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Progressive Die Sequence Design for Deep Drawing Round Cups Using Finite Element Analysis
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Abstract：
A methodology for progressive die sequence design for forming round cups using finite element method (FEM) based simulations is discussed. The process sequence design developed was applied to forming of an automotive part and was compared with the design obtained from past experience. The methodology proposed in this paper has shown that the integration of design experience and FEM simulations can enhance the robustness of the procedure for die design sequence and reduces the die development cost considerably.37166
1 Introduction：
In the stamping industry, the design of progressive dies relies heavily on past experience and several prototype die tryouts. Figure 1 (Part A) shows the process sequence of a round part manufactured using progressive dies. A progressive die performs a series of fundamental forming operations at two or more stations during each press stroke as the strip stock moves through the die. The most critical and challenging issues in this task are how to determine (a) the minimum number of required forming steps and (b) the corresponding tooling shapes while maintaining the specified thickness distribution in the formed part. This procedure requires extensive resources and increases the process development time and cost. A computer aided approach is highly desirable to design a robust progressive die sequence quickly and at reduced expense.
Knowledge-based systems have been explored to determine required forming stages in deep drawing and two-dimensional forging problems (1-5). Knowledge for these systems is derived from plasticity theory, experimental results, and the empirical know-how of field engineers. This approach has shown some success. However, it cannot consider the process conditions that are not already stored in the knowledge base. In earlier studies, related to the subject of this paper, Cao (6) used numerical simulations and sensitivity analysis to optimize the number of forming stages in a multi-step deep drawing problem. Kim (7) carried out tool design analysis for multi-step drawing using the finite element method (FEM). In these studies, only design improvements in existing multi-step tooling were carried out.
In the present study, an attempt is made to develop a FE simulation-based design strategy for progressive die sequence in deep drawing of round cups. The analysis was carried out by a commercial implicit FEM code, DEFORM 2D . The design sequence obtained from FEM was compared with that obtained using past experience and trial-and-error approach. The results indicated that the FEM based strategy is approximately equivalent to that practiced by engineers with many years of experience.
2 Die Design Strategy for FEM Based Approach：
The objective of this study was to design the progressive die sequence for an automotive part shown in Fig. 2 (Part B) using FEM simulation. The die design procedure must determine: (a) ：number of forming stages, (b)： tool geometry for each stage (punch/die diameter, punch corner and die corner radii), (c) ：drawing depth for each stage and (d) ：blank holder force for each stage. In order to develop an appropriate die design strategy, for forming part B (Fig. 2), the forming stages of an example part, part A shown in Fig. 1, were investigated using FE simulations. Geometric parameters for various stages of the example part were provided by the stamping company sponsoring this research. The following design guidelines were obtained from this investigation:
•Higher draw ratios are used in the initial forming stages. Figure 3 shows the trends for the variation of punch diameters and maximum wall thinning. The punch diameter is reduced rapidly during the initial stages of deformation and relatively little in the later stages. Based on this trend, it was decided to constrain the maximum wall thinning below 4% in the first forming stage of part B. In the example part, A, the ratio of the punch corner radius to die corner radius was kept to less than 1 in all the forming stages, i.e., the ratio varied from 0.75 to 0.95. This condition was taken into account in determining the punch corner and die corner radii for various forming stages of part B.