In powder forming processes, the analysis of detailed mechanism of densification in the powder forming processes is crucial in planning of forming process and designing of equipment and die set necessary to produce full densification products. In this paper, cold forward extrusion of sintered pure iron and copper P/M cylindrical billets was experimented. In order to examine the densification during extrusion, the semicone die angles of 6.4˚, 8.7˚, 10.4˚ and 12.8˚ and the length of die land of 3㎜, 5㎜, and 8㎜ were used. The initial relative densities used in experiments were 0.6 and 0.7 and 0.8 for sintered pure iron and copper P/M cylindrical billets. For lubrication between die and billet, $MoS_2$, grease and teflon tape was used. The Vickers and Rockwell hardness testers were used for measurement of local hardness distributions and volume calculation method was employed to numerically determine local relative density distributions. It was found out Vickers hardness data was more reliable compared to Rockwell hardness data. The correlation between the calculated relative density and hardness distributions was not high for the present experimental data. The extrusion load increased as the semicone die angle increased. However, the densification level was almost the same when the semicone die angle was larger than 8.7˚. It was also found out the optimum semicone die angle was 8.7˚. In addition, microstructure was examined for the extruded billet.
According to the experimental results, the sintered iron and copper P/M cylindrical billets with the initial relative density of 0.7 were fractured in case of die land length of 3㎜. By changing the die land length to 5㎜, a sound extruded billet was obtained for the iron billet. For copper billet, the die land length of 8mm should be used in order to obtain a sound extruded billet. Thus, it was concluded that the length of die land in cold forward extrusion was critical in extruding sintered pure iron and copper P/M billets under the present experimental conditions.
