Se-Ho Kim

Tool design in a multi-stage drawing and ironing process of a rectangular cup with a large aspect ratio using finite element analysis

Tool design is carried out for a multi-stage deep drawing and ironing process of a rectangular cup with the large aspect ratio using the result of the finite element analysis. The analysis incorporates three-dimensional continuum elements for an elasto-plastic finite element method with the explicit time integration scheme using LS-DYNA3D. The analysis simulates the five-stage deep drawing and ironing process with the thickness control of the cup wall. Simulation is performed in order to investigate the failure by tearing during the forming process at the initial state of tool design. The analysis reveals that the difference of the drawing ratio within the cross section induces non-uniform metal flow which causes severe local extension. The irregular contact condition between the blank and the die also induces non-uniform metal flow which causes local wrinkling. This paper identifies such unfavorable mechanism in the rectangular cup drawing with ironing and proposes a new tool design with the guideline for modification in the design of the process and the sequential tool shape. The finite element analysis result with the improved tool design confirms that the proposed design not only reduces the possibility of failure but also improves the quality of a deep-drawn product. The numerical result shows fair coincidence with the experimental result.

Finite element inverse analysis for the design of intermediate dies in multi-stage deep-drawing processes with large aspect ratio

Abstract An inverse finite element approach for multi-stage deep-drawing processes is introduced for robust capability to determine the optimum blank shape from the desired final shape and to obtain the thickness strain distribution in the final shape with a small amount of computing time and effort. A direct numerical analysis of multi-stage deep-drawing processes is extremely difficult to carry out because of its complexities and convergence problems as well as tremendous computing time. The analysis of elliptical or rectangular cup drawing with large aspect ratio is likewise very difficult with respect to the design process parameters including the intermediate die profiles. In order to overcome the difficulties, an inverse scheme is proposed in the present analysis and design. The multi-stage inverse analysis deals with the convergence among intermediate shapes and the corresponding sliding constraint surfaces. In this paper, finite element inverse analysis is applied to multi-stage deep-drawing processes in order to calculate the thickness strain distribution in each intermediate shape and to design the intermediate die shapes. The original design has been modified to enhance the discrepancy in the thickness strain distribution for each intermediate shape.

Optimum Process Design in Sheet-Metal Forming With Finite Element Analysis

Process optimization is carried out to determine process parameters which satisfy the given design requirements and constraint conditions in sheet-metal forming processes. The scheme incorporates with a rigid-plastic finite element method for calculation of the final shape and the strain distribution. The optimization scheme adopts a direct differentiation method or a response surface methodology in order to seek for the optimum condition of process parameters. The algorithm developed is applied to design of the draw-bead force and the die shapes in deep drawing processes. Results show that design of process parameters is well performed to increase the amount of strain for increasing the strength or to decrease the amount of strain for preventing fracture by tearing. The present algorithm also enhances the stable optimum solution with small number of iterations for optimization.

Stress-Based Springback Reduction of a Channel Shaped Auto-Body Part With High-Strength Steel Using Response Surface Methodology

In this paper, an optimum design is carried out with finite element analysis to determine process parameters which reduce the amount of springback and improve shape accuracy of a deep drawn product with the channel shape. Without springback simulation usually performed with an implicit solving scheme, the study uses the amount of stress deviation through the sheet thickness direction in the deep drawn product as an indicator of spring-back. The simulation incorporates the explicit elasto-plastic finite element method for calculation of the final shape and the stress deviation of the final product. The optimization method adopts the response surface methodology in order to seek the optimum condition of process parameters such as the blank holding force and the draw-bead force. The present optimization scheme is applied to the design of the variable blank holding force in the U-draw bending process and the application is further extended to the design of draw-bead force in a front side member formed with advanced high-strength steel (AHSS) sheets made of DP600. Results demonstrate that the optimum design of process parameters decreases the stress deviation throughout the thickness of the sheet and reduces the amount of springback of the channel shaped part. The present analysis provides a guideline in the tool design stage for controlling the evolution of springback based on the finite element simulation of complicated parts.

Design modification in a multi-stage rectangular cup drawing process with a large aspect ratio by an elasto-plastic finite element analysis

Abstract Finite element analysis of multi-stage deep drawing processes is carried out for the process design of rectangular cup drawing with a large aspect ratio. The analysis incorporates shell elements for an elasto-plastic finite element method with an explicit time integration scheme using LS-DYNA3D. Simulation is performed for thorough investigation of failures such as tearing and wrinkling during the forming process. The analysis reveals that the difference of the drawing ratio within the cross-section produces non-uniform metal flow to cause wrinkling and severe extension. The irregular contact condition between the blank and the die also induces non-uniform metal flow. This paper identifies such an unfavorable mechanism in rectangular cup drawing and proposes a modification guideline in the design of the process and the tool shape. The analysis result confirms that the modified design not only improves the quality of a deep-drawn product but also reduces the possibility of failure.

Optimum Tool Design in a Multi-stage Rectangular Cup Drawing and Ironing Process with the Large Aspect Ratio by the Finite Element Analysis

Optimum tool design is carried out fur a multi-stage rectangular cup deep-drawing and ironing process with the large aspect ratio. Finite element simulation is carried out to investigate deformation mechanisms with the initial design made by an expert. The analysis considers the deep drawing process with ironing for the thickness control in the cup wall. The analysis reveals that the difference of the drawing ratio within the cross section and the irregular contact condition produce non-uniform metal flow to cause wrinkling and severe extension. For remedy, the modification guideline is proposed in the design of the tool and the process. Analysis results confirm that the modified tool design not only improves the quality of a deep-drawn product but also reduces the possibility of failure. The numerical result shows fair coincidence with the experimental one. After tryouts of the tool shape, the rectangular cup has been produced in the transfer press.

Optimum Design of the Process Parameter in Sheet Metal Forming with Design Sensitivity Analysis using the Direct Differentiation Approach (II) -Optimum Process Design-

Process optimization is carried out to determine process parameters which satisfy the given design requirement and constraint conditions in sheet metal forming processes. Sensitivity -based-approach is utilized for the optimum searching of process parameters in sheet metal forming precesses. The scheme incorporates an elasto-plastic finite element method with shell elements . Sensitivities of state variables are calculated from the direct differentiation of the governing equation for the finite element analysis. The algorithm developed is applied to design of the variablc blank holding force in deep drawing processes. Results show that determination of process parameters is well performed to control the major strain for preventing fracture by tearing or to decrease the amount of springback for improving the shape accuracy. Results demonstrate that design of process parameters with the present approach is applicable to real sheet metal forming processes

Optimum Design of the Process Parameter in Sheet Metal Forming with Design Sensitivity Analysis using the Direct Differentiation Approach (I) -Design Sensitivity Analysis-

Design sensitivity analysis scheme is proposed in an elasto -plastic finite element method with explicit time integration using a direct differentiation method. The direct differentiation is concerned with large deformation, the elasto-plastic constitutive relation, shell elements with reduced integration and the contact scheme. The design sensitivities with respect to the process parameter are calculated with the direct analytical differentiation of the governing equation. The sensitivity results obtained from the present theory are compared with that obtained by the finite difference method in a class of sheet metal forming problems such as hemi-spherical stretching and cylindrical cup deep-drawing. The result shows good agreement with the finite difference method and demonstrates that the preposed sensitivity calculation scheme is a pplicable in the complicated sheet metal forming analysis and design.Ā