Abstract
In producing complex parts by metal injection molding (MIM), various defects are encountered. Most of them can be introduced in the molding stage and they are affected by many factors such as molding condition, binder and powder used, mold design and so on. It is, at present, very difficult to predict the occurrence of the defects in advance; however, they should be completely eliminated to ensure the reliability of the products.
This paper describes the molding defect (crack) found in the thin-wall complex part. In order to eliminate this defect, the effects of molding condition, binder content, binder and powder characteristics and recycling of compound have been investigated. Holding pressure, mold temperature and molding temperature (temperature at the nozzle) have a significant effect on the formation of the defect, while the effect of injection speed is relatively small. Binder content, binder and powder characteristics and recycling of compound also have a considerable effect, and their effects can be consistently attributed to their effects on the flowability of the compound.
Based on the above mentioned results and the short-shot test result, it has been concluded that the mechanism by which the defect forms is very similar to that of weldline cracks.
