Method and apparatus for vibration casting of vehicle wheels

Abstract

A vehicle wheel mold is vibrated at a frequency within a range of 0.1 to 10,000 Hz during a casting process. The vibration reduces the solidification time needed to form a wheel casting while improving the tensile strength of the wheel.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a Continuation-in Part of U.S. patent application Ser. No. 09/760,074, filed on Jan. 12, 2001, which claims priority from International Application No. PCT/US99/15,719 filed on Jul. 12, 1999, which claims the benefit of U.S. Provisional Application No. 60/092,684, filed on Jul. 13, 1998. The disclosures of all three of the above applications are incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not Applicable

REFERENCE TO A SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISC APPENDIX

[0003] Not Applicable

BACKGROUND OF THE INVENTION

[0004] This invention relates in general to casting of vehicle wheels and in particular to a method and apparatus for vibration casting of vehicle wheels.

[0005] Vehicle wheels include a circular wheel disc attached to an annular wheel rim. The wheel disc includes a central wheel hub having a pilot hole and plurality of wheel mounting holes formed therethrough. A plurality of equally circumferentially spaced radially extending spokes support the wheel hub within the wheel rim. The wheel rim is adapted to support a pneumatic tire.

[0006] In the past, vehicle wheels typically have been formed entirely from steel. However, one piece wheels formed entirely from light weight metals, such as aluminum, magnesium and titanium or alloys thereof, are becoming increasingly popular. In addition to weighing less than conventional all-steel wheels, such light weight wheels can be manufactured having a pleasing esthetic shape. Weight savings also can be achieved with two piece wheels formed by attaching a light weight metal alloy wheel disc to a steel wheel rim.

[0007] Light weight wheels are typically formed by forging or casting operations. During a forging operation, a heated billet of the light weight metal alloy is squeezed by very high pressure between successive sets of dies until the final shape of the wheel is formed. During a casting operation, molten metal is poured or forced under pressure into a cavity formed in a multi-piece wheel mold. After the metal cools sufficiently to solidify, the mold is opened and a rough wheel casting is removed. The wheel casting is then machined to a final shape. Machining can include turning the outside and inside surfaces of the wheel rim, facing the inboard and outboard wheel disc surfaces and drilling the center pilot hole and the mounting holes through the wheel hub.

[0008] Conventional casting operations include numerous processes, such as die casting, low pressure injection casting and gravity casting. Conventional casting operations typically utilize a wheel mold formed from a number of movable segments which are opened to allow removable of the wheel casting from the mold. Referring now to the drawings, there is illustrated in FIG. 1, generally at 10, a typical multi-segment wheel mold used for gravity casting. The mold 10 includes a base segment 11 which supports a plurality of movable side segments 12, two of which are shown in FIG. 1. The side segments 12 can be retracted and extended in a horizontal direction by a conventional mechanism 13. A movable top core 14 extends between the side segments 12. The top core 14 can be raised and lowered in a vertical direction by the mechanism 13. When the mold 10 is closed, the top core 14 cooperates with the side and base segments 12 and 11 to define a wheel mold cavity 15. The outline of a finished vehicle wheel cast in the mold 10 is illustrated in FIG. 1 by the dashed line labeled 16.

[0009] For high volume production of castings, such as vehicle wheels, a highly automated gravity casting process is frequently used. Such automated gravity casting processes typically use a casting machine having a plurality of multi-segment molds mounted upon a moving structure, such as a rotatable carousel. Each mold is indexed past a refractory furnace containing a pool of molten metal. A charge of molten metal is poured into a gate formed in the mold which communicates with the mold cavity. Gravity causes the metal to flow from the gate into the mold cavity. The mold and the molten metal cool as the casting machine indexes the other molds to the refractory furnace for charging with molten metal. After a sufficient cooling time has elapsed for the molten metal to solidify, the mold is opened and the wheel casting removed. The mold is then closed and again indexed to the refractory furnace to be refilled with another charge of molten metal.

BRIEF SUMMARY OF THE INVENTION

[0010] This invention relates to a method and apparatus for vibration casting of vehicle wheels. As explained above, casting of vehicle wheels is a highly automated process. However, the production of a casting machine is constrained by the length of time required for the molten metal to solidify within the individual wheel molds. A reduction in the length of time needed for the molten metal to solidify would allow an increase in the speed of operation of the casting machine, thereby increasing the number of wheels produced in a given time period. Accordingly, it would be desirable to reduce the length of time needed for the molten metal to solidify.

[0011] The present invention contemplates an apparatus for casting a vehicle wheel component which includes a multi-segment mold for the vehicle wheel component and a device for vibrating a portion of the mold. In the preferred embodiment, the device for vibrating includes a pneumatically powered ball vibrator. The ball vibrator is mounted adjacent to the mold and is operable to vibrate a top core of the mold. The wheel component can be either a one piece vehicle wheel or a full face wheel disc.

[0012] Alternately, the device for vibrating can be a pneumatically powered reciprocating hammer or an electrically powered device. The invention contemplates vibrating the mold at a frequency within the range of 0.1 Hz to 10,000 Hz. Additionally, the vibration frequency may be varied as a function of time. The invention also contemplates mounting an manifold upon the mold for injection of an inert gas into the mold cavity after the cavity is charged with molten metal. In the preferred embodiment, helium is used as the inert gas.

[0013] The invention also contemplates a method for forming a vehicle wheel component which includes providing a multi-segment mold for casting the wheel component and a device for vibrating a portion of the wheel mold. The cavity of the wheel component mold is filled with a charge of molten metal. A portion of the wheel component mold is vibrated at a frequency within the range of 0.1 Hz to 10,000 Hz while the molten metal solidifies. The wheel component casting is then removed from the mold. The molten metal can be poured into the mold cavity with gravity causing the molten metal to flow throughout the mold cavity or forced under pressure into the mold cavity with the pressure causing the molten metal to flow throughout the mold cavity. The invention also contemplates injecting an inert gas into the mold cavity as the molten metal cools. Additionally, the vibration can be started either before or after the mold cavity is charged with the molten metal.

[0014] Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is a sectional view of a multi-segment vehicle wheel mold according to the prior art.

[0016] FIG. 2 is a sectional view of a multi-segment vehicle wheel mold in accordance with the invention.

[0017] FIG. 3 is a sectional view of the multi-segment vehicle wheel mold shown in FIG. 2 equipped with an alternate embodiment of the invention.

[0018] FIG. 4 is a sectional view of the multi-segment vehicle wheel mold shown in FIG. 2 equipped with another alternate embodiment of the invention.

[0019] FIG. 5 is a flow chart for a method for casting a vehicle wheel in accordance with the invention.

[0020] FIG. 6 is a flow chart for an alternate embodiment of the method for casting a vehicle wheel shown in FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0021] The inventor has determined that vibrating a wheel mold can significantly reduce the amount of time needed for the molten metal contained within the mold cavity to solidify. Referring again to the drawings, there is illustrated in FIG. 2 a multi-segment wheel mold 20 used for gravity casting of wheels which is in accordance with the present invention. Components of the mold 20 which are similar to components shown in FIG. 1 have the same numerical designators. As shown in FIG. 2, a conventional commercially available ball vibrator 21 is mounted upon the mold top core 14. The vibrator 21 is secured to the top core 14 by a plurality of threaded fasteners 22. In the preferred embodiment, the vibrator 21 selected has a base which fits upon the top core 14 to minimize installation effort and time.

[0022] In the preferred embodiment, the vibrator 21 is operated by compressed air supplied though an air line 23; however, the invention also can be practiced with ball vibrators operated by other mediums, such as a hydraulically powered vibrator, or the vibrator can be powered by an electric motor. For the vibrator 21 shown, compressed air forces a chrome steel ball around bearing grade races to impart vibratory energy through the top core 14 to the molten metal contained in the mold cavity 15.

[0023] The compressed air, which is not affected by the high temperatures encountered in a foundry, can be supplied from a readily available source, such as tapping into the foundry air supply. The compressed air flows though a regulator (not shown) for controlling the pressure to adjust the speed and force of the vibrator. In the preferred embodiment, the air pressure is adjustable over range of from 60 pounds per square inch (psi) to 100 psi.

[0024] The compressed air also flows through either a manual valve or a solenoid valve (not shown) which is connected between the regulator and the vibrator 21. The valve controls the operation of the vibrator 21. In the preferred embodiment, a solenoid valve is utilized with the valve coil connected to a microprocessor which controls the casting machine. This assures that the vibrator 21 is actuated during the appropriate periods in the cycle. A filter (not shown) also is included in the air supply to remove an contaminants from the supplied air which may damage the vibrator 21. The compressed air is vented from the vibrator 21 through an exhaust port 24. An optional muffler (not shown) can be attached to the exhaust port 24 to reduce the noise generated by the discharge of the compressed air.

[0025] The inventors have found that vibration of the mold 20 while the molten metal contained therein solidifies has significantly reduced the solidification time for a wheel casting. The cooling of the molten metal is accelerated as the vibration of the mold increases contact between the molten metal and the steel mold segments. During tests, the solidification time has been reduced from six minutes without vibration to 4 to 5 minutes. Thus, vibration can reduce solidification time by 20 to 33 percent. Additionally, the inventor has observed that, with vibration, the microstructure grain size of a wheel casting is reduced from the size resulting without vibration. Also, the dendrite arms within the casting are broken off while the spacing of the dendrite arms within the casting is reduced when the mold is vibrated while the metal solidifies. Accordingly, the tensile and other mechanical strength of the wheel is improved by the application of vibration.

[0026] An alternate embodiment of the invention is illustrated by the mold 30 shown in FIG. 3. As before, components of the mold 30 which are similar to components shown in FIG. 1 have the same numerical designators. As shown in FIG. 3, a conventional pneumatic knock out hammer 31 is mounted adjacent to the mold top core 14. The hammer 31 is held in position by a mounting bracket (not shown) which is attached to the mold support mechanism 13. The hammer is 31 actuated by compressed air supplied through an air line 32. Similar to the ball vibrator 21 described above, the compressed air is vented through an exhaust port (not shown). The hammer 31 has a reciprocating head 33 which is located adjacent to a top plate 34 of the mold top core 14. When actuated, the hammer head 33 taps the top plate 34 to impart vibrations through the top core 14 to the molten metal contained within the mold cavity 15. Operation of the hammer 31 produces results similar to those described above for the ball vibrator 21.

[0027] While the preferred embodiments of the invention have been illustrated and described above for a ball vibrator 21 and a knock out hammer 31, it will be appreciated that the invention also can be practiced with other conventional devices for imparting vibrations to the wheel mold 10. For example, electrically operated vibrator 35, as illustrated in FIG. 4, may be mounted upon the mold top plate 34. As shown in FIG. 4, the electric vibrator 35 receives power from an oscillator 36. The oscillator 36 is connected through a switch 37 to a power supply 38. In the preferred embodiment, the timer and oscillator frequency are controlled by a control unit 39, that also receives energy from the power supply 38. In the preferred embodiment, the control 39 activates the electric vibrator 35 at a predetermined time in the casting operation and, as will be described below, times a vibration cycle with the vibrator 35 being deactivated after a predetermined time period T1 passes. The oscillator frequency is adjusted for the particular mold and metal being cast. While an oscillator with an adjustable frequency is shown in FIG. 4, it will be appreciated that the invention also may be practiced with a fixed frequency oscillator (not shown). The invention also contemplates that similar control equipment (not shown) is utilized with the ball vibrator 21 and knock out hammer 31 described above.

[0028] Additionally, while gravity casting has been shown and described above, it will be appreciated that the invention also can be practiced with other conventional casting processes, such as, for example, low pressure and die casting.

[0029] The invention contemplates that the mold is vibrated at a frequency within the range of 0.1 Hz to 10,000 Hz. Preferably, the mold is vibrated at a frequency within the range of 10 Hz to 1,000 Hz, or within the range of 10 Hz to 500 Hz. Additionally, the invention contemplates varying the vibration frequency as a function of time. For example, the vibration may commence at 1,000 Hz and be reduced to 10 Hz as the molten metal solidifies. The frequency reduction may be either a linear or non-linear function of time.

[0030] The present invention also contemplates enhancing the casting process by injecting an inert gas into the mold cavity after the cavity has been charged with molten metal. In the preferred embodiment, helium is used; however, other inert gases also may be utilized. The gas displaces any air that may remain between the metal and the mold segments to increase conduction of heat from the molten metal to the mold segments, thereby further decreasing the cooling time for the casting. As the mold cavity is charged, the molten metal displaces air contained within the cavity through vents provided in the mold. The vents are sized sufficiently small to prevent molten metal from entering the vents and thereby plugging them upon solidification. Therefore, the invention also contemplates mounting a manifold 40 upon the mold that is in communication with the air vents, as illustrated in FIG. 4. Inert gas is supplied to the manifold 40 via external piping or hoses 41. Once the air has vented from the mold cavity, and an initial skin formed on the casting, the inert gas would be admitted via the manifold and air vents into the mold cavity. The manifold would have valves (not shown) mounted thereupon to allow the air within the mold cavity to vent to the atmosphere as the molten metal is added. The valves would then be switched to close the vents to the atmosphere and to receive the pressurized inert gas. Alternately, the manifold could be mounted to communicate with the bores holding the ejector pins with the inert gas being injected through the injector pin holes. Again, valves would be provided on the vents to seal the mold from the atmosphere as the inert gas is injected. Additionally, the manifold could cover both the vents and injector pin bores and inject the inert gas through both types of openings. Thus, while the manifold 40 has been shown mounted upon the upper portion of the mold 30 in FIG. 4, it will be appreciated that the manifold also may be mounted upon other portions of the mold. Additionally, the invention also contemplates mounting a similar manifold upon molds 20 and 30 shown in FIGS. 2 and 3, respectively.

[0031] The present invention also contemplates a method for vibratory casting of a vehicle wheel. The method is illustrated by the flow chart shown in FIG. 4. In functional block 42, a wheel mold, which is equipped with a vibratory device, is charged with molten metal. The metal may be poured under gravity or injected into the mold cavity by a low pressure. The vibratory device is activated and the mold vibrated in functional block 43. The vibration continues at a constant frequency for a predetermined time period, T1, which is a function of the volume of metal being cast. Alternately, as described above, the vibration frequency may be varied as a function of time. In the preferred embodiment, the vibration time is between 200 and 250 seconds; however, it will be appreciated that the invention also can be practiced with other vibration time periods. For example, the vibration may continue until the casting is completely cooled and ready to be removed from the mold (not shown). In decision block 44, it is determined whether the time T1 has passed. If, in decision block 44, the total vibration time is less than T1, the method returns to functional bock 43 and vibration continues. If, in decision block 44, the total vibration time is greater than or equal to T1, the method advances to functional bock 46 and the vibratory device is turned off. If the total cooling time needed for the casting has not elapsed, the mold and casting are allowed to continue to cool for a additional time period, T2, in functional block 48; however, as indicated, this step is optional. In functional block 50, the mold is opened and the wheel casting removed therefrom.

[0032] In the preferred embodiment, the method is be practiced with vibration being applied to the mold while the mold cavity is being charged with the molten metal. This enhances release of gases entrapped within the molten metal. A flow chart for the preferred method is shown in FIG. 5, where functional blocks that are similar to those shown in FIG. 4 have the same numerical identifiers. The method begins with activation of the vibratory device in functional block 52. The vibration continues for a predetermined time period, T1′, which is a function of the volume of metal being cast and includes the time needed to charge the mold. In the preferred embodiment, the vibration time is between 200 and 250 seconds; however, as before, it will be appreciated that the invention also can be practiced with other vibration time periods. In functional block 54, the wheel cavity is charged with molten metal as the mold continues to be vibrated. The metal may be poured under gravity or injected into the mold cavity by a low pressure. Once the mold cavity is charged with molten metal, an inert gas, such as helium, is injected into the mold, as shown in functional block 56. As indicated in FIG. 5, such use of inert gas is optional and may be omitted from the method. Once the inert gas is added, the method advances to functional block 58 where vibration of the mold continues for the remainder of the predetermined time period T1′. The remainder of the method is the same as described above. Accordingly, the method advances to decision block 44, where it is determined whether the time T1′ has passed. If, in decision block 44, the total vibration time is less than T1′, the method returns to functional bock 58 and vibration continues. As described above, the vibration applied to the mold may be at a constant frequency or the vibration frequency may vary as a function of time. For example, one frequency may be used while the mold cavity is being charge, and another frequency may be used as the molten metal solidifies. If, in decision block 44, the total vibration time is greater than or equal to T1′, the method advances to functional bock 46 and the vibratory device is turned off. If the total cooling time needed for the casting has not elapsed, the mold and casting are allowed to continue to cool for a additional time period, T2, in functional block 48; however, as indicated, this step is optional. In functional block 50, the mold is opened and the wheel casting removed therefrom.

[0033] Another alternate embodiment of the method contemplates a delay before actuating the vibrator to allow the mold to be charged with molten metal and for the molten metal to be begin to solidify (not shown). In the preferred embodiment, the delay is in the range of from zero to 30 seconds; however, it will be appreciated that the invention also can be practiced with delays which exceed 30 seconds.

[0034] While the preferred embodiment of the invention has been illustrated and described with vibration applied to the top core of a wheel mold, it will be appreciated that the invention also can be practiced with the vibration applied to other portions of the mold, such as, for example, to a side segment (not shown) or to the base segment (not shown). Additionally, vibration can be applied simultaneously to a plurality of mold segments (not shown).

[0035] In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope. For example, while the preferred embodiment of the invention has been illustrated and described for casting a one piece wheel, it will be appreciated that the invention also can be practiced for casting a component of a vehicle wheel, such as a full face wheel disc or a wheel rim.

Claims

1. An apparatus for casting a one piece vehicle wheel comprising:

a mold base segment;

a plurality of movable mold side segments;

a movable top core segment, said top core segment co-operating with said base and side segments to define a gravity fed mold cavity for gravity casting a vehicle wheel; and

a vibration device mounted upon one of said mold segments, said vibration device being operative to selectively vibrate said mold segment at a frequency within a range of 0.1 to 10,000 Hz whereby the cooling of molten metal contained within said mold cavity is accelerated and the mechanical strength the resulting cast vehicle wheel is enhanced.

2. The apparatus according to claim 1 wherein said vibration device is operative to selectively vibrate said mold segment at a frequency within a range of 1 Hz to 1,000 Hz.

3. The apparatus according to claim 2 further including a timer device connected to said vibration device, said timer device operative for controlling the duration of the mold vibration.

4. The apparatus according to claim 3 wherein said vibration device is pneumatically powered and adapted to be connected to a supply of compressed air and further wherein the apparatus includes a solenoid valve for controlling the flow of compressed air into said vibration device and an adjustable pressure regulator for controlling the frequency and force of said vibration device.

5. The apparatus according to claim 3 wherein said vibration device is electrically actuated.

6. The apparatus according to claim 5 further including a frequency controlling device connected to said vibration device, said frequency controlling device operative to vary the frequency of vibration as a function of time.

7. The apparatus according to claim 5 further including a manifold mounted upon said mold and communicating with said mold cavity, said manifold operative to inject an inert gas into said mold cavity.

8. The apparatus according to claim 7 wherein said inert gas is helium.

9. A method for forming a one piece vehicle wheel casting comprising the steps of:

(a) providing a multi-segment gravity fed mold for gravity casting the vehicle wheel, the mold having a vibration device mounted upon a segment thereof, the vibration device being selectively operable to vibrate the mold;

(b) filling the cavity of the wheel mold by gravity with a charge of molten metal;

(c) activating the vibration device to vibrate mold at a frequency within the range of 0.1 Hz to 10,000 Hz upon completion of the filling of the mold cavity with molten metal;

(d) deactivating the vibration device;

(e) opening the mold; and

(f) removing the wheel casting from the mold.

10. The method according to claim 9 further including, subsequent to step (d), allowing the metal in the mold cavity to continue to cool before the mold is opened.

11. The method according to claim 10 wherein the top core is vibrated in step (c) after a predetermined time period has elapsed following the filling of the mold cavity.

12. The method according to claim 10 wherein the vibration device provided in step (a) is pneumatically powered.

13. The method according to claim 10 wherein the vibration device provided in step (a) is electrically powered.

14. The method according to claim 10 further including a manifold mounted upon the wheel mold, the manifold in communication with the mold cavity, and further wherein step (d) includes using the manifold to inject an inert gas into the mold cavity.

15. The method according to claim 14 wherein the inert gas is helium.

16. A method for forming a one piece vehicle wheel casting comprising the steps of:

(a) providing a multi-segment gravity fed wheel mold for gravity casting the vehicle wheel, the mold having a vibration device mounted upon a segment thereof, the vibration device being selectively operable to vibrate the mold;

(b) activating the vibration device to vibrate the wheel mold at a frequency within a range of 0.1 Hz to 10,000 Hz;

(c) filling the cavity of the wheel mold by gravity with a charge of molten metal;

(d) continuing to vibrate the top core while the molten metal cools;

(d) deactivating the vibration device;

(e) opening the mold; and

(f) removing the wheel casting from the mold.

17. The method according to claim 16 further including, subsequent to step (d), allowing the metal in the mold cavity to continue to cool before the mold is opened.

18. The method according to claim 17 wherein the vibration device provided in step (a) is pneumatically powered.

19. The method according to claim 17 wherein the vibration device provided in step (a) is electrically powered.

20. The method according to claim 17 further including a manifold mounted upon the wheel component mold, the manifold in communication with the mold cavity, and further wherein step (d) includes using the manifold to inject an inert gas into the mold cavity.

21. The method according to claim 20 wherein the inert gas is helium.