The effect of anisotropic dimensional change on the precision of steel parts produced by powder metallurgy

The dimensional characteristics of ring-shaped parts produced with an Fe–Cu–P alloy by a conventional powder metallurgy process were measured on both green and sintered parts. The dimensional change was investigated by dilatometry, and the work highlighted that the anisotropy observed is mainly due to the early sintering stage. In this study, where the alloy is characterised by a slight densification, the anisotropic behaviour has a negligible effect on the precision of the height and the internal diameter, while the effect on the precision of the external diameter may be relevant. The results have been generalised, considering larger volume variations and different anisotropy parameters, and some relations between the anisotropy parameters and the attainable ISO tolerance classes have been determined.