The Behaviour of Low Alloy Steel Powder during Uniaxial Cold Compaction – Influence of the Geometry

Abstract

This work investigates the influence of geometry on the behaviour of a commercial diffusion bonded low alloy steel powder (added by 0.65% graphite and 0.6% lubricant) during uniaxial cold compaction. Cylindrical specimens and ring-shaped specimens were produced, characterized by different geometrical parameters. The whole analysis has been performed using experimental data, the forces and displacements continuously recorded by an industrial press without any additional device, aiming at obtaining results representing the actual conditions in the production of real parts. The stress field acting on the powder column was derived from the recorded data, obtained from two different compaction strategies. By single action cold compaction experiments the parameters characteristics of the powder mix were derived, such as the radial stress transmission coefficient, the flow stress, the friction coefficient with the die walls, and the friction coefficient with the core in case of rings. These results were used investigating the powder behaviour during double action cold compaction, which represents the most common compaction strategy. Densification curves were derived from this analysis, reporting the relative density as a function of both the applied and the mean axial stress. The influence of the geometry on the densification was highlighted and discussed.