ASPECT RATIO OF GREEN MIM PARTS ON SHRINKAGE DURING SINTERING

摘要

Metal injection moulding (MIM) is a process that can produce small, complex, and near-net-shape parts with excellent mechanical properties. The shrinkage during sintering in MIM parts is one of the most important parameters in production. In this work, stainless steel 316L feedstock was injection moulded to form three different shapes, which were tensile test specimen, three-step specimen and square-donut specimen. Multi-step specimen and square-donut specimen were specially designed for observation of shrinkage behaviour. In addition, nine sets of square-donut specimens with different aspect ratios were investigated. The results shown that the shape of injected parts did not affect the sintered density and volumetric shrinkage as they were sintered using the same condition. The main driving force for densification were diffusing and gravity. Gravity enhanced densification in the vertical direction and hence became more significant for a thicker section. Parts with significantly larger length than width had larger longitudinal shrinkage than width shrinkage. The thickness shrinkage decreased as the aspect ratio of width/thickness increased, i.e. parts became wider and thinner. In addition, the width shrinkage increased as the aspect ratio of width/thickness decreased, i.e. parts became narrower and thicker.