A study of material grade changes of automotive rear body floors for cost reduction using finite element analysis

Abstract

This research work constitutes a part of a project on Finite Element Analysis (FEA) due to the influence of material grade changes in sheet metal forming. First, the forming process simulation and springback prediction of an automotive rear body floor were implemented by using JSTAMP/LS-DYNA. Springback is a common problem in the sheet metal stamping process. To solve this problem, the cushion pressure in the process was adjusted and optimized to correct the springback in the drawing process. The simulation of the entire forming process included: Drawing 1, Drawing 2 and Trimming-Piercing- Stamping with a quality rate of the check points of 80% in terms of surface springback, trim line and bead dimension. The simulation results effectively reduced the die tryout time and greatly improved the quality of the part. Second, a rigidity and strength testing simulation was implemented by using NX. Finally, the quality of the stamping parts was inspected by checking fixture (C/F) and Coordinate Measuring Machine (CMM) after die tryout. The inspection results demonstrated that 75 of 94 measuring points could satisfy the tolerances, thus indicating that the quality rate of the part could reach 80% and could be adopted in the production line. The experimental results agreed with the simulation results well. Moreover, the new material grade is cheaper than the current material grade by 2.5 baht per kilogram. According to the part weight of 13.6 kg, the cost can be reduced by 34 baht per piece or approximately 221,000 baht per month. Therefore, we can save the cost of material production around 2.65 million baht per year.