On the mechanism behind the punch-blank surface conformation in stretch-forming and deep-drawing

Abstract

In industrial sheet-metal forming operations such as deep-drawing and stretching, friction and evolution of surface texture are very important factors, especially to secure optimum forming depth and acceptable surface finish, and to prevent defects in the final products. The punch profile region experiences a severe tribological condition as the blank elements are subjected to sub-surface plastic flow and moderate-to-high tool-contact-pressure at extremely low relative sliding speeds. In the present paper a brief literature survey is presented concerning the surface interaction and friction between a workpiece experiencing bulk plastic flow and a polished, rigid tool. A friction measuring apparatus is described which could be used to investigate various tribological relationships pertaining to the sliding friction characteristics of the tool—workpiece interface. Results of a series of sliding friction tests, surface profile traces and their digital analyses and micro-hardness surveys are discussed and, based on these, an attempt has been made to understand the mechanism leading to the high tool—blank conformation at the punch profile in stretch-forming and deep-drawing operations.