AN INVESTIGATION OF POWDER COMPACTION PROCESSES

A programme on the uniaxial compaction of iron, bronze, ceramic and ca rbon powders is described. The work focuses on the compaction mechanis m of a simple bushing part during which a complete force balance was r ecorded and the results show the progressive increase in force as comp action proceeds. The evidence indicates that for the iron, bronze and carbon powder there is a particle rearrangement phase which occupies a pproximately 30% of the compaction stroke for the iron and bronze powd er and 45% for the carbon powder: The ceramic powder undergoes elastic deformation early on in the compaction process with plastic deformati on initiated at about 50% of the compaction stroke. Friction between t he powder and fooling was derived using both elastic and plastic model s. The former yielded a constant coefficient of about 0.10 for the iro n and bronze powders while a value of 0.35 was deduced for the ceramic and carbon powders. Using a plastic model, the wail friction was foun d to vary with compact density from a high value initially, falling to a value close to that derived from the elastic model at higher densit y levels, possibly due to plastic deformation of powder particles at t he fooling surface early in compaction. A large displacement finite el ement model employing a Mohr-Coulomb material model was tested against the experimental data and gave good agreement with both fool stresses and compact density levels. A dynamic friction model was also incorpo rated and found to have a significant effect on both stress and densit y gradients. The latter confirms the need for accurate determination o f the friction coefficient and ifs variation with powder density at th e fooling surface.