Abstract
Powder metallurgy (PM) part makers heavily rely on part density as a mean of controlling part performance. Higher compaction pressures may be used to obtain higher densities and better properties. However,ejection stresses usually increases with compacting pressure. Those stresses may affect significantly part quality (surface finish, formation of cracks and lamination) and tool wear.Different methods may be used to minimise ejection stresses, such as the use of admixed lubricant, die wall lubrication and the modification of tool surfaces. This paper presents an approach to evaluate the effect of tool coatings on the ejection of ferrous compacts. The method consists of evaluating the ejection characteristics of core rods with different coatings. The results obtained show that ejection characteristics are sensitive to tool coatings. Coating the surface of the core rods yields important variations of the stripping pressure (2×) and ejection energy (1·6×). No clear correlations between the ejection characteristics and the part surface finish were observed.
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