Abstract:
A golf club head which includes a main body provided with a socket, and a weight member disposed in the socket, wherein the socket is a tubular portion extending to the inside of the main body and deforming a through-hole extending therethough, the weight member having a main portion accommodated by the through-hole, and secured in the through-hole by a crushable portion which, after being crushed by the application of pressure causes the socket to expand, locking the weight member in the socket.

Description:
This nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No(s). 2002-279541 filed in JAPAN on Sep. 25, 2002, which is(are) herein incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a golf club head, more particularly to the structure of a weight member and a socket therefor. 
     In golf club heads, a weight member separate from the main body of the club head is often used in order to obtain desired weight distributions to adjust, for example, the gravity point, the sweet spot, the moment of inertia and the like of the golf club head (for example). 
     In case the of metal wood-type hollow club heads, on the other hand, light-weight, strong metal materials such as titanium alloys have been widely used in recent years. The use of such materials can decrease the wall thickness of the golf club head. Therefore, if a large-sized, heavy weight member can be used in a club head whose wall thickness is relatively thin, then the design freedom will be remarkably increased. 
     In the laid-open Japanese patent application P2001-276287A, a method of securing a weight member to the main body of the golf club head is disclosed, wherein, as shown in  FIGS. 14(   a ) and  14 ( b ), a cylindrical weight member (c) is positioned in a cylindrical socket (e), with its smaller diameter end portion (c 2 ) protruding from the inner end (e 1 ) of the socket through a smaller diameter opening formed at the inner end (e 1 ) of the socket. The protruding portion (c 2 ) is pressed to deform, expanding over the surface of the inner end (e 1 ) of the socket. In order to facilitate such deformation, the end of the protruding portion (c 2 ) is provided with a hollow (c 3 ). 
     When the size of the weight member is increased, the pressing force necessary to deform it as indicated above increases at an accelerating pace. Therefore, in this method, near the base of the socket, as indicated by the circles in  FIG. 14(   b ), the wall (a) is subjected to a large stress due to the large compressive stress transferred by the socket as indicated by arrows, which results in unfavorable residual stress or strain or, in the worst case, cracks in the finished article. 
     SUMMARY OF THE INVENTION 
     It is therefore, an object of the present invention to provide a golf club head, in which, even if the size of the weight member is relatively large, the weight member is firmly and easily secured to the head main body of the golf club without the above-mentioned drawbacks, whereby the design freedom is greatly increased. 
     According to one aspect of the present invention, the golf club head comprises 
     a main body provided with a socket, and 
     a weight member disposed in the socket, wherein 
     the socket loc a tubular configuration extending towards the inside of the main body and having a through-hole extending therethough, 
     the weight member containing a main portion accommodated in the through-hole, said weight member being secured in the through-hole by crushing a crush portion, which is formed at the inner end of the main portion of the weight member within the region of the inner end, to protrude from the inner end of the socket, into the main portion so that the main portion expands, pressing on the surface of the through-hole. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional view of a wood-type golf club head according to the present invention taken along line A—A of  FIG. 2 . 
         FIG. 2  is a bottom view thereof. 
         FIG. 3  is an exploded perspective view of the golf club head showing an exemplary two-piece structure comprising a hollow main part and a platy part to which a weight member is attached. 
         FIG. 4  is an enlarged perspective view showing a weight member with a crush portion and a socket therefor. 
         FIGS. 5 and 6  are cross sectional views each showing another example of the crush portion. 
         FIGS. 7(   a ) and  7 ( b ) are cross sectional views of the weight member put in the socket showing the states before and after the crush portion is crushed. 
         FIGS. 8(   a ) and  8 ( b ) are plan views of the weight member for explaining various dimensions of the main portion and crush portion. 
         FIG. 9  is a cross sectional view showing another example of the weight member. 
         FIG. 10  is a cross sectional view showing another example of the weight member and socket therefor. 
         FIG. 11  is a cross sectional view showing still another example of the socket. 
         FIGS. 12 and 13  are cross sectional views each showing a weight member used in the undermentioned comparison test. 
         FIGS. 14(   a ) and  14 ( b ) show the prior art. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In  FIGS. 1 ,  2  and  3 , an embodiment of the present invention is a metal wood-type hollow golf club head  1  for a fairway wood. 
     The wood-type golf club head  1  comprises a face portion  2  whose front face defines a club face for striking a ball, a crown portion  3  intersecting the club face at the upper edge thereof, a sole portion  4  intersecting the club face at the lower edge thereof, a side portion  5  between the crown portion  3  and sole portion  4  which extends from a toe-side edge  2   t  to a heel-side edge  2   h  of the club face 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  provided on the top thereof with a shaft inserting hole  6   a  for accommodating a club shaft. 
     The hollow (i) of the head  1  is a void in this embodiment, but it is also possible to dispose therein a filler made of a resin, elastomer or the like in a form of a solid or a foam. 
     According to the present invention, the club head  1  comprises a main body and a weight member  1   b . In this embodiment, the club head  1  comprises a hollow main part  1   a   2  having an opening O, a platy part  1   a   1  welded thereto so as to close the opening O, and a weight member  1   b  attached to the platy part  1   a   1 , whereby the main body is made up of the hollow main part  1   a   2  and platy part  1   a   1 . 
       FIG. 3  shows an example of such a structure. In this example, in order to make the center of gravity of the head lower and deeper, the weight member  1   b  is disposed in the sole portion  4 . The opening O is formed in the bottom of the hollow main part  1   a   2 , and the platy part  1   a   1  is welded to the bottom of the main part  1   a   2 . The platy part  1   a   1  in this example forms almost the entirety of the sole portion  4  (thus hereinafter, the “sole plate”). The hollow main part  1   a   2 , accordingly forms the remaining portions, namely, the face portion  2 , crown portion  3 , side portion  5  and neck portion  6 . As shown in  FIG. 1 , at the weld J, two parts  1   a   1  and  1   a   2  are butt welded. 
     To make the main part  1   a   2  and platy part  1   a   1 , various metal materials such as titanium alloys, aluminum alloys, stainless steel, steel the like can be used. Further, it is also possible to use a fiber reinforced resin to form a part of the head  1 . In this embodiment, each of the hollow main part  1   a   2  and platy part  1   a   1  is made of a titanium alloy using a lost wax precision casting method. By the way, depending on the material, shape, and region of the part to be formed, another method, e.g. forging, press molding and the like may be also employed. 
     In order to secure the weight member  1   b , a socket  7  into which the weight member  1   b  fits is integrally formed on the platy part  1   a   1  (in this embodiment, on the sole portion  4  at a position biased towards the back end thereof). 
     The socket  7  is a tubular portion having a substantially constant wall thickness and protruding from the inner surface of the platy part  1   a   1  or the inner surface of the head to the hollow (i). The socket  7  has a through-hole  8  having an opening to the inside (i) of the head  1  and an opening to the outside of the head. 
       FIGS. 2 ,  3 ,  4  and  5  show an example of the socket  7 . In this example, the through-hole  8  has a generally rectangular cross sectional shape with rounded corners, and the cross sectional shape is substantially constant throughout the depthwise direction. Aside from such a rectangle, various shapes, e.g. a square with rounded corners, a circle, a oval, a triangle with rounded corners, and the like can be used. 
     On the other hand, the weight member  1   b  is made of a plastically deformable, relatively heavy material M. For example, tungsten, a tungsten alloy, copper, a copper alloy, brass, stainless steel and the like can be used. Usually, a metal material whose specific gravity is larger than the platy part  1   a   1  and main part  1   a   2  is used. Especially, a tungsten-nickel alloy is preferably used. The specific gravity is preferably in the range of from 8 to 20, more preferably about 12 to about 18. 
     The weight member  1   b  is provided at the inner end of its main portion  10  with a crushable portion  11 . 
     The main portion  10  has a cross sectional shape which is almost the same but slightly smaller than that of the through-hole  8  so as to snuggly fit in the through-hole  8 . For the socket  7  shown in  FIG. 4 , therefore, a rectangle with rounded corners is used as the cross section shape of the main portion  10 . 
     The depth H of the main portion  10  is the same as or slightly larger (but very small as compared with “h”) than the depth Ha of the through-hole  8 , namely, the depth H is substantially the same as the depth Ha. 
     The crushable portion  11  is a protrusion formed at the inner end  12  of the main portion  10  and tapering towards its end. Around the crushable portion  11 , a flat surface  14  remains while defining the inner end  12 . 
       FIG. 4  shows an example of the crushable portion  11 , which has a trapezoidal cross sectional shape in almost any cross section which is parallel with the depthwise direction (H) of the weight member  1   b  from the outer end  15  to the inner end  12 . Thus, in this example, the top surface  11   b  of the crushable portion  11  is substantially flat and parallel with the above-mentioned flat surface  14 . 
     Further, in any cross section which is perpendicular to the depthwise direction, the crushable portion  11  has a similar figure to the contour of the main portion  10  at the inner end  12  which figure becomes smaller from its basal plane at the end  12  to the top surface  11   b . Thus, in this particular case where the contour is a rectangle, the top surface  11   b  is also a rectangle, and the crushable portion  11  has four side faces  11   a  inclined towards the center of the weight member  1   b  at an angle of from 40 to 60 degrees with respect to the flat surface  14 . 
     Aside from the trapezoidal cross sectional shape where the top surface is flat, another shape where the top surface is slightly swelled may be used as well.  FIG. 5  shows an example of such a shape which is defined by a comparatively flat arc, e.g. a part of an ellipse, a part of a circle and the like. 
     Further, as shown in  FIG. 6 , a comparatively flat triangular shape such as isosceles triangle may be used when the central region is higher than the peripheral region ( 14 ). 
     When the cross sectional shape of the main portion  10  of the weight member  1   b  is a rectangle, an oval or the like, the crushable portion  11  may be formed to have such a cross sectional shape along a direction parallel to the long sides or major axis of the cross sectional shape of the main portion. 
     The weight member  1   b , as shown in  FIG. 7(   a ), is put into the socket  7  of the platy part (sole plate)  1   a   1 . The platy part  1   a   1  is put on a mold  17  to hold the platy part  1   a   1  while keeping the weight member  1   b  in its place such that the outer end or surface  15  of the main portion  10  aligns with the outer surface F of the platy part  1   a   1 . Then, as shown in  FIG. 7(   b ), using a press die P, the crushable portion  11  is crushed towards the main portion  10  as indicated by arrows. At this time, due to the opening of the through-hole  8  at the surface F, the mold  17  can support and press the outer end  15  in the counter direction. In this example, the entire volume is crushed into the main portion  10  so as to become flat with the inner end of the socket  7 . 
     As the weight member  1   b , crushed in the through-hole  8 , expands radially near the inner end  12 , the through-hole  8  is radially expanded, accordingly, such that the expansion becomes larger towards the end of the tubular portion, whereby the end of the tubular portion flares and the weight member  1   b  is tightly locked.
 
Then, the assembly of the platy part  1   a   1  and weight member  1   b  is welded to the main part  1   a   2  to form the head  1 .
 
     It is preferable that the expansion Wb−Wa at the inner end  12  is more than 0.3 mm, but not more than 0.6 mm. More definitely, when the dimension is measured, before the crushable portion  11  is crushed, across the contour shape of the inner end  12  of the weight member  1   b , passing the centroid Sg 1  of the contour shape in every direction around the centroid Sg 1 , the minimum Wa thereof shows a difference (Wb−Wa) of not less than 0.3 mm but not more than 0.6 mm from the dimension Wb measured in the same direction across the deformed contour shape after the crushable portion  11  is crushed. 
     To achieve the desired radial expansion, the protruding height h of the crushable portion  11  from the inner end  12  is set in the range of from 0.5 to 1.5 mm. If the height h is more than 1.5 mm, it becomes difficult to radially expand the main portion from a suitable deep position and as a result, the flared part becomes shorter which results a the reduced engage force, OR a fracture is liable to occur at the end of the socket because an extremely large crushing force is required. If the height h is less than 0.5 mm, it is difficult to obtain the desired sufficient engaging force. 
     On the other hand, if the above-mentioned flat surface  14  around the crushable portion  11  is too narrow in width, fracture is liable to occur at the end of the socket. If the width is too wide, it becomes difficult to obtain the necessary expansion. Therefore, it is preferable that the width of the flat surface  14  is not less than 0.8 mm, preferably not less than 1.5 mm, but not more than 2.5 mm, preferably not more than 2.0 mm. 
     Further, if the wall thickness of the socket  7  is too small, fracture is liable to occur at the end of the socket. If too large, it becomes difficult to obtain the appropriate flared portion. Although the desirable range somewhat varies depending on the material, it is preferable that the wall thickness of the socket  7  is set in a range of from about 1.5 to about 3.0 mm. 
     Given that average width W3 of the inner end  12  is the average of dimensions (W3a, W3b, W3c—) which are, as shown in  FIG. 8(   a ), measured across the shape of the inner end  12 , passing through the centroid Sg 1  of the shape, for every predetermined small angle (for example 10 degrees) around the centroid Sg 1 , the ratio (W3/h) of the average width W3 to the above-mentioned height h is preferably set in the range of from 7 to 20, more preferably 9 to 15. 
     Further, similarly to the width W3, when the average width W2 of the basal plane of the crushable portion  11  is defined as the average of dimensions (W2a, W2b, W2c—) which are, as shown in  FIG. 8(   b ), measured across the shape of the basal plane, passing through the centroid Sg 2  of the shape, for every predetermined small angle (for example 10 degrees) around the centroid Sg 2 , 
     the ratio (W2/W1) of the average width W2 to the average W1 of widths (W1a, W1b, W1c—) of the flat surface  14  is preferably set in the range of 5 to 9, more preferably 6 to 8. 
       FIG. 9  shows a modification of the above-mentioned weight member  1   b , wherein a crushable portion  11  is formed at the outer end  15  in addition to the inner end  12  so as to form a flared part on each side of the weight member  1   b . In this case, it is preferable that the through-hole  8  is provided at the outer end with a gradually expanded part  8   b  in advance. 
       FIG. 10  shows a further modification of the above-mentioned weight member  1   b , wherein to facilitate the positioning of the weight member, a flange  10   b  is provided at the outer end  15  of the main portion  10 . The through-hole  8  is accordingly, provided immediately inside the outer end with a stepped expanded part  8   b . The expanded part  8   b  is shaped to accommodate the flange  10   b  so as to make these surfaces flat. 
       FIG. 11  shows a modification of the above-mentioned through-hole  8 , wherein, in order to increase the engaging force between the weight member  1   b  and socket  7 , the inner surface of the through-hole  8  is provided with a continuously or discontinuously extending circumferential groove  8   g . The position of the circumferential groove  8   g  is set in the flaring part at a small distance from the end of the hole. 
     Instead of a discontinuous groove  8   g , it is also possible to provide a plurality of holes or dents arranged circumferentially at small intervals. 
     The depth of the groove, dent or hole is set in the range of 0.5 to 1.5 mm. 
     Comparison Tests 
     Several kinds of weight members were made, changing the crushable portion only as shown in Table 1. The main portion  10  has, as shown in  FIG. 4 , a 19.9×4.9 mm rectangular cross sectional shape with corners rounded in a radius R of 0.5 mm, and a depth H of 6 mm. The material of the weight member is a tungsten-nickel alloy having a specific gravity of 14.5. 
     Using these weight members in combination with the sole plate  1   a   1  shown in  FIG. 3 , the weight member is put in the socket and, by crushing the crushable portion as explained above, they are fixed to each other. The socket is formed on the sole plate  1   a   1  and as shown in  FIG. 4 , the through-hole had a depth Ha of 6 mm and a 20×5 mm rectangular cross sectional shape with rounded corners at a radius R of 0.5 mm for accommodating the main portion of the weight member. 
     50 pieces of such assembly are made with respect to each of the weight members. 
     The flared end portion of the socket is checked for fracture. The percentage of occurrence of fracture is shown in Table 1. The engaging force between the weight member and socket is measured as a force at which the weight member starts to move relatively to the socket when the inner end of the weight member is pushed towards the outer end. The measured force is indicated by an index based on Ex.1 being 100. The larger the index number, the larger the engaging force. 
     
       
         
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Weight member 
                 Ex. 1 
                 Ex. 2 
                 Ex. 3 
                 Ex. 4 
                 Ex. 5 
                 Ref. 1 
                 Ref. 2 
               
               
                 Crush portion 
                 FIG. 4 
                 FIG. 4 
                 FIG. 4 
                 FIG. 4 
                 FIG. 4 
                 FIG. 12 
                 FIG. 13 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 h (mm) 
                 0.5 
                 0.2 
                 1.5 
                 0.5 
                 0.5 
                 1.0 
                 1.0 
               
               
                 W3 (mm) 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
               
               
                 W3/h 
                 20 
                 50 
                 6.7 
                 20 
                 20 
                 10 
                 10 
               
               
                 W1 (mm) 
                 1.0 
                 1.0 
                 1.0 
                 0.5 
                 2.0 
                 10 
                 1.0 
               
               
                 W2 (mm) 
                 8.0 
                 8.0 
                 8.0 
                 9 
                 6.0 
                 10 
                 — 
               
               
                 W2/W1 
                 8.0 
                 8.0 
                 8.0 
                 18 
                 3.0 
                 1.0 
                 — 
               
               
                 Engaging force 
                 100 
                 53 
                 100 
                 73 
                 53 
                 33 
                 50 
               
               
                 Fracture (%) 
                 0.5 
                 0.5 
                 1.4 
                 1.3 
                 0.5 
                 1.5 
                 2 
               
               
                   
               
             
          
         
       
     
     As apparent from the test results, in comparison with Ref.1 and Ref.2, Ex.1–Ex.5 show a decrease in the occurrence of fracture and an increased in the engaging force. In addition, as the weight member can fit tightly to the socket by its radial expansion, the weight member was not required to have high accuracy. Therefore, the production efficiency may be greatly improved and also the production cost may be reduced. 
     In the above-mentioned embodiment, the weight member  1   b  is disposed in the sole portion  4 . But, the weight member  1   b  may be disposed in another portion such as the side portion  5  and crown portion  3 . 
     The present invention is suitably applied to a metal wood-type hollow golf club head as described above. But, it can be also applied to other types such as iron-type, patter-type and utility-type.