EP1797977A2

EP1797977A2 - Die casting in investment mold

Info

Publication number: EP1797977A2
Application number: EP06125467A
Authority: EP
Inventors: Russell G. Vogt; David S. Lee; John Corrigan; Debra Whitaker; Leonard L. Ervin
Original assignee: Howmet Corp
Current assignee: Howmet Corp
Priority date: 2005-12-19
Filing date: 2006-12-05
Publication date: 2007-06-20
Also published as: JP2007167954A; EP1797977A3

Abstract

Method and apparatus for casting a metallic material involves the steps of disposing an investment mold in a container, holding the container with the mold therein relative to a platen of a casting machine such that one or more mold cavities communicate to a shot sleeve to receive molten metallic material therefrom, introducing the molten metallic material in the shot sleeve under hydraulic pressure into the one or more mold cavities of the mold while the container is held adjacent the platen, and at least partially solidifying the metallic material in the one or more mold cavities.

Description

FIELD OF THE INVENTION

The present invention relates to casting of metals and alloys and, more particularly, to casting of metals and alloys under pressure in a non-metallic investment mold.

BACKGROUND OF THE INVENTION

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.
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.
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.
US Patent 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.
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. Patent 5 287 910 . Casting of aluminum, copper, and iron based castings using permanent metal molds is described in U.S. Patent 5 119 865 .
An object of the present invention to provide method and apparatus for 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

The present invention provides method and apparatus for casting a metallic material involving the steps of disposing a non-metallic mold in a container, holding the container with the mold therein relative to a platen of a casting machine such that one or more mold cavities communicate to a shot sleeve to receive molten metallic material therefrom, flowing the molten metallic material in the shot sleeve under pressure into the one or more mold cavities of the mold while the container is held relative to the platen, and at least partially solidifying the metallic material in the one or more mold cavities.
In a particular embodiment of the invention, a plunger in the shot sleeve is moved in response to hydraulic fluid pressure, which is vented or returned to sump a preselected distance before the plunger reaches an end of its injection stroke so as to reduce prospect of cracking of the non-metallic mold. The container includes refractory particulates about the mold to contain any metallic material leakage from the mold from mold cracking.
In a particular embodiment of the invention, the mold comprises a ceramic investment shell mold that is cast at ambient temperature. The mold cavities of the shell mold can be evacuated to subambient pressure, such as less than 100 microns, to die cast an oxygen reactive metal or alloy such as a titanium alloy, titanium aluminide, nickel base superalloy, cobalt base superalloy, and others. The container includes a chamber in which the investment mold is disposed with refractory particulates disposed about the investment mold. The mold can include a pour cup or other feature that is clamped to an end closure of the container. The mold also typically includes a sprue passage betweeen the pour cup and the one or more mold cavities to convey molten metallic material thereto.
In an illustrative embodiment of the invention, the container with the investment mold therein is held relative to a fixed (non-movable) platen of a die casting machine. In alternative embodiments of the invention, an end of the container can be connected to a base plate itself connected to the fixed platen of the die casting machine, or the container can be formed as part of a base plate connected to the fixed platen of the die casting machine. In still a further alternative embodiment of the invention, a second, movable platen of the die casting machine can be moved to engage an opposite end of the container.
Another embodiment of the present invention provides casting apparatus comprising a container having a non-metallic mold disposed therein, a platen of a casting machine relative to which platen the container is held such that one or more mold cavities communicate to a shot sleeve for receiving metallic material therefrom, and means for introducing molten metallic material in the shot sleeve under pressure into the one or more mold cavities. Refractory particulates are disposed in the container about the non-metallic mold.
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.)
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 high cost of metal dies, and without the need for significant chemical and/or mechanical rework of the die cast component.
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

Figure 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.
Figure 2 is an end elevation of the container taken with the rear closure removed to show the mold therein.
Figure 3 is a perspective view of the investment shell mold.
Figure 4 is a perspective view showing the investment shell mold clamped inside the container against an end closure thereof.
Figure 5 is a perspective view showing the investment shell mold clamped inside the container against an end closure thereof with refractory particulates partially about the mold.
Figure 6 is a diagram of the hydraulic fluid system for the plunger.

DETAILED DESCRIPTION OF THE INVENTION

Referring to Figure 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 may include a thixotropic metallic material, under hydraulic pressure into an evacuated non-metallic investment shell mold 31. 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.
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. The non-metallic investment shell mold 31 includes first and second mold cavity-forming regions 31a, 31b that define a respective turbocharger wheel shape therein.
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 base plate 30 fastened to the platen 14 by conventional bolts and clamps (not shown). 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 die cast.
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 hydraulic actuator 25'' having movable 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.
A cylindrical plunger 27 is disposed in the cylindrical bore of the shot sleeve 24 for movement by movable ram 25a'' between a start injection position located to the left of a melt entry or inlet 50 in Figure 1 and a finish injection position proximate mold base 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 means for introducing the molten metallic material under superambinet pressure into 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.
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.
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.
A die casting machine having the features described above is disclosed in US Patent 6 070 643 of common assignee herewith, the teachings of which patent are incorporated herein by reference.
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 an evacuated non-metallic (e.g. ceramic) investment shell mold 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 US Patent 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.
The particular ceramic flours and stucco materials from which the investment mold 31 is made depends on the metal or alloy to be die cast in the mold as well as the parameters of casting, such as melt superheat, mold preheat temperature and others.
Referring to Figures 1-5, a ceramic investment shell mold 31 for casting two turbocharger wheels is shown. The shell mold 31 includes gating having a pour cup 33, a sprue 32, and first and second runners 34 communicated to two turbocharger wheel-shaped mold cavity-forming sections 31a, 31b. A tubular ceramic sealing collar 38 is sealingly adhered or otherwise fastened about or formed integral with the pour cup 33. The collar 38 sealingly abuts the discharge end of the shot sleeve 24 as shown in Figure

1. Molten metal or alloy flows through the pour cup 33 and through a passage in the sprue 32 and a passage in the respective runners 34 into the mold cavities 36 formed in sections 31a, 31b. The turbocharger wheel-shaped mold cavities 36 have 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 cavity 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.

The invention envisions providing a ceramic core (not shown) in the turbocharger wheel-shaped mold cavity-forming sections 31a, 31b 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 cavities 36 so as to be incorporated in the cast component.
Referring to Figures 1-5, pursuant to one embodiment of the invention, a metal (e.g. steel) gas impermeable container 60 is provided for enclosing the investment mold 31 during the die casting method. The container 60 comprises a tubular body 60a which can be circular, square or any other cross-sectional shape. The container 60 includes a welded-on end closure 62. The container 60 also includes a removable end closure 64 fastened to welded-on annular flange 66 by fasteners 67 in a manner to define an internal container chamber 68 in which the mold 31 is received for casting with the space about the mold 31 filled with refractory particulates 70.
The removable end closure 64 engages an O-ring vacuum seal S1, Figures 2 and 4, for establishing a vacuum tight seal between the end closure 64 and the annular flange 66 of the container 60, Figure 4, when the end closure 64 is fastened on the container using fasteners 67.
An O-ring vacuum seal S2 is provided between the end closure 62 and the base plate 30 for establishing a vacuum tight seal therebetween, Figure 1, when the container 60 is abutted to the base plate 30 as will be described below. The container 60 is not permanently fastened to the base plate 30. The vacuum seals S1, S2 may comprise Viton material or other suitable high temperature sealing material.
The container end closure 62 includes a passage 62p that is adapted to receive the shot sleeve 24, Figure 1, in flow relationship to the pour cup 33 of the mold 31 when the mold 31 is clamped in position in the container 60. In particular, the container 60 includes internally thereof a plurality of elongated clamping fingers 60f that are tightened over the surface of the collar 38, Figures 1-2 and 4-5, to clamp the mold 31 in fixed position against end closure 62 in the chamber 68. The clamp fingers 60f are tightened using fasteners 70' which are threaded into the end closure 62.
Although the mold 31 is shown clamped in the container 60 with its runners 34 oriented generally horizontally, the invention is not so limited since the mold 31 can be oriented in any suitable orientation such as, for example, with the runners 34 oriented generally vertically, generally horizontally or any orientation therebetween.
When so clamped, the passages of pour cup 33 and the sprue 32 of the mold communicate to the shot sleeve 24 for receiving molten metallic material from the shot sleeve 24 as pushed by the plunger 27. The shot sleeve 24 is sealingly received in passage 62p. The collar 38 seals against leakage of molten metallic material from the shot sleeve and the mold pour cup.
The container 60 includes nipples 60n to permit loose (free-flowing) refractory particulates 70, such as alumina or zirconia ceramic back-up sand, about the mold 31 in the container 60 chamber 68. The nipples 60n are closed by a removable vacuum fitting F to prevent the loose particulates 70 from falling out. The container 60 also includes hoist rings 60r to allow use of a conventional overhead hoist to lift and transport the container 60 for mold loading and unloading purposes.
In practicing a method embodiment of the invention, a solid ingot of the metallic material to be die cast is charged into the crucible 54 in the vacuum melting chamber 40. The container 60 with the investment mold 31 therein is held between the base plate 30 and the platen 16 by movement of platen 16 relative to platen 14. The container 60 is filled with the loose back-up particulates 70 via nipples 60n before the container 60 is held in position relative to the fixed platen 14 by movement of the movable platen 16. The loose particulates 70 are introduced manually or by machine through the nipples 60n into the chamber 68 and about the mold 31. 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 container 60 with the investment mold 31 therein held between the base plate 30 and the platen 16 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 container vacuum seals S1, S2.
The investment mold 31 typically is at ambient (room) temperature when it is placed in the container 60. Alternately, the mold 31 can be preheated to a suitable elevated temperature before being placed in the container 60 or while it is in the container using cartridge or resistance heaters.
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 Figure 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.
The plunger 27 then is advanced in the shot sleeve 24 by actuator 25'' to inject the molten metal or alloy under hydraulic pressure into the mold cavities 36 via mold pour cup 33, sprue 32, and runners 34. 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 cavities 36 in the investment mold 31.
The plunger 27 is advanced in the shot sleeve 24 using a hydraulic system shown in Figure 6 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 hyradulic 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 Figure 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 normallly 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.
Components of the hydraulic system of Figure 6 include:

1'- manifold;
2'-SV310-00 115AP directional valve from Vickers Hydraulics (hereafter Vickers);
3'-NS 800 S flow control valve from Parker Hannitin Corp. (hereafter Parker);
4'-CV5-10-PO5 check valve from Vickers;
5'-PRV 1-10 SO 24 pressure regulator from Vickers;
6'-A9K2310D3KPN 10 gal. accumulator from Parker;
7'-A9675 3AA pressure switch from Barksdale Control Products, Barksdale, Inc.;
8'-pressure gage (3000 psi);
9'-flow control (1/4 inch NPT);
10'-DG4S4 012A 50 directional valve from Vickers;
11'-SO63C 10 02 P cover (ports) from Oilgear Company (hereafter Oilgear);
12'-SEO 63 10 K1 0001.5/3V5 insert (cartridge valve) from Oilgear;
13'-CV1 16 D11 2L10 insert (cartridge valve) from Vickers;
14'-CVCS 16A S2 10 cover (ports) from Vickers;
15'-DG4V 3S 2A MFW B60 directional valve from Vickers;
16'-CV1 40D1 2L10 cover (ports) from Vickers;
17'-CVCS 40D1 S2 10 cover (ports) from Vickers;
18'-A7K 1155 K3 K PL 5 gal. accummulator from Parker;
19'- manifold;
20'-CVCS 16D1 S2 10 cover (ports) from Vickers;
21'-SE6310 K2 000 A1.5/3P insert (cartridge valve) from Oilgear;
22'-SO63 A10P cover (ports) from Oilgear;
23'-TDAD1097E40LAF proportional valve from Parker;
24'-WO 0179-1 63MM-40MM adapter from Parker;
25'-15 P1 10 B M 50 MM1 filter from Parker;
26'-manifold;
27'-DG4S4 012A B 60 directional valve from Vickers;
28'-CVC 50 D2 S2 10 insert (cartridge valve) from Vickers; and
29'- manifold

After the molten metal or alloy has been injected, the base plate 30 and platen 16 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 cavities 36. The container 60 then is removed from the base plate 30 and transported by a hoist's engaging hoist rings 60r to an unloading station where the back-up particulates 70 are removed by opening nipples 60n. Then, the end closure 64 is removed so that the melt-filled mold 31 can be unclamped and removed from the container 60. The metallic material solidified in the mold cavities 36 typically is substantially solidified by the time the mold 31 is removed from the container. The investment mold 31 then is removed from the die cast components by conventional techniques forming no part of the invention. The castings then can be inspected visually and by techniques according to customer requirements.
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 or TZM alloy, ceramic material such as alumina, graphite, 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.
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.
The following EXAMPLE is offered to further illustrate the invention without limiting it.

EXAMPLE 1

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: 15 inches and 3 inches; and limit switch 80a set to dump plunger fluid pressure when the plunger 27 is about 0.5 inch from its final injection position.
Although the mold 31 is illustrated above for making cast turbocharger wheels, the invention is not so limited and can be 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.
Moreover, although the invention has been described above with respect to separate container 60 held between base plate 30 and platen 16, the invention is not so limited and envisions in another embodiment attaching the container 60 to the base plate 30 or forming the container 60 as an integral part of base plate 30.
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.

Claims

A method of casting a molten metallic material, comprising
disposing a non-metallic mold in a container, said mold having one or more mold cavities,
holding the container with the mold therein relative to a platen of a casting machine such that the one or more mold cavities communicate to a shot sleeve to receive molten metallic material therefrom,
introducing the molten metallic material in the shot sleeve under pressure into the one or more mold cavities of the mold while the container is held relative to the platen, and
at least partially solidifying the metallic material in the one or more mold cavities.
The method of claim 1 including providing refractory particulates in the container about the mold.
The method of claim 1 wherein the metallic material is introduced into the mold which is unheated prior to being disposed in the container.
The method of claim 1 including disposing a ceramic investment shell mold in the container.
The method of claim 4 wherein at least one of the one or more mold cavities includes a cavity region having a thickness of 0.35 inch or less.
The method of claim 1 wherein at least one of the mold cavities 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.
The method of claim 1 wherein at least one of the one or more mold cavities is configured as an airfoil-forming region of said thickness.
The method of claim 1 wherein the container comprises a tubular body having end closures, said container having a chamber in which the mold is disposed with refractory particulates about the mold.
The method of claim 8 wherein the mold is clamped to one of the end closures of the container.
The method of claim 9 wherein the mold includes a pour cup communicated to the one or more mold cavities by a sprue passage, said pour cup being clamped against one of the end closures such that the sprue passage communicates to the shot sleeve for receiving the molten metallic material.
The method of claim 1 including connecting the container to a base plate connected to a fixed platen.
The method of claim 1 including holding the container in a position between first and second platens of a die casting machine.
The method of claim 1 including forming the container as part of a base plate connected to the platen.
The method of claim 1 including evacuating the one or more mold cavities to subambient pressure.
The method of claim 13 evacuating the one or more mold cavities via the shot sleeve communicated thereto.
The method of claim 12 wherein the subambient pressure is about 100 microns or less.
The method of claim 1 including melting the metallic material in a vacuum chamber communicated to the shot sleeve.
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.
The method of claim 1 wherein a plunger is moved in the shot sleeve in response to hydraulic pressure and wherein the hydraulic pressure is vented to a sump a preselected distance before the end of the injection stoke of the plunger.
Casting apparatus, comprising:
a) a container having a non-metallic mold disposed therein and having one or more mold cavities,

b) a platen relative to which the container is held such that the one or more mold cavities communicate to a shot sleeve for receiving molten metallic material therefrom,

c) means in the shot sleeve for introducing the metallic material in the shot sleeve under pressure into the one or more mold cavities of the mold while it is disposed in the container relative to the platen.
The apparatus of claim 20 wherein the mold comprises a ceramic investment shell mold.
The apparatus of claim 20 wherein at least one of the one or more mold cavities includes a cavity region having a thickness of 0.100 inch or less.
The apparatus of claim 22 wherein at least one of the one or more mold cavities 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.
The method of claim 22 wherein at least one of the one or more mold cavities is configured as an airfoil-forming region of said thickness.
The apparatus of claim 20 wherein the container comprises a tubular body having end closures, said container having a chamber in which the mold is disposed with refractory particulates about the mold.
The apparatus of claim 25 including a clamping device to clamp the mold to one of the end closures of the container.
The apparatus of claim 26 wherein the mold includes a pour cup communicated to the one or more mold cavities by a sprue passage, said pour cup being clamped against one of the end closures such that the sprue passage communicates external of the can for receiving the metallic material.
The apparatus of claim 20 including means for evacuating the one or more mold cavities to subambient pressure.
The apparatus of claim 29 wherein said means comprises the shot sleeve which is under subambient pressure and communicated to the one or more mold cavities.
The apparatus of claim 29 including vacuum tight seals operably associated with end closures of the container.
The apparatus of claim 20 including a base plate connected to the platen, which is fixed, said container being connected to the base plate.
The apparatus of claim 20 wherein the container is held in a position between first and second platens of a die casting machine.
The apparatus of claim 20 including a plunger that is moved in the shot sleeve in response to hydraulic pressure and wherein the hydraulic pressure is vented to a sump a preselected distance before the end of the injection stoke of the plunger.