WO2009158532A1 - Mold assembly apparatus and method for molding metal articles - Google Patents

Mold assembly apparatus and method for molding metal articles

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Publication number
WO2009158532A1
WO2009158532A1 PCT/US2009/048711 US2009048711W WO2009158532A1 WO 2009158532 A1 WO2009158532 A1 WO 2009158532A1 US 2009048711 W US2009048711 W US 2009048711W WO 2009158532 A1 WO2009158532 A1 WO 2009158532A1
Authority
WO
Grant status
Application
Patent type
Prior art keywords
metal
mold
cavity
method
recited
Prior art date
Application number
PCT/US2009/048711
Other languages
French (fr)
Inventor
Paul E. Lewis
Dan E. Fischer
Original Assignee
Ultradent Products, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date

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Classifications

    • BPERFORMING OPERATIONS; TRANSPORTING
    • B22CASTING; POWDER METALLURGY
    • B22DCASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D35/00Equipment for conveying molten metal into beds or moulds
    • B22D35/06Heating or cooling equipment
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B22CASTING; POWDER METALLURGY
    • B22DCASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D17/00Pressure die casting or injection die casting, i.e. casting in which the metal is forced into a mould under high pressure
    • B22D17/007Semi-solid pressure die casting
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C45/00Amorphous alloys
    • C22C45/10Amorphous alloys with molybdenum, tungsten, niobium, tantalum, titanium, or zirconium or Hf as the major constituent
    • GPHYSICS
    • G04HOROLOGY
    • G04DAPPARATUS OR TOOLS SPECIALLY DESIGNED FOR MAKING OR MAINTAINING CLOCKS OR WATCHES
    • G04D3/00Watchmakers' or watch-repairers' machines or tools for working materials
    • G04D3/0002Watchmakers' or watch-repairers' machines or tools for working materials for mechanical working other than with a lathe
    • G04D3/0017Watchmakers' or watch-repairers' machines or tools for working materials for mechanical working other than with a lathe for components of gearworks
    • G04D3/002Watchmakers' or watch-repairers' machines or tools for working materials for mechanical working other than with a lathe for components of gearworks for gear wheels or gears

Abstract

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.

Description

MOLD ASSEMBLY APPARATUS AND METHOD

FOR MOLDING METAL ARTICLES

BACKGROUND OF THE INVENTION

1. 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. Patent 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 INVENTION

The 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. BRIEF DESCRIPTION OF THE DRAWINGS

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:

Figure 1 is a perspective view of an exemplary apparatus for molding metal articles according to one embodiment of the present invention; Figure 2 is a right side view of the apparatus of Figure 1;

Figure 3 is front side view of the apparatus of Figure 1;

Figure 4 is a cross-sectional view of the apparatus of Figure 1;

Figure 5 is a perspective view of the apparatus of Figure 1, with the mold in a raised position so that the RF induction heating coil surrounds the mold cavity; Figure 6A is a close up perspective view of one side of the mold cavity and surrounding mold of Figure 5;

Figure 6B is a close up perspective view of the opposite side of the mold cavity and surrounding mold of Figure 5;

Figure 7A is a cross-sectional view of the apparatus of Figure 5, in which a metal billet rests against the closed first gate member;

Figure 7B is a cross-sectional view of the apparatus of Figure 5, in which the metal billet of Figure 7 A passes through the open first gate member;

Figure 8 A is a cross-sectional view of the apparatus of Figure 5, in which the metal billet of Figure 7 A rests against the closed second gate member; Figure 8B is a cross-sectional view of the apparatus of Figure 5, in which the metal billet of Figure 7 A passes through the open second gate member;

Figure 9 is a cross-sectional view of the apparatus of Figure 5, in which the metal billet of Figure 7A is being melted by activation of the RF induction heating coil; Figure 10 is a cross-sectional view of the apparatus of Figure 5, in which the pressing member forces all molten metal into the cavity; Figure 1OA is a close up view of a contact surface of the pressing member of

Figure 10;

Figure 1OB is a close up view of the filled mold cavity after the pressing member forces all molten metal into the cavity and applies a pattern into the exposed surface of the metal within the cavity; Figure 11 is a cross-sectional view of the apparatus of Figure 5, in which the pressing member and mold have been retracted;

Figure 12 is a cross-sectional view of the apparatus of Figure 5, in which the mold has been rotated 180° and the molded metal article removed from the mold cavity; Figure 13 is a perspective view of the molded metal bracket;

Figure 14 is a side view of the bracket of Figure 13 once the bonding pad of the bracket has been bent so as to create undercuts within the pressed in pattern;

Figure 15A is a perspective view of an alternative bracket that may be molded according to the inventive method; and Figure 15B is a perspective view of another alternative bracket that may be molded according to the inventive method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS I. Introduction

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 Apparatus

Figures 1-4 illustrate an exemplary molding apparatus 100 including a mold assembly 102, a delivery chute 104, and an RF induction heating coil 106. Mold assembly 102 includes a first portion 108a and a second portion 108b, with a mold cavity 110 defined between the two portions 108a and 108b, respectively. In the illustrated configuration, mold portion 108b is mounted on a carriage 112 so as to allow sliding movement of portion 108b away from portion 108a so as to open the mold. Advantageously, the portion of mold assembly 102 including mold cavity 110 is configured as a cylinder 114 to allow the cylinder to be received within RF induction coil 106. Of course, other configurations of portion 114 may be possible (e.g., a square cross-section or other cross-section small enough to be received within coil 106).

As perhaps best seen in the cross-sectional view of Figure 4, delivery chute 104 includes an internal channel 115 that runs from a proximal end 116 to a distal end 118, which is adjacent to the mold cavity 110 when mold assembly 102 is in a raised position. In the illustrated configuration, chute 104 is oriented at an angle relative to a vertical axis Y, and the apparatus further includes a pressing member 120 along vertical axis Y for selectively pressing a molten metal billet into molding cavity 110. The illustrated embodiment of delivery chute 104 further includes first and second gate members 122 and 124, respectively, for selectively impeding and allowing movement of a metal billet through channel 115 towards molding cavity 110. Such a double gate configuration may be particularly helpful if the heating, melting, and subsequent cooling of the meltable metal billet is to be carried out under vacuum or in an inert atmosphere. Pressing member 120 is disposed within a vertical press housing 121 aligned with axis Y. Pressing member 120 slides within a channel defined by an upper portion 117 and a lower portion 115, which also serves as the distal portion of delivery channel 115.

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, NY. 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 20C above the melting temperature of the metal, more preferably at least about 50C above the melting temperature of the metal, and most preferably at least about 1O0C above the melting temperature of the metal. In addition, it may be desirable to heat the metal no higher than about 5O0C 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. Patent No. 6,682,611, incorporated herein by reference. Specific examples of LIQUID METAL amorphous alloys disclosed in U.S. Patent 6,682,611 include (Zr41Ti14Cu125Ni1OBe22 5)98Y2, (Zr34Ti15Cu12 5NiπBe28)98Y2, Zr34Ti15Cu12Ni11Be28Y2, (Zr34Ti15Cu12Ni1 iBe28)98Y2, (Zr34Ti15Cu10Ni11Be22 S)98Y2, (Zr55Al15Ni10Cu20)98Y2, and (Zr55Al15Ni10Cu2O)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 Figure 13), small gears for craftsman quality analog watches, gold, silver or other metallic jewelry, springs, or any other small metal article. Advantageously, there is little or no excess metal (i.e., runners and/or sprue) that remain adhered to the molded article when released from the mold. This reduces or eliminates the need for post molding finishing or machining. In addition, it reduces or eliminates costs associated with recycle of the material making up the runners and/or sprue. Reduction and/or elimination of finishing steps (e.g., polishing, grinding, deburring) is particularly beneficial when working with LIQUID METAL alloys containing beryllium, as beryllium has been found to be carcinogenic. III. Exemplary Method of Use

According to one embodiment, mold assembly 102 can be vertically raised and lowered. For example, as shown in Figure 1 the mold cavity within cylindrical portion 114 is shown retracted relative to RF induction coil 106, and in Figure 5 it is shown raised so that the mold cavity within portion 114 is inserted within and surrounded by RF induction coil 106. Figures 6A and 6B illustrate the separate halves 110a and 110b of mold cavity 110 within cylindrical mold portion 114. In the illustrated example, the mold cavity 110 is in the shape of a non self-ligating orthodontic bracket to be molded of metal (e.g., a LIQUID METAL alloy). Brackets of other shapes, even single piece self-ligating brackets, may also be similarly formed. Two-part self-ligating brackets (e.g., including a bracket base and a separate hinged or sliding cover) may be molded in two or more parts (i.e., a mold cavity for the base and another mold cavity for the cover, and then assembled together).

As best seen in Figures 6A-6B, there is no runner connected to mold cavity 110, but rather the portion of mold cavity 110 that forms the bonding pad of the orthodontic bracket is adjacent the top surface 126 of mold portion 114. Advantageously, the metal billet passes through delivery channel 115 in solid phase right up to molding cavity 110, where it is melted by RF induction at approximately the same time it is introduced (e.g., by gravity and/or force of pressing member 120) into molding cavity 110, reducing or eliminating the formation of any runner as a result of metal cooling within a runner channel adjacent the mold cavity. In other words, melting may be accomplished only at the last possible moment, greatly simplifying the process related to maintaining the material in a molten condition from melting until introduction into the mold.

As seen in Figure 7A, a metal billet 128 is introduced into channel 115 of delivery chute 104. In the illustrated example, chute 104 includes a first gate member 122, which is initially closed so as to impede progress of billet 128 past gate member 122 until gate 122 is opened. Metal billet 128 may advantageously be of a mass that is approximately equal to the mass of the finished article. Assuming differences in density at various temperatures and phases are negligible, billet 128 is also of a volume that is approximately equal to the volume of the mold cavity 110. There is no runner channel that must be filled with the molten metal from the metal billet, as the solid metal billet 128 passes through the channel 115 to a location directly adjacent the molding cavity 110. It is at this location that the billet 128 is melted at approximately the same time as being introduced into the molding cavity 110. There is no need for complex heating mechanisms to maintain the raw metal in a molten state as it travels from a reservoir to the molding cavity. This configuration advantageously reduces waste, subsequent finishing steps required to finish the molded article, and recycling costs.

As shown in Figure 7B, first gate member 122 is opened, allowing metal billet 128 to pass through gate member 122 (e.g., by force of gravity) down towards second gate member 124 (see Figure 8A). Second gate member 124 may then be opened (see Figure 8B), allowing billet 128 to continue downward into the portion of channel 115 defined by press housing 121 surrounded by RF induction heating coil 106. Gate members 122 and 124 may be helpful in maintaining the heating, melting, and cooling steps of the method in a vacuum or inert atmosphere while allowing introduction of the metal billet 128 from atmospheric conditions. For example, gate members 122 and 124 are not opened simultaneously, but when gate member 122 is opened, the vacuum or inert atmosphere within lower channel 115 and mold cavity 110 is maintained by closed gate member 124. As shown in Figure 9, upon activation of RF induction heating coil 106, metal billet 128 quickly melts, and begins to flow down (e.g., by force of gravity and/or vacuum suction) into mold cavity 110. 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 Figure 10). As shown in Figure 1OA, advantageously, the contacting surface 123 of the pressing member 120 may optionally include a pattern to be pressed into the molten metal, particularly if the metal is already beginning to cool and solidify so that any such pressed shape would be retained within the soft metal. For example, as perhaps best seen in Figure 1OB, a mesh or sawtooth pattern or other texture 125 may be pressed into the adjacent molten metal so as to form a rough, textured, or uneven bonding pad for the orthodontic bracket. As perhaps best seen in Figure 14, the bonding pad 127 of the orthodontic bracket 130 including the applied pattern 125 may be subsequently bent so as to achieve a desired curvature for aligning with the curved labial surface of a tooth. Advantageously, such bending of the bonding pad 127 alters the applied pattern so as to create undercuts within the bonding pad 127, which are advantageous in strongly bonding the bracket 130 to a tooth. Such bending may be performed after the bracket 130 has been released from the mold 110. Depending on the metal material of the bracket, heating of the bonding pad 127 may be required to achieve the desired bending without fracture of the bracket. Of course, when molding metal articles of other shapes, different shapes or textures may be pressed into such a surface. As shown in Figure 11, after molten metal fills mold cavity 110 and is further pressed using pressing member 120, pressing member 120 is retracted to its original raised position, and the mold assembly 102 may then be retracted from surrounding RF induction coil 106. This causes the molded article within mold cavity 110 to quickly cool as a result of the relatively cool surrounding mold portion 114, which is insensitive to heating from RF induction coil 106. In this way, the mold surrounding mold cavity 110 remains relatively cool (e.g., room temperature), while the molten metal fills mold cavity 110 and is forced therein by pressing member 120. Heat, which may otherwise build up within mold assembly 102 may be withdrawn through cooling lines (e.g., carrying a cooling fluid such as water or other liquid and/or gas) that may run through or otherwise exchange heat with the mold assembly 102.

As shown in Figure 12, mold 102 may be rotated 180° (e.g., inverted) and opened as mold portion 108b and the adjoining portion of cylindrical portion 114 slide along carriage 112, opening mold cavity 110 so that molded article 130 (e.g., an orthodontic bracket) may be removed. Figure 13 illustrates an exemplary orthodontic bracket 130 molded with the apparatus, although it will be understood that various other bracket configurations may be formed in a similar manner by altering the shape of mold cavity 110. Figure 14 shows a bracket having a curved bonding pad 127 having a bonding pattern 125.

Exemplary alternative bracket configurations that may be formed according to the present method and apparatus are shown in Figures 15 A and 15B. Figure 15 A shows a two-part self-ligating bracket 230 including a bracket base and a sliding ligation cover. The sliding cover and bracket base may be molded as two separate parts and then assembled together. Figure 15B illustrates a one-piece integral self- ligating bracket 330 that may be molded as a single piece from an amorphous metallic alloy (e.g., LIQUID METAL). Glass-like LIQUID METAL alloys have been found to surprisingly provide flexibility and resiliency when molded with very small cross sections, which allows the elongate film hinge connecting the bracket base to the ligation cover of bracket 330 to resiliently flex and bend as needed during opening and closing. The flexibility of the LIQUID METAL in the region of the film hinge connecting the bracket base to the ligation cover allows the cover to be closed without fracture at the connecting film hinge. 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. What is claimed is:

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 (Zr41Ti14Cu125Ni10Be22 5)98Y2, (Zr34Ti15Cu12 5Ni11Be2S)9SY2, Zr34Ti15Cu12Ni11Be28Y2, (Zr34Ti15Cu12Ni11Be2S)9SY2, (Zr34Ti15Cu10Ni11Be22 5)98Y2, (Zr55Al15Ni10Cu2O)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 (Zr41Ti14Cu125Ni10Be22 5)98Y2, (Zr34Ti15Cu12 5NiπBe28)98Y2, Zr34Ti15Cu12Ni11Be28Y2, (Zr34Ti15Cu12Ni1 iBe28)98Y2, (Zr34Ti15Cu10Ni11Be22 S)98Y2, (Zr55Al15Ni10Cu20)98Y2, and (Zr55Al15Ni10Cu2O)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 (Zr41Ti14Cu125Ni10Be22 5)98Y2, (Zr34Ti15Cu12 5NiπBe28)98Y2, Zr34Ti15Cu12Ni11Be28Y2, (Zr34Ti15Cu12Ni1 iBe28)98Y2, (Zr34Ti15Cu10Ni11Be22 S)98Y2, (Zr55Al15Ni10Cu20)98Y2, and (Zr55AIi5Ni10Cu2O)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 (Zr41Ti14Cu125Ni10Be22 5)98Y2, (Zr34Ti15Cu12 5NiπBe28)98Y2, Zr34Ti15Cu12Ni11Be28Y2, (Zr34Ti15Cu12Ni1 iBe28)98Y2, (Zr34Ti15Cu10Ni11Be22 S)98Y2, (Zr55Al15Ni10Cu20)98Y2, and (Zr55Al15Ni10Cu2O)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.
PCT/US2009/048711 2008-06-27 2009-06-25 Mold assembly apparatus and method for molding metal articles WO2009158532A1 (en)

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