First Paper: Extrusion of Aluminium and Copper

Abstract

This paper describes the results of cold backward extrusion tests on aluminium and copper specimens, using test rigs in which impact velocities up to 300 ft/s could be obtained. The maximum energy available was 10 000 ft lbf, but for the work described here, 6000 ft lbf were adequate for the extrusion of billets of 1-in diameter, 1.5-in long. Comparison was made with extrusion at very low speed, and the effect of impact velocity on extrusion pressure and mean work of deformation assessed. For aluminium, reductions of area of between 44 and 86 per cent were examined. Surprisingly little variation in deformation energy over the speed range was noted, but the optimum impact speed appeared to be in the region of 50-80 ft/s. In the case of copper, where impact speeds up to 240 ft/s were investigated, the optimum impact velocity was about 60 ft/s. A limited series of tests in combined forward and backward extrusion was also carried out in both materials. It was found that both reduction in area and impact velocity had a marked effect on the relative proportions of metal extruded in the two directions. Mention is also made of metallurgical examination into the effect of high-speed working on the properties of extruded metals.