Three novel techniques for forming hemispherical cups with flexible tooling

Abstract

In recent years the friction-actuated blank-holding technique has been developed for drawing cylindrical, hemispherical and conical cups. Three distinct variations of this technique have been developed for drawing hemispherical cups. The first technique uses a hemispherical steel punch as in the conventional drawing of cups, in the second technique a cylindrical urethane pad together with a female die of hemispherical shape is used, whilst in the third method an annular urethane pad and a shaped steel punch are used. In the latter technique the steel punch does not touch the sheet metal, but guides the urethane to deform the blank, taking advantage of drawing action by friction. Tooling for these methods was designed and constructed, and experiments into the drawing of hemispherical cups conducted with it. Experimental results include the draw force-stroke characteristics of these drawing techniques, and the variation of the strains in the cup wall. Interrupted drawing tests were conducted also to determine the modes of deformation with these techniques. The principles involved in the techniques, the tooling, the theoretical and the experimental findings, and the advantages of the techniques are discussed and compared in the paper.