Patent Grant
7621824
1. Field of the Invention
The present invention relates to a golf club head and method manufacturing the same, more particularly to a club face with a high-strength part which can improve its durability, directionality for hit ball and rebound performance.
2. Description of the Prior Art
In general, in order to increase a distance of a hit ball, a golf club head with a great volume is proposed. Such a golf club head, for example, comprises a titanium alloy such as Ti-15-Mo-5Zr-3Al or Ti-6Al-4V.
By the way, in order to use a golf club in an official competition, a club head must have a coefficient of restitution less than 0.830. Most of club heads already sold have a coefficient of restitution exceeding 0.830. Therefore, club head makers have to make a club head with coefficient of restitution smaller than before.
In general, the coefficient of restitution of a club head becomes large by making rigidity of a face portion thereof small. For example, if a thickness of a face portion of a club head is made small, the coefficient of restitution of the club head will become large. Therefore, in order to reduce a coefficient of restitution of a club head, it is necessary to enlarge a thickness of a face portion.
However, if the thickness of the face portion is enlarged, a weight of the face portion will increase relatively and a depth of center of gravity of a club head will become small.
For example, in a hollow driver club head made of titanium alloy with a head volume of 400 cm3 and an area of club face of 40 cm2, if a thickness of the face portion of the club head increase by 0.5 mm, a weight of the face portion will increase 5 g or more in general.
Such a club head with a small depth of the center of gravity does not have the good directionality of a hit ball since the rotation of the club head becomes large at the time of a misshot.
It is therefore, an object of the present invention to provide a golf club head with a high durability, a great depth of center of gravity and a proper coefficient of restitution.
According to one aspect of the present invention, a golf club head comprises a club face provided with a high-strength part whose tensile strength is in the range of from 950 to 2200 MPa, wherein the high-strength part has Young's modulus in the range of from 120 to 160 GPa.
Embodiment of the present invention will now be described in detail in conjunction with the accompanying drawings.
A golf club head 1 according to the present invention is preferably a metal wood-type hollow structure. The golf club head 1, as illustrated in
The golf club head 1 in
A volume of the club head 1 is not particularly limited, but if the volume of the club head 1 becomes too small, it is hard to enlarge the moment of inertia of the club head 1. On the contrary, if the volume becomes too large, there is a tendency that the weight of the club head 1 is increased and is hard to be swung. Therefore, it is desirable that the volume of the head 1 is preferably set not less than 300 cm3, more preferably not less than 350 cm3, further preferably not less than 400 cm3, especially preferably not less than 410 cm3. Further, it is desirable that an upper limit thereof is preferably set not more than 500 cm3, more preferably not more than 450 cm3 and more preferably not more than 420 cm3.
A weight of the club head 1 is not particularly limited, but it is desirable that the weight is preferably set not less than 170 g, more preferably not less than 175 g, and further preferably not less than 180 g. Further, it is desirable that an upper limit thereof is not more than 200 g, more preferably not more than 195 g, and further preferably not more than 190 g.
The club head 1 in accordance with the present embodiment is made up at least two parts including a face component 1A and a head main body 1B. The face component 1A is a single metal part. The head main body 1B is also a single metal part in this embodiment, but it may be an assembly of two or more parts. Therefore, in this embodiment as shown in
As shown in
The head main body 1B is provided along the edge of the opening (O) with a plurality of catches 17 for locating the face component 1A accurately during welding while forming a small gap therebetween to be bridged with a weld metal.
As for the material of the head main body 1B, various metal materials, e.g. titanium alloys, pure titanium, aluminum alloys, stainless steel and the like may be used.
Further, the head main body 1B can be manufactured, for example, by preparing a plurality of parts, and approximately attaching the parts each other. For example, in order to set a center of gravity of the club head 1 to suitable position, a weight member with a certain specific gravity such as tungsten alloy, aluminum, aluminum alloy or fiber reinforced resin may be attached to the head main body 1B.
In this embodiment, as for the material of the head main body 1B, an alpha-beta titanium alloy Ti-6Al-4V is used, and the head main body 1B is integrally molded, using a lost-wax precision casting method.
The face component 1A is a major part (in this embodiment, the entire) of the club face F. The face component 1A is further provided with a turnback 9 at the edge E (generic expression of the edges Ea, Eb, Ec and Ed) of the club face F.
The turnback 9 extends backwards to form part of the crown portion 3, sole portion 4 and side portion 5. Therefore, the turnback 9 includes: a crown-side turnback 9a forming a front end zone of the crown portion 3; a sole-side turnback 9b forming a front end zone of the sole portion 4; a toe-side turnback 9c forming a front end zone of the toe-side part of the side portion 5; and a heel-side turnback 9d forming a front end zone of the heel-side part of the side portion 5. These turnback portions 9a to 9d are formed by methods such as bending, a casting process, or a forging method except welding. Also, a dent portion corresponding to the hosel 6 is provided in the heel side of the face component 1A.
A welding portion j between the turnback 9 of the face component 1A and the edge of the opening (O) of the head main body 1B is in a position apart from the edge E of the club face F as shown in
In this point of view, a length L of the turnback 9 in a front-back direction is preferably set not less than 7 mm, more preferably not less than 10 mm and further preferably not less than 15 mm. On the other hand, if the length L of the turnback 9 becomes too long, it is hard to form such a great face component 1A. Therefore, the length L is preferably set not more than 30 mm, more preferably not more than 28 mm and further preferably not more than 25 mm.
The face component 1A comprises a high-strength part 7 at least partially in the face portion 2 whose Young's modulus is in the range of from 120 to 160 GPa and whose tensile strength is in the range of from 950 to 2200 MPa. In this embodiment, the whole of the face component 1A is formed as the high-strength part 7. Therefore, the front zones of the crown portion 3, sole portion 5 and the side portion 6 also have the high-strength parts 7.
On the contrary, the high strength part 7 in accordance with the present embodiment is formed by an alloy with a great Young's modulus. Therefore, such a club head makes it possible to reduce the coefficient of restitution thereof even if the thickness of the face portion 2 is made small. With this, the club head in accordance with the present invention makes it possible to control the rebound performance thereof without reducing the depth of the center of gravity. Also, since the alloy has a high tensile strength, it is possible to maintain the durability of the club head enough even if the thickness of the face portion 2 is made small.
Here, if the Young's modulus of the high-strength part 7 is less than 120 GPa, the depth of the center of gravity becomes small since it is necessary to enlarge a thickness of the face portion in order to control the coefficient of restitution into suitable value defined by USGA. In this point of view, Young's modulus of the high-strength part 7 is preferably set not less than 125 GPa, and more preferably not less than 130 GPa. On the other hand, if the Young's modulus of the high-strength part 7 is more than 160 GPa, the coefficient of restitution becomes too small. So, Young's modulus of the high-strength part 7 is preferably set not more than 155 GPa, more preferably not more than 150 GPa and further preferably not more than 145 GPa.
Further, if the tensile strength of the high-strength part 7 is less than 950 MPa, a great thickness of the face portion 2 is required in order to maintain the durability and strength thereof. Such a club has a problem such that the coefficient of restitution and the depth of center of gravity become too small. In this point of view, the tensile strength of the high-strength part 7 is preferably set not less than 1000 MPa, more preferably not less than 1100 MPa and further preferably not less than 1200 MPa. On the other hand, if the tensile strength of the high-strength part 7 is more than 2200 MPa, the durability of the club head is reduced since toughness thereof becomes decrease. In this point of view, the tensile strength of the high-strength part 7 is preferably set not more than 1800 MPa, and more preferably not less than 1600 MPa.
As for the high-strength part 7, for example, it is suitable that a titanium alloy consist of, in weight %, Al:3.5-6.5%, Fe:0.1-2.0%, and the balance of Ti and at least one inevitable impurity. such a titanium alloy has a specific gravity not more than 4.38, so that the depth of the center of gravity of the club head 1 can be enlarged.
Here, if the content of Al of the titanium alloy is less than 3.5 weight %, there is a tendency that an omega phase which makes the tensile strength of the titanium alloy reduce is generated in the crystal organization thereof. Also, if the content of Al of the titanium alloy is more than 6.5 weight %, it is hard to make the alloy into a certain shape by using plastic deformation thereof. In this point of view, the content of Al is preferably set not less than 4.0 weight %, more preferably not less than 4.5 weight %, but preferably not more than 6.0 weight %, and more preferably not more than 5.5 weight %.
The addictive Fe in the titanium alloy prevents forming of an intermetallic compound, and stabilizes a beta phase of the titanium alloy. Also, ease of workability of the titanium alloy can be improved by adding Fe therein. If the content of Fe of the titanium alloy is less than 0.1 weight %, it is hard to get those effects from the titanium alloy. The content of Fe in the titanium alloy is preferably set not less than 0.5 weight %, more preferably not less than 0.7 weight %, but preferably not more than 1.5 weight %, and more preferably not more than 1.3 weight %.
As for the inevitable impurity of the titanium alloy, for example, at least one of O, N, C and/or H is included. The inevitable impurity is very less.
In order to get a great distance of a hit ball, the coefficient of restitution of the club head 1 is preferably set not less than 0.800, more preferably not less than 0.810, further preferably not less than 0.820 and still further preferably not less than 0.825. On the contrary, in order to comply with the Rules of Golf for Clubs as defined by the USGA, the coefficient of restitution of the club head 1 is preferably less than 0.830.
Here, the coefficient of restitution of the club head 1 is obtained by calculating on the basis of Procedure for Measuring the velocity Ratio of a Club Head for Conformance to Rule 4-1e, Revision 2 (Feb. 8, 1999) in USGA.
As shown in
Here, in order to maintain the durability and the suitable coefficient of restitution of the club head 1, the thickness t1 of the center portion 2A is preferably set not less than 2.90 mm, more preferably not less than 2.95 mm, and further preferably not less than 3.00 mm, but it is preferably set not more than 3.20 mm, and more preferably not more than 3.10 mm.
Further, the thickness t2 of the periphery portion 2B is preferably set not less than 2.35 mm, more preferably not less than 2.40 mm and further preferably not less than 2.50 mm, but it is preferably set not more than 2.70 mm, and more preferably not more than 2.60 mm.
In this embodiment, the face portion 2 also comprises a transit portion 2C connecting between the center portion 2A and periphery portion 2B. The transit portion 2C has a thickness gradually changing from the thickness t1 to the thickness t2 so as to improve the durability of the face portion 2.
In order to improve a directionality of hit ball and the distance, the depth of center of gravity of the club head 1 is preferably set not less than 35.5 mm, more preferably not less than 36.0 mm, and further preferably not less than 37.5 mm, but it is preferably set not more than 43.0 mm, more preferably not more than 41.5 mm, and further preferably not more than 40.0 mm.
Here, the depth of center of gravity of the club head 1 is a length of a normal line N which is drawn perpendicular to the club face F from the center G of gravity of the club head 1. Also, a sweet spot SS is defined as a point on the club face F which is the intersecting point of the normal line N with the club face F.
The club head 1 has a moment M of inertia around a vertical axis passing through a center G of gravity of the club head 1 under the standard condition being not less than 4100 g·cm2, more preferably not less than 4200 g·cm2, and further preferably not less than 4400 g·cm2, but it is preferably set not more than 5700 g·cm2, and more preferably not more than 5500 g·cm2. Since the club head 1 in accordance with the present embodiment has the great moment of inertia, it is possible to get an excellent directionality of the hit ball. The moment of inertia mentioned above corresponds to a value of a club head simple substance.
For example, the face component 1A is manufactured by the process which comprises the steps of heating the titanium alloy in the range of from 930 to 950 degrees Celsius for 3 to 30 minutes, and forging the titanium alloy into the face component 1A after the heating.
By using such a manufacturing method, the titanium alloy which has a fine crystal organization without segregation can be obtained so that the durability of the face portion 2 is improved. Also, especially in the hot forging, the mechanical properties, such as tensile strength, hardness, toughness and fatigue-resistant characteristic of the titanium alloy are improved. Further, since the forging can form complicated shape, the face component 1A having the turnback 9 and the face portion 2 with a varying thickness can be formed from the billet easily.
In this embodiment, the forging is performed by heating a billet made of the titanium alloy up to the above-mentioned temperature range and beating or pressing the billet into the specific target shape. At the time of forging, the temperature of the billet is kept the temperature range above-mentioned. In order to improve the strength of the titanium alloy and workability thereof, in advance of the forging, the billet is heated with an electric furnace. When the temperature of the billet is less than 930 degrees Celsius or the heating time is less than 3 minutes, the workability will be deteriorated because the alloy of the billet is difficult to make a plastic flow. On the contrary, when the temperature is more than 950 degrees Celsius or the heating time is more than 30 minutes, the crystal organization of the titanium alloy becomes brittle, and the durability of the face portion 2 is reduced.
As for the forging, various types of forging such as die forging (inclusive of flat die, open die, closed die and semi-closed die) are included. In case of die forging, two-stage forging, namely, pre-forming and finish forging using a rougher and a finisher, respectively, or three-stage forging including additional intermediate forming between the pre-forming and finish forging is desirable. In this embodiment, in order to avoid scale, closed die forging is desirable.
Comparison Tests
Wood-type golf clubs having the specifications shown in Table 1 and the basic structure as illustrated in
Head volume: 420 cm3
Loft angle: 10 degrees
Head main body: A single casting part made of Ti-6Al-4V
An area of center portion of the club face: 10 cm2
An area of periphery portion of the club face: 33 cm2
Each face component of examples was used a forged part made of titanium alloy of Ti-5Al-1Fe containing of, in weight %, Al:5%, Fe:1% and the balance of Ti and an inevitable impurity.
The heat treatment condition is as follows.
Heating temperature: 940 degrees C.
Heating time: 10 minutes
Each face component of references 1 and 2 is used a forged part made of titanium alloy of Ti-6Al-4v containing of, in weight %, Al:6%, v:4% and the balance of Ti and an inevitable impurity. The heat treatment condition is as follows.
Heating temperature: 990 degrees C.
Heating time: 10 minutes
These face components were welded with head main bodies by TIG welding. The test methods are as follows.
Rebound Performance Test
According to the “Procedure for Measuring the velocity Ratio of a club Head for conformance to Rule 4-1e, Appendix 2, Revision 2 (Feb. 8, 1999), United states Golf Association”, the coefficient of restitution (e) of each club head was obtained.
Directionality of Hit Ball Test
The test was executed by hitting golf balls ten times per a test club by ten right-handed golfers whose handicaps ranged from 10 to 20, and measured the difference between a ball stop position and the straight line extending from the position of the golfer to a target point, the directionality of hit ball was evaluated. Here, the measured difference is set to a plus value, even if the stop position of the ball is shifted to the right or the left with respect to the straight line. An average of the differences of each test club was calculated, and evaluated based on the following standard. Further, the results indicate averages of ten golfers. The larger the numerical value is, the better the directionality is.
5: The average of the differences is not more than 7.5 yards.
4: The average of the differences is more than 7.5 and not more than 10.0 yards.
3: The average of the differences is more than 10.0 and not more than 12.5 yards.
2: The average of the differences is more than 12.5 and not more than 15.0 yards.
1: The average of the differences is more than 15.0 and not more than 17.5 yards.
Durability Test
The wood-type club was attached to a swing robot and hit golf balls repeatedly at a head speed of 55 m/s. Then, the number of hit ball was checked until the club head was broken. The result was expressed as the index which sets the number of hit times of Example 1 to 100. The larger the numerical value is, the better the durability is.
Fatigue-Resistant Test of Face Portion
A test piece was made from the face portions of each test club head with a length of more than 30 mm, a width of 20 mm and a thickness of 2.5 mm. The test piece was supported by two jigs with a span of 30 mm, and was applied a vertical force of 1200 MPa with 2 Hz periodically at the center of the span. Then, the number of load times was checked until the test piece was broken. The result was expressed as the index which sets the number of load times of Example 1 to 100. The larger the numerical value, the better the fatigue resistant.
Impact Test of Face Portion
A test piece was made from the face portions of each test club head with a width of 10 mm and a thickness of 2 mm, and measured an impact strength of each test piece by the Charpy test with test energy of 30 j. The result was expressed as the index which sets the impact strength of Example 1 to 100. The larger the numerical value, the better the impact strength.
Test results and the specification of the club heads are shown in Table 1.
Since the references 1 and 3 each have a small thickness of the face portion, they have the coefficient of restitution greater than 0.830, and the low durability.
Since each reference 2 and 4 each have a great thickness of the face portion and a great weight of the club head, each head has a large depth of center of gravity and a small moment of inertia. So, the directionality is not good.
On the contrary, each example has a coefficient of restitution less than 0.830, and a great depth of center of gravity and the moment of inertia so that the directionality is good.
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