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

Powder injection molding (PIM) is an important net-shape manufacturing proc ess. Thermal debinding is a common methodology for the final removal of res idual polymer from a PIM compact prior to sintering. This process is an int ricate combination of evaporation, liquid and gas migration, pyrolysis of p olymer, and heat transfer in porous media. A better understanding of therma l debinding could lead to optimization of the process to prevent the format ion of defects. Simulation of the process based on an integrated mathematic al model for mass and heat transfer in porous media is proposed. The mechan isms of mass transport, i.e., liquid flow, gas flow, vapor diffusion, and c onvection, as well as the phase transitions of polymer, and their interacti ons, are included in the model. The macroscopic partial differential equati ons are formulated by volume averaging of the microscopic conservation laws . The basic equations consist of mass conservation and energy conservation and are solved numerically. Polymer residue, pressure, and temperature dist ributions are predicted. The importance of the various mass transfer mechan isms is evaluated. The effects of key mass transfer parameters on thermal d ebinding are discussed. It is revealed from the results that the assumed bi nder front, which is supposed to recede into the powder compact as removal progresses, does not exist. The mass flux of polymer liquid is of the same order of the mass flux of polymer vapor in the gas phase, and the polymer v apor diffusion in the liquid phase is negligible.