Golf club head with highly polished hard contact fact
A head for a golf club used for hitting balls long distances, or for putting, has a hitting or contact surface formed by an insert placed within a pocket formed within the club head face. The insert has at least a surface layer made of polycrystalline diamond or cubic boron nitride. The insert may be polished very smooth to place less backspin on the ball and reduce surface flaws. The edges of the insert may also be rounded or chamfered to reduce chipping or cracking of the insert. Furthermore, the pocket into which the insert is set may be reinforced to reduce deformation of the pocket during ball contact that places stress on the insert.
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TECHNICAL FIELD OF THE INVENTION
 The invention relates to golf club heads.
BACKGROUND OF THE INVENTION
 Designers of golf equipment have long sought optimum designs for golf clubs, both in terms of physical design and selection of materials, for achieving maximum performance. There have been numerous efforts to arrive at innovative designs of club heads, club head materials, and shaft materials for maximum performance, i.e. distance that the ball is propelled after being struck.
 Traditionally, “woods” (clubs usually used for tee shots and longer fairway shots) have heads made of hard wood, the preferred wood being persimmon. The tendency of wood to warp or split, however, coupled with increasing costs of material and labor, has led to the development of woods fabricated of materials other than wood. For example, there are many different kinds of engineered materials currently being used in the construction of the club head or club face, such as steels, cast irons, aluminum, copper, titanium, graphite, plastics, woods, and carbides and their alloys and composites.
 U.S. Pat. Nos. 4,951,953 and 5,029,865 of Kim and U.S. Pat. No. 5,620,382 of Cho et al. both recognize the desirability of using rigid materials, i.e. materials with a high “Young's Modulus,” for the ball contact faces of golf clubs in order to increase the distance traveled by the ball. A rigid material tends to impart more energy of the moving club to the ball. A particularly preferred material is a diamond-containing coating, because diamond is the hardest material known and has the highest Young's Modulus. Kim recognizes that a coating of pure diamond would be ideal, but states that such coatings are difficult and costly to apply, and the pure diamond material is itself costly. Therefore, Kim teaches electroless coatings, 10-100 micrometers thick, of composite material wherein diamond particles are embedded in a metal or metal alloy matrix, such as a nickel matrix, such that the diamond particles are weakly cemented together by the soft metal without any diamond-diamond bonds.
 Cho et al. discloses an insert for a face of a golf club head, the insert having a flat, front face that is comprised of a polycrystalline diamond (PCD) or polycrystalline cubic boron nitride (PCBN) compact wherein the individual crystals are bonded together, respectively, by diamond-diamond or CBN—CBN bonds. In particular, the ball striking face of the club has a cavity formed that receives an insert. The insert has a surface layer of a compact material comprising a member selected from the group consisting of diamond and CBN crystals wherein the crystals are bonded together by diamond-diamond or CBN—CBN bonds between adjacent crystals, and a support layer of a hard, rigid material to which the surface layer is bonded. The insert is disposed in the cavity such that the surface layer is coplanar with the ball striking face. The compact material is preferably a member selected from the group consisting of PCD, thermally stable PCD, reinfiltrated PCD, and CVD diamond film, and the surface layer preferably has a thickness of about 0.1 to about 20 mm. The insert can be adapted for use in a putter or for use in a wood or iron. Grooves can be formed in the surface layer to spin the ball upon contact.
SUMMARY OF INVENTION
 Though flat and smooth on a macroscopic scale, inserts for golf head faces with surfaces made from polycrystalline materials, like those of Cho et al., are, in fact, relatively rough on a microscopic scale. Inserts with super-hard surface material made from PCD, CBN, and CVD, which are made according to methods in Cho et al., have a surface roughness of over 50 micro inches after fabrication. Generally, fabrication of such inserts involves lapping the surface of the insert to remove macroscopic variations in the surface after compacting, deposition or sintering of the material. Hard ceramic materials, such as tungsten carbide, also have surface roughnesses in the same range.
 Some degree of roughness has been thought to be desirable, as it provides more friction to spin the ball. However, a smoother finish on a hard, contact face on at least some types of golf clubs is more desirable. First, a smoother finish will result in less spin. For some clubs less spin may be undesirable, such as clubs that are used to place back-spin on the ball. However, shots taken with certain clubs may benefit from placing less spin on the ball. One example of such a club is a driver or other club that is hit for distance. Excessive back spin leads to excessive aerodynamic lift of the ball, which can cause “ballooning” of the ball. Reducing backspin allows the ball to penetrate the air better, which gives it a better “boring” trajectory. Furthermore, less backspin increases roll distance of the ball after it lands. Placing grooves in the face of a hard insert for such a club is thus actually counter productive in some cases. Another example is a putter. An inside-out or outside-in stroke during putting will tend to impart a sideways spin to a ball that causes it to roll off the desired line. A putter with a smoother face will lessen the effect of a poor stroke.
 Second, a smoother surface finish will tend to have fewer or smaller surface flaws, as those flaws are removed or reduced in size during surface finishing. Hard materials, especially super hard materials such as polycrystalline diamond, cubic boron nitride and other similar materials, are relatively brittle. Surface flaws reduce impact strength or toughness of the materials and lead to cracking and chipping. As golf club heads, especially those used for driving a ball long distances, regularly impact golf balls, surface flaws in super hard and hard face inserts often lead to premature failure of the insert.
 According to one aspect of the invention, a golf club head has a ball-contacting surface formed from hard or super hard material with a very smooth finish. The very smooth finish is achieved by polishing it to 20 micro-inches or finer, though it is preferable to polish it to less than 10 micro-inches, and best if it is finished to less than 2 micro-inches or finer. These faces may take the form of an insert that is placed in a pocket milled or otherwise formed in the head of a golf club head. The super hard or hard contact surface of the insert may be formed on a base made from a less hard material. For example, the polycrystalline diamond layer may be formed on a base of tungsten carbide. Though it is preferable to use polycrystalline diamond (such as polycrystalline diamond compacts or thermally stable polycrystalline diamond), cubic boron nitride (CBN) or other super-hard material for the surface of a contact area of a golf club head, other hard materials can be finished to the same degree of smoothness, such as tungsten carbide, silicon carbide, and other ceramics.
 According to a different aspect of the invention, reducing the sharpness of the front edge(s) of a ball contacting insert (whether it be round or multi-sided) of a golf club head also reduces chipping and cracking of the insert. These edges are formed by the transitions between a flat front surface and one or more side surfaces of the insert. The edges may be ground to form a chamfer (or bevel) or a radius (“rounded”), or they may be honed (by hand, for example) and thus have a more irregular edge. The ball contact surfaces of such inserts may or may not be also polished as described above. However, when combined with a highly polished surface, an insert with at least its front (ball-contacting) edge(s) having a smoother transition will tend to have substantially improved resistance to cracking and chipping.
BRIEF DESCRIPTION OF THE DRAWINGS
 FIG. 1 is a drawing of a representative example of a golf club head.
 FIG. 2 is a cross-section of a ball-contacting insert for the golf club head of FIG. 1.
 FIG. 3A is a cross-section of a ball-contacting insert with a chamfered front edge.
 FIG. 3B is a cross-section of a ball-contacting insert with a radiused or curved edge.
 FIGS. 4A-4F are rear views of several examples of faces for a golf club head with re-enforced pockets for a ball-contacting insert.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
 Referring to FIGS. 1 and 2, club head 10, which is a driver, is a representative example of a golf club head of a type used in situations in which it is desirable to reduce the amount of spin placed on a ball when striking it. Other examples include a putter and low loft woods and irons.
 The club head face 12 has a contact surface that is formed by, for example, an insert 14 resting in a pocket or recess formed in the golf club head, such as by casting, milling or other machining operations. The insert has a front face or surface, which contacts the ball. When placed in the recess, it should form a substantially continuously smooth, ball-striking surface on the face of the club head. It may be circular, rectangular, octagonal, triangular, trapezoidal, hexagonal, polygonal, or other shape. The diameter of the insert can be as large or as small as desired within the limits of functionality. More accomplished players may benefit from a smaller diameter insert, while less accomplished players would likely need a larger diameter insert. The insert is positioned in the club face in the so-called “sweet spot” to provide optimum energy transfer to the ball.
 The front surface of the insert is formed from a hard or, preferably, super-hard material. The inelastic character of the insert resulting from the stiffness of the material results in a more efficient transfer of kinetic energy from the club to the ball, thus increasing the length of the shot.
 Examples of super hard materials are polycrystalline diamond or PCD or cubic boron nitride (CBN) compacts (including thermally stable and reinfiltrated PCD and cemented compacts), polycrystalline CBN (PCBN), chemical vapor diamond (CVD) and single crystal diamond.
 Briefly, a compact is a mass of diamond or CBN crystals, in whole or in portions, that are bonded, joined, or united together, respectively, by diamond-diamond bonds or CBN—CBN bonds obtained between many adjacent crystals. Polycrystalline diamond is a diamond material containing a high degree of diamond-diamond bonds. PCD ordinarily contains in the range of about 50-99% by volume of diamond and about 1-50% by volume of a sintering aid material used in the process of fabricating PCD to catalyze the formation of diamond-diamond bonds. In general, the greater the amount of diamond material in the PCD compact and the lesser the amount of sintering aid material, the greater the number of diamond-diamond bonds and thus the greater the strength of the PCD compact. Suitable sintering aid materials include iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, platinum, titanium, chromium, manganese, and tantalum and alloys thereof. CVD means a processed diamond or diamond-like material fabricated by chemical vapor deposition. PCBN or polycrystalline cubic boron nitride compact is a compact formed of crystals of the cubic form of boron nitride. A cemented compact is a cemented diamond and/or CBN compact wherein diamond-diamond or CBN—CBN bonding is not required. In such cemented compacts, the diamond and/or CBN content can be in the range of about 5-93% by volume with the remaining 7-95% of the cemented compact comprising a binder. Preferably, the cemented compact comprises about 50-92% by volume of diamond and/or CBN and about 8-50% by volume of binder. Suitable binder matrices include the same materials that are suitable as sintering aid materials in forming PCD compacts as described above.
 Examples of hard materials include ceramics, cermets, and carbides, such as tungsten carbide.
 Inserts may be formed by one or more layers of material. In the example shown in the drawings, the hard or super hard surface material of the insert is formed as a layer on a base material. For example, in a preferred embodiment, insert 14 includes a surface layer 16 of polycrystalline diamond formed on a base layer 18 of tungsten carbide. Additional layers could be included, if desired. The layers may be bonded in any suitable way, such as by hot pressing, infiltration, chemical joining, and similar processes. Furthermore, another example of a multiple layer insert is one made from a functionally graded composite with, for example, variable diamond content in intermediate layers between a diamond top surface and a bottom carbide layer.
 The insert is preferably attached in the pocket using a high strength adhesive, such as a cyanoacrylic glue or high strength epoxy. These types of adhesives impart less stress on the insert as compared to brazing, soldering or other welding methods, which tend to result in placing the insert under more stress, making it more susceptible to breakage. The golf club head insert is attached to a conventional golf club face by soldering, brazing, or by mechanical and/or thermal attachment methods that are well known in the art.
 Fabrication of the hard or superhard material in the insert, such as by compacting, sintering, processing or otherwise, usually creates a front edge 20 where ball contacting surface 22 and the side of the insert meet. To take this edge off, and make the transition between ball contact surface 22 and the side of the insert more gradual, the edge 20 after its fabrication is preferably chamfered, as illustrated in FIG. 3A, radiused, as illustrated in FIG. 3B or honed. Back edge 24 is preferably also chamfered (beveled), radiused or honed. Chamfering and rounding operations are preferably performed by grinding the edge of the insert after it is initially formed. If a chamfer or bevel is formed, it is preferable that it is in the range of 0.005″ to 0.007″at or about 45 degrees. Honing is also performed after the insert is initially formed. Removing the sharpness of the front edge, thus making the transition between the front and side more gradual, which tends to reduce chipping and cracking. Removing the sharpness of the back edge of the insert will tend to reduce further chipping and cracking and also assist with fitting the insert into the pocket formed in the face of club 10. The comers of the pocket or recess in the club face tend not to be formed at precisely ninety degree angles. Indeed, milling of the pocket will tend to leave some curvature or non-square transition between the bottom of the pocket and its sides. Rounding, chamfering or honing the back edge(s) allows it to sit better in the pocket.
 The front or ball contact face 22 of insert 14 is also polished after the insert is initially formed to a smoothness of less than 20 micro-inches, and preferably to a smoothness of less than 10 micro-inches. Best results are, however, achieved with a finished smoothness of less than 2 micro-inches. Polishing removes at least some surface flaws in the hard or superhard material that contacts the ball. It also imparts less friction on the ball. Polishing of the insert is accomplished by conventional material removal techniques, such as lapping.
 Referring to FIGS. 4A-4F, most club heads of the type referred to as “woods” and “drivers” will have a contact face that deforms upon striking of the ball. Traditional “woods”, made of solid or laminated persimmon wood, will deform and absorb energy. Modern “woods” and “drivers”, typically made of a metal, are hollow to reduce weight. As illustrated in the figures, a relatively thin wall 26 of material therefore forms the contact face of the club head. The wall is generally straight or flat, except for pocket 28 that is formed to receive an insert of hard or superhard material as described above. Because it is made relatively thin to save weight, the wall forming the face will tend to bend upon ball impact. Some club heads try to take advantage of bending to create a “trampoline” effect. However, bending of the face in the vicinity of insert pocket 28 causes the pocket to flex or deform, applying stress to the insert and possibly causing it to crack or break due to its brittleness.
 Bending can be reduced to some degree by using very stiff materials, such as titanium alloys, that are also relatively lightweight. Therefore, it is preferable that the golf club head be made of very stiff material, such as a titanium alloy. However, titanium alloys are expensive and even if used does not completely eliminate flexure of the pocket in some situations.
 In order to stiffen the pocket in which an insert of hard or super hard material is placed, and thus reduce the possibility of the insert cracking, reenforcing ribs 30 may be placed on rear surfaces of the walls defining the pocket, whether or not a titanium alloy or similarly stiff material is used. In FIGS. 4A-4E, various configurations of ribs 30 on pocket 28 are illustrated as examples of how reenforcing ribs can be used. The ribs are preferably integrally formed with the wall forming face of the club in order to reduce the number of fabrication steps, improve performance and avoid adding weight. However, the ribs could be separately fabricated and then attached. In the figures, ribs 30 are integrally formed with wall 26.
 Generally speaking, the reenforcing ribs are used to reduce the tendency of the pocket to deform through flexure when stressed, such as the stress caused by the face of the club bending or flexing during ball impact. The examples of rib configurations shown in FIGS. 4A-4E are not intended to be an exhaustive list of all possible configurations that reduce flexure or deformation of the pocket. Rather, they are illustrative of several areas around the pocket that can be stiffened. One such area is around the transition between a pocket's sidewall(s) (if the insert is non-circular, it will have more than one sidewall) and the wall forming the face of the club. Such stiffening is found in each of the examples where there is at least a portion of a rib disposed in the comer formed by the sidewall 32 and the flat portion of the wall 26 surrounding the pocket. Other candidate areas are the pocket's bottom wall and the transition between the bottom wall and the sidewall. Such stiffening is also found in the examples of FIGS. 4A-4E, as evidenced by ribs 30 extending across back wall 34 of pocket 28 and then along sidewall 32 to the comer of the transition between the sidewall and the flat portion of the face surrounding the pocket.
 Furthermore, the face of the golf club head surrounding the insert can also be stiffened, such as by extending ribs beyond the comer of pocket 28, to the flat portions of the wall around the pocket, as illustrated in the examples of FIGS. 4A and 4F. Reducing flexure in the face around the pocket will tend to reduce stress on the pocket.
1. A golf club head with a ball contact surface area on its face comprising a hard or superhard material polished to a smoothness of less than 20 micro-inches.
2. The golf club head of claim 1 wherein the hard or superhard material is polished to a smoothness of less than 10 micro-inches.
3. The golf club head of claim 1 wherein the hard or superhard material is polished to a smoothness of less than 2 micro-inches.
4. The golf club head of claim 1, wherein the ball contact surface area is comprised of superhard material, and the superhard material is comprised of polycrystalline diamond or cubic boron nitride.
5. The golf club head of claim 4 wherein the superhard material is polished to a smoothness of less than 10 micro-inches.
6. The golf club head of claim 4 wherein the superhard material is polished to a smoothness of less than 2 micro-inches.
7. The golf club head of claim 1 wherein the ball contact area includes an insert disposed within a recess formed in the club head, the insert having on its front face a hard or super hard material.
8. The golf club head of claim 7, wherein the insert further includes at least one base layer with which the hard or superhard material is supported.
9. The golf club head of claim 8, wherein the front face of the insert is comprised of a layer of polycrystalline diamond or cubic boron nitride, and one of the one or more base layers is comprised of tungsten carbide.
10. A golf club head with a contact area comprised of an insert within a recess formed on the golf club head's face, the insert having a front face having hard or super hard material, wherein one or more edges around the front face of the insert are chamfered, radiused or honed.
11. The golf club head of claim 10 wherein the front face is polished to a smoothness of less than 20 micro-inches.
12. The golf club head of claim 10 wherein the front face is polished to a smoothness of less than 10 micro-inches.
13. The golf club head of claim 10 wherein the front face is polished to a smoothness of less than 2 micro-inches.
14. The golf club head of claim 10, wherein the front face is a superhard material comprised of polycrystalline diamond or cubic boron nitride.
15. The golf club head of claim 14 wherein the superhard material is polished to a smoothness of less than 10 micro-inches.
16. The golf club head of claim 14 wherein the superhard material is polished to a smoothness of less than 2 micro-inches.
17. The golf club head of claim 10, wherein the insert further includes a base material for supporting the hard or superhard material.
18. The golf club head of claim 10, wherein the front face of the insert is comprised of a surface layer of polycrystalline diamond or cubic boron nitride supported by one or more base layers, or regions of material different from that of the surface layer.
19. The golf club head of claim 18 wherein one of the one or more base layers or regions is comprised of tungsten carbide.
20. The golf club head of claim 10, where the insert has a back face having hard or super hard material, wherein one or more edges around the back face of the insert are chamfered, radiused or honed.
21. A golf club comprised of an elongated shaft connected with a hollow golf club head, the golf club head having a face formed by a wall with a front and a rear surface, the wall having defined therein a pocket for receiving an insert comprised of hard or super hard material that forms at least part of a ball contacting surface; the rear surface having disposed on it at least one reinforcing rib for reducing deformation of the pocket when under stress.
22. The golf club of claim 21, wherein the at least one reinforcing rib extends across the pocket.
23. The golf club of claim 21 wherein the insert having a front face having hard or super hard material, wherein one or more edges around the front face of the insert are chamfered, radiused or honed.
24. The golf club of claim 21 wherein the front face is polished to a smoothness of less than 20 micro-inches.
25. The golf club of claim 21 wherein the front face is polished to a smoothness of less than 10 micro-inches.
26. The golf club of claim 21 wherein the front face is polished to a smoothness of less than 2 micro-inches.
27. The golf club of claim 21, wherein the front face is a superhard material comprised of polycrystalline diamond or cubic boron nitride.
28. The golf club of claim 26 wherein the superhard material is polished to a smoothness of less than 10 micro-inches.
29. The golf club of claim 26 wherein the superhard material is polished to a smoothness of less than 2 micro-inches.
30. The golf club of claim 21, wherein the insert further includes a base material for supporting the hard or superhard material.
31. The golf club of claim 21, wherein the insert has a front face comprised of a layer of polycrystalline diamond or cubic boron nitride supported by one or more base layers, one of the one or more base layers being comprised of tungsten carbide.
32. The golf club of claim 21, wherein the rear surface has disposed on it multiple ribs.
33. The golf club of claim 21, wherein the at least one rib is disposed on the rear surface to stiffen the pocket to reduce flexure of the pocket during ball impact.
34. The golf club of claim 33, wherein the at least one rib extends fully across the pocket.
35. The golf club of claim 21 wherein the at least one rib is disposed to strengthen the wall around the pocket.
International Classification: A63B053/04;