Three Dimensional Modeling of Unfired Ceramics During Lamination

A finished ceramic component with complex geometries such as micro-channels requires a high degree of dimensional accuracy. This accuracy depends upon precise control of the unfired ceramic body before sintering. One method for creating precise micro-channel geometries is the fugitive phase approach. In this approach, a sacrificial material, the fugitive phase, is used to form channels or voids in the unfired ceramic body. The fugitive phase is removed or sacrificed during the subsequent sintering. For this paper, the authors examine the lamination step of the fugitive phase approach computationally. The lamination step is where the unfired ceramic and fugitive phase pieces are layered and pressed together to remove voids before sintering. The compression of the unfired ceramic during pressing causes pressure gradients, viscoelastic deformation, displacement of the fugitive phase pieces, and rebounding. Three dimensional modeling is used to capture out of plane movement or bending of the long fugitive phase pieces that are used to form long micro-channels. For this research, the unfired ceramic phase consists of tape cast mullite and the fugitive phase is paper. This work primarily examines viscoelastic material models of the unfired ceramic phase for a range of temperatures. The filling of voids, movement of the fugitive phases, pressure gradients, and the rebounding that occurs when the unfired ceramic body is removed from the die press are also noted. The information obtained from computational simulations is used to help direct concurrent experimental investigations.