Evolution of die surfaces during repeated stretch-bend sheet steel deformation

The friction and wear characteristics of several die materials used for sheet metal forming have been investigated. The study examines five die materials tested in conjunction with three commercially produced automotive sheet steels. The die materials were: A2 tool steel, weld overlay, tungsten carbide, physical vapor deposited titanium nitride and transformation toughened zirconia. The three steels were: a low carbon uncoated aluminum killed drawing quality (AKDQ) sheet, a zinc-coated galvannealed sheet and a hot dip galvanized sheet. Each die material was tested using a repeated stretch-bend deformation with each steel sheet in order to examine the initial stages of die wear. The changes in the die surface profile were examined after approximately 140 tests and compared to the profile before testing. The tungsten carbide die material exhibited the least amount of change. Even though it was the smoothest before testing, the zirconia die material showed the most significant change, especially when tested with the two zinc-coated sheet steels.