Vacuum forming of a sheet of thermoplastic material around a mandrel conforming to the shape of the finished object provides a pattern for an investment mold. The thickness of the metal part is determined by the thickness of the plastic pattern

Clarke, A. E., Jr.

English

NASA Technical Reports Server

March 1964	 Brief 63-10008 
NASA TECH BRIEF 
This NASA Tech Brief is issued by the Technology Utilization Division to acquaint industry 
with the technical content of an innovation derived from the NASA space program. 
Vacuum Forming of Thermoplastic Sheet Results in Low-Cost Investment

Casting Patterns 
The problem: Thin-walled metal objects of various 
shapes can be made by a number of methods, such as 
electroforming, machining, stamping, and investment 
casting. In research and development work where pre-
cision metal parts are required for trial runs and to 
test various cast alloys for particular shapes, invest-
ment casting has become the preferred method. In the 
conventional method, the wax or plastic patterns 
which are required are made with metal dies and 
female molds. These steps for limited runs are 
expensive and time consuming. 
The solution: A plastic (e.g., cellulose acetate 
butyrate) pattern of the thin-walled object to be cast 
is simply and quickly made by vacuum forming of a 
sheet of the thermoplastic material around a mandrel 
conforming to the shape of the finished object. This 
pattern is then used to prepare an investment mold 
with a ceramic slurry as in the conventional invest-
ment casting process. 
Notes: 
1. After investing the plastic pattern with the ceramic 
slurry in a flask, the flask and contents are fired in
a furnace to burn out the plastic pattern com-
pletely. The molten metal is preferably centrifu-
gally cast in the resulting mold. These steps, of 
course, follow standard investment casting proce-
dure. 
2. The thickness of the metal part is determined by 
the thickness of the plastic pattern, with allowances 
made for plastic deformation in the vacuum form-
ing operation. 
3. The several steps involved in the method of casting 
thin-walled metal shapes are given in the following 
reference: "Thermoforming + Investment Process 
= Ultrathin-Wall Castings," by A. E. Clarke, Jr., 
in Product Engineering, February 27, 1961, pp 42-
44. 
Patent status: NASA encourages the immediate 
commercial use of this invention. It was invented by a 
NASA employee and a patent application has been 
filed. Inquiries concerning license rights may be made 
directly to the inventor, A. E. Clarke, Jr. at Ames 
Research Center, Moffett Field, California. 
Source: Ames Research Center (ARC-7) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States Govern-
ment, nor NASA, nor any person acting on behalf of NASA: A. Makes 
any warranty or representation, express or im plied, with respect to the 
accuracy, completeness, or usefulness of the information contained in
this document, or that the use of any information, apparatus, method, 
or process disclosed in this document may not infringe privately-owned 
rights; or B. Assumes any liabilities with respect to the use of, or for 
damag es resulting from the use of, any information, apparatus, method, 
or process disclosed in this document,
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Vacuum forming of thermoplastic sheet results in low-cost investment casting patterns

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