An experimental study on densification of sintered iron P/M cylindrical billets in forward extrusion

Abstract

In this paper, an experimental study into the cold forward extrusion of sintered pure iron powder metallurgy (P/M) cylindrical billets in order to examine densification during extrusion, is reported. Semi-cone die angles of 6.4, 8.7, 10.4 and 12.8°, and lengths of die land of 3 and 5 mm were used. The initial relative densities used in the experiments were 0.6 and 0.7. A mixture of MoS 2 and calcium grease was used for die-billet lubrication. Vickers and Rockwell hardness testers were used for the measurement of local hardness distributions and the volume calculation method was employed to determine local relative density distributions numerically. It was found that Vickers hardness data were more reliable than Rockwell hardness data. The correlation between the calculated relative density and measured hardness distributions was linear for the present experimental results. The relatively optimum semi-cone die angle for densification was found to be 8.7° for the present investigations. According to the experimental results, the sintered iron P/M dylindrical billets with the initial relative density of 0.7 were fractured in the case of the length of die land of 3 mm, but by changing the length of the die land to 5 mm, a sound extruded billet wasobtained. Thus, it was construed that the length of the die land in cold forward extrusion is important in extruding sintered pure iron P/M cylindrical billets without causing their fracture.