Development of Shrinkage-Fit Die Coated with Film Possessing Low Friction Coefficient for Compacting Metal Powders

摘要

A surface-coated die that can reduce the ejection force needed to obtain green compact has been developed to produce powder metallurgical parts constantly without the occurrence of scuffing or cracking. A plasma CVD (Chemical Vapor Deposition) method, which is able to be performed at temperatures below 823K, was applied to shrinkage-fit dies. Optimal conditions for the surface-finishing treatment of the die and die holder were examined. For a shrinkage-fit die composed of a die holder made of a steel tempered at a temperature equal to or higher than the PCVD treatment temperature, there was little effect of the PCVD treatment on the shrink-fitting force and the hardness of the die holder. However when a die holder made of a steel tempered at 453K was used for the shrinkage-fit die, the shrink-fitting force was increased and the hardness of the die holder was decreased by the PCVD treatment. Taking these results into consideration, a surface-coated die having an optimal combination of the die and die holder materials was devised and its performance was evaluated. The ejection force exhibited by the surface-coated dies decreased in the following order: non-coated die>TiN>TiCN>DLC-coated dies. That is to say, all surface coatings examined were found to be effective in reducing the ejection force.