Quantitative Evaluation of Tool Wear in Cold Stamping of Ultra-High-Strength Steel Sheets

The body of an automobile must be lightweight and crash-worthy. The use of advanced high-strength steel reduces the manufacturing cost for automobile body and improves energy absorption during an impact. However, increasing the strength of the steel sheet results in a variety of issues related to tool wear due to a higher forming pressure in the sheets than that in the conventional low-strength steel sheets. Therefore, systematic wear experimentation and evaluation procedure are required to quantify the extent of tool wear during the press forming process. This study aims to develop a methodology for quantifying the wear of a sheet metal forming tool using experimental databases. A progressive die set is designed to conduct the wear test systematically, saving both time and money. The testing machine is capable of testing four different types of punches simultaneously under a variety of tooling and process parameters, such as different tool materials, punch shapes, and coating conditions. The wear depth, roughness, and surface imaging of the tool are all used to establish quantitative evaluation methods for tool wear in the sheet metal forming process. Consequently, we found that punches with small radius of curvature wear rapidly, while tools and coatings with a high hardness have high resistance against wearing. Additionally, by referring to the measured wear database, it is confirmed that analyzing the reasonable tool wear characteristics is appropriate. The proposed testing method can be used to obtain reliable results for quantitatively and qualitatively evaluating the wear lifetime of various tool materials.