Lubrication Effects on Automotive Steel Friction between Bending under Tension and Draw Bead Test

Zinc-based electrogalvanized (EG) and hot-dip galvanized (HDGI) coatings have been widely used in automotive body-in-white components for corrosion protection. The formability of zinc coated sheet steels depends on the properties of the sheet and the interactions at the interface between the sheet and the tooling. The frictional behavior of zinc coated sheet steels is influenced by the interfacial conditions present during the forming operation. Friction behavior has also been found to deviate from test method to test method. In this study, various lubrication conditions were applied to both bending under tension (BUT) test and a draw bead simulator (DBS) test for friction evaluations. Two different zinc coated steels; electrogalvanized (EG) and hot-dip galvanized (HDGI) were included in the study. In addition to the coated steels, a non-coated cold roll steel was also included for comparison purpose. The results revealed that the non-coated cold roll steel has the highest friction coefficient, and the HDGI has the lowest among test steels. Extra lubricant tends to increase the friction coefficient for the GI steel, and similar trend was also found for EG in the draw bead test. Well, there is a transition point found for each test steel where the friction behavior tends to be stabilized after the lubricant amount reaching the transition point. Bend under tension test tends to deliver a slightly lower friction than the draw bead test which is associated with higher surface coating deformation.