FINITE-ELEMENT MODELING OF BINDER REMOVAL FROM CERAMIC MOLDINGS

The article is devoted to the numerical simulation of the thermal debi nding process during powder injection moulding. The model of the binde r removal incorporates both main transport mechanisms during debinding , namely, the diffusion of the low molecular weight component and the forced or capillar flow of the binder. Optimization of the heating reg imes is proposed to be based on the prediction of the internal stress distribution in the workpiece. Internal pressure is induced by the swe lling of the binder during thermal degradation of the polymer or its s hrinkage, accompanying the loss of the low molecular weight component. Calculations were accomplished for poly-alphamethylstyrene as organic vehicle for which sufficient data are available. The stress distribut ion and damage conditions were assessed in the case of a cylindrical a nd a slab shaped workpiece. The results of the modelling correspond we ll with experimental data. They confirm that damage during thermal deb inding can be explained as a result of the development of internal str esses due to imbalance between degradation of the polymer and outward transportation of resulting products. (C) 1998 Elsevier Science Limite d. All rights reserved.