A comparison of correlations between press performance and dome tests results using two dome test procedures

Two dome test procedures were compared by seeking correlation of the test results with press performance in a small hood outer panel tool set. The first procedure involves selecting the sample width in the dome test so that the critical minor strains in the panel and the dome test are matched. In the second procedure the dome test sample width which yields the minimum dome height is used, and that height is taken as a general measure of near-plane strain stretchability. The minihood tools were “tuned” by adjusting blank shape, blank holder load, tool radii, etc., so that a slight neck consistently occurred when a “typical” lot of 6010-T4 aluminum auto body sheet (ABS) was formed. The tools were then used to rate 24 lots of 6010-T4 as “good” or “bad.” The correlation between the dome test results and press performance was slightly better for the second procedure (minimum dome height), because lot-to-variability in the critical minor strains in the panel and the dome test caused the match to be less than perfect for the other procedure. It was concluded that the minimum point procedure is a viable test method, which is highly attractive because it does not require gridding.In addition, the effects of punch speed and lubrication on dome test results were studied. Punch speed was found to have no effect on dry test results using the minimum point procedure. Punch speed did affect lubricated test results, and different alloys were found to respond to changes in punch speed differently.