A debinding step using the supercritical state of a fluid has been increasingly investigated for extracting organic binders from components obtained by metal-injection molding. It consists of placing the component in an enclosure subjected to pressure and temperatures higher than the critical point to perform polymer extraction of the Metal-injection molding (MIM) component. It is an alternative to conventional solvent debinding. The topic of this study is to model and simulate the supercritical debinding stage to elucidate the mechanism of polymer degradation and stabilization with a three-dimensional model. Modelling this extraction process would optimize the process on an industrial scale. It can be physically described by Fick’s law of diffusion. The model’s main parameter is the diffusion coefficient, which is identified by using linear regression based on the least-squares method. In the model, an effective length scale is specially developed to take into account the diffusion in all directions. The tests were performed for extracting polyethylene glycol, an organic additive, using supercritical CO2 in injected components. The feedstock is composed of polypropylene, polyethylene glycol, and stearic-acid as binder mixed with Inconel 718 super-alloy powders. The identified parameters were used to calculate the diffusion coefficient and simulate the supercritical debinding step on the Comsol Multiphysics® finite-element software platform to predict the remaining binder. The obtained numerical simulation results are in good agreement with the experimental data. The proposed numerical simulations allow for the determination of the remaining polyethylene glycol (PEG) binder distribution with respect to processing parameters for components during the supercritical debinding process at any time. Moreover, this approach can be used in other formulation, powder, and binder systems.

Metal injection molding (MIM) is a process combining advantages of thermoplastic injection molding and powder metallurgy process in order to manufacture components with complex and near net-shape geometries. The debinding of a green component can be performed in two steps, first by using solvent debinding in order to extract the organic part of the binder and then by thermal degradation of the rest of the binder. A shorter and innovative method for extracting an organic binder involves the use of supercritical fluid instead of a regular solvent. The debinding via a supercritical fluid was recently investigated to extract organic binders contained in components obtained by Metal Injection Molding. It consists to put the component in an enclosure subjected to high pressure and temperature. The supercritical fluid has various properties depending on these two conditions, e.g., density and viscosity. The high-pressure combined with the high temperature during the process affect the component structure. Three mechanisms contributing to the deformation of the component can been differentiated: thermal expansion, binder extraction and supercritical fluid effect on the outer surfaces of the component. If one supposes that, the deformation due to binder extraction is negligible, thermal expansion and the fluid effect are probably the main mechanisms that can produce several stress. A finite-element model, which couples fluid-structures interaction and structural mechanics, has been developed and performed on the Comsol Multiphysics^® finite-element software platform allowed to estimate the stress distribution during the supercritical debinding of MIM component composed of Inconel 718 powders, polypropylene, polyethylene glycol and stearic acid as binder. The proposed numerical simulations allow the estimation of the stress distribution with respect to the processing parameters for MIM components during the supercritical debinding process using a stationary solver.