based on 2 types of tests: tribological testing for an initial range of contact configurations and press testing of the forming tool for the final evaluation of a range of configurations. 18 configurations, involving various materials, tool coatings and lubricants, were initially evaluated using a warm pin test on an AW5083 H111 sheet. According to the analysis of wear surfaces, adhesion/galling type damage occurred on pins and highlights the importance of lubricating with a beneficial influence of tool coatings. The analysis of the coefficient of friction alone cannot explain the degraded aspect of the pins obtained. Then press tests with a tunnel-shaped part were carried out on 4 selected configurations. If the coated and lubricated configurations are satisfactory, the uncoated and lubricated configurations are surprisingly good and better than the tribological results have shown. In addition to the risks of pick-up and galling, the deposits of residues on the tool are compared for the lubricants tested.