DIE CASTING SYSTEM FOR AMORPHOUS ALLOYS

Abstract

Provided is a system and method for metering an amount of molten amorphous alloy into a mold cavity of an injection system. A melting chamber in the system is heated to or above a solidus temperature of the alloy to form a hot chamber. Both the chamber and mold are maintained in an inert atmosphere. The molten alloy is metered from the chamber using a valve system and injected into the mold cavity for molding into a part. A feed tube may extend from the hot chamber to the valve system. The valve system may use gravity or pressure from a pump to meter a volume of molten alloy. In another case, the valve system may include a plunger and a shot sleeve for injecting alloy into the mold. In one embodiment, the plunger itself meters a volume of the alloy. The shot sleeve and plunger may optionally be heated.

Claims

1. A method comprising: providing an amorphous alloy to a melting chamber in an injection system, the injection system also comprising a mold cavity for molding the alloy, and the melting chamber and the mold cavity being maintained in an inert atmosphere; heating the melting chamber to or above a solidus temperature of the amorphous alloy to form a hot chamber; melting the amorphous alloy within the hot chamber to form molten alloy; supplying the molten alloy from the hot chamber to the mold cavity using a valve system; and molding the molten alloy into a molded part using the mold cavity, wherein the valve system is configured to inject a metered amount of the molten alloy into the mold cavity.

2. The method of claim 1, wherein the injection system further comprises a feed tube extending from the hot chamber to the valve system, and wherein the method further comprises supplying the molten alloy from the hot chamber to the feed tube, and supplying the metered amount of the molten alloy from the feed tube into the mold cavity.

3. The method of claim 1, wherein the valve system comprises a plunger housed in a shot sleeve, and wherein the method further comprises supplying molten alloy from the hot chamber to the shot sleeve, and injecting the metered amount of the molten alloy into the mold cavity using the plunger.

4. The method of claim 3, further comprising using the plunger to meter a volume of molten alloy before the injecting into the mold cavity.

5. The method of claim 3, further comprising heating the plunger and the shot sleeve to or above the solidus temperature of the amorphous alloy.

6. The method of claim 3, wherein the plunger comprises a plunger tip, and wherein the method further comprises sealing the molten alloy within the shot sleeve from atmospheric air using the plunger tip.

7. The method of claim 1, further comprising using gravity or pressure from a pump as part of the valve system to meter a volume of molten alloy for injection into the mold cavity.

8. The method of claim 1, wherein the inert atmosphere is provided via a vacuum using a vacuum source or an inert gas using an inert gas source.

9. An injection system comprising: a melting chamber and a mold cavity, the melting chamber being configured to receive an amorphous alloy for melting into molten alloy and configured be heated by a heat source to or above a solidus temperature of the amorphous alloy to form a hot chamber for containing the molten alloy and the mold cavity being configured to mold the molten alloy into a molded part, both the melting chamber and the mold cavity being configured to be maintained in an inert atmosphere; and a valve system between the hot chamber and the mold cavity for supplying the molten alloy from the hot chamber to the mold cavity, wherein the valve system is configured to inject a metered amount of the molten alloy into the mold cavity.

10. The system of claim 9, wherein the injection system further comprises a feed tube extending from the hot chamber to the valve system, and wherein the feed tube is configured to receive the molten alloy from the hot chamber and supply the metered amount of the molten alloy into the mold cavity.

11. The system of claim 9, wherein the valve system comprises a plunger housed in a shot sleeve, and wherein the shot sleeve is configured to receive molten alloy from the hot chamber and the plunger is configured to inject the metered amount of the molten alloy into the mold cavity.

12. The system of claim 11, wherein the shot sleeve is oriented at an acute angle relative to a horizontal axis.

13. The system of claim 11, the plunger is oriented at an acute angle relative to a horizontal axis.

14. The system of claim 9, wherein the valve system is configured to use gravity or pressure from a pump to meter a volume of molten alloy for injection into the mold cavity.

15. The system of claim 9, wherein the inert atmosphere is provided via a vacuum using a vacuum source or an inert gas using an inert gas source.

Description

DEFINITIONS

[0043] Biscuitthe portion of a casting that is where the melt first entered the mold cavity. The biscuit is waste material that is trimmed off the casting after its ejection from the mold cavity. The function of the biscuit is to serve as a sink for shrinkage in the critical areas of the casting, and to serve as a collector for gas bubbles and oxidized particulates that tend to be entrained in the last bit of melt to be injected into the die.

[0044] Feed tubea tube connecting, and feeding melt between, a hot chamber an another element (e.g., a cold shot chamber).

[0045] Diestwo large plates that clamp together and provide the force required to constrain the pressurized melt during injection. Dies generally contain mold cavity inserts. Die casting machines generally have a moving, or ejector, die, and a stationary, or cover, die. The melt is generally first injected through the cover die. Dies must come together (close) to allow the melt to be injected into the mold cavity, and separate (open) to eject the solidified casting.

[0046] Mold cavitythe internal, formed surfaces within the dies that create the exterior surface of the finished casting itself. The mold cavity is generally constructed of mold inserts that are affixed to the dies, as well as various components such as cores and sliders that are used to create certain features.

[0047] Inert gasa gas, or mixture of gases, that has little or no tendency to react chemically with the melt.

[0048] Cold chamber, or cold shot chambera piston-and-cylinder arrangement that injects melt into the mold cavity at high pressure. The cold chamber is generally maintained at a nominal temperature well below that of the melt itself.

[0049] Shot sleevethe cylinder that houses the plunger. A shot sleeve generally has a fill port into which melt is poured. As the melt is rammed into the mold cavity by the plunger, the shot sleeve must withstand significant pressure.

[0050] Plungerthe piston in the shot sleeve.

[0051] Shota specific volume of melt that is injected into the mold cavity to form the casting.

[0052] Waterfallinga condition in which melt flows down a surface, often leaving artifacts such as gas bubbles and solidification-induced particulates and layers in the casting.

[0053] Advancemovement of a plunger, pump, or melt itself that causes melt to progress toward the mold cavity

[0054] Retractmovement of a plunger, pump, or melt itself that causes melt to progress away from the mold cavity

[0055] Meteringpumping, or allow the transfer, of a predetermined volume of melt (a shot) that will completely fill the mold cavity with a calculated, small amount of excess

[0056] Define and give values for solidus and liquidus temperature

System Objectives

[0057] Low melt fluid velocities (no turbulence) [0058] No gas bubble entrapment in casting [0059] No reaction of melt with air or container (hot chamber, pump, etc.) materials [0060] Cosmetic finish on certain surfaces (defect freeno surface or internal defects, generally pure and clean)

[0061] The concepts disclosed herein relate to atmospheric control (including sealing) and mechanical devices necessary to make the systems and methods work. Further aspects include maintaining a melt temperature throughout the cycle, injecting the melt at a (slower) rate to reduce turbulence and flow-related spraying, reducing cycle time (e.g., below 30 seconds), e.g., reducing the time to at or around 15 seconds, thereby increasing efficiency in terms of costs and the die casting process, and isolating melt from the atmosphere during the processes.

[0062] Where the atmosphere in the mold cavity is inert gas, that gas may be used at roughly atmospheric pressure, or its pressure may be increased to provide counter pressurethat is, pressure greater than atmospheric pressure. One benefit of counter pressure is that it may be used to control the properties of the advancing front of melt. The tendency of the melt to wet the mold cavity surface is affected by counter pressure. Another benefit of counter pressure is that to the extent that there are any gas bubbles in the melt, counter pressure will compress those bubbles to a smaller size. Further, flow-induces effect such as cavitation, which can cause damage to the mold cavity surfaces and leave defects in the casting, are suppressed by counter pressure. Each concept disclosure has a table that identifies whether use of counter pressure is a viable option with the given configurations.

[0063] The concepts disclosed herewith include different ways of metering each shot for each casting that is made. In some of them it has a metering pump. In others the plunger tip itself does the metering. In others there's a couple of valves that do the metering. Each describes a way of controlling how much volume is taken out of the hot chamber and put into the shot sleeve for each casting.

[0064] Generally, in each concept the melt never sees, never is in contact with any metal that's at a lower temperature than its solidest temperature and never in contact with any atmosphere that it would react to from the time that it's molten until the time that it solidifies in the die, in the mold cavity. The material is never being transferred to a cold chamber per seor a cold shot sleeve. It gets all the way to the cavity in an environment that is heated. Further, it may be transferred in protected environment (e.g., vacuum) to the die cavity.

[0065] In some cases parts are lined with ceramic material.

Summary of Overall System Concepts A Through C for Die Casting of Amorphous Metals

[0066] Concepts A through C all involve a valve means adjacent to the cover die to seal the melt supply/hot chamber from exposure to air while the dies are open. The valving mechanisms require mating contact between two components, and when they come into contact, there is initially molten metal between them. There is a danger that the molten metal may solidify and braze the two together; thus, it is necessary to ensure that any molten metal between the two never drops below its solidus temperature. In these concepts, then, the conduits between the hot chamber and the cover die are all heated above the solidus temperature; inner surfaces, at least, are ceramic to prevent the melt from reacting with those surfaces. The plunger and shot chamber (where used) are also heated, and made of, or coated with, ceramic.

[0067] In a conventional cold shot chamber system, the plunger and shot sleeve are generally steel, and thus their exposure to melt must be of a very short duration. This limits the orientations that can be used, and generally dictates that the melt be poured into an opening on the top side of the shot sleeve. In Concepts A-C, since the shot sleeve and plunger are by necessity heated, and constructed of ceramic, these requirements do not exist. So, a variety of plunger and feed orientations are possible. For example, a plunger may be vertical, pointed up, and the feed port in the shot sleeve may be in constant contact with the melt. This may lead to advantages such as quicker cycle times and less likelihood of turbulent flow of melt into the shot chamber.

[0068] Concept A:

[0069] Melt is supplied by a hot chamber, protected by an inert atmosphere from contact with air, to a plunger that is housed in a shot chamber. In addition to driving the melt into the mold cavity, the plunger has two novel functions, 1.) to meter the volume of melt being injected and 2.) to seal the hot chamber/gooseneck from intrusion by air while the dies are open. The melt may be driven from the hot chamber to the plunger by a pump, by gravity in versions in which the pressure differential between the hot chamber and the mold cavity is either positive or zero, or by gas pressure in versions in which a positive pressure differential exists between the hot chamber and the mold cavity. Squeeze pin(s) are necessary to provide the desired high pressure at the end of the injection cycle. There are two possible combinations of atmospheric protection for the melt:

TABLE-US-00001 Concept Hot chamber atmosphere Die atmosphere A1 Vacuum Vacuum A2 Inert gas Vacuum

[0070] The design of the plunger/metering valve requires gravity to transfer the melt from the metering chamber to the shot chamber. Thus, the plunger axis must be in orientations 1 or 2 (see definitions at the end of this document) as defined herein. This requirement also limits the inert atmosphere in the mold cavity to vacuum only.

[0071] Concept B:

[0072] Melt is supplied by a hot chamber, protected by an inert atmosphere. There is no plunger; melt is driven into the mold cavity by either a pump, or (as in Concept A, depending on whether pressure differential conditions allow these methods) by gravity or gas pressure. A valve allows the melt to enter the mold cavity once the dies are closed and the proper inert atmosphere has been established in the mold cavity; the valve closes prior to the dies opening to protect the melt in the hot chamber/gooseneck from reaction with air. In one version, the pump may meter the melt volume injected into the mold cavity; in other versions, vacuum/gas shutoff valves in the die(s) are relied upon to control the melt volume. Squeeze pin(s) are necessary to provide the desired high pressure at the end of the injection cycle; the valve may be used to withstand the pressure generated by the squeeze pins. The inert atmosphere combinations are similar to those of Concept A, but use of inert gas in the mold cavity is also possible.

TABLE-US-00002 Concept Hot chamber atmosphere Die atmosphere B1 Vacuum Vacuum B2 Inert gas Vacuum B3 Inert gas Inert gas B4 Vacuum Inert gas

[0073] Concept C:

[0074] As in Concept A, melt is supplied by a hot chamber, protected by an inert atmosphere, to a plunger that is housed in a shot chamber. In this case, the plunger does not meter the melt, but does have a tip that seals and functions as a valve to protect the melt from exposure to air while the dies are open. Again, squeeze pins are needed to provide high pressure. The feed options and inert atmosphere combinations are the same as in Concept B.

TABLE-US-00003 C1 Vacuum Vacuum C2 Inert gas Vacuum C3 Inert gas Inert gas C4 Vacuum Inert gas

[0075] The concepts above, and various feed and orientation options are outlined in more detail in the table below:

Concept A: Shot Metered by Combined Plunger/Metering Valve (PMV)

System Description

[0076] The supply source of molten alloy (the melt) is a hot chamber (i.e., crucible or holding furnace containing a large volume (more than one shot) of melt). [0077] The melt in the hot chamber is protected from reacting with oxygen in the atmosphere by blanketing the melt with a constant inert (vacuum or inert gas) environment. [0078] After each casting solidifies and the dies open to eject the casting, the dies close and the mold cavity is purged by vacuum (e.g., to get rid of oxygen and nitrogen molecules that will and react with the melt). [0079] To prevent air from making contact with the melt in the feed tube/hot chamber while the dies are open, the plunger/metering valve (PMV) has a tip that seals on a mating valve seat in the cover die. [0080] The PMV also has a waist section that functions as a metering chamber to meter an exact shot size when in the fill position. [0081] The PMV is actuated to 4 positions (see graphics on last page): [0082] 1. Sealing vacuum against atmospheric pressure when the dies are open [0083] 2. Filling the metering chamber [0084] 3. Dumping melt from the metering chamber to the shot chamber [0085] 4. Driving the melt into the mold cavity. [0086] The PMV and metering/shot chamber axis are inclined at an angle with respect to horizontal (in the example shown, 45 degrees) to cause the melt to transfer by gravity from the metering chamber to the shot chamber. [0087] The feed tube axis is preferably connected to the bottom side of the shot chamber so that the melt feeds from the bottom up, to minimize turbulence. [0088] The metering chamber may be supplied with melt from the hot chamber by various means, including gravity, gas differential pressure, or a pump. [0089] In the case of a pump, two basic pump versions may be used. The first is a non-metering, or non-positive displacement, pump; that is, it does not displace a specific or known amount of fluid. It merely pushes fluid (i.e., melt) upon command until it is shut off. Low pressure pumps such as electromagnetic (EM) pumps or vane pumps are acceptable methods. In Concept A it is not necessary for the pump to meter the volume of melt, because the PMV performs that function. [0090] Alternatively, a positive-displacement pump such as a plunger pump may be used (although its metering functionality would be redundant). In this case, the pump will push fluid until the PMV metering chamber is full, then hold position until the PMV strokes and injects that fluid into the mold cavity. Ideally such a pump will have a check valve, so that a supply of melt remains in the feed tube while the plunger retracts and sucks in more melt in preparation for the next injection cycle. [0091] It is advantageous for all the elements mentioned above to be: [0092] Made of ceramic to avoid wetting and reaction to/degradation from the melt [0093] (As opposed to a tradition cold chamber system) heated to a constant temperature (above the solidus temperature of the melt) to: [0094] Minimize thermal cycling that could break down the ceramic and thereby contaminate the melt [0095] Prevent the melt from locally solidifying at the wall boundaries when passing through these elements. This is particularly an issue due to the injection velocities used, which will be much lower than those used in conventional high pressure die casting. [0096] The feed tube and hot chamber linings, and hot chamber pump materials may be made of various ceramic materials including fused silica, aluminum oxide, aluminum titanate, zirconium oxide, and magnesium oxide; specific examples are Al.sub.2O.sub.3+MgO and Al.sub.2O.sub.3+SiO.sub.2 ceramics. [0097] The PMV protects the melt while the dies are open, and also allows a high quality vacuum to be built up in the dies in the interval while they are closed but before the valve is opened. The best way to achieve a vacuum seal in this situation is with a ceramic-to-ceramic face seal (in this case on conical faces) as opposed to a small-gap (leaky) seal as would be typical when sealing between the OD of the plunger and the ID of the shot sleeve (as has been tried in the past). [0098] It is critical that the melt does not solidify in the PMV area. The melt between the PMV tip and mating valve seat must be heated to above its solidus temperature to prevent the melt from solidifying between the sealing faces of each and brazing these together. One method is to resistively heat at least one, or preferably both, of the PMV tip and mating shot chamber valve seat. The preferred method is to inductively heat the melt alone using an induction coil surrounding the valve seat. In this case the valve and valve seat are made from a ceramic material such as fused silica, which has low thermal and electrical conductivity (low dielectric loss factor); thus only the melt and not the valve and valve seat themselves will be heated by the induction coil. [0099] The best ceramic valve material is considered to be fused silica. Other options may include aluminum oxide, and aluminum titanate. PMV stroke is monitored by a displacement sensor. In the event that a metering/positive displacement pump is used, a control signal must be sent to the pump to shut it off when PMV displacement reaches Position 3 (such that the feed tube is shut off by the PMV). [0100] Once the melt reaches the shot chamber, it is driven into the mold cavity by a controlled plunger speed to eliminate turbulence which could cause imperfections in the finished casting. [0101] The PMV must bottom out at the end of its stroke to provide vacuum sealing when the dies are opened. As such, the PMV cannot be relied upon to provide a predictable final pressure to the mold cavity, because the exact volume injected may vary slightly from shot to shot. Final pressure can be provided by squeeze pins. These could be driven by hydraulic pressure, or simply be spring-loaded to provide a predetermined pressure. The latter case is preferred, because it would not be necessary for the control system to either anticipate, or use sensing means to determine, the correct instant at which to activate the squeeze pins. In the latter case, the PMV would provide the source of pressure, and the squeeze pins would regulate that pressure once the die is full (similar to pressure relief valves). In this case, the metered melt volume would be sized such that when the plunger bottoms out, there is a small excess volume of melt in the mold cavity to ensure that the squeeze pins will have to be depressed to compensate for that excess volume.

[0102] An example injection cycle for a non-metering pump is as follows:

TABLE-US-00004 Die position PMV Position Action Feed tube Pump Open 1 (sealed Ejecting previous Shut off Off against die) cast part Closed 2 (fully Filling plunger Open to On retracted) metering chamber; metering pulling vacuum on die chamber Closed 3 (melt Transferring melt from Shut off On transfer) metering chamber to shot chamber Closed 4 (moving from Driving melt into die Shut off On 3 to 1) cavity at controlled rate Closed 1 Allowing melt in die Shut off On to solidify Open 1 (sealed Eject cast part Shut off On against die)

[0103] In the example above, since the pump is non-metering, it may be left on continuously so that melt is always in contact with the shot sleeve feed port. The same is true of gravity or gas pressure feed.

Discussion

[0104] The advantages of this system are: [0105] Allows use of a large (not single-shot) crucible/hot tank, eliminating thermal cycling which has been a source of crucible breakdown and resulting melt contamination [0106] Provides a means of sealing the melt system from exposure to the atmosphere while the dies are open [0107] Allows a high quality vacuum to be built up quickly in the mold cavity before introducing the melt [0108] Allows use of dies which do not need to be enclosed in a large vacuum chamber, also eliminating various vacuum shuttle ports [0109] Provides a means of metering an exact shot volume to the die [0110] May be used with either vacuum/inert gas for protecting the melt in the hot chamber from exposure to atmosphere.

[0111] A potential drawback of this system is that the requirements on the PMV are more demanding than they are on most other systems/elements; the PMV must hold vacuum, yet also be exposed to molten alloy flowing past it, and must be maintained at above the alloy solidus temperature.

[0112] Because of the need for a valve that is exposed to melt near the supply and also must hold vacuum, this disclosed approach has not been attempted or known. (Most vacuum valves in vacuum die cast systems are at the top of the die, at the last point reached by the inflowing melt, and as such are exposed to much lower temperature.

[0113] The overall system concept is shown below in Figures A1 and A2 (sectional views):

[0114] In accordance with another embodiment, inert gas is used in the crucible along with vacuum in the die (see A2 below). A2 is mechanically similar to Concept A1; the only differences pertain to atmosphere control. For example, the crucible/hot chamber is under constant pressure from an inert gas, such as argon. In addition to the previously noted advantages, due to the positive pressure in the crucible/hot tank, A2 does not rely heavily on the extent to which the PMV can hold vacuum.

[0115] The PMV must hold vacuum in the die, yet also be exposed to molten alloy flowing past it, and must be maintained at slightly above the alloy liquidus temperature.

[0116] In another embodiment, an inert gas is in the crucible, still vacuum in the die, but the melt is driven by gas pressure from the crucible and a pump is not used (see Figure below). Here, this concept is using the pressure of the inert gas to drive melt into that shot sleeve metering chamber or valve. So, while the above two embodiments have a non-metering pump in the crucible, e.g., this embodimentwith no pump in the crucibleuses the inert gas pressure in the crucible (which would be slightly higher than the atmospheree.g., 15 PSI absolute) to drive the melt into the metering chamber in the plunger. The pressure difference in the crucible (just over atmospheric, at about 15 psia) and that in the vacuum-evacuated mold cavity (essentially zero psia) pushes the melt into the PMV metering chamber. [0117] In this embodiment, when PMV displacement reaches Position 3 (see Figure later below), such that the feed tube is shut off by the PMV, there is no mechanism to relieve the pressure driving the fluid up the feed tube. As such, the entire feed tube must be heated to above the liquidus temperature to prevent the molten alloy therein from solidifying.

[0118] In yet another embodiment, an inert gas is in the hot chamber but now instead of having vacuum in the die, an inert gas is introduced into the die as a different means of having atmospheric control. This gas may be used for what we call counter pressure. That is, there is a positive pressure in the die and the gas is pushing against that; this positive pressure has some beneficial effects as far as the front of the melt is concerned.

[0119] The front of the melt is the first part of the melt that is advancing into the mold cavity. So counter pressure has some effects on the surface tension of the melt, and affects the way that melt front behaves. It makes it behave better with respect to not breaking up and not spraying as it comes out of the gates, for example, and not getting turbulent.

[0120] This inert gas introduced into the mold cavity may or may not be controlled as counter pressure, however. But it's possible it may be quicker to get rid of oxygen and nitrogen in the mold cavity by first applying vacuum, then applying an inert gas and then possibly vacuum again, then inert gas again. For example, the first time vacuum is applied to the die cavity, say, 99% of the oxygen and nitrogen are removed, but then to get the rest of it out, one may either keep on pulling vacuum to get that last 1% out, or quickly fill that vacuum volume with inert gas, and it still has 1% air in it and 99% inert gas, then suck out that inert gas and oxygen combination again. This may reduce it down to 0.1% oxygen and nitrogen, if you apply the same level of vacuum to it.

[0121] In Summary, in addition to the previously noted mechanical features referenced above (e.g., see A2), this embodiment describes the use of inert gas and positive pressure in the mold cavity)

[0122] The die is purged by vacuum first, then filled with inert gas (e.g., argon) to provide counter pressure during injection to help prevent turbulence and breakdown of the melt front.

[0123] The die fill process may involve a single step each of vacuum and inert gas fill, or multiple steps such as vacuum/inert gas fill/re-vacuum/re-inert gas fill to further reduce the oxygen level in the mold cavity.

[0124] As with Concepts A1 and A2, but unlike the third, a pump pushes fluid upon command to the metering chamber; a low pressure pump such as an EM pump is an acceptable method. In this embodiment it is not necessary for the pump to meter the volume of melt, because the PMV performs that function.

[0125] It can introduce a positive pressure to prevent those bubbles from ever forming to begin with which is also an advantage.

[0126] This system may require additional overflow areas for the counter pressure gas, and/or pressure relief valves that limit the maximum pressure and vent the inert gas back to the inert gas source to recycle it.

[0127] Allows a high quality vacuum and positively-pressured inert gas atmosphere to be built up in the mold cavity before introducing the melt.

[0128] In one embodiment, the overall concept is to have a plunger that meters the shots, so the plunger itself has two functions. It pushes the melt into the mold cavity but it also meters the shot itself so it allows use of any kind of pump in the hot chamber. This disclosure uses amorphous metals with the hot chamber concept, which has never been done before, and it does solve some problems. For example, it solves that problem of repeated thermal cycling and individual one-shot melts.

[0129] In the figure shown in Concept A1, we're pumping some melt to the shot chamber, but because we're no longer melting an individual ingot which is perfectly sized to the size of shot that we need, we now use a method of metering the amount of melt that is given to the shot chamber of the shot sleeve. In this case, the plunger itself is that metering method.

[0130] As shown in the figures above and below, the angle of the plunger is shown at about 45 degrees. The reason for that is with this particular concept, it requires gravity so that once the metering chamber is full, then the plunger is put in a different position that requires gravity to allow the melt to progress down to the next session of the chamber (gravity feed). So that's the reason for the inclined plunger. The pump in this case it can be something like an EM (electromagnetic) pump, which in this case would not need to have its own metering. Pumps can be used in conjunction with a sensor such as an EM sensor where you control the current that's sent to the pump based on what the sensor says the volume is or has been. So those two things in combination can be a metering pump. But a metering pump can be just used in an on/off mode to supply a chamber as long as that chamber has a fixed volume.

[0131] The biscuit would be part of the casting that's injected. The configuration as shown is a draft angle that's easily ejectable. So instead of having a conventional sort of round biscuit with a little bit of a draft angle on the sides of it, it would be shaped a little less like that so that it's ejectable.

[0132] In Concept A1, it's all vacuum system and so there wouldn't be air, and that melt would find its own level and the plunger would approach it until just hits melt and it would start pushing it in.

[0133] In an embodiment, that there can be a plurality of rotating circular dies such as that pumping and flowing it simply keeps going on constantly.

[0134] Squeeze pins are also shown in the figures. Squeeze pins in die casting are used to increase the pressure generally at the end of the cyclee.g., at the end of the injection cycle. Basically they are piston-like devices that either extend into the mold cavity a little bit or can be forced by the melt to retract into their bores a little bit. The same pins can be used as ejector pins, so once the casting has solidified and once the die is open and the casting is ready to be ejected, the squeeze pins are used to push the casting back out. Squeeze pins can perform that dual role.

[0135] In one embodiment, in the bore that squeeze pin resides in, a spring in that bore pushes on the squeeze pin to form a spring-loaded pin. In some embodiments, by putting a preload on it, the plunger is made to retract with a predetermined pressure.

[0136] Position 1 shows an angled shot chamber and the plunger. The tube that branches off down to the lower right is the feed tube that connects with the hot chamber itself (the source of molten alloy). In position 1, the plunger tip seals off the hot chamber. All these components are maintained above the liquidus temperature of the alloy because when this plunger tip is pressed against that ceramic seat, we don't want the alloy to serve as a brazing material and braze the plunger tip to the seat. So it is maintained above the solidus temperature. Also in the position 1 shown, the dies are open and the plunger tip itself is acting as a valve to seal everything elseeverything upstream of that if you willfrom the atmosphere. Then once the dies are closed and we have pulled a vacuum on the dies, the plunger is pulled back to position 2, which is the fill position.

[0137] In position 2 there's annular sealing around the OD of the plungerthat is, there is a very small gap between the plunger OD and the shot sleeve ID that functions as a sealand so that volume shown there is going to define the metering volume. So in position 2 the pump in the hot chamber is actuated to fill that volume with melt. Once it fills, which will just take a fraction of a second, we move on to position 3.

[0138] In position 3, the large OD of the plunger has closed off the feed tube that goes down to the hot chamber. Now the volume that was in that annular area around that neckdown area of the plunger, it's now able to gravity feed past the plunger tip and into the mold areathat is, into that biscuit area.

[0139] Then finally in position 4, once we know that all the melt has gravity-fed past that plunger tip empirically; (e.g., based on a predetermined amount of time, e.g., 0.05 sec)then the plunger is advanced. Once the plunger enters that final diameter within the shot sleeve, then it becomes a piston instead of a valve and it is driven further forward. Now this is where the squeeze pins may come into play. If you just push that plunger tip all the way until it bottomed out on the mating valve seat, if then the fluid volume that was in that shot was a little bit low, the pressure in the die cavity won't build up. On the other hand, if it was a little bit high, the plunger tip wouldn't be able to stroke fully and seal on the valve seat. Thus, the squeeze pins may be employed to compensate for any differences in volume. As such, they could be simply preloaded by a spring, or they could be preloaded hydraulically or pneumatically to a certain pressure. The key is that they are able to be pushed in by the pressure that the plunger generates when it bottoms out on the seat, and compensate for any variation in volume.

[0140] In yet another embodiment, no plunger and no pump are provided. Instead, it has just a valve that is right next to the biscuitthat is, right next to the casting. This valve is simply open and shut, so there's a source of pressure. That source of pressure is the pressure differential. There's a higher pressure in the hot chamber than there is in the die cavity because one has inert gas, the other has vacuum in it.

[0141] For example, melt is drawn to the mold cavity by the pressure difference in the crucible (just over atmospheric, at about 15 psia) and that in the vacuum-evacuated mold cavity (essentially zero psia).

[0142] To isolate the crucible/hot tank from contamination by the atmosphere when the dies are open, there is a valve adjacent to the biscuit.

[0143] Unlike the previous concepts, there is no ability to meter the shot. The valve is simply left open until the mold cavity is full.

[0144] After the mold cavity is full, the valve is shut, and shortly thereafter hydraulically-driven squeeze pins are to be activated to increase the final mold pressure. The purpose of increasing pressure is to minimize porosity in the casting, and in doing so, increase mechanical properties and improve the surface finish of the casting. The valve, since it is not a plunger per se, cannot generate this pressure, but nevertheless must withstand it. [0145] In particular, at least one, or preferably both, of the valve and the mating valve seat, must be heated to above the liquidus temperature to prevent the melt from solidifying between the sealing faces of each and brazing these together. [0146] There is no mechanism to relieve the pressure driving the fluid up the feed tube. As such, the entire feed tube must be held at a temperature above the liquidus (or at least solidus) temperature to prevent the molten alloy therein from solidifying. Roughly the same temperature as that of the melt in the crucible/hot tank would be ideal.

[0147] The injection cycle is as follows:

TABLE-US-00005 Die Valve position Position Action Feed tube Pump Open Closed Ejecting previous cast part Shut off from n/a mold cavity Closed Closed Pulling vacuum on die Shut off from n/a mold cavity Closed Open Transferring melt from Connected to n/a crucible/hot tank to mold mold cavity cavity Closed Closed Activating squeeze pins to Shut off from n/a increase pressure in mold mold cavity cavity Closed Closed Allowing melt in die to Shut off from n/a solidify mold cavity Open 1 (closed) Eject cast part Shut off from n/a atmosphere

Discussion

[0148] The advantages of this system are: [0149] Allows use of a large (not single-shot) crucible/hot tank, eliminating thermal cycling which has been a source of crucible breakdown and resulting melt contamination [0150] Provides a means of sealing the melt system from exposure to the atmosphere while the dies are open, but due to the positive pressure in the crucible/hot tank, does not rely as heavily as Concept A1 on the extent to which the PMV can hold vacuum [0151] Allows a high quality vacuum to be built up in the mold cavity before introducing the melt [0152] Allows use of dies which do not need to be enclosed in a large vacuum chamber, also eliminating various vacuum shuttle ports [0153] This concept is simpler that other concepts in that it does not require a pump, and the valve actuation may be somewhat simpler than that of the PMV. For example, its speed does not have to be controlled. Further, it only has to actuate to two positions (fully open and fully shut), so there is no need for a stroke sensor or high-speed feedback control loop. Thus, its control system requirements are simpler.

[0154] As with previous concepts, a potential drawback of this system is that the requirements on the valve are more demanding than they are on most other systems/elements; the valve must hold vacuum in the die, yet also be exposed to molten alloy flowing past it, and must be maintained at slightly above the alloy liquidus temperature.

[0155] There are other potential drawbacks are unique to this embodiment (illustrated as Concept 5 below). One is that since the melt volume is simply drawn in by vacuum, it is not positively controlled/metered. Also, the fill rate is not controlled as it is with a PMV or plunger type system, and may be too slow or too fast.

[0156] Such an approach is not known and has not been done before, probably because of the need for a valve that is exposed to melt near the supply and also must hold vacuum. (Most vacuum valves in vacuum die cast systems are at the top of the die, at the last point reached by the inflowing melt, and as such are exposed to much lower temperature.)

[0157] The valve protects the melt while the dies are open, and also allows a high quality vacuum to be built up in the dies in the interval while they are closed but before the valve is opened. The best way to achieve a vacuum seal in this situation is with a ceramic-to-ceramic face seal (in this case on conical faces) as opposed to a small-gap (leaky) seal as would be typical when sealing between the OD of the plunger and the ID of the shot sleeve (as has been tried in the past).

[0158] It is critical that the melt does not solidify in the valve area. This is the reason that the valve is designed and oriented so that no internal surfaces are horizontal (so that the melt cannot pool), and that the valve must be maintained close to, or above, liquidus temperature. As such, all valve body internal surfaces and the valve itself must be a ceramic material which the melt will not wet.

[0159] The best ceramic material is considered to be zirconia. Other options may include alumina, magnesia, and silica; specific examples are Al.sub.2O.sub.3+MgO and Al.sub.2O.sub.3+SiO.sub.2 ceramics.

[0160] The overall system concept is shown below:

Concept B: Valve Adjacent to Mold Cavity (No Plunger)

System Description

[0161] 1) The supply source of molten alloy (the melt) is a hot chamber (i.e., crucible or holding furnace containing a large volume (more than one shot) of melt). [0162] 2) The melt in the hot chamber is protected from reacting with oxygen in the atmosphere by blanketing the melt with a constant inert (vacuum or inert gas) environment. [0163] 3) After each casting solidifies and the dies open to eject the casting, the dies close and the mold cavity is purged by vacuum. [0164] 4) This system does not use a plunger in a cold shot chamber to fill the mold cavity. The mold cavity is filled by either: [0165] a) A pressure differential, for example 1 to 2 bar, between the gas pressure in the hot chamber, and the gas (or vacuum) pressure in the mold cavity, [0166] b) Gravity (i.e., the hot chamber is elevated as compared to the mold cavity) [0167] c) A pump in the hot chamber. [0168] 5) To isolate the melt from contamination by the atmosphere when the dies are open, there is a valve adjacent, and connecting, to the mold cavity. In one embodiment, the valve may be adjacent to the biscuit. [0169] 6) The valve axis optimally is vertical (pointed upwards), or between vertical and horizontal (also pointed upwards. The figure below shows the axis oriented at 45 degrees. In the angled orientation the shot chamber may be filled from the feed tube through a port the low side of the shot chamber. This bottom-filling configuration will cause a minimum of flow disturbance as the melt enters the shot chamber. In the event that gas is used in the mold cavity, either of these orientations ensures that gas is likely to progress through the mold casting first, and exit the vacuum valves at the top of the mold cavity, and thus reducing the possibility of gas being trapped in the casting. [0170] 7) A heated feed tube connects the hot chamber to the valve. During operation, the feed tube is constantly full of melt. [0171] 8) The feed tube axis is also optimally between vertical and horizontal (shown vertical) to facilitate filling of the shot chamber with a minimum of turbulence. [0172] 9) There are at least three methods to meter the shot volume. One is that the valve is simply left open until the mold cavity is full. This concept will require gas/vacuum valve(s) that stop the inflow of melt and hold squeeze pressure. Valves that stop the inflow of melt are known in the art. The valve(s) may perform that function by: [0173] a) Freezing (solidifying) the melt (or chill block), [0174] b) Shutting off the inflow of melt by inertia [0175] c) Shutting off the inflow of melt by a solenoid, [0176] d) Other means. [0177] 10) Another method to meter pump volume is to use a metering pump to deliver a precise volume to the mold cavity. An example may be a plunger pump that delivers a specific volume for a known stroke length. [0178] 11) A third method is to use a non-positive-displacement pump in conjunction with a flow measurement means, such as a flowline sensor. [0179] 12) In the case of a system that uses vacuum valves, the control system may use temperature sensors for chill block valves, or electrical contact or stroke sensors for inertia or solenoid valves, to determine that the mold cavity is full. In the case of a system that meters the pump volume, pump stroke or flow sensors may be used to determine that the mold cavity is full. [0180] 13) Immediately after the mold cavity is full, the control system will shut the valve, and very shortly thereafter one or more squeeze pins are be activated to increase the final mold pressure. The pump itself may be then shut off. The squeeze pin(s) may be driven by hydraulic, pneumatic, electrical, or mechanical means. A hydraulic cylinder with the pressure controlled to produce a desired pressure in the melt itself is an exemplary method. The purpose of increasing pressure is to minimize porosity in the casting, and in doing so, increase mechanical properties and improve the surface finish of the casting. The valve, since it is not a plunger per se, cannot generate this pressure, but nevertheless must withstand it. [0181] 14) The melt between the valve tip and mating valve seat must be heated to above its solidus temperature to prevent the melt from solidifying between the sealing faces of each and brazing these together. One method is to resistively heat at least one, or preferably both, of the valve tip and mating valve seat. The preferred method is to inductively heat the melt alone using an induction coil surrounding the valve seat. In this case the valve and valve seat are made from a ceramic material such as fused silica, which has low thermal and electrical conductivity (low dielectrnc loss factor); thus only the melt and not the valve and valve seat themselves will be heated by the induction coil. [0182] 15) It is advantageous for all the elements mentioned above to be: [0183] a) Made of ceramic to avoid wetting and reaction to/degradation from the melt [0184] b) (As opposed to a tradition cold chamber system) heated to a constant temperature above the solidus temperature of the melt to: [0185] i) Minimize thermal cycling that could break down the ceramic and thereby contaminate the melt [0186] ii) Prevent the melt from locally solidifying at the wall boundaries when passing through these elements. This is particularly an issue due to the injection velocities used, which will be much lower than those used in conventional high pressure die casting. [0187] 16) It is not necessary to provide a mechanism to relieve the pressure driving the fluid in the feed tube in accordance with an embodiment. Shot volume metering will be the simplest, and the most accurate, if the feed tube is always full of melt. As such, the entire feed tube must be held at a temperature above the solidus temperature of the melt to prevent the molten alloy therein from solidifying. Roughly the same temperature as that of the melt in the crucible/hot tank would be ideal.

[0188] An injection cycle for a non-metering pump is as follows:

TABLE-US-00006 Die Valve position Position Action Feed tube Pump Open Closed Ejecting previous Shut off from On, or holding cast part mold cavity Closed Closed Pulling vacuum Shut off from On, or holding on die mold cavity Closed Open Transferring melt Connected to On from crucible/hot mold cavity tank to mold cavity Closed Closed Activating Shut off from On, or holding squeeze pins to mold cavity increase pressure in mold cavity Closed Closed Allowing melt in Shut off from On, or holding die to solidify mold cavity Open 1 (closed) Eject cast part Shut off from On, or holding atmosphere

[0189] The table above gives the cycle for a pump; however, it is the same for gravity- or pressure-feed systems.

[0190] In accordance with embodiments, the pump may be an EM pump, centrifugal pump, piston pump, or any pump that can survive long term exposure in the melt. High pressure is not a requirement.

[0191] It is useful to control the pump flow rate, but not necessary to meter the shot. The valve may be simply left open until the mold cavity is full.

Discussion

[0192] The advantages of this system are: [0193] Allows use of a large (not single-shot) crucible/hot tank, eliminating thermal cycling which has been a source of crucible breakdown and resulting melt contamination [0194] Provides a means of sealing the melt system from exposure to the atmosphere while the dies are open [0195] Allows a high quality vacuum to be built up in the mold cavity before introducing the melt [0196] Allows use of dies which do not need to be enclosed in a large vacuum chamber, also eliminating various vacuum shuttle ports [0197] It only has to actuate to two positions (fully open and fully shut), so there is no need for a stroke sensor or high-speed feedback control loop. Thus, its control system requirements are simpler. [0198] The flow rate into the mold cavity can be more controllable. This is especially true if a positive displacement pump (e.g., a piston pump) or EM pump is used.

[0199] As with previous concepts, a potential drawback of this system is that the requirements on the valve are more demanding than they are on most other systems/elements; the valve must hold vacuum in the die, yet also be exposed to molten alloy flowing past it, and must be maintained at slightly above the alloy liquidus temperature.

[0200] Generally, this disclosed approach is not known, most likely because of the need for a valve that is exposed to melt near the supply and also must hold vacuum. (Most vacuum valves in vacuum die cast systems are at the top of the die, at the last point reached by the inflowing melt, and as such are exposed to much lower temperature. Further, the melt does not go through the valve itself; rather, the valve control mechanism is designed to shut the valve just before the melt actually passes through it.)

[0201] The valve protects the melt while the dies are open, and also allows a high quality vacuum to be built up in the dies in the interval while they are closed but before the valve is opened. The best way to achieve a vacuum seal in this situation is with a ceramic-to-ceramic face seal (in this case on conical faces) as opposed to a small-gap (leaky) seal as would be typical when sealing between the OD of the plunger and the ID of the shot sleeve (as has been tried in the past).

[0202] It is critical that the melt does not solidify in the valve area. This is the reason that the valve must be maintained close to, or above, liquidus temperature.

[0203] The best ceramic valve material is considered to be fused silica. Other options may include aluminum oxide, and aluminum titanate. The feed tube and hot chamber linings, and hot chamber pump materials may be made of various ceramic materials including fused silica, aluminum oxide, aluminum titanate, zirconium oxide, and magnesium oxide; specific examples are Al.sub.2O.sub.3+MgO and Al.sub.2O.sub.3+SiO.sub.2 ceramics.

[0204] The overall system concept is shown below:

[0205] The above Concept B2 shows an inert gas in crucible/hot tank, with melt driven into mold cavity by a pump, and with a valve to isolate crucible/hot tank from atmosphere while dies are open.

[0206] In the above illustrated Concept B2 there is no shot chamber or plunger but instead the system has a valve in place of a plunger. This concept provides the melt from the hot chamber purely by pressure and the hot chamber is positively pressured. As described above, the mold cavity has a vacuum so that once the valve is opened, the mold cavity fills based on that pressure differential. Once the mold is full, the valve is simply shut and then the squeeze pins are actuated.

[0207] Traditionally hot chamber die casting is a relatively low pressure process because the pump is submerged in the hot chamber, and because at such a high temperature, the components of the pump can't take a whole lot of stress. It is typically a piston or plunger type pump. So the hot camber process is typically relatively low pressure, say 500 to 1500 PSI or thereabout. But in the last 10-15 years, industry has realized, especially in aluminum products, that they need a high pressure squeeze to get high quality castings. So some known processes involve injecting with the low pressure pump in the hot chamber, then freezing in this sprue area to provide essentially a valve (a stopper) there. As soon as that sprue area has cooled, or actively cooled, as soon as that melt freezes there but before the rest of the melt in the casting solidifies, they'll use squeeze pins to jack the pressure up (to maybe 10,000 PSI). It has been found that high pressurization makes a difference between getting good mechanical properties, and especially low porosity properties, in castings, and getting bad properties.

[0208] In this disclosure, the melt is introduced in the die cavity with a low pressure gas differential but then once the cavity fills, we close that valvethat same valve that is used to isolate the hot chamber from the atmosphere with the die opening. So once the cavity is full, we close that valve and activate the squeeze pins to increase the pressure in the melt in the mold cavity, before it solidifies. That's crucial to this process.

[0209] In one embodiment, a metering pump is used instead of gas to drive the melt from the hot chamber into the die, into the mold cavity.

[0210] In another embodiment, a non-metering pump is used to drive the melt in.

[0211] In either case, vacuum valves in the mold cavity may apply vacuum to the cavity when fluid melt is not being pushed in, and then when the fluid hits those valves, the molten fluid, it freezes up quickly and basically seals off the cavity. At that point you can further apply pressure.

[0212] In one embodiment, the vacuum is in both the hot chamber and in the die, and inert gas is used in the hot chamber and vacuum in the die.

[0213] In another embodiment, the crucible/hot chamber is under a vacuum environment, but does not require an inert gas system.

Concept C: Plunger with Sealing Tip

System Description

[0214] 1. The supply source of molten alloy (the melt) is a hot chamber (i.e., crucible or holding furnace containing a large volume (more than one shot) of melt). [0215] 2. The melt in the hot chamber is protected from reacting with oxygen in the atmosphere by blanketing the melt with a constant inert (vacuum or inert gas) environment. [0216] 3. After each casting solidifies and the dies open to eject the casting, the dies close and the mold cavity is purged by vacuum. [0217] 4. A plunger housed in a shot chamber drives the melt into the mold cavity. Unlike conventional cold chamber die casting systems, though, the plunger and shot sleeve are maintained hot (i.e., above the solidus temperature of the melt). [0218] 5. The plunger tip serves as the valve that seals the shot chamber and the feed tube/hot chamber from atmosphere when the dies are open. The plunger tip seals on a mating valve seat in the cover die. [0219] 6. The plunger is actuated to 3 positions (see graphics on last page): [0220] a. Sealing vacuum against atmospheric pressure when the dies are open [0221] b. Filling the shot chamber [0222] c. Closing off the feed tube from the shot chamber and driving the melt into the mold cavity. [0223] 7. The shot sleeve axis optimally is between vertical and horizontal (shown at 45 degrees). In this range the shot chamber may be filled from the feed tube through a port the low side of the shot chamber. This bottom-filling configuration will cause a minimum of flow disturbance as the melt enters the shot chamber. [0224] 8. The feed tube axis is also optimally between vertical and horizontal (shown vertical) to facilitate filling of the shot chamber with a minimum of turbulence. [0225] 9. The shot chamber may be supplied with melt from the hot chamber by various means, including gravity, gas differential pressure, or a pump. [0226] 10. In Concept B it is necessary to meter the volume of melt delivered to the shot chamber. [0227] 11. In versions in which the feed of melt from the hot chamber to the shot chamber is provided by gravity feed, gas pressure, or non-positive displacement pump (e.g., EM or vane pumps), the flow rate must be monitored (e.g., by an EM flow sensor). Plunger movement and flow rate must be timed and controlled so that the plunger seals off the feed tube port (Position 3 in the figures below) when the correct volume of melt has been pumped into the shot chamber. [0228] 12. Alternatively, the preferred configuration uses a positive-displacement pump such as a plunger pump. In this case, the pump, based on its piston area and stroke, will push a known volume of melt, then hold position until the plunger strokes and injects that melt into the mold cavity. Ideally such a pump will have a check valve, so that a supply of melt remains in the feed tube while the plunger retracts and sucks in more melt in preparation for the next injection cycle. [0229] 13. It is advantageous for all the elements (valve seat, plunger tip, etc.) mentioned above to be: [0230] a. Made of ceramic to avoid wetting and reaction to/degradation from the melt [0231] b. (As opposed to a tradition cold chamber system) heated to a constant temperature (above the solidus temperature of the melt) to: [0232] i. Minimize thermal cycling that could break down the ceramic and thereby contaminate the melt [0233] ii. Prevent the melt from locally solidifying at the wall boundaries when passing through these elements. This is particularly an issue due to the injection velocities used, which will be much lower than those used in conventional high pressure die casting. [0234] 14. The melt between the plunger tip and mating valve seat must be heated to above its solidus temperature to prevent the melt from solidifying between the sealing faces of each and brazing these together. One method is to resistively heat at least one, or preferably both, of the PMV tip and mating shot chamber valve seat. The preferred method is to inductively heat the melt alone using an induction coil surrounding the valve seat. In this case the valve and valve seat are made from a ceramic material such as fused silica, which has low thermal and electrical conductivity (low dielectric loss factor); thus only the melt and not the valve and valve seat themselves will be heated by the induction coil. [0235] 15. Once the melt reaches the shot chamber, it is driven into the mold cavity by a controlled plunger speed to eliminate turbulence which could cause imperfections in the finished casting. [0236] 16. The plunger tip must bottom out at the end of its stroke to provide vacuum sealing when the dies are opened. As such, the plunger cannot be relied upon to provide a predictable final pressure to the mold cavity, because the exact volume injected may vary slightly from shot to shot. Final pressure can be provided by squeeze pins. These could be driven by hydraulic pressure, or simply be spring-loaded to provide a predetermined pressure. In the latter case, the plunger would provide the source of pressure, and the squeeze pins would simply regulate that pressure once the die is full (similar to pressure relief valves). In this case, the metered melt volume would be sized such that when the plunger bottoms out, there is a small excess volume of melt in the mold cavity to ensure that the squeeze pins will have to be depressed to compensate for that excess volume.

[0237] The pump may be a metering pump, for example (i.e., a pump that delivers the melt from the hot chamber to the plunger to the shot chamber, and is capable of delivering a specific volume of melt).

[0238] An example injection cycle for a metering pump is as follows:

TABLE-US-00007 Die Plunger position Position Action Feed tube Pump Open 1 (sealed Ejecting Shut off Intake stroke against die) previous cast part Closed 1 (sealed Pulling vacuum Shut off Intake stroke against die) on mold cavity Closed 2 (fully Filling shot Open to shot Exhaust stroke retracted) chamber chamber Closed (moving from Driving melt Shut off Holding 3 to 1) into die cavity position at controlled rate Closed 1 Allowing melt Shut off Holding in die to position solidify Open 1 (sealed Eject cast Shut off Intake stroke against die) part

[0239] In the example above, since the pump is metering (i.e., positive displacement), it may be held in position while the plunger shot chamber is not filling, so that melt is always in contact with the shot sleeve feed port.

[0240] The various combinations of atmosphere and feed methods are shown in the table below:

Discussion

[0241] The advantages of this system are: [0242] Allows use of a large (not single-shot) hot chamber, eliminating thermal cycling which has been a source of crucible breakdown and resulting melt contamination [0243] Provides a means of sealing the melt system from exposure to the atmosphere while the dies are open [0244] Allows a high quality vacuum to be built up quickly in the mold cavity before introducing the melt [0245] Allows use of dies which do not need to be enclosed in a large vacuum chamber, also eliminating various vacuum shuttle ports [0246] Provides a means of metering an exact shot volume to the die [0247] May be used with either vacuum/inert gas for protecting the melt in the hot chamber from exposure to atmosphere.

[0248] A potential drawback of this system is that the requirements on the plunger are more demanding than they are on most other systems/elements; the plunger tip must hold vacuum, yet also be exposed to the molten alloy flowing past it, and must be maintained at above the alloy solidus temperature.

[0249] Because of the need for a valve that is exposed to melt near the supply and also must hold vacuum this disclosed approach has not been attempted or known. (Most vacuum valves in vacuum die cast systems are at the top of the die, at the last point reached by the inflowing melt, and as such are exposed to much lower temperature.

[0250] The plunger tip, serving as a valve, protects the melt while the dies are open, and also allows a high quality vacuum to be built up in the dies in the interval while they are closed but before the valve is opened. The best way to achieve a vacuum seal in this situation is with a ceramic-to-ceramic face seal (in this case on conical faces) as opposed to a small-gap (leaky) seal as would be typical when sealing between the OD of the plunger and the ID of the shot sleeve (as has been tried in the past).

[0251] It is critical that the melt does not solidify in the plunger area. This is the reason that the plunger must be maintained close to, or above, liquidus temperature.

[0252] In the particular configuration shown, the plunger tip seals against a separate valve seat. This seat is made of ceramic. A separate valve seat is considered to be the ideal configuration, as it may exhibit a different wear rate, or necessitate different material properties, than that of the shot sleeve. However, as the shot sleeve in this concept must also be either made of ceramic, or lined with ceramic, the valve seat alternatively could be formed integrally into the shot sleeve.

[0253] The best ceramic valve material is considered to be fused silica. Other options may include aluminum oxide, and aluminum titanate. The feed tube and hot chamber linings, and hot chamber pump materials may be made of various ceramic materials including fused silica, aluminum oxide, aluminum titanate, zirconium oxide, and magnesium oxide; specific examples are Al.sub.2O.sub.3+MgO and Al.sub.2O.sub.3+SiO.sub.2 ceramics.

[0254] The overall system concept is shown below:

[0255] For illustrative purposes, the shot chamber is shown as being oriented at a 45 degree angle so as to reduce negative effects such as waterfalling or bubbles.

Concept D: Vacuum+Inert GasConventional Plunger/Shot Sleeve

[0256] System Description: A Low Pressure Pump in the Hot Chamber Feeds a Metered Shot to a Cold Shot Chamber (or Cold Shot Sleeve), which Forces the Melt into the Mold at Hither Pressure. Inert Gas Pressure on Back Side of Plunger Prevents Air Intrusion while Dies are Open. [0257] The supply source of molten alloy is a hot chamber. [0258] The hot chamber is maintained at a relatively constant temperature, about 200 C. above the liquidus temperature of the melt, through the use of insulation and heating. [0259] The hot chamber feeds a cold shot chamber, comprising a plunger housed in a cold shot sleeve, which drives the molten alloy into the mold cavity. The shot sleeve is maintained at a relatively constant temperature, below the solidus temperature of the melt, through insulating and/or heating and/or cooling. [0260] At all points in the system, and throughout the injection process, the melt is protected from any exposure to air by a blanket of an inert gas, such as argon, or by vacuum. As such, there is a port in the shot sleeve that supplies inert gas to the chamber on the backside of the plunger. This is key for this system, because the plunger is not capable of positively sealing against atmospheric pressure. The gas pressure is slightly higher than atmospheric pressure; for example, 15 to 16 psia. The intent is that when the dies are open, the positive gas pressure will prevent atmosphere from leaking past the plunger tip and into the hot chamber (as it would if the plunger backside chamber and/or hot chamber were under vacuum). [0261] This positive pressure inert gas system obviates the need for the plunger to fully seal, thus allowing use of traditional OD gap sealing. (That is, the small gap, or diametral clearance, between the plunger OD and the shot sleeve ID allows so little leakage that it provides enough of a seal to draw a reasonable vacuum level in the mold cavity). [0262] The hot chamber likewise is filled with inert gas at a similar pressure. [0263] While the dies are open, the shot chamber plunger is in the position identified herein as Position 1 (see figures on last page of this document). Due to the slight pressure differential between the plunger backside chamber and atmosphere, no air will enter the feed tube; only a slight amount of inert gas will leak past the plunger and into the atmosphere. [0264] With the shot chamber plunger still in Position 1, the dies are closed, and vacuum is applied to the mold cavity to evacuate oxygen that would react with the melt. A small amount of inert gas will leak past the plunger into the mold cavity. This is acceptable, since the objective in evacuating the mold cavity with vacuum is not just to lower its pressure, but primarily to remove oxygen/nitrogen that may contaminate the melt. [0265] Prior to injection, the atmosphere in the mold cavity may remain as vacuum, or it may be filled with inert gas. [0266] Once a sufficient vacuum/gas quality has been achieved in the mold cavity, the shot chamber plunger will be retracted to the fill position, identified herein as Position 2. In this position the shot chamber fill port communicates with the feed tube and hot chamber, and the pump in the hot chamber fills the shot chamber. [0267] This system will work best with a positive displacement pump in the hot chamber that can meter the shot volume (that is, deliver a specific, predetermined amount). An ideal pump is a piston/plunger pump similar to that of a conventional gooseneck hot chamber system; the volume that it pumps may be controlled by the length of its stroke. Unlike conventional hot chamber plunger pumps, though, the components are made of a ceramic material that can survive long term exposure to the melt without breaking down and failing, or contaminating the melt. [0268] Hot chamber pumps have an inherent pressure limitation due to the fact that they are submerged in molten metal. The high temperature in such an environment reduces the tensile and yield strength of tool steels to a fraction of their strength at room temperature. Ceramic materials also suffer a strength reduction, though not as great, but have a further limitation in that they have limited strength in tension. Piston cylinders are subjected to hoop stress, which is a form of tensile stress. Further, amorphous alloys have even higher liquidus and solidus temperatures than those of many alloys, such as aluminum, that are considered to be beyond the range of normal plunger pumps. For this reason, a dual pump system is used; a low-pressure pump in the hot chamber, which then feeds a cold chamber shot sleeve adjacent to the dies. The hot chamber pump may be limited to 1,000 psi, or even less, but the cold chamber is capable of boosting the final pressure to 10,000 psi or greater because temperature excursions remain below the temperature that significantly reduce the strength of the tool steel of which it is made. [0269] Once the required shot volume is delivered from the hot chamber to the shot chamber, the hot chamber pump shuts off and holds fluid level in the fill tube, and the shot chamber plunger begins to move. [0270] Shot chamber plunger position is monitored by a displacement sensor. As the shot chamber plunger reaches the position identified as Position 3, the fill port is closed off by the plunger; at this point the control system will command the hot chamber pump to begin to retract. Once past Position 3, the plunger pushes the melt into the mold cavity until pressure in the mold cavity builds. In this system, squeeze pins are optional but not necessary. The plunger, since it does not bottom out on a face seal as in concepts A-C, may stroke as far as necessary (shown below as Position 5) to apply the maximum desired pressure to the melt. [0271] On its way to full stroke, the plunger passes through Position 4, at which point the inert gas chamber on the backside of the plunger connects to the feed tube. The retraction of the hot chamber pump that initiated when the plunger passed Position 3 will cause a suction pressure in the melt in the feed tube, so that when the feed port opens up to the back side chamber the melt will be urged to retreat into the feed tube as opposed to intruding into the back side chamber. Inert gas will fill the feed tube from the shot chamber backside chamber. [0272] The system is designed so that the melt is only in contact with the plunger/shot sleeve for a very short duration (i.e., on the order of a second, or less) to prevent these elements from heating to a temperature at which 1.) their strength is reduced beyond an acceptable level, or 2.) soldering of the melt to these elements may occur. [0273] In a bottom fill or side fill design, the feed tube is connected to either the bottom, or sideas opposed to the topof the shot sleeve. In these designs it is desirable that after the shot chamber has filled, the melt in the feed tube should drain back to a predetermined level in the feed tube so that the melt does not remain long in contact with the shot chamber plunger. The feed tube orientation should be vertical, or angled upwards (orientations 4 or 5 in the orientation key below) to facilitate this draining action. The melt should only retract to a predetermined level, though, so that on each filling stroke a metered volume may be pumped. The hot chamber pump may be designed with check valves on the inlet and outlet and a shuttle piston. The shuttle piston does not allow melt to pass through, but allows a certain amount of fluid to retract on each stroke (see FIG. 1). This will ensure precise metering of the next shot. [0274] The hot chamber pump and shuttle piston materials should be made of the same material, or at least from materials with a similar coefficient of thermal expansion (CTE), so that clearances will not change excessively at the high operating temperatures in the hot chamber. [0275] The check valve components may be made of a high-density material such as tungsten carbide to prevent them from floating in the melt and not seating. Alternatively, the check valves in the pump may be loaded with rods (not shown) extending upwards in their passageseven extending through the cover plate and out of the hot chamber, if necessaryto provide additional sealing force. [0276] In the case of a top fill design it is not necessary for the hot chamber pump to utilize the shuttle piston feature. In these designs the feed tube is connected to the top side of the shot sleeve (See FIGS. 2 and 3). This connection location makes it possible for the feed tube axis to be angled with respect to a horizontal plane (as shown in these figures), or the axis may even be vertical (i.e., orientations 1 or 2 in the orientation key below). The section connecting to the shot sleeve feed port is referred to as Section 1. This section is made of a ceramic material with low thermal conductivity (see insulating spacer later in this document) to prevent heat from the feed tube, which is heated to above the melt liquidus temperature, from overheating the shot sleeve. The feed tube then has an elbow that makes a turn and points downwards enters the hot chamber. The section pointing downward to the hot chamber is referred to as Section 2. At the top of the turn, an inert gas supply line connects via a valve (not shown) to the feed tube. [0277] While pulling vacuum in the mold cavity, the valve is open so that any vacuum that is able to pull through the plunger OD gap will simply pull a small amount of inert gas into the mold cavity. Once an acceptable atmosphere in the mold cavity has been established, the inert gas valve is closed and the plunger is withdrawn to open the fill port to the feed tube. The hot chamber pump is activated, pumping melt into the shot chamber. When the hot chamber pump reaches the end of its stroke, any melt in melt in Section 1 will drain into the shot chamber feed port and very quickly will be injected into the mold cavity; any melt in Section 2 will settle level with the bottom of the inside radius of the elbow. The inert gas valve will be opened, and melt in the feed tube elbow will be blanketed with inert gas to prevent exposure to air. [0278] In a top-fill configuration, it is useful for the melt to exit from the feed tube into the shot chamber port through a nozzle, or opening that is smaller than the size of the port, so that the melt does not contact, wet, and adhere to the shot sleeve around the fill port area. [0279] Once the mold cavity is full and the melt in the biscuit area that is in contact with the plunger solidifies, if desired the plunger may be retracted to Position 1. (It may be useful to withdraw the plunger from contact with the biscuit in order to manage plunger temperature.) In this position, the dies may be opened to eject the casting. The exact location of Position 1 is not important as long as the plunger remains displaced far enough towards the dies that the fill port is not open to atmosphere. The fact that the shot sleeve back side chamber has a slight positive pressure ensures that inert gas will, at most, leak slightly past the plunger OD and prevent atmosphere from intruding past the plunger and into the fill tube/hot chamber. [0280] Since the fill port is filled by a pump, as opposed to gravity poured, the plunger axis may be other than horizontal; even vertical if desired. Also, the fill port may be somewhere other than on the high side. In fact, it is advantageous for the plunger to be vertical (pointed up), or closer to vertical than to horizontal, and if angled, for the fill port to be on the low side, or closer to the low side than to the high side (i.e., orientations 4 or 5, referring to the Orientation Key below). FIG. 4, below, shows an angled plunger orientation with a bottom fill feed tube/fill port orientation. In bottom-fill configurations, the molten fluid may fill the shot chamber smoothly without turbulence and/or waterfalling, a condition which can lead to inclusion of gas/void pockets and/or premature solidification of particulates. Turbulence and/or waterfalling are particularly of concern if the shot chamber is (as is the design intent) at a lower temperature than the solidus temperature of the alloy, because the alloy may locally solidify around gas/void pockets, and such artifacts may remain in the final casting product as defects. [0281] In fact, one of the advantages of this system is that it is not necessary to heat the shot chamber to as high a temperature as is required in Concepts A-C. Though some heating of the shot sleeve may be beneficial, it may be maintained at a temperature below the solidus temperature as long as the melt does not dwell long enough in the shot sleeve to develop localized solidification zones. [0282] Having stated the above, the system could be configured (say, for manufacturing convenience) with the shot chamber axis on a horizontal plane (orientation 3). The system still maintains the benefits of protection of the melt (by positively pressured inert gas) from contamination by the atmosphere. In a horizontal shot chamber axis configuration, it is still beneficial (though not an absolute requirement) for the fill port to be on the low side, rather than the high side, to avoid the waterfall effect. This configuration is shown in FIG. 5 below. [0283] The shot sleeve axis may also be oriented between horizontal and vertical, pointed down (i.e., Orientation 2, referring to the Orientation Key below). This orientation may only be used with vacuum in the mold cavity/shot chamber, though [0284] The feed tube should be continuously heated to above the solidus temperature of the melt to prevent premature solidification of the melt in the tube. An insulating spacer, made of a material with low thermal conductivity (e.g., aluminum titanate ceramic) is used between the feed tube and the shot chamber to minimize conductive transfer of heat between the two. [0285] It is advantageous for all the elements inside the hot chamber, the hot chamber itself, and those between the hot chamber and the insulating spacer, to be: [0286] Either made of, or lined with, ceramic to avoid wetting and reaction to/degradation from the melt [0287] Heated to a constant warm (above solidus) temperature to: [0288] Minimize thermal cycling that could break down the ceramic and thereby contaminate the melt [0289] Prevent the melt from locally solidifying at the wall boundaries when passing through these elements. This is particularly an issue due to the injection velocities used, which will be much lower than those used in conventional high pressure die casting. [0290] The best ceramic valve material is considered to be fused silica. Other options may include aluminum oxide and aluminum titanate. The feed tube and hot chamber linings, and hot chamber pump materials may be made of various ceramic materials including fused silica, aluminum oxide, aluminum titanate, zirconium oxide, and magnesium oxide; specific examples are Al.sub.2O.sub.3+MgO and Al.sub.2O.sub.3+SiO.sub.2 ceramics. [0291] Depending on variables such as the shot volume (as defined by casting size), casting cross-section minimum thickness, and the extent of die heating used, the plunger and shot chamber, due to the relatively short-term exposure (as compared to Concepts A-C) to molten liquid, may be made of high-temperature tools steels without compromising the ability to deliver the melt to the mold cavity at sufficiently high enough temperature and low enough velocity to avoid compromising casting quality. However, some large and/or complex castings may require the plunger and/or shot chamber also to be constructed from ceramics, and maintained at higher temperatures (i.e., near or even above solidus temperature). [0292] Once the melt reaches the shot chamber, it is driven into the mold cavity by a controlled plunger speed to prevent turbulence which could cause imperfections in the finished casting. A maximum melt velocity of 0.5 meters/sec is recommended.

[0293] The injection cycle is as follows:

TABLE-US-00008 Die Plunger position Position Action Feed tube Pump Open 1 (intermediate Ejecting previous Connected to Off (holding position) cast part shot chamber position with back side inert melt retracted gas supply in feed tube) Closed 1 (intermediate Drawing vacuum Partially or fully Off (holding position) on mold cavity connected to shot position with (and/or filling chamber back melt retracted mold cavity with side inert gas in feed tube) inert gas) supply Closed 2 (fully Filling shot Open to shot Moving through retracted) chamber sleeve cavity full metering stroke Closed 3 (mid stroke) Moves to position Shut off Starting at which plunger retraction shuts off feed port Closed 4 (mid stroke) Retraction of melt Opens to shot Retracting melt in feed tube chamber back in feed tube; side inert gas reloading supply plunger chamber Closed 5 (full stroke) Die cavity full; Connected to Off (holding increasing shot chamber position with pressure back side inert melt retracted gas supply in feed tube) Closed 5 (full stroke) Allowing melt in Connected to Off (holding contact with shot chamber position with plunger to solidify back side inert melt retracted gas supply in feed tube) Open 1 (intermediate Allowing casting Connected to Off (holding position) to cool sufficiently shot chamber position with to be ejected; back side inert melt retracted ejecting cast part gas supply in feed tube)

[0294] The above described embodiment provides a way of keeping atmosphere from getting in and contaminating the melt in cases where we don't want a chamber that has to be heated above the solidest temperature.

[0295] The melt is going to be about a thousand degrees C./about 1800 degrees F. and about 1500 where iron-based materials get red hot. At such temperatures the materials lose almost if not all of their strength properties. (At about 1200 degrees F. is where most materials start to degrade in strength.) Thus, when trying to use a ferrous alloy at those temperatures, it would have no strength whatsoever and wouldn't be able to obtain high pressure out of it. Further, it would scour and scratch easily and there would be braising of the alloy to the steel.

[0296] Thus, this embodiment aims to keep the shot sleeve below that temperature range, dump the molten alloy into it very quickly, and inject it very quickly.

[0297] The various combinations of atmosphere and feed methods are shown in the table below:

Discussion

[0298] The unique advantages of this system are: [0299] Provides a means of sealing the melt system from exposure to the atmosphere while the dies are open, but due to the positive pressure in the hot chamber and plunger back side chamber, does not rely as heavily as Concepts A-C on the extent to which the cold chamber plunger can positively seal in order to hold vacuum. [0300] Provides a means (i.e., a low pressure pump in the hot chamber) of metering an exact shot volume to the mold cavity along with the means (i.e., a cold chamber shot sleeve) to generate high pressure at the end of the injection cycle. [0301] Provides a means (i.e., the shuttle piston) of retracting the melt from contact with the cold shot sleeve to prevent it from overheating. [0302] The shot chamber may utilize a bottom-fill feed port, and also may be oriented in orientations 4 or 5, both of which offer a less-turbulent flow profile than other orientations. [0303] The system has a minimum of complexity; in particular, there are no valves that must seal against both melt and vacuum.

[0304] The shot chamber or shot sleeve doesn't necessarily have to be maintained above the solidest temperature of the alloy.

[0305] Typically when the dies are open, air can leak past the plunger into the melt chamber and it will contaminate the melt. Once the dies are closed it can also take a long time to draw a vacuum and suck the air back out of that chamber. This disclosure solves the challenge of making the process more efficient by simply pressurizing that chamber that houses the crucible/ladle with inert gas at slightly higher than atmospheric pressure (e.g., 15-16 psi atmospheric).

[0306] In accordance with an embodiment, the shot chamber is oriented somewhere between vertical and horizontal (e.g., pointing upwards toward the die, as opposed to being horizontal as a conventional shot chamber normally is).

[0307] The hot chamber pump with the shuttle piston is shown below in FIG. 1:

[0308] FIG. 2, below, shows the feed tube and nozzle configuration used in conjunction with a top-feed, horizontally-oriented shot sleeve (shown in the mode of pulling vacuum):

[0309] FIG. 3, below, shows the feed tube and nozzle configuration used in conjunction with a top-feed, horizontally-oriented shot sleeve (shown here in the mode of filling the shot sleeve with melt):

[0310] The overall system concept in Configuration D1, with the plunger in orientation 4 (angled, pointed up) is shown below in FIG. 4:

[0311] The overall system concept in Configuration D1, with the plunger in orientation 3 (horizontal) is shown below in FIG. 5:

[0312] The terminology for Concept D is shown below (note that the shot sleeve, insulating spacer, and bushing are sectioned for clarity):

[0313] The images below are typical of both concept D1 and D2; the only difference in D2 is that the mold cavity is first evacuated with vacuum, then filled with inert gas.

[0314] In this position (position 1, above), the dies are open and basically we're just holding the plunger where it's stroked out, at its last stroke, or retracted a little bit, so it doesn't maintain contact with the biscuit as it's solidifying or as it's still real hot. In this position, this plunger backside area connects to the port that supplies it with inert gas and the inert gas also goes down and fills the feed tube. So everything is surrounded by inert gas that's at a slightly higher pressure than atmospheric pressure.

[0315] Position four shows where the piston first begins to open up the feed tube to that backside chamber and now inert gas can push the melt, or really just allow the melt to fall back down the feed tube and back into the hot chamber.

Concept E: Two Valves Inline Forming a Metering Chamber Between Hot Chamber and Cold Shot Chamber

[0316] System Description: A Low Pressure Pump Feeds Melt from a Hot Chamber to a Metering Chamber, which Feeds a Cold Shot Chamber. The Metering Chamber Volume is Defined by the Space Between Two Valves. The Valves Also Isolate the Melt in the Feed Tube/Hot Chamber from Exposure to Air while the Dies are Open. Final High Pressure Injection is Provided by the Cold Shot Chamber. [0317] The supply source of the melt is a hot chamber. [0318] The hot chamber is maintained at a relatively constant temperature, about 200 C. above the liquidus temperature of the melt, through the use of insulation and heating. [0319] The hot chamber feeds a metering chamber, created by two valves positioned inline between the hot chamber and the shot sleeve. The volume of the passage between the two valves serves to define the volume of each shot. The metering chamber is designed, by its inside diameter (or other cross-section dimensions) and length, to meter the shot. [0320] The lowermost of the two valves serves to isolate the melt from atmosphere while the dies are open. [0321] The method of feeding melt from the hot chamber to the metering chamber/cold chamber may be a pump, a pressure differential created by inert gas, or gravity. [0322] The metering chamber feeds a cold shot chamber, comprising a plunger housed in a cold shot sleeve, which drives the molten alloy into the mold cavity. The shot sleeve is maintained at a relatively constant temperature, below the solidus temperature of the melt, through insulating and/or heating and/or cooling. [0323] At all points in the system, and throughout the injection process, the melt is protected from any exposure to air by a blanket of an inert gas, such as argon, or by vacuum. [0324] Prior to injection, the mold cavity is purged by vacuum to evacuate oxygen that would react with the melt. [0325] On the first cycle, the lower valve must be left open during vacuum purging; the metering chamber must be evacuated in order to be filled completely by melt. During evacuation, the plunger should be withdrawn to the fill position, opening the shot chamber fill port to the fill tube, to allow any air to evacuate quickly from the fill tube and metering chamber body. On subsequent cycles, the metering chamber will remain in a vacuum state as long as the lower valve is left closed while the dies are open, so repeated evacuation of the metering chamber is not necessary. [0326] Both valves must withstand continuous exposure to molten alloy, and must be maintained (as a minimum) above the solidus temperature of the alloy. [0327] Since the upper valve isolates the melt from exposure to air while the dies are open, the plunger/shot sleeve does not have to perform this function. The plunger thus may utilize conventional diametral gap clearances, and the plunger itself does not have to effect a positive seal to the shot sleeve. The plunger and shot sleeve thus need not be heated beyond the usual requirements for conventional die casting. [0328] The feed tube from the hot chamber to the valves, both valves, and the metering chamber must all be maintained (by use of heating elements and/or insulation) at a temperature above the solidus temperature of the melt, to prevent the melt from solidifying between a valve and mating seat and brazing the two together. [0329] Although the melt may be transferred from the hot chamber to the metering chamber by various methods, the melt is transferred from the metering chamber to the shot chamber by gravity. Thus, the metering chamber body (i.e., tube) and the inlet tube connecting the lower valve and the shot sleeve fill port optimally should be inclined at an angle that is sufficiently high enough (with respect to horizontal) that the melt will flow quickly, but low enough that the melt flows smoothly without turbulence. 10 degrees to 45 degrees is considered to be an optimum range. [0330] As such, the shot chamber fill port must be on the top, or near the top side of the shot sleeve (not on the bottom). [0331] Due to the necessary orientation of the fill tube, this concept may only be used with vacuum (not gas) in the mold cavity. If gas were used, as the melt were to fill the shot chamber, the gas would rise upwards and be trapped in the metering chamber near the top valve. (This would prevent accurate metering of subsequent shots.) [0332] The orientation (see Orientation Key, below) of the shot sleeve/plunger axis may be horizontal, or inclined between vertical and horizontal (i.e., orientations 3 or 2, respectively). Each may have advantages and disadvantages, but a horizontal (orientation 3), or near-horizontal, shot sleeve orientation is preferable because the shot chamber can be filled completely before starting injection into the mold cavity. (In orientations 1 or 2, the melt will begin to fill the mold cavity before the shot chamber is full, and there is a risk of the melt beginning to solidify prematurely.) [0333] As with Concept D, it is beneficial to use a nozzle at the fill port so that the melt does not contact, and wet, the feed port itself (see FIG. 2, at end of document). [0334] One of the advantages of this system is that it is not necessary to heat the shot chamber to as high a temperature as is required in Concepts 1-4. Though some heating of the shot sleeve may be beneficial, the design intent of this system is to maintain the shot sleeve below the solidus temperature of the melt. To do so, injection rates must be fast enough that the melt is not allowed to dwell long enough in the shot sleeve to develop localized solidification zones. [0335] It is necessary for all the elements lining, and inside, the hot chamber, and those between the hot chamber and lower valve (including valves and valve bodies), to be: [0336] Made of ceramic to avoid wetting and reaction to/degradation from the melt [0337] Heated to a constant temperature (above the solidus temperature of the melt) to: [0338] Minimize thermal cycling that could break down the ceramic and thereby contaminate the melt [0339] Prevent the melt from locally solidifying at the wall boundaries when passing through these elements. This is particularly an issue due to the injection velocities used, which will be much lower than those used in conventional high pressure die casting. [0340] The best ceramic valve and valve seat material is considered to be fused silica. Other options may include aluminum oxide, and aluminum titanate. The feed tube and hot chamber linings, and hot chamber pump materials may be made of various ceramic materials including fused silica, aluminum oxide, aluminum titanate, zirconium oxide, and magnesium oxide; specific examples are Al.sub.2O.sub.3+MgO and Al.sub.2O.sub.3+SiO.sub.2 ceramics. [0341] As the valves are heated above the solidus temperature of the melt, but the shot sleeve is designed to remain below that temperature, the inlet tube between the lower valve and the shot sleeve is a ceramic material selected for low thermal conductivity and high resistance to thermal shock. An exemplary material is aluminum titanate. [0342] Depending on variables such as the shot volume (as dictated by casting size), casting cross-section minimum thickness, and the extent of die heating used, the plunger and shot chamber, due to the relatively short-term exposure (as compared to Concepts 1-4) to molten liquid, may be made of high-temperature tools steels without compromising the ability to deliver the melt to the mold cavity at sufficiently high enough temperature and low enough velocity to avoid compromising casting quality. However, some large and/or complex castings may require the plunger and/or shot chamber also to be constructed from ceramics, and maintained at higher temperatures (i.e., near or above solidus temperature). [0343] Although the plunger tip is not required to seal against vacuum in this design, the plunger rod must still hold a vacuum seal (or, the shot sleeve and the plunger actuator must either be enclosed in a vacuum chamber) so that vacuum can effectively be established once the dies are closed. It is beneficial to provide a separate vacuum port to the plunger backside chamber, so that the vacuum applied to this area does not have to travel through the die cavity and around the plunger OD gap. [0344] Once the dies close, the vacuum source(s) for the mold cavity may also serve to evacuate the shot chamber cavity. [0345] Once the melt reaches the shot chamber, it is driven into the mold cavity by a controlled plunger speed to eliminate turbulence which could cause imperfections in the finished casting. A maximum melt velocity of 0.5 meters/sec is recommended.

[0346] The injection cycle is as follows:

TABLE-US-00009 Die Plunger Lower Upper position Position Action valve valve Pump Closed 2 (fully Drawing vacuum Closed Open On retracted) on mold cavity; filling metering chamber Closed 2 (fully Filling shot Open Closed Off retracted) chamber Closed Moving from Injecting melt Closed Open On 2 to 3 into mold cavity Closed 3 (full Allowing casting Closed Open On stroke) to solidify Open 1 (intermediate Ejecting cast Closed Open On position) part; filling metering chamber

[0347] Note that the pump may be on as long as the lower valve is closed (which allows the upper valve to be open). However, it may not be necessary to run the pump for such a large percentage of the overall cycle.

[0348] The various combinations of atmosphere and feed methods are shown in the table below:

Discussion

[0349] The advantages of this system are: [0350] Provides a positive means of isolating the melt system from exposure to the atmosphere while the dies are open, but without requiring the plunger to seal, thus allowing use of a conventional cold chamber shot sleeve system. [0351] The two-valve-based metering system eliminates the need for a metering pump in the hot chamber. In fact, this system provides a means of metering an exact shot volume to the die without using a metering pump or flow sensors, even if using gravity or gas pressure as the feed method. [0352] Provides an effective system for using only vacuum (not inert gas) to establish an inert atmosphere in the mold cavity and shot sleeve.

[0353] The overall system concept (version with horizontal shot sleeve) is shown in FIG. 1, below:

[0354] This embodiment provides the ability of getting a metered shot by putting two valves in the system prior to the shot chamber. The valves are between the hot chamber and the shot chamber. In this concept, the plunger doesn't have any means of the sealing against atmosphere. The lower most of those two valves will be closed when the dies are open. When the dies are open, atmosphere can enter into the plunger cavity. Once the dies are closed, a vacuum is pulled on the mold cavity that will also suck the air out of the plunger cavity (i.e. the shot chamber). In the meantime, the top valve is opened and the feed tube between the two valves fills up with a specific volume. That volume is defined by the length and the diameter of that feed tube. Once vacuum has been established, with the die closed, the bottom valve is opened and the melt is allowed through and then shot it into the dies.

[0355] In accordance with an embodiment, this disclosed concept uses gravity feed. In another embodiment, the same two valve configuration is used with a pump.

[0356] A nozzle may be used to prevent wetting of feed port in top-fill configuration:

[0357] An example valve is shown below:

[0358] As for the materials and type of valve, in one embodiment, both the body of the valve and the valve stopper itself are made from ceramic. In another embodiment, at least the valve stopper is made of ceramic. In yet another embodiment, the valve stopper and stem are made of ceramic. The valve needs to be heated above the solidest temperature continuously. In an embodiment, the valve may be manufactured such that the area of the seat of this valve and its angle is such that there isn't a surface that's horizontal, so that the melt never touches a surface that's horizontal. The valve has to be kept heated so that the material never braises, it never solidifies and braises the valve to the body.

[0359] To get rid of any air in or around the valves, when the dies are open, the plunger is left in its fully extended position so that there's only a small gap between the plunger and the inside diameter of the shot chamber. Any air that leaks in will be done slowly so it doesn't create thermal shock for that valve. Then there is drawing vacuum on the dies once the dies are closed. Once vacuum on the dies is being drawn, the plunger is pulled back so that it's open to the feed port and therefore open to this passage below the bottom of the valve and suck all the air out of there.

Concept F: One Valve Inline Between Hot Chamber and Cold Shot Chamber

[0360] System Description: Combination hot chamber/cold shot chamber system. Final injection is provided by a cold shot chamber. A valve in the feed tube, proximal to the shot chamber, isolates the melt from atmosphere while the dies are open. The shot must be metered by the hot chamber pump and/or control system.

[0361] (Note: This system is similar in many respects to Concepts D and E. The use of a valve is similar to that of Concept E, but since there is only one valve, shot metering must be performed by a means other than a metering chamber. As with Concept D, the metering function is provided by either by a positive displacement hot chamber pump, or by a non-positive displacement pump combined with flow sensor(s) and a control system. [0362] The supply source of the melt is a hot chamber. [0363] The hot chamber is maintained at a relatively constant temperature, about 200 C. above the liquidus temperature of the melt, through the use of insulation and heating. [0364] The hot chamber feeds a cold chamber that drives the molten alloy into the mold cavity. The cold chamber comprises a shot chamber plunger housed in a shot sleeve. The shot sleeve is maintained at a relatively constant temperature (below the solidus temperature of the melt) through insulating and/or heating and/or cooling. [0365] At all points in the system, and throughout the injection process, the melt is protected from any exposure to air by a blanket of an inert gas, such as argon, or by vacuum. [0366] Prior to injection, the mold cavity is purged by vacuum to evacuate oxygen that would react with the melt. [0367] After purging, the mold cavity may be left in the vacuum state for injection, or may be filled with inert gas. [0368] In addition, in this concept, a valve is positioned inline in the feed tube between the hot chamber and the shot sleeve. The function of the valve is to isolate the melt from atmosphere while the dies are open. [0369] The valve must withstand continuous exposure to molten alloy, and must be maintained (as a minimum) above the solidus temperature of the alloy. [0370] Unlike Concept E, there is no separate metering chamber between the hot chamber pump and the shot chamber. Rather, as with Concept D, the metering function must be performed by the hot chamber pump. As with Concept D, a positive displacement pump is the best method of feeding melt from the hot chamber to the cold chamber. [0371] A piston pump such as described in Concept D may be used. As in Concept D, it is desirable for the melt to retract down the feed tube to minimize contact between the melt and the plunger/shot sleeve, to keep those elements from overheating. The functionality and material requirements are the same as described in Concept D. [0372] Alternatively, gas pressure in the hot chamber (at a higher pressure than that of gas, if used, in the mold cavity) or gravity feed could be used to transfer the melt from the hot chamber to the cold shot chamber. Flow sensors would be required to allow the pump to be shut off at the correct time. [0373] The inline feed tube valve must be left open during the plunger stroke to allow the melt to retract. The valve may only be closed once the melt has retracted to a level below that of the valve. [0374] As with Concept E, the feed tube from the hot chamber and the inline valve must each be maintained (by use of heating elements and/or insulation) at a temperature above the solidus temperature of the melt, to prevent the melt from solidifying between a valve and mating seat and brazing the two together. [0375] As with Concepts D and E, an inlet tube or insulating spacer tube connects the inline valve and the shot sleeve. This element should be made of a ceramic material with low thermal conductivity and high thermal shock resistance. An exemplary material is aluminum titanate. [0376] As with Concept E, since the inline feed tube valve isolates the melt, the plunger/shot sleeve does not have to perform this function. It may thus utilize conventional diametral gap clearances, and the plunger itself does not have to effect a positive seal to the shot sleeve. The plunger and shot sleeve also need not be heated beyond the usual requirements for conventional die casting. [0377] Since the valve positively isolates the melt, though, the range of inert atmosphere options is wider than those of Concept D; in fact, the same as Concept E. Specifically, vacuum may be used as an alternative to inert gas in the plunger backside chamber, and also may be used in the hot chamber. [0378] Unlike Concept E, gravity is not required in the final transfer of melt into the cold shot chamber. As such, the same range of shot chamber and feed tube orientations may be used as in Concept D. [0379] As with Concepts D and E, with the shot chamber in, or near, the horizontal orientation (orientation 3) it is beneficial to use a nozzle at the fill port so that the melt does not contact, and wet, the feed port itself (see FIG. 2, at end of document). [0380] As with Concepts D and E, the shot sleeve should only be positioned in orientations 1 and 2 only when used with vacuum in the shot chamber/mold cavity. (If used with gas, the melt would settle to the lower region of the shot chamber, and gas would be trapped near the plunger. Once the plunger were to drive the melt into the mold cavity, some gas may remain near the plunger/biscuit area, and some may migrate as bubbles that may become trapped in the solidified casting . . . an undesirable effect.) [0381] One of the advantages of this system is that it is not necessary to heat the shot chamber to as high a temperature as is required in Concepts 1-4. Though some heating of the shot sleeve may be beneficial, the design intent of this system is to maintain the shot sleeve below the solidus temperature of the melt. To do so, injection rates much be fast enough that the melt may not be allowed to dwell long enough in the shot sleeve to develop localized solidification zones. [0382] It is necessary for all the elements lining, and inside, the hot chamber, and those between the hot chamber and lower valve (including valves and valve bodies), to be: [0383] Either made of, or lined with, ceramic to avoid wetting and reaction to/degradation from the melt [0384] Heated to a constant temperature (above the solidus temperature of the melt) to: [0385] Minimize thermal cycling that could break down the ceramic and thereby contaminate the melt [0386] Prevent the melt from locally solidifying at the wall boundaries when passing through these elements. This is particularly an issue due to the injection velocities used, which will be much lower than those used in conventional high pressure die casting. [0387] The best ceramic valve and valve seat material is considered to be fused silica. Other options may include aluminum oxide, and aluminum titanate. The feed tube and hot chamber linings, and hot chamber pump materials may be made of various ceramic materials including fused silica, aluminum oxide, aluminum titanate, zirconium oxide, and magnesium oxide; specific examples are Al.sub.2O.sub.3+MgO and Al.sub.2O.sub.3+SiO.sub.2 ceramics. [0388] As the valves are heated above the solidus temperature of the melt, but the shot sleeve is designed to remain below that temperature, the inlet tube between the lower valve and the shot sleeve is a ceramic material selected for low thermal conductivity and high resistance to thermal shock. An exemplary material is aluminum titanate. [0389] Depending on variables such as the shot volume (as dictated by casting size), casting cross-section minimum thickness, and the extent of die heating used, the plunger and shot chamber, due to the relatively short-term exposure (as compared to Concepts 1-4) to molten liquid, may be made of high-temperature tools steels without compromising the ability to deliver the melt to the mold cavity at sufficiently high enough temperature and low enough velocity to avoid compromising casting quality. However, some large and/or complex castings may require the plunger and/or shot chamber also to be constructed from ceramics, and maintained at higher temperatures (i.e., near or above solidus temperature). [0390] As with Concept E, although the plunger tip is not required to seal against vacuum in this design, the plunger rod must still hold a vacuum seal (or, the shot sleeve and the plunger actuator must either be enclosed in a vacuum chamber, or in a chamber filled with inert gas) so that vacuum can effectively be established once the dies are closed. [0391] Once the dies close, the vacuum source(s) for the mold cavity may also serve to evacuate the shot chamber cavity. [0392] Once the melt reaches the shot chamber, it is driven into the mold cavity by a controlled plunger speed to eliminate turbulence which could cause imperfections in the finished casting. A maximum melt velocity of 0.5 meters/sec is recommended.

[0393] The injection cycle is as follows:

TABLE-US-00010 Die Plunger Lower position Position Action valve Pump Open 1 (intermediate Ejecting previous Closed Off position) cast part Closed 2 (fully Drawing vacuum on Closed retracted) mold cavity; filling metering chamber Closed 2 (fully Drawing vacuum on Closed retracted) mold cavity Closed 2 (fully Filling shot chamber Open retracted) Closed 2 (fully Shot chamber full Closed retracted) Closed 2-3 Injecting melt into Closed mold cavity Open 3 (full Allowing casting Closed stroke) to solidify Open 1 (intermediate Ejecting cast part Closed position)

[0394] The various combinations of atmosphere and feed method are shown in the table below:

Discussion

[0395] The unique advantages of this system are: [0396] Provides a positive means of isolating the melt system from exposure to the atmosphere while the dies are open, but without requiring the plunger to seal, thus allowing use of a conventional cold chamber shot sleeve system. [0397] Provides a means of metering an exact shot volume to the die. [0398] Allows a wider variety of shot chamber and feed tube orientations than Concept E. In particular, the shot chamber may utilize a bottom-fill feed port, and also may be oriented in orientations 4 or 5, both of which offer a less-turbulent flow profile than other orientations. [0399] Provides an effective system for using only vacuum (not inert gas) to establish an inert atmosphere in the mold cavity and shot sleeve.