STRESS DISTRIBUTION AND DENSIFICATION IN UNIAXIAL COLD COMPACTION – FROM EXPERIMENTS TO MECHANICS RELATIONSHIPS

In previous works a preliminary analytical model describing the reversible and irreversible deformations of the powder column during uniaxial cold compaction was developed using experimental data. Densification curves were derived, density was reported as a function of the pressure applied by the upper punch.This work aims at investigating in depth the distribution of axial and radial stresses, again from experimental data, relating the force applied to the die to the frictional force at the die surface. Single action experiments are performed, both using only upper punch compression, and using only lower punch compression. The friction coefficient between the powder column and the die wall, the radial stress transmission coefficient and the dependence of the flow stress of the material on density are determined. The results are used to process the data obtained by double action experiments. Densification curves are obtained, where density is reported as a function of the whole stress field acting on the powder column.