Method for producing golf club head and said golf club head

Abstract

Provided are a method for producing a golf club head and said golf club head wherein deformation in the neck part, occurring as a result of using low-carbon steel, is prevented to improve the feel of a golf club when hitting a ball.　A punch 3 is pressed against an outer peripheral surface 131 of a neck part 13 of a golf club head, which is produced with S10C-S15C low-carbon steel, during the final step of hot forging. The shape of the punch 3 is obtained by halving a hollow cylinder, and in the punch 3, four cross-sectional arc-shaped recessed sections are formed to be evenly spaced as straight bands parallel with one another, causing cross-sectional arc-shaped protruding sections 41 to be formed on the neck part 13. A hardened part that prevents deformation in the neck part 13 is formed by coining the cross-sectional arc-shaped protruding sections 41.

Description

A method for manufacturing a golf club head and the golf club head itself.

[0001] This invention relates to a method for manufacturing a golf club head with a stamped finish, and to a golf club head made of low-carbon steel that provides a good feel when struck. More specifically, it relates to a method for manufacturing a golf club head with a stamped finish on the neck portion, and to a golf club head made of low-carbon steel that provides a good feel when struck.

[0002] Generally, forged soft iron irons are said to have a softer feel when struck by the ball. Forged soft iron irons use carbon steel as the material, and it is said that low-carbon steel, which has a lower carbon content, has a softer feel when struck. The applicant has proposed a golf club manufactured by hot forging low-carbon steel in which multiple protrusions are formed on the face, and these protrusions are flattened by cold forging to refine the crystal grain of the metal structure, thereby improving the sound and feel when struck (Patent Document 1, Patent Document 2). On the other hand, in iron golf clubs, it is known that the loft angle of the face is adjusted by bending the neck (hosel). Since cracks or fractures may occur in the neck and other parts due to this angle adjustment, it has also been proposed that a part of the neck be softened by heat treatment to reduce its hardness (Patent Document 3).

[0003] Japanese Patent Publication No. 2013-128765, Japanese Patent Publication No. 2016-77487, Japanese Patent Publication No. 2019-524340

[0004] However, in order to improve the hitting feeling, when using low-carbon steel with a carbon content of 0.18% or less as the steel material for iron golf clubs, an impact is applied during hitting, and a phenomenon occurs where the neck part bends. Therefore, there is a limit to using low-carbon steel. In terms of hardness, if the Vickers hardness Hv is less than 128, the neck part may bend. Incidentally, since the face is thick, even if it is low-carbon steel with 0.18% or less, there is no problem even if an impact is applied during hitting. The golf club heads and their manufacturing methods described in the aforementioned Patent Documents 1 and 2 partially work-harden the face part to improve the hitting feeling, and do not improve the deformation of the neck part that occurs with the adoption of low-carbon steel. The one described in Patent Document 3 softens the neck part to prevent cracks or fractures, and does not prevent the deformation of the neck of a golf club using low-carbon steel for improving the hitting feeling.

[0005] The present invention achieves the following objects based on the above background. An object of the present invention is to provide a manufacturing method of a golf club head and the golf club head that prevent deformation of the neck part that occurs with the adoption of low-carbon steel for improving the hitting feeling. Another object of the present invention is to provide a manufacturing method of a golf club head and the golf club head with high productivity for forming a hardened part that prevents deformation of the neck part that occurs with the adoption of low-carbon steel for improving the hitting feeling.

[0006] The above problems are solved by the following means. That is, the manufacturing method of a golf club head according to the first aspect of the present invention is a manufacturing method of a golf club head manufactured by hot forging low-carbon steel, and includes a convex part forming step of forming a plurality of convex parts on the neck part of the golf club head by the hot forging process, and a neck part pressing step of flattening and partially increasing the hardness of only the convex parts by cold or warm forging process.

[0007] The method for manufacturing a golf club head according to the second invention is characterized in that, in the first invention, the golf club head is an iron golf club, and the protrusion is formed on the outer circumferential surface near the bottom of the shaft mounting hole formed in the neck portion of the golf club head. The method for manufacturing an iron golf club head according to the third invention is characterized in that, in the first or second invention, the low carbon steel has a carbon content of 0.18% or less. The golf club head according to the fourth invention is a golf club head manufactured by hot forging low carbon steel, wherein the low carbon steel has a carbon content of 0.18% or less, and the neck portion of the golf club head has a partially high-hardness portion that is partially different in hardness from the rest. The golf club head according to the fifth invention is characterized in that, in the fourth invention, the partially high-hardness portion is formed by a pressing process that applies pressure to the protrusion.

[0008] [Low Carbon Steel] In this invention, "low carbon steel" refers to the material for the golf club head, specifically a general carbon steel material for machine structures with a carbon content of 0.18% or less, characterized by high weldability and workability. It is also known that increasing the carbon content in carbon steel increases the hardness during quenching. The neck portion of this invention may bend due to the use of the golf club head, so the strength to prevent bending requires a hardness of HV (Vickers) 129 or higher. In steel materials, it is known that mechanical strength such as tensile strength and bending strength correlates with hardness. Therefore, in this invention, the bending strength of the neck portion is set by hardness from the viewpoint of ease of quality control. Specifically, S10C, which has the lowest carbon content among the low carbon steels referred to in this invention, is set to a hardness of HV (Vickers) 129 or higher, and under normal impact with the golf club head, there is no deformation of the neck portion.

[0009] [Hot forging, cold forging, warm forging] In this invention, "hot forging" refers to a general forging method performed after heating low-carbon steel to the temperature at which it recrystallizes (approximately 900°C to 1250°C), "cold forging" refers to forging performed at room temperature (below the recrystallization temperature), and "warm forging" refers to a forging method in which the steel is heated at an intermediate temperature (approximately 300°C to 900°C) and shaped. [Hardness] In this invention, "hardness" refers to a measure of the hardness of low-carbon steel, and refers to the numerical value measured by Rockwell hardness, Vickers hardness, etc., which are general methods for measuring the hardness of metal materials. [Impacting] In this invention, "impacting" refers to a process in which one or more protrusions formed on the surface of the neck of a golf club head by hot forging are crushed with a punch having a flat, linear, or convex surface by cold forging or warm forging, and pressure is applied to partially increase the hardness.

[0010] The present invention provides a method for manufacturing a golf club head and a golf club head that can prevent deformation of the neck portion that occurs when low-carbon steel is used to improve feel. More specifically, even when low-carbon steel with a carbon content of 0.18% or less is used as the material for the head, deformation of the neck portion can be prevented by setting the hardness of at least the neck portion to HV (Vickers) 129 or higher. Furthermore, since a stamping process is used to form the hardened portion that prevents this deformation, a highly productive process has been achieved.

[0011] Figure 1 shows a golf club head manufactured by the manufacturing method of the present invention, where Figure 1(a) is an overall front view and Figure 1(b) is a cross-sectional view taken along line A-A in Figure 1(a). Figure 2 is a longitudinal cross-sectional view of the neck portion of Figure 1(a). Figure 3 is an explanatory diagram showing the convex portion formation process of the present invention, where Figure 3(a) is a plan view and Figure 3(b) is a cross-sectional view taken along line B-B in Figure 3(a). Figure 4 is an explanatory diagram showing the neck portion stamping process of the present invention, where Figure 4(a) is a plan view and Figure 4(b) is a cross-sectional view taken along line C-C in Figure 4(a). Figure 5 is an explanatory diagram showing the neck portion stamping process at the end of the present invention, where Figure 5(a) is a plan view and Figure 5(b) is a cross-sectional view taken along line D-D in Figure 5(a). Figure 6 is an explanatory diagram showing an example of the shape of the convex portion of the neck portion of the present invention. Figure 7 is a cross-sectional view taken 30 mm from the tip of the neck portion. Figure 8 shows the change in surface irregularities (axial direction) of the outer circumferential surface of the neck before and after the stamping process. Figure 8(a) shows the surface irregularities after hot forging, and Figure 8(b) shows the surface irregularities of the outer circumferential surface after stamping.

[0012] Embodiments of the present invention will be described below with reference to the drawings. Figure 1 shows a golf club head manufactured by the manufacturing method of the present invention, where Figure 1(a) is an overall front view, Figure 1(b) is a cross-sectional view taken along line A-A in Figure 1(a), and Figure 2 is a longitudinal cross-sectional view of the neck portion in Figure 1(a). The golf club head 1 shown in Figures 1 and 2 is an iron golf club head, and is a cavity-back type iron golf club head with a recess 11 formed on the back. The front of the golf club head 1 has a face portion 12 having a striking surface for striking the ball, a neck portion (hosel portion) 13 which is the shaft connection portion on the shaft side, a top portion 14 at the top, a toe portion 15 at the front, a sole portion 16 at the bottom that contacts the ground, and a heel portion 17 at the rear. The face portion 12 has 12 scorelines (grooves) 2 formed parallel to each other at equal intervals in a direction intersecting the toe-heel direction, with the toe-heel direction as the longitudinal direction.

[0013] The golf club head 1 is made of low-carbon steel, specifically S10C to S15C. As shown in Figure 2, a shaft 19 is inserted into a shaft mounting hole 18 formed in the neck portion 13 of the golf club head 1 and fixed with adhesive or the like. The shaft mounting hole 18 is drilled. When the impact of a strike is applied to the neck portion 13, stress concentrates in the thin-walled portion 182 from the bottom 181 of the shaft mounting hole 18 up to about 5 mm above, causing the neck portion 13 to bend and wrinkle.

[0014] Next, the manufacturing method of the golf club head 1 described above will be explained. Figure 3 is an explanatory diagram showing the convex portion formation process of the present invention, where Figure 3(a) is a plan view and Figure 3(b) is a cross-sectional view taken along line B-B in Figure 3(a). As shown in Figures 3(a) and (b), a punch 3 is pressed against the outer circumferential surface 131 of the neck portion 13 in a hot forging process. The punch 3 is shaped like a hollow cylinder cut in half, and four parallel arc-shaped recesses 31 are formed at equal intervals on the arc-shaped inner circumferential surface 32 of the punch 3. The arc-shaped recesses 31 are formed on the face side and the back side, respectively, which are 180° opposite each other. The shape of the vertical cross-section of the arc-shaped recesses 31 is semi-circular. Figures 6(a) to (c) are explanatory diagrams showing examples of the shape of the convex portion of the neck portion 13 of the present invention, with the arc-shaped convex portion 41 formed in Figures 3(a) and (b) shown in Figure 6(a). Next, scorelines 2 are formed on the face portion 12 using a scoreline press (not shown).

[0015] Figure 4 is an explanatory diagram showing the neck portion stamping process of the present invention, where Figure 4(a) is a plan view and Figure 4(b) is a cross-sectional view taken along line C-C in Figure 4(a). In Figure 4, the arc-shaped protrusions 41 are formed on the neck portion 13 after the protrusion formation process of Figure 3. As shown in Figure 4, the protrusion formation process of Figure 3 results in four arc-shaped protrusions 41 being formed at equal intervals on the face side and back side of the neck portion 13, which has a circular cross-sectional shape, parallel to each other in a direction perpendicular to the axial direction of the neck portion 13. The height H of the arc-shaped protrusions 41 is 1.0 mm.

[0016] The punch 5 in Figure 4 is shaped like a hollow cylinder cut in half, and has a flat, arc-shaped inner surface 51 formed on it for flattening the arc-shaped protrusion 41. As shown in Figure 4, the arc-shaped protrusion 41 is a part that protrudes from the outer surface of the circular solid neck portion 13. The punch 5 is pressed against this arc-shaped protrusion 41 while cold or warm to flatten it. Figure 5 is an explanatory diagram showing the end of the neck portion stamping process of the present invention, where Figure 5(a) is a plan view and Figure 5(b) is a cross-sectional view taken along line D-D in Figure 5(a). Even after flattening the arc-shaped protrusion 41 in the neck portion stamping process of Figure 4, minute protrusions (partially high-hardness portions) 42 with a height of 0.05 to 0.5 mm remain on the neck portion 13 due to the springback phenomenon. After the neck portion stamping process is completed, finishing such as polishing or plating is performed to complete the manufacturing process of the golf club head 1.

[0017] Figure 6(b) shows an example in which four arc-shaped protrusions 43 are formed at equal intervals, parallel to each other and in a direction that intersects the axial direction of the neck portion 13 at an angle. Figure 6(c) shows an example in which seven arc-shaped protrusions 441 are formed at equal intervals, parallel to each other and in a direction that intersects the axial direction of the neck portion 13, and one linear protrusion 442 is formed in a straight line parallel to the axial direction of the neck portion 13. The cross-sectional shape of the arc-shaped protrusions 41, 43, 441 and the linear protrusion 442 is semi-circular, but it may also be triangular, mountain-shaped, or trapezoidal.

[0018] Figure 7 is a cross-sectional view taken 30 mm from the tip of the neck. As shown in Figure 7, 0° is the toe side, 90° is the back side, 180° is the heel side, and 270° is the face side, and minute protrusions 42 are formed on the face side and the back side. In Figure 7, the minute protrusions 42 are exaggerated, but after finishing such as polishing or plating, the minute protrusions 42 become invisible to the naked eye. In other words, the stamped neck 13 has finer crystal grains in its metal structure compared to the neck 13 without stamping, resulting in higher hardness, and it is possible to prevent deformation of the neck 13 that occurs when low carbon steel is used to improve the feel of the ball.

[0019] [Experimental Example] In the following example of the present invention, the "cross-sectional hardness of the neck portion" was measured, and a comparative experiment was conducted between a neck portion that was not stamped and one that was stamped, to confirm the effect of the present invention. Table 1 below shows examples of hardness of the neck portion (material: S10C). The face and neck portion of the golf club head are formed by hot forging using a conventional method, and multiple protrusions (height 0.5 mm) are formed on the neck portion. Table 1 below shows the hardness data comparing a neck portion that has undergone a stamping process (see Figure 4) in which these protrusions are flattened by cold (room temperature) or hot forging at 750°C to partially increase the hardness, with a neck portion that has not undergone stamping. Figure 8 shows the change in the unevenness (axial direction) of the outer surface of the neck portion before and after stamping. Figure 8(a) shows the state after hot forging, and Figure 8(b) shows the unevenness of the outer surface after stamping. In this experiment, instead of completely flattening the protrusions, the material was pressed with a linear mold, and any remaining protrusions were scraped off. Pressing with a linear mold makes it easier to flatten the protrusions and improves hardness.

[0020] The hardness (Pickers hardness (HV)) at a depth of 1.0 mm from the outer circumferential surface (31.0 mm from the upper end) of the neck portion (see Figure 2 for the neck portion used in the experiment) is higher for the stamped portion. The stamped portion did not deform even after a predetermined number of ball impact tests (product conditions set by the applicant). Although there is a method of hardening the neck portion by high-frequency induction hardening, high-frequency induction hardening cannot be used when the workpiece shape is complex, such as the neck portion of a club head with an internal cavity, as it is difficult to heat uniformly due to thermal deformation, etc. [Other embodiments] In the embodiments of the present invention described above, the arc-shaped protrusions 41, 43, 441 and the linear protrusions 442 are formed on the face side and back side, respectively, which are 180° opposite each other, but they may be formed on either the face side or the back side. Furthermore, they are not limited to the face side or the back side, but may be formed on any outer circumferential surface of the neck portion.

[0021] 1...Golf club head 11...Recess 12...Face 13...Neck (hosel) 131...Outer surface 14...Top 15...Toe 16...Sole 17...Heel 18...Shaft mounting hole 181...Bottom of hole 182...Thin wall 19...Shaft 2...Scoreline 3...Punch 31...Arc-shaped recess 32...Inner surface 41...Arc-shaped protrusion 42...Micro-protrusion 43...Arc-shaped protrusion 441...Arc-shaped protrusion 442...Linear protrusion 5...Punch 51...Arc-shaped flat inner surface

Claims

1. A method for manufacturing a golf club head produced by hot forging low-carbon steel, characterized by comprising: a convex portion forming step of forming a plurality of convex portions on the neck portion of the golf club head by the hot forging process; and a neck portion pressing step of flattening only the convex portions by cold or hot forging to partially increase their hardness.

2. A method for manufacturing a golf club head according to claim 1, wherein the golf club head is an iron golf club, and the protrusion is formed on the outer circumferential surface near the bottom of the shaft mounting hole formed in the neck portion of the golf club head.

3. A method for manufacturing a golf club head according to claim 1 or 2, characterized in that the low-carbon steel has a carbon content of 0.18% or less.

4. A golf club head manufactured by hot forging low-carbon steel, wherein the low-carbon steel has a carbon content of 0.18% or less, and the neck portion of the golf club head has a partially high-hardness portion that differs in hardness from the rest of the head.

5. The golf club head according to claim 4, characterized in that the high-hardness portion is formed by a pressing process that applies pressure to the convex portion.

Images