An Investigation For Optimal Tool Kinematics In Powder Compaction Cycle To Minimize Density Gradient In Green Powder Compacts

The major disadvantage of powder metallurgy (PM) is the density variation throughout the powder compact. During the compaction process, due to the existence of friction at powdertool interfaces, the contact surfaces experience a non-uniform stress distribution having to do with a variable friction coefficient and tool kinematics, consequently resulting in density gradient throughout the green powder compact. This represents a serious problem in terms of reliability and performance as it may contribute to a crack-defect generation during the compaction and ejection cycle, and more importantly a non-uniform powder compact shrinkage during the sintering process. The geometrical distortion caused by non-uniform shrinkage may require secondary operations, thus, compromising the competiveness of PM technology. Simulation analyses, consisting of two parts, were conducted to study and suppress the causes of density variation. First, simulation analyses were conducted using a newly proposed friction-assisted compaction technique for compaction of cylindrical parts. Second study extended to a more complex geometry, consisting of a multi-stepped part, which indirectly used friction-assisted compaction by varying the tool kinematics of the press system. The overall focus of both studies was to establish optimal tool kinematics in powder compaction cycle to minimize density gradient in both cylindrical and multi-stepped green powder compacts. Consequently, optimal tool kinematics were determined producing the least variation in density throughout the corresponding powder compacts.