US20160354652A1

US20160354652A1 - Manufacturing method, golf club head, and design method

Info

Publication number: US20160354652A1
Application number: US15/138,357
Authority: US
Inventors: Wataru Ban
Original assignee: Bridgestone Sports Co Ltd
Current assignee: Bridgestone Sports Co Ltd
Priority date: 2015-06-02
Filing date: 2016-04-26
Publication date: 2016-12-08
Also published as: JP2016221099A

Abstract

The present invention relates to a method of manufacturing a wood type golf club head including a face portion, a crown portion, and a sole portion. The method includes a setting step of setting a surface roughness of the face portion and a step of forming the face portion based on the surface roughness set in the setting step. In the setting step, the larger a moment of inertia of the golf club head is, the larger the surface roughness outside an impact area of the face portion is set, and the smaller the moment of inertia is, the smaller the surface roughness outside the impact area of the face portion is set.

Description

BACKGROUND OF THE INVENTION

Field of the Invention
The present invention relates to a wood type golf club head.
Description of the Related Art
In a golf club head having a relatively large loft angle, the larger the surface roughness of the face portion is, the larger the spin amount of a shot tends to be. However, in a golf club head having a relatively small loft angle (for example, 20° or less), the larger the surface roughness of the face is, the smaller the spin amount of a shot tends to be. Japanese Patent Laid-Open No. 2008-79969 and 2004-222905 propose golf club heads with a focus on this point.
In a golf club head, generally, the position of a hit on the face portion may degrade the carry or spin amount of a shot. To improve this, each of Japanese Patent Laid-Open No. 2004-222905, 5-237206, and 62-144674, Japanese Utility Model Laid-Open No. 3-16963, U.S. Patent Application Publication No. 2012/0052980, and U.S. Pat. No. 6,309,310 discloses a golf club head that changes the specifications of the surface roughness or grooves depending on a portion on the face portion.
In a wood type golf club head, since the loft angle is relatively small, the larger the surface roughness of the face portion is, the smaller the spin amount of a shot tends to be. When a focus is placed only on distance performance, increasing the surface roughness of the face portion is advantageous. However, if the spin amount of a shot is small, and it is difficult for the golfer to intentionally bend the shot to the left or right. This is disadvantageous from the viewpoint of shot control.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a wood type golf club head including a face portion with a surface roughness suitable for the specifications of the golf club head.
According to an aspect of the present invention it is provided a method of manufacturing a wood type golf club head including a face portion, a crown portion, and a sole portion, comprising: a setting step of setting a surface roughness of the face portion; and a step of forming the face portion based on the surface roughness set in the setting step, wherein in the setting step, the larger a moment of inertia of the golf club head is, the larger the surface roughness outside an impact area of the face portion is set, and the smaller the moment of inertia is, the smaller the surface roughness outside the impact area of the face portion is set.
Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of a golf club head according to an embodiment of the present invention;

FIG. 1B is a front view showing the golf club head in FIG. 1A viewed from a face side;

FIG. 2A is a sectional view taken along a line I-I in FIG. 1B;

FIG. 2B is a sectional view taken along a line II-II in FIG. 1B;

FIGS. 3A and 3B are explanatory views of a face center and the like;

FIG. 4A is a flowchart showing an example of a method of manufacturing the golf club head shown in FIG. 1A;

FIGS. 4B to 4E are views showing examples of the relationship between a surface roughness and a moment of inertia;

FIG. 5A is an explanatory view of an example of a shallow groove forming method;

FIG. 5B is a view showing another example of the arrangement of a face portion;

FIGS. 6A to 6E are explanatory views of another example of shallow grooves;

FIG. 7A is an explanatory view of a bulge; and

FIG. 7B is a view showing an example of the relationship between a bulge and a moment of inertia.

DESCRIPTION OF THE EMBODIMENTS

First Embodiment

FIG. 1A is a perspective view of a golf club head 10 according to an embodiment of the present invention. FIG. 1B is a front view showing the golf club head 10 viewed from the side of a face portion 11.
The golf club head 10 forms a hollow member. Its peripheral walls form the face portion 11, a crown portion 12, a sole portion 13, and a side portion 14. The surface of the face portion 11 forms a face (striking face). A bulge and a roll are formed on the face. The crown portion 12 forms the upper portion of the golf club head 10. The sole portion 13 forms the bottom portion of the golf club head 10. The side portion 14 forms the portion between the sole portion 13 and the crown portion 12. The golf club head 10 also includes a hosel portion 15 to which a shaft is attached.
An arrow d1 in FIG. 1A indicates a face-back direction, and an arrow d2 indicates a toe-heel direction. An arrow d3 in FIG. 1B indicates the vertical direction of the face portion 11. The face-back direction is normally a target line direction (the target direction of a shot). The toe-heel direction can be defined as, for example, a direction in which the toe-side end and the heel-side end of the sole portion 13 are connected or a direction perpendicular to the face-back direction. The vertical direction of the face portion 11 is defined based on the golf club head grounded in accordance with a predetermined lie angle. In this embodiment, the vertical direction is the direction of sole portion 13−crown portion 12. Note that the lie angle is an angle θ1 made by a shaft axis line L1 and the ground surface, as shown in FIG. 1B.
The golf club head 10 is a golf club head for a driver. However, the present invention is applicable to wood type golf club heads including a fairway wood other than drivers. The present invention is particularly suitable for a golf club head having a loft angle of 20° or less. This embodiment assumes a golf club head having a loft angle of 20° or less.
The golf club head 10 can be made of a metal material. Examples of the metal material are a titanium-based metal (for example, titanium alloy 6Al-4V-Ti), stainless steel, and a copper alloy such as beryllium copper.
The golf club head 10 can be assembled by joining a plurality of parts. For example, the golf club head 10 can be formed from a main body member and a face member. The main body member forms the crown portion 12, the sole portion 13, the side portion 14, and a peripheral portion of the face portion 11. An opening is formed at part of the portion corresponding to the face portion 11. The face member is joined to the opening of the main body member.
A plurality of shallow grooves G1 to G3 (to be generically referred to as shallow grooves G) are formed in the surface of the face portion 11. The plurality of shallow grooves G will be described with reference to FIGS. 2A and 2B in addition to FIGS. 1A and 1B. FIG. 2A is a sectional view taken along a line I-I in FIG. 1B. FIG. 2B is a sectional view taken along a line II-II in FIG. 1B. The line I-I and the line II-II are lines in the direction d3.
The plurality of shallow grooves G are arrayed in the vertical direction (direction d3) of the face portion 11. In this embodiment, the shallow grooves G are straight grooves extending in the toe-heel direction and are parallel to each other. The shallow grooves G are formed so as to be level when the golf club head 10 is grounded toward the target direction. In this embodiment, each shallow groove G need not always be a straight continuous groove and may break halfway.
In this embodiment, the plurality of shallow grooves G1 are formed in an impact area IA. The plurality of shallow grooves G2 are formed in a toe-side area TA out of areas other than the impact area IA, and the plurality of shallow grooves G3 are formed in a heel-side area HA out of areas other than the impact area IA. A structure without the shallow grooves in the impact area IA can also be employed.
In a driving club or a fairway wood, the impact area IA is a band-shaped portion passing through the center of the club face and having a width of 1.68 inches (42.67 mm) under the rules (R & A rules). A supplementary description of the impact area IA will be made here with reference to FIGS. 3A and 3B as well.
Referring to FIGS. 3A and 3B, a plane S1 is a virtual vertical plane that passes through a geometric center FC of the face portion 11 and is perpendicular to the ground surface and the toe-heel direction when the golf club head 10 is grounded at the predetermined lie angle θ1 and a predetermined loft angle θ2. As shown in FIG. 1B, the impact area IA is a band-shaped portion having a width of 1.68 inches (42.67 mm) with respect to the intersection between the plane S1 and the face portion 11 as the center.
Referring to FIGS. 1A, 1B, 2A, and 2B, the surface roughness of the face portion 11 can be adjusted by the specifications, for example, the pitch, width, and depth of the plurality of shallow grooves. In this embodiment, the specifications (here, for example, only the pitch) of the shallow grooves G are changed between the impact area IA and the areas TA and HA other than the impact area IA. However, the specifications of the shallow grooves G may be the same between the impact area IA and the areas TA and HA other than the impact area IA.
All or some of the specifications of the shallow grooves G may be changed between the toe-side area TA and the heel-side area HA. In this embodiment, however, the specifications of the shallow grooves G are the same in both areas. Hence, in the following explanation, a description concerning the shallow grooves G2 in the toe-side area TA also applies to the shallow grooves G3 in the heel-side area HA, unless otherwise specified.
A depth D1 of each shallow groove G1 and a depth D2 of each shallow groove G2 are less than, for example, 0.025 mm. If the depth is less than 0.025 mm, the shallow grooves G are handled not as so-called score lines but as elements (for example, elements by milling) that roughen the face under the rules (R & A rules) of golf club heads. The shallow grooves G are formed to adjust the surface roughness of the face portion 11. Hence, the depths D1 and D2 can be 0.005 mm or more. A width W1 of each shallow groove G1 and a width W2 of each shallow groove G2 can range, for example, from 0.1 mm (inclusive) to 0.3 mm (inclusive). Note that the widths W1 and W2 are the widths of the shallow grooves G in the vertical direction (the direction d3 or the planar direction of the face portion 11).
In the examples shown in FIGS. 2A and 2B, the cross section of each shallow groove G has an elliptic arc outline. However, the outline shape of the cross section of each shallow groove G is not limited to this, and various outline shapes such as an arc shape, triangular shape, rectangular shape, and trapezoidal shape can be employed.
In this embodiment, the plurality of shallow grooves G are formed at an equal pitch. However, the pitch may change depending on a part. In this embodiment, the pitch between adjacent shallow grooves G1 is P1, and the pitch between adjacent shallow grooves G2 is P2. A relationship P2<P1 holds. That is, the surface roughness of the impact area IA is made smaller (smoothened) at least in the direction d3 as compared to the surface roughness in the areas TA and HA other than the impact area IA. The reason for this is as follows.
The golf club head 10 according to this embodiment is assumed to be a golf club head having a loft angle of 20° or less. The larger the surface roughness of the face portion 11 is, the smaller the back spin amount tends to be, and the longer the carry of a shot tends to be. On the other hand, in a case in which the surface roughness of the face portion 11 is uniform, if a hit exists outside the impact area IA, the carry tends to deteriorate as compared to a case in which a hit exists in the impact area IA. With the relationship P2<P1, the back spin amount is made relatively large if a hit exists in the impact area IA, or the back spin amount is made relatively small if a hit exists outside the impact area IA. This can decrease the difference in the carry caused by the difference in a hit and implement more stable distance performance.
The surface roughness of the areas TA and HA other than the impact area IA will be described next. In this embodiment, the surface roughness of the areas TA and HA other than the impact area IA is set in accordance with the moment of inertia of the golf club head 10. More specifically, the larger the moment of inertia of the golf club head 10 is, the larger (rougher) the surface roughness of the areas TA and HA is set to be. The smaller the moment of inertia is, the smaller (smoother) the surface roughness of the areas TA and HA is set to be. The reason for this is as follows.
In a case in which the moment of inertia of the golf club head 10 is relatively large, if a ball strikes outside the impact area IA, a so-called gear effect becomes relatively weak. Not much of spin is given to a shot, and little bending of the trajectory of the shot to the left or right occurs. In other words, the design intent for making the moment of inertia relatively large includes emphasizing distance performance while suppressing bending of the shot to the left or right. Hence, the larger the moment of inertia of the golf club head 10 is, the larger the surface roughness of the areas TA and HA is set. This can decrease the difference in the carry caused by the difference in a hit and implement more stable distance performance.
On the other hand, in a case in which the moment of inertia of the golf club head 10 is relatively small, if a ball strikes outside the impact area IA, a so-called gear effect becomes relatively strong. The spin amount is easily given to a shot, and bending of the shot to the left or right readily occurs. In other words, the design intent for making the moment of inertia relatively small includes allowing a golfer to easily bend a shot to the left or right, that is, emphasizing shot control performance. Hence, the smaller the moment of inertia of the golf club head 10 is, the smaller the surface roughness of the areas TA and HA is set. This can increase the spin amount of a shot and implement improvement of shot control performance.
In this way, according to this embodiment, it is possible to provide a wood type golf club head including a face portion with a surface roughness suitable for the specification (in particular, the moment of inertia) of the golf club head.
FIG. 4A shows an example of a method of manufacturing the golf club head 10, and particularly, steps concerning adjustment of the surface roughness of the areas TA and HA. In step S1, the moment of inertia of the golf club head 10 is referred to. The moment of inertia of the golf club head 10 can be a design value or a measured value. The measured value may be the measured value of the moment of inertia of the golf club head 10 before the shallow grooves G are formed.
In step S2, the surface roughness of the face portion 11 is set. Details will be described later. In step S3, the face portion 11 is formed based on the set surface roughness. Details will be described later.
Setting of the surface roughness of the face portion 11 in step S2 will be described. First, the surface roughness of the areas TA and HA other than the impact area IA is set. As already described, the surface roughness of the areas TA and HA other than the impact area IA is set in accordance with the moment of inertia of the golf club head 10. As an example, the correlation between the moment of inertia and the surface roughness of the areas TA and HA is decided in advance by experiments and the like and saved as data, as shown in FIG. 4B.
In the example of FIG. 4B, the moment of inertia and the surface roughness of the areas TA and HA have a linear relationship. The larger the moment of inertia is, the larger the surface roughness is. The smaller the moment of inertia is, the smaller the surface roughness is.
As another example of the correlation, in the example shown in FIG. 4C (a line C1 or a line C2), the moment of inertia and the surface roughness of the areas TA and HA have a nonlinear relationship. In this case as well, the larger the moment of inertia is, the larger the surface roughness is. The smaller the moment of inertia is, the smaller the surface roughness is. When the line C1 is compared with the line C2, the line C1 exhibits a characteristic that increases the surface roughness as a whole.
As still another example of the correlation, in the example shown in FIG. 4D, the surface roughness is set for each range of the moment of inertia. The contents of the example shown in FIG. 4D are as follows.
moment of inertia: smaller than m1, surface roughness: R1
moment of inertia: from m1 (inclusive) to m2 (exclusive), surface roughness: R2
moment of inertia: from m2 (inclusive) to m3 (exclusive), surface roughness: R3
moment of inertia: m3 or more, surface roughness: R4
In this example as well, the larger the moment of inertia is, the larger the surface roughness is, and the smaller the moment of inertia is, the smaller the surface roughness is.
As yet another example of the correlation, in the example shown in FIG. 4E, the range of the surface roughness is set for each range of the moment of inertia. The designer sets the surface roughness within the range of the surface roughness corresponding to a moment of inertia. The contents of the example shown in FIG. 4E are as follows.
moment of inertia: smaller than m1, surface roughness: smaller than R1
moment of inertia: from m1 (inclusive) to m2 (exclusive), surface roughness: from R1 (inclusive) to R2 (exclusive)
moment of inertia: from m2 (inclusive) to m3 (exclusive), surface roughness: from R2 (inclusive) to R3 (exclusive)
moment of inertia: m3 or more, surface roughness: from R3 (inclusive) to R4 (exclusive)
In this example as well, the larger the moment of inertia is, the larger the surface roughness is, and the smaller the moment of inertia is, the smaller the surface roughness is.
The surface roughness of the areas TA and HA can be set within the range of, for example, 2.0 μm (inclusive) to 8.0 μm (inclusive) as an arithmetic mean roughness Ra. In addition, the surface roughness of the areas TA and HA can be set within the range of 2.0 μm (inclusive) to 6.0 μm (inclusive) at minimum or within the range of 4.0 μm (inclusive) to 8.0 μm (inclusive) at maximum. The moment of inertia of the golf club head 10 can fall within the range of 2000 g·cm²(inclusive) to 6000 g·cm²(inclusive). The arithmetic mean roughness Ra can be the arithmetic mean roughness Ra when the average line is set in the direction d3.
The surface roughness of the areas TA and HA is thus set on design. In this embodiment, the areas TA and HA have the same surface roughness but may have different surface roughnesses.
Setting of the surface roughness of the impact area IA will be described next. The surface roughness of the impact area IA can be set within the range of, for example, 1.0 μm (inclusive) to 4.0 μm (inclusive) as the arithmetic mean roughness Ra. When the surface roughness of the impact area IA is made smaller than the surface roughness of the areas TA and HA, the difference in the carry caused by the difference in a hit can be made small, and more stable distance performance can be implemented.
The surface roughness of the face portion 11 is thus set. In this embodiment, the surface roughness of the face portion 11 is controlled by the shallow grooves G. Hence, the specifications of the shallow grooves G to implement the set surface roughness are decided, and the process advances to step S3.
In step S3, the shallow grooves G are formed in the face portion 11. As the method of forming the shallow grooves G, machining, laser machining, chemical milling, etching, and press working are usable. Laser machining is preferably used. As a procedure of processing, for example, the golf club head 10 formed as a hollow member is fixed in a numerically controlled processing apparatus, thereby forming the shallow grooves G in the face portion 11. FIG. 5A shows an example. In the example of FIG. 5A, the golf club head 10 is fixed in a processing apparatus via a jig (not shown). A laser light irradiation device 100 is arranged facing the face portion 11. The irradiation device 100 moves while irradiating the face portion 11 with laser light, thereby forming the shallow grooves G.
As another procedure of processing, when assembling the golf club head 10 by joining a plurality of parts, a flat face member is fixed in a numerically controlled processing apparatus, and the shallow grooves G are formed. When formation of the shallow grooves G is completed, the face member is bent to form a bulge and a roll. After that, the face member is joined to the opening of the main body member. In this procedure, since the face member is flat in the step of forming the shallow grooves G, the shallow grooves G can be formed more accurately.
In this embodiment, the surface roughness of the face portion 11 is controlled by the shallow grooves G. However, the shallow grooves G need not always be used. For example, the surface roughness of the face portion 11 may be adjusted by a process such as sand blast or shot peening.

Second Embodiment

Score lines can be formed in a face portion 11 in addition to shallow grooves G. FIG. 5B shows an example. In the example of FIG. 5B, score lines 20 are formed in areas TA and HA other than an impact area IA. The score lines 20 are straight grooves extending in the toe-heel direction and are formed in parallel to each other.
The score lines 20 may be formed in the impact area IA as well. A structure without the score lines 20 in the areas TA and HA other than the impact area IA can also be employed.

Third Embodiment

In the first embodiment, the shallow grooves G have been explained as straight grooves. However, shallow grooves G may be grooves having another shape. FIGS. 6A to 6D show examples. FIGS. 6A and 6B show examples of the shallow grooves G having wavy shapes. FIG. 6A shows a case in which the shallow grooves G are formed into a triangular wave shape, and FIG. 6B shows a case in which the shallow grooves G are formed into a sine wave shape. FIG. 6C shows an example in which the shallow grooves G are grooves having an arc shape. FIG. 6D shows an example in which shallow grooves Ga having a triangular wave shape and shallow grooves Gb having a sine wave shape are repetitively formed. As in this example, the shallow grooves G may be formed by periodically forming grooves having different shapes.
In the first embodiment, the shallow grooves G are formed so as to be level when the golf club head 10 is grounded toward the target direction. However, the shallow grooves G need not be level. FIG. 6E shows an example. FIG. 6E shows the shape of each shallow groove G when the golf club head 10 is grounded toward the target direction. The shallow grooves G tilt from a level state.

Fourth Embodiment

In the first embodiment, the surface roughness of the areas TA and HA other than the impact area IA is set in accordance with the moment of inertia of the golf club head 10. However, the surface roughness may be set in accordance with the bulge of a face portion 11. FIG. 7A is an explanatory view of a bulge, which is the radius of curvature of the curved surface (see an arrow) of the face portion 11 in a direction d2.
In this embodiment, the larger (flatter) the bulge of the face portion 11 of a golf club head 10 is, the larger the surface roughness of areas TA and HA is set. The smaller (rounder) the bulge of the face portion 11 is, the smaller the surface roughness of the areas TA and HA is set. The reason for this is as follows.
In general, in a case in which the bulge of the face portion 11 of the golf club head 10 is relatively large, if a ball strikes outside an impact area IA, the launch angle to the left or right becomes relatively small. In other words, the design intent for making the bulge relatively large includes emphasizing distance performance while suppressing bending of the shot to the left or right. Hence, the larger the bulge of the face portion 11 is relatively, the larger the surface roughness of the areas TA and HA is set. This can decrease the spin amount of a shot and make it such that the shot tends not to bend to the left or right.
Conversely, in a case in which the bulge of the face portion 11 of the golf club head 10 is relatively small, if a ball strikes outside the impact area IA, the launch angle to the left or right becomes relatively large. For this reason, it is preferable to easily give a spin amount to a shot and return the shot in the target direction by spin. In other words, the design intent for making the bulge relatively small includes allowing a golfer to intentionally bend a shot to the left or right, that is, emphasizing shot control performance. Hence, the smaller the bulge of the face portion 11 is relatively, the smaller the surface roughness of the areas TA and HA is set. This can increase the spin amount of a shot and make it easy to return the shot in the target direction.
In this way, according to this embodiment, it is possible to provide a wood type golf club head including a face portion with a surface roughness suitable for the specification (in particular, the bulge) of the golf club head.
In this embodiment, as for setting of the surface roughness of the areas TA and HA in step S2, the correlation between the bulge and the surface roughness of the areas TA and HA is decided in advance by experiments and the like and saved as data, as in the first embodiment. FIG. 7B shows an example. The bulge and the surface roughness of the areas TA and HA have a linear relationship. The larger the bulge is, the larger the surface roughness is. The smaller the bulge is, the smaller the surface roughness is. In addition to the example of FIG. 7B, the examples shown in FIGS. 4C to 4E are also applicable.
Note that the bulge of the face portion 11 may fall within the range of 200 mm (inclusive) to 600 mm (inclusive), and the surface roughness of the areas TA and HA may fall within the range of 2.0 μm (inclusive) to 8.0 μm (inclusive) as an arithmetic mean roughness Ra.

Fifth Embodiment

The methods of setting the surface roughness of the areas TA and HA according to the first and fourth embodiments are applicable to design a plurality of golf club heads.
For example, when designing a driver and a fairway wood, the head of the driver relatively has a large moment of inertia, and the head of the fairway wood relatively has a small moment of inertia. Hence, the surface roughness of areas TA and HA in each golf club head can be set such that the surface roughness of the areas TA and HA in the head of the driver becomes larger than in the head of the fairway wood, and conversely, the surface roughness of the areas TA and HA in the head of the fairway wood becomes smaller than in the head of the driver.
As another example, when designing a plurality of types of drivers, for example, the head of a driver for skilled players may relatively have a small moment of inertia, and the head of a driver for beginners may relatively have a large moment of inertia. Hence, the surface roughness of areas TA and HA in each golf club head can be set such that the surface roughness of the areas TA and HA in the head of the driver for beginners becomes larger than in the head of the driver for skilled players, and conversely, the surface roughness of the areas TA and HA in the head of the driver for skilled players becomes smaller than in the head of the driver for beginners.
Similarly, if the bulge changes between a plurality of types of drivers, the surface roughness of areas TA and HA in each golf club head can be set such that the surface roughness of the areas TA and HA in the head of the driver having a relatively large bulge becomes larger than in the head of the driver having a relatively small bulge, and conversely, the surface roughness of the areas TA and HA in the head of the driver having a relatively small bulge becomes smaller than in the head having a relatively large bulge.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2015-112389, filed Jun. 2, 2015 which is hereby incorporated by reference herein in its entirety.

Claims

What is claimed is:

1. A method of manufacturing a wood type golf club head including a face portion, a crown portion, and a sole portion, comprising:

a setting step of setting a surface roughness of the face portion; and

a step of forming the face portion based on the surface roughness set in the setting step,

wherein in the setting step, the larger a moment of inertia of the golf club head is, the larger the surface roughness outside an impact area of the face portion is set, and the smaller the moment of inertia is, the smaller the surface roughness outside the impact area of the face portion is set.

2. A method of manufacturing a wood type golf club head including a face portion, a crown portion, and a sole portion, comprising:

a setting step of setting a surface roughness of the face portion; and

wherein in the setting step, the larger a bulge is, the larger the surface roughness outside an impact area of the face portion is set, and the smaller the bulge is, the smaller the surface roughness outside the impact area of the face portion is set.

3. The method according to claim 1, wherein in the setting step, the surface roughness of the impact area of the face portion is made smaller than the surface roughness outside the impact area of the face portion.

4. The method according to claim 2, wherein in the setting step, the surface roughness of the impact area of the face portion is made smaller than the surface roughness outside the impact area of the face portion.

5. The method according to claim 1, wherein in the setting step, the surface roughness of the impact area of the face portion is set within a range of 1.0 μm (inclusive) to 4.0 μm (inclusive) as an arithmetic mean roughness.

6. The method according to claim 2, wherein in the setting step, the surface roughness of the impact area of the face portion is set within a range of 1.0 μm (inclusive) to 4.0 μm (inclusive) as an arithmetic mean roughness.

7. The method according to claim 1, wherein the moment of inertia falls within a range of 2000 g·cm²(inclusive) to 6000 g·cm²(inclusive), and

the surface roughness outside the impact area falls within a range of 2.0 μm (inclusive) to 8.0 μm (inclusive) as an arithmetic mean roughness.

8. The method according to claim 2, wherein the bulge falls within a range of 200 mm (inclusive) to 600 mm (inclusive), and

9. A wood type golf club head including a face portion, a crown portion, and a sole portion, wherein

the larger a moment of inertia of the golf club head is, the larger a surface roughness outside an impact area of the face portion is set, and the smaller the moment of inertia of the golf club head is, the smaller the surface roughness outside the impact area of the face portion is set.

10. A wood type golf club head including a face portion, a crown portion, and a sole portion, wherein

the larger a bulge of the face portion is, the larger a surface roughness outside an impact area of the face portion is set, and the smaller the bulge of the face portion is, the smaller the surface roughness outside the impact area of the face portion is set.