Lost-core molded polymeric golf club head

A method of forming a golf club head includes forming a core of the golf club head from a material having a first melting temperature and affixing a club face to the core. The club face includes a first, hitting surface, a second surface that is opposite the first surface, and a locking feature. A body is then molded about the core and such that it surrounds at least a portion of the locking feature, the body formed from a polymeric material having a second melting temperature that is greater than the first melting temperature. Finally, the core is removed from within the body.

TECHNICAL FIELD

The present invention relates generally to manufacturing techniques for forming a cavity in a golf club head through lost-core molding.

BACKGROUND

A golf club may generally include a club head disposed on the end of an elongate shaft. During play, the club head may be swung into contact with a stationary ball located on the ground in an effort to project the ball in an intended direction and with a desired vertical trajectory. This impact may generate momentary impact forces on the club face that can peak in the range of about 6520 N to about 18000 N (about 1520 lbf to about 4000 lbf).

Many design parameters must be considered when forming a golf club head. For example, the design must provide enough structural resilience to withstand repeated impact forces between the club and the ball, as well as between the club and the ground. The club head must conform to maximum size requirements set by different rule setting associations, and the face of the club must not have a coefficient of restitution above a predefined maximum (measured according to applicable standards). Assuming that certain predefined design constraints are satisfied, a club head design is typically quantified by the magnitude and location of the center of gravity, as well as the head's moment of inertia about the center of gravity and/or the shaft.

The club's moment of inertia relates to the club's resistance to rotation (particularly during an off-center hit), and is often perceived as the club's measure of “forgiveness.” In typical driver designs, high moments of inertia are desired to reduce the club's tendency to push or fade a ball. Achieving a high moment of inertia generally involves placing mass as close to the perimeter of the club as possible (to maximize the moment of inertia about the center of gravity), and as close to the toe as possible (to maximize the moment of inertia about the shaft).

While the moment of inertia affects the forgiveness of a club head, the location of the center of gravity behind the club face (and above the sole) generally affects the trajectory of a shot for a given face loft angle. A center of gravity that is positioned as far rearward (away from the face) and as low (close to the sole) as possible typically results in a ball flight that has a higher trajectory than a club head with a center of gravity placed more forward and/or higher.

While a high moment of inertia is obtained by increasing the perimeter weighting of the club head, an increase in the total mass/swing weight of the club head (i.e., the magnitude of the center of gravity) has a strong, negative effect on club head speed and hitting distance. Said another way, to maximize club head speed (and hitting distance), a lower total mass is desired; however a lower total mass generally reduces the club head's moment of inertia (and forgiveness).

In the tension between swing speed (mass) and forgiveness (moment of inertia), it may be desirable to place varying amounts of mass in specific locations throughout the club head to tailor a club's performance to a particular golfer or ability level. In this manner, the total club head mass may generally be categorized into two categories: structural mass and discretionary mass.

Structural mass generally refers to the mass of the materials that are required to provide the club head with the structural resilience needed to withstand repeated impacts. Structural mass is highly design-dependant, and provides a designer with a relatively low amount of control over specific mass distribution. On the other hand, discretionary mass is any additional mass that may be added to the club head design for the sole purpose of customizing the performance and/or forgiveness of the club. In an ideal club design, the amount of structural mass would be minimized (without sacrificing resiliency) to provide a designer with a greater ability to customize club performance, while maintaining a swing weight that is expected by the consumer.

In the interest of minimizing the total structural mass, most metal woods, for example, generally employ a thin metal face and hollow structural shell formed from a high strength, lightweight metal alloy. Such a design, while effective in reducing structural mass, may involve complex, multi-stage manufacturing processes, and may be limited in further advancements due to the cost prohibitive nature of more advanced alloys.

Another design factor involves the type of face style that is chosen for the club. In metal woods, the majority of designs can be categorized as either cup-faced, or edge-welded. An edge-welded design typically involves a substantially planar metallic plate that is fused onto the forward, face portion of the club to form the hitting surface. This plate is typically inlaid into a slight recess, and welded or fused to the body at, or proximate to the edge of the plate.

A cup-faced design includes a similar metallic plate/hitting surface, however, the plate extends beyond just the forward, face portion and onto the sole/skirt/crown of the body. Such a design extends the weld-line rearward, behind the hitting surface. In this manner, the cup-face design can provide a slightly larger possible hitting surface, and reduces the possibility for a welded edge, or portion of the body, to be directly impacted by the ball.

SUMMARY

A method of forming a golf club head includes forming a core of the golf club head from a material having a first melting temperature and affixing a club face to the core. The club face includes a first, hitting surface, a second surface that is opposite the first surface, and a locking feature. A body is then molded about the core and such that it surrounds at least a portion of the locking feature, the body formed from a polymeric material having a second melting temperature that is greater than the first melting temperature. Finally, the core is removed from within the body, such as by melting or dissolving.

In one configuration, the locking feature that is used to secure the face to the body includes a flange. The flange may be generally parallel to a portion of the first, hitting surface (i.e., to within about 30 degrees), and may be separated from the second surface by a distance. Molding a body such that it surrounds at least a portion of the locking feature may therefore include molding the body such that the polymeric material flows to opposing sides of the flange. This may provide a mechanical interference between the body and the club face, which inhibits all relative translation between the club face and the body. In one configuration, the molding may be performed through an injection molding process, such as by positioning the core and club face within a mold, and injection molding a polymeric material between the mold and the core.

In an embodiment, a golf club head assembly may include a core, a club face, and a polymeric body. The core may be formed from a first material and having a first melting temperature. The club face may be affixed to the core and may include a first, hitting surface, a second surface that is opposite the first surface, and a flange that is separated from the second surface by a transverse distance that is greater than zero.

The polymeric body is disposed about the core and on opposing sides of the flange. The polymeric body has a second melting temperature that is greater than the first melting temperature. The core is configured to be removed from the polymeric body by heating the core to a temperature between the first melting temperature and the second melting temperature, or by using a solvent.

The flange is parallel to a portion of the first surface to within about +/−30 degrees, and the polymeric body disposed on opposing sides of the flange provides a mechanical interference between the body and the club face to inhibit all relative translation between the club face and the body. In one configuration, the flange is a single, continuous flange that is aligned with a circumference of at least one of the first surface and the second surface.

DETAILED DESCRIPTION

Referring to the drawings, wherein like reference numerals are used to identify like or identical components in the various views,FIG. 1schematically illustrates a schematic perspective view of a wood-type golf club head10(i.e., “club head10”) that generally includes a face portion12(i.e., the “face12”) and a body portion14(i.e., the “body14”). As generally illustrated inFIG. 2, the club head10may be mounted on the end of an elongate shaft16, which may, in turn, be gripped and swung by a user to impart a generally arcuate motion to the club head10during a typical swing.

The face12of the club head10may generally define a hitting surface18that is intended to contact a golf ball during a normal swing. The hitting surface18may be a planar surface, or may have a slight convex/arcuate curvature that extends out from the club head10. Additionally, as is commonly understood, the hitting surface18may be disposed at an angle to a vertical plane when the club is held in a neutral hitting position. This angle may be generally referred to as the loft angle or slope of the club. Wood-type club heads (including hybrid woods) may most commonly have a loft angle of from about 8.5 degrees to about 24 degrees, though other loft angles are possible and have been commercially sold.

The body14of the club head10may generally be configured to support the face12and to provide a connection means between the face12and the elongate shaft16. Referring again toFIG. 1, the body14may generally include a lower portion20(i.e., a “sole20”), an upper portion22(i.e., a “crown22”), a side portion24that generally couples the sole20with the crown22(i.e., a “skirt24”), and a hosel28that is configured to receive and/or otherwise couple with the elongate shaft16. In an edge-welded-style club head, the body may further include a forward-facing wall26that at least partially abuts the face12, Axes30further define directionally-related portions of the club head10, including a fore-aft axis32extending through the face12(generally indicating front and rear portions/directions of the club head10), a vertical axis34extending perpendicular to the fore-aft axis32and between the sole20and crown22, and a toe-heel axis36extending perpendicular to both the fore-aft axis32and the vertical axis34.

FIGS. 3 and 4generally illustrate schematic cross-sectional views40,42taken along a vertical, fore-aft plane and respectively facing in opposite directions (i.e.,FIG. 3is generally toe-facing, andFIG. 4is generally heel-facing). As shown, the body14may at least partially surround and/or define an internal volume/cavity44that may be filled with air. WhileFIGS. 3 and 4illustrate the cavity44as being a closed cavity (i.e., isolated from the external environment), in other embodiments the cavity44may be partially open, such as by removing a portion of one or both of the crown22and sole20.

The views40,42provided inFIGS. 3 and 4further illustrate the thin-walled nature of the crown22and sole20, and provide further illustration of the portion generally referred to as the skirt24. In one configuration, the skirt24may include and/or be defined by a band of thicker material46disposed about the perimeter of the body14and between the crown22and the sole20. This band of material46may serve a structural function by reinforcing the outward edge of the body14against impacts, though may also be varied throughout the skirt24to increase the moments of inertia and/or alter the center of gravity.

The face12may generally be formed from a metal or metal alloy, and may be structurally supported on the body14by a face support48. The face support48may be an integrated portion of the body14and may generally receive a load/stress from the face12during an impact. The face support48may be operative to transmit this received load/stress to the remainder of the body14where it may be dissipated and/or absorbed. The face support46may be slightly recessed behind the face12and/or forward-facing wall26, and may contact a rear-facing surface50of the face12that is opposite the hitting surface18. In one configuration, the face support48may generally be disposed proximate to the perimeter52of the face12, and may define an open central region54where the rear-facing surface50of the face12is exposed to the cavity44. Additionally, as generally illustrated inFIG. 3, the face support48may have an angled nature (i.e., where the rear-facing surface50of the face12may contact the support48) to permit some amount of face-flexure prior to the face making flush contact with the support48(i.e., to promote a limited “trampoline-like effect”).

To reduce structural mass beyond what is economically viable with metal alloys, the body14of the club head10may be formed from a polymeric material having a yield strength that is great enough to withstand the repeated stress imparted by the ball impact. Examples of such materials may include certain polyamides, polyimides, polyamide-imides, polyetheretherketones (PEEK), polycarbonates, engineering polyurethanes, and/or other similar materials. In general, the polymeric material may be a either thermoplastic or thermoset, and may be unfilled, glass fiber filled, carbon fiber filled, or may have other suitable fillers and/or additives to promote increased strength. In one configuration, a suitable material may have a tensile strength of at least about 180 MPa, while in other configurations it may have a tensile strength of at least about 220 MPa.

In one configuration, the entire polymeric body14may be formed as a single, continuous piece. Such a design may have strength benefits by reducing seams, weld lines, or other parting lines that may act as stress concentration points. In another configuration, the design of the body14may include a single seam60located within the sole20, where a sole plate62may be subsequently bonded/fused to the body14to form a closed cavity44(if desired). As discussed above, however, in some designs, this sole plate62may be omitted to provide an open-cavity club head10. While reducing seam lines may provide certain structural and manufacturing advantages, the previous examples are intended to be illustrative, and should not exclude other designs that have two or more seams.

To provide a rigid connection between the face12and the face support48, the face12may include one or more mechanical locking features70disposed about its perimeter52that are configured to interlock with a portion of the body14. In one configuration, the locking feature may include a flange72that extends from the rear-facing surface50of the face12and may be embedded within the face support48during the fabrication of the body14. For example, the polymer used to form the body14may be over-molded around the flange72, such that the polymer contacts and surrounds the flange72up to, for example, the rear-facing surface50of the face12. Once the polymer has solidified, it may firmly secure the flange within the face support48, and interfere with the flange's ability to withdraw from the support48.

In addition to providing a rigid coupling means, the over-molded flange72may also efficiently transfer forces between the face12and the body14. More specifically, the geometry of the flange72may increase the contact area between the face12and the body14(thus lowering contact pressures). Additionally, the molding process may provide uniform contact between the flange72and face support48across the entire surface area of the flange72. Such a design may promote a more uniform force transfer than a club head with an affixed face inlay that may only make firm contact at a plurality of discrete points.

While suitable flanges may include a variety of shapes and sizes, the example illustrated inFIGS. 3 and 4is generally an “L”-shaped flange72that includes a first portion extending from the rear-facing surface50of the face12in direction that is generally perpendicular to the surface50, and a second portion extending radially outward from the first portion.FIGS. 5-6generally illustrate other flange configurations that may be used to mechanically retain the face12within the club body14. These examples include a dual-flange design (FIG. 5) and a radially inward facing “L” flange design (FIG. 6). Still other configurations may include hooks, tabs, angled posts, or other such protrusions that may likewise mechanically interlock with the body14. The face12may generally include either a plurality of discrete locking features70disposed around its perimeter52at spaced intervals, or may include a single continuous flange72that extends around the entire perimeter52, such as shown inFIG. 7.

Common to all of the above-described designs is a flange72extending in a direction that is generally parallel to the face12, while being separated from the face12by a distance. By “generally parallel,” it is intended that the flange72be parallel to the hitting surface18to within about +/−30 degrees. Such a design allows the polymer of the body14to flow between the flange72and the rear-facing surface50of the face12to form a mechanical interlock that prevents the face12from freely withdrawing from the body14. The flange72is connected to the remainder of the face12through an extension member that spans the distance between the rear-facing surface50of the face12and the flange72. In an edge-welded-style face, this extension member may be entirely surrounded by polymer (as shown inFIGS. 3-6). In a cup-faced design, the extension member may form an outer surface of the club head10. Regardless of the design, the hitting surface18, extension member, and flange72may have a similar material construction and/or may be formed from a single material.

As discussed above, the present club head10may be fabricated by molding a high tensile strength polymer material into the shape of the club body14, while ensuring that the polymer material also over-molds certain retaining features of a metallic face12.FIG. 8generally illustrates a manufacturing method80that may be used to fabricate a club head10of the current design. The method80may generally employ a molding technique known as “lost-core molding” to create the substantially hollow body geometry and face-interlock. Lost-core molding typically involves creating a core mold from a material having either a low melting temperature (e.g., from about 120° C. to about 200° C.) or a high solubility, over-molding the core with a polymeric material having a compatible melting temperature (or solubility), allowing the polymeric material to cool and (if thermoplastic) solidify, and subsequently melting or dissolving out the core so that only the molded polymeric part remains. This process permits complex internal geometries to be formed during a seamless, single molding operation (as opposed to forming the body in multiple discrete sections and attempting to bond/fuse them together).

With continued reference toFIG. 8, the manufacturing method80begins at82with the production of the face12. The face12may generally be formed from a light-weight metal alloy that may be either cast (e.g., through an investment casting process) or forged into the proper shape. Non-limiting examples of suitable face materials may include stainless steel (e.g., AISI type 304 or AISI type 630 stainless steel) or titanium (e.g., Ti-6Al-4V Titanium alloy), however other metal alloys, metal amorphous alloys, and/or non-metallic materials known in the art may similarly be used (for example, and without limitation, high-strength polymers or metal-polymer laminates).

In a separate process, a meltable core may be formed at84to generally resemble the internal cavity44of the club head10.FIG. 9generally illustrates an exploded view100of a club head10, with one embodiment of a meltable core102illustrated above the body14. Such a core102may be composed of a polymeric material that may be soluble in water, acetone, or another known or specially tailored solvent. Alternatively, the core102may be composed of a metal alloy having a relatively low melting temperature. Examples of typical low-melting temperature alloys include various compositions of bismuth, tin, lead, and zinc. The core102may be formed into a desired shape using typical fabrication methods, such as for example, casting, machining, or injection molding, or combinations thereof.

Referring again toFIG. 8, at86the face12may be affixed to the meltable or dissolvable core102.FIGS. 10 and 11respectively illustrate a top perspective view110and a side view112of a meltable core102having a face12affixed to a front portion114of the core102. Additionally,FIGS. 12 and 13illustrate a schematic cross-sectional view116of the face12and core102, taken along a vertical, fore-aft plane. In general,FIG. 12illustrates the face12affixed to the core102prior to an over-molding, andFIG. 13illustrates the same assembly with the body14molded in place (i.e., an intermediate golf club head assembly).

As generally illustrated in each ofFIGS. 10-13, in one configuration, the flange72may extend in a radially outward direction from a central portion74of the face12. As best illustrated inFIGS. 12-13, in one configuration, the core102may contact the rear-facing surface50of the face12only in a central area118that will form the open central region54where the rear-facing surface50of the face12is exposed to the cavity44. As such, the core102may be separated from the flange72by an amount that is sufficient to provide a properly dimensioned face support48that is capable of supporting the face12and transferring the repetitive impact loads from the face12to the body14.

The face12may be affixed to the core102using any suitable means of temporary attachment. Ultimately, the temporary attachment may allow the face12and core102to maintain a proper relative position and alignment when being positioned in a molding cavity to receive the over-mold. In one configuration, the attachment means may include a plurality of locating pins120that may extend from the face12into corresponding locating holes provided in the core102.FIG. 7generally illustrates one embodiment of such locating pins120that may extend from a portion of the flange72. These pins120may be cast in place, or may be joined to the face12through a separate process.FIGS. 12 and 13generally illustrate the use of locating pins120to affix the face to the core102.

In another configuration, similar locating pins may extend out from the hitting surface18of the face12. Instead of extending into locating holes within the core102, the locating pins120may be used to properly position the face12within a molding die. For the purpose of this description, holding the face12and core102in direct, adjoining contact, through an intermediate body, such as the mold, is one manner of “affixing,” as used herein. Once the body14is over-molded onto the core, the hitting surface18may be machined to remove the locating pins.

In still another configuration, the face12may be positioned on the core102using one or more locating features, such as unique surface contours, embossings, indexing protrusions or other similar features, which may ensure that the face12is properly positioned and oriented relative to the core102. Referring again toFIG. 7, in one embodiment, the rear-facing surface50of the face may have a structural reinforcing portion122in relief, which may extend outward from the face12to provide a locally increased face thickness. As generally illustrated inFIG. 9, the core102may include a similar, though inverse relief pattern124configured to receive the structural reinforcing portion122of the face12. Prior to over-molding, the structural reinforcing portion122or other localizing features of the face12may be mated with the inverse features124on the core102. In another embodiment, a temporary and/or soluble adhesive may be used to adhere the face12to the core102, with the locating features used as an alignment guide.

Referring again toFIG. 8, once the face12is affixed to the core102in step86, the polymeric club head body14may be molded about the face/core assembly at88. In general, any traditional molding techniques may be used, however injection molding may be the most straightforward process. During the injection molding process, two or more molding dies may surround the face/core assembly to form a molding cavity. A suitable molten polymer may be injected into the mold cavity, between the molding dies and the core102, to form the club-head body14. The result of this molding process is generally illustrated inFIG. 13. In general, the injected polymer may have a higher melting temperature, and may be injected at a higher temperature than the melting temperature of the core102. As such, precautions may need to be taken to guard against deformation and/or melting of the core during the molding process. Such precautions may include, for example, pre-cooling the core102prior to molding and/or actively cooling the core102during the injection of the molten polymer. While injection molding is one manner to over-mold the body onto the face/core assembly, in other configurations different molding processes may be used, such as for example, compression molding or dip coating.

Referring again toFIG. 8, once the body14of the club head10is over-molded onto the face/core assembly at88, the combined club head10/core assembly may be removed from the molding dies at90. At this point, the meltable core102may be removed from the assembly at92by heating the core102above its melting temperature, and allowing the molten core to flow out of the cavity44through one or more drain ports or open portions provided in the sole20. The process of removing the core102may be a controlled process that is careful not to melt or deform the newly formed body14. The core removal process may involve one or more fluid immersion baths, solvents that may act only on the core, focused induction heating, autoclave/oven heating, or other processes that may be known in the art. Alternatively, in some techniques, step90may be omitted and the core-removal process may occur directly within the mold.

As generally shown inFIGS. 9, 12, and 13, in one configuration, the core102may define one or more internal voids126that may be strategically placed to accelerate the core-removal process. By removing material from the core102that is not structurally required during the injection molding process, a smaller quantity of material may then need to be heated and removed from the club head10. As shown inFIG. 13, in one configuration, the void126in the core102may align with a corresponding opening128in the sole20. While this opening128in the sole20may provide an adequate drain port through which the molten core may be removed, it may also permit the core102to be internally fixed/fixtured within the molding cavity during the molding process. Such a configuration may eliminate the need for various suspension pegs that may otherwise be required to properly locate the core102within the molding cavity.

Referring again toFIG. 8, once the core102has been removed from the club head10(at92), the drain port or opening128may be (optionally) covered at94, such as using a plug or sole plate62. As generally illustrated inFIG. 13, in one configuration, a recessed shelf130may be molded into the body14to receive the sole plate62(the sole plate62generally being illustrated in the exploded view provided inFIG. 9). Using the recessed shelf130, the sole plate62may be maintained in an externally flush arrangement with the remainder of the body14where it may then be bonded, adhered, fused, welded or otherwise mechanically attached to the body14.

As mentioned above, the lost-core manufacturing technique may permit unique geometries to be internally molded into a generally seam-free polymeric club head10, which may not have been possible through more traditional club manufacturing techniques. For example, internal ribs, gussets and buttresses can be placed into the core to mold such features into the head. Likewise, as generally illustrated inFIG. 9, the core may be formed to have one or more protrusions140extending radially outward from a skirt portion142. In the finally manufactured club head10, these protrusions140may form specifically located voids in the body14that may receive weight inserts (i.e., discretionary mass) to alter the center of gravity and moments of inertia of the head10. In another embodiment, the aforementioned weight inserts may be mechanically adhered directly to the core102(in lieu of the protrusions140), where they may be molded in place once the core102is removed. In one configuration, these molded-in-place weights may have a particular geometry or retaining features that may prohibit their withdrawal from the body14. In still other embodiments, a continuous (yet variable) weight band may extend around the skirt portion142of the core102, where the weight band may be integrally molded into the body14following the removal of the core102. In each instance, the use of the present manufacturing techniques with high strength polymers may enable great flexibility in the design and discretionary weighting of club heads.

While the present description has focused on wood-type clubs having a single cavity44, in other embodiments, club heads with multiple cavities may also be formed through this method80. For example, in one configuration, a club head10may include a first, forward-located cavity that is substantially closed or isolated from the surrounding environment, and a second, rearward-located cavity that may be an “open” cavity, though may be isolated from the first cavity by a divider wall. In other embodiments, the size and dimension of various cavities and/or the position of various cavity dividers may be easily altered by merely creating a new core design.

While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not as limiting.

“A,” “an,” “the,” “at least one,” and “one or more” are used interchangeably to indicate that at least one of the item is present; a plurality of such items may be present unless the context clearly indicates otherwise. All numerical values of parameters (e.g., of quantities or conditions) in this specification, including the appended claims, are to be understood as being modified in all instances by the term “about” whether or not “about” actually appears before the numerical value. “About” indicates that the stated numerical value allows some slight imprecision (with some approach to exactness in the value; about or reasonably close to the value; nearly). If the imprecision provided by “about” is not otherwise understood in the art with this ordinary meaning, then “about” as used herein indicates at least variations that may arise from ordinary methods of measuring and using such parameters. In addition, disclosure of ranges includes disclosure of all values and further divided ranges within the entire range. Each value within a range and the endpoints of a range are hereby all disclosed as separate embodiment. In this description of the invention, for convenience, “polymer” and “resin” are used interchangeably to encompass resins, oligomers, and polymers. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated items, but do not preclude the presence of other items. As used in this specification, the term “or” includes any and all combinations of one or more of the listed items. In other words, “or” means “and/or.” When the terms first, second, third, etc. are used to differentiate various items from each other, these designations are merely for convenience and do not limit the items.