Analysis of Consolidation During Powder Forging

Abstract

PM preform material is regarded as two-phase, consisting of a mixture of matrix metal and pores. During the upsetting stage of the powder-forging process, the metallic portion deforms in accordance with the ideal plastic Poisson's ratio (ν=0·5) while previously published experimental observations suggest that the porosity diminishes at a decreasing rate. This gives rise to the assumption that the total volume of the porosity decreases exponentially in the longitudinal direction for corresponding increases in radial strain, which leads to the concept of a ‘coefficient of consolidation’ C. The actual value of this coefficient varies between 0 and 0·5 depending upon the initial preform density, mode of deformation, and prevailing frictional conditions. Compatibility equations are derived which take into account the combined effects of ν and C and the relative proportions of solid metal to porosity. These equations are combined to provide a general equation connecting apparent plastic Poisson's ratio and relative density. Experimental results are obtained which confirm the existence of a coefficient of consolidation and also provide a measure of various values for C for frictionless and unlubricated axisymmetric upsetting over two distinct density ranges. PM/0114