A powder-compaction model and its application to extrusion

The work which is presented here concentrates upon the compaction which takes place within the container in the extrusion of powder materials. By the use of a model-material technique the material flow in compaction is studied. This information is utilized for the proposing of velocity fields which are used as the starting point for an upper-bound analysis. The proposed velocity fields are optimized by minimizing the rate of energy dissipation considering the location of characteristic coordinates defining the upper-bound solution. The compaction is followed incrementally until a coherent material is obtained. The pressure necessary for each incremental step is calculated. The compaction model has been checked by the results of experiments using lead-shot and encapsulated aluminium powder, the densification predicted from the model being found to be in satisfactory agreement with the experimental results. The compaction model is finally linked up with the extrusion process. Thus the pore volume fraction for the material which is located in the extrusion chamber, as influenced by specific process parameters such as reduction, semi-die angle and friction, is derived.