# Patent

## Title
Controlled pressure casting

## Abstract

A method of forming metal castings includes positioning a first end of a structural member in a first mold cavity and a second end of the structural member in a second mold cavity. The first and second mold cavities are fluidly coupled to a reservoir of molten metal. A main pressure is applied to the molten metal in the reservoir to force the molten metal into the first and second mold cavities. First and second auxiliary pressures are applied to the first and second mold cavities to densify the castings formed in the first and second mold cavities. Another method for casting includes maintaining a main pressure at or less than an initial, mold-filling pressure after the first and second mold cavities have been filled. Additionally, a method for detecting whether a first mold cavity is sufficiently filled with molten metal includes monitoring a moveable element.

## Background
FIELD OF THE INVENTION
The present invention relates to casting metal structures. More specifically, the present application illustrates embodiments of the present invention, including those relating to the improvement of casting metal structures using controlled, auxiliary pressure and to improvements in filling casting molds.
BACKGROUND
Conventional aluminium high pressure die casting utilizes a hydraulic cylinder to advance a shot tip, displacing molten aluminium from the shot sleeve into the die cavity, overcoming the resistance to flow through the restricted gate area. When the die cavity is filled with molten aluminium, the pressure applied to the hydraulic shot cylinder is transferred to the molten aluminium based upon the ratio of the shot cylinder and shot tip cross-sectional area. If the die cavity containing one end of a submerged member fills and becomes pressurized before the die cavity or region of the die containing the opposing end of the submerged member, a resultant force is imposed on the end of the submerged member. To avoid movement of the submerged member, a mechanism must be employed, such as a clamp or a friction or form fitting die, to resist the force. As the cross-sectional area of the member increases, the forces become very high and difficult to manage with such mechanisms. Subsequent to filling of the die cavity, the pressure applied to the hydraulic cylinder advancing the shot tip is typically increased (i.e., intensified) by, for example, a factor of two times to reduce the volume of entrapped air and increase the rate of heat transfer. Also, once the in-gates have frozen-off through solidifying, which usually occurs prior to the solidifying of the entire die cavity, even the increased pressure fails to reach the material within the cavities being molded.
U.S. Pat. No. 3,664,410 to Groteke and U.S. Pat. No. 4,779,666 to Ruhlandt et al., disclose each a die casting process and apparatus.
SUMMARY OF THE INVENTION
One aspect of the invention relates to a method of forming composite metal castings. A first end of a structural member is positioned in a first mold cavity and a second end of the structural member is positioned in a second mold cavity. The first and second mold cavities are fluidly coupled to a reservoir of molten metal. A main pressure is applied to the molten metal in the reservoir to force the molten metal into the first mold cavity and the second mold cavity. A first auxiliary pressure is applied to the molten metal in the first mold cavity and a second auxiliary pressure is applied to the molten metal in the second mold cavity to densify the casting formed in the first mold cavity and in the second mold cavity.
Another aspect of the invention relates to a method of forming metal castings, comprising: positioning a first end of a structural member in a first mold cavity, the first mold being fluidly coupled to a reservoir of molten metal; applying a main pressure to the molten metal in the reservoir at an initial, mold-filling pressure to force the molten metal into the first mold cavity; applying a first auxiliary pressure to the molten metal in the first mold cavity; and maintaining the main pressure at or less than the initial, mold-filling pressure after the first mold cavity has been filled.
Another aspect of the invention is a method of forming metal castings, comprising: positioning a first end of a structural member in a first mold cavity, the first mold cavity being fluidly coupled to a reservoir of molten metal; applying a main pressure to the molten metal in the reservoir to force the molten metal into the first mold cavity; detecting whether the first mold cavity is sufficiently filled with molten metal by monitoring a moveable element; and applying a first auxiliary pressure to the first mold cavity after detecting that the first mold cavity is sufficiently filled.
Other aspects, features, and advantages of this invention will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, which are a part of this disclosure and which illustrate, by way of example, the principles of this invention.



BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings facilitate an understanding of the various embodiments of this invention. In such drawings:
FIG. 1 illustrates a schematic of one illustrated embodiment of the present invention;
FIG. 2 illustrates the embodiment of FIG. 1 with the molten metal partially filling the molds;
FIG. 3 illustrates the embodiment of FIG. 1 with the molten metal completely filling the molds;
FIG. 4 illustrates the embodiment of FIG. 1 with the auxiliary pressure being applied to the molten metal in the molds;
FIG. 5 illustrates the embodiment of FIG. 1 with the molten metal partially solidified, in the reservoir;
FIG. 6 illustrates a perspective view of an example of a vehicle cradle that may be produced by an illustrated embodiment of the present invention;
FIG. 7 illustrates a method in accordance with one aspect of the invention;
FIG. 8 illustrates a method in accordance with another aspect of the invention;
FIG. 9 illustrates a method in accordance with yet another aspect of the invention;
FIG. 10 illustrates a schematic of another embodiment of the present invention wherein four molds are in operation simultaneously to form two vehicle cradles; and
FIGS. 11-17 illustrate various examples of tube end closing and mechanical interlock for use with the present invention.



DESCRIPTION OF ILLUSTRATED EMBODIMENTS
FIGS. 1-5 illustrate one embodiment of the present invention. FIG. 1 illustrates, schematically an assembly 10 for casting metal parts, such as a vehicle cradle 50 as seen in FIG. 6. The assembly 10 includes a main or shot tip pressure source 12 illustrated in the form of a shot tip 14 and a hydraulic cylinder 16. The shot tip 14 is fluidly coupled to a reservoir or biscuit 18 and contains, along with the reservoir 18 a quantity of molten metal 20. The reservoir 18 forms a shot sleeve that is fluidly connected to two die assemblies 22 and 24. Die assembly 22 is comprised of at least two die elements 26 and 28, which form a first die cavity or casting area 30. Die assembly 22 has a restricted in-gate area 32 that is fluidly coupled to the shot sleeve 18 such that molten metal 20 is capable of being forced through in-gate 32 and into cavity 30. Similarly, die assembly 24 is comprised of at least two die elements 34 and 36, which form a second die cavity or casting area 38. Die assembly 24 has a restricted in-gate area 40 that is fluidly coupled to the shot sleeve 18 such that molten metal 20 is capable of being forced through in-gate 40 and into cavity 38.
In the Figures, the die assemblies 22 and 24 have been illustrated as separate assemblies. It is apparent to those skilled in the art that the die assemblies 22 and 24 can be combined into a single die assembly. The intermediate section between the two die assemblies can be utilized to provide support to the support member 52, as described below.
Each die assembly 22 and 24 has at least one auxiliary pressure source 42 and 44, respectively, that is attached to a point in the respective cavity 30, 38 that is remote or distal from the in-gates 32, 40. Preferably, auxiliary pressure sources 42 and 44 are spaced as far as possible from the in-gates 32, 40 and most preferably on opposite ends of the cavities 30, 38. The auxiliary pressure sources 42 and 44 perform two functions. First, each auxiliary pressure source 42, 44 provides an indication that its respective cavity 30, 38 is sufficiently filled with molten metal 20 and, second, to apply auxiliary pressure to each respective cavity 30, 38 as described below. Auxiliary pressure source 42 is illustrated in the figures as an auxiliary hydraulic cylinder having a piston 45 that is connected directly to the die cavity 30. Piston 45 operatively communicates with the cavity 30 and moves in a reciprocating fashion to define an expanded volume and a desired volume.
Movement of the piston 45, including movement caused by molten metal 20 filling cavity 30, can be monitored in various ways. FIG. 1 illustrates a limit switch 46 adjacent piston 45 to track its movement in and out of the die cavity 30. Auxiliary pressure source 44 is also illustrated in the figures as an auxiliary hydraulic cylinder having a piston 47 that is operatively connected directly to the die cavity 38. Movement of the piston 47, including movement caused by molten metal 20 filling cavity 38, can be monitored in various ways, but is illustrated as a limit switch or position sensor 48 adjacent piston 47 to track its movement in and out of the die cavity 38.
In the illustrated embodiment of FIG. 1, the composite or hybrid casting assembly is casting the ends of a vehicle cradle 50, which has multiple support members 52, 84 extending between multiple castings 80, 82, as seen in FIG. 6. In FIG. 1, only one support member 52 is illustrated but it should be understood that the other support members can be made in a substantially identical manner or in different configurations, as desired, such as seen in FIG. 6. Support member 52 can take various configurations, but is typically a tubular member, such as a high strength steel, hollow tube. Tubes such as tube 52 can be made by operations such as hydroforming, preferably according to known methods as described in U.S. Pat. Nos. 5,979,201; 6,014,879; 6,065,502; 6,474,534; 6,609,301; and 6,662,611.
To form cradle 50, tube 52 is to have a casting on each of two ends 54 and 56 of the tube 52. Die assembly 22 has been configured to provide the casting for end 54 and die assembly 24 has been configured to provide the casting for end 56. Although FIG. 1 only shows only tube 52 extending into cavities 30 and 38, multiple tubes such as tube 52 may extend into each of cavities 30 and 38 and become integral with the castings produced by die assemblies 22 and 24, as seen in FIG. 6.
The ends 54 and 56 of tube 52 extend into each cavity 30 and 38, respectively, and each end 54, 56 is closed so that molten metal 20 does not enter the hollow tube 52. FIGS. 11 to 17 illustrate various examples of hollow tubes with a closed end. The various examples provide two functions: closing the end of the hollow tube and providing a mechanical interlock between the casting to be formed and external surface of the hollow tube. The mechanical interlock prevents relative movement, torsional and axial, between the hollow tube and the casting. The mechanical interlock is enhanced by providing a mechanical interlock surface.
In FIG. 11, the tube end is crushed between two dies to present a flat end that is wider than the tube. A hole is provided through the flat end to present an interlock surface.
In FIG. 12, a separate stamped cap is positioned in the inside of the tube, closing the end. The cap is tack welded or crimped to the tube. The cap may have a flange having a non-circular configuration to provide a mechanical interlock surface.
In FIG. 13, a separate stamped cap is positioned in the outside of the tube, closing the end. The cap is tack welded or crimped to the tube. The cap may have a flange having a non-circular configuration to provide a mechanical interlock surface.
In FIG. 14, a separate stamped cap is positioned on the end of the tube, closing the end. The cap is welded to the tube. The cap may have a flange or tang having a non-circular configuration to provide a mechanical interlock surface.
In FIG. 15, the tube end is subjected to rotary swaging to shape the end in a bayonet shape.
In FIG. 16, the material is spun around the ends of the tube, with indents provided on the tube.
In FIG. 17, an end cap is welded to the end of the tube and a knurl is applied to the outside surface of the tube to present a mechanical interlock surface.
Each of the die assemblies 22 and 24 has a tube-receiving opening 55 and 57 and the split or parting line between die elements 26, 28 and 34, 36, respectively. Tube-receiving openings 55 and 57 are configured to complementarily receive tube ends 54, 56 respectively in a friction or interference fit. The tube-receiving openings 55 and 57 will clamp and retain the tube 52 in place after the die elements 26, 28 and 34, 36, respectively, have been closed. Although tube 52 has been illustrated as being straight and symmetrical, hydroforming enables tube of complex geometries be utilized in the present invention. To enhance the clamping capabilities, an intermediate die between the die assemblies 22, 24, can be provided to receive the tube 52 and provide support thereto, retaining the tube 52 is position during the casting process.
Preferably, the assembly 10, as illustrated in FIG. 1, is controlled by controller 60, which may take the form of a computer-based controller assembly or other automated or manually monitored controller assembly. Controller 60 can monitor and control the main pressure 12, the auxiliary pressures 42 and 44, and filling of the cavities 30 and 38. In the illustrated embodiment, the filling of the cavities can be monitored by controller 60 monitoring the sensors or limit switches 46 and 48.
The operation of the embodiment illustrated in FIG. 1 is best illustrated by viewing FIG. 1 in combination with FIGS. 2-5. The tube 52 is positioned in the casting assembly 10 such that first end 54 of tube 52 is positioned within first mold 22 and a second end 56 of the tube 52 is positioned within second mold 24.
The first and second molds 22 and 24 are fluidly coupled to reservoir 18 of molten metal 20. A main pressure is applied by hydraulic cylinder 16 and the molten metal 20 in reservoir 18 is forced into the first mold cavity 30 through in-gate 32 and simultaneously into the second mold cavity 38 through in-gate 40. The amount of pressure needed from cylinder 16 to fill the cavities 30 and 38 is preferably merely the pressure to overcome the resistance of pushing the molten metal 20 through the restricted in-gates 32 and 40. Thus, main pressure is applied by cylinder 16 to the molten metal 20 in the reservoir 18 at an initial, mold-filling pressure to force or inject the molten metal 20 into the mold cavities 30 and 38. As seen in FIG. 2, as the molten metal 20 begins filling the cavities 30 and 38, the molten metal 20 encapsulates the ends 54 and 56 of tube 52.
The molten metal 20 is preferably aluminium. At the moment of injection, the molten metal 20 preferably contains about 40-50% solids at less than 600° C., most preferably 583-595° C.
As seen in FIG. 3, the cylinder 16 continues applying the initial filling pressure and the molten metal 20 completely fills each of the mold cavities 30 and 38. The pistons 45, 47 for the auxiliary cylinders 42, 44 are free to move with the molten metal 20. The molten metal 20 contacts the pistons 45, 47, and urges the pistons 45, 47 outwardly, increasing the volume of the cavities 30, 38 such that the volume of each cavity is increased to an expanded volume. Pistons 45, 47 are pushed and displaced by the molten metal 20.
The displacement of the piston 45 and 47 may be measured or observed in any variety of ways well known in the art, such as by position sensor or limit switches 46, 48, respectively. Limit switches 46 and 48 each generate a respective fill signal once the piston 45, 47 has traveled a predetermined amount. The fill signal is transmitted to the controller 60 which responsively activates the auxiliary power sources 42 and 44.
Other devices or mechanisms can be used to determine when the cavities 30 and 38 are filled. Those devices may be integral or separate from the auxiliary pressure sources 42 and 44 or interactively connected such as illustrated. For example, after experimentation with the process to determine how much time it takes to fill each cavity 30 and 38, the timing routine may be established wherein pressures of the main 16 and auxiliary cylinders 42 and 44 are turned on and off based on a predetermined timing sequence. Also, a computer controlled system using controller 60 may be used to automatically monitor the position sensors or limit switches 46, 48 or other monitoring devices or methodologies to determine when the cavities 30 and 38 are filled and when to activate the auxiliary cylinders 42 and 44 and to control the main cylinder 16. Auxiliary cylinders 42 and 44 provide merely one mechanism for determining the fill of the cavities 30 and 38 and other mechanisms can be used that are part of or separate from the auxiliary pressure devices.
As seen in FIG. 4, with the main cylinder 16 still applying an initial, fill pressure, or with the main cylinder 16 being turned off or relaxed, the auxiliary cylinders 42 and 44 apply auxiliary pressure to the molten metal 20 in mold cavities 30 and 38, respectively. This application of auxiliary pressure by cylinders 42 and 44 moves the pistons 45, 47 from the expanded volume to a desired volume and thereby injects a small amount of molten metal 20 back into the mold cavities 30 and 38 to compensate for or densify the solidifying metal, which shrinks upon cooling. The cylinders 42, 44 maintain a predetermined pressure on the molten metal 20 in each of the mold cavities 30 and 38 instead of relying solely on the main cylinder 16. Without the use of auxiliary cylinders 42, 44, the main cylinder 16 would necessarily have to be operated to provide a relatively high pressure once the cavities 30 and 38 were filled with molten metal 20 to provide sufficient pressure on the molten metal 20 in reservoir 18 to continue injection of molten metal 20 into the cavities 30 and 38 during the solidifying stage to ensure that the solidified metal casting conforms to the mold cavity. However, the use of the auxiliary cylinders 42 and 44 permits the main cylinder 16 to apply a relatively lower pressure than in previous casting systems and, as a result, the main cylinder 16 of the subject casting assembly 10 is permitted to be smaller than a main cylinders used in a system without auxiliary pressure supplies 42, 44.
Depending on the casting process being carried out, the main cylinder 16 may continue providing a low pressure to the molten metal 20 during solidification while the necessary pressure on the molten metal 20 for solidifying in cavities 30 and 38 is applied by auxiliary cylinders 42 and 44. Alternatively, the main cylinder 16 may be turned off or relaxed once the auxiliary cylinder 42 and 44 begin applying pressure or at sometime thereafter.
Eventually, as seen in FIG. 5, the molten metal 20 begins solidifying. The molten metal 20 may initially begin solidifying at places such as at the in-gates 32 and 40 and in the shot sleeve 18. Once the in-gates 32 and 40 solidify, any pressure applied by the main cylinder 16 will cease to be effective in applying the appropriate pressure to any metal still semi-molten in the cavities 30 and 38. FIG. 5 illustrates a benefit of the auxiliary cylinders 42 and 44 in that each cylinder continues applying pressure to the molten metal in cavities 30 and 38, respectively, even after the in-gates 32 and 40 are blocked by solidified metal 70.
Once the molten metal 20 is completely and sufficiently solidified, the auxiliary cylinders 42 and 44 are turned off and the die elements 26 and 28 and die elements 34 and 36 are opened, respectively, to reveal casts 80 and 82 that are formed from the solidified molten metal 20 in mold cavities 30 and 38, respectively. As seen in FIG. 6, the casts 80 and 82 are rigidly connected to the tubular members 52 and 84 to form, for example, a vehicle cradle 50, such as a cradle front engine cradle or a rear cradle for an automobile, as illustrated.
As seen in FIG. 7, one aspect of forming a metal casting is illustrated in the method of forming metal castings, comprising a position step 88 of positioning a first end 54 of a structural member 52 in a first mold cavity 30; a second positioning step 89 of positioning a second end 56 of the structural member 52 in a second mold cavity 38, the first and second mold cavities 30 and 38 being fluidly coupled to a reservoir 18 of molten metal 20; an applying step 90 of applying a main pressure to the molten metal 20 in the reservoir 18 to force the molten metal 20 into the first mold cavity 30 and the second mold cavity 38; and an applying step 91 of applying a first auxiliary pressure to the molten metal in the first mold cavity 30 and a second auxiliary pressure to the molten metal in the second mold cavity 38 such that the metal pressure in the first mold cavity 30 is substantially equal to the metal pressure in the second mold cavity 38.
As seen in FIG. 8, another aspect of forming a composite metal casting is illustrated in the method of forming metal castings, comprising: a positioning step 88 positioning a first end 54 of a structural member 52 in a first mold cavity 30, the first mold cavity 30 being fluidly coupled to a reservoir 18 of molten metal 20; an applying step 92 applying a main pressure to the molten metal 20 in the reservoir 18 at an initial, mold-filling pressure to force the molten metal 20 into the first mold cavity 30; another application step 93 of applying a first auxiliary pressure to the molten metal in the first mold cavity 30; and a maintaining step 94 of maintaining the main pressure at or less than the initial, mold-filling pressure after the first mold cavity 30 has been filled.
As seen in FIG. 9, another aspect of forming a metal casting is illustrated in the method of forming composite metal castings, comprising: the positioning step 88 of positioning a first end 54 of a structural member 52 in a first mold cavity 30, the first mold cavity 30 being fluidly coupled to a reservoir 18 of molten metal 20; an application step 95 of applying a main pressure to the molten metal 20 in the reservoir 18 to force the molten metal 20 into the first mold cavity 30; a detecting step 96 of detecting whether the first mold cavity 30 is sufficiently filled with molten metal 20 by monitoring a moveable element 45; and an application step 97 of applying a first auxiliary pressure to the molten metal in the first mold cavity after detecting that the first mold cavity 30 is sufficiently filled.
The size of a semi-solid sub-liquidus casting (SLC) machine is defined by the platen size and the clamp tonnage. The platen size determines the largest die dimension that can physically fit under the clamp of the press. The clamp tonnage is defined by the product of the “projected area” times the metal pressure. Metal pressure relative to the size of casting defects and associated material properties is significant up to a metal pressure of 4 tons per square inch. Further increases in metal pressure in excess of 4 tons per square inch are reported to provide little additional value.
In one embodiment of the system of FIGS. 1-5, the sub-liquidus casting (SLC) process semi-solid casting process includes the biscuit or molten metal reservoir 18 (typically 20′′ diameter) from which molten metal 20 is transferred into the die cavities 30 and 38 via a hydraulic cylinder 16 and shot tip assembly 14. The machine tonnage required is determined by the product of the metal pressure (i.e., approximately 4 tons per square inch) times the sum of the projected area of the shot tip (biscuit) assembly 14 and 18 and the projected area of the castings outside the perimeter if the shot tip biscuit assembly 14, 18.
The SLC process would ordinarily assume that the majority of the casting projected area is located directly above the shot tip/biscuit area. The platen size is thus designed to accommodate a relatively large die, presenting metal pressure and casting projected area (shot tip plus casting area) as the limiting features which define the machine tonnage requirements.
The “controlled pressure” method of the subject application is particularly applicable to the manufacture of “hybrid material” cast automotive components such as cradles which are typically separated by high strength steel tubes. Separation of the castings results in a significant amount of the casting area to be outside of the projected area of the biscuit 18, thus increasing the machine size tonnage requirement of, for example, main cylinder 16. The controlled pressure method utilizes the shot tip assembly 14, 18 to inject metal into the dies 30 and 38 and auxiliary cylinders 42 and 44 provide pressure after the die cavities 30 and 38 are full. This technique results in limiting the metal pressure during the die fill and initial solidification phase to that of the machine clamp tonnage divided by the total projected area associated with the biscuit 14, 18 and casting area 30, 38. Once the cavities 30, 38 are full, the shot tip pressure is reduced and auxiliary cylinders 42 and 44 integral to the die cavities 30 and 38, respectively, are actuated, providing pressure to only the casting projected area.
Specifically, this can be seen when taking a specific rear cradle example:










CONVENTIONAL SLC CASTING METHOD

















Shot tip/biscuit diameter:
20
in


Shot tip/biscuit projected area:
314
in2


Casting projected area (outside perimeter of shot
192
in2


tip)


Total projected area (casting & shot tip):
506
in2 (192 + 314)


Required machine tonnage @ 8,000 psi (4 tons/
2,000
ton


in2) metal pressure



















CONTROLLED PRESSURE SLC CASTING METHOD IN


ACCORDANCE WITH EMBODIMENTS OF SUBJECT APPLICATION

















Shot tip/biscuit diameter:
20
in


Shot tip/biscuit projected area:
314
in2


Casting projected area (outside perimeter of shot tip)
192
in2


Metal pressure permitted at end of die fill
2
ton/in2


Required machine tonnage @ 8,000 psi (4 tons/in2) metal
768
ton


pressure









Thus, when using the method in accordance with the embodiments of the subject application, the required machine tonnage is less than the required machine tonnage using conventional methods and apparatus. The embodiments of the subject application, which are referred to as “controlled pressure” casting, provides the capability to cast components such as a rear cradle or front engine cradle in one casting machine cycle, in a reduced machine tonnage that is relative to only the “saleable” casting projected area (the casts 80, 82 themselves) rather the sum of the projected area of the castings 80 and 82 and biscuit 18.
FIG. 10 illustrates a casting assembly 100 in accordance with another embodiment of the invention wherein one shot tip pressure assembly 112 supplies molten metal to four casting die assemblies 114, 116, 118, 120 so that two vehicle cradles 122 and 124 may be cast simultaneously. Each vehicle cradle 122 and 124 is shown with two structural members 123 and 125, respectively, and each engine cradle 122 and 124 can be similar to cradle 50 in FIG. 6. The structural members 123 and 125 may be substantially identical to tube 52 in composition and make-up. Of course, the specific shape of any structural members 123 and 125 will vary dependent upon the specific vehicle cradle formed. As mentioned above, such an arrangement as illustrated in FIG. 10 is possible due to the efficiencies of the casting assemblies disclosed herein in the embodiments of the subject application.
In FIG. 10, main pressure assembly 112 is fluidly coupled to the die cavity of each die assembly 114, 116, 118, 120 by shot sleeves 126, 128, 130 and 132, respectively. Each die assembly 114, 116, 118, 120 receives the ends of two structural members 123, 125 so that the castings formed in each die assembly 114, 116, 118, 120 will encapsulate two ends of the structural members 123 and 125. Each die assembly 114, 116, 118, 120 also has an auxiliary pressure source 140, 142, 144, and 146, which is similar to auxiliary pressure sources 42 and 44 described above. Also, the casting assembly 100 can be controlled by controller 60 in a manner as described above with respect to controller 60. Other than the main pressure 112 supplying molten metal to four die assemblies 114, 116, 118, 120 the configuration of the casting assembly 100 is substantially identical to casting assembly 10 described above.
The embodiment of FIG. 10 illustrates one of the efficiencies of the illustrated embodiments of the subject application. That is, since auxiliary pressures are applied to each die 114, 116, 118, 120 during solidifying, the main pressure supplied to each die 114, 116, 118, 120 by main cylinder 16 is less than the pressures typically applied by main cylinders in prior art casting arrangements. Thus, since the main pressure in the embodiments of the subject application are lower, the size requirements of the pressure system and for the main hydraulic cylinder is less. This permits the embodiments of the subject application to utilize smaller main hydraulic cylinders and smaller pressure requirements. Alternatively, with the same size and pressure constraints found in the prior art, embodiments of the subject application can be used to fill a greater number of die cavities with molten metal 20. For example, wherein the a prior art configuration may only be used to cast one vehicle cradle member, embodiments of the subject application may be used to produce more castings, for example, two cradle assemblies that each require two castings. Thus, whereas the prior art could make, for example, two castings per cycle, the embodiment of FIG. 10 may produce, for example, four casting per cycle using the same pressure and sized machinery.
Thus, embodiments of the subject application utilize a minimum level of hydraulic pressure required to transfer molten metal 20 from the shot sleeve 18 through the in-gates 32 and 40 to the die cavities 30 and 38. The hydraulic pressure from the main pressure cylinder 16 that is needed to fill the cavities 30 and 38 is much less than the hydraulic pressure needed from a main pressure cylinder of, for example, a prior art device that only relies upon one pressure source—the main pressure source—to provide pressure during solidifying to reduce the volume of entrapped air and increase the rate of heat transfer during solidifying. The embodiments of the subject application also incorporate moveable cores (squeeze pins) in the form of auxiliary hydraulic cylinders 42 and 44 in each die cavity 30 and 38, respectively. The auxiliary cylinders 42 and 44 are capable of detecting that their respective die cavity 30 and 38 is full, prior to increasing the metal pressure within the cavities 30 and 38.
Embodiments of the subject application also simultaneously actuate the auxiliary hydraulic cylinders 42 and 44 acting as moveable cores to increase metal pressure integral to each die cavity 30 and 38, respectively, which share a common submerged member 52. Thus, embodiments of the subject application illustrate a method of densifying the metal in multiple cavity dies 30, 38 to minimize the main pressure force.
Also, embodiments of the subject application also provide a method of detecting whether die cavities such as cavities 30 and 38 are filled with molten metal 20 by using a moveable core, such as in the form of auxiliary hydraulic cylinders 42 and 44.
The foregoing specific embodiments have been provided to illustrate the structural and functional principles of the present invention, and are not intended to be limiting. To the contrary, the present invention is intended to encompass all modifications, alterations, and substitutions within the scope of the appended claims.

## Claims

1. A method of forming composite metal castings, comprising:
positioning a first end of a first structural member in a first mold cavity and a second end of the structural member in a second mold cavity, the first and second mold cavities being fluidly coupled to a reservoir of molten metal;
applying a main pressure to the molten metal in the reservoir to force the molten metal into the first mold cavity and the second mold cavity until the molten metal expands into the first mold cavity to a first expanded volume and the second mold cavity to a second expanded volume;
encapsulating the first and second ends with molten metal to secure the first structural member to castings being formed from the molten metal in the first and second cavities; and
applying a first auxiliary pressure to the molten metal in the first mold cavity to reduce the volume of the first mold cavity to a first desired volume and applying a second auxiliary pressure to the molten metal in the second mold cavity to reduce the volume of the second mold cavity to a second desired volume, wherein applying said first and second auxiliary pressures is initiated after sensing each of said mold cavities respectively attaining said expanded volume.

2. A method of forming composite metal castings according to claim 1, further comprising:
positioning a first end of a second structural member in a third mold cavity and a second end of the second structural member in a fourth mold cavity, the third and fourth mold cavities being fluidly coupled to the reservoir of molten metal;
forcing the molten metal into the third and fourth mold cavities as the molten metal is forced into the first and second mold cavities until the molten metal expands into the third mold cavity to a third expanded volume and the fourth mold cavity to a fourth expanded volume;
encapsulating the first and second ends of the second structural member with molten metal to secure the second structural member to castings being formed from the molten metal in the third and fourth cavities; and
applying a third auxiliary pressure to the molten metal in the third mold cavity to reduce the volume of the third mold cavity to a third desired volume and a fourth auxiliary pressure to the molten metal in the fourth mold to reduce the volume of the fourth mold cavity to a fourth desired volume while applying the first and second auxiliary pressures.

3. A method of forming composite metal castings according to claim 2, wherein each of said auxiliary pressures is applied to the respective mold cavity at a location remote from where the molten metal is forced into the respective mold cavity.

4. A method of forming composite metal castings according to claim 1, wherein said molten metal contains between 40 to 50% solids.

5. A method of forming composite metal castings according to claim 1, wherein the method further comprises a pre-step of forming a structural member by providing a hollow member and closing opposite ends of said hollow member.

6. A method of forming composite metal castings according to claim 5, wherein said step of closing opposite ends of said hollow member includes forming a mechanical interlock surface and subsequently contacting the mechanical interlock surface with molten metal.

7. A method of forming composite metal castings according to claim 6, wherein said step of closing includes one of crushing, capping, swaging, and spinning.

8. A method of forming composite metal castings according to claim 7, wherein said pre-step includes hydroforming the hollow member.

9. A method of forming composite metal castings according to claim 1, further comprising positioning a first end of a third structural member in said first mold cavity and a second end of the third structural member in said second mold cavity.

10. A method of forming composite metal castings according to claim 9, further comprising positioning a first end of a fourth structural member in a third mold cavity and a second end of the fourth structural member in a fourth mold cavity.

11. A method of forming composite metal castings according to claim 10, wherein the auxiliary pressures are substantially equal.

12. A method of forming composite metal castings according to claim 10, wherein the main pressure is reduced after the auxiliary pressures are applied.

13. A method of forming composite metal castings according to claim 10, wherein the main pressure is relaxed when the auxiliary pressures are applied.

14. A method of forming composite metal castings according to claim 1, wherein the first and second cavities are spaced apart from one another.

15. A method of forming composite metal castings according to claim 1, further comprising a pre-step of providing each mold cavity with a hydraulic cylinder having a sliding piston, said sliding piston respectively communicating with said mold cavity and movable to define said expanded volume and said desired volume.

16. A method of forming composite metal castings according to claim 15, further comprising a pre-step of providing a sensor for each hydraulic cylinder, each of said sensors respectively generating a signal when said mold cavities respectively attain said expanded volume.

17. A method of forming composite metal castings according to claim 16, wherein the applying the main pressure includes applying the main pressure at an initial, mold-filling pressure and maintaining the main pressure at or less than the initial, mold-filling pressure after the mold cavities have been filled.

18. A method of forming composite metal castings, comprising:
positioning a first end of a structural member in a mold cavity, the mold cavity being fluidly coupled to a reservoir of molten metal;
applying a main pressure to the molten metal in the reservoir to force the molten metal into the mold cavity through an in-gate;
contacting the first end with the molten metal to fix the structural member to a casting formed from the molten metal;
detecting whether the mold cavity is sufficiently filled with molten metal by monitoring a moveable element communicating with said mold cavity, said moveable element defining an expanded volume and a desired volume; and
applying an auxiliary pressure to the molten metal in the mold cavity after detecting that the mold cavity has attained said expanded volume.

19. A method of forming composite metal castings according to claim 18, wherein said monitoring includes tracking a position of a piston of an auxiliary hydraulic cylinder, the piston cooperating with said moveable element, and the applying the auxiliary pressure is accomplished by driving the piston of the auxiliary hydraulic cylinder moving the moveable element reducing said mold cavity from the expanded volume to the desired volume.

20. A method of forming composite metal castings according to claim 19, wherein the applying the main pressure includes applying the main pressure at an initial, mold-filling pressure and maintaining the main pressure at or less than the initial, mold-filling pressure after detecting that the mold cavity has attained said expanded volume.

21. A method of forming composite metal castings according to claim 19, wherein the main pressure is reduced when the auxiliary pressure is applied.

22. A method of forming composite metal castings according to claim 19, wherein the main pressure is relaxed when the auxiliary pressure is applied.

23. A method of forming composite metal castings according to claim 18, wherein said auxiliary pressure is applied to the mold cavity at a location remote from the inlet.

24. A method of forming composite metal castings according to claim 18, wherein said molten metal contains between 40 to 50% solids.