Powder Flow During Dynamic and Quasistatic Compaction

Abstract

An experimental study has been made of the flow of metal powders in an axisymmetric die incorporating a shoulder marking an abrupt reduction of diameter in the direction of compaction. A comparison has been made between powder flow in quasistatic and dynamic (shock wave) compaction when both methods produce a compact of the same average density. With the commercial grades of aluminium, iron, and copper powders studied, higher peak pressures were necessary during dynamic compaction to produce compacts with the same average density as those made quasistatically. Measurements of powder displacement and hardness distribution showed that compacts made using the dynamic compaction had a more uniform density distribution and were appreciably denser and harder near the die walls below the shoulder. With common levels of admixed lubricant, all the powders flowed smoothly around the shoulder during quasistatic compaction. For the more ductile aluminium this was also true for dynamic compaction. However, with the powders that more strongly work hardened, closed shear surfaces were formed near the shoulder when compacted dynamically. PM/0444