Finite element analysis and experimental study of metal powder compaction

Abstract

In metal powder compaction, density non-uniformity due to friction can be a source of flaws. Currently in industry, uniform density distribution is achieved by the optimization of punch motions through trial and error. This method is both costly and time consuming. Over the last decade, the finite element (FE) method has received significant attention as an alternative to the trial and error method; however, there is still lack of an accurate and robust material model for the simulation of metal powder compaction. In this study, Cam-clay and Drucker-Prager cap (DPC) material models were implemented into the commercial FE software ABAQUS/Explicit using the user-subroutine VUMAT. The Cam-clay model was shown to be appropriate for simple geometries. The DPC model is a pressure-dependent, non-smooth, multi-yield surface material model with a high curvature in the cap yield surface. This high curvature tends to result in instability issues; a sub-increment technique was implemented to address this instability problem. The DPC model also shows instability problems at the intersection of the yield surfaces; this problem was solved using the corner region in DPC material models for soils. The computational efficiency of the DPC material model was improved using a novel technique to solve the constitutive equations. In a case study it was shown that the numerical technique leads to a 30% decrease in computational cost, while degrading the accuracy of the analysis by only 0.4%. The forward Euler method was shown to be accurate in the integration of the constitutive equations using an error control scheme. Experimental tests were conducted where cylindrical-shaped parts were compacted from Distaloy AE iron based powder to a final density of 7.0 g/cm3. To measure local density, metallography and image processing was used. The FE results were compared to experimental results and it was shown that the FE analysis predicted local relative density within 2% of the actual experimental density.