Richman, Mark Wayne
Powder metallurgy is a manufacturing process in which metal powder is compacted, ejected from its die, and sintered to form a part. During the compaction process the powder and die expand radially outward. After compaction, the system elastically recovers which results in the die radially compressing the compact. Due to these residual forces, a substantial pressure is required to eject the compact. This paper considers a system with a central core rod in addition to the die wall for producing bushing-like parts. In a balanced die, an external radial pressure is applied to the outer surface of the die wall during compaction. The purpose of this external pressure is to reduce: the elastic deformation of the die wall and core rod during compaction, the resulting elastic recovery after the compacting load is removed, and the frictional forces that that must be overcome to remove the slightly oversized compact from the die. In principal, the ejection forces required by a balanced die should be less than those required by an unbalanced die. Previous work has shown that a balancing force applied to the outer die wall does reduce ejection pressure, but mathematical models up to this point have only considered uniform external pressure distributions. Due to the frictional forces developed during compaction, the compaction pressure distribution and resulting elastic deformation and recovery of the system are non-uniform. The goal of this project is to extend previous work to determine if certain axial variations in the external pressure may actually decrease the ejection forces without increasing the total compressive load applied to the die.
Worcester Polytechnic Institute
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