The Effects of Zinc Coatings, Die Materials and Lubricants on Sheet Metal Formability

The results of a program Co evaluate lubricity test methods and different lubricant-tool-material combinations are described. This effort was specifically directed towards understanding soft and hard tool interactions and identifying the causes contributing to the discrepancies that exist between soft and hard tool trials on bare and zinc coated sheet steels. Both the LDH and drawbead simulation tests were evaluated, and it was concluded that either test can be used to adequately identify main effects and the Important lubricant-tool-sheet material interactions. However, the drawbead test was judged to be slightly superior because of its sensitivity to speed effects. More importantly, these results indicate that only for bare steels will the soft tool trials adequately predict hard tool performance. Zinc coated steels, with their more variable surface topographies, will give more unpredictable results because of the strong lubrleant-tool-material and speed-lubricant-tool interactions. Galvannealed steel was shown to exhibit an exceptionally strong interaction with soft tooling at low speeds. Because of these interactions, lubricants for soft tool trials on zinc coated steels must be carefully chosen to produce results equivalent to those obtained on hard tools.