Golf club head and method of manufacturing the same

Abstract

A golf club head comprises a face portion formed by: forging a beta type titanium alloy while keeping the temperature of the alloy lower than the lower critical solution temperature of the alloy; and aging the forged alloy under the lower critical solution temperature Tc so as not to become a solution state. A method of manufacturing a golf club head comprises: preparing a billet of a beta type titanium alloy; forging the billet into the face member while keeping the temperature of the billet lower than the lower critical solution temperature Tc of the beta type titanium alloy; and aging the face member under the lower critical solution temperature Tc so as not to become a solution state.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a golf club head and a method of manufacturing the same, more particularly to a thermal treatment incorporated into a plastic forming process which can improving the restitution coefficient.

[0002] In recent years, in order to improve the restitution coefficient of the golf club heads, beta type titanium alloys are used to form the club face. In general, the beta type titanium alloys are low in the Young's modulus in comparison with alpha and alpha-beta type titanium alloys, and it is considered as being easier to make the face portion having a good restitution coefficient.

[0003] In case the face portion is shaped from a beta type titanium alloy through hot forging, if the hot forging is carried out as usual at a temperature of about 20 to 50 deg.C higher than the lower critical solution temperature of the alloy, the forging is provided with a single phase of platy beta crystal structure as shown in FIG. 5(a). Then, if the forging is subjected to an aging treatment, microscopic granular alpha crystals occur in the platy beta crystal as shown in FIG. 5(b). This structure is superior to the others in respect of the strength and hardness, but the elongation percentage is vary small. Thus, this is breakable. In order to cover this breakable nature, if the thickness of the face material is increased, the durability may be increased but it becomes difficult to get a good restitution coefficient because the rigidity is also increased.

SUMMARY OF THE INVENTION

[0004] It is therefore, an object of the present invention to provide a golf club head and a method of manufacturing the same, in which the restitution coefficient and durability can be improved to a higher dimension in a balanced manner.

[0005] According to one aspect of the present invention, a golf club head comprises a face portion whose front face defines a club face for hitting a ball, wherein the face portion is formed by: forging a beta type titanium alloy while keeping the temperature of the alloy lower than the lower critical solution temperature of the alloy; and aging the forged alloy under the lower critical solution temperature so as not to become a solution state.

[0006] Here, the lower critical solution temperature means the lower limit of the temperature range within which the alloy becomes platy beta phase as time goes by.

[0007] According to another aspect of the present invention, a method of manufacturing a golf club head which comprises a main body and a face member attached thereto, comprises:

[0008] preparing a billet of a beta type titanium alloy;

[0009] forging the billet into the face member while keeping the temperature of the billet lower than the lower critical solution temperature of the beta type titanium alloy; and

[0010] aging the face member under the lower critical solution temperature so as not to become a solution state.

[0011] Here, the "billet" means not only that produced by casting but also by another method such as extrusion and forging.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a front view of a golf club head according to the present invention.

[0013] FIG. 2 is a cross sectional view thereof taken along a line X-X in FIG. 1.

[0014] FIG. 3 is an exploded perspective view showing an example of the structure of the head.

[0015] FIGS. 4(a) and 4(b) are diagrams for explaining the change in the crystallographic structure of a beta type titanium alloy according to the present invention.

[0016] FIGS. 5(a) and 5(b) are diagrams for explaining the change in the crystallographic structure of a beta type titanium alloy according to the conventional temperature control.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Embodiments of the present invention will now be described in detail in conjunction with the accompanying drawings.

[0018] In the drawings, club head 1 according to the present invention is a metal wood-type hollow golf club head comprising a face portion 2 whose front face defines a club face F for hitting a ball, a crown portion 3 intersecting the club face F at the upper edge 2a thereof, a sole portion 4 intersecting the club face F at the lower edge 2b thereof, a side portion 5 between the crown portion 3 and sole portion 4 which extends from a toe-side edge 2t to a heel-side edge 2e of the club face F through the back face of the club head, and a neck portion 6 to be attached to an end of a club shaft (not shown). The neck portion 6 is provided with a shaft hole 6a into which a club shaft is inserted and fixed with an adhesive agent or the like.

[0019] In FIG. 1 and FIG. 2, the club head 1 is in its address position, namely, the club head 1 is set on a horizontal plane HP such that the center line CL of the clubs haft is inclined at the lie angle alpha while keeping the center line CL on a vertical plane, and the club face F forms its loft angle beta with respect to the horizontal plane HP. Incidentally, when setting the club head 1 alone in its address position, the center line of the shaft inserting hole 6a may be used instead of the center line CL of the clubs haft.

[0020] In order to widen the area of the face portion which area can deform at impact and contribute to improving of the restitution coefficient, the size of the wood-type club head is designed as follows.

[0021] The volume of the club head 1 is preferably set in a range of not less than 300 cc, more preferably 300 to 500 cc, still more preferably 310 to 450 cc. The horizontal width B of the club face F between its toe-side extreme end and heel-side extreme end is preferably set in a range of not less than 90 mm, more preferably not less than 95 mm, but not more than 130 mm, more preferably not more than 115 mm. The height (A) of the club face F between its upper end and lower end is preferably set in a range of not less than 45 mm, more preferably not less than 48 mm, still more preferably not less than 50 mm, but not more than 70 mm when measured along a direction inclined at the loft angle beta as shown in FIG. 2. The aspect ratio (A/B) of the height (A) to the width (B) is preferably set in a range of from 0.346 to 0.667. If the face height (A) is more than 70 mm and/or the face width (B) is more than 130 mm and/or the aspect ratio (A/B) is more than 0.667, then the deformation at impact becomes too large and the durability will be decreased rapidly. If the face height (A) is less than 45 mm and/or the aspect ratio (A/B) is less than 0.346, then the area becomes insufficient, and it becomes difficult to improve the restitution coefficient. If the face width (B) is less than 90 mm, as the deformation at impact becomes less, the improvement in the restitution coefficient is decreased.

[0022] In this embodiment, as shown in FIG. 2, the face portion 2 is provided along the circumferential edge thereof with a comparatively thin peripheral region 2B. Accordingly, the face portion 2 is made up of the thin peripheral region 26 and a thicker central region 2A including the sweet spot and surrounded by the thin peripheral region 26. The thickness t1 of the thick central region 2A is preferably set in a range of not less than 1.8 mm, more preferably not less than 2.1 mm, but not more than 2.9 mm. The thickness t2 of the thin peripheral region 26 is preferably set in a range of not less than 1.0 mm, more preferably not less than 1.3 mm, but not more than 2.8 mm. The thickness difference (t1-t2) is set in a range of less than 1.9 mm, preferably less than 1.5 mm, but more than 0.1 mm, preferably more than 0.2 mm. The thin peripheral region 26 has a groove width more than about 2 or 3 mm. Such thickness arrangement may further improve the restitution coefficient of the club face F without decreasing the strength and durability of the face portion 2.

[0023] FIG. 3 shows a two-piece structure which is suitably employed in the above-mentioned metal wood-type hollow golf club head 1. This two-piece structure comprises an open-front hollow main body 9 and a face member 7 welded to the front of the main body 9 to form the club face F. The face member 7 is made up of a platy main portion 7A defining substantially the entirety of the club face F and an extension 7B extending backward from the edge (2a, 2b, 2t, 2h) of the main portion 7A. In this example, the extension 7B includes a crown-side extension 7B1 extending from the entire length of the upper edge 2a forming a front part of the crown portion 3, and a sole-side extension 7B2 extending from the entire length of the lower edge 2b forming a front part of the sole portion 4. But, an extension is not provided at the toe-side edge 2t and heel-side edge 2h. The head main body 9 in this example is therefore, made up of the remaining part of the crown portion 3, the remaining part of the sole portion 4, the side portion 5, and the neck portion 6. The front edge of the head main body 9 is shaped to fit to the face member 7, more specifically, set back in a portion corresponding to the extension 7B. The depth S of the extension (7B1, 7B2) which is defined as the shortest distance from any point at the rear edge 7e to the club face edge (2a, 2b) is preferably set in a range of from 5 to 20 mm, more preferably 5 to 15 mm.

[0024] The face member 7 is shaped from a billet of a beta type titanium alloy through hot forging at a temperature lower than the lower critical solution temperature Tc of the alloy. For example, Ti--15V--3Cr--3Al--3Sn, Ti--15Mo--5Zr--3Al, Ti--13V--11Cr--3Al, Ti--8Mo--8V--2Fe--3Al, Ti--22V--4Al, Ti--15Mo--5Zr and the like can be used. The billet of the beta type titanium alloy has a fibrous beta crystal structure as shown in FIG. 4(a). Here, the "billet" means not only that produced by casting but also by another method such as extrusion and forging. The billet in this example is a round bar having a diameter of about 20 mm.

[0025] As mentioned above, the lower critical solution temperature Tc corresponds to the lower limit of the temperature range within which the alloy becomes solution and as time goes by platy beta phase crystal is produced. In other words, Tc corresponds to the upper limit of the temperature range within which platy beta phase crystal is never produced. This temperature Tc may be varied depending on the components of the alloy but determined uniquely to the components. For example, Tc of Ti--15V--3Cr--3Al--3Sn is 760 deg.C, and Tc of Ti--15Mo--5Zr--3Al is 780 deg.C.

[0026] The forging temperature at which the hot forging is carried out is therefore, set to be lower than the lower critical solution temperature Tc deg.C, preferably not less than (Tc-100 deg.C), more preferably not less than (Tc-50 deg.C), but preferably not more than (Tc-20 deg.C). Further, the forging temperature is set to be not less than the recrystallization temperature of the beta type titanium alloy. Therefore, due to stress during forging and the forging temperature decreased to under Tc, the fibrous beta crystal structure can be maintained after forging as show in FIG. 4(a).

[0027] If the forging temperature decreased to lower than (Tc-100) deg.C, it becomes hard for the alloy to cause plastic flow, and as the workability deteriorates, a costly high-power forging machine will be necessitated. Further, during forming, cracks and breakage become liable to occur. By setting the forging temperature less than (Tc-20) deg.C, the alloy is prevented from becoming solution without fail.

[0028] In this invention, the hot forging means a process of forming the material billet into a specific shape utilizing its compressive plastic deformation caused by hitting and/or pressing while heating up the material to the above-mentioned specific temperature. For example, so called free forging, open die forging, closed die forging, semi-closed die forging, high-speed forging, isothermal forging and the like are included.

[0029] If the surface of the forging or face member 7 is covered with unwanted oxidized film after the hot forging, it is removed by polishing or the like. In view of prevention of scales, therefore, closed die forging is preferred. In view of production efficiency, on the other hand, two or three step forging where preforming and finish up forming and optional intermediate second forming are carried out changing dies is preferred.

[0030] In this embodiment, the main body 9 is a precision casting of a metal material formed by lost-wax process. For the main body, various materials may be used, for example, the same material as the face member may be used. In this example, however, a high-strength titanium alloy Ti--6Al--4V which is different from the beta type titanium alloy of the face portion 2 is used.

[0031] The face member 7 which is made through the forging as explained above is welded to the head main body 9. Then, an aging treatment is carried out on the face member 7 together with the main body 9, in other words, carried out on the entirety of the club head, while preventing the alloy from becoming solution.

[0032] The aging treatment is thus such that the object is kept at a temperature of from Tc-220 to Tc-130 deg.C (specifically 550 to 650 deg.C in this example) for a predetermined time period of from 4 to 20 hours, and subsequently it is air cooled at a room temperature, namely, slow cooled.

[0033] Therefore, during aging, microscopic granular alpha crystals occur in the fibrous beta crystal structure as shown in FIG. 4(b), whereby the strength becomes somewhat lower if compared with the structure show in FIG. 5(b) but maintains an improved sufficient level, and the decrease in the elongation can be effectively prevented.

[0034] If quenching or rapid cooling such as water-cooling is made on the face portion, the internal stress and/or internal strain occured during forging remains and the strength is decreased.

[0035] The aging treatment can free the strain and stress from the welded part and its vicinity as well and thereby the weld junction can be improved in the durability. If the welding is made after the aging treatment, the welding region becomes a single-phase of platy beta crystal and the strength will be decreased.

[0036] The above-mentioned extension 7B can shift the weld bead (w) at a distance from the circumferential edge of the club face F. Therefore, the formation of a rigid part near the face portion 2 which may hinder the improvement of the restitution coefficient can be avoided.

[0037] Further, during welding, the heat transfer from the welding part to the club face can be decreased or dispersed by the extension 7B, and accordingly, the undesirable change in the crystallographic structure to the platy beta crystal of the face portion can be effectively prevented.

[0038] Comparison Tests

[0039] Wood-type golf club heads were made by welding various face members to identical main bodies. All the main bodies were a precision casting of Ti--6Al--4V having the structure shown in FIG. 3. The face members had an identical shape shown in FIG. 3 but they were made changing the conditions of the forging and aging treatment as shown in Table 1, using two materials:Ti--15V--3Cr--3Al--3Sn and Ti--15Mo--5Zr--3Al. The club heads were then tested for the restitution coefficient and durability, and the tensile strength and elongation at rupture of the face member materials were measured as follows.

[0040] Strength and Elongation of Face Member Materials:

[0041] To determine the tensile strength and elongation at rupture, a platy 3 mm thick test piece shaped from a round bar by hot forging under the same conditions as each face member was used, and these parameters were measured using a tensile tester.

[0042] Restitution Coefficient:

[0043] According to the "Procedure for Measuring the velocity Ratio of a club Head for conformance to Rule 4-1e, Appendix II, Revision 2 (Feb. 8, 1999), United states Golf Association.", the restitution coefficient "e" was obtained.

[0044] Durability:

[0045] The club heads were attached to identical shafts to make wood clubs. Each club was attached to a swing robot and hit golf balls at a head speed of 50 m/s repeatedly until the face portion was broken. The number of hits is shown in Table 1. If the number of hits reached to 5000 without break, the head is appraised as passable and indicated as "OK" in Table 1.

[0046] Production Efficiency in Forging Process:

[0047] With respect to each face member, ten pieces were made and their dimensional variations were evaluated into three ranks (A, B and C) as follows.

[0048] A: All the ten pieces had dimensions as designed.

[0049] B: Four to nine pieces had dimensions as designed.

[0050] (The remainder needed adjustments by machine work)

[0051] C: Three or less pieces had dimensions as designed.

[0052] (The remainder needed adjustments by machine work)

[0053] From the test results, it was confirmed that the club heads according to the present invention can be improved in the restitution coefficient and durability in a balanced manner.

1TABLE 1 Club head Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ref. 1 Ref. 2 Ex. 6 Ex. 7 Ex. 8 Face member Material *1 T1 T1 T1 T1 T1 T1 T1 T2 T2 T2 Lower critical solution 780 780 780 780 780 780 780 760 760 760 temperature Tc (deg. C.) Forging temperature 750 760 690 660 730 800 800 730 740 680 (deg. C.) Aging treatment Temperature (deg. C.) 600 600 600 600 600 480 600 570 570 570 Time (Hour) 5 5 5 5 5 10 5 5 5 5 Face center thickness t1 2.75 2.75 2.75 2.75 2.75 2.75 2.75 2.75 2.75 2.75 (mm) Tensile strength (MPa) 1430 1412 1489 1466 1440 1780 1988 1330 1321 1365 Elongation at rupture (%) 7.5 8 7.2 7.1 7.4 3.1 1.9 8.5 9.1 8.5 Restitution coefficient 0.853 0.86 0.857 0.858 0.854 0.855 0.85 0.85 0.849 0.852 Durability OK OK OK OK OK 2200 1500 OK OK OK Production efficiency A A B C A A A A A B Club head Ex. 9 Ex. 10 Ref. 3 Ref. 4 Face member Material *1 T2 T2 T2 T2 Lower critical solution 760 760 760 760 temperature Tc (deg. C.) Forging temperature 650 710 800 800 (deg. C.) Aging treatment Temperature 570 570 480 570 Time (hour) 5 5 10 5 Face center thickness t1 2.75 2.75 2.75 2.75 (mm) Tensile strength (MPa) 1344 1336 1650 1898 Elongation at rupture (%) 8.2 8.6 4.9 2.1 Restitution coefficient 0.848 0.85 0.852 0.845 Durability OK OK 2500 1800 Production efficiency C A A A *1) T1 = Ti-15Mo-5Zr-3Al, T2 = Ti-15V-3Cr-3Al-3Sn

Claims

1. A golf club head comprising a face portion whose front face defines a club face for hitting a ball, wherein the face portion is formed by: forging a beta type titanium alloy while keeping the temperature of the alloy lower than the lower critical solution temperature of the alloy; and aging the forged alloy under the lower critical solution temperature Tc so as not to become a solution state.

2. A method of manufacturing a golf club head, the golf club head comprising a face member comprising a face portion whose front face defines a club face for hitting a ball, and a main body to which the face member is attached, the method comprising: preparing a billet of a beta type titanium alloy; forging the billet into the face member while keeping the temperature of the billet lower than the lower critical solution temperature Tc of the beta type titanium alloy; and aging the face member under the lower critical solution temperature Tc so as not to become a solution state.

3. A golf club head according to claim 1, wherein the temperature of the hot forging is not less than Tc-50 deg.C and not more than Tc-20 deg.C.

4. A golf club head according to claim 1 or 2, wherein the face portion is provided with a backward extension, the backward extension extending from an edge of the face portion and formed integrally with the face portion through said forging, and the backward extension is welded to a main body of the head which is formed by casting.

5. A method according to claim 2, wherein the temperature of the hot forging is not less than Tc-50 deg.C and not more than Tc-20 deg.C.

6. A method according to claim 2, which further comprises casting the main body.

7. A method according to claim 2, wherein the face member further comprises a backward extension extending from an edge of the face portion to be welded to the main body.

8. A method according to claim 2, 5, 6 or 7, which further comprises welding the face member to the main body before aging the face member.