Kostiv, O., Behdinan, K., and Hashemi, S., "Finite Element Analysis of Friction-Assisted Powder Compaction Process," SAE Int. J. Mater. Manf. 5(2):333-344, 2012, doi:10.4271/2012-01-0051.
The major disadvantage of powder metallurgy (PM) is the density gradient throughout the green powder compacts. During the compaction process, due to the existence of friction at powder-tool interfaces, the contact surfaces experience a non-uniform stress distribution having to do with variable friction coefficient and tool kinematics, consequently resulting in density gradient throughout the powder compacts. This represents a serious problem in terms of the reliability and performance of a final product, as the density gradient may contribute to a crack-defect generation during the compaction cycle, and more importantly a non-uniform compact shrinkage during the sintering process. Simulation analyses were conducted using the finite element software, MSC.Marc Mentat, and Shima and Oyane powder constitutive model, to study and suppress the causes of density gradient in the cylindrically shaped green powder compacts. A newly proposed friction-assisted compaction technique was employed, consisting of a moving upper-punch and a die, which uses friction force at the powder-die interface to assist in the compaction of powder. Numerical results are presented and compared with the literature and experimental tests. The simulation analyses had shown that the overall heterogeneity of the corresponding green powder compacts may be considerably reduced by using the proposed friction-assisted compaction technique.