Characterization of Trimmed Edge of Advanced High Strength Steel

In recent years, implementation of dual phase (DP) Advanced High Strength Steels (AHSS) and Ultra High Strength Steels (UHSS) is increasing in automotive components due to their superior structural performance and vehicle weight reduction capabilities. However, these materials are often sensitive to trimmed edge cracking if stretching along sheared edge occurs in such processes as stretch flanging. Tool wear is another major issue in the trimming of UHSS because of higher contact pressures at the interface between cutting tools and sheet metal blank caused by UHSS’s higher flow stresses and the presence of a hard martensitic in the microstructure. The objective of the present paper is to study the influence of trimming conditions and tool wear on quality of trimmed edge of DP980 steel sheet. For this purpose, mechanically trimmed edges were characterized for DP980 steel, sheared with six different cutting clearances (from 4% to 40% of the sheet thickness). In addition, the burr height for DP980 has been compared to two other sheet materials including IF and HSLA350. It has been shown that the burr height increases with the growth of the clearance between the upper and lower trimming tools for all materials. Almost no measurable burr occurs at a trimming clearance below 17% for DP980, but increasing the clearance above this threshold often leads to burr height growth. Presented results will be also compared with the measurements of burnished area depth. It also gives an indication of the condition of the trimming tool which will be illustrated by comparison of burnished areas of the samples trimmed with the new trimming tool and with the tool which has already performed 35,000 cuts.