Effect of Workpiece Material and Reduction in Thickness on Friction Coefficient in Strip Drawing.

Abstract

In view of the fact that lubrication in metal forming processes often differs from one workpiece material to another with other conditions being the same, experiments on strip drawing are carried out with mild steel, commercially pure copper and commercially pure aluminum as workpiece materials and a paraffinic oil as a lubricant. Theoretical analysis is also carried out by taking account of heat generation due to friction at the tool-workpiece interface. Since this analysis includes not only the yield stress but also the heat conductivity of the workpiece material, the effect of the workpiece material on temperature rise and hence on the friction coefficient can be calculated. It is thus shown, both experimentally and theoretically, that the friction coefficient for aluminum is smaller than that for both mild steel and copper. This is due to the fact that the yield stress is smaller and the heat conductivity is larger for the former than for the latter two. It is also shown that the friction coefficient increases with increasing thickness reduction, while it appears to decrease when the surface roughness of the workpiece is larger.