Force and energy during the cold hooker extrusion of sintered iron preforms

Abstract

The advantages gained by the forging of a powder metallurgical preform are well known. Cold extrusion of a P/M preform combines the advantages inherent in the cold extrusion process with the forging of a preform, but for successful deformation of a P/M preform, the inherent brittleness has to be overcome. In this paper various cold extrusion methods are examined, based on the state of stress, from which the Hooker extrusion process is chosen as the deformation method due to its favourable (compressive) state of stress. The paper then goes on to deal with the experimental tooling evolved for the Hooker extrusion of sintered iron preforms. Compacts made under different compacting pressures (loads) and therefore of different preform densities have been Hooker extruded at different extrusion ratios. The forces and energies have been evaluated and the results compared with values calculated for the equivalent wrought steel. An empirical relationship has been obtained for the estimation of force during the Hooker extrusion of iron preforms, making use of force equations for the cold Hooker extrusion of wrought steel.