Molds for casting with customized internal structure to collapse upon cooling and to facilitate control of heat transfer

Abstract

A new mold solves problems that arise from differential changes in geometry inherent to casting metal in a ceramic mold, by control of the internal morphology between the surfaces of the mold that face the casting, and that face the external environment. Layered fabrication techniques are used to create a ceramic mold. For example, an internal geometry composed of a cellular arrangement of voids may be created within the mold wall. Structures may be designed and fabricated so that the ceramic mold fails at an appropriate time during the solidification and/or cooling of the casting. Thus, the casting itself is not damaged. The mold fails to avoid rupture, or even distortion, of the casting. A thin shell of ceramic defines the casting cavity. This shell must be thin enough to fail due to the stresses induced (primarily compressive) by the metal next to it and partly adherent to it. A support structure is provided with a morphology that supports the thin shell that defines the casting geometry, yet that also fails as the casting solidifies and/or cools. Typically, the support structure is a skeletal network with voids therebetween. The skeletal elements may be struts, or sheets or both. At least the following two failure mechanisms may be exploited in the design of the support structure: bending in the structure; and under compressive loads, either by buckling of a support member or, breakage under compressive loading. The failure of the support structure may also be due to a combination of bending and compression.