US 6,629,559 B2 · 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.

Claims84

Dependent claims

A mold for casting a part made from a molding material, which material experiences dimensional change during a mold process, said mold comprising:

a. a thin inner shell, which:
i. defines a three dimensional cavity that will establish locations of features of the casting part;
ii. is impervious to flow of liquid molding material therethrough;
iii. is configured to not fail under any stresses arising within said inner shell due to pouring of said liquid molding material into said cavity;
and
iv. is configured to fail under stresses arising within said inner shell as any such molding material solidifies or cools;
and
b. a three-dimensional support body that supports said inner shell, which support body is defined by an internal structure of supporting skeletal elements in predetermined locations and orientations relative to features of the casting part, and voids between said skeletal elements, and which:
i. is configured to not fail under any stresses arising within said support body due to pouring of said liquid molding material into said cavity;
and
ii. is configured through the locations and orientations of the skeletal elements within its internal structures to fail at predetermined regions relative to the locations of features of the casting part, under stresses arising within said support body as any such molding material solidifies and cools.

8 more elements

A method of making a mold, said method using a solid free form layered fabrication technique, comprising the steps of:

a. providing a machine readable model of a mold geometry comprising:
i. a thin inner shell, which:
A. defines a three dimensional cavity;
B. is impervious to flow of liquid molding material therethrough;
C. is configured to not fail under any stresses arising within said inner shell due to pouring of said liquid molding material into said cavity;
and
D. is configured to fail under stresses arising within said inner shell as any such molding material solidifies or cools;
and
ii. a three-dimensional support body that supports said inner shell, which support body:
A. is configured to not fail under any stresses arising within said support body due to pouring of said liquid molding material into said cavity;
and
B. is configured to fail under stresses arising within said support body as any such molding material solidifies and cools;
and
b. using said model to drive a solid free form layered fabrication machine, building up, by layers, a mold that is defined by said geometry.

11 more elements

A method of making a mold, said method using a solid free form layered fabrication technique, comprising the steps of:

a. providing a machine readable model of a mold geometry comprising:
i. a thin inner shell that defines a three dimensional cavity that will establish locations of features of the casting part;
and
ii. a three-dimensional support body that is contiguous with and substantially surrounds said inner shell, said support body being constructed of skeletal elements with voids therebetween, the voids comprising a network having an open pathway from each void to outside said support body and said skeletal elements being positioned and oriented according to a designed morphology at predetermined regions relative to the locations of features of the casting part;
and
b. using said model to drive a solid free form layered fabrication machine, building up, by layers of material, a mold that is defined by said geometry.

3 more elements

Dependencies are inferred from the claim text.

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

Life of this patent

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

Life of this patent

Abstract

Claims84