bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluating Material Constitutive Equations for the Simulation of Incremental Sheet Forming Applied to Form Thermoplastic Materials
Authors: Bagudanch Isabel , Elías-Zúñiga Alex , Garcia-Romeu Maria Luisa
Published: June 2013

Incremental Sheet Forming (ISF) is able to produce highly customized products at a reasonable manufacturing cost and it has gain importance in the last years, becoming the focus of interest for many researchers and institutions. Some recent publications have revealed an increasing interest in forming thermoplastic materials. There is a tremendous amount of effort put in developing a model that may describe the equilibrium hysteresis and rate-dependence of thermoplastic materials in ISF. This paper will present a brief review of the most common constitutive equations that are able to model the behaviour of glassy polymers. It will be shown that by using a small number of material parameters defined in the Marlow model, it is possible to accurately predict experimental data collected on samples of PVC subjected to simple uniaxial test performed at room temperature. Additionally, some parts have been formed with ISF in order to verify whether the material is incompressible or not. It can be concluded that Marlow model might be used in future work to model the ISF manufacturing process.
The Influence of Toolpath Strategy on Geometric Accuracy in Incremental Forming
Authors: Malyer Elif
Published: June 2013

Incremental sheet metal forming is a new process to manufacture sheet metal parts and it is becoming a remarkable technology for fast prototyping and small lot production because of the advantages of this technology such as process flexibility, product independent tooling and higher formability. On the other hand, limited maximum drawing angle, relatively coarse surface roughness, low geometrical accuracy and long forming time are common disadvantages of the process. Furthermore, it is affected by process parameters which are tool diameter, forming velocity, spindle speed, forming geometry and depth, etc. Toolpath strategy which is used to form sheet metal by CNC machine has a key role among these parameters. The present study has been undertaken in order to investigate the suitable toolpath strategy which is developed for metal cutting by commercial CAD/CAM software to increase geometrical accuracy and decrease thinning and forming time. For the intended purpose, seven different toolpath strategies which are rough and finish strategies were used to form a truncated frustum by using one millimeter thick S235JR steel alloy. The effect of each strategy on the surface roughness, geometrical accuracy and thinning distribution of formed product was studied by measuring thickness, drawing angle and depth of formed parts. Therefore, formed parts scanned by 3D laser scanner and STL files of parts were generated then STL files were converted into CAD file. CAD data of parts was used for measurements. The measurements showed that not only forming movements but also transition movements along the tool path affected the geometric accuracy and thinning distribution, surface roughness and forming time of formed parts. On the other hand it was observed that rough strategies were given good results as finish strategies and tool paths generated by CAM software need to be editing for better geometric accuracy, thinning, forming time and surface quality.
Tool Path Generation for Single Point Incremental Forming Using Intelligent Sequencing and Multi-Step Mesh Morphing Techniques
Authors: Behera Amar Kumar , Lauwers Bert , Duflou Joost R.
Published: June 2013

A new methodology of generating optimized tool paths for incremental sheet forming is proposed in this work. The objective is to make parts with improved accuracy. To enable this, a systematic technique of creating features using a morph mapping strategy is developed. This strategy is based on starting with a shape different from the final shape, available as a triangulated STL model, and using step-wise incremental deformation to the original mesh to arrive at the final part shape. Further, optimal tool path generation requires intelligent sequencing of partial tool paths that may be applied specifically to certain features on the part. The sequencing procedure is discussed next and a case study showing the application of the integrated technique is illustrated.
Manufacturing of Geared Sheet Metal Components Using Flexible Rolled Tailored Blanks
Authors: Opel Simon , Schneider Thomas , Merklein Marion
Published: June 2013

Manufacturing of functional sheet metal products with integrated gear teeth by form-ing can be realised with the application of bulk forming operations on sheet metals. Due to the desired part geometry simultaneous 2D and 3D stress and strain states occur during the forming operations. The main challenges of sheet-bulk metal form-ing are high resulting forming forces and the demand on a specific control of the material flow. In addition, there is a distinctive interaction between blank thickness and resulting part quality. To meet these challenges at high material efficiency, the application of tailored blanks with a defined sheet thickness distribution is a promising way. The process adapted semi-finished used in the presented work are formed by a flexible rolling process. First of all, the forming concept for the realization of geared sheet metal components using flexible rolled tailored blanks is presented. Afterwards, the developed rolling machine to produce rotational symmetric tailored blanks is shown, as well as the fundamental process influences during rolling. Based on that, the development of suitable process strategies to produce tailored blanks with a thickened sheet edge is presented. The further processing of those tailored blanks for the realization of external geared sheet metal components will show the advantages compared to the application of conventional sheet metals of constant sheet thickness. Therefore the concept of a combined deep drawing and ironing process is presented. The results show, that on the one hand the material efficiency is increased in comparison to the usage of conventional sheets of the same maximum thickness. On the other hand, the application of flexible rolled tailored blanks improves the accuracy of shape of the gear teeth. Both approaches prove that the application of flexible rolled is an appropriate procedure to enhance the limits of using conventional sheet metals within sheet-bulk metal forming.
Novel Five-Axis Forming Press for the Incremental Sheet-Bulk Metal Forming
Authors: Sieczkarek Peter , Kwiatkowski Lukas , Ben Khalifa Nooman , Tekkaya A. Erman
Published: June 2013

The incremental procedure of sheet-bulk metal forming was classified into two different forming sequences, the discrete and the continuous. Based on these two groups, a movement matrix was developed, which captures required kinematic motions to manufacture a variety of functional components. With the objective of producing near-net-shape workpiece geometries within the Collaborative Research Centre TR73 – sheet-bulk metal forming, the required positioning accuracies of conventional metal forming machines exceed the current state of the art. Therefore, a suitable machine concept was developed and realized. This new machine represents a unique prototype for a flexible application of bulk forming operations to 2 – 3 mm sheets with five motion axes. During continuous forming, such as rolling, and also during simultaneous operations, increased lateral forces prevail. The machine was provided with a high stiffness. That enables a positioning accuracy which, also under load and at rest, correlates the high demands of the sheet-bulk metal forming within a range of ±0.01 mm.
Influence of Superimposing of Oscillation on Sheet-Bulk Metal Forming
Authors: Behrens Bernd-Arno , Hübner Sven , Vucetic Milan
Published: June 2013

Due to novel processes like sheet-bulk metal forming, the requirements for sheet metal forming are increased. Sheet-bulk metal forming is a new interconnected process in which the part itself is manufactured by deep drawing and the gearing will be produced with bulk forming in a combined process at room temperature. This process is characterized by a triaxial state of stress and a triaxial dimensional change with true strains up to  = 1-2 by using sheet blanks. Within the use of superimposing of oscillation on a sheet-bulk metal forming process the required forming force can be reduced and the accuracy of dimension of the part can be improved. Within this paper the influence of the superimposing of oscillation on the sheet bulk metal forming will be shown on combined ironing and external extrusion process. For the superimposing of oscillation different excitation frequencies will be analysed. Furthermore the die clearance will be varied to increase the requirements on the process. Finally the influence of the different excitation frequencies and the different die clearances will be summarized in cause and effect relationship diagram.
Innovative Tools to Improve Incremental Bulk Forming Processes
Authors: Sieczkarek Peter , Kwiatkowski Lukas , Tekkaya A. Erman , Krebs Eugen , Kersting Petra , Tillmann Wolfgang , Herper Jan
Published: June 2013

Sheet-bulk metal forming is an innovative process with a high potential to generate load-adapted parts with high precision. Bulk forming processes of sheet metals especially require high process forces, resulting in an intense contact pressure and, thus, in a very high abrasive and adhesive wear. As a method to reduce or avoid these common wear phenomena, even hardened or coated tool surfaces are not sufficient. The objective of this paper is to show an improvement of the tool resistance during an incremental forming process by an adapted tool design and the application of structured tool surfaces combined with coatings. For the tool surface the structure of the scarabaeus beetle serves as the basis for a bionic structure. This structure was manufactured by micromilling. Despite the high hardness of the tool material and the complex geometry of the forming tools, very precise patterns were machined successfully using ball-end milling cutters. The combination of bionic structures with coating techniques like physical vapor deposition (PVD) on plasma nitrided tool surfaces is very promising. In this work, the influence of process parameters (workpiece material, lubrication, tool design, stepwise infeed) on the tool resistance during the forming operation was analyzed experimentally. The results of the optimized forming tools were compared to conventional, unstructured, uncoated, and only plasma nitrided forming tools. The different tools were applied to 2 mm thick metal sheets made of aluminum (AlMg3) and steel (non-alloy quality steel DC04). As a result, the process forces could be reduced by a modified shape and surface of the tools. Thus, the lifetime of the tools can be enhanced.
Effect of Material Model on Finite Element Modeling of Aerospace Alloys
Authors: Saboori Mehdi , Gholipour Javad , Champliaud Henri , Gakwaya Augustin , Savoie Jean , Wanjara Priti
Published: June 2013

Increasing acceptance and use of hydroforming technology within the aerospace industry requires a comprehensive understanding of critical issues such as the material characteristics, friction condition and hydroformability of the material. Moreover, the cost of experiments that can be reduced by accurate finite element modeling (FEM), which entails the application of adapted constitutive laws for reproducing with confidence the material behavior. In this paper, the effect of different constitutive laws on FEM of tubular shapes is presented. The free expansion process was considered for developing the FEM. Bulge height, thickness reduction and strains were determined at the maximum bulge height using different constitutive models, including Hollomon, Ludwik, Swift, Voce, Ludwigson. In order to minimize the effect of friction, the free expansion experiments were performed with no end feeding. The simulation results were compared with the experimental data to find the appropriate constitutive law for the free expansion process.
Temperature and Displacement Fields Measurements to Assist the Numerical Simulation of the Welding-Brazing Process of Thin Automotive Parts
Authors: Beaubier Benoît , Lavernhe-Taillard Karine , Billardon René , Boucq Clara
Published: June 2013

Car manufacturers use many different mechanical or thermo-mechanical processes to assemble thin metal sheets. Each of these processes may induce –more or less localizedundesirable deformations of the assembled sheets. The numerical simulation of these deformations via the use of predictive thermo-mechanical finite element analyses may help and reduce development time and cost. To validate such complex non-linear numerical simulations by comparison of the numerical results with experimental evidence, it is necessary to develop well-controlled and highly instrumented tests. Welding-brazing is one the various assembly processes involving a heat source used by car manufacturers to assemble thin –typically 0.7 to 1mm thick- metal sheets. Predictive heat transfer simulations of this process require accurate modelling of both the heat source and the boundary conditions imposed onto the assembled sheets –including the contact between the sheets. Using ABAQUS general-purpose finite element code for this study, the welding-brazing heat source is modelled as the combination of a 3D volumetric source corresponding to the welding-brazing joint, and a 2D surface source corresponding to the heat flux emitted by the laser beam onto the sheets in the vicinity of the joint. Besides, the contact between the sheets is modelled by a thermal resistance depending on the pressure between the sheets when they are in contact, or the distance between them when they are apart. Identification of heat source and contact models is derived from the results of weldingbrazing tests instrumented with thermocouples and infrared cameras. Micrographic observations in the vicinity of the welding-brazing joint are used to (partially) validate the numerical predictions of the Heat Affected Zone (HAZ). After validation of this heat transfer numerical analysis, the thermo-mechanical analysis of the process will be validated by comparison of the predicted displacement fields with the results of 3D Digital Image Correlation (stereo-correlation) measurements made during the welding-brazing tests.
Characterization of Roll Bite Heat Transfers in Hot Steel Strip Rolling and their Influence on Roll Thermal Fatigue Degradation
Authors: Legrand Nicolas , Weisz-Patrault Daniel , Horský Jaroslav , Luks Tomáš , Labbe Nathalie , Picard Michel , Ehrlacher Alain
Published: June 2013

A temperature sensor with a thermocouple placed at ~0.5 mm from roll surface is used in hot rolling conditions to evaluate by inverse calculation heat transfers in the roll bite. Simulation analysis in industrial hot rolling conditions with short contact lengths (e.g. short contact times) and high rolling speeds (7 m./sec.) show that the temperature sensor + inverse analysis with a high acquisition frequency (> 1000 Hz) is capable to predict with a good accuracy (5 to 10% error) the roll bite peak of temperature as well as the roll surface temperature evolution all around the roll rotation. However as heat flux is more sensitive to noise measurement, the peak of heat flux in the bite is strongly under-estimated (40% error) by the inverse calculation and thus only an average roll bite heat flux could be expected from the sensor (these simulation results will be verified with an industrial trial that is being prepared). Rolling tests on a pilot mill with low rolling speeds (from 0.3 to 1.5 m./sec.) and strip reductions varying from 10 to 40% have been performed with the temperature sensor. Analysis of the tests by inverse calculation show that at low speed (<0.5 m="" sec="" and="" large="" contact="" lengths="" reduction:="" 30="" to="" 40="" the="" roll="" bite="" peak="" of="" heat="" flux="" reconstructed="" by="" inverse="" calculation="" is="" correct="" at="" higher="" speeds="" 1="" 5="" smaller="" reduction="" :="" 10-20="" reconstruction="" incorrect:="" in="" under-estimated="" though="" its="" average="" value="" analysis="" reveals="" also="" that="" transfer="" coefficient="" htc="" sub="">roll-bite (characterizing heat transfers between roll and strip in the bite) is not uniform along the roll bite but is proportional to the local rolling pressure. Finally, based on the above results, simulations with a roll thermal fatigue degradation model in industrial hot rolling conditions show that the non uniform roll bite Heat Transfer Coefficient HTCroll-bite may have in certain rolling conditions a stronger influence on roll thermal fatigue degradation than the equivalent (e.g. same average) HTCroll-bite taken uniform along the bite. Consequently, to be realistic the roll thermal fatigue degradation model has to incorporate this non uniform HTCroll-bite.
Submicrocristalline Structure and Dynamic Recovery of Cold Flowformed ELI Grade Ti-6Al-4V
Authors: Depriester Dorian , Massoni Elisabeth
Published: June 2013

Flowforming is a means to produce seamless tubes by plastic deformation at room temperature. It consists in reducing the thickness of a tubular part mounted on a mandrel by deforming it using several rollers translating along the tube axis, while the tube is rotating along its axis. Thanks to the high compressive stresses, and to the incremental nature of the deformation process, flowforming can lead to a high thickness reduction and thus to high elongation of the deformed tubes. Ti-6Al-4V (Extra Low Interstitial grade) tubes have been deformed by cold flowforming, with a thickness reduction ratio higher than 60%, and their microstructures have been investigated using light optical microscopy (LOM), scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). Based on EBSD data, a post-processing analysis has been performed in order to study the texture of the flowformed parts. Optical Microscopy showed that the material could be deformed without displaying flow instability such as adiabatic shear banding, despite the fact that it has been processes out of the stable processing maps (high strain rate and low temperature). It also evidenced a major deformation along the tube axis accompanied with a slight twist due to torsion stress. EBSD analysis indicated the occurrence of continuous dynamic recrystallization, which is rarely reported in the α-β domain of such alloys. The recovery/ recrystallization effects resulted in a submicrocrystalline equiaxed structure, which is consistent with that previously reported for Ti-6Al-4V subjected to severe plastic deformation (SPD). The texture of the hexagonal α-phase appeared to be similar to that obtained on extruded Ti-6Al-4V, with a basal component perpendicular to the tube axis.
Numerical Simulation of Plug-Assisted Thermoforming Process: Application to Polystyrene
Authors: Bernard Chrystelle A. , Correia Joao Pedro M. , Bahlouli Nadia , Ahzi Saïd
Published: June 2013

In the present work, the thickness distribution in a plug-assisted thermoforming process is investigated using finite element (FE) simulations. Numerical simulations have been performed with the FE code ABAQUS/Explicit. The contact between sheet and tools is considered as isothermal. Moreover, the coefficient of friction between plug and sheet is assumed constant. The behavior of the material is described by three hyperelastic laws available in the FE code. The comparison between experimental and FE results highlights that the neglected thermal effects (conduction and convection) and the thermal dependence of coefficient of friction should be considered. For future work, we propose an elasto-viscoplastic model which appears to better describe the behavior of the material than a hyperelastic model.
In-Line Visualisation of Polymer Plastication in an Injection Moulding Screw
Authors: Pham T.L. , Balcaen J. , Charmeau J.Y. , Bereaux Yves
Published: June 2013

In injection moulding or in extrusion, plastication is the step during which polymer pellets are melted by the means of mechanical dissipation provided by a rotating screw and by thermal conduction coming from a heated metallic barrel. This step is crucial for melt thermal homogeneity, charge dispersion and fibre length preservation. Although there have been a large number of theoretical and experimental studies of plastication during the past decades, mostly on extrusion and mostly using the screw extraction technique, extremely few of them have dealt with trying to visualise plastication, let alone measuring the plastication profile in real-time. As a matter of fact, designing such an equipment is an arduous task. We designed an industry-sized metallic barrel, featuring 3 optical glass windows, each window possessing 3 plane faces itself to allow for visualisation and record by synchronised cameras and lightening by lasers. The laser can be used in a laser induced fluorescence or in a particle imaging velocity measurement framework. The images recorded can be further analysed by digital image processing. Preliminary results confirm the plastication theory and show a compacted solid bed and a melt pool side by side. The total plastication length is a direct function of screw rotation frequency as it is obvious from results on the melt pool width, which increases when the screw rotation frequency decreases. However, some evidence of solid bed breakage has been recorded, whereby the solid bed does not diminish continuously along the screw but is fractured in the compression zone These experimental findings are compared to predictions by a one-dimensional model of plastication
Transversely Isotropic Hyperelastic Constitutive Models for Plastic Thermoforming Simulation
Authors: Oueslati Zied , Rachik Mohamed , Lacrampe Marie France
Published: June 2013

For several years, modeling hyperelasticity has been focused on and leaded to a large choice of strain energy potential forms. Since then, many advances have been made in constitutive modeling of rubber like materials. These models are nowadays widely used in many applications like constitutive modeling of soft tissues in biomechanics problems or plastic thermoforming simulation. In this work, constitutive modeling of TPO sheets for thermoforming application is considered. Experimental measurements have shown that the material is transversely isotropic. To take into account this anisotropy, we implemented some new transversally isotropic hyperelastic constitutive models in Abaqus software with the help of user subroutines. Furthermore, different particular forms of the strain energy potential are investigated and their hyperelatic constants are fitted to the measurement data from tensile tests performed in different directions. Based on the results of these investigations, a transversely isotropic form of the energy potential derived from the Yeoh constitutive model is adopted and several tests are analyzed for validation purpose. The chosen model is a good compromise that achieves accurate predictions with limited amount of tests and limited identification efforts. Another key finding of this work is the influence of the anisotropy on the thermoformed parts.
Influence of Steaming and Boiling at 180 °C Plus on the Injectability of Bamboo Powder
Authors: Kajikawa Shohei , Iizuka Takashi
Published: June 2013

In this study, we investigated changes in the injectability of bamboo powder and the Vickers hardness of compacted products resulting from differences in heat-treatment conditions such as steaming and boiling. We conducted injection tests and test fabrications of compacted products using bamboo powder treated under various conditions. From the injection tests of heat-treated bamboo powder, we found that injectability was improved by heat treatment. While bamboo powder steamed at 200 °C showed good injectability, boiling at 200 °C yielded better injectability. Vickers hardness tests conducted on compacted products showed that hardness was increased by heat treatment under appropriate conditions. In addition, we found that the heat-treatment condition required to increase the hardness of product was different from that needed to improve injectability.
Electrical Discharge Machining of Alumina-Zirconia-TiC Composites with Varying Zirconia Content
Authors: Landfried Richard , Kern Frank , Gadow Rainer
Published: June 2013

Ceramic injection molding (CIM) or extrusion requires molds and dies with high hardness to reduce tool wear which occurs due to processing of highly abrasive ceramic compounds. Besides the wear resistance high strength and toughness are necessary for mold materials to withstand the loads during application. Recent work of the authors has shown the high potential of electrical discharge machinable ceramic composites based on oxide ceramic matrices for high wear applications. The use of alumina zirconia composites (AZC) as matrix for electrically conductive composites enables the combination of high hardness of alumina and high strength and toughness of zirconia in order to customize the properties of the mold material. This study focuses on development of ED machinable AZCs with addition of 24 vol.-% titanium carbide as electrically conductive phase. The composition of the matrix was varied from pure alumina to pure zirconia in 5 steps. Disks for mechanical and electrical characterization and electric discharge machining experiments were manufactured by hot pressing. Results show that hardness, strength and toughness can be almost linearly correlated to composition from pure alumina matrix with a 4-point bending strength of 430 MPa, a hardness of 2250 HV10 and a toughness of 3.7 MPa√m to pure zirconia matrix with 1020 MPa bending strength, 1490 HV10 and a toughness of 5.9 MPa√m. Variation of matrix composition also leads to significantly different EDM characteristics. The material removal rate shows a maximum at 19 vol.-% zirconia and 58 vol.-% alumina while surface roughness of the machined composites decreases significantly with increasing zirconia amount. SEM and EDX analysis were made to identify removal mechanisms of each ceramic matrix phase. It was found that alumina tends to be removed by vaporization due to electrical discharges. Zirconia, which has a higher melting and vaporization point than alumina melts during the formation of the plasma channel. Zirconia cannot be removed in total from the surface but forms a smooth and compact amorphous layer of resolidified material on both sample and electrode.
Effect of the Process Parameters on the Machinability Characteristics of a CoCrMo Alloy
Authors: Bruschi Stefania , Ghiotti Andrea , Bordin Alberto
Published: June 2013

The paper investigates the machinability characteristics of the CoCrMo alloy ASTM F1537, usually utilized for the production of joint replacements and fixation devices thanks to its high strength, good wear and corrosion resistance, and excellent biocompatibility. This research work intends to overcome the lack of literature data about this alloy machinability, even if its use in the biomedical sector is intensive and it is usually subjected to various machining operations for the implants production. Orthogonal cutting tests were carried out under both dry and lubricated conditions at different cutting speeds and feeds typical of finishing operations. The alloy machinability was analysed in terms of tool wear, cut surface integrity, and chip morphology. In particular, the cut surface integrity was evaluated through its mechanical properties, metallurgical state and topological parameters, highlighting the influence of the process parameters.
Implementation of Advanced Frictional Laws for Modelling of High Speed Machining
Authors: Senecaut Yannick , Watremez Michel , Meresse Damien , Dubar Laurent
Published: June 2013

High-speed machining is submitted to economical and ecological constraints. Optimization of cutting processes must increase productivity, reduce tool wear and control residual stresses in the workpiece. Developments of numerical approaches to simulate accurately high-speed machining process are therefore necessary since in situ optimization is long and costly. To get this purpose, rheological behaviour of both antagonists and representative friction models at tool-chip interface has to be studied as encountered during high-speed machining process. The study is led with AISI 1045 steel and an uncoated carbide tool. An experimental device has been first designed to simulate the friction behaviour at the tool-chip interface only in the zone near the cutting edge. Several tests are then performed to provide experimental data and these data are used to define the friction coefficient versus to the contact pressure, the sliding velocity and the interfacial temperature by a new formulation frictional law given by Brocail et al (2010). A two-dimensional finite element model of orthogonal cutting is developed with Abaqus/explicit software. An Arbitrary Lagrangian-Eulerian (ALE) formulation is used to predict chip formation, temperature, chip-tool contact length, chip thickness, and cutting forces. This numerical model of orthogonal cutting is then validated by comparing these process variables to experimental and numerical results obtained by Filice et al. (2006). This model makes possible qualitative analysis of input parameters related to cutting process and frictional models. A sensitivity analysis has been performed on the main input parameters (coefficients of the Johnson-Cook law, contact and thermal parameters) with the finite element model. The interfacial law determined by Brocail et al (2010) is implemented on this finite element model of machining and leads to improve numerical approaches of machining. Nevertheless, even if this law enables to reduce results between experimental and numerical approaches, some differences are still substantial. The advanced friction law must be complemented for higher sliding velocities and this work using a new specific experimental device will be presented in the second part of this paper.
An Experimental Study of Drilling Parameters Effect on Composite Carbon/Epoxy Damage
Authors: Turki Yosra , Habak Malek , Velasco Raphael , Laurent Jean Noel , Vantomme Pascal
Published: June 2013

The main purpose of composite materials drilling is the need to put together different parts of a structure, in aeronautics for example. The objective of this study is to experimentally analyze the influence of drilling on a carbon/epoxy composite. Three geometries of drill, a range of cutting speed and feed have been tested. Thrust forces and moments have been recorded during machining and macroscopic analyses have been conducted to examine outside and inside surfaces of the holes. Damages have been also quantified using delamination factor Fd. Experimental results have shown significant influences of feed and drill geometry on delamination and the best results have been obtained using a spur drill.
An Error Model in Micro Dimple Milling
Authors: Matsumura Takashi , Watanabe Ryosuke , Musha Yuji
Published: June 2013

A micro dimple machining is studied to control the surface functions with the micro-scale structures on the solid surfaces. The micro dimples are machined in milling with the inclined ball end mill. When the feed rate of the tool is high enough that the removal area of an edge does not overlap with that of the previous edge, periodical concave dimples are machined. A mechanistic model is presented to control the shape and the size of the dimples to be machined. Then, a machining error model is presented to control the deviation of the dimple shapes. Some machining examples are shown to verify the dimple model and the error model.
The Effects of Cutting Conditions on Surface Integrity in Machining Inconel 718 Alloy
Authors: Umbrello Domenico
Published: June 2013

Machining of advancedaerospace materials have grown in the recent years although the hard-to-machinecharacteristics of alloys like titanium or nickel based alloys cause highercutting forces, rapid tool wear, and more heat generation. This paper presentsan experimental evaluation of machining of Inconel718 alloy under dry conditions at varying of cutting speeds and feed rates.The influence of the cutting conditions on surface integrity was studied interms of surface roughness, affected layer, grain size variations and phasechanges/modification. Also, the machining process performance was evaluatedthrough the power consumption and tool-wear.
Inverse Identification of CDM Model Parameters for DP1000 Steel Sheets Using a Hybrid Experimental-Numerical Methodology Spanning Various Stress Triaxiality Ratios
Authors: Yue Zhen Ming , Soyarslan Celal , Badreddine Houssem , Saanouni Khemais , Tekkaya A. Erman
Published: June 2013

A hybrid experimental-numerical methodology is presented for the identification of the model parameters regarding a mixed hardening anisotropic finite plasticity fully coupled with isotropic ductile damage in which the micro-crack closure effect is given account for, for steel sheets made of DP1000. The experimental tests involve tensile tests with smooth and pre-notched specimens and shear tests with specimen morphologies recently proposed by D.R. Shouler, J.M. Allwood (Design and use of a novel sample design for formability testing in pure shear, Journal of Materials Processing Technology, Volume 210, Issue 10, 1 July 2010, Pages 1304-1313). These tests cover stress triaxiality ratios lying between 0 (pure shear) and 1/√3 (plane strain). To neutralize machine stiffness effects displacements of the chosen material surface pixels are kept track of using the digital image correlation system ARAMIS, where recorded inputs are synchronized with force measurements. On the numerical part, developed constitutive model is implemented as user defined material subroutine, VUMAT, for ABAQUS/Explicit. FE models for the test cases are built using 3D brick elements (rather than thin shells) and devising developed VUMAT for the constitutive model, model parameters are identified using an inverse parameter identification procedure where the objective function relies on the difference of experimentally observed-numerically predicted forces for the selected pixel displacements. The validity of the material model and transferability of its parameters are tested using tests involving complex strain paths.
Calibration of Material Parameters of Anisotropic Yield Criterion with Conventional Tests and Biaxial Test
Authors: Zhang Shun Ying , Leotoing Lionel , Guines Dominique , Thuillier Sandrine
Published: June 2013

Bron and Besson yield criterion has been used to investigate the plastic anisotropic behavior of an aluminum alloy AA5086. The parameters of this anisotropic yield model have been identified by two different methods: a classical one, considering several homogeneous conventional experiments and an exploratory one, with only biaxial test. In this paper, the parameter identification with conventional experiments has been carried out with uniaxial tensile tests and simple shear tests in different orientations to the rolling direction and with a hydraulic bulge test. For comparison’s sake, Hill’s 48 yield function has also been calibrated analytically from uniaxial tensile tests. Numerical simulation for the cross biaxial test has been carried out with the anisotropic parameters identified from the conventional tests. From this simulation, the principle strains along a specified path in the gauge area of the cruciform specimen have been evaluated. A good agreement is observed between experimental and numerical values of principal strains for a large range of strain paths.
The Internal Stress Evaluation of Pultruded Blades for a Darrieus Wind Turbine
Authors: Baran Ismet , Tutum Cem C. , Hattel Jesper Henri
Published: June 2013

This paper investigates the integrated modeling of a pultruded NACA0018 blade profile which is a part of the FP7 EU project DeepWind. The pultrusion process simulation is combined with the preliminary subsequent in-service load scenario. In particular, the process induced residual stresses and distortions are predicted by using a new approach combining a 3D Eulerian thermo-chemical analysis, in which the temperature and the cure degree distributions are obtained, and a 2D quasi-static plane strain mechanical analysis. The post-die region where convective cooling prevails is also included in the process model. The bending into shape of the pultruded blade profile is simulated with and without taking the residual stresses into account. The internal stress distribution in the profile is evaluated after the bending analysis and it is found that the process induced residual stresses have the potential to promote or to demote the internal stresses in the structural analysis.
Sensitivity Analysis of Process Parameters in the Drawing and Ironing Processes
Authors: Simões Vasco M. , Coër Jeremy , Laurent Hervé , Oliveira Marta C. , Alves José Luis , Manach Pierre Yves , Menezes Luis Filipe
Published: June 2013

Deep drawing is one of the most important operations used in sheet metal forming. Within this, forming of cylindrical cup is one of the most widely studied deep drawing processes since it allows analysing the effect of different process parameters in phenomena such as earing, springback and ironing. In fact, during the deep drawing of a cylindrical cup the blank thickness gradually increases as the blank outer diameter is reduced to the die inner diameter, resulting in a thickness increase from a point near the bottom radius until the maximum value at the top of the cup. Therefore, if the gap between the punch and the die is not sufficiently large to allow the blank material to flow, ironing of the cup wall will occur. The ironing process typically imposes high contact forces, normal to the surface of the punch and the die, which can lead to the occurrence of galling, particularly for aluminium alloys. In this work an experimental device, adopted in previous studies, was used to analyse the influence of the lubricant conditions in the deep drawing of a cylindrical cup. The study considers an AA5754-O aluminium alloy blank with a diameter of 60 mm, which is fully deep drawn with a 33 mm diameter punch. Due to the forming conditions, the cup is deep drawn and ironing of the cup wall also occurs. The experimental tests were performed considering different amounts of lubricant in the blank surfaces in the contact with the die and with the blank-holder in order to better understand the influence of these tools on the process. The experimental study was complemented with numerical simulations, exploring the conditions induced by the ironing operation, quite challenging for the numerical simulation of the process using the finite element method. Besides the influence of the contact with friction conditions in the forming process (i.e. punch force evolution, thickness distribution along the cup wall and contact pressure), the influence of the die shoulder and inner radius were also analysed.
Comparison of Hyper- and Hypoelastic-Based Formulations of Elastoplasticity with Applications to Metal Forming
Authors: Brepols Tim , Vladimirov Ivaylo N. , Reese Stefanie
Published: June 2013

The aim of this work is to examine two specific finite strain elastoplasticity models in terms of their applicability in metal forming processes, namely a hyperelastic-based model which relies upon a multiplicative decomposition of the deformation gradient into elastic and plastic parts and a hypoelastic-based model which makes use of an additive elastic-plastic split of the rate of deformation tensor. Both models allow for nonlinear isotropic and kinematic hardening and were implemented as user material subroutines (UMAT) into ABAQUS/Standard. Various sample calculations were performed to assess the respective properties and capabilities of the models. The FE simulation of a deep drawing process produced nearly congruent results for both models which suggests that they are equally well-suited for modeling metallic materials in metal forming processes.
Effect of Different Finish-Rolling Parameters on the Microstructure and Mechanical Properties of Twin-Roll-Cast (TRC) AZ31 Strips
Authors: Gorelova Sofya , Ullmann Madlen , Oswald Matthias , Kawalla Rudolf
Published: June 2013

The microstructure and the resulting mechanical properties of Twin Roll-Cast (TRC) AZ31 strips have been investigated after rolled from thickness of 5.2 mm to 1.00 mm and 1.25 mm, respectively. Twin-Roll-Casting (TRC) was used to produce AZ31 strips with a near-net final thickness directly from the liquefied material. The two-stage rolling experiments were carried out on the four high reversing mill at the Institute of Metal Forming in Freiberg. The first stage was two roughing passes followed by intermediate annealing. The second stage was subsequent finish rolling with 1 to 3 rolling passes. The influence of the finish-rolling on the properties of the final strip was investigated, including the variations of rolling pass and pass reduction. The TRC strip exhibits a heterogeneous microstructure with random texture due to a deformed structure combined with partial cast columnar and equiaxed grains. Significant grain refinement was achieved using high deformation degree per pass (> 30 %). Increasing rolling passes to 3 during finish-rolling reduces the strain per pass and also leads to a temperature drop so that incomplete dynamic recrystallization after the final rolling pass occured, leading to a more coarse and heterogeneous microstructure. It was found, that a 2-pass finish rolling provides the optimum strategy for the material properties as well as the process stability. Due to homogeneous fine grained microstructure, the 2-pass rolled strip showes high mechanical properties with low anisotropy. This includes yield point of 234 MPa, tensile strength of 285 MPa and total elongations of 25 %.
Computer Aided Design of Manufacturing of Anchors and Formulation of the Optimization Task for in Use Properties
Authors: Skóra Mariusz , Weglarczyk Stanislaw , Kusiak Jan , Pietrzyk Maciej
Published: June 2013

Computer aided design of the manufacturing technology for anchors is presented in the paper. Evaluation of applicability of various materials for anchors, as well as analysis of the influence of process parameters on the in use properties of product, were the objectives of the research. In the material part, bainitic steels were considered as an alternative for the commonly used C-Mn steels. Possibility of elimination of the heat treatment was evaluated. Rheological models for the investigated steels were developed and implemented into the finite element code for simulations of drawing and multi stage forging. Criteria for the selection of the best manufacturing chain composed dimensional accuracy, tool life and product properties. Industrial trials were performed for the selected cycle and the efficiency of this cycle was evaluated. Finally, simulations of the in use behaviour of the anchor-concrete joint were performed. On the basis of the simulations the optimization task using strength of the joint as the objective function was formulated
Experimental Study of Steel and Glass Knitted Fabrics Thickness under Pre-Strain and Shear
Authors: Barburski Marcin , Lomov Stepan , Lanckmans Filip , de Ridder Frank , Verpoest Ignaas
Published: June 2013

In this paper the compression behaviour after different pre-strain and different shear angle of steel and glass fibre knitted fabrics will be analysed. These types of materials are used during the production of automotive windshields and other glasses in a car. The production of a windshield involves a step whereby the glass is deformed to the desired shape by using a mould. It is important that during this forming step the glass is not damaged and that the optical quality of the glass falls within the specifications of the customer. A knitted steel fibre fabric covers the mould. Since this fabric comes in direct contact with the glass, it is a key factor that determines the quality of the formed windshield. Variation of the fabric thickness can affect the optical quality of the glass. Thus far fabric very often manufacturers operate on the basis of empirical trial and error results to design their products. The challenge of the present work is to establish an experimental procedure for identification of the material laws for knitted fabrics deformation resistance. The paper describes an experimental procedure for derivation of the fabric thickness dependence on its deformation, using biaxial tension, shear and compression tests. The compression tests are performed on an Instron mechanical testing machine. During the test, a load cell (1 kN) pushes down with a constant speed of 1 mm/min onto the sample, compressing it. The load cell is attached to a cylinder which has a diameter of 70mm. The knitted fabrics was tested in the relaxed state and after pre-tension on the biaxial tester with pre-strains of 5x5%, 10x10%, 15%x15%, 0x10%, 10x0%, 0x20%, 20x0% and they was also tested after different shear angle (5°, 10°, 15°, 25°). Difference of thickness of fabrics after pres-strain is till 90 µm and for 25°shear angle is about 30 µm. Acknowledgements The work was funded by the grant 631/MOB/2011 of the Polish Ministry of Science and High Education, with the support from K.U.Leuven and N.V. Bekaert S.A.
Two-Scales Kinetic Theory Model of Short-Fibers Aggregates
Authors: Abisset-Chavanne Emmanuelle , Mezher Rabih , Chinesta Francisco
Published: June 2013

This paper proposes a first attempt to define a two scales kinetic theory to describe concentrated suspensions involving short fibers, nano-fibers or nanotubes. In this case, fiber-fiber interactions can not be neglected and rich microstructures issued from these interactions can be observed, involving a diversity of fibers clusters or aggregates with complex kinematics, and different sizes and shapes. These clusters can interact to create larger clusters and also break because the flow induced hydrodynamic forces. In this paper we propose a double-scale model to describe such microstructure: at the finest scale we study the cluster kinematic based on the behaviour of the rods that constitute it, at a coarser scale, we use clusters distribution to derive the effect of the clusters presence on the suspensions properties.
Identification of Forming Limits for Unidirectional Carbon Textiles in Reality and Mesoscopic Simulation
Authors: Böhler Patrick , Härtel Frank , Middendorf Peter
Published: June 2013

In several fields of engineering the use of carbon fibre reinforced material (CFRP) is increasing. Minimized weight due to CFRPs could lead to lower consumption of raw materials especially in the automotive area. The goal within the research project TC² is the decrease of costs and production time for composite materials. To achieve better performance to weight ratio and to get acceptable production conditions the draping of dry unidirectional textiles and a following RTM process is investigated. Due to the high degree of complexity of automotive structures the forming process is challenging. Gapping in the textile could appear at corners as well as wrinkling or flexion of the fibres. To be able to define the amount and direction of layers or patches it is necessary to know the limits of forming for unidirectional material and to be able to predict the behaviour of the textile during the forming process. For the definition of the process limits several draping strategies are performed on different corner blend geometries. The goal of that work is to define the critical gradient of the flange to get first failures such as wrinkling or gapping. It is also important to understand the influence of different draping strategies. Parallel to the experimental tests a mesoscopic simulation method using an approach with roving and sewing thread is developed and presented. It is able to predict the material behaviour in critical areas (gapping, wrinkling). Different Young’s moduli and failure criteria can be implemented for the two main directions as well as for the bending of the textile. A validation with the experimental results is performed with the aim to enable the prediction of the textile behaviour using simulation methods.