Patent Publication Number: US-6986380-B1

Title: Vehicle wheel mold having a screenless gate

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
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     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
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     REFERENCE TO A SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISC APPENDIX 
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     BACKGROUND OF THE INVENTION 
     This invention relates in general to molds for casting vehicle wheels and in particular to a vehicle wheel mold having a screenless gate. 
     Vehicle wheels have 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 spokes typically support the wheel hub within the wheel rim. The wheel rim is adapted to support a pneumatic tire. 
     In the past, vehicle wheels typically have been formed entirely from steel. However, wheels formed 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 by attaching a wheel disc formed from a light weight metal alloy to a steel wheel rim. 
     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 inserted 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. 
     Conventional casting operations include numerous processes, such as die casting, low pressure injection casting and gravity casting. All the conventional casting operations typically utilize a wheel mold formed from a number of segments. The wheel mold defines a mold cavity which includes a rim cavity for casting the wheel rim and a disc cavity for casting the wheel disc. 
     For high volume production of castings, such as vehicle wheels, highly automated gravity casting processes are frequently used that typically use a casting machine having a plurality of 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, filling the rim and disc cavities. 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, the mold is opened and the wheel casting removed for machining to a final shape. The mold is then closed and again indexed to the refractory furnace to be refilled with molten metal. 
     Referring now to the drawings, a sectional view of a typical known gravity casting wheel mold  10  is shown in  FIG. 1 . The mold  10  is formed from a high temperature resistant metal, such as a steel alloy. The mold  10  includes a base segment  12  which can include a plurality of subsegments. The mold  10  further includes a pair of movable side segments, one of which is shown in  FIG. 1  and labeled  18 . Each of the side segments is supported by the base segment  12  and can include a plurality of subsegments. The side segments can be extended to a closed position or retracted to an open position by a conventional mechanism which, for clarity, is not shown in  FIG. 1 . The side segments carry a pair of gate members, one of which is shown in  FIG. 1  and labeled  20 . The gate member  20  extends from the right side of the side segment  18  in  FIG. 1 . The gate members co-operate to form a gate  21  that receives molten metal for casting the wheel. The gate  21  includes a tappered inlet chamber  22  into which the molten metal is poured. The inlet chamber  22  communicates through a gate passageway  25  with an intermediate chamber  26  formed within the gate member  20 . A narrow axial opening  27  is formed through the inner wall of the side member  18 , the purpose for which will be explained below. 
     The mold  10  also includes a filter, or screen,  28 , which is formed from a porous material, which is typically a ceramic, such as, for example, alumina foam, zirconia, silicon carbide or mica, is disposed across the base of the inlet chamber  22 . Alternately, the filter can comprise a fiberglass screen (not shown). As shown in  FIG. 1 , the filter  28  is received in the bottom of the inlet chamber  21  and supported by a shoulder  29  formed therein. 
     The side segments receive an axially movable top segment  30 . The top segment  30  can be extended to a closed position and retracted to an open position by a conventional mechanism which, for clarity, is not shown in  FIG. 1 . Similar to the other segments, the top segment  30  can include a plurality of subsegments. A ball riser segment  32  having an inverted cup shape is mounted in the center of the top segment  30 . The ball riser segment  32  defines an interior chamber that is referred to as a ball riser cavity  34  in the following. A vent opening  36  is formed through the top of the ball riser segment  32 . 
     When the top and side segments are extended to their closed positions, the mold  10  is closed and the top segment  30  cooperates with the base segment  12  and the side segments to define a mold cavity  40  for casting a vehicle wheel. The mold cavity  40 , as shown in  FIG. 1 , includes a generally circular disc cavity  42  for casting the wheel disc and an annular rim cavity  44  for casting the wheel rim. The disc cavity  42  communicates with the ball riser cavity  34  while the rim cavity  44  terminates in an annular rim riser cavity  46 . As described above, the axial opening  27  in the side segment  18  provides communication between the gate intermediate chamber  26  and the mold cavity  40 . 
     The operation of the apparatus  10  will now be described. The side and top segments are moved to their extended positions to close the mold  10 . Molten metal is poured into the gate  21 . Gravity causes the molten metal to flow through the filter, or screen,  28  and the gate passageway  25  and into the intermediate chamber  26 . The filter  28  removes oxides and other impurities from the molten metal. The filter  28  also reduces turbulence in the molten metal as the mold cavity  40  is filled, reducing oxidation of the molten metal. From the intermediate chamber  26 , molten metal flows through the axial opening  27  and into the mold cavity  40 . The molten metal flows across the disc cavity  42  and into the ball riser cavity  34 . Similarly, molten metal fills the rim cavity  46  and enters the rim riser cavity  46 . Pouring continues until the gate inlet chamber  22  is filled with molten metal. Contraction occurs as the molten metal solidifies, and molten metal flows from the rim and ball riser cavities  34  and  46  to fill any voids caused by the shrinkage. After the casting has cooled sufficiently, the top and side segments are retracted from the base segment  12 , allowing removal of the casting. 
     During the casting operation, the filter  28  solidifies with the metal of the sprue formed in the gate  22 . After each casting operation, the filter  28  removed with the wheel casting and discarded with when the sprue is cut from the casting. Accordingly, it is necessary to insert a new filter  28  into the gate before using the mold to cast another wheel. The replacement of the filter  28  is a time consuming operation and thus adds to the cost of manufacturing the wheel Additionally, the cost of the replacement screens further increases the total wheel manufacturing costs. Therefore, it would be desirable to provide an alternate reusable device in place of the screen. 
     BRIEF SUMMARY OF THE INVENTION 
     This invention relates to a mold for casting a vehicle wheel that has a screenless gate. 
     The present invention contemplates a mold for casting a vehicle wheel that includes a base segment, a top segment movable between a retracted position and an extended position and first and second side segments movable between retracted positions and extended positions. The base, top and side segments cooperate when extended to define a mold cavity with the first and second side segments further cooperating to define a gate cavity. The gate cavity is adapted to receive molten metal and communicates with the mold cavity. The invention further contemplates a pair of matrices of fingers with each of the matrices mounted within the gate cavity portion of one of said side segments. The matrices extend in a generally orthogonal direction from the surface of the side members portion and co-operate with one another when the side segments are extended to restrain the flow of molten metal through the gate cavity. The fingers may be either mounted directed upon the mold side segments or upon removable support members that are attached to the mold side segments. 
     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 
         FIG. 1  is a sectional view of prior art gravity casting wheel mold. 
         FIG. 2  is a sectional view of a gravity casting wheel mold according to the present invention. 
         FIG. 3  is an enlarged fragmentary sectional view taken along the line  3 — 3  in  FIG. 2 . 
         FIG. 4  is an enlarged fragmentary sectional view taken along the line  4 — 4  in  FIG. 2 . 
         FIG. 5  is a sectional view of an alternate embodiment of the mold shown in  FIG. 2 . 
         FIG. 6  is an enlarged fragmentary sectional view taken along the line  6 — 6  in  FIG. 5 . 
         FIG. 7  is an enlarged fragmentary sectional view of a portion of the mold shown in  FIG. 2  that includes another alternate embodiment of the invention. 
         FIG. 8  is a fragmentary sectional view taken along the line  8 — 8  in  FIG. 7 . 
         FIG. 9  is a fragmentary sectional view taken along the line  9 — 9  in  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring again to the drawings, there is illustrated in  FIG. 2  an improved gravity casting vehicle wheel mold  50  that includes a screenless gate  52  in accordance with the invention. Components shown in  FIG. 2  that are similar to components shown in  FIG. 1  have the same numerical identifiers. Thus, the mold includes a base segment  12  that supports a pair of side segments, one of which is shown in  FIG. 2  and labeled  18 , and a top segment  30 . The top segment carries a ball riser segment  32 . Upon closing the mold segments, a mold cavity  40  is formed for casting a one piece vehicle wheel. 
     The gate  52  is formed from a pair of gate members  54  and  55 , one of which is shown in  FIG. 2 . The gate members  54  and  55  are mounted upon corresponding mold side segments with gate member  54  shown as mounted upon side segment  18  in  FIG. 2 . The gate members close with the mold side segments to form the gate  52 . While the figures illustrate separate gate members mounted upon mold side segments, it will be appreciated that the invention also contemplates forming the gate  52  in an extended portion of the mold side segments (not shown). Similar to the prior art mold described above, the gate  52  includes a tapered inlet chamber  56  formed in the gate members that receives molten metal. The tapered inlet chamber  56  communicates with a generally rectangular filter chamber  58 . The filter chamber  58  communicates with the intermediate chamber  26  that, in turn, communicates with the mold cavity  40  through the axial opening  27  formed in the side segments. 
     A plurality of generally tapered, or conical, fingers  60  having rounded ends extend orthogonally into the filter chamber  58  from both gate members  54  and  55  and are arranged to form a pair of filtering matrixes. As best seen in  FIGS. 3 and 4 , the individual fingers  60  are tapered sufficiently that each of the fingers  60  of one of the matrixes extending from the sidewall of one of the gate members intervenes between two corresponding fingers  60  of the other matrix extending from the sidewall of the other gate member. In the preferred embodiment, the diameter of the fingers  60  at the base is 0.274 inches and the spacing between the centerlines of adjacent fingers is 0.494 inches; however, the invention also may be practiced with fingers having greater or lesser base diameters and spacing. The height of the fingers  60  is a function of the width of the filter chamber  58 . As also shown in  FIGS. 3 and 4 , the fingers on each of the gate members  54  and  55  extend sufficiently between the corresponding fingers on the opposite gate member such that only a narrow gap “g” exists between sets of intervening fingers  60 . In the preferred embodiment, the gap “g” between the fingers  60  is within the range of 0.060 to 0.080 inches; however, the invention also may be practiced with smaller or larger gaps. Thus, the matrixes of fingers  60  extending from the gate members  54  and  55  co-operate within the filter chamber  58  to form a web or sieve across the filter chamber  58 . 
     As shown in  FIG. 2 , in the preferred embodiment, the fingers  60  are spaced in parallel lines that are in a slightly upward direction from right to left in the figure; however, the fingers may also be staggered (not shown) in a non-parallel orientation and oriented in a different direction than shown in  FIG. 2 . Also, as shown in  FIGS. 3 and 4 , the fingers  60  are formed continuously, or integrally, with the gate members  54  and  55  and are thus comprised of the same material, which, in the preferred embodiment, is H13 alloy steel. Alternately, the individual fingers  60  may be formed separately and attached to the surface of the filter chamber portion of the gate members  54  and  55  by a conventional method, such as welding or use of threaded fasteners. Also, in the preferred embodiment, the fingers are hardened to HRC 47±2 and then nitrated for strength and durability. 
     The operation of the improved screenless mold  50  will now be described. The side and top segments are moved to their extended positions to close the mold  50 . As the side members are extended, the gate members  54  and  55  co-operate to form the gate  52 . Molten metal is poured into the gate inlet chamber  56 . Gravity causes the molten metal to flow between the fingers  60  in the filter chamber  58  and into the intermediate chamber  26 . The high velocity of the molten metal in the gate inlet chamber  56  is slowed by the metal impinging upon the fingers  60  and the flow is broken into a number of smaller, low velocity streams as it enters the intermediate chamber  26 . Thus, the fingers  60  co-operate with one another to reduce turbulence in the molten metal as the mold cavity  40  is filled, reducing oxidation of the molten metal. Depending upon the size of the gap g, the fingers  60  also may co-operate to entrap and thus remove oxides and other impurities from the molten metal. From the intermediate chamber  26 , molten metal flows through the axial opening  27  and into the mold cavity  40 . The molten metal flows across the disc cavity  42  and into the ball riser cavity  34 . Similarly, molten metal fills the rim cavity  46  and enters the rim riser cavity  46 . Pouring continues until the gate inlet chamber  22  is filled with molten metal. Contraction occurs as the molten metal solidifies, and molten metal flows from the rim and ball riser cavities  34  and  46  to fill any voids caused by the shrinkage. After the casting has cooled sufficiently, the top and side segments are retracted from the base segment  12 , allowing removal of the casting. 
     Upon opening the mold  50 , the movement of the gate members  54  and  55  withdraws the fingers  60  in the filter chamber  58  from the casting gate sprue. The portion of the gate sprue formed in the filter chamber  58  will include a plurality of conical recesses formed therein by the fingers  60 . However, the fingers  60  remain upon the gate members  54  and  55  and are available for the next casting cycle. Thus, the present invention contemplates replacing the prior art filter, or screen,  28  mounted in the base of the gate inlet chamber  22 , as shown in  FIG. 1 , with the plurality of reusable intertwined generally conical fingers  60  extending across a portion of the gate passage. Because the fingers  60  are reusable, the inventors expect a significant reduction in costs while eliminating the mold down time required for insertion of a new screen after every casting operation. The elimination of screen replacement downtime provides a corresponding increase in production rate. 
     The inventors have found that the molten metal passing between the fingers and the cyclical heating and cooling as castings are formed may cause undue erosion and cracking of the fingers  60 . Therefore, the inventors have found that it is necessary to periodically replace the fingers  60 . Accordingly, an alternate embodiment  70  of the invention is shown in  FIGS. 5 and 6  that enhances replacement of the fingers  60 . As before, components shown in  FIGS. 5 and 6  that are similar to components shown in the preceding figures have the same numerical identifiers. In the alternate embodiment  70 , each matrix of fingers  60  is mounted upon one of a pair of removable support members  72  and  74 , one of which is shown in  FIG. 5 . The support members  72  and  74  are received in recesses or openings formed in the gate members  54  and  55  and removably attached thereto. The support members  72  and  74  have shapes that match the filter chamber  58 . Thus, in  FIG. 5 , the support members  72  and  74  generally have a shape of a parallelogram; however, it will be appreciated that the support members also may be formed having different shapes, such as, for example, a square or rectangle. 
     The support members  72  and  74  and the fingers  60  may be formed from the same or a different material than the gate members  54  and  55 . In the preferred embodiment, the support members  72  and  74  and the fingers  60  are formed from Anviloy which the inventors have found to more durable that H13 alloy steel; however, other materials also may used. Also, in the preferred embodiment, the fingers are hardened to HRC 47±2 and then nitrated for strength and durability. As before, the fingers  60  may be formed continuously, or integrally, with the support members  72  and  74  or the individual fingers  60  may be formed separately and attached to the surface of the support members  72  and  74  by a conventional method, such as welding or threaded fasteners. By using a different material for the fingers  60 , the inventors have found that more cycles may be completed before replacing the fingers. Additionally, by mounting the fingers  60  upon removeable support members  72  and  74 , replacement time is greatly reduced. 
     Another alternate embodiment of the screenless gate is illustrated in  FIGS. 7 through 9  where components that are similar to components shown in the preceding Figs. again have the same numerical identifiers. As before, a plurality of fingers  80  extend orthogonally into the filter chamber  58  from both gate members  54  and  55  and are arranged to form a pair of filtering matrixes. However, the fingers  80  are formed as truncated cones having a greater base diameter than the fingers  60  shown in the previous Figs. In the preferred embodiment, the diameter of the fingers  80  at the base is 0.582 inches and the spacing between the centerlines of adjacent fingers is 0.660 inches; however, the invention also may be practiced with fingers having greater or lesser base diameters and spacing. The height of the fingers  80  is a function of the width of the filter chamber  58 . The ends of the fingers  80  may be either generally flat or have a slightly convex shape. As shown in  FIGS. 8 and 9 , the individual fingers  80  of one of the matrixes extending from the sidewall of one of the gate members again intervenes between two corresponding fingers  80  of the other matrix extending from the sidewall of the other gate member. However, the fingers do not extend as far toward the opposite side of the filter chamber  58 . As best seen in  FIG. 8 , the end of each finger extends past the center line of the filter chamber  58  by an overlap distance “d”. In the preferred embodiment, the overlap distance d is within the range of 0.1000 to 0.1500 inches and preferably about 0.1250 inches; however, the invention may also be practiced with a greater or smaller overlap distance. As before, in the preferred embodiment, the fingers are hardened to HRC 47±2 and then nitrated for strength and durability. The fingers  80  may be formed either with the gate members continuously, or integrally, with the gate members  54  and  55  or separately and attached to the surface of the filter chamber portion of the gate members by a conventional method, such as welding or the use of threaded fasteners. While the matrixes of fingers  80  extending from the gate members  54  and  55  co-operate within the filter chamber  58  to form a web or sieve across the filter chamber  58 , they do not extend as far into the resulting casting gate sprue  58  as the fingers  60  described above. Accordingly the withdrawal of the fingers  80  from the casting sprue is enhanced. Additionally, due to the larger base diameters of the fingers  80 , fewer fingers are needed to form the matrixes. 
     The invention also contemplates that the fingers  80  may be mounted upon removable support members that 74 are received in recesses or openings formed in the gate members (not shown) similar to the embodiment illustrated in  FIGS. 5 and 6 . 
     While invention has been illustrated and described with the mold  50  shown in  FIG. 2  for casting a complete one piece wheel, it will be appreciated that the invention also can be practiced on a mold for gravity casting a wheel component, such as a wheel disc or a partial wheel rim. Furthermore, while the preferred embodiment has been illustrated and described for a gravity casting vehicle wheel mold, it also will be appreciated that the invention also may practiced with molds for other types of casting, such as, for example, low pressure casting. Additionally, the invention also may be practiced with molds utilized to cast objects other than vehicle wheels. Finally, while the fingers  60  forming the matrixes have been illustrated and described as being generally conical in shape, it will be appreciated that the invention also may be practiced with fingers having other shapes than shown or described. For example, a conical finger would have a circular cross sectional shape; however the invention also may be practiced with fingers having oval or elliptical cross sectional shapes. 
     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.