Influence of Process Parameters on Precision of PM Parts

Abstract

Powder metallurgy is normally considered a very good technology for producing mechanical parts with high precision. This is generally confirmed by comparison with other mass production technologies. In the present study, typical precision levels achieved by various fabrication operations are considered. Since the final precision is determined by the various contributions of each production stage, each contribution has been considered separately. The influence of various chemical compositions (always on an iron base) has also been considered. Another important consideration is the dimensions of the part to be produced. For simple geometries, it is demonstrated that the ISO system of classifying tolerances is not suitable for classifying correctly the precision levels achievable on parts of the same shape but with different dimensions. The problems of dimensional tolerance increase as the part dimensions increase. The theoretical evaluations are based on information supplied by the producers of iron powders, on the stress state during pressing, and on the diffusion phenomena occurring during sintering. From the theoretical provisions derived and current trends in production, some general suggestions are made that can be considered as a basis for a useful standard of typical precision levels in PM parts produced from different ferrous materials. PM/0312