Attempts to facilitate low volume production of soft aluminium cups with large drawing ratios by deep drawing based on Maslennikov's technique

Abstract

When producing cylindrical cups by conventional deep drawing with metal tools, the maximum first-stage drawing ratio seldom exceeds 2.2. For a larger drawing ratio, therefore, re-drawing in one or more stages is necessary. Since a punch and die are required for each stage, tooling costs increase relatively as the total drawing ratio increases and as the number of products decreases. Two methods, based on Maslennikov's process, are investigated to facilitate low volume production of cylindrical cups with very large drawing ratios. Firstly, a conventional direct re-drawing is carried out as a subsequent operation to increase the total drawing ratio and to correct the shape and dimensions of cups produced by Maslennikov's process. Secondly, a modified form of Maslennikov's process employing a metal punch is examined and the additional effects resulting from the introduction of the punch are discussed. When these methods are applied to soft aluminium sheets of 1 mm thickness, a fully-drawn cup with an extremely large drawing ratio can be produced using only one metal punch and one or two dies throughout the drawing process. The process does not seem to be too slow for the production of cups with drawing ratios of less than about 6. The shape, dimensional accuracy and surface finish of the cups produced are also adequate for practical use.