Some aspects of cold extrusion of sintered copper preforms

Abstract

In production engineering considerable attention is devoted to energy saving and to the recycling of material in the manufacture of parts. The cold processing of sintered powder-metal preforms is gaining considerable importance on these grounds, whilst the cold extrusion technique appears to be supportive, to a large extent, of this general trend. Cold extrusion is influenced by tool stresses, and the cold processing of P/M preforms by this technique accentuates the effect of tool stresses in terms of unpredictable densification and internal friction. The formability is sensitive to the initial preform densities of the preforms. Cold hooker extrusion of sintered copper powder-metal preforms has been successfully carried out for varying initial preform densities of 7.64, 7.78 and 7.82 g/cc, the theoretical (i.e. solid) density of this material being 8.95 g/cc. Experimentally observed values of maximum force have been compared with values from other sources of information concerning the estimation of forces and appropriate correction factors have been generated to be used as ‘ready reckoners’ where P/M copper hooker extrusion is concerned. The properties — in terms of density, hardness and toughness — have been evaluated for these P/M extrudes and the optimal condition reported. Metallographic examination has also been carried out for analysis of particle distribution and void closure phenomena. Fracture specimens have also been metallographed for identifying the mode of fracture.