Effect of molding conditions on residual stress in powder injection molding

The layer removal method was used to assess residual stress distributions in 10 mm thick plates injection molded from a 56 v/o alumina suspension in polypropylene. Three different molding techniques were examined. Conventional moldings present a center-tensile, surface compressive distribution with the magnitude of the tensile stress strongly influenced by hold pressure. Heated sprue moldings show a distribution which is within the limits of experimental error and is effectively negligible. Modulated pressure moldings present an unbalanced distribution which indicated that oscillatory flow influenced the elastic modulus of the polypropylene, probably as a result of orientation effects...