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The risk of skid lines for Class A panels has to be assessed before releasing the die development for hard tooling. Criteria are needed to predict skid lines in the formability evaluation stage to avoid expensive changes to tooling and process for resolving skid line issue in production. In this study, criteria using three different measured parameters were developed and validated. A draw-stretch-draw (DSD) test procedure was developed to generate skid lines on lab samples for the physical evaluation. This was done using tooling with various die entry radii and different draw beads. The skid line severity of lab samples was rated by specialists in the inspection of automotive outer panel surface quality. The skid line rating was correlated with geometric measurements of the lab samples after the DSD test. The sensitivity of the appearance of skid lines to tooling and process parameter variations was identified.

To improve the formability of advanced high strength steels, the interaction between steel sheet, tool material and tool coating was investigated. Square cup drawing experiments were conducted to determine the range of binder forces for forming good cups without wrinkling or splitting. Binder Span of Control (BSC) tests were conducted for DP590, TRIP590, DP780, DP780 EG and DP980 using three uncoated tool steels and two coatings on a standard tool steel substrate. The experimental results indicate that the binder span for forming good cups is sensitive to the choice of tool material and tool coating and the effect of lubricant on formability also varies with tooling material and coating. The obtained binder spans were compared and the best coating plus tool steel combinations for steels of different grades were identified. In addition, roughness of the tooling surface was measured before and after stamping.

The traditional practice of setting up a new forming operation relies on years of experience and expensive die try-outs to gather the information for die design. Today's complete modeling of a 3D sheet metal forming can provide accurate information but is usually too time consuming. Currently, the time and cost effective method used in industries is to model the straight side of a 3D part as a plane strain problem and the corner section as an axisymmetric problem. Unfortunately, the axisymmetric solution often over-predicts the severity of the deformation at the corner and leads to a very conservative design. In an effort to improve the predictability of the simplified 2D model, an axisymmetric model with a center offset is proposed in this study. The proposed center offset is found to be a function of the center strains, failure height, and process parameters, which include tooling geometry, material properties, friction coefficient, and restraining force.