Friction and Lubrication in the Deformation Processing of Metals : 3rd Report, Effect of Grain-Size of Material on Lubrication

Abstract

By deep-drawing sheet metals of aluminium which have various grain-sizs, the friction occurring in the flange part is measured under different lubricating conditions. It is found that the material with a larger grain-size has a higher coefficient of friction, and this phenomenon becomes noticeable at high tool pressure. As to the surface texture, the roughness of deformed material increases with grain size. The high coefficient of friction observable in a large grain size seems to originate in the fact that, on account of the relatively large space occupied by the surface pits, a lubricant previously applied on the metal blank becomes insufficient to fill up that pit-space, and so can not be squeezed and pressurized. It has been concluded that the difference in the lubricating conditions according to the grain-size is attributable to the hydro-static pressure generated in those trapped lubricants.