FACTORS AFFECTING THE RADIAL AND AXIAL SHRINKAGE IN SOFT-METAL POWDER COMPACTS

Abstract

The variables affecting the radial: axial (R/A) shrinkage ratio in copper-powder compacts have been investigated. The value of R/A is linearly dependent on compacting pressure, green density, and sintering temperature, and also increases with decrease in the particle size of the powder. The observed variation of R/A is attributed to the differences in density in the green compacts, which result in anisotropic stresses in sintering. Surface-tension forces or residual stresses introduced during compaction cannot alone be regarded as the main driving forces responsible for shrinkage; anisotropic stresses also play an important role in the densification of metal-powder compacts. By proper control of these variables, parts can be produced from the compacts to close dimensional tolerances.