Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – Of inorganic materials
Reexamination Certificate
1999-02-16
2001-11-20
Zimmerman, John J. (Department: 1775)
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
Of inorganic materials
C264S610000, C264S643000, C264S645000, C419S006000, C419S012000, C419S027000
Reexamination Certificate
active
06319437
ABSTRACT:
BACKGROUND OF THE INVENTION
Powder Metallurgy
Powder metallurgy is a well-known technology. Crude forms of this technology were practiced in ancient Egypt as early as 3000 BC. This prior art process normally consists of four basic steps:
1. Producing a fine powder.
2. Mixing the powder and preparing the mixture for use.
3. Pressing the mixture into a desired shape.
4. Heating (sintering) the shape at a desired temperature.
The pressing and sintering operations of powder metallurgy are of special importance. The pressing and repressing greatly affect the density of the product, which has a direct relationship to the strength properties. Sintering promotes bonding of the powder particles, with densification resulting in a single piece of material with good mechanical properties. Sintering of metals and some compounds usually is done in a controlled, inert or reducing atmosphere, while oxide ceramics are sintered in air. Many products having complex shapes can be produced at relatively low cost because subsequent machining steps are either minimal or are eliminated all together.
Infiltration
It is known that placing products made using powder metallurgy processes in a bath of certain molten metals and allowing the molten metal to infiltrate into the voids of the product may produce composite products. A good discussion of this process of infiltration of a solid-phase powder compact with liquid metals is contained in an article entitled“Infiltration” by Claus G. Goetzel which is contained in the Powder metallurgy Volume of the Metals Handbook published by ASM International which article is incorporated herein by reference. The powder skeleton material must have a melting point substantially higher than the melting point of the infiltrant. This article in Table I lists 135 possible composites by making a matrix table of 25 skeleton materials (such as aluminum, chromium, copper, iron, molybdenum, nickel, silver, titanium carbide, tungsten and tungsten carbide) and 19 infiltrants (such as bismuth, cobalt, copper, lead, mercury, nickel, silver and tin). Only 22 of these possible combinations were reported as being commercially significant. Such examples were copper skeleton infiltrated with bismuth, lead or tin, and a tungsten skeleton infiltrated with copper, lead, nickel or silver. Sintering usually causes the molded product to shrink. The shrinkage is predicable and is allowed for in the pressing die.
Injection Molding
Injection molding techniques are well known. Plastic material in the form of powder, pellets or grains is placed in a hopper above a heated cylinder called the barrel. From the hopper, an appropriate amount of material is metered into the barrel every cycle. The plastic material, under pressures up to about 36,000 psi, is forced into a closed mold. The mold cools for a few seconds and is then opened and the molded parts are ejected.
Complex Shapes
Many products such as golf club heads have complex shapes and there is a need to permit a golf club designer to be able to specify various weight distributions within the part and to specify variations in other properties such as hardness, elasticity and strength at various locations within the part. In U.S. Pat. No. 4,768,787, Shira discloses a metallic surface layer containing hard particles on a golf club face in order to improve friction between the ball and the club.
The Need
A need exists for an improved powder injection molding and infiltration process which can further reduce the costs of producing complex shaped products and permit the cost effective commercial production of products having desired shapes, strengths, color and weights or to permit cost effective production of parts having desired weight distributions.
SUMMARY OF THE INVENTION
The present invention provides a powder injection molding and infiltration process. A powder for a skeleton material having a relatively high melting point is mixed with a composite binder to form a molding mixture. The composite binder is comprised of at least two different binder materials. The molding mixture is molded into a desired shape in a mold device to produce a molded part. The composite binder is then removed to produce voids in the molded part and the voids are filled by infiltrating an infiltrant comprised of an infiltrant material having a relatively low melting point to produce a composite molded part.
In a preferred embodiment the skeleton material is TiB
2
and the infiltrant material is aluminum and the composite binder is comprised of a plastic and a wax. In this embodiment the wax portion of the composite binder is removed using a solvent and the plastic is removed during the infiltration step. The resulting composite part has a TiB
2
skeleton with voids substantially filled with aluminum. This process is especially useful for making light and strong parts with complex shapes such as golf club heads, bicycle parts, cutting tools and wear resistant applications. The process can be automated to very efficiently produce high quality parts having complex shapes with physical properties characteristic of the properties of both the skeleton material and the infiltrant material.
In another preferred embodiment where the process is used to make a golf club head, the golf club head is comprised of three parts: a non-sintered TiB
2
part for the body of the head, a sintered TiB
2
part for the striking surface of the head, and a heavy tungsten part to provide weight for the head. In this embodiment, the aluminum infiltrant serves to substantially fill the voids in all three parts and to join the three parts to create a composite golf club head.
REFERENCES:
patent: 3929476 (1975-12-01), Kirby, Jr. et al.
patent: 4297421 (1981-10-01), Turillon et al.
patent: 4327156 (1982-04-01), Dillon et al.
patent: 4861641 (1989-08-01), Foster et al.
patent: 5735332 (1998-04-01), Ritland et al.
patent: 5944097 (1999-08-01), Gungor et al.
patent: 5976205 (1999-11-01), Andrews et al.
Clark Ian Sidney R.
Elsner Norbert B.
Leavitt Fred
Zalkind Stanley
Hi-Z Technology, Inc.
Ross John R.
Ross, III John R.
Zimmerman John J.
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