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Technical Paper

Stamping Effect on Oil Canning and Dent Resistance Performances of an Automotive Roof Panel

The objective of this paper is to investigate the effect of stamping process on oil canning and dent resistance performances of an automotive roof panel. Finite element analysis of stamping processes was carried out using LS-Dyna to obtain thickness and plastic strain distributions under various forming conditions. The forming results were mapped onto the roof model by an in-house developed mapping code. A displacement control approach using an implicit FEM code ABAQUS/Standard was employed for oil canning and denting analysis. An Auto/Steel Partnership Standardized Test Procedure for Dent Resistance was employed to establish the analysis model and to determine the dent and oil canning loads. The results indicate that stamping has a positive effect on dent resistance and a negative effect on oil canning performance. As forming strains increase, dent resistance increases while the oil canning load decreases.
Technical Paper

Laminated Steel Forming Modeling Techniques and Experimental Verifications

Laminated steel sheets sandwiched with a polymer core are increasingly used for automotive applications due to their vibration and sound damping properties. However, it has become a major challenge in finite element modeling of laminated steel structures and forming processes due to the extremely large differences in mechanical properties and in the gauges of the polymer core and the steel skins. In this study, circular cup deep drawing and V-bending experiments using laminated steels were conducted in order to develop a modeling technique for laminate forming processes. The effectiveness of several finite element modeling techniques was investigated using the commercial FEM code LS-Dyna. Furthermore, two production parts were selected to verify the modeling techniques in real world applications.
Technical Paper

Crashworthiness of Automotive Stamped Parts Using High Strength Steel Sheets

Forming and strain rate effects on crashworthiness of automotive body components were investigated in this study. Dynamic tensile tests were carried out to establish the stress-strain relationships at elevated strain rates. Dynamic tests of bending and axial crashing at various speeds were conducted using a stamped hat square column. The experimental results indicate that the absorbed energy of the hat square column decreased with the increase of material thinning in case of high strength steels. FEM analyses using material models with both strain rate sensitivity and forming effects were carried out to evaluate the computer prediction accuracy of crashworthiness.
Technical Paper

Techniques to Improve Springback Prediction Accuracy Using Dynamic Explicit FEA Codes

Finite Element Analysis (FEA) has been successfully used in the simulation of sheet metal forming process. The accurate prediction of the springback is still a major challenge due to its sensitivity to the geometric modeling of the tools, strain hardening model, yield criterion, contact algorithm, loading pattern, element formulation, mesh size and number of through-thickness integration points, etc. The objective of this paper is to discuss the effect of numerical parameters on springback prediction using dynamic explicit FEA codes. The example used in the study is from the Auto/Steel Partnership High Strength Steel Rail Springback Project. The modeling techniques are discussed and the guidelines are provided for choosing numerical parameters, which influence the accuracy of the springback prediction and the computation cost.
Technical Paper

Springback of Sheet Metal Subjected to Multiple Bending-Unbending Cycles

A Draw Bead Simulator (DBS), with modified draw beads, was employed in this study to understand the springback behavior of sheet metal subjected to multiple bending-unbending cycles. The investigations were carried out in both the rolling and the transverse rolling directions on four types of materials: Electro-Galvanized DQ steel, light and heavy gauge Hot-Dip Galvanealed High Strength Steels, and Aluminum alloy AL6111. The sheet geometries, thickness strains, pulling forces and clamping forces were measured and analyzed for the purpose of establishing a benchmark database for numerical predictions of springback. The results indicate that the springback curvature changes dramatically with the die holding force. The conditions at which the springback is minimized was observed and found to depend on the material properties and the sheet thickness. Analysis with an implicit FEM showed that the predicted and the experimental results are in very good agreement.
Technical Paper

A Study on the Effects of Simulation Parameters on Springback Prediction

The use of commercial finite element analysis (FEA) software to perform stamping feasibility studies of automotive components has grown extensively over the last decade. Although product and process engineers have now come to rely heavily on results from FEA simulation for manufacturability of components, the prediction of springback has still not been perfected. Springback prediction for simple geometries is found to be quite accurate while springback prediction in complex components fails to compare with experimental results. Since most forming simulation FEA software uses a dynamic explicit solution method, the choice of various input parameters greatly affects the prediction of post formed stresses in the final component. Accurate stress prediction is critical for determination of springback, therefore this study focuses on the effects of some of the simulation parameters such as, element size, tool/loading speed and loading profile.
Technical Paper

Analytical and Experimental Examination of Tubular Hydroforming Limits

Tubular hydroforming processes provide a number of advantages over conventional stamping processes including reduction in the number of parts, and reduction in the tooling and material costs. As a result, the technology has drawn increasing attention in the automotive industry. However, there is still little experience available of both the forming process and its FEM simulation. The current experimental and FEM simulation study has been initiated to gain a better understanding of the fundamentals of hydroforming processes. This paper summarizes experimental and analytical results of a hydroforming process which expands a circular tube into a rectangular cross-section. A better understanding is obtained of the relationship between internal pressure and axial displacements, mechanisms of buckling, splitting and corner fill-ins. Splitting, buckling and the tubular hydroforming zones are identified on the traditional Forming Limit Diagram.