Abstract
Inner defects of metal injection molded specimen at varied injection speed were investigated by secondary electron images, acoustic images, radiographs and finite element method.
In particular, the inner defects occurred near gate, the shape and distribution state at low injection speed differed from high injection speed. We consider that the irregular tensile stress caused by shrinkage of crystallized polymer (polypropylene) as binder used in this study had occurred the inner defects. The shrinkage area of polymer with crystallized at cooling is differ at injection speed, and at termination of injection molding, the area is at center at low injection speed and is near capillary wall at high injection speed. At the area, the particle size and distribution of metal powder (SUS316L) were not uniform in scale of them. Therefore, tensile stress occurred partially among metal powders, the partial tensile stress causes the origin of crack.
The results of comparison surface with inner defects of acoustic images show that inner defects exist under surface where compound consisted of metal powder and binder composition, changes as contrast of acoustic surface images.
