bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.
The effect of microalloying on the sheared edge ductility of ferritic steels
Authors: Hannula J. , Kaijalainen A. , Porter D. , Kesti V. , Kömi J. 
Published: November 2019

Abstract
Sheared edge ductility plays a critical role in many automotive and structural applications. The effect of microalloying elements on the microstructure, mechanical properties, sheared edge quality and hole expansion properties of six thermomechanically laboratory hot rolled and coiled, approximately 4 mm thick, precipitation hardened ferritic steels have been investigated. The studied V-microalloyed steels had low carbon contents, 0.05 and 0.09 wt.%, and, in some cases, microalloying additions of either Nb or Nb+Ti. Yield strengths were in the range 500 MPa to 750 MPa and hardness values between 176 and 260 HV10 depending on the carbon content and level of precipitation strengthening. Detailed microstructural analysis using laser scanning confocal microscopy (LCSM), FESEM and FESEM-EBSD revealed that all the steels consisted of mainly single-phase ferrite. FESEM analysis revealed the presence of relatively coarse precipitates at grain boundaries and inside some of the ferrite grains, but the number density of visible precipitates varied greatly between grains. The addition of Nb or Nb+Ti reduced the ferrite grain size, especially the size of the largest grains as defined by the 90th percentile in the cumulative grain area distribution (d90%). Mean hole expansion (HE) ratios varied from 39 % to 76 % with the highest values associated with the lowest carbon contents. Despite raising the strength, microalloying with Nb or Nb+Ti had little if any detrimental effect on HE ratios compared to the V-microalloyed variants without Nb or Ti, presumably as a result of the grain refinement. Titanium nitrides acted as void nucleation sites close to the sheared edge. Microalloying with Nb and Nb+Ti led to a decrease in the depth of the shear affected zone (SAZ) and a smaller difference in hardness between the base material and the SAZ.
Novel roll stand for flexible profile bending
Authors: Martschin J. , Meya R. , Löbbe C. , Tekkaya A. E. 
Published: November 2019

Abstract
A new method and roll stand for the manufacturing of structural profiles with tailored dimensions and properties based on the combination of rolling and profile bending is developed. Through this merged process the outer contour of a semi-finished product is shaped by a set of driven flexible and rigid rollers. The profile inner side is supported by an adjustable mandrel, so that an arbitrary variation of the cross-section along the profile can be achieved. Additionally, a moveable guiding roll facilitates the bending of the product. Conventionally, the manufacturing of load-optimized bent profiles requires a sequence of operations, whereas the novel method enables the manufacturing of those components in one process step. This leads to a reduction in tooling cost and setup time. Hence, the production of lightweight structures in small batch sizes is facilitated. In this contribution, the new forming method and the design of the developed roll stand are presented alongside with an investigation of the effects of stress superposition on bending stresses during combined bending and rolling as well as the possible processes applications.
Parameter identification of 3D yield functions based on a virtual material testing procedure
Authors: Butz A , Wessel A , Pagenkopf J , Helm D 
Published: November 2019

Abstract
The parameter identification of anisotropic 3D yield functions for sheet metals based on experimental data is very difficult, because material properties associated to the out-of-plane stress states cannot be directly measured. An alternative and promising approach for identifying parameters of anisotropic yield models, and particularly for 3D yield models, is the concept of virtual testing. Within the presented work, a full-field microstructure simulation framework based on a crystal plasticity (CP) model is used to determine macroscopic mechanical properties of a ferritic deep drawing steel DX56 within 3D stress space. The results are utilized to identify the parameter of anisotropic 2D and 3D yield models according to Hill [1] and Barlat [2, 3].
Pressure and sliding velocity dependent surface asperity based friction model: Application to springback simulation
Authors: Lee K J , Lee M G 
Published: November 2019

Abstract
For accurate predictions of the formability and springback in the finite element sheet forming simulations, significant advances have been achieved in constitutive modeling that captures complex deformations occurring in the sheet forming process. However, friction behavior has been still modeled and implemented as a simple way though it is one of critical factors for accurate numerical simulations. For instance, sheet metal forming simulations often employ the Coulomb friction law with a constant friction coefficient, but it is known to be a function of other factors such as contact pressure, sliding rate and other surface quality. In this study, the microscopic surface asperity based friction model originally proposed by Westeneng [1], as one of microscale level friction models, was revisited by using additional contact assumptions. In particular, the model added the strain rate effect to the existing contact pressure dependent model in order to include the effect of both contact pressure and sliding velocity during sheet forming process. The calculated contact friction coefficient was compared to that by the measured for dual-phase 780 steel sheet under different pressure and sliding velocity. Moreover, the predicted friction model was employed in the simulation of U-draw bending springback by using a user friction subroutine, which was evaluated by the comparison of experimentally measured springback profile
Parameter Measurement and Conductive Heating During Press Hardening by Hot Metal Gas Forming
Authors: Bach M , Degenkolb L , Reuther F , Psyk V , Mauermann R , Werner M 
Published: November 2019

Abstract
Press hardening of steels for the production of car body components is very common. The reason for this is that the process allows the use of blanks with low wall thickness and the production of ultra-high strength components with complex geometries. The Hot Metal Gas Forming (HMGF) process for closed profiles combines the advantages of hydroforming, such as increased rigidity, functional integration or elimination of joining operations, with those of press hardening. In this paper results of continuous tests with actively cooled tools are presented in combination with temperature and displacement measurement. Furthermore, test results for HMGF with tool integrated conductive heating are demonstrated. Tests were done with tube material PHS1800 by SSAB, part temperatures over the Point of austenitisation and maximum internal pressure of 70 MPa. Thermocouples recorded the heat distribution in the tools. Other measured and recorded variables were the displacement of the component wall while forming under increasing internal pressure by a tactile displacement sensor and simultaneous temperature of its surface with a thermal sensor head. For the first time, information on pressure, the corresponding deformation stage and temperature profile could be documented during an entire forming step. A close to series production geometry DP4 was used to investigate the tool-integrated conductive heating of components.
Feedback control of laser forming using flattening simulations for error determination
Authors: Thomsen Anders Noel , Endelt Benny , Kristiansen Morten 
Published: November 2019

Abstract
Laser forming is a non-contact forming method. By control of different process parameters, different forming mechanisms can be achieved. The forming mechanisms allows for bending, compression and buckling. Process control to ensure correct combination and usage of each forming mechanism is still an open issue. Present work is an attempt to implement a feedback control loop using measurements of the current shape between laser scan pass. This work presents an initial case study used to evaluate a feedback control loop. A flattening model is used to determine the difference in strains between a target shape and the current shape. The current shape is updated between laser scan paths. The case study examines different shapes including the dome, saddle and v-bend shapes. By examining different shapes that require different forming mechanisms, this work takes steps toward formulating process design principles for use in feedback control of laser forming. The results show decent agreement with the target shape and the formed shape for the v-bend. As the cases increase in complexity, requiring a combination of forming mechanisms, the disagreement increases. The analysis of the process indicates that the boundary conditions of the flattening model and the design of the controller could be improved to reduce tolerances.
Strain Rate and Temperature Dependent Plastic Response of AA7075 during Hot Forming
Authors: Pandya K. S. , Roth C. C. , Mohr D. 
Published: November 2019

Abstract
High strength 7xxx series aluminum alloys are being increasingly considered for automotive applications due to their superior specific strength compared to 6xxx series alloys. Complex structural components made from 7xxx series alloys need to be manufactured through warm forming or hot stamping due to their low ductility at room temperature. For hot stamping, the AA7075 blanks are heat treated to above 480°C, yielding a supersaturated solid solution, corresponding to a W temper state. The preheated blanks are then simultaneously formed and rapidly quenched using cooled dies. The entire forming process takes place in the W temper condition. The stamped parts are further subject to an artificial aging heat treatment to achieve the desired temper through precipitation hardening. Therefore, understanding the strain rate and temperature dependent plasticity behavior of AA7075-W is critical to establish optimum design parameters for the hot stamping process. The present work is concerned with the strain rate and temperature dependent plastic response of AA7075 in the W temper state. In particular, the results from a comprehensive experimental program on uniaxial tension specimens are presented. High temperature experiments are carried out at strain rates ranging from 0.001-2/s in a universal testing machine. An induction heating system with infrared high speed imaging is used to span the entire temperature range from 180°C to 480°C, over the full range of strain rates considered. Based on the experimental results, a candidate plasticity model with an empirical mixed Swift-Voce hardening law and a Johnson-Cook type strain rate and temperature dependence is calibrated.
Towards neural network models for describing the large deformation behavior of sheet metal
Authors: Gorji Maysam B. , Mohr Dirk 
Published: November 2019

Abstract
Neural networks provide a potentially viable alternative to a differential equation based constitutive models. Here, a neural network model is developed to describe the large deformation response of a Levy-von Mises sheet material with isotropic strain hardening. Using a conventional return-mapping scheme, virtual experiments are performed to generate stress-strain data for random monotonic biaxial loading paths (up to strains of 0.2). Subsequently, a basic feedforward neural network model is trained and validated using the results from virtual experiments. The results for a shallow network with only two hidden layers show remarkably good agreement with all experimental data. The identified neural network model is implemented into a user material subroutine and used in basic structural simulations such as uniaxial tensile and notched tension experiments. In addition to demonstrating the potential of neural networks for modeling the rate-independent plasticity of metals, their application to more complex problems involving strain-rate and temperature effects is discussed.