Evaluation of friction conditions in powder compaction for admixed and die wall lubrication

For the purpose of modelling powder compaction, a quantitative evaluation of the friction conditions at the die wall interface is required. Using an instrumented compaction die, the friction at the interface between powder compact and die wall was evaluated through an empirical parameter called the slide coefficient, obtained from the applied pressure/transmitted pressure ratio. For powder compaction modelling, knowledge of the friction coefficient at the interface, however, is much more useful but its measurement is difficult in real experimental conditions. A procedure based on the evaluation of the radial stress/axial stress ratio leads to the quantitative determination of the friction coefficient in admixed zinc stearate added to iron powder with and without die wall lubrication. The resulting decreasing friction coefficient at the end of compaction gives amore uniform density characterised by low loss of pressure through the compact and lower ejection energy per unit volume of the compact.