Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles – Utilizing diverse solid particles
Reexamination Certificate
1998-11-23
2001-03-20
Kuhns, Allan R. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
Utilizing diverse solid particles
C264S109000, C264S220000, C264S225000
Reexamination Certificate
active
06203734
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for the rapid manufacture of soft tooling for the production of complex metal and ceramic parts from powders using injection molding techniques. The finished parts are near-net shape, requiring little or no machining, and have excellent sintered properties. More particularly, the invention is directed to a molding process utilizing soft materials such as organic polymer-based resins to produce the tooling for use in an injection molding machine.
BACKGROUND OF THE INVENTION
The production of sintered parts from “green bodies” is well known in the prior art. Generally, the green body is formed by filling a die with a powder/binder mixture and compacting the mixture under pressure. The green body, which is a self-supporting structure, is then removed from the die and sintered. During the sintering process, the binder is volatilized and burned out. The sintered part is typically not fully dense (approximately 85-90% of theoretical density) and has substantially reduced mechanical properties compared to wrought material.
Injection molding is a preferred process for manufacturing complex, near-net shape parts from metal and ceramic powders. The tools for producing injection molded parts are generally made from metals, such as aluminum and tool steels in particular, due to the high pressures and temperatures normally required for state-of-the-art metal and ceramic feedstocks. Construction of hard tooling frequently involves long manufacturing turnaround times and is very costly. Furthermore, determination of accurate shrinkage factors for the tool material typically requires multiple iterations of successive, expensive machining.
Most state-of-the-art molding formulations use organic waxes and/or polymers as the molding, fluidizing medium. Polymer-based molding formulations require high molding pressures up to about 15,000 psi and molding temperatures above 212° F. (R. M. German and A. Bose, “
Injection Molding of Metals and Ceramics
,” Metal Powder Industries Federation, p53, p144, Princeton, N.J. 1997). The high pressures and temperatures employed by these systems necessitate the use of metal tooling, such as aluminum and steel, and preclude the use of “soft” tooling, such as organic polymer-based materials. The use of such soft tooling, utilizing plastic resins which are usually fortified with a particulate filler, obviates much of the high cost of manufacture and long turnaround times associated with hard tools. Furthermore, soft tooling can be more easily modified than can hard tooling, thus facilitating more accurate determination of shrinkage factors for net shape fabrication of metal and ceramic parts.
The advantages of soft tools for net shape fabrication can be realized using injection molding feedstock materials which permit the use of low molding pressures below about 1500 psi and low temperatures below about 212° F.
Typical examples of these feedstock materials are aqueous, polysaccharide-based injection molding compounds.
BRIEF SUMMARY OF THE INVENTION
The present invention overcomes these shortcomings by providing a method of fabricating complex, net and near-net shape parts using relatively inexpensive soft tooling and fast turnaround times. According to the invention, a method for the rapid manufacture of a soft tool includes the steps of providing a pattern of a desired shape, pouring material around the pattern to form a soft tool, curing the soft tool material to a rigid solid, and removing the pattern from the soft tool material to form a cavity therein. The soft tool produced by this process is considered a near-net shape tool requiring little or no final machining. Such near-net shape tools are used to manufacture metal, ceramic or plastic parts by traditional manufacturing techniques including injection molding, press-forging, blanking or drawing. Among the advantages of using soft tools to manufacture near-net shape parts in an injection molding machine is the use of feedstock materials which can be molded at pressures below about 1500 psi and temperatures below about 212° F.
The invention further includes a method for manufacturing near-net shape parts using the soft tooling manufactured in accordance with the present invention. The method includes the steps of providing a pattern of a desired shape, pouring material around the pattern to form a soft tool, curing the soft tool material to a rigid solid, removing the pattern from the soft tool material to form a cavity therein, mounting an ejector system on the soft tool, mounting the soft tool on an injection molding machine, and introducing a powder feedstock material into the injection molding machine at appropriate temperatures and pressures and for the appropriate amounts of time to mold the desired part.
REFERENCES:
patent: 3811175 (1974-05-01), Garner et al.
patent: 4734237 (1988-03-01), Fanelli et al.
patent: 4940561 (1990-07-01), Fritz
patent: 5260014 (1993-11-01), Holton et al.
patent: 5358211 (1994-10-01), Sterett
patent: 6066274 (2000-05-01), Antonson et al.
patent: 0-412-891 (1991-02-01), None
patent: 58-084718 (1983-05-01), None
patent: 63-202411 (1988-08-01), None
patent: 4-284207 (1991-03-01), None
patent: 7-186151 (1995-07-01), None
patent: 7-232332 (1995-09-01), None
R.M. German and A. Bose, “Injection Molding of Metals and Ceramics”, Metal Powder Industries Federation, p53, p. 144, Princeton, New Jersey 1997.
Behi Mohammad
Schoonover James
Zedalis Michael Sean
Allied-Signal Inc.
Criss Roger H.
Kuhns Allan R.
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