U.S. patent application number 11/311433 was filed with the patent office on 2007-06-21 for die casting in investment mold.
This patent application is currently assigned to Howmet Corporation. Invention is credited to Leonard L. Ervin, David S. Lee, Russell G. Vogt, George W. Wolter.
Application Number | 20070137827 11/311433 |
Document ID | / |
Family ID | 37807905 |
Filed Date | 2007-06-21 |
United States Patent
Application |
20070137827 |
Kind Code |
A1 |
Vogt; Russell G. ; et
al. |
June 21, 2007 |
Die casting in investment mold
Abstract
Method and apparatus for casting a metallic material involves
the steps of providing a non-metallic mold in a mold-receiving
chamber disposed in at least one of relatively movable first and
second members, communicating a mold cavity in the mold to a gating
passage disposed in at least one of the first and second metallic
members, communicating the gating passage to a shot sleeve, and
flowing metallic material from the shot sleeve to the gating
passage and into the non-metallic mold.
Inventors: |
Vogt; Russell G.; (Yorktown,
VA) ; Lee; David S.; (Muskegon, MI) ; Wolter;
George W.; (Whitehall, MI) ; Ervin; Leonard L.;
(Whitehall, MI) |
Correspondence
Address: |
Mr. Edward J. Timmer
P.O. Box 770
Richland
MI
49083-0770
US
|
Assignee: |
Howmet Corporation
|
Family ID: |
37807905 |
Appl. No.: |
11/311433 |
Filed: |
December 19, 2005 |
Current U.S.
Class: |
164/113 ;
164/312 |
Current CPC
Class: |
B22D 21/005 20130101;
B22D 17/2209 20130101; B22D 17/203 20130101; B22C 9/082 20130101;
B22D 17/10 20130101; B22C 9/28 20130101; B22C 9/04 20130101 |
Class at
Publication: |
164/113 ;
164/312 |
International
Class: |
B22D 17/08 20060101
B22D017/08 |
Claims
1. A method of casting a metallic material, comprising providing a
non-metallic mold in a mold-receiving chamber disposed in at least
one of relatively movable first and second members, communicating a
mold cavity in the mold to a gating passage disposed in at least
one of the first and second metallic members, communicating the
gating passage to a shot sleeve, and flowing metallic material
under pressure from the shot sleeve to the gating passage and into
the non-metallic mold.
2. The method of claim 1 including holding the mold in position in
the chamber to communicate to the gating passage.
3. The method of claim 2 wherein the mold is held by a plate
received in a groove of the mold.
4. The method of claim 1 including supporting the mold in position
in the chamber against force of the metallic material introduced
into the mold via the gating passage.
5. The method of claim 4 wherein the mold is abutted at the closed
end of the mold by a support plate.
6. The method of claim 5 wherein the support plate is pressed
toward the closed end of the mold.
7. The method of claim 1 wherein the metallic material is
introduced into the mold which is unheated prior to being disposed
in the chamber.
8. The method of claim 1 including disposing a ceramic investment
shell mold in the chamber.
9. The method of claim 4 wherein the mold cavity includes a cavity
region having a thickness of 0.35 inch or less.
10. The method of claim 1 wherein the mold cavity is configured as
a turbocharger wheel-shaped cavity having multiple vane-forming
cavity regions of said thickness spaced apart on a hub-forming
cavity region.
11. The method of claim 1 wherein the mold cavity is configured as
an airfoil-forming region of said thickness.
12. The method of claim 1 wherein the first and second members are
relatively movable by being mounted on respective first and second
platens of a die casting machine.
13. The method of claim 1 wherein the mold includes a pour cup
communicated to the mold cavity by a sprue passage, said pour cup
being communicated to the gating passage.
14. The method of claim 1 including evacuating the mold cavity to
subambient pressure.
15. The method of claim 14 evacuating the mold cavity via the shot
sleeve communicated thereto.
16. The method of claim 15 wherein the subambient pressure is about
100 microns or less.
17. The method of claim 1 including melting the metallic material
in a vacuum chamber communicated to the shot sleeve.
18. The method of claim 1 wherein the metallic material is selected
from the group consisting of titanium alloy, titanium aluminide,
nickel base superalloy, and cobalt base superalloy.
19. The method of claim 1 wherein a plunger in the shot sleeve is
moved in response to hydraulic pressure to flow the metallic
material and wherein the hydraulic pressure is vented to a sump a
preselected distance before the end of the injection stoke of the
plunger.
20. Casting apparatus, comprising: a) relatively movable first and
second members at least one of which includes a mold-receiving
chamber and at least one of which includes a gating passage for
receiving metallic material from a shot sleeve, b) a non-metallic
mold disposed in the chamber in a position to receive the metallic
material from the gating passage, and c) means communicated to the
shot sleeve for flowing metallic material under pressure through
the gating passage into the non-metallic mold.
21. The apparatus of claim 20 wherein the mold comprises a ceramic
investment shell mold.
22. The apparatus of claim 20 wherein the first and second members
are connected to respective first and second platens of a die
casting machine, said first and second platens being relatively
movable.
23. The apparatus of claim 20 wherein the means for flowing
comprises a plunger in the shot sleeve.
24. The apparatus of claim 23 wherein the plunger is moved in
response to hydraulic pressure and a hydraulic pressure control
system includes means for venting hydraulic pressure to a sump at a
preselected distance before the end of the injection stoke of the
plunger.
25. The apparatus of claim 20 includes a mold-holding member in the
chamber for holding the non-metallic mold in said position.
26. The apparatus of claim 24 wherein the mold-holding member
comprises a plate received in a groove on the mold.
27. The apparatus of claim 20 including a mold-supporting member in
the chamber for supporting the mold against force of the metallic
material introduced into the mold via the gating passage.
28. The apparatus of claim 27 wherein the mold-supporting member
comprises a support plate abutting a closed end of the mold.
29. The apparatus of claim 28 wherein the support member is pressed
toward the closed end of the mold.
30. The apparatus of claim 20 wherein the mold includes at least
one mold cavity that includes a cavity region having a thickness of
0.100 inch or less.
31. The apparatus of claim 30 wherein said at least one mold cavity
is configured as a turbocharger wheel-shaped cavity having multiple
vane-forming cavity regions of said thickness spaced apart on a
hub-forming cavity region.
32. The apparatus of claim 30 wherein said at least one more mold
cavity is configured as an airfoil-forming region of said
thickness.
33. The apparatus of claim 20 wherein the mold includes a pour cup
communicated to one or more mold cavities by a sprue passage, said
pour cup being communicated to the gating passage.
34. The apparatus of claim 20 including means for evacuating the
interior of the mold to subambient pressure.
35. The apparatus of claim 34 wherein said means comprises the shot
sleeve which is under subambient pressure and communicated to the
mold interior.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to casting of metals and
alloys and, more particularly, to casting of metals, alloys, and
intermetallics under pressure in a non-metallic investment
mold.
BACKGROUND OF THE INVENTION
[0002] Titanium based alloys (e.g. Ti-6Al-4V) and intermetallics
(e.g. TiAl) are used as cast components in the aerospace industry.
Many such cast components are made by the well known gravity
investment casting process wherein an appropriate melt is cast into
a preheated ceramic investment shell mold formed by the lost wax
process.
[0003] Although commonly used, investment casting of complex shaped
components of such titanium based materials can be characterized by
relatively high costs and low yields. Low casting yields are
attributable to several factors, in particular inadequate filling
of certain mold cavity regions such as especially thin wall mold
cavity regions. For example, filling of thin wall mold cavity
regions having a thickness of less that 0.050-0.060 inch with a
titanium alloy or titanium aluminide melt is difficult due to melt
fluidity, low superheat, and out-gassing problems.
[0004] In attempts to improve filling of the ceramic investment
shell mold, high mold preheat temperatures (e.g. above 700 degrees
F.) have been tried. However, such an approach is disadvantageous
in that the molten titanium alloy or titanium aluminide can react
with the mold at such high temperatures to form deleterious phases
on the surface of the castings produced in such shell molds. This
phase must then be removed by chemical treatment. Moreover, it is
oftentimes necessary to increase the thickness of one or more thin
wall mold cavity regions when the mold is being made in order to
subsequently achieve satisfactory mold filling during casting. The
result is an oversize casting that must then be mechanically and/or
chemically treated to reduce cast dimensions to print dimensions
for the particular component involved.
[0005] U.S. Pat. No. 6,070,643 describes vacuum die casting of
oxygen reactive alloys such as titanium alloys, nickel based
superalloys, and cobalt superalloys in metal molds. Drawbacks of
using metal die casting molds include the high cost of the metal
dies and the presence of die parting line between the metal dies,
which parting line sometimes limits the complexity of the die
cavity and thus the casting that can be die cast. A further
drawback of using metal dies when die casting titanium aluminide
material is the generation of cracking in the casting as a result
of rapid solidification of the melt in the metal mold.
[0006] Permanent mold casting of reactive metals and alloys such as
titanium and titanium and nickel based alloys using permanent,
reusable, multi-part metal molds based on iron and titanium is
described in Colvin U.S. Pat. No. 5,287,910. Casting of aluminum,
copper, and iron based castings using permanent metal molds is
described in U.S. Pat. No. 5,119,865.
[0007] An object of the present invention to provide method and
apparatus for die casting metals and alloys, especially titanium
alloys, titanium aluminides and others, under pressure in an
investment mold in a manner that overcomes the above-discussed
disadvantages and drawbacks.
SUMMARY OF THE INVENTION
[0008] The present invention provides method and apparatus for
casting a metallic material involving the steps of providing a
non-metallic mold in a mold-receiving chamber disposed in at least
one of relatively movable first and second members, communicating a
mold cavity in the mold to a gating passage disposed in at least
one of the first and second metallic members, communicating the
gating passage to a shot sleeve, and flowing metallic material
under pressure from the shot sleeve to the gating passage and into
the non-metallic mold.
[0009] In an illustrative embodiment of the invention, the first
and second members are relatively movable by being mounted on
respective first and second platens of a die casting machine.
[0010] In another illustrative embodiment of the invention, the
metallic material is flowed by movement of a plunger in the shot
sleeve. The plunger is moved in response to hydraulic pressure to
flow the metallic material, and the hydraulic pressure is vented to
a sump a preselected distance before the end of the injection stoke
of the plunger.
[0011] Casting apparatus pursuant to another embodiment of the
invention comprises relatively movable first and second metallic
members at least one of which includes a mold-receiving chamber and
at least one of which includes a gating passage for receiving
metallic material from a shot sleeve, a non-metallic mold disposed
in the chamber in a position to communicate to the gating passage,
and means communicated to the shot sleeve for flowing the metallic
material through the gating passage into the non-metallic mold.
[0012] In a further illustrative embodiment of the invention, a
ceramic investment shell mold is held in position in the chamber to
communicate to the gating passage, while the mold is supported in
the chamber against force of molten metallic material introduced
into the mold via the gating passage. For example, a support plate
abuts the closed end of the mold and is biased thereagainst. The
mold can include an open pour cup or other feature that
communicates to the gating passage. The mold also typically
includes a sprue passage between the pour cup and the one or more
mold cavities to convey molten metallic material thereto. The mold
cavities of the shell mold can be evacuated to subambient pressure,
such as less than 100 microns, to die cast a reactive metal or
alloy such as a titanium alloy, titanium aluminide, nickel base
superalloy, cobalt base superalloy, and others. The mold can
include a pour cup or other feature that communicates to the gating
passage. The mold also typically includes a sprue passage between
the pour cup and the one or more mold cavities to convey molten
metallic material thereto.
[0013] The invention is useful in casting molten metals or alloys,
such as titanium alloys and titanium aluminide alloys, that
otherwise have difficulty in filling thin wall mold cavity regions
using conventional investment casting processes. For example, the
invention is useful in casting titanium alloy or titanium aluminide
turbocharger compressor and turbine wheels having multiple airfoil
vanes of thin wall thickness (e.g. 0.025 to 0.200 inch wall
thickness) disposed about a hub. The invention likewise is useful
in casting compressor blades and turbine blades having thin-wall
airfoils (e.g. 0.025 to 0.35 inch wall thickness.)
[0014] Moreover, the invention can be used to cast complex
investment molds having backlocks, undercuts, or other features
that can not be cast using metal dies. Practice of the invention
permits complex mold geometries to be cast, without the need for
significant chemical and/or mechanical rework of the die cast
component.
[0015] Further details and advantages of the present invention will
become more readily apparent from the following detailed
description taken with the following drawings.
DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a schematic side elevation of a casting machine
pursuant to an embodiment of the invention for practicing a method
of the present invention with the vacuum chamber shown broken
away.
[0017] FIG. 2 is a perspective, exploded view of one of a pair of
mold-receiving members connected to the platens of a die casting
machine.
[0018] FIG. 3 is a perspective, exploded view of the pair of
mold-receiving members.
[0019] FIG. 4 is a perspective view of the investment shell
mold.
[0020] FIG. 5 is a diagram of the hydraulic fluid system for the
plunger.
DETAILED DESCRIPTION OF THE INVENTION
[0021] Referring to FIG. 1, a die casting machine 10 adapted to
practice an embodiment of the present invention is shown. For
purposes of illustration and not limitation, the casting machine is
shown adapted to cast a molten metallic material, which includes
metals, alloys, intermetallics, and thixotropic metallic material,
under hydraulic pressure into one or more evacuated non-metallic
investment shell molds 31 (four molds shown), the number of molds
31 being cast being selected as desired for a particular casting
job. Such metallic materials for casting include, but are not
limited to, titanium alloys, titanium aluminide alloys, nickel base
superalloys, cobalt base superalloys and other materials that have
difficulty in filling certain thin or narrow regions of an
investment mold cavity and/or are reactive with oxygen.
[0022] An embodiment of the invention will be described below with
respect to vacuum casting of titanium alloy turbocharger wheels
having multiple airfoil vanes of thin wall thickness disposed about
a hub. Each non-metallic investment shell mold 31 includes a mold
cavity-forming region 36 that defines a respective turbocharger
wheel shape therein. Although only one mold cavity-forming region
36 is shown, each mold 31 can include one or more mold
cavity-forming regions 36.
[0023] The die casting machine is shown comprising a base 11 which
includes a reservoir (not shown) therein for hydraulic fluid that
is used by hydraulic actuator 12 to move the movable die platen 16
relative to the fixed (stationary) die platen 14 to open and close
the die platens 14, 16. The platen 16 is disposed for movement on
stationary guide rods or bushings 18. A die platen clamping linkage
mechanism (not shown) is connected to the movable die platen 16 in
conventional manner not considered part of the present invention.
The die casting apparatus also comprises a tubular, horizontal shot
sleeve 24 having intermediate section that is received in the
stationary die platen 14 and a mold-receiving member or plate 30
fastened to the platen extension 14a by bolts, clamps, and other
fastening means. The shot sleeve 24 extends into a vacuum melting
chamber 40 where the metal or alloy to be die cast is melted under
high vacuum conditions, such as less than 100 microns, in the event
an oxygen reactive metal or alloy, such as titanium alloy, titanium
aluminide alloy, superalloy, etc., is to be cast.
[0024] The vacuum chamber 40 is defined by a vacuum housing wall 42
that extends about and encompasses or surrounds the charging end
section 24a of the shot sleeve 24 and the plunger hydraulic
actuator 25'' having ram 25a''. The chamber wall 42 is vacuum tight
sealed about the stationary, horizontal shot sleeve and plunger
support member 44. The vacuum chamber 40 is evacuated by a
conventional vacuum pump P connected to the chamber 40. The base 11
and the vacuum housing wall 42 rest on a concrete floor or other
suitable support.
[0025] A cylindrical plunger 27 is disposed in the cylindrical bore
of the shot sleeve 24 for movement by ram 25a'' between a start
injection position located to the left of a melt entry or inlet 50
in FIG. 1 and a finish injection position proximate mold-receiving
member or plate 30. The melt inlet 50 comprises a melt-receiving
vessel 52 mounted on the shot sleeve 24. The melt-receiving vessel
52 is disposed beneath a melting crucible 54 to receive a charge of
molten metal or alloy therefrom for die casting. The invention is
not limited to a hydraulic plunger as a means for introducing the
molten metallic material under superambient pressure in the mold
31. For example, superambient gas pressure may be applied at the
end of the shot sleeve with or without the plunger present for
introducing the molten metallic material under pressure into the
mold 31.
[0026] The melting crucible 54 may be an induction skull crucible
comprising copper segments in which a charge of solid metal or
alloy to be die cast is melted. The charge of solid metal or alloy
can be positioned in the crucible 54 before a vacuum is established
in chamber 40 and melted by energization of induction coils 56
after the vacuum is established. Alternately, the solid metal or
alloy charge can be charged into the crucible 54 in evacuated
chamber 40 via a vacuum port (not shown) and melted by energization
of induction coils 56. Known ceramic or refractory lined crucibles
also can be used in practicing the present invention. Any melting
method such as arc melting, electron beam melting, and others may
be employed in practice of the invention. The crucible 54 can be
tilted to pour the molten metal or alloy charge into the
melt-receiving vessel 52, which is communicated to the shot sleeve
24 via an opening 58 in the shot sleeve wall. The molten metal or
alloy charge is introduced through opening 58 into the shot sleeve
24 in front of the plunger 27.
[0027] The plunger 27 is moved from the start injection position to
the finish injection position by conventional hydraulic actuator
25''. Typical radial clearances between the shot sleeve 24 and the
plunger 27 are in the range of 0.001 to 0.008 inch.
[0028] A die casting machine having the features described above is
disclosed in U.S. Pat. No. 6,070,643 of common assignee herewith,
the teachings of which patent are incorporated herein by
reference.
[0029] Pursuant to an embodiment of the invention, the die casting
machine 10 is modified or adapted to cast a molten metallic
material under hydraulic pressure into one or more evacuated
non-metallic (e.g. ceramic) investment shell molds 31, which can be
made by the well known lost wax process. Such an investment shell
mold 31 is made by repeatedly dipping one or more fugitive patterns
(such as wax or plastic patterns) of the component to be cast
connected as part of a pattern assembly in a ceramic flour slurry,
draining excess ceramic slurry, and applying a coarse ceramic
stucco on the wet slurry followed by air or oven drying until a
shell mold of desired wall thickness is built up on the patterns.
The one or more patterns then are selectively removed by steam
autoclaving, flash dewaxing, and other conventional pattern removal
techniques, leaving an empty ceramic shell mold with one or more
cavities where the one or more patterns formerly resided. The
ceramic shell mold then is fired at elevated temperature to develop
adequate mold strength for casting. Manufacture of ceramic shell
molds using the lost wax process is well known and described in
U.S. Pat. Nos. 4,966,225; 5,983,982; 6,749,006 and many others. For
purposes of illustration and not limitation, the invention can be
practiced using conventional colloidal silica-bonded or sodium
silicate-bonded investment shell molds, although other investment
shell molds can be used.
[0030] The particular ceramic flours and stucco materials from
which the investment molds 31 are made depends on the metal or
alloy to be die cast in the mold as well as the parameters of
casting, such a melt superheat, mold preheat temperature and
others.
[0031] Referring to FIGS. 1-4, ceramic investment shell molds 31
for casting a turbocharger wheel are shown. Each shell mold 31
includes a pour cup 33, a sprue 32, and a turbocharger wheel-shaped
mold cavity-forming region 36. Molten metal or alloy flows through
the pour cup 33 and through a passage 32a in the sprue 32 and into
the mold cavity-forming region 36. The turbocharger wheel-shaped
mold cavity-forming region 36 has an airfoil or vane-forming cavity
regions 36v of small or narrow dimension (thickness) spaced apart
on a hub-forming cavity region 36h. The airfoil or vane-forming
regions 36v have a small internal thickness typically between 0.025
to 0.100 inch to form the thin walls of the airfoils or vanes on
the hub of the die cast turbocharger wheel. Those skilled in the
art will appreciate that the molds 31 can be ganged to provide a
ganged mold such that one pour cup and multiple sprues and runners
can be used to supply molten metallic material to the ganged mold.
The invention is not limited to the type of non-metallic,
refractory or ceramic mold that is used.
[0032] The pour cup 33 forms a first annular lip L1 that is axially
spaced form a second annular lip L2 formed as part of each mold to
define a peripheral positioning groove G about the pour cup. The
invention envisions providing a ceramic core (not shown) in the
turbocharger wheel-shaped mold cavity-forming region 36 of each
mold 31 in order to produce an internal cavity in the cast
turbocharger wheel at selected location(s). The ceramic core can be
configured to produce the desired internal cavity in the cast
turbocharger wheel, or other casting produced in the mold 31. The
invention also envisions providing a reinforcement material or
preform, porous or solid, in the mold cavity 36 so as to be
incorporated in the cast component.
[0033] Referring to FIGS. 1-4, pursuant to one embodiment of the
invention, the mold-receiving member 30 is adapted to mate with a
mold-receiving member 29 to form a chamber C for receiving the
molds 31 and to form a mold gating system 35 therebetween when the
members 29, 30 are abutted at a vertical parting plane. The gating
system is formed by machined, replaceable gating inserts 40, 42
that are received in respective members 29, 30 and that are
coplanar at their outermost surfaces with those of the respective
members 29, 30 in which they are received. When the members 29, 30
are abutted at the parting plane, the gating inserts form a gating
system that comprises runners R that communicate with a common
passage CP that communicates with the end of the shot sleeve 24. A
respective runner R extends from the passage CP to a respective
mold 31. The members 29, 30 as well as inserts 40, 42 typically are
steel or other suitable permanent metal or alloy (metallic
material) and are mounted on or connected to respective platens 14,
16 of the die casting machine.
[0034] An O-ring vacuum seal S1 is provided between the members 29,
30 for establishing a vacuum tight seal therebetween, FIG. 1. The
vacuum seal S1 extends about and surrounds the gating system
35.
[0035] The molds 31 are shown positioned in the chamber C with
their pour cups 33 residing in complementary configured
cylindrical-shaped recesses 41a on a shelf or ledge 41 forming the
bottom wall of the chamber C when the members 29, 30 are abutted at
the parting plane. In FIGS. 2-3, one-half of the ledge or shelf 41
as well as each recess 41a is shown formed on the member 29 and the
other half is formed on member 30. The molds 31 thereby are
positioned vertically inverted such that their rear closed ends 31e
face upwardly.
[0036] The end surface of each pour cup 33 sealingly engages the
shelf or ledge 41 in the recesses 41a to prevent molten material
from leaking out at the interface when the mold is clamped or
pressed on the ledge as described below. A flat seal or gasket
optionally may be used if needed between the pour cup end surface
and the ledge 41 to this end. The molds 31 are positioned relative
to the runners R using a fixed positioning plate 51 having slots
51a formed between fingers 51b. Each mold 31 is inserted in a
respective slot 51a with the adjacent fingers 51b being received in
the mold positioning groove G to this end. One half of each mold
pour 33 thereby is positioned to straddle a respective runner R to
receive molten material therefrom. The positioning plate 51 is
fixedly fastened to one of the members 29, 30 in a horizontal
orientation such that the fingers 51b are received in the facing
other of the members 29, 30 overlying the shelf or ledge of that
member.
[0037] When so positioned, the pour cup 33 and the sprue passage
32a of each mold 31 communicates to the shot sleeve 24 via the
gating system for receiving molten metallic material from the shot
sleeve 24 as pushed by the plunger 27. The shot sleeve 24 is
sealingly received in the member 30.
[0038] Each mold 31 is supported in position in the chamber C
against upward force of molten metallic material introduced into
the mold via the gating system. For example, the upwardly facing
closed end of each mold 31 is abutted by a respective support plate
60. Support plates 60 are connected to shafts 62 each of which is
mounted on a hinge 64 such that the plates 60 can be brought into
position to abut the closed ends 31e of the molds after they are
positioned in positioning plate 51. The support plates 60 are
pressed gently toward the closed end of the molds by a main shaft
66 connected to a respective hinge 64 and a pressing device 63,
such as a spring, pneumatic cylinder, hydraulic cylinder, and/or
mechanical clamp, to bias the shafts 66 downwardly.
[0039] The vacuum chamber 40 then is evacuated to a suitable level
for melting the particular charge (e.g. less than 100 microns for
titanium alloys such as Ti-6Al-4V alloy and titanium aluminide such
as TiAl) by vacuum pump P. The investment mold 31 in chamber C is
concurrently evacuated to the same vacuum level through the
connection to the vacuum melting chamber 40 via the shot sleeve 24
and by virtue of being isolated from surrounding ambient air
atmosphere by the vacuum seal S1 between members 29, 30. Optionally
or in addition, the mold 31 can be evacuated using a separate
vacuum conduit or line communicated to the mold interior.
[0040] The investment mold 31 typically is at ambient (room)
temperature when it is placed in the chamber C. Alternately, the
mold 31 can be preheated to a suitable elevated temperature before
being placed in the chamber C. Still further, heaters (not shown)
can be provided in the chamber C to heat or maintain the
temperature of the mold 31.
[0041] The solid charge of the metal or alloy in crucible 54 is
melted by energizing induction coil 56, the melt then is poured
under vacuum into the shot sleeve 24 via the melt inlet 50 with the
plunger 27 initially positioned at the start injection position of
FIG. 1. The molten metal or alloy is poured into the shot sleeve 24
and resides therein for a preselected dwell time to insure that no
molten metal gets behind the plunger 27. The melt can be poured
directly from the crucible 54 via inlet 50 into the shot sleeve 24,
thereby reducing time and metal cooling before injection can
begin.
[0042] The plunger 27 then is advanced in the shot sleeve 24 by
actuator 25'' to inject the molten metal or alloy under hydraulic
pressure through the gating system and into the mold cavity 36 via
the mold pour cup 33 and sprue 32. The molten metal or alloy is
forced at velocities, such as 10-120 inches per second for titanium
alloys and titanium aluminides, down the shot sleeve 24 and into
the evacuated mold cavity 36 in the investment mold 31.
[0043] The plunger 27 is advanced in the shot sleeve 24 using a
hydraulic system shown in FIG. 5 that comprises a supply manifold
70', shot speed manifold 72' for controlling speed of the plunger,
shot return manifold 74' for controlling the return of the plunger
27 to its start injection position, and a pressure dump manifold
76' for dumping or returning fluid pressure to a tank S' when the
plunger 27 is a preselected distance from its final injection
position. The hydraulic system is controlled by a programmable
logic controller (not shown). However, the limit switch 80a, which
is fastened to the fixed support frame for actuator (hydraulic
cylinder) 25'', is directly electrically connected to a relay (not
shown) which in turn is directly electrically connected to the
directional valve 27' of the pressure dump manifold 76' to control
energization of the directional valve 27'. The limit switch 80a is
activated by the switch trip member 80b, which is fastened to the
ram 25a'' and which trips or actuates limit switch 80a shown in
FIG. 1 as it travels with the ram. Before the limit switch 80a is
tripped, the directional valve 27' is deenergized in a manner to
maintain cartridge valve 28' closed (e.g. valve 27' is always in a
deenergized state except when the limit switch 80a is tripped).
When the limit switch 80a is tripped, the directional valve 27' is
energized to vent the normally closed pressure holding valve 28' to
return tank S' via line 81 and allow hydraulic pressure downstream
of the valve 28' to vent through open valve 28' to line 83 to tank
S'. The pressure dump manifold 76' functions to control fluid
pressure on the mold 31 as the molten metallic material is injected
under pressure therein so as to avoid cracking of the mold 31
during casting. The location of the switch 80a and thus the
preselected distance from the final injection position where fluid
pressure is dumped can be determined empirically and adjusted to
avoid mold cracking. Components of the hydraulic system are
described below.
[0044] Components of the hydraulic system of FIG. 6 include: [0045]
1'--manifold; [0046] 2'--SV310-00 115AP directional valve from
Vickers Hydraulics (hereafter Vickers); [0047] 3'--NS 800 S flow
control valve from Parker Hannifin Corp. (hereafter Parker); [0048]
4'--CV5-10-PO5 check valve from Vickers; [0049] 5'--PRV 1-10 SO 24
pressure regulator from Vickers; [0050] 6'--A9K2310D3 KPN 10 gal.
accumulator from Parker; [0051] 7'--A9675 3AA pressure switch from
Barksdale Control Products, Barksdale, Inc.; [0052] 8'--pressure
gage (3000 psi); [0053] 9'--flow control (1/4 inch NPT); [0054]
10'--DG4S4 012A 50 directional valve from Vickers; [0055]
11'--SO63C 10 02 P cover (ports) from Oilgear Company (hereafter
oilgear); [0056] 12'--SEO 63 10 K1 0001.5/3V5 insert (cartridge
valve) from Oilgear; [0057] 13'--CV1 16 D11 2L10 insert (cartridge
valve) from Vickers; [0058] 14'--CVCS 16A S2 10 cover (ports) from
Vickers; [0059] 15'--DG4V 3S 2A MFW B60 directional valve from
Vickers; [0060] 16'--CV1 40D1 2L10 cover (ports) from Vickers;
[0061] 17'--CVCS 40D1 S2 10 cover (ports) from Vickers; [0062]
18'--A7K 1155 K3 K PL 5 gal. accumulator from Parker; [0063]
19'--manifold; [0064] 20'--CVCS 16D1 S2 10 cover (ports) from
Vickers; [0065] 21'--SE6310 K2 000 A1.5/3P insert (cartridge valve)
from Oilgear; [0066] 22'--S063 A10P cover (ports) from Oilgear;
[0067] 23'--TDAD1097E40LAF proportional valve from Parker; [0068]
24'--WO 0179-1 63MM-40MM adapter from Parker; [0069] 25'--15 P1 10
B M 50 MM1 filter from Parker; [0070] 26'--manifold; [0071]
27'--DG4S4 012A B 60 directional valve from Vickers; [0072]
28'--CVC 50 D2 S2 10 insert (cartridge valve) from Vickers; and
[0073] 29'--manifold
[0074] After the molten metal or alloy has been injected, the
members 29, 30 are opened by movement of platen 16 away from platen
14 within a typical time period that can range from 5 to 25 seconds
following injection to provide enough time for the molten metal or
alloy to form at least a solidified surface on the cast
component(s) in the mold cavity 36. The mold 31 then is removed
from the chamber C and transported to a demolding station where the
investment mold 31 is removed from the cast component by
conventional techniques forming no part of the invention. The
metallic material solidified in the mold cavity 36 typically is
substantially solidified by the time the mold 31 is removed from
the chamber C. The casting then can be inspected visually and by
techniques according to customer requirements.
[0075] In die casting titanium alloys, titanium aluminide, nickel
base superalloys, and cobalt based superalloys, the shot sleeve 24
contacting the molten metal or alloy can be made of an iron based
material, such as H-13 tool steel, or a refractory material such as
based on Mo alloy, W alloy, or TZM alloy, ceramic material such as
alumina, or combinations thereof that are compatible with the metal
or alloy being melted and die cast. The forward plunger tip 27a can
comprise a permanent or alternately a disposable tip that is thrown
away after each molten metal or alloy charge is injected in the
investment mold 31. A plunger tip can comprise a copper based alloy
such as a copper-beryllium alloy, or steel, graphite, or other
appropriate material.
[0076] The particular casting parameters employed to die cast a
component will depend upon several factors including mold size,
gating, pour weight, and the fragility of the investment mold to
the melt injection pressures involved. The injection pressure is
selected to retain the investment mold 31 intact (no mold cracking
under pressure) while achieving a satisfactory fill of the mold
cavity regions. The nominal weight of metal or alloy in the
crucible 54 depends on the mold size and the number of components
to be die cast in the mold.
[0077] The following EXAMPLE is offered to further illustrate the
invention without limiting it.
EXAMPLE 1
[0078] Turbocharger wheels have been successfully die cast of
titanium and titanium aluminide (TiAl) alloys in conventional lost
wax investment shell molds 31 by practice of the invention. In
general, the turbocharger wheels were made using casting parameters
in the following ranges: melt injection pressure settings: 400-1800
psi, melt injection velocities (plunger speed): 10-120 in/sec, melt
superheat: 0 to 75 degrees F., mold preheat: room temperature to
600 degrees F., lost wax investment shell mold wall thickness: 0.20
to 1.0 inch, shot sleeve length and diameter: 17.38 inches and 2.80
inches; and limit switch 80a set to dump plunger fluid pressure
when the plunger 27 is about 0.75 inch from its final injection
position.
[0079] Although the mold 31 is illustrated above for making cast
turbocharger wheels, the invention is not so limited and can
practiced to make other components that include, but are not
limited to, internal combustion engine valves, automotive or truck
turbocharger compressor and turbine wheels, compressor and turbine
blades and vanes for gas turbine engines, and medical components
including hip stems, acetabular knees, tibial trays, and spinal
components.
[0080] Further, while the invention has been described in terms of
specific embodiments thereof, it is not intended to be thereto but
rather only to the extent set forth in the following claims.
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