Evaluating die wear-induced edge quality degradation in trimmed DP980 steel sheets from in situ force response monitoring

Abstract

Assessing trimmed part quality involves periodic examinations of cut edges and shear affected zones to characterize rollover, burnish, fracture and burr formation. Established techniques are thorough and reliable but inherently time consuming. This study correlated die wear-induced force response evolutions and the observed transitions between shear-induced deformation zones for DP980 (C-0.15 wt%Mn-1.5 wt%Si-0.31 wt%) steel sheets subjected to trimming with AISI D2 steel dies. The findings are useful for peripheral assessment of part quality and tool wear via in situ trimming force/displacement response monitoring. Measurements were collected from a load cell and a non-contact laser displacement transducer embedded within the instrumented trimming press. The sliding wear damage and failure processes induced by die–workpiece interactions were correlated to force/displacement response phases. Trimming tests were conducted for 20,000 cycles to observe and assess transformations between rollover and burnish zones with increasing tool wear after the initial contact and at every subsequent 5000 cycle interval. The mean trimming force and maximum die penetration increased, primarily due to die edge blunting, by 1.33 kN (44.3%) and 194 μm (32.2%), respectively. An enlarged die–workpiece contact area increased the resistance force and delayed the onset of fracture with increased sliding damage between sheared surfaces and nearly doubled burnish zone depths. Quantitative attributes of the trimming force/displacement responses were linked to die impact and sliding contact induced damage features of trimmed parts, demonstrating the potential for straightforward, rapid and detailed in-field monitoring of acceptable limits to sheared edge quality.