Processing Defects and Resulting Mechanical Properties After Metal Injection Molding

Abstract

The paper is concerned with occurrence of processing defects and resulting mechanical properties associated with material processing by metal injection molding (MIM). MIM process is a multistep one that consists first in the injection of metallic powders mixed with a thermoplastic binder, followed by a debinding stage that permits to evacuate the polymeric binder, and then followed by a sintering stage by solid state diffusion that normally leads to a nearly dense component. The main defects arising during MIM processing are associated with powder segregation during injection molding, and uncompleted or heterogeneous mechanical properties resulting from solid state diffusion. The paper first describes a biphasic fluid flow approach that can accurately predict powder volume fraction after injection molding and consequently the associated segregation defects. This analysis is followed and continued by a proper sintering model based on an elastic-viscous analogy that predicts the resulting local densities after sintering and also associated defects. So, from the two subsequent models, it becomes possible to get the final powder densities after processing and to localize the possible resulting defects. This analysis is completed by an analysis using a porous material model to get the final resultant mechanical properties after processing.