Evolution of liquid-bond strength in powder injection moulding compact during thermal debinding: numerical simulation

Abstract

Debinding is a critical processing step in the powder injection moulding (PIM) process. Thermal debinding is a common methodology for the final removal of residual polymer from a PIM compact prior to sintering. During debinding, the strength of the compact decreases rapidly due to heating and polymer removal. Liquid-bond strength plays a key role in the strength of the compact. Simulation of the liquid-bond strength in the compact during thermal debinding, based on the model which has previously been validated experimentally, is proposed. The pyrolysis of polymer, heat transfer, and multi-phase fluid flow, i.e. liquid flow, gas flow, vapour diffusion, and convection, as well as liquid-bonding forces arising from capillary suction pressure and interfacial surface tension, and their interactions, are considered simultaneously. The simulated results revealed that the liquid-bond strength in the compact decreases rapidly as furnace temperature increases, because the surface tension and capillary pressure decrease rapidly with an increase in temperature. The effect of softening caused by elevated temperature is more significant than the effect of weakening caused by polymer removal. Thus, thermal debinding at lower temperatures will contribute towards prevention of defect formation.