DIMENSIONAL CONTROL IN HARD-METAL MANUFACTURE

Abstract

All hard-metal alloys contract ～50% by volume during sintering and, in addition, the continuous network of liquid phase makes them extremely weak. Hence, the two major problems in dimensional control are coping with this large contraction and at the same time preventing distortion during sintering.

Green compacts of closely controlled and very uniform density are essential to ensure that the contraction is both predictable and uniform. Methods of predicting contraction and of powder preparation and pressing to achieve this end are described.

Distortion results not only from mechanical weakness during sintering but also from the carburizing, decarburizing, oxidation, and reduction reactions that occur when the green compact is heated.

In conclusion, indications are given of the order of dimensional accuracy that can be expected in hard-metal manufacture.