WO2011126878A1

WO2011126878A1 - Vacuum die casting apparatus

Info

Publication number: WO2011126878A1
Application number: PCT/US2011/030497
Authority: WO
Inventors: Bruce Declark; Scott Tilma
Original assignee: Superior Press & Automation, Inc.
Priority date: 2010-03-30
Filing date: 2011-03-30
Publication date: 2011-10-13

Abstract

A die casting apparatus having a first die platen (12) and a second die platen (14) movable relative to the first die platen (12), first (16) and second die sections (18) disposed to define a die cavity therebetween, a melting vessel (20) having a heat source (22) for melting metal or alloy in the melting vessel (20), a pour chamber (24), a shot cylinder (26), an ejector mechanism (28), a first rigid clamshell (30) affixed to the first die platen (12) and a second rigid clamshell (32) affixed to the second die platen (14), the first (30) and second rigid clamshells (32) facing each other so that they contact each other to form an airtight seal and to define a vacuum chamber (34) when the second die platen (14) moves toward the first die platen (12) to close the first (16) and second die sections (18), and means (36) to draw a vacuum in the vacuum chamber (34) wherein the first (16) and second die sections (18), the melting vessel (20), the pour chamber (24), the shot cylinder (26), and the ejector mechanism (28) are all in the vacuum chamber (34).

Description

VACUUM DIE CASTING APPARATUS

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application Serial No.

61/318,849, filed March 30, 2010, which is incorporated herein in its entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

[0002] The invention relates generally to a die casting apparatus, which may perform all or a portion of its operation under vacuum.

Description of the Related Art

[0003] Forming products using die casting machines includes injecting a molten metal into a mold and pressurizing the metal until the molten metal is solidified. Before the injection of the molten metal occurs, a vacuum may be drawn in the mold cavity and maintained until the injection cycle is completed. Such a vacuum enables better quality products having less bubbles and micropitting.

[0004] An efficient cost effective vacuum die casting apparatus is needed for forming good quality castings from high-temperature injections of molten materials, such as nickel and titanium based superalloys, under vacuum.

BRIEF SUMMARY OF THE INVENTION

[0005] The invention relates to a die casting apparatus having a first die platen and a second die platen movable relative to the first die platen, first and second die sections, carried by the first and second die platens, respectively, and disposed to define a die cavity therebetween when the first and second die sections are closed, a melting vessel disposed between the first and second die platens, the melting vessel having a heat source for melting metal or alloy in the melting vessel, a pour chamber between the melting vessel and the first die section, a shot cylinder between the first and second die platens and in communication with the pour chamber, and an ejector mechanism between the first and second die platens and in communication with one of the first and second die sections. With a first rigid clamshell affixed to the first die platen and a second rigid clamshell affixed to the second die platen, the first and second rigid clamshells facing each other so that they contact each other to form an airtight seal and to define a vacuum chamber when the second die platen moves toward the first die platen to close the first and second die sections and means to draw a vacuum in the vacuum chamber wherein the first and second die sections, the melting vessel, the pour chamber, the shot cylinder, and the ejector mechanism are all in the vacuum chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] In the drawings:

[0007] FIG. 1 is a schematic side view of a vacuum die casting apparatus, having portions cross-sectioned for illustrative purposes, according to a first embodiment of the invention.

[0008] FIG. 2 is a schematic cross-sectional view of the vacuum die casting apparatus of FIG. 1 taken along the line 2-2 shown in FIG. 1.

DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

[0009] FIG. 1 illustrates a die casting apparatus 10 capable of melting and casting nickel and titanium based superalloys and the like. The die casting apparatus 10 may include a first die platen 12, a second die platen 14, a first die section 16, a second die section 18, a melting vessel 20 having a heat source 22, a pour chamber 24, a shot cylinder 26, a plunger 27, an ejector mechanism 28, a first rigid clamshell 30 and a second rigid clamshell 32 that may contact each other to form an airtight seal to define a vacuum chamber 34, and means for drawing a vacuum in the vacuum chamber 34. As illustrated, the first and second die sections 16, 18, the melting vessel 20, the pour chamber 24, the shot cylinder 26, and the ejector mechanism 28 are all located in the vacuum chamber 34.

[00010] In the illustrated embodiment, the first die platen 12 is fixed and the second die platen 14 is operably coupled to a slide assembly 38 such that the second die platen 14 may move linearly toward and away from the first die platen 12. The slide assembly 38 is not germane to the invention and will not be described further herein. For exemplary purposes only, the second die platen 14 has been illustrated in both a first closed position and a second open position (shown in phantom). The first die platen 12 need not be fixed; it is enough that the first and second die platens move, relatively, toward and away from each other, and the movement need not be linear.

[00011] The first and second die sections 16, 18 may be carried by the first and second die platens 12, 14, respectively. A die cavity (not shown) may be formed at the parting line of the first and second die sections 16, 18 when the first and second die sections 16, 18 are closed. It has been contemplated that the first and second die sections 16, 18 may be removable from the first and second die platens 12, 14 such that alternative die sections may be readily inserted and used in the die casting apparatus 10. In this manner the first and second die sections 16, 18 may be easily repaired or replaced. Further, the ability to readily insert new die sections allows alternative die sections to be used such that alternative castings may be formed.

[00012] It has been contemplated that at least one of the first and second die sections 16, 18 may be designed with one or more auxiliary core slides (not shown), which may be embedded in the body of the die section itself. Such core slides may be activated from within the vacuum chamber 34 thereby minimizing the penetrations required in the walls forming the vacuum chamber 34. Further, it has been contemplated that the die sections may be designed with integral die heaters (not shown) to maintain a die section temperature of 1200 - 1380 °F during the process. Such die heaters may be electric, infrared or hot oil systems.

[00013] A melting system may include the melting vessel 20 having the heat source 22. The melting system may be disposed between the first and second die platens 12, 14 and may thus be located within the vacuum chamber 34. It is contemplated that the vessel 20 may be any suitable crucible in which metals or other substances may be subjected to very high temperatures in order to be melted. The heat source 22 may be any suitable heat source for melting a metal or alloy charge located in the melting vessel 20.

[00014] It has been contemplated that the melting system may utilize a standard induction melt system or that it may utilize an induction skull melting (ISM) system, which is integrated into the vacuum chamber 34. In the instance of the ISM system, the heat source 22 would be a melting coil and power may be supplied from a solid state induction power supply (not shown) specifically designed to supply the correct power and frequency to the melting coil for such an ISM process. The power supply may be taken through the seal of the vacuum chamber 34 by means of a sealed water-cooled coaxial rotary power feed-through or power port assembly to the melting coil of the ISM system. Such an ISM system may allow for a wide variety of alloys to be melted successively in the same melting vessel 20 without chemical cross contamination.

[00015] As illustrated, the melting vessel 20 and pour chamber 24 are disposed near the first die section 16 between the first die platen 12 and the first die section 16. The pour chamber 24 fluidly couples the melting vessel 20 and the first die section 16. A valve assembly 40 may be used to allow for pouring of the molten material directly from the bottom of the melting vessel 22. A heating mechanism 42 may extend along the pour chamber 24 from the bottom of the melting vessel 20 to the shot cylinder 26 to reduce cooling of the alloy during the pour.

[00016] The shot cylinder 26 is also illustrated as being located between the first and second die platens 12, 14. The shot cylinder 26 may be fluidly coupled with the pour chamber 24 and may extend through the first die platen 12 into the first die section 16. A plunger 27 may be operably moveable within the shot cylinder 26 and both the plunger 27 and shot cylinder 26 may be sealed relative to each other and the first die platen 12 by a sealing mechanism 44. The sealing mechanism 44 may be located at the outboard side of the fixed first die platen 12 where the shot cylinder 26 passes through the first die platen 12. The sealing mechanism 44 aids in creating a totally enclosed vacuum chamber 34 such that a vacuum may be drawn during the operation of the die casting apparatus 10.

[00017] The ejector mechanism 28 has been schematically illustrated and may be any suitable mechanism for ejecting formed parts. The ejector mechanism 28 may be located between the first and second die platens 12, 14 and may be operably coupled with one of the first and second die sections 16, 18. More specifically, the ejector mechanism 28 has been illustrated as being mounted between the second die section 18 and the moving second die platen 14. Because the ejector mechanism 28 may be so located, actuation of the ejector mechanism 28 may be from within the vacuum chamber 34 thereby minimizing the penetrations required in the walls forming the vacuum chamber 34. The ejector pins (not shown) of the ejector mechanism 28 may be hydraulically actuated from a cylinder and a right angle actuation mechanism (not shown) embedded in the ejector mechanism 28. Any hydraulic lines necessary for the ejector mechanism 28 may be fed into the vacuum chamber 34 through isolated and sealed bulkhead connections.

[00018] The first rigid clamshell 30 may be affixed to the first die platen 12 and the second rigid clamshell 32 may be affixed to the second die platen 14. The first and second rigid clamshells 30, 32 face each other so that they may contact each other, when the second die platen 14 is in the first closed position, to form an airtight seal and to define the vacuum chamber 34. The first and second rigid clamshells 30, 32 may be formed from any suitable material. By way of a non-limiting example the first and second rigid clamshells 30, 32 may be formed of heavy half-inch stainless steel plate. It is contemplated that first and second rigid clamshells 30, 32 may be reinforced and lined with a thermal barrier to mitigate heat loss and strategically reinforce the first and second rigid clamshells 30, 32 to minimize deformation during operation of the die casting apparatus 10 under vacuum.

[00019] When the first and second rigid clamshells 30, 32 are brought together the entire region between the first and second die platens 12, 14 is enclosed in the first and second rigid clamshells 30, 32, which act to define the vacuum chamber 34. The vacuum chamber 34 thus encompasses the first and second die sections 16, 18, the melting vessel 20, the pour chamber 24, the shot cylinder 26, and the ejector mechanism 28. The first and second rigid clamshells 30, 32 may form a compliant sealing system which compensates for minor changes in die height during operation of the die casting apparatus 10.

[00020] The means 36 for drawing a vacuum in the vacuum chamber 34 may include one or more pumps forming a vacuum system. By way of non-limiting example, an exemplary vacuum system may include a dry roughing vacuum pump 50, which may bring the entire vacuum chamber 34 to a vacuum level of at least 1 x 10^"3 Torr. An exemplary dry vacuum pump may include the GV160 Drystar pump by Edwards, which has a displacement of (341m³hr^_1). It has been contemplated that such a vacuum system may also include a booster pump 52. An exemplary booster pump 52 may include the EH1200C booster pump by Edwards or a high throughput diffusion pump such as the HT16B diffusion pump by Edwards. The pumps of the vacuum system may be fluidly coupled to the vacuum chamber 34 through a vacuum line 54, which may be appropriately sealed.

[00021] As more easily seen with reference to FIG. 2 the shot cylinder 26 may be centered relative to the first die platen 12 and the first die section 16. This location results in a reduced length of the pour chamber 24 required for filling of the shot cylinder 26 and aids in assuring the proper molten metal distribution throughout the die cavity before the solidification process may begin. Additionally, due to the rapid cooling that is experienced with the superheated alloys, locating the melting vessel 20 and pour chamber 24 so close to the first die section 16 minimizes the heat loss during the pour and shot portion of the casting cycle of the die casting apparatus 10.

[00022] A control mechanism (not shown) may include a controller and a user interface and may be included in the die casting apparatus 10. Such a control mechanism may be operably coupled to various components of the die casting apparatus 10 to implement a cycle of operation of the die casting apparatus 10. It is contemplated that the control mechanism may also be used to trouble shoot operation of the die casting apparatus 10. An exemplary die casting machine and control mechanism which may be used as portions of the die casting apparatus 10 include the UBE530is high speed die casting machine with a control mechanism manufactured by

Mitsubishi.

[00023] Prior to operating the die casting apparatus 10 an operator may load an appropriately sized charge 60 into the melt system. The die casting apparatus 10 may include an appropriate access opening, which may allow an operator to load the charge 60 into the melting vessel 20 and may then properly seal such that a vacuum may be drawn within the vacuum chamber 34. The charge may be of a superalloy material although it should be noted that the die casting apparatus 10 is not limited to a particular charge size or particular material. If the melting system is an ISM the vessel may be charged with chunks, plates, turnings, high purity sponge or mixtures of these material forms.

[00024] The operator may then select and initiate a cycle for the die casting apparatus 10. During operation the second die platen 14 moves towards the first die platen 12 into the closed position and the first and second die sections 16 and 18 are closed together to form the die cavity. When the second die platen 14 moves into the closed position the second rigid clam shell 32 affixed thereto also moves toward the first die platen 12 until the first and second rigid clamshells 30 and 32 come in contact with each other and form an airtight seal that encompasses the entire area between the first and second platens 12 and 14 along with the shot cylinder 26.

[00025] The die casting apparatus 10 may then operate such that a vacuum may be drawn in the vacuum chamber 34 by means 36 forming the vacuum system. Specifically the vacuum system may evacuate the vacuum chamber 34 through the vacuum line 54 allowing the interior of the chamber 34 to be pumped down to at least lxl 0^"3 Torr, which is an appropriate vacuum level for the successful melting and casting of superalloys. More specifically, a vacuum may be initially created by the roughing pump 50, which may rapidly evacuate the vacuum chamber 34 to a low vacuum. The operation of the booster pump 52 may then begin, which may bring the total vacuum in the vacuum chamber 34 down to the desired level of at least 1 x 10^"3 Torr.

Alternatively, the booster pump 52 may be started at the same time as the roughing pump 50 to lessen the total evacuation time.

[00026] Drawing such a vacuum in the vacuum chamber 34 evacuates the die cavity between the first and second die sections 16 and 18, the melting vessel 20, the pour chamber 24, the shot cylinder 26, and the ejector mechanism 28. After the appropriate vacuum is pulled the melting system may begin to melt the charge 60. Then the valve assembly 40 may be operated to allow the molten material to enter the pour chamber 24 and the shot cylinder 26. The molten material only partially fills the shot cylinder 26 and the plunger 27 may be advanced to inject the molten material into the die cavity to produce an article having the shape of the cavity. After solidification or curing, the movable second die platen 14 retracts from the stationary first die platen 12 and the ejector mechanism 28 may be operated to remove the manufactured article from the die cavity. After the ejector mechanism 28 may eject the formed parts and the second die platen moves into the open position the operator may remove the formed product and insert another charge such that the process may be repeated.

[00027] The above described die casting apparatus 10 isolates the die, melt system, pour and shot systems, and ejector mechanisms from the surrounding atmosphere. The die casting apparatus 10 allows for the proper melting and casting of nickel and titanium based superalloy materials and the like, which reach high temperatures of approximately 3200 °F when molten, because it is capable of performing the melting of the charge, pouring of the molten material in the shot cylinder, and making the shot into the die to cast the product, all while under vacuum. The die casting apparatus 10 described above requires minimal action from outside of the vacuum chamber 34 and allows full operator access to the die area between casting shots before closing the die casting apparatus 10 and brings the vacuum chamber 34 to operating vacuum levels.

[00028] While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation. For example, a load system may be included in the apparatus, which may allow for integration of an automatic score and break system and automated charge loading. Reasonable variation and modification are possible within the scope of the forgoing disclosure and drawings without departing from the spirit of the invention which is defined in the appended claims.

Claims

CLAIMS What is claimed is:

1. A die casting apparatus comprising:

a first die platen (12) and a second die platen (14) movable relative to the first die platen (12),

first (16) and second die sections (18), carried by the first (12) and second die platens (14), respectively, and disposed to define a die cavity therebetween when the first (16) and second die sections (18) are closed,

a melting vessel (20) disposed between the first (12) and second die platens (14), the melting vessel (20) having a heat source (22) for melting metal or alloy in the melting vessel (20),

a pour chamber (24) between the melting vessel (20) and the first die section (16), a shot cylinder (26) between the first (12) and second die platens (14) and in communication with the pour chamber (24), and

an ejector mechanism (28) between the first (12) and second die platens (14) and in communication with one of the first (16) and second die sections (18), characterized by:

a first rigid clamshell (30) affixed to the first die platen (12) and a second rigid clamshell (32) affixed to the second die platen (14), the first (30) and second rigid clamshells (32) facing each other so that they contact each other to form an airtight seal and to define a vacuum chamber (34) when the second die platen (14) moves toward the first die platen (12) to close the first (16) and second die sections (18), and

means (36) to draw a vacuum in the vacuum chamber (34) wherein the first (16) and second die sections (18), the melting vessel (20), the pour chamber (24), the shot cylinder (26), and the ejector mechanism (28) are all in the vacuum chamber (34).

2. The die casting apparatus of claim 1 wherein the first die platen (12) is fixed and the second die platen (14) moves linearly toward and away from the first die platen (12).

3. The die casting apparatus of any one of claims 1 and 2 wherein the melting vessel (20) and pour chamber (24) are disposed near the first die section (16) between the first die platen (12) and the first die section (16).

4. The die casting apparatus of any one of claims 1-3 wherein the shot cylinder (26) is centered relative to the first die platen (12) and the first die section (16).

5. The die casting apparatus of any one of claims 1-4 wherein the first (16) and second die sections (18) are removable from the respective first (12) and second die platens (14).

6. The die casting apparatus of any one of claims 1-5 wherein the shot cylinder (26) extends through the first die platen (12) and is sealed relative thereto.

7. The die casting apparatus of any one of claims 1-6 wherein the first (30) and second rigid clamshells (32) are formed of stainless steel plate.

8. The die casting apparatus of claim 7 wherein the stainless first (30) and second rigid clamshells (32) are reinforced and lined with a thermal barrier.

9. The die casting apparatus of any one of claims 1-8 wherein the means (36) to draw a vacuum comprises a dry vacuum pump (50) to draw a vacuum to at least 1 x 10^"3 Torr.

10. The die casting apparatus of claim 9 further comprising a booster pump (52).

11. The die casting apparatus of any one of claims 1- 10 wherein the heat source (22) utilizes an induction skull melting system.