GOLF CLUB HEAD

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No. 2009-298199 filed Dec. 28, 2009, which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a golf club head, and more particularly, relates to a golf club head having improved material thickness on the back surface of the face part thereof, and also a face part formed by forging of a rolled material.

The heads of a majority of recent wood clubs are formed with at least the face part made of a metallic material. The material thickness of the face part must be made thick in order to maintain the strength to be able to withstand the impact with a ball. Although heads are increasing in size, because the rules require that they have a volume less than 460 cm³plus a tolerance of 10 cm³, the majority of heads have become large 460-cm³driver heads that are very close to the upper limit. When the head size is increased, because the sweet area increases, the peripheral weight distribution is emphasized, and the left-right and top-bottom moments of inertia increase, it is possible to reduce poor shots when an off-center hit occurs. However, when the head size is increased and the head weight is also increased, the swing balance becomes large and the head speed drops, and so the carry might be reduced. Given this, a method is adopted of forming the entire head from titanium, which has a low specific gravity and a high strength, or an alloy thereof (these being referred to simply as “titanium” unless otherwise noted) or of using a composite head made of carbon and titanium.

Additionally, a large number of high-restitution heads, which have not only an increased head size, but also an increased coefficient of restitution, have been developed. Since 2008, high-restitution heads having a coefficient of restitution of 0.830 or greater have been unusable in competition. At present, along with an increase in head size, there is active use of thick-material faces having an increased coefficient of restitution. However, even with a high-restitution head, it is not possible to achieve a spring effect for hits other than at the sweet area, that is, off-center hits, and there has been a tendency for a sharp decrease in carry in such cases. Also, it is known that, from the standpoint of face strength, it is preferable to make the material of a center part, which greatly deforms, thick, and not to provide grooves such as score lines in the center part of the ball-striking surface of the face.

Japanese Patent Application Publication No. 9-192273 discloses a golf club head having a thickness at the center location that includes the sweet spot of the part that forms the face is formed with a thickness to maintain strength sufficient to withstand the impact with a ball, the material thickness of the periphery of the center location being made thinner than the center location, so as to impart springiness to the overall face.

Also, Japanese Patent Application Publication No. 2007-307143 discloses a golf club head having a face part formed from a rolled titanium alloy material having an α phase, the rolling direction of the face part being along the toe-heel direction.

SUMMARY OF THE INVENTION

In the case in which the material at the center of the face part, such as described in Japanese Patent Application Publication No. 9-172273, is thick, there is the problem that, if the ball is hit at a location that is removed from the sweet spot, the restitution performance of the face is greatly reduced from the case in which the ball is hit at the sweet spot, and if the restitution performance at the sweet spot is suppressed so as to be low, the restitution performance other than at the sweet spot is considerably reduced. Also, generally there is a tendency that the thinner the material of the face is made, the greater the restitution performance of the face and the weaker the strength of the face.

Additionally, in the case of using a titanium alloy having an α phase for the face, the strength of the titanium alloy that is obtained by rolling in one direction has a directionality that is caused by the α phase crystal structure (close-packed hexagonal lattice). For this reason, consideration must be given to the rolling direction when using a rolled material, leading to the problem of extreme difficulty of use, and there is a particular tendency for cracks to form at score line grooves in the surface of the face, the material of which has been made thin.

Given the above, in consideration of the above-noted problems, the present invention has as an object to provide a golf club head in which the restitution of the face part can be held to within a range that conforms to the rules, while maintaining the light weight and strength of the face part, the golf club head being capable of preventing a large decrease of restitution performance even in the case in which a ball is hit at a part away from the sweet spot, and capable of preventing the occurrence of cracks in the relatively low-strength thin-material part.

To achieve the above-noted object, the present invention is a golf club head having a hollow part including a head body having a face aperture part and a face member held to the face aperture part by welding, wherein the face member is formed by forging of a rolled material of a titanium alloy having an α phase; the face member has a thick-material part positioned in the center of the face member, an outer peripheral part positioned at the periphery of the thick-material part, and a thin-material part partially positioned between the thick-material part and the outer peripheral part; the thick-material part, the thin-material part, and the peripheral part are formed by the forging so as to destroy the α-phase orientation. The thick-material part is formed in an area having a shape obtained by depressing a substantially elliptical or substantially circular shape in a substantially arcuate shape toward the center of the ellipse at two opposite sides thereof. The thick-material part has a material thickness that is thickest at the center part of the face member and also that gradually becomes thin from the center part toward the outer peripheral part. The thick-material part has a material thickness that is thicker than the peripheral part and the thin-material part has a material thickness that is thinner than the outer peripheral part.

In a golf club head according to the present invention, the forging may be hot forging.

In a golf club head according to the present invention, the thin-material part may be disposed so as to be inclined in the sole direction at the toe side of the thick-material part, and to be inclined in the crown direction at the heel side of the thick-material part, and have a score line groove on the surface of the face.

In a golf club head according to the present invention the face member may further have a rib that passes through the center part of the thick-material part and extends from the outer edge of both the heel side and the crown side of the face toward the outer edge of both the toe side and sole side, wherein the rib has a material thickness that is thicker than the outer peripheral part.

In a golf club head according to the present invention, the rolling direction of the rolled material may be a direction at an angle within ±5° with respect to the score line.

In a golf club head according to the present invention, the face member may be either an α titanium alloy or an α-β titanium alloy.

According to a golf club head according to the present invention, because a thin-material part having a material thickness that is thinner than the outer periphery part of the face member is formed in a region that is caused to be recessed by forging of the thick-material part of the face member, not only is it possible to maintain the light weight of the face part and suppress the restitution to within an amount that is compliant with the rules, it is also possible to prevent a large decrease in the restitution performance even in the case in which the ball is hit at a part other than the sweet spot. Additionally, by forming the face member by forging a rolled material, it is possible to weaken the characteristic directionality of strength by destroying the α-phase crystal structure of the titanium alloy, thereby preventing the occurrence of cracks in the thin-material part that has relatively low strength.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevational view showing an embodiment of a golf club head according to the present invention.

FIG. 2 is a rear elevational view showing a face member of the golf club head shown in FIG. 1.

FIG. 3 is a front elevational view showing another embodiment of a golf club head according to the present invention, the embodiment having a rib.

FIG. 4 is a rear elevational view showing a face member of the golf club head shown in FIG. 3.

FIG. 5 is a schematic cross-sectional view showing the face member of FIG. 4 along the line A-A.

FIG. 6 is a schematic cross-sectional view showing the face member of FIG. 4 along the line B-B.

FIG. 7 is a rear elevational view showing the angle of the rib in the face member of FIG. 4.

FIG. 8(
a) is a cross-sectional view showing an embodiment of a forging process in the present invention before pressing.

FIG. 8(
b) is a cross-sectional view showing one embodiment of the forging process in the present invention after pressing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Embodiments of a golf club head according to the present invention will now be described with reference to the accompanying drawings.

As shown in FIG. 1, a golf club head 1 is made up of a face member 10 including a part of a face part, and a main body member 20 of the head. The body member 20 includes a crown part 4, a sole part 5, a hosel part 6, and a side part 7, which are integrally formed. The face member 10 and the body member 20 are joined by welding, and thereby the interior of the head is made to be a hollow structure. A construction appearing on the surface on the hollow side of the face member 10, that is, the back surface of the face member 10, is indicated by broken lines. On the back surface of the face member 10, irregularities for altering the thickness of the face member 10 are formed. The back surface of the face member 10 is explained.

As shown in FIG. 2, an elliptical line 12 on the back surface of the face member 10 shows an elliptical region in which the thickness of the face member is varied in contrast to the outer peripheral part 11 having a flat surface. A thick-material part 15, in which the thickness gradually increases toward the center of the ellipse, is formed within a thick-material part outer periphery line 19, which includes both end parts of the elliptical line 12 with respect to the minor axis of the ellipse and depression lines 14 that are depressed in an arcuate shape toward the center of the ellipse in both end parts of the major axis of the ellipse.

As shown in FIG. 2, in the center part of the ellipse, there is formed a circular central part 17, which has a flat surface and has the greatest thickness in the face member 10. The thick-material part 15 is configured so that its thickness gradually decreases from the center part 17 to the elliptical line 12 or to the depression lines 14. An outer peripheral part 11 that is formed outside the elliptical line 12 has a uniform thickness. Thin-material parts 13 having a thickness smaller than that of the outer peripheral part 11 are formed in parts of the ellipse that are surrounded by the elliptical line 12 at both ends of the major axis of the ellipse and the depression lines 14, respectively. As shown in FIGS. 3 and 4, a singular rib 18 having a thickness greater than that of the outer peripheral part 11 can be formed on the back surface of the face member 10. FIGS. 5 and 6 show schematic cross-sectional views of the face member of FIG. 4 along the line A-A and the line B-B, respectively. In order to represent the changes in thickness of the thick-material part 15 in FIGS. 1 and 2, contour lines 16 have been drawn.

FIGS. 1 to 6 are not drawn to scale. The various parts of the face member 10 are described in further detail below.

The center part 17 includes a sweet spot of the golf club head 1. The center part 17 includes the center point of the ellipse indicated by the line 12. The center point of the ellipse and the sweet spot may be identical or different. The radius of the center part 17 is preferably at least approximately 3.0 mm and more preferably at least approximately 3.5 mm. Also, the radius of the center part 17 is preferably at most approximately 6 mm, and more preferably at most approximately 5 mm. By making the radius of the center part 17 in this range, the weight of the face part can be kept low. The shape of the center part 17 is not limited to the circular shape shown in FIG. 2, and may be may be elliptical or polygonal such as tetragonal, e.g., rectangular and rhombic, pentagonal and hexagonal. The thickness of the center part 17 is preferably at least approximately 3.4 mm, and more preferably, is at least approximately 3.6 mm. Also, the thickness of the center part 17 is preferably at most approximately 4.0 mm, and more preferably at most approximately 3.8 mm. By making the thickness of the center part 17 in this range, the restitution coefficient of the face part can be kept in the range specified by the rule.

The major axis of the ellipse indicated by the line 12 is inclined so that the toe side 2 thereof shifts to the crown side and the heel side 3 thereof shifts to the sole side. The reason for this is as described below. In general, the variations in hitting points of golfers are biased to the crown side on the toe side 2 and to the sole side on the heel side 3. By this inclination, more hitting points at the time when a ball is hit by a face part deviating from the sweet spot can be allowed to enter the region of the thin-material parts 13. Specifically, as shown in FIG. 7, when the golf club head is placed at a normal addressed position, an inclination angle θa of a major axis 42 of the ellipse with respect to the horizontal line 40 is preferably at least approximately 5° and more preferably at least approximately 10°. Also, the inclination angle θa of the major axis 42 is preferably at most approximately 40° and more preferably at most approximately 30°. However, the thin-material parts 13 are not limited to the above-noted disposition, as long as they are disposed to the outside of the thick-material part 15. They may be disposed, for example, at the crown side and the sole side.

The ratio of the length of the major axis of the ellipse indicated by the line 12 to the length of the minor axis thereof is preferably in the range of 100:50 to 50:50, more preferably in the range of 95:50 to 70:50 (in the case in which the major axis and the minor axis have an equal length, the shape is not elliptical, but is circular). The thick-material part 15 is depressed by the depressions 14 at two opposite sides of the ellipse or circle thereof. It is preferable that the depressions 14 be formed to match the disposition of the thick-material part 13, at either the toe and heel sides or crown and sole sides. In the case of having depressions 14 at the toe and heel sides, it is preferable that the ratio between the length of the thick-material part 15 on the major axis of the ellipse (that is, the length between the depressions 14) and the length of the thick-material part 15 on the minor axis of the ellipse be in the range from about 5:4 to about 5:6. The radius of curvature of the depression 14 on the heel side is preferably at least approximately 12 mm, and more preferably at least approximately 13 mm. The radius of curvature of the depression 14 on the heel side is preferably at most approximately 25 mm, and more preferably at most approximately 20 mm.

As shown in FIG. 5, the thick-material part 15 has a curved surface spreading toward the bottom such that the thickness thereof continuously decreases from the center part 17 to the depression 14 or to the elliptical line 12, but it is not limited to this shape. For example, the thick-material part 15 may have a stepwise surface such that the thickness thereof decreases stepwise, or it may have a surface of a truncated cone shape such that the thickness thereof decreases continuously in a fixed ratio. As shown in FIG. 2, the thick-material part 15 has four ridges, but it is not limited to this. The presence or absence of and number and position of the ridges can be changed as appropriate.

The outer peripheral part 11 has a uniform thickness and occupies a region in which the thin-material part 13 and the thick-material part 15 are not formed. The thickness of the outer peripheral part 11 is preferably at least approximately 2.1 mm, and more preferably, is at least approximately 2.2 mm. The thickness of the outer peripheral part 11 is preferably at most approximately 2.5 mm, and more preferably at most approximately 2.4 mm. By making the thickness of the outer peripheral part 11 be within this range, it is possible to reduce the weight of the face part while restraining the coefficient of restitution thereof.

The thin-material part 13 is formed to be thicker than the outer peripheral part 11. The difference in thickness between the thin-material part 13 and the outer peripheral part 11 is preferably at least approximately 0.1 mm, and more preferably, is at least approximately 0.2 mm. The thickness of the thin-material part 13 is preferably at least approximately 1.8 mm, and more preferably at least approximately 1.9 mm. The thickness of the thin-material part 13 is preferably at most approximately 2.2 mm, and more preferably at most approximately 2.1 mm. By making the thickness of the thin-material part 13 be within this range, it is possible to improve the restitution performance on the toe and heel sides, on which the restitution performance is usually low.

As shown in FIGS. 3 and 4, the rib 18 has a thickness that is at least greater than the outer peripheral part 11. As shown in FIG. 5, the thickness of the rib 18 decreases continuously from the thickness that is the same as the thickness of the center part 17 toward the outer peripheral part 11. By making the rib 18 thickness continuously decrease from the center part 17 toward the outer peripheral part 11 in this manner, it is possible to minimize the decrease in restitution performance of the face surface, while maintaining the strength of the face surface. The rib is not limited to this configuration. The thickness of the rib 18 may be, for example, made uniform. The thickness of the rib 18 is preferably at least approximately 2.5 mm, and more preferably at least approximately 2.7 mm. The thickness of the rib 18 is preferably at most approximately 2.9 mm, and more preferably at most approximately 3.6 mm.

The rib 18, as shown in FIG. 4, is formed so as to extend substantially in a straight line, passing through the center part 17 of the thick-material part 15, from a crown side on the heel side 3 of the outer peripheral part 11 to a sole side on the toe side 2 of the outer peripheral part 11. The angle of inclination θb of the center line 44 of the rib 18 with respect to the horizontal line 40 when the golf club head is place in the normal addressed position, as shown in FIG. 7, is preferably at least approximately 45°, and more preferably at least approximately 50°. The angle of inclination θb is preferably less than approximately 90° and more preferably at most approximately 80°. By making the rib inclination angle θb be within this range, it is possible to maintain the strength of the face surface without a large loss of restitution performance in the case of an off-center hit because the variations in the ball impact points are biased as discussed above. As shown in FIG. 4, the rib 18 is formed to have a width that increases along the direction from the center part 17 toward the outer peripheral part 11, but it is not limited to this. The width of the rib 18 can, for example, be uniform.

Over the entire surface area of the face part 10, the proportionality of the surfaces that are occupied by the outer peripheral part 11, the thin-material part 13, the thick-material part 15 (including in this case the center part 17) and the rib 18 is preferably about 16-20:2-6:14-18:1-6, and more preferably about 17-19:3-5:15-17:1-5. By making the proportionalities be within these ranges, it is possible to achieve a balance between weight and strength over the entire face part. Also, in the case in which the rib 18 is not provided, the proportionality of the surface that is occupied by the outer peripheral part 11, the thin-material part 13, and the thick-material part 15 (including in this case the center part 17) is preferably 8-10:1-3:7-9, and more preferably 17-19:3-5:15-17.

The above-noted constitution of the face member 10 is formed by forging a rolled material made of a titanium alloy having an α phase. An α alloy or an α-β alloy may be used as the titanium alloy having an α phase. In particular, the α-β alloy can be more preferably used than the α alloy, because the α-β alloy has a higher strength than the α alloy, thereby improving the durability of the face part of the club head, reducing the weight of the club head by making the material of the face member thin, and increasing the degree of freedom for designing the center of gravity by making the material thin.

Exemplary α alloys include Ti-5Al-2.5Sn. Exemplary α-β alloys include Ti-4.5Al-3V-2Fe-2Mo, Ti-4.5Al-2Mo-1.6V-0.5Fe-0.3Si-0.03C, Ti-8Al-1Mo, Ti-1Fe-0.35O-0.01N, Ti-5.5Al-1Fe, Ti-6Al-4V, Ti-6Al-6V-2Sn, Ti-6Al-2Sn-4Zr-6Mo, Ti-6Al-2Sn-4Zr-2Mo, and Ti-8Al-1Mo-1V. In particular, Ti-6Al-4V and Ti-8Al-1Mo-1V are preferable.

The strength of the rolled material made from a titanium alloy having an α phase exhibits directionality, because the crystal texture (close-packed hexagonal lattice) of the α phase titanium alloy has directionality. The close-packed hexagonal lattice has two axes, the first axis being easily deformed, and the second axis being substantially orthogonal thereto and being hard to deform. When the alloy having the close-packed hexagonal lattice structure is rolled in one direction, the easily deformed axis is orientated in the rolling direction with the hard-to-deform axis being orthogonal thereto, and thus, a prominent anisotropy with regard to the strength of the alloy occurs.

Accordingly, the face member used in the golf club head of the present invention is formed by forging the rolled material, at which time the crystal directionality of the α phase is destroyed.

The rolled material is manufactured by grabbing a titanium alloy between a pair of rotating rollers by friction, and subjecting it to rolling to reduce its thickness or cross-sectional area. The rolling is performed repeatedly in the same one direction. As a result, the easy-to-deform axis in the close-packed hexagonal lattice is oriented substantially in parallel with the rolling direction, and the hard-to-deform axis of the close-packed hexagon lattice is oriented substantially perpendicularly to the rolling direction, and thus, a prominent anisotropy in strength can occur. The titanium alloy having an α phase rolled only in one direction can exhibit a more prominent anisotropy than a β titanium alloy. It is preferable that the direction of rolling be parallel to a score line in the face surface, or at an angle within ±5° thereof.

The rolled material manufactured in this manner is subjected to plastic deformation by forging in order to form the thick-material part and the thin-material part of the face member. The rolled material is punched out using various methods such as pressing or laser cutting. The punched out rolled material is placed between upper and lower dies and is forged.

As shown in FIG. 8a, the upper die 50 of the dies used in the forging has a pressing part 52 which is depressed in the center so as to make the center part the deepest. The center part thereof forms the center part 17 and the thick-material part 15 of the face member. The upper die 50 also has a protruding pressing part 51 for forming the thin-material part 13 of the face member, and a depressed pressing part (not shown) for forming the rib 18 of the face member. The lower die 53 has a shallow depressed part 54 with a width that is slightly wider than a rolled material for face member 55. The rolled material 55 is disposed on the shallow depressed part 54 and is pressed between the upper and lower dies 50 and 53.

As shown in FIG. 8b, the upper die 50 presses the entire rolled material 55 and causes it to plastically deform. The thin-material part 13 of the face member is formed by the protruding pressing part 51, and the thick-material part 15 is formed by the center depressed pressing part 52. The directionality of the α phase of the rolled material is changed by the pressing so as to be in accordance with the plastic deformation of the rolled material. Therefore, at least in the thick-material part 15 and the thin-material part 13, the pressing sufficiently destroys the directionality of the α-phase crystal grains. For example, in the thin-material part 13, the rolled material 55 is elongated in all directions, over 360°, and thus, the α-phase orientation is destroyed in all directions, over 360°. In the thick-material part 15, the rolled material 55 is pulled and elongated in the central direction and also is spread outward in all directions, over 360°, thereby intricately destroying the α-phase orientation. In the neighboring periphery between the thin-material part 13 and the thick-material part 15, the elongating and spreading of the rolled material 55 are complexed together, thereby achieving a more intricate destruction of the α-phase orientation. The α-phase crystal grains (tissues) spread along the rolling direction are separated (finely divided) by forging in this manner. In addition, the metal structure is moved along the directions from the thin-material part to the thick-material part, thereby, changing the orientation of the α-phase metal tissue, i.e., the α-phase metal tissue that had been uniformly oriented in the rolling direction is no longer uniformly oriented. Therefore, the anisotropy in strength is destroyed.

The forging process is preferably hot forging performed after heating to at least the recrystallization temperature. FIGS. 8a and 8b show a single die for forging of the face material, but a plurality of dies may be used to form the face member by a series of forging steps.

The face member obtained by forging can be joined by welding to the face aperture of the golf club head to manufacture the golf club head. The volume of the golf club head 1 is preferably at least approximately 100 cm³, and more preferably at least approximately 350 cm³. The volume of the golf club head 1 is also preferably at most approximately 500 cm³, and more preferably at most approximately 480 cm³. The weight of the golf club head 1 is preferably at least approximately 150 g, and more preferably at least approximately 160 g. The weight of the golf club head 1 is also preferably at most approximately 250 g, and more preferably at most approximately 200 g.

As shown in FIGS. 1 and 3, the face surface of the golf club may have score lines 8. The score lines 8 each have a groove shape and are arranged parallel to each other. In the embodiment shown in FIGS. 1 and 3, the golf club head has a design that does not have score lines in the center of the face. Exemplary methods for forming the score lines 8 include machining, forging, and casting or other known conventional methods. This process may be performed on the face member after forging or on the face surface after welding to the golf club head. The rules allow score line grooves to a depth of up to 0.5 mm. However, it is preferable that the face surface of a hollow wood golf club be thin, and it is preferable that the depth be within the range from approximately 0.1 mm to approximately 0.3 mm, and more preferably in the range from approximately 0.1 mm to approximately 0.2 mm. For example, this can be made approximately 0.15 mm. In the case of making the material of the face member thin, there is a problem with the occurrence of cracking at the score lines. It is possible by forging to destroy the anisotropy in strength caused by rolling, thereby preventing cracking at the score line grooves.

FIGS. 5 and 6 show the ball-striking surface of the face member as being flat to facilitate an understanding of the constitution of the present invention, but a bulge having a radius of curvature of about 250 mm to about 800 mm may be formed on the ball-striking surface of the face member 10. In the same manner, it is possible to form a roll having a radius of curvature of about 250 mm to about 800 mm on the ball-striking surface of the face member.

FIGS. 1 and 3 show the embodiment with the face member 10 as the center part of the face of the golf club head 1 and the remaining part of the face as being formed integrally with the head body, but the present invention is not limited to this embodiment. For example, the entire face may be made the face member.

GOLF CLUB HEAD

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