Edge Stretch Performance of 6DR1 Aluminum in Typical Automotive Blanking Conditions

Abstract

This work investigates the edge stretch response of 6DR1 aluminum sheet trimmed at various conditions typical in blanking die operation. Three investigatory trimming parameters were studied in the experiment: upper trim edge shape, galling depth, and gap distance in the lower trim tool. Additionally, three other trimming parameters were included in various combinations to each of the investigatory parameters studied: clearance, sample orientation with respect to the rolling direction, and offal support. A sharp lower trim tool edge was maintained for all trimming conditions, as well as blanking die trimming standards of 90° trim angle and no shear angle were strictly adhered to. Electro discharge machined (EDM) custom tensile test specimens, referred to as half-dog bone specimens, were trimmed in a laboratory trimming die with various settings and edge-stretch was measured by total elongation of the trimmed specimens in a tensile test. A regression analysis was performed to determine statistically significant trimming parameters. Optimal trimming conditions were identified by fitting a range of levels for each trimming parameter that maximized elongation to a probability distribution, which provided feasibility from an engineering perspective. Statistical metrics, namely the mean and standard deviation of the distribution, were utilized to identify a robust lower limit expectation of elongation response with optimal trimming conditions. Clearance between upper and lower trim tools had the most significant influence on elongation: as clearance increased, elongation response decreased. Optimal clearance was defined as equal to or less than 30%. As upper trim tool radius increased, elongation response decreased. Optimal radius was defined as equal to or less than 0.14 mm. Galling had a significant reduction effect on elongation, where gall marks with increased penetration depth and length exhibited larger reductions in edge stretch response. Optimal gall depth was defined as equal to or less than 50 𝜇𝑚. Gap distance in the lower trim tool had no statistically significant effect on edge stretch. Measured elongations for optimal trimming conditions followed a left-skewed Weibull distribution with greater statistical probability of low elongation to failure than that predicted with a normal distribution.