Simulation of polymer removal from a powder injection molding compact by thermal debinding

Modeling was carried out on the heat and mass transport of polymer removal from a powder injection molding compact by thermal debinding, and the subsequent stress and deformation of the compact. The technique was developed based on heat and mass transfer in porous media and elasticity theory. The primary mechanisms of mass transfer, i.e., liquid flow, gas flow, vapor diffusion and convection, as well as the pyrolysis of polymer, and their interactions, were included in the model. The stress and strain caused by polymer content change, temperature change, and gas pressure were considered. Integrated control volume finite difference and finite element methods were adopted to simulate the process. The simulated results revealed that the polymer removal process was controlled by polymer degradation and mainly affected by liquid flow. Stress and strain were dominated by polymer content change. The non-uniform distribution of the polymer content and the non-uniform flow of the liquid polymer resulted in the non-uniform shrinkage in the compact and thus distortion of the compact. The failure of powder compact occurred most easily at the moment of rapid compact distortion, which was accompanied by rapid weight loss.