U.S. patent application number 12/488144 was filed with the patent office on 2009-12-31 for mold assembly apparatus and method for molding metal articles.
This patent application is currently assigned to Ultradent Products, Inc.. Invention is credited to Dan E. Fischer, Paul E. Lewis.
Application Number | 20090321037 12/488144 |
Document ID | / |
Family ID | 41444958 |
Filed Date | 2009-12-31 |
United States Patent
Application |
20090321037 |
Kind Code |
A1 |
Lewis; Paul E. ; et
al. |
December 31, 2009 |
MOLD ASSEMBLY APPARATUS AND METHOD FOR MOLDING METAL ARTICLES
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.
Inventors: |
Lewis; Paul E.; (Midvale,
UT) ; Fischer; Dan E.; (Sandy, UT) |
Correspondence
Address: |
Workman Nydegger;1000 Eagle Gate Tower
60 East South Temple
Salt Lake City
UT
84111
US
|
Assignee: |
Ultradent Products, Inc.
South Jordan
UT
|
Family ID: |
41444958 |
Appl. No.: |
12/488144 |
Filed: |
June 19, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61076252 |
Jun 27, 2008 |
|
|
|
61076258 |
Jun 27, 2008 |
|
|
|
Current U.S.
Class: |
164/501 ;
164/513 |
Current CPC
Class: |
G04D 3/002 20130101;
B22D 17/007 20130101; B22D 35/06 20130101; C22C 45/10 20130101 |
Class at
Publication: |
164/501 ;
164/513 |
International
Class: |
B22D 27/02 20060101
B22D027/02 |
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
(Zr.sub.41Ti.sub.14Cu.sub.12.5Ni.sub.10Be.sub.22.5).sub.98Y.sub.2,
(Zr.sub.34Ti.sub.15Cu.sub.12.5Ni.sub.11Be.sub.28).sub.98Y.sub.2,
Zr.sub.34Ti.sub.15Cu.sub.12Ni.sub.11Be.sub.28Y.sub.2,
(Zr.sub.34Ti.sub.15Cu.sub.12Ni.sub.11Be.sub.28).sub.98Y.sub.2,
(Zr.sub.34Ti.sub.15Cu.sub.10Ni.sub.11Be.sub.22.5).sub.98Y.sub.2,
(Zr.sub.55Al.sub.15Ni.sub.10Cu.sub.20).sub.98Y.sub.2, and
(Zr.sub.55Al.sub.15Ni.sub.10Cu.sub.20).sub.96Y.sub.4.
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
(Zr.sub.41Ti.sub.14Cu.sub.12.5Ni.sub.10Be.sub.22.5).sub.98Y.sub.2,
(Zr.sub.34Ti.sub.15Cu.sub.12.5Ni.sub.11Be.sub.28).sub.98Y.sub.2,
Zr.sub.34Ti.sub.15Cu.sub.12Ni.sub.11Be.sub.28Y.sub.2,
(Zr.sub.34Ti.sub.15Cu.sub.12Ni.sub.11Be.sub.28).sub.98Y.sub.2,
(Zr.sub.34Ti.sub.15Cu.sub.10Ni.sub.11Be.sub.22.5).sub.98Y.sub.2,
(Zr.sub.55Al.sub.15Ni.sub.10Cu.sub.20).sub.98Y.sub.2, and
(Zr.sub.55Al.sub.15Ni.sub.10Cu.sub.20).sub.96Y.sub.4.
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
(Zr.sub.41Ti.sub.14Cu.sub.12.5Ni.sub.10Be.sub.22.5).sub.98Y.sub.2,
(Zr.sub.34Ti.sub.15Cu.sub.12.5Ni.sub.11Be.sub.28).sub.98Y.sub.2,
Zr.sub.34Ti.sub.15Cu.sub.12Ni.sub.11Be.sub.28Y.sub.2,
(Zr.sub.34Ti.sub.15Cu.sub.12Ni.sub.11Be.sub.28).sub.98Y.sub.2,
(Zr.sub.34Ti.sub.15Cu.sub.10Ni.sub.11Be.sub.22.5).sub.98Y.sub.2,
(Zr.sub.55Al.sub.15Ni.sub.10Cu.sub.20).sub.98Y.sub.2, and
(Zr.sub.55Al.sub.15Ni.sub.10Cu.sub.20).sub.96Y.sub.4.
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
(Zr.sub.41Ti.sub.14Cu.sub.12.5Ni.sub.10Be.sub.22.5).sub.98Y.sub.2,
(Zr.sub.34Ti.sub.15Cu.sub.12.5Ni.sub.11Be.sub.28).sub.98Y.sub.2,
Zr.sub.34Ti.sub.15Cu.sub.12Ni.sub.11Be.sub.28Y.sub.2,
(Zr.sub.34Ti.sub.15Cu.sub.12Ni.sub.11Be.sub.28).sub.98Y.sub.2,
(Zr.sub.34Ti.sub.15Cu.sub.10Ni.sub.11Be.sub.22.5).sub.98Y.sub.2,
(Zr.sub.55Al.sub.15Ni.sub.10Cu.sub.20).sub.98Y.sub.2, and
(Zr.sub.55Al.sub.15Ni.sub.10Cu.sub.20).sub.96Y.sub.4.
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.
Description
RELATED APPLICATIONS
[0001] 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 INVENTION
[0002] 1. The Field of the Invention
[0003] The present invention relates to apparatus assemblies and
methods for melting and molding metal articles from a meltable
metal material.
[0004] 2. The Related Technology
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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 INVENTION
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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
[0014] 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:
[0015] FIG. 1 is a perspective view of an exemplary apparatus for
molding metal articles according to one embodiment of the present
invention;
[0016] FIG. 2 is a right side view of the apparatus of FIG. 1;
[0017] FIG. 3 is front side view of the apparatus of FIG. 1;
[0018] FIG. 4 is a cross-sectional view of the apparatus of FIG.
1;
[0019] FIG. 5 is a perspective view of the apparatus of FIG. 1,
with the mold in a raised position so that the RF induction heating
coil surrounds the mold cavity;
[0020] FIG. 6A is a close up perspective view of one side of the
mold cavity and surrounding mold of FIG. 5;
[0021] FIG. 6B is a close up perspective view of the opposite side
of the mold cavity and surrounding mold of FIG. 5;
[0022] FIG. 7A is a cross-sectional view of the apparatus of FIG.
5, in which a metal billet rests against the closed first gate
member;
[0023] FIG. 7B is a cross-sectional view of the apparatus of FIG.
5, in which the metal billet of FIG. 7A passes through the open
first gate member;
[0024] FIG. 8A is a cross-sectional view of the apparatus of FIG.
5, in which the metal billet of FIG. 7A rests against the closed
second gate member;
[0025] FIG. 8B is a cross-sectional view of the apparatus of FIG.
5, in which the metal billet of FIG. 7A passes through the open
second gate member;
[0026] FIG. 9 is a cross-sectional view of the apparatus of FIG. 5,
in which the metal billet of FIG. 7A is being melted by activation
of the RF induction heating coil;
[0027] FIG. 10 is a cross-sectional view of the apparatus of FIG.
5, in which the pressing member forces all molten metal into the
cavity;
[0028] FIG. 10A is a close up view of a contact surface of the
pressing member of FIG. 10;
[0029] FIG. 10B 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;
[0030] FIG. 11 is a cross-sectional view of the apparatus of FIG.
5, in which the pressing member and mold have been retracted;
[0031] FIG. 12 is a cross-sectional view of the apparatus of FIG.
5, in which the mold has been rotated 180.degree. and the molded
metal article removed from the mold cavity;
[0032] FIG. 13 is a perspective view of the molded metal
bracket;
[0033] FIG. 14 is a side view of the bracket of FIG. 13 once the
bonding pad of the bracket has been bent so as to create undercuts
within the pressed in pattern;
[0034] FIG. 15A is a perspective view of an alternative bracket
that may be molded according to the inventive method; and
[0035] FIG. 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
[0036] 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.
[0037] 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.
[0038] 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
[0039] FIGS. 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).
[0040] As perhaps best seen in the cross-sectional view of FIG. 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.
[0041] 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.
[0042] 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.
[0043] 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.
[0044] 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.degree. C. above the melting
temperature of the metal, more preferably at least about 5.degree.
C. above the melting temperature of the metal, and most preferably
at least about 10.degree. C. above the melting temperature of the
metal. In addition, it may be desirable to heat the metal no higher
than about 50.degree. 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.
[0045] 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
(Zr.sub.41Ti.sub.14Cu.sub.12.5Ni.sub.10Be.sub.22.5).sub.98Y.sub.2,
(Zr.sub.34Ti.sub.15Cu.sub.12.5Ni.sub.11Be.sub.28).sub.98Y.sub.2,
Zr.sub.34Ti.sub.15Cu.sub.12Ni.sub.11Be.sub.28Y.sub.2,
(Zr.sub.34Ti.sub.15Cu.sub.12Ni.sub.11Be.sub.28).sub.98Y.sub.2,
(Zr.sub.34Ti.sub.15Cu.sub.10Ni.sub.11Be.sub.22.5).sub.98Y.sub.2,
(Zr.sub.55Al.sub.15Ni.sub.10Cu.sub.20).sub.98Y.sub.2, and
(Zr.sub.55Al.sub.15Ni.sub.10Cu.sub.20).sub.96Y.sub.4.
[0046] 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.
[0047] The apparatus and related methods may be used to form
various metal articles, for example, orthodontic brackets (e.g., as
illustrated in FIG. 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
[0048] According to one embodiment, mold assembly 102 can be
vertically raised and lowered. For example, as shown in FIG. 1 the
mold cavity within cylindrical portion 114 is shown retracted
relative to RF induction coil 106, and in FIG. 5 it is shown raised
so that the mold cavity within portion 114 is inserted within and
surrounded by RF induction coil 106. FIGS. 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).
[0049] As best seen in FIGS. 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.
[0050] As seen in FIG. 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.
[0051] As shown in FIG. 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 FIG.
8A). Second gate member 124 may then be opened (see FIG. 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 FIG. 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.
[0052] 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 FIG. 10). As shown in FIG. 10A,
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 FIG. 10B, 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.
[0053] As perhaps best seen in FIG. 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.
[0054] As shown in FIG. 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.
[0055] As shown in FIG. 12, mold 102 may be rotated 180.degree.
(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. FIG. 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. FIG. 14 shows a bracket having a curved
bonding pad 127 having a bonding pattern 125.
[0056] Exemplary alternative bracket configurations that may be
formed according to the present method and apparatus are shown in
FIGS. 15A and 15B. FIG. 15A 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. FIG. 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.
[0057] 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.
[0058] 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.
[0059] 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.
[0060] 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.
* * * * *