Abstract:
A wax pattern mold and molding process are disclosed for forming a wax pattern of a hollow, thin walled object, in particular, a golf club head. A mold is provided in at least two halves defining a mold cavity. A core made up of a plurality of interfitted parts is placed in the mold to precisely define the thin walls. The core and mold are provided with a registration channel such that the core is properly registered in the cavity to ensure dimensional integrity of the thin walls. Pins, holes, slots, and fingers are provided to lock the core parts together while the wax pattern is formed and to permit the core parts to be disassembled through an opening in the mold without separating the mold halves.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to lost wax casting of thin walled hollow objects, especially metal golf club heads, more particularly to the molding process for creating the wax pattern of the club head to be cast, and even more particularly to a core for; a wax mold that can be readily stripped from the mold without first removing the wax pattern therefrom. 
     Many golf clubs, in particular the metal woods, have hollow metal heads with precisely formed thin walls to provide advantages in striking a golf ball. Typically such heads are made by lost wax casting. Precision is required in the casting process in order to ensure that precise dimensions are maintained so that the final product incorporates the advantages which may be achieved from the thin walled head. Such thin walls have created difficulties in the casting process due, at least in part, to the need to provide a core to create the hollow wax pattern, which core must be stripped from the wax pattern before use. The typical prior art process required a skilled operator to open the wax pattern mold and remove the core from the wax pattern by hand. Such hand stripping of the core often causes deformation or other damage to the wax pattern, which jeopardizes the precision of the casting. 
     A wax pattern molding process using a stripable core which attempts to address some of these difficulties with the prior art is described in U.S. Pat. Nos. 5,204,046, 5,417,559 and 5,547,630. In these patents, a molding process is described in which a core made of multiple pieces, held together by T-shaped sliding interconnections, is wedged within a double door mold. One door of the mold creates at least part-of the mold cavity and the second door has a wedge which forces the core in place within the cavity. While addressing certain difficulties with stripping of the mold, this solution is not ideal. In particular, the wedging action which holds the core in place does not necessarily guarantee the precise positioning of the core due to inconsistencies as a result of force application being dependent on the degree of mold closure in such a wedging arrangement. Also the double door configuration adds complication to the mold. There thus remains a need in the art for an easily stripable mold which locates the core with precision. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a wax pattern mold with a stripable core that permits greater control over dimensional integrity of the walls of hollow thin walled objects to be molded. 
     This and other objects are achieved according to the present invention by a mold which comprises a mold body and a mold core. The mold body is made up of at least two mating parts together defining a cavity configured and dimensioned to define the outside of the hollow object to be molded, preferably the wax pattern of a metal wood golf club head. The mold parts also define a channel for delivering molten wax to the cavity and an opening configured and dimensioned to receive the mold core therethrough and extending into the cavity. The mold parts are separable to remove the molded object. In a preferred embodiment, the mold body parts are two halves hinged together for opening and closing. 
     The mold core has an upper portion configured and dimensioned to define the inside of the hollow object to be molded and a stem portion configured and dimensioned to be received in the mold body opening and mate with the mold body parts. The core is made up of a plurality of interfitted parts configured and dimensioned to be sequentially removable through the mold body opening without opening the mold halves. Also part of the invention are means for registering the position of the mold core in the mold cavity, and means for locking the core parts together. 
     According to one embodiment of the invention, the registering means comprises at least one registration member extending out from the core stem and at one least recess defined in the mold body around the mold body opening to receive the registration member in close fitting, positive engagement. In various alternative embodiments the registration member is a ridge formed at least partly around the core stem, at least one pin extending out from the core stem or a key extending out from the core stem wherein the recess receiving the registration member is a keyway. 
     In another alternative embodiment the registering means comprises at least one registration member extending out from the mold body around the mold body opening and at least one recess defined in the core stem to once again receive the registration member in close fitting, positive engagement. The same alternatives are again possible, in opposite relationship. 
     According to a further aspect of the invention, locking means comprises an extendable locking finger mounted on one core part and a slot for receiving the finger defined in a mating core part. In an alternative embodiment, locking means may comprise a locking member and at least one slot for receiving the locking member, wherein the slot is formed in one of the mold parts and the locking member bears against the core to lock the core in position when received in the slot. According to this alternative, the locking member may comprise an extendable locking finger disposed on an outer surface of the core, the finger being extendable from the core to be received in the slot, or a locking gate, slidably received over the core in two opposed slots defining in the mold parts. In further alternative embodiments, the locking means may comprise dowels inserted through close-fitting holes in the core stem portion to lock the parts together, either through the mold body or outside the mold body, or a locking gate carried in grooves in the mold body that bears against the mold stem portion. 
     The core according to the invention also may comprise a base plate with one of the plurality of core parts fixed thereto and a plurality of upstanding pins also fixed to the base plate. In this embodiment the other core parts have holes defined in them to receive the pins such that the parts may be removably assembled over the pins. 
     A further aspect of the invention is a method for forming a wax pattern of a hollow, thin walled object, such a golf club head, including the following steps: providing a wax pattern mold made up of at least two parts together defining a cavity configured and dimensioned to form the outside of the wax pattern, placing in the mold cavity a core configured and dimensioned form the hollow inside of the wax pattern wherein said core is comprised of multiple core parts, said placing including registering the core with the mold cavity to ensure dimensional integrity of the thin walls of the object, closing the mold parts together, locking the multiple core parts together in a step separate from said placing step, flowing molten wax into the mold cavity, permitting the wax to harden to form the thin walled wax pattern, removing the core while maintaining mold parts closed, opening the mold parts, and removing the wax pattern. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and advantages of the present invention will be more readily apparent from the following detailed description illustrated in the drawing figures, wherein: 
     FIG. 1 is a perspective view of a closed wax pattern mold according to the present invention with the core in place; 
     FIG. 2 is an enlarged side view of one embodiment of stripable core according to the present invention; 
     FIG. 3 is a top side view of the core of FIG. 2; 
     FIG. 4 is a plan view of an open mold according to an embodiment of the invention, with the core in place; 
     FIG. 5 is a partial perspective view of a portion of an open mold and core according to an alternative embodiment of the invention; 
     FIG. 6 is an exploded view of one embodiment of a core according to the present invention; 
     FIGS. 7-12 are partial perspective views, sequentially illustrating stripping of the core according to an embodiment of the present invention; 
     FIG. 13 is a side view of an alternative core according to the present invention; 
     FIG. 14 is a plan view of a core having an alternative locking means shown in hidden lines; 
     FIG. 15 is a perspective view of an alternative mold according to a further embodiment of the present invention; 
     FIG. 16 is a perspective view of the mold shown in FIG. 13 with the locking gate removed; 
     FIG. 17 is an exploded perspective of an alternative core and locking means according to the invention; 
     FIG. 18 is a partial perspective view of a closed mold using the core and locking means shown in FIG. 17; and 
     FIG. 19 is a partial perspective view of a closed mold according to another alternative embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, wax pattern mold  10  for forming the wax pattern of a metal wood is shown with core  20  in place. The mold is preferably made of two mold halves  12 ,  14  (although any number of mold parts may be used), held together at one side by hinge  16 . Shown outside the mold is hosel pin  18 , which forms the core for the hosel portion of the wax pattern club head. Note that throughout the description and FIGS. numbers are repeated where they refer to similar parts. 
     Enlarged views of the core are shown in FIGS. 2 and 3. In this embodiment core  20  includes a plurality of core pieces  20 A-F, mounted on base plate  22 . In this case, six core pieces are shown by way of example, but any number may be used. Upper core portion  24  is shaped to match the hollow interior of the club head and, in combination with the mold cavity, provide the precise wall thickness for the thin club head walls. Core stem portion  26  is smaller in diameter, to match the opening in the sole of the club head (the opening through which the core is stripped) and is held between mold halves  12 ,  14  to ensure precise positioning of the core. It is not required that the opening be through the sole. Alternatively, the opening may be provided through the face or the crown of the club head. The opening also may be provided in the heel of the club, but that may require that the core be made up of a higher number of pieces due to the heel having a smaller area than other club surfaces. Registration channel  28  extends at least partially around core stem portion  26 . Channel  28  cooperates with registration ring  46  (FIG. 4) to precisely locate the core with respect to the mold cavity, as explained in greater detail below. Rotatable handle  30  controls the internal locking finger  56  (see FIG.6) which holds the core together while in the mold. 
     Core  20  is shown in place in open mold  10  in FIG.  4 . As is generally known in the art, mold halves  12  and  14  provide wax flow channel  32 , cavity halves  34 ,  36  for the club head and cavity halves  38 ,  40  for the sole plate. Preferably the cavity halves may be lined with epoxy. At the bottom of each mold half is a recess that defines the mold core opening  44  (best seen, for example, in FIG.  11 ). Mold core opening  44  has registration ring  46  disposed therearound to mate with registration channel  28  in core stem portion  26 . Ring  46  does not extend across flat  48  in order to permit first core piece  20 A to be removed as described below. Ring  46  may be machined directly out of the metal mold halves or it may be a separate part (such as epoxy) inserted into a corresponding groove in the mold halves. 
     The interfitting of registration channel  28  and registration ring  46  provides a precise and positive location for core  20  within the mold cavity. In this manner the location cannot be accidentally varied and is not dependent upon a degree of wedging or other force applied between mating parts. Alternatives to the ring and channel may be used. For example, discontinuous ring segments or individual, short pins may be used. FIG. 5 illustrates the use of pin  43  received in hole  45  in core  20  to replace the registration ring and channel. A similar pin and hole on the opposite mold half and side of core  20  are not visible in the figure. Pins also may be employed in pairs. Various key and keyway constructions would also be suitable for positively guaranteeing proper registration as between the mold cavity and core. Whatever registration means is used in combination with the core pieces, it should permit a first piece to be removed when the core is stripped. For example, as shown in FIG. 14, a center core piece may be alternatively provided as the first piece to be removed. 
     Referring to FIG. 6, assembly and placement of the core will be described. Base plate  22  has a number of upstanding pins  52  which closely mate with holes  54 B-F in the bottom of core pieces  20 B-F. The fit between the pins and holes should be close enough so that the core pieces do not wobble when placed thereon, but also loose enough to allow easy placement and removal of the core pieces. Core piece  20 A is fixed to base plate  22  by screws or other suitable means. Handle  30  extends into core piece  20 A and cooperates with locking finger  56 . Locking finger  56  is disposed in slot  58  on the interior surface of core piece  20 A and rotates in and out when handle  30  is rotated in the corresponding in or out direction. A suitable geared, cammed, pin and slot or other mechanism may be provided for this purpose by a person skilled in the art. The interior surface of core piece  20 B, which mates with core piece  20 A, is provided with locking slot  60  to receive locking finger  56 . Other than slots  58  and  60 , the interior mating surfaces of the core pieces are preferably, but not necessarily, square and free of slots, grooves or ridges in order to provide a close and relatively seam free fit. To assemble core  20 , each core piece  20 B-F is placed over its corresponding pins  52  on base  22  with its interior surfaces mating with adjacent core pieces. Handle  30  is turned to cause locking finger  56  to engage locking slot  60 . The core thus assembled appears as shown, for example, in FIG.  2 . The assembled core  20  is then placed in the open mold as shown in FIG.  4 . Once placed in mold  10 , registration ring  46  engages registration channel  28  to ensure the proper location of the core within the mold cavity. The mold is then closed and the cavities are filled with wax via channel  32  as is known in the art. 
     Once the wax pattern has cooled to the desired degree, the core may be stripped, without opening the mold. In this manner, the dimensional integrity of the wax pattern is ensured. Handle  30  is rotated to move locking finger  56  into core piece  20 A and disengage it from core piece  20 B. Once this is done, core piece  20 A, including base plate  22  and handle  30 , may be removed from the mold, without opening the mold as shown in FIG.  7 . This can be accomplished because flat  48  (which provides a break in registration ring  46 ) mates against the outside of core piece  20 A, permitting its sliding removal once the locking finger is disengaged. Removal of core piece  20 A with base plate  22  also causes pins  52  to be removed from the other core pieces. With the pins removed, the other core pieces may be sequentially, laterally moved into the void left by core piece  20 A and then withdrawn through the opening in the sole plate of the club head as shown in FIGS. 8-12. 
     An alternative embodiment of the invention is shown in FIG.  13 . In this embodiment, core  20 ′ is provided with locking finger  56  on the outside of core piece  20 A′; which extends outward in the locking position, rather than locking internally as in the previous embodiment. Thus, locking slot  60  instead is provided in flat  48  on mold half  14  to receive the locking finger. This alternative is otherwise as described above in connection the embodiment of FIGS. 1-12. 
     Another alternative embodiment is illustrated in FIG.  14 . In this embodiment, core  20 ″ is provided with a double finger mechanism  56 A,  56 B. An additional, outer core piece  20 G is provided so that first core piece  20 A″ is a center piece. Finger  56 A extends from center core piece  20 A″ into slot  60 A in outer core piece  20 B″. Similarly, finger  56 B extends from center core piece  20 A″ outward, into slot  60 B in outer core piece  20 G. The double finger arrangement provides more secure holding and greater stability for the core. Also, because first core piece  20 A″ is a center piece, the registration channel and ring (or other registration means) may engage every outer core piece to provide further stability for the core and still permit the first core piece to be removed without opening the mold. 
     In a further alternative embodiment shown in FIGS. 15 and 16, mold  110  employs locking gate  164  instead of a locking finger and slot. Core  120  is assembled as explained above except for the lack of locking finger and slot. Registration ring  46  and channel  28  may be used to ensure proper registration of the core within the mold. However, in order lock the core pieces in the mold during the molding process, locking gate  164  is slid into locking grooves  166  on both mold halves  112 ,  114 . Locking gate  164  abuts against base plate  22  of core  120  to prevent its movement. As shown in FIG. 16, recess  168  may be provided to receive base plate  22  and the extending part of core stem portion  26 . Once the wax pattern has suitably hardened, the locking gate is removed and the core may be stripped from the mold as described above. 
     An additional alternative embodiment is shown in FIGS. 17 and 18. In this embodiment the locking means comprises a double dowel arrangement rather than the lever arrangement previously described. Here, double dowel member  270  has two dowels  272  extending parallel from handle  274 . Alternatively, a single dowel may be used in the same manner. First core piece  220 A has two half-channels  276  which align mating half-channels  278  on core pieces  220 E and  220 F, respectively, when the core is assembled. The half channels may be lined with bushings  277 , such as brass or bronze if desired. Thus, when the core is assembled, holes are formed by the mated half-channels to receive dowels  272  and lock together the core pieces. As shown in FIG. 17, it is preferred that the half-channels are also formed in mating relationship in core pieces  220 D,  220 B and  220 C so that dowels  272  may directly lock all core pieces. Pins  52  (not shown) are used as previously described to hold together the core pieces in a lateral direction. The pins may be mounted in base plate  22  or passed through appropriately sized holes in the base plate. Also as shown in FIG. 17, the registration means comprises channel  28 . Alternative registration means such as keys, pins, etc. previously described, may be used. 
     FIG. 18 shows the assembled mold  10  using alternative core  220 . Core  220 , when employing channel  28 , may be used with mold halves  12  and  14 , previously described. In an alternative preferred embodiment core  220  is provided with hole  45 , as shown in FIG. 5, so that pin  43  may be used as registration means. Once again, a person of ordinary skill in the art will appreciate that the core pieces must be configured in cooperation with the registration means to permit removal of the first piece without opening the mold. For example, a first center piece as in FIG. 14 may be preferable with the pin arrangement shown in FIG.  5 . 
     FIG. 19 illustrates yet another alternative embodiment. In this embodiment, upper half  312  of mold  310  is provided with dished area  380  to permit double dowel member  270  as previously described to be passed through lined holes  376  and into core  320 . By passing dowels  272  through upper mold half  312 , greater security of the core parts may be achieved. Core  320  is otherwise formed in a similar configuration to core  220 , previously described. With core  320  only a single registration pin  43  and hole  45  is required between the core and lower mold half  314 . 
     As will be apparent to persons of ordinary skill in the art, various modifications and adaptions of the structure and method above described will be possible without departure from the spirit and scope of the invention, the scope of which is defined in the appended claims. For example, a person of skill in the art may elect to provide a suitable taper to selected interfitting parts such as various pins or dowels to facilitate sliding fits and compensate for machining tolerances without departing from the scope of the invention.