Friction and Lubrication in the Deformation Processing of Metals : 1st Report, Quantitative Assessment of the Surface Texture of Materials being deformed under Rigid Tool

Abstract

Utilizing the plastic deformation occurring in the flange part of semi-formed cups of aluminium being drawn into the die, the authors investigated the mechanism of lubrication in metal forming processes. A model of lubrication is proposed, at first, on the basis of the observation of the surface. By means of a light reflectivity method, percentage of the surface areas occupied by the micro-plateaus (which were depressed and flattened by rigid and smooth tool surface) of the asperities on the deforming flange is estimated. The percentage varies according to the hold down pressure and the included lubricant. It is ascertained that the areas of the micro-plateaus being virtually in contact with the tool surface are responsible for the frictional resistance of the flange part. Then the mean hydrostatic pressure self-generated in the lubricant trapped in the pits of the surface is estimated, and the frictional shearing stresses acting on the plateaus are found.