U.S. patent application number 11/035062 was filed with the patent office on 2005-05-26 for semi-solid metal casting process.
This patent application is currently assigned to SPX Corporation (DE Corp). Invention is credited to DasGupta, Rathindra, Hollacher, Robert, Musser, Mark, Szymanowski, Richard Brian, Xia, Yun.
Application Number | 20050109479 11/035062 |
Document ID | / |
Family ID | 34376176 |
Filed Date | 2005-05-26 |
United States Patent
Application |
20050109479 |
Kind Code |
A1 |
DasGupta, Rathindra ; et
al. |
May 26, 2005 |
Semi-solid metal casting process
Abstract
A method of semi-solid metal casting without the need for
retrofitting of conventional casting equipment is provided. A
method of direct-feed casting of semi-solid metals is also
provided.
Inventors: |
DasGupta, Rathindra;
(Portage, MI) ; Hollacher, Robert; (St. Joseph,
MI) ; Musser, Mark; (Osceola, IN) ; Xia,
Yun; (Portage, MI) ; Szymanowski, Richard Brian;
(Saint Joseph, MI) |
Correspondence
Address: |
Baker & Hostetler LLP
Washington Square, Suite 1100
1050 Connecticut Avenue, N.W.
Washington
DC
20036
US
|
Assignee: |
SPX Corporation (DE Corp)
|
Family ID: |
34376176 |
Appl. No.: |
11/035062 |
Filed: |
January 14, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11035062 |
Jan 14, 2005 |
|
|
|
10671707 |
Sep 29, 2003 |
|
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Current U.S.
Class: |
164/113 ;
164/312; 164/900 |
Current CPC
Class: |
B22D 17/007 20130101;
B22D 17/12 20130101 |
Class at
Publication: |
164/113 ;
164/900; 164/312 |
International
Class: |
B22D 017/08; B22D
023/00; B22D 025/00 |
Claims
What is claimed is:
1. A semi-solid metal (SSM) casting process, comprising: providing
a metal and a vertical die casting machine, heating the metal to a
chosen temperature, cooling the metal for a determined period of
time to form a semi-solid metal, wherein the time can be zero; and
casting the semi-solid metal in the vertical die casting
machine.
2. An SSM casting process according to claim 1, wherein the metal
is an Al--Si alloy.
3. An SSM casting process according to claim 2, wherein Al--Si
alloy is a hypereutectic Al--Si alloy comprising more than about
11.7 weight percent Si in Al.
4. An SSM casting process according to claim 2, wherein Al--Si
alloy is a hypoeutectic Al--Si alloy comprising less than about
11.7 weight percent Si in Al.
5. An SSM casting process according to claim 2, wherein Al--Si
alloy is a 380 alloy.
6. An SSM casting process according to claim 1, wherein the
vertical die casting machine is an indexing type vertical die
casting machine.
7. An SSM casting process according to claim 5, wherein the
vertical die casting machine is a 1000 Ton Shuttle Machine.
8. An SSM casting process according to claim 2, wherein the
vertical die casting machine is an indexing type vertical die
casting machine comprising a shot sleeve that indexes between a
pour station and a transfer station requiring an indexing time.
9. An SSM casting process according to claim 5, wherein the
temperature of metal is chosen such that the metal will form a
semi-solid metal as it cools from indexing between the pour station
to the transfer station..
10. An SSM casting process according to claim 8, wherein the
indexing time is chosen to achieve a determined rate of
cooling.
11. A means for SSM casting, comprising: providing a metal and a
vertical die casting means, heating the metal to a chosen
temperature, cooling the metal for a determined period of time to
form a semi-solid metal, wherein the time can be zero; and casting
the semi-solid metal.
12. A means for SSM casting according to claim 11, wherein the
metal is an Al--Si alloy.
13. An A means for SSM casting according to claim 11, wherein the
vertical die casting means is an indexing type vertical die casting
means.
14. A means for SSM casting according to claim 13, wherein the
vertical die casting means is a 1000 Ton Shuttle Machine.
15. A means for SSM casting according to claim 11, wherein Al--Si
alloy is a hypereutectic Al--Si alloy comprising more than about
11.7 weight percent Si in Al.
16. A means for SSM casting according to claim 11, wherein Al--Si
alloy is a hypoeutectic Al--Si alloy comprising less than about
11.7 weight percent Si in Al.
17. A means for SSM casting according to claim 11, wherein Al--Si
alloy is a 380 alloy.
18. A means for SSM casting according to claim 11, wherein the
vertical die casting machine is an indexing type vertical die
casting machine comprising a shot sleeve that indexes between a
pour station and a transfer station requiring an indexing time.
19. A means for SSM casting according to claim 11, wherein the
temperature of metal is chosen such that the metal will form a
semi-solid metal as it cools from indexing between the pour station
to the transfer station.
20. A means for SSM casting according to claim 11, wherein the
chosen temperature is above the liquidus temperature of the metal.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to the field of
processes for casting metal alloys. More particularly, the present
invention relates to a process and apparatus for semi-solid metal
casting of metal alloys.
BACKGROUND OF THE INVENTION
[0002] Regular casting methods such as conventional die casting,
gravity permanent mold casting, and squeeze casting have long been
used for metals and their alloys. However, these current processes
when used to manufacture parts with relatively complex geometries
often yield products with undesirable shrink porosity, which can
adversely impact the quality and integrity of the part. Shrink
porosity defines a condition that arises as a metal part begins to
shrink as it cools and solidifies along the outer surface, leaving
pockets of air (referred to as "voids") trapped in the center of
the part. If the voids are not reconstituted with metal, the cast
part is termed "porous". Particularly in the design of complex
parts, such as, for example, automotive transmission valve bodies
or engine bedplates, the greatest shrink porosity is found in the
thicker areas.
[0003] One method of reducing shrink porosity is to cast semi-solid
metal (SSM) instead of liquid molten metal. SSM casting, which
generally involves low temperature, low velocity, and less
turbulent injection of metal, typically reduces the occurrence of
shrink porosity. Where SSM casting of metal materials has been
involved however, the conventional methods have not been employed
successfully to date. Rheocasting and thixocasting are casting
methods that were developed in an attempt to convert conventional
casting means to SSM casting, but these SSM methods require costly
retrofitting to conventional casting machinery and attempts at
conventional casting of SSM have been unsuccessful.
[0004] Another method to reduce porosity levels is to apply a
direct-feed system. The direct-feed system allows molten metal to
continue to feed directly into the areas of thick geometry during
solidification, thereby filling the air pockets with metal as they
form. In this way, shrink porosity can be significantly reduced in
those areas. Preferably, the direct feed can be localized to
multiple areas within particularly complex parts or as
required.
[0005] Accordingly, it is desirable to provide a method of casting
SSM metals and alloys utilizing conventional and/or rheocasting die
casting devices that can impart desirable mechanical properties. It
is further desirable to provide a process to control the shrink
porosity of cast parts at multiple locations though out a part.
Further still, it is desirable to provide a method of producing
products with metal alloy castings wherein the temperature of the
semi-solid metal slurry can be controlled.
SUMMARY OF THE INVENTION
[0006] The foregoing needs are met, to an extent, by the present
invention, wherein in one embodiment a process and an apparatus is
provided that enables the use of conventional die casting machinery
in SSM casting.
[0007] In accordance with one embodiment of the present invention,
a semi-solid metal casting process is provided, comprising heating
a metal alloy to a chosen temperature, cooling the metal alloy for
a determined period of time to form a semi-solid metal, wherein the
time can be zero, and then casting the semi-solid metal in a
vertical die casting machine. The metal alloys of the invention can
be aluminum-silicon alloys, including hypoeutectic alloys and
hypereutectic alloys. The vertical die casting machines may also be
an indexing-type machine. In embodiments where an indexing type
vertical die casting machine is used, the time required to index
from the pour station to a transfer station may be chosen so that
the metal alloy within will form a semi-solid slurry.
[0008] In accordance with another embodiment of the present
invention, an SSM cast product that is manufactured by casting a
metal alloy in an SSM casting process using a vertical die casting
machine is provided. The vertical die casting machine may
optionally include an indexing feature described herein. The
product may be manufactured by heating a metal alloy to a chosen
temperature and then cooling the metal for a determined period of
time to form a semi-solid metal, wherein the time can be zero, and
then casting the semi-solid metal alloy in the vertical die casting
machine. The metal alloy may be an aluminum-silicon based alloy,
including hypoeutectic and hypereutectic alloys.
[0009] There has thus been outlined, rather broadly, certain
embodiments of the invention in order that the detailed description
thereof herein may be better understood, and in order that the
present contribution to the art may be better appreciated. There
are, of course, additional embodiments of the invention that will
be described below and which will form the subject matter of the
claims appended hereto.
[0010] In this respect, before explaining at least one embodiment
of the invention in detail, it is to be understood that the
invention is not limited in its application to the details of
construction and to the arrangements of the components set forth in
the following description or illustrated in the drawings. The
invention is capable of embodiments in addition to those described
and of being practiced and carried out in various ways. Also, it is
to be understood that the phraseology and terminology employed
herein, as well as the abstract, are for the purpose of description
and should not be regarded as limiting.
[0011] As such, those skilled in the art will appreciate that the
conception upon which this disclosure is based may readily be
utilized as a basis for the designing of other structures, methods
and systems for carrying out the several purposes of the present
invention. It is important, therefore, that the claims be regarded
as including such equivalent constructions insofar as they do not
depart from the spirit and scope of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 illustrates a cross section of an exemplary vertical
die casting press of a type suitable for carrying out the functions
of an embodiment of the invention.
[0013] FIG. 2 is a perspective view of an exemplary vertical die
casting press of a type suitable for carrying out the functions of
an embodiment of the invention.
[0014] FIG. 3 is a front view of a mold with multiple "gates" in
one embodiment.
DETAILED DESCRIPTION
[0015] The invention will now be described with reference to the
drawing figures, in which like reference numerals refer to like
parts throughout. An embodiment in accordance with the present
invention provides a method of SSM casting without the need for
retrofitting of conventional casting equipment. Moreover, other
embodiments of the instant invention provide a direct-feed
semi-solid casting process.
[0016] In one embodiment, vertical die casting machines or presses
of the general type disclosed in U.S. Pat. Nos. 5,660,233 and
5,429,175, assigned to and commercially available from THT Presses,
Inc., Dayton, Ohio, are desirable. The THrr presses such as a 200
Ton Indexing Shot Machine, a 1000 Ton Shuttle Machine or a 100 Ton
Shuttle Machine, in particular, are capable of operating at a
higher speed and with a shorter cycle time than previously known
die casting presses and which, as a result, produce higher quality
parts without porosity. The die casting presses are also simpler
and less expensive in construction, requiring less maintenance and
therefore more convenient to service.
[0017] One of ordinary skill in the art will appreciate from the
descriptions herein, that some or all of the features of the
presses of the instant invention may differ to some extent from
those specified below depending on the specific press, but that
variations are to be expected and are within the scope and spirit
of the present invention. By way of example, the TTF presses of
this invention may be classified as "indexing-type" or
"shuttle-type." Though the indexing press will be detailed in an
embodiment below, both types of presses may be used in the instant
invention.
[0018] Referring now to FIGS. 1 and 2, in accordance with one
embodiment of the present invention, a vertical die casting press
10 includes a frame 20 having a base 30 supporting a vertical
pedestal 40 or post on which is mounted a rotary indexing table 50.
The table 50 supports a pair of diametrically opposite shot sleeves
60 each of which receives a shot piston 65 connected to a
downwardly projecting piston rod 67. A gate plate 90 extends
horizontally between the side walls of the frame 20 and above the
indexing table 50 for supporting a lower mold 70 section defining a
cavity 61. When the table 50 is indexed in steps of 180 degrees,
the shot sleeves 60 are alternately located at a metal receiving or
pour station 80 and a metal injecting or transfer station 85 under
the gate plate 90. A hydraulic clamping cylinder 100 is supported
by the frame 20 above the transfer station 85 and moves an upper
mold 110 section vertically above the lower mold 70 section.
[0019] A high pressure hydraulic shot cylinder 120 is mounted on
the base under the transfer station 85, and a substantially smaller
hydraulic ejection cylinder 130 is mounted on the base 30 under the
metal receiving or pour station 70. Each of the hydraulic cylinders
120 and 130 has a non-rotating vertical piston rod 121 and 131
which carries a set of spaced coupling plates 140. Each set of
plates 140 defines laterally extending and opposing undercut
grooves for slidably receiving an outwardly projecting bottom
flange on each of the shot piston rods. Thus when the rotary table
50 is indexed, the shot piston rods rotate with the shot sleeves 60
and alternately engage the piston rods of the two fixed hydraulic
shot 120 and ejection cylinders 130.
[0020] The upper platen moves downwardly to close and clamp the
upper mold 110 against the lower mold 70 or against a cavity
defining part P confined between the upper and lower molds 110 and
70. The hydraulic shot cylinder 120 is actuated for transferring
the molten metal from each shot cylinder 60 upwardly into the
cavity 61 defined by the clamped mold sections 70 and 110. The
cavity 61 is evacuated, and the shot piston 65 is forced upwardly
to inject the molten metal into the mold cavity or cavities. The
molds 70 and 110 and the shot piston 65 are then cooled, optionally
by circulating water through passages within the molds and shot
piston, to solidify the die cast material. The shot cylinder 120
then retracts the connected sprues 150 or biscuit downwardly into
the shot sleeve 60 after the metal has partially solidified within
the gate plate 90. After the table 50 is indexed 180 degrees, the
smaller hydraulic ejection cylinder 130 is actuated for ejecting
the biscuit upwardly to the top of the indexing table 50 where the
biscuit is discharged. The cycle is then repeated for die casting
another part or set of parts.
[0021] In operation of the vertical die casting machine or press
described above in connection with FIG. 1, a predetermined charge
or shot of molten metal is poured into the shot sleeve 60 in the
pour station 80. The shot sleeves 60 can be equipped with heaters
and temperature sensors to heat and or cool the metal as is
desirable at any time, including the period while table 50 indexes
180 degrees. The lateral transfer of the molten metal and the
upward injection of the metal into the mold cavities is also
effective to degas the molten metal, thereby minimizing porosity of
the solidified die cast parts. Preferably, a light suction is
applied to the cavities 108 and runner 202 and the injecting
chamber 146 to remove air from the chamber and to remove the gas
separated from the molten metal within the shot cylinder.
[0022] It has now been found that the above described press can
also be used for SSM casting. The use of metal slurry metal over
molten metal reduces fluid turbulence when injected into the die,
which also reduces the amount of air that may be trapped in the
final part. Less air in the final part lends greater mechanical
integrity and allows cast products to be heat treated. In addition,
metals that are SSM casting requires less heat thereby reducing
cost and improving longevity of the molds and dies.
[0023] Without being limited to or bound by theory, the
microstructure of SSM cast products can determine the mechanical
properties of the product. Moreover, it is understood by those of
ordinary skill in the art that the microstructure can be
manipulated prior to casting. One way to manipulate the final
microscructure of an SSM cast part is to control, thereby reduce,
the time the metal remains in the SSM range. The presses described
above afford such an opportunity. Specifically, the indexing time
(i.e., the delay between indexing between the pour station 80 and
transfer station 85) can be used to control the time the molten
metal is cooled in the shot sleeve to reach the SSM range. That is,
the amount of time the metal spends in the shot sleeve before it is
injected into the molds can be regulated or optimized for a
desirable microstructure. Alternatively, molten metal at a
predetermined temperature may be poured into the shot sleeve of
shuttle presses, i.e. presses that lack the indexing feature.
[0024] Many metals and alloys known in the art can be used for SSM
casting and can be employed with the instant invention. In some
embodiments aluminum-silicon alloys can be used. By definition,
aluminum alloys with up to but less than about 11.7 weight percent
Si are defined "hypoeutectic", whereas those with greater than
about 11.7 weight percent Si are defined "hypereutectic". In all
instances, the term "about" has been incorporated in this
disclosure to account for the inherent inaccuracies associated with
measuring chemical weights and measurements known and present in
the art. In yet other embodiments, aluminum-silicon copper alloys
and/or aluminum-copper alloys may be used with the present
invention.
[0025] Preferably, the metal is be cast is heated in a range from
about 10.degree. C. to about 15.degree. C. above the liquidus
temperature (i.e., the semi-solid temperature). For Al--Si alloys
this generally ranges from about 585.degree. C. to about
590.degree. C. The melt temperature is then allowed to cool to form
a semi-solid slurry before it is finally cast.
[0026] In one embodiment, a 380 alloy, (Al--Si--Cu alloy commonly
used in the art) is heated to 590 to 595.degree. C. Once heated to
the desired temperature, the metal is then transferred to the shot
sleeve 60 in the pour station 85. The metal is then indexed to the
transfer station 80, taking about 2 seconds. During that period,
the metal is cooled to between 585.degree. C. and 590.degree. C.
before being cast.
[0027] The optimal transfer time from the pour station 80 to
transfer station 85 can be experimentally determined and will vary
depending on the metal or alloy being cast. Generally, for Al--Si
alloys, a transfer time in the ranging from about 0.5 seconds to
about 5 seconds is preferred. In other embodiments, the time may
range from about 1 seconds to about 30 seconds.
[0028] FIG. 3 exemplifies a gate plate that may be used in
accordance with the invention. As mentioned above, gated plates
allow for direct feed of metal to multiple locations within a part
simultaneously. Especially true in complex parts, direct feed
enables metal to be selectively injected into specific locations
within a part as the part cools. As a part cools and contracts
along the edges, voids emerge within the center or thicker portions
of a cast. With gated plates, however, the potential voids may be
continually supplied with metal so as to reduce the likelihood of
their emergence and thereby reduce porosity.
[0029] The present invention may be applied to cast a variety of
parts known in the art and all such applications are within the
scope of the present invention. In a preferred embodiment of the
present invention, the die cast process described herein is used to
cast parts with relatively complex geometries. Such parts may
include automotive parts, for example, suspension components
including knuckles and control arms, bed plates, swashplates, air
conditioning compressor pistons, engine valve bodies and pump
housings.
[0030] The present invention may be preferable suited for complex
parts in that the presses described herein have a smaller ratio of
upper die to lower die parting position than found in conventional
die casting presses which can reduce the gas content in the part.
Also, where in conventional die casting processes the dwell time is
controlled by biscuit thickness, the ingate controls dwell time in
the present invention. The smaller ingates have smaller volumes to
be cooled, and thereby solidification time is reduced. The casting
process described herein also requires less clamping force than
required by other casting processes such as with high pressure die
casting and/or squeeze casting. Moreover, the present invention
employs a large number of cavities which allows for more parts to
be produced per given amount of time.
[0031] The many features and advantages of the invention are
apparent from the detailed specification, and thus, it is intended
by the appended claims to cover all such features and advantages of
the invention which fall within the true spirit and scope of the
invention. Further, since numerous modifications and variations
will readily occur to those skilled in the art, it is not desired
to limit the invention to the exact construction and operation
illustrated and described, and accordingly, all suitable
modifications and equivalents may be resorted to, falling within
the scope of the invention.
* * * * *