Sintered powder metal forming is one of the near net shape manufacturing processes, which is the manufacturing technology for high strength machine parts. The research and developement for sintered powder metal forming process have led to the enhancement of material of sintered powder metals with excellent alloy elements. Among sintered powder metal forming processes, the extrusion process is employed for production of superalloy barstock since it involves an effective densification mechanism with more volume deformation and shear deformation. In the present work the deformation characteristics in forward extrusion of sintered powder metal are analyzed, and calibration curve is proposed for sintered powder metal extrusion processes. The necessary informations are then obtained for the die making so that high strength machine parts can be developed from the extrusion process of sintered powder metal. A method of approach is developed for determination of process parameters for extrusion analysis of sintered powder metal. The present work is presented as in the following stages:
1) The existence of voids leads to volume change. The established wellknown plasticity equations for sintered powder metal are composed among then and they are represented in the uniform. And then the rigid-plastic finite element formulation is introduced considering the compressibility of the material.
2) A new experimental method is proposed for the determination of relative density of sintered powder metal. Using the curve generation technique for the measured data of a grid marking specimen, the density distribution is obtained in the systematic way. The experimental density distribution is then compared with the simulation.
3) In order to clarify the effect of various parameters in the extrusion process, extrusion experiments for copper powder metal specimens are carried out for various reductions of area with two kinds of die shape, that is; curved dies and conical dies of axial symmetry. The extrusion process is also simulated by the rigid-plastic finite element method. In order to consider the compressibility of powder metal effectively calibration curves are suggested for the proper determination of compressibility parameter. Analysis and experiment are carried out for axisymmetric tube extrusion and the calibration curve is used in the analysis for the verification of the proposed scheme.
4) From the calibration curve obtained in the axisymmetric analysis, three-dimensional extrusion of sintered powder metal through curved dies is analyzed for different area reductions. The computed deformed pattern shape compared with the experimental results. The distribution of relative density, mean stress and effective strain through curved extrusion dies of the elliptic, clover and trochoide gear sections are studied.
From the present investigation, sintered powder metal products with high density can be obtained by the extrusion process through curved dies with reduction of area over 60%. The effectiveness of the proposed method of solution has been verified through the comparison between theory and experiment.
