The Effects of Die Materials and Electro-Etching on Frictional Characteristics of Automotive Sheet Steels 920635

Circle grid analysis is often used throughout the different stages of stamping tool development to locate and correct critical strains in stampings based on the forming limit diagram of the sheet steel. Understanding the interaction among the grid, tooling, and sheet steel to be formed is important in making a reliable part strain analysis. It has been observed that a given sheet steel may produce acceptable parts in soft tool, yet split or neck in the hard tool/production stage even with similar tooling geometry. Four different automotive sheet steels and five different fixed bead material types were selected for draw bead simulator testing to determine the effect of electro-etching of the grid on frictional characteristics. Of the sheet steels examined - uncoated cold roll, hot dip galvanized, hot dip galvanneal, and electrogalvanized, circle gridding tended to increase the coefficient of friction for all but hot dip galvanneal, where the friction decreased with gridding. Electrogalvanized was the most adversely affected by circle gridding. Kirksite (soft tool) die material generally exhibited lower friction than untreated gray cast iron (hard tool) for all sheet steels tested, both gridded and ungridded, with the exception of electrogalvanized. Treated gray cast iron beads (flame hardened and ion nitrided) tended to produce relatively equal or less friction than untreated gray cast iron for all sheet steels examined (gridded/ungridded) except hot dip galvanneal, which exhibited an increase.