Simulation of polymer removal from a powder injection molding compact by thermal debinding
- PDF / 306,758 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 5 Downloads / 219 Views
I. INTRODUCTION
POWDER injection molding (PIM) is an important netshape manufacturing process and has received much attention. One of the most critical steps in PIM process is debinding. It consumes a major part of the processing time. Failure of the powder compact often results if the process is accelerated. Thermal debinding is a common methodology for the final removal of residual polymer from a PIM compact prior to sintering. During debinding, polymer is heated thermally, melted into liquid, and decomposed into vapor. The overall removal of residual polymer is an intricate combination of evaporation, liquid and gas migration, pyrolysis of polymer, and heat transfer in porous media. A successful modeling of thermal debinding provides the potential for optimization of the process to prevent the formation of defects during the decomposition of the polymer. As summarized in Table I, several researchers attempted to model thermal debinding by considering various mass transport mechanisms.[1–9] German[1] modeled isothermal debinding by two separate controlling processes: vapor diffusion and vapor permeation. The pyrolysis of binder and the diffusion of organic species within the binder phase, as well as the liquid transport processes, were neglected. The binder-vapor interface was modeled as a planar front, which receded into the compact as removal progressed. The effects of particle size, porosity, and component size on debinding times were assessed. Tsai[5] analyzed the gas pressure buildup and the stresses on the powder skeleton during binder burnout based on gas transport in a porous medium combining with the pyrolysis of Y.C. LAM, S.C.M. YU, and K.C. TAM, Associate Professors, and YING SHENGJIE, Research Fellow, are with the School of Mechanical and Production Engineering, Nanyang Technological University, Singapore 639798. Manuscript submitted November 29, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS A
binder and elasticity theory. Evans et al.[6] modeled the removal of polymer from molded ceramic bodies as an unsteady-state diffusion of degradation products in solution in the parent polymer and with degradation of polymer, and they evaluated the critical heating rates for the initial stage of polymer removal process. Mater et al.[7] further developed the work of Evans et al. and assumed that there was an undegraded shrinking core (or planar liquid-gas interface front) that receded into the compact as removal progressed so that the model would be applied not only for the initial stage of polymer removal process. Their model was extended to include gas transport in the porous outer layer of the compact. Lewis and Galler[8] applied the Monte-Carlo method to investigate the diffusion of volatile species in the binder phase and the capillary-driven binder redistribution processes in the isothermal removal of plasticizer species. Barone and Ulciny[3] studied the capillary-driven liquid flow during the removal of organic binders from injection-molded ceramic components. They neglected the gas transport phenomenon
Data Loading...
