MOLD ASSEMBLY APPARATUS AND METHOD FOR MOLDING METAL ARTICLES
Apparatus assemblies and methods for melting and injection molding an article from a meltable metal that is sensitive to heating by radio frequency (RF) induction. An exemplary apparatus includes a mold including a cavity having a shape of an article to be molded, a delivery chute including a channel for delivering a solid metal billet from a proximal end of the delivery chute to a distal end which is adjacent to the mold, and an RF induction heating coil that surrounds the cavity of the mold and the distal end of the delivery chute. Advantageously, the portion of the mold defining the cavity and at least the distal end of the delivery chute (i.e., those portions surrounded by the RF coil) are formed of materials that are substantially insensitive to heating by RF induction so that the metal billet is melted and molded at approximately the same time.
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The present application claims the benefit of U.S. Patent Application Ser. No. 61/076,252, filed Jun. 27, 2008, entitled “MOLD ASSEMBLY APPARATUS AND METHOD FOR MOLDING METAL ARTICLES”, and U.S. Patent Application Ser. No. 61/076,258, filed Jun. 27, 2008, entitled “METHODS FOR MOLDING ORTHODONTIC BRACKETS FROM METAL”, the disclosure of each of which is incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION1. The Field of the Invention
The present invention relates to apparatus assemblies and methods for melting and molding metal articles from a meltable metal material.
2. The Related Technology
Metal articles can be manufactured in a variety of ways, including machining solid metal or injection molding the metal in the form of a metal powder mixed with a binder followed by sintering the green body to form the finished article. It is also possible to injection mold with molten metal. Machining is often used to manufacture relatively small numbers of parts as the cost of the molds needed for injection molding metals are very expensive. If the number of articles to be manufactured is large, injection molding may be preferred, as the molds can often be used repeatedly for tens of thousands or hundreds of thousands of cycles.
When injection molding any article (e.g., from plastic or metal), the molten raw material is injected through a channel to the area defining the article to be molded. When injection molding with molten metals, the metal is typically heated just prior to being forced towards the molding cavity under tremendous pressure and heat. It is important to move the metal quickly so that it does not solidify by cooling before the molten metal can be introduced into the mold cavity. Typically the mold remains relatively cool so as to aid in cooling of the molded metal article and to prevent undue repeated temperature cycling of the mold, which results in premature wear and cracking of the mold. Because of this, the state of the art typically relies on forcing the heated metal into the mold as quickly as possible.
When the article is removed from the mold, a portion of material, known as a “runner” or “sprue” remains adhered to the article. The runner and sprue are a result of the excess material present within the channels adjacent to the area of the mold cavity defining the article, which solidifies at the same time as the molded article. Technically, the sprue refers to that portion of material which solidifies within the main channel running from the reservoir of molten material to the mold cavity, while the runner refer to that portion of material which solidifies within the secondary channels connecting multiple mold cavities (i.e., runners convey molten material to the point(s) of injection at individual mold cavities). Often, a runner will connect multiple molding chamber areas, such that multiple articles are molded simultaneously, all connected by one or more runners. The runners and sprues must be removed in a subsequent finishing/deburring step. For the sake of simplicity, runners and sprues will be referred to hereafter as runners.
Recently, a new type of moldable metal, called “LIQUID METAL,” was developed and described in U.S. Pat. No. 6,682,611. Although this type of metal has been touted as providing increased moldability, current molding apparatus and techniques, including those employed by the manufacturer of “LIQUID METAL” continue to yield molded products with attached runners and sprue.
BRIEF SUMMARY OF THE INVENTIONThe present invention is directed to apparatus and methods for melting and injection molding an article from meltable metal. An exemplary apparatus includes a mold including a cavity in the shape of an article to be molded, a delivery chute including a channel for delivering an initially solid metal billet having a mass equal to the molded article from a proximal end of the delivery chute to a distal end which is adjacent to the mold and mold cavity, and a radio frequency (RF) induction heating coil that surrounds the cavity of the mold and the distal end of the delivery chute. Advantageously, the mold defining the mold cavity and at least the distal end of the delivery chute (i.e., the portion surrounded by the RF coil) are formed of materials that are substantially not sensitive to heating by RF induction. Such a configuration allows for activation of the RF induction coil without substantial heating of the mold and the adjacent portion of the delivery chute. The apparatus is used to mold articles from metals which are sensitive to heating through RF induction.
In a related method of manufacture, an initially solid metal billet is introduced into the channel of the delivery chute that leads to the molding cavity of the mold. The metal billet is selectively heated and melted by activating the RF induction heating coil when the metal billet has dropped down the channel to a location surrounded by the RF induction heating coil, just before the material enters the adjacent mold cavity. The apparatus may include one or more gates along the length of the delivery chute so as to hold the metal billet at the gate location until the gate is opened to allow passage further into the channel, towards the molding cavity. Advantageously, the activation of the RF induction coil results in substantially no direct heating of the delivery chute or the mold because of the materials (e.g., ceramic) from which these structures are formed. As a result of heating by the RF induction coil, the metal billet melts, allowing the molten metal to flow into the molding cavity of the mold. The RF induction coil may remain activated as long as necessary to ensure that the metal fills the molding cavity. Because the metal billet can have a mass and volume substantially equal to the mass and volume of the finished molded article, all of the molten metal enters the cavity with little or no excess. Once the metal fills the molding cavity, the RF induction coil is deactivated so as to allow the molten metal in the molding cavity to solidify by cooling so as to form the molded metal article.
The molded article is allowed to solidify, which may occur relatively quickly because the mold is cool relative to the molten metal within the molding cavity. The mold acts as a heat sink to draw the heat quickly out of the molten metal through cooling and solidification of the molded article. The mold may further include cooling lines (e.g., running through the mold) to draw heat away from the mold to prevent build up of heat within the mold through repeated molding cycles.
The inventive apparatus and methods make it possible to mold metal parts that have minimal or no excess metal attached to the molded part (i.e., in the form of a runner and/or sprue). This, in turn, minimizes or eliminates the need for post molding machining or debriding to remove the excess metal. Of course, the molded parts can be machined or polished as desired to yield a final part suitable for an intended use.
These and other advantages and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.
To further clarify the above and other advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:
The present invention is directed to apparatus and methods for melting and injection molding an article from a meltable metal. An exemplary apparatus includes a mold including a cavity having a shape of an article to be molded, a delivery chute including a channel for delivering an initially solid metal billet from a proximal end of the delivery chute to a distal end which is adjacent to the mold, and a radio frequency (RF) induction heating coil that surrounds at least the cavity of the mold and the distal end of the delivery chute. Advantageously, at least a portion of the mold and at least the distal end of the delivery chute (i.e., those portions surrounded by the RF coil) are formed of materials that are substantially insensitive to heating by RF induction.
According to one aspect, the present invention is directed to apparatus and methods for melting and injection molding an orthodontic bracket from a meltable metal. According to one method, an initially solid metal billet from which a single orthodontic bracket is to be formed is selectively heated by RF induction heating adjacent to a mold cavity of a mold. According to one embodiment, at least that portion of the mold defining the mold cavity may be formed of a material that is not insensitive to heating by RF induction, and the mold cavity is in the shape of an orthodontic bracket or portion thereof to be formed. The adjacent delivery channel or chute may also comprise a material that is insensitive to heating by RF induction.
The metal billet is selectively heated and melted by activating an RF induction heating coil when the metal billet is in the delivery channel or chute adjacent (e.g., just above) the mold cavity and surrounded by the RF induction heating coil. As a result of heating by the RF induction coil, the metal billet melts, allowing the molten metal to flow into the mold cavity of the mold. The RF induction coil may remain activated as long as necessary to ensure that the metal fills the mold cavity. Because the metal billet can have a mass and volume substantially equal to the mass and volume of the finished molded bracket (and the volume of the billet can be substantially equal to the volume of the mold cavity), all of the molten metal can enter the cavity with little or no excess. Once the metal fills the mold cavity, the RF induction coil may be deactivated so as to allow the molten metal in the molding cavity to solidify by cooling so as to form the molded metal bracket.
II. Exemplary Molding ApparatusAs perhaps best seen in the cross-sectional view of
At least portion 114 of mold 102 (i.e., that portion which is received within surrounding RF induction heating coil 106) is formed of a material that is substantially insensitive to heating by RF induction. At least the distal portion 118 of delivery chute 104 (i.e., that portion which is received within surrounding RF induction heating coil 106) is also formed of such a material so that the apparatus allows selective heating and melting of just the metal billet introduced into channel 115, without any substantial direct heating of mold portion 114 or distal end 118 of delivery chute 104 by RF induction heating coil 106. Advantageously, the heating induced by coil 106 is limited to just the metal billet to be used in molding the metal article. In addition, the heating and melting is performed immediately prior to molding, such that melting and molding are performed at approximately the same time. Because the billet can have the same or similar volume as mold cavity 110, there is no need to maintain a stream of metal in a molten state as it travels from a reservoir to the mold cavity.
An example of a material that is substantially insensitive to heating by RF induction include various ceramics. Suitable ceramics preferably will be substantially smooth and non-porous so as to aid in removal of the molded article. One specific example of an exemplary ceramic that may be used includes a partially stabilized zirconia ceramic. One such material, Mg-PSZ, is available from Carpenter Advanced Ceramics located in Reading, Pa.
The RF induction coil 106 is configured to induce melting of a metal billet just prior to the metal entering the mold cavity. Coil 106 may be operated so that the metal material may be heated until the metal material completely fills the mold cavity 110, and longer, if needed. The design and operating parameters of the RF coil 106 may depend on the composition of the metal being melted, heat capacity of the metal being melted, electrical and thermal conductivity of the metal, the mass of the metal billet being melted, the number of windings present within the coil 106, the current, voltage, and frequency applied through the coil, among other things. Suitable commercial RF induction heating coil systems are available from Ameritherm, located in Scottsville, N.Y. Suitable designs and operating parameters will be apparent to one skilled in the art in light of the present disclosure.
For example, it may be preferable to provide sufficient induced current and heat to the metal billet so as to melt the billet within about 5 seconds or less, more preferably within about 3 seconds or less, and most preferably within about 1 second or less. Ideally, melting is achieved almost instantaneously (e.g., within about 0.1 second). The metal is heated at least to its melting temperature so as to melt the metal. Preferably, heating may be performed to at least about 2° C. above the melting temperature of the metal, more preferably at least about 5° C. above the melting temperature of the metal, and most preferably at least about 10° C. above the melting temperature of the metal. In addition, it may be desirable to heat the metal no higher than about 50° C. above its melting temperature so as to reduce energy consumption, as the heat must later be removed during solidification and cooling of the molded article.
Any metal material that can be heated and melted through subjecting the material to RF induction may be molded with the inventive apparatus and method. Exemplary materials include, but are not limited to silver, iron, steel, other iron containing metal alloys, gold, nickel-titanium alloys, titanium alloys, and “LIQUID METAL”, which refers to specific zirconium based metallic amorphous glass-like alloys formed from low purity materials, preferred examples of which include the addition of a small amount of yttrium (Y). Disclosed examples of such materials are a combination of Zr, Al, Ni, Cu and Y or Zr, Ti, Ni, Cu, Be, and Y. Examples of LIQUID METAL alloys are disclosed in U.S. Pat. No. 6,682,611, incorporated herein by reference. Specific examples of LIQUID METAL amorphous alloys disclosed in U.S. Pat. No. 6,682,611 include (Zr41Ti14Cu12.5Ni10Be22.5)98Y2, (Zr34Ti15Cu12.5Ni11Be28)98Y2, Zr34Ti15Cu12Ni11Be28Y2, (Zr34Ti15Cu12Ni11Be28)98Y2, (Zr34Ti15Cu10Ni11Be22.5)98Y2, (Zr55Al15Ni10Cu20)98Y2, and (Zr55Al15Ni10Cu20)96Y4.
As noted above, although LIQUID METAL may provide increased moldability relative to traditionally used metals, current molding apparatus and techniques continue to yield molded products with attached runners and sprue, limiting the utility of the material to date. In the case of LIQUID METAL, heating and melting of the metal, as well as cooling, is performed under vacuum (or possibly in an inert atmosphere, for example of argon, helium, or nitrogen), as LIQUID METAL oxidizes when heated in air, which is undesirable. As a practical matter, the entire process may be performed under such conditions.
The apparatus and related methods may be used to form various metal articles, for example, orthodontic brackets (e.g., as illustrated in
According to one embodiment, mold assembly 102 can be vertically raised and lowered. For example, as shown in
As best seen in
As seen in
As shown in
In order to ensure that all of the molten metal is introduced into mold cavity 110, and to avoid the formation of any voids or bubbles within the cavity and finished molded metal article, pressing member 120 may be activated, pressing all molten metal into the mold cavity (see
As perhaps best seen in
As shown in
As shown in
Exemplary alternative bracket configurations that may be formed according to the present method and apparatus are shown in
In addition, articles of various other shapes (e.g., jewelry) may be formed in a similar manner by altering the shape of mold cavity 110. As shown, the molded article requires little or no finishing, as there is no runner of unwanted metal material present to be removed after molding of parts. Reduction and/or elimination of finishing steps (e.g., polishing, grinding, deburring) which result in formation of metal dust is particularly beneficial when working with LIQUID METAL alloys containing beryllium, as inhalation of beryllium dust has been found to be carcinogenic.
In addition, use of an RF induction heating coil and a ceramic or similar insensitive material for forming at least the portion of the mold surrounding mold cavity 110 minimizes any temperature cycling of the mold assembly, reducing stress and wear on these parts.
Additional details regarding exemplary brackets and methods of manufacture by molding are disclosed in a United States Patent Application bearing attorney docket number 7678.1087.2.1, filed the same day as the present application, entitled ORTHODONTIC BRACKETS HAVING A BENDABLE OR FLEXIBLE MEMBER FORMED FROM AMORPHOUS METALLIC ALLOYS. The above patent application is hereby incorporated by reference.
The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.
Claims
1. An apparatus for melting and molding an article from a solid metal billet, comprising:
- a mold including a cavity having a shape of an article to be molded;
- a delivery chute including a channel for delivering a solid metal billet from a proximal end to a distal end, the distal end being adjacent to the cavity of the mold, at least that portion of the mold defining the mold cavity and at least the distal end of the delivery chute being formed of a material that is substantially not sensitive to heating by RF induction; and
- an RF induction heating coil surrounding the cavity of the mold and the distal end of the delivery chute.
2. An apparatus as defined in claim 1, wherein at least the mold and distal end of the delivery chute are contained with a chamber under vacuum or an inert atmosphere.
3. An apparatus as defined in claim 1, wherein the delivery chute further comprises at least one gate member for selectively allowing passage of a metal billet through the channel.
4. An apparatus as defined in claim 1, further comprising a pressing member for selectively pressing a molten metal billet into the cavity.
5. A apparatus as recited in claim 4, wherein the pressing member includes a contacting surface having a mesh, sawtooth, or textured pattern.
6. An apparatus as defined in claim 1, wherein at least the portion of the mold defining the mold cavity is formed of ceramic.
7. An apparatus as defined in claim 1, wherein at least the distal end of the delivery chute is formed of ceramic.
8. A method of manufacturing a molded metal article, comprising:
- introducing a solid metal billet into a delivery chute having a channel leading to a molding cavity of a mold, at least that portion of the mold defining the cavity being formed of a material that is not sensitive to heating by RF induction;
- selectively heating the metal billet by RF induction heating adjacent the mold cavity so as to melt the metal billet such that the metal fills the molding cavity without substantial heating of the mold;
- allowing the metal within the molding cavity to cool so as to form a metal molded article; and
- removing the metal article from the molding cavity.
9. A method as recited in claim 8, wherein the volume of the metal billet is substantially equal to the volume of the mold cavity, the method further comprising maintaining the metal in a heated molten configuration until substantially all metal material has entered the molding cavity and the cavity is substantially filled.
10. A method as recited in claim 8, wherein at least that portion of the mold defining the mold cavity is formed of ceramic.
11. A method as recited in claim 8, wherein at least the distal end of the delivery chute is formed of a material that is insensitive to heating by RF induction.
12. A method as recited in claim 11, wherein at least the distal end of the delivery chute is formed of ceramic.
13. A method as recited in claim 8, wherein the metal billet comprises a zirconium based metallic amorphous alloy formed from low purity materials.
14. A method as recited in claim 13, wherein the zirconium based metallic amorphous alloy comprises at least one of the compositions selected from the group consisting of (Zr41Ti14Cu12.5Ni10Be22.5)98Y2, (Zr34Ti15Cu12.5Ni11Be28)98Y2, Zr34Ti15Cu12Ni11Be28Y2, (Zr34Ti15Cu12Ni11Be28)98Y2, (Zr34Ti15Cu10Ni11Be22.5)98Y2, (Zr55Al15Ni10Cu20)98Y2, and (Zr55Al15Ni10Cu20)96Y4.
15. A method as recited in claim 8, wherein the metal billet comprises at least one of iron, silver, or gold.
16. A method as recited in claim 8, wherein the method is performed under vacuum or in an inert atmosphere.
17. A method as recited in claim 8, further comprising pressing a surface of the metal within the mold cavity with a pressing member before the metal completely cools.
18. A method as recited in claim 17, wherein the pressing member applies a mesh, sawtooth, or textured pattern to a surface of the metal within the mold cavity.
19. A method as recited in claim 8, wherein RF induction heating of the metal billet melts the metal billet within about 5 seconds or less.
20. A method as recited in claim 8, wherein RF induction heating of the metal billet melts the metal billet within about 1 second or less.
21. An apparatus for melting and molding an article from a solid metal billet, comprising:
- a mold including a cavity having a shape of an article to be molded, at least that portion of the mold defining the cavity being formed of ceramic so as to be substantially not sensitive to heating by RF induction;
- a delivery chute including a channel for delivering a metal billet from a proximal end to a distal end of the chute, the distal end being adjacent to the cavity of the mold, at least the distal end of the delivery chute being formed of ceramic so as to be substantially not sensitive to heating by RF induction;
- an RF induction heating coil surrounding the cavity of the mold and the distal end of the ceramic delivery chute; and
- a pressing member for selectively pressing a molten metal billet into the cavity.
22. A method of manufacturing an orthodontic bracket from metal, comprising:
- selectively heating a metal billet by RF induction heating adjacent to a molding cavity defined by a mold, the cavity being in the shape of at least a portion of an orthodontic bracket so as to melt the metal billet such that substantially all of the metal enters the molding cavity and substantially fills the molding cavity, the mold being formed of a material that is substantially insensitive to heating by RF induction such that there is substantially no heating of the mold by RF induction;
- allowing the metal within the molding cavity to cool so as to form a solid metal orthodontic bracket; and
- removing the solid metal orthodontic bracket from the molding cavity.
23. A method as recited in claim 22, wherein at least that portion of the mold defining the molding cavity is formed of ceramic.
24. A method as recited in claim 22, wherein the metal billet comprises a zirconium based metallic amorphous alloy.
25. A method as recited in claim 24, wherein the zirconium based amorphous metallic alloy is selected from the group consisting of (Zr41Ti14Cu12.5Ni10Be22.5)98Y2, (Zr34Ti15Cu12.5Ni11Be28)98Y2, Zr34Ti15Cu12Ni11Be28Y2, (Zr34Ti15Cu12Ni11Be28)98Y2, (Zr34Ti15Cu10Ni11Be22.5)98Y2, (Zr55Al15Ni10Cu20)98Y2, and (Zr55Al15Ni10Cu20)96Y4.
26. A method as recited in claim 22, wherein the method is performed under vacuum and/or in an inert atmosphere.
27. A method as recited in claim 22, wherein the molding cavity is configured such that the molten metal enters the molding cavity through an entrance portion of the molding cavity corresponding to a bonding pad of the orthodontic bracket.
28. A method as recited in claim 27, further comprising pressing a surface of the metal within the molding cavity adjacent to the entrance with a pressing member before the metal completely cools.
29. A method as recited in claim 28, wherein the pressing member applies a mesh, sawtooth, or textured pattern to a bonding pad surface of the orthodontic bracket.
30. A method as recited in claim 29, further comprising bending the bonding pad surface of the orthodontic bracket subsequent to removing the metal orthodontic bracket from the molding cavity so as to, form a curved bonding pad with undercuts within the bonding pad surface.
31. A method as recited in claim 22, wherein selective heating of the metal billet so as to melt the metal billet is accomplished substantially simultaneously with the metal entering the molding cavity.
32. A method of manufacturing an orthodontic bracket from a zirconium based metallic amorphous alloy, comprising:
- selectively heating a metal billet of a zirconium based metallic amorphous alloy material by RF induction heating adjacent to a molding cavity defined by a mold, the cavity being in the shape of an orthodontic bracket so as to melt the metal billet, the metal billet having a volume substantially equal to a volume of the molding cavity such that substantially all of the metal enters the molding cavity and substantially fills the molding cavity, the mold being formed of a material that is substantially insensitive to heating by RF induction such that there is substantially no heating of the mold by RF induction;
- allowing the metal within the molding cavity to cool so as to form a solid metal orthodontic bracket; and
- removing the solid metal orthodontic bracket from the molding cavity;
- wherein heating and molding of the orthodontic bracket is performed under vacuum.
33. A method as recited in claim 32, wherein the zirconium based metallic amorphous alloy comprises at least one alloy selected from the group consisting of (Zr41Ti14Cu12.5Ni10Be22.5)98Y2, (Zr34Ti15Cu12.5Ni11Be28)98Y2, Zr34Ti15Cu12Ni11Be28Y2, (Zr34Ti15Cu12Ni11Be28)98Y2, (Zr34Ti15Cu10Ni11Be22.5)98Y2, (Zr55Al15Ni10Cu20)98Y2, and (Zr55Al15Ni10Cu20)96Y4.
34. A method as recited in claim 32, wherein at least the portion of the mold defining the molding cavity is formed of ceramic.
35. A method as recited in claim 32, wherein selective heating of the metal billet so as to melt the metal billet is accomplished substantially simultaneously with the metal entering the molding cavity.
36. A method of manufacturing an orthodontic bracket from metal, comprising:
- selectively heating a metal billet by RF induction heating adjacent to a molding cavity defined by a mold formed of a material that is substantially insensitive to heating by RF induction, the molding cavity being in the shape of an orthodontic bracket, the metal billet melting such that substantially all of the metal enters the molding cavity through an entrance portion of the molding cavity corresponding to a bonding pad of the orthodontic bracket, the metal substantially filling the molding cavity;
- pressing a surface of the metal within the molding cavity adjacent to the entrance with a pressing member before the metal completely cools so as to apply a mesh, sawtooth, or textured pattern to a bonding pad surface of the orthodontic bracket;
- allowing the metal within the molding cavity to cool;
- removing the metal orthodontic bracket from the molding cavity; and
- bending the bonding pad surface of the orthodontic bracket so as to form a curved bonding pad having undercuts within the bonding pad surface.
37. A method as recited in claim 36, wherein at least that portion of the mold defining the molding cavity is formed of ceramic.
38. A method as recited in claim 36, wherein the metal billet comprises a zirconium based metallic amorphous alloy.
39. A method as recited in claim 38, wherein the zirconium based metallic amorphous alloy comprises at least one alloy selected from the group consisting of (Zr41Ti14Cu12.5Ni10Be22.5)98Y2, (Zr34Ti15Cu12.5Ni11Be28)98Y2, Zr34Ti15Cu12Ni11Be28Y2, (Zr34Ti15Cu12Ni11Be28)98Y2, (Zr34Ti15Cu10Ni11Be22.5)98Y2, (Zr55Al15Ni10Cu20)98Y2, and (Zr55Al15Ni10Cu20)96Y4.
40. A method as recited in claim 36, wherein selective heating of the metal billet so as to melt the metal billet is accomplished substantially simultaneously with the metal entering the molding cavity.
Type: Application
Filed: Jun 19, 2009
Publication Date: Dec 31, 2009
Applicant: Ultradent Products, Inc. (South Jordan, UT)
Inventors: Paul E. Lewis (Midvale, UT), Dan E. Fischer (Sandy, UT)
Application Number: 12/488,144
International Classification: B22D 27/02 (20060101);