Effects of Surface Roughness of Workpiece on Friction Behavior in Metal Forming

A series of experiments have been conducted using a rolling-type tribometer to investigate the effects on friction behavior of the average velocity of the lubricant at the inlet to the contact zone V and the relative sliding velocity ΔV during deformation. Experiments using mild steel strips with various kinds of surface texture for various lubricants showed that the variation in the friction coefficient with V and ΔV is largely dependent on the initial surface texture of the workpiece. With increasing V, the friction coefficient decreases for the smooth surface workpiece, but increases for the rough surface workpiece. With increasing ΔV, the friction coefficient remains constant under small V and decreases at large V for the smooth surface workpiece but decreases at all times for the rough surface workpiece. Observation of the rolled surface suggested that friction was determined by the performance of the lubricant film. With increasing V, the surface is roughened for the smooth surface workpiece and oilpits largely remained for the rough surface workpiece. With increasing ΔV, the rolled surface became smooth for the rough surface workpiece.