Abstract:
A golf club head includes two metal parts which are connected each other by welding their opposite surfaces. A method of making the golf club head constitutes: making the two metal parts, wherein at least one of them is provided with a small protrusion along the surface to be welded; and laser welding the opposite surfaces by applying a laser beam to at least the protrusion so that the molten material of the protrusion penetrates into a gap between the opposite surfaces to connect the two metal parts.

Description:
This nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No(s). 2002-264460 filed in JAPAN on Sep. 10, 2002, which is(are) herein incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a method of making a golf club head, more particularly to a method of welding metal parts of a club head. 
     In the golf club heads made up of two or more metal parts such as metal wood-type head and iron-type head, such metal parts are usually connected with each other by one side welding of butt joint, and in recent years, the use of laser welding instead of the widely employed tungsten inert gas (TIG) welding has been suggested or proposed in the Japanese patent No.2600529 and laid-open Japanese patent application JP-A-2001-293115. 
     On the other hand, in case of metal wood-type club heads for example, the golfers have a tendency to prefer the recent large-sized heads. Thus, the wall thickness in the welded place of such a large-sized head also has a tendency to decrease. Further, to achieve the desired performance (strength, weight and the like), the use of different metal materials is preferred. Therefore, if such metal parts are, as shown in  FIG. 13(   a ), temporally butt jointed and a laser beam is applied to the joint part, a joint dent (g) is very liable to occur as shown in  FIG. 13(   b ). As the wall thickness is relatively small, the joint dent (g) greatly decrease the joint strength. Further, as the wall thickness is small, if the laser beam is penetrate through the joint part, there is a possibility that the molten material trickles down towards the backside hollow, causing the shortage of the filling material. Thus, the possibility of occurrence of pinholes is also high. 
     SUMMARY OF THE INVENTION 
     It is therefore, an object of the present invention to provide a method of making a golf club head by which the joint dent can be effectively prevented to reduce poor weld and improve the joint strength as well as the appearance around the joint part, and thereby the productivity can be greatly increased. 
     According to one aspect of the present invention, a method of making a golf club head which head comprises two metal parts connected each other by welding their opposite surfaces comprises 
     making the two metal parts, wherein at least one of the two metal parts is provided with a small protrusion along the surface to be welded, and 
     laser welding the opposite surfaces by applying a laser beam to at least the protrusion so that the molten material of the protrusion penetrates into a gap between the opposite surfaces to connect the two metal parts each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a wood-type golf club head according to the present invention. 
         FIG. 2  is an exploded perspective view showing a two-piece structure for the wood-type golf club head. 
         FIGS. 3 ,  4 ,  5  and  6  are cross sectional views each showing a structure of a welding part of the club head according to the present invention. 
         FIG. 7  is an exploded sectional view of another example of the two-piece structure for the wood-type golf club head. 
         FIG. 8  is an enlarged sectional view showing a modification of the welding part shown in  FIG. 7 . 
         FIG. 9  is an exploded sectional view of showing a three-piece structure for the wood-type golf club head. 
         FIGS. 10 and 11  are cross sectional views each showing an iron-type golf club head according to the present invention, taken along a vertical plane passing the center of the club face. 
         FIGS. 12(   a ),  12 ( b ) and  12 ( c ) are enlarged sectional views to explain the laser welding according to the present invention. 
         FIGS. 13(   a ) and  13 ( b ) are enlarged cross sectional views for explaining the problem arising when one side laser welding of butt joint is applied between thin metal parts. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will now be described in detail in conjunction with the accompanying drawings. 
     Wood-type Head 
       FIG. 1  shows a metal wood-type hollow golf club head  1  according to the present invention, which comprises a face portion  2  having a front face defining a club face F for hitting a ball, a crown portion  3  intersecting the club face F at the upper edge Ea thereof, a sole portion  4  intersecting the club face F at the lower edge Eb thereof, a side portion  5  between the crow portion  3  and sole portion  4  extending from the toe side edge Ec to the heel side edge Ed of the club face F, and a neck portion  6  with a cylindrical bore for receiving a golf club shaft (not shown). 
     The wood-type club head  1  is formed by laser welding two or more metal parts P (P 1 , P 2  - - - ) together. 
     As to the materials of the metal parts P, various metallic material may be employed such as titanium alloys, pure titanium, stainless steel, aluminum alloys, SC steel, maraging steel, magnesium alloys, copper alloys and titanium-zirconium alloys since the laser welding method is employed, it does not matter whether the welded metal parts P are the same or different in the material or alloy&#39;s major component. 
     Two-piece Structure  1   
       FIG. 2  shows an example of two piece structure for the head  1 , which comprises a first metal part P 1  for forming an open-front head main  1   a  including the crown portion  3 , sole portion  4 , side portion  5  and neck portion  6 , and a second metal part P 2  which is a face plate  1   b  for forming the almost entirety of the face portion  2 . The face plate  1   b  is attached to the front of the head main  1   a  so as to close a front opening O thereof. 
     The head main  1   a  is, as shown in  FIG. 2 , provided along the internal circumference of the opening o with one continuous protrusion or a plurality of discontinuous protrusions  9  for the purpose of supporting as well as positioning the backside of the face plate  1   b.    
     The face plate  1   b  is shaped to accommodate the opening O to fit in snug or loose therewith when the face plate  1   b  is put in the opening o, and as shown in  FIG. 3 , the gap D between the opposite surface  10  and  11  of the two metal parts P to be welded is preferably set in a range of from 0.1 to 0.5 mm, more preferably from 0.1 to 0.3 mm. 
     According to the present invention, along one of or each of the opposite surface  10  and  11  to be welded, a small protrusion  7  which functions as a filler rod is continuously formed.  FIGS. 2 ,  3 ,  4  and  5  show examples in which a protrusion  7  is formed along only one of the opposite surface  10  and  11 .  FIG. 6  shows an example in which a protrusion  7  is formed along each of the opposite surface  10  and  11 . In these example, the protrusion  7  protrudes from the outer surface  12  more specifically front surface F of the head  1 , while tapering through to the extreme end. 
     The protrusion  7  has a surface  7   a  as an extension of the surface  10 / 11  beyond the outer surface  12 , and a surface  7   b  inclined towards the surface  7   a  while extending from the outer surface  12  towards the end of the surface  7   a . In the drawings, the surface  7   a  is depicted as straight and aligned with the surface  10 / 11  in the cross section perpendicular to the surface  10 / 11  and also to the longitudinal (circumferential) direction of the surface  10 / 11 . However, as far as the insertion of the face plate  1   b  to the opening O is not hindered, the surface  7   a  may be slightly curved and/or inclined on the other hand, as the inclined surface  7   b  will not hinder the insertion, it may be straight (as depicted in the drawings) or bent or concave or convex. Therefore, various shapes, e.g. a triangle such as right triangle, quadrant, trapezoid and the like may be employed as the cross sectional shape of each protrusion  7 . In the example shown in  FIGS. 2 and 3 , a protrusion  7  having a substantially triangular cross sectional shape is formed annularly along the circumferential surface  10  of the opening o and integrally with the head main  1   a  by casting. 
     In the example shown in  FIG. 4 , a protrusion  7  which is provided with a trapezoidal cross sectional shape having a straight side (the surface  7   a ), an inclined side (the surface  7   b ) and an additional side  7   c  (surface perpendicular to  7   a ) is formed in the same way as in the former example. 
     In contrast to the former to examples, in the example shown in  FIG. 5 , a triangular protrusion  7  is formed on the second metal part P 2 , namely the face plate  1   b , annularly along the circumferential surface  11  of the face plate  1   b.    
     The example shown in  FIG. 6  is a combination of the head main  1   a  (metal part P 1 ) shown in  FIG. 3  and the face plate  1   b  (metal part P 2 ) shown in  FIG. 5 . 
     In the particular cases shown in  FIGS. 3 ,  4  and  6 , in order to facilitate the insertion of the face plate  1   b  to the opening, the surface  7   a  as an extension of the surface  10  of the opening may be inclined toward the outside so that such surface functions as a guide slope. 
     Two-piece Structure  2   
       FIG. 7  shows another example of the two-piece structure for the wood-type club head  1 , which comprises a first metal part P 1  for forming an open-top head main  1   c  including the face portion  2 , sole portion  4 , side portion  5  and neck portion  6 , and a second metal part P 2  which is a crown plate  1   d  for forming the almost entirety of the crown portion  3 . The crown plate  1   d  is attached to the top of the head main  1   c  so as to close a top opening O thereof. Thus, the crown plate  1   d  is shaped to accommodate the opening O to fit in snug or loose therewith when the crown plate  1   d  is put in the opening O. In this example, a protrusion  7  is provided on the head main  1   c  only. The protrusion  7  is formed annularly along the circumferential surface  10  of the opening O and integrally with the head main  1   c  by casting. Further, similar to the former example, one or more protrusions  9  are formed along the opening O. The crown plate  1   d  is on the other hand, formed by press molding to provide a specific curvature. However, it may be also possible to employ another method such as casting. 
       FIG. 8  shows a modification of the structure shown in  FIG. 8 , wherein a protrusion  7  is provided on the crown plate  1   d  instead of the head main  1   c . In this case, it is preferred that the crown plate  1   d  is formed by press molding to provide its specific curvature and to form the protrusion  7  at the same time. In this type of two-piece structure too, a protrusion  7  may be provided on each of the parts P 1  and P 2 . 
     Three-piece Structure 
       FIG. 9  shows a three-piece structure for the wood-type club head  1 , which comprises a first metal part P 1  for forming an open-top-and-front head main  1   e  including the sole portion  4 , side portion  5  and neck portion  6 , a second metal part P 2  which is the above-mentioned face plate  1   b  for forming the almost entirety of the face portion  2 , and a third metal part P 3  which is the above-mentioned crown plate  1   d  for forming the almost entirety of the crown portion  3 . In this illustrated example, the protrusions  7  are formed along the two openings of the head main  1   e  as explained in the former examples. 
     Iron-type Club Head 
       FIGS. 10 and 11  show iron-type club heads  20  according to the present invention, wherein each head  20  comprises a head main  20   a  as one metal part P 1  and a face plate  20   b  as one metal part p 2 . 
     In the example shown in  FIG. 10 , the head main  20   a  is provided with an opening or hole penetrating therethrough from the front to the back of the head, and the face plate  20   b  is put in the opening to contact with the above-explained continuous protrusion  9  for the purpose of supporting and positioning the backside of the face plate  20   b . The protrusion  7  is provided on the head main  20   a  only in the same way as in the example shown in  FIGS. 2 and 3 . 
     In the example shown in  FIG. 11 , the head main  20   a  is provided with an opening or hole penetrating therethrough from the front to the back of the head, and the face plate  20   b  is shaped to accommodate the shape of the front of the head main and disposed directly thereon. The protrusion  7  is provided on the face plate  20   b  annularly along the circumference thereof. In this example, in order to form a gap D, the outer circumferential edge of the font surface of the head main  20   a  is provided with a chamfer  16  formed by a double slope merging into a flat face contacting with the back face of the face plate  20   b.    
     In these two examples, due to the through hole, a significant portion of the backside of the face plate  20   b  is exposed. 
     Making Method 
     As described above, the metal parts P (P 1 , P 2 , P 3  - - - ) are formed by appropriate methods, e.g. lost wax precision casting (head main  1   a ,  1   c ,  1   e ,  20   a ), press molding (face plate  1   b , crown plate  1   d ), forging and the like, depending on the material, position, size, shape and the like of the part. In case of the face plate  1   b ,  20   b , however, plastic forming such as cold forging and cold press working is preferably used because it is easy to control the crystallographic structure of the metal material in comparison with casting. In the foregoing examples, therefore, the face plate is formed by press molding to give a specific face bulge and roll. 
     According to the present invention, utilizing the above-mentioned protrusion  7 , the opposite surfaces  10  and  11  of the metal parts P (P 1 , P 2 , P 3  . . . ) are laser welded. 
     Next, taking the structure shown in  FIGS. 2 and 3  as an example, the laser welding according to the present invention will now be explained. 
     First, the metal parts P 1  and P 2  are temporarily fixed to each other, utilizing a holder or a self-retention force or another appropriate method. Then, as shown in  FIG. 12(   a ), using a laser beam machine (f), high-power laser beam such as CO 2  laser or YAG laser is applied to the protrusion  7  and the vicinity of the gap D to melt the metal materials near the surfaces  10  and  11 . The molten metal materials  15  flow into the gap D as shown in  FIG. 12(   b ) and are fused to connect these two parts P 1  and P 2 . After the welding is completed, as shown in  FIG. 12(   c ), the weld bead  14  or swelling part on the head outer surface  12  formed along the welded place  13  by the overflow is removed by grinding or the like and further the surface is polished. 
     If the volume of the protrusion  7  is too small, a dent along the welded place  13  is formed. If the volume is too large, the applied heat is dispersed and a higher power laser is required, and as a result, the crystallographic of the metal is liable to alter partially. Therefore, to achieve the most effective results in the welding process, as shown in  FIG. 3 , the height H of the protrusion  7  is preferably set in a range of from 0.3 to 1.0 times, more preferably 0.4 to 0.7 times a thickness (t) of one of the metal parts P 1  and P 2  which is not larger than the thickness of the other, when measured at the positions of the surfaces  10  and  11 , excluding the protrusion  7  by extending the adjacent outer surface  12  of the head along its course. Further, the maximum width W of the protrusion  7  which occurs at the outer surface  12  is preferably set in a range of from 0.5 to 2.0 times, more preferably 0.7 to 1.5 times the height H when measured in parallel with the outer surface  12 . 
     If the gap D is too narrow, it is difficult for the molten metal to penetrate into the gap, which results in a longer laser beam applying time. This is not desirable in view of prevention of the undesirable alternation in the metal structure. Further, as a high degree of precision is required, in view of the production efficiency, production cost and the like, the excessively narrow gap is not desirable. On the other hand, if the gap D is too wide, the molten metal is liable to trickle down and it becomes difficult to bridge the gap. Therefore, the gap D is preferably set in a range of from 0.1 to 0.5 mm, more preferably from 0.1 to 0.3 mm. 
     Additionally, if the thickness (t) is relatively large, to facilitate the reaching of the laser beam to a deeper point of the gap in the initial stage of the laser applying, and also to facilitate the reaching of the molten metal to the bottom of the gap, a chamfer  16  is preferably provided on the corner on the opposite side of the protrusion  7  as shown in  FIG. 5  by chain line for example. 
     In the foregoing examples, the protrusion  7  extends continuously through its overall length, but the protrusion  7  may be provided with discontinuity as far as the shortage of the molten metal is not caused thereby. 
     Comparison Test 
     Metal parts having the specification given in Table 1 were made and laser welded to produce 100 pieces of golf club heads. Then, the welded place was observed visually to check the occurrence of dent. The results are shown in Table 1. 
     From the test results, it was confirmed that in the golf club heads Ex.1–Ex.5 according to the present invention, the occurrence of dent was effectively reduced, when compared with golf club heads Ref.1–Ref.5. 
     
       
         
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Club head 
                 Ex. 1 
                 Ex. 2 
                 Ex. 3 
                 Ex. 4 
                 Ex. 5 
                 Ref. 1 
                 Ref. 2 
                 Ref. 3 
                 Ref. 4 
                 Ref. 5 
               
               
                   
               
             
             
               
                 Structure 
                 FIG. 2 
                 FIG. 9 
                 FIG. 7 
                 FIG. 10 
                 FIG. 11 
                 FIG. 2 
                 FIG. 9 
                 FIG. 7 
                 FIG. 10 
                 FIG. 11 
               
               
                 Head main 
                 crown + sole + 
                 sole + side + 
                 face + sole + 
                   
                   
                 crown + sole + 
                 sole + side + 
                 face + sole + 
               
               
                 (casting) 
                 side + neck 
                 neck 
                 side + neck 
                   
                   
                 side + neck 
                 neck 
                 side + neck 
               
               
                 Material 
                 titanium alloy 
                 titanium alloy 
                 stainless 
                 stainless 
                 stainless 
                 titanium alloy 
                 titanium alloy 
                 stainless 
                 stainless 
                 stainless 
               
               
                 Face plate 
                 press molding 
                 press molding 
                 — 
                 casting 
                 casting 
                 press molding 
                 press molding 
                 — 
                 casting 
                 casting 
               
               
                 Material 
                 titanium alloy 
                 titanium alloy 
                   
                 stainless 
                 stainless 
                 titanium alloy 
                 titanium alloy 
                   
                 stainless 
                 stainless 
               
               
                 Crown plate 
                 — 
                 press molding 
                 casting 
                 — 
                 — 
                 — 
                 press molding 
                 casting 
                 — 
                 — 
               
               
                 Material 
                   
                 titanium alloy 
                 stainless 
                   
                   
                   
                 titanium alloy 
                 stainless 
               
               
                 Thickness t 
                 2 
                 face 2.0 
                 0.6 
                 2 
                 2 
                 2 
                 face 2.0 
                 0.6 
                 2 
                 2 
               
               
                 (mm) 
                   
                 crown 0.8 
                   
                   
                   
                   
                 crown 0.8 
               
               
                 Protrusion 
               
               
                 Height H (mm) 
                 1.2 
                 face 1.2 
                 0.6 
                 1.2 
                 1.2 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                   
                   
                 crown 0.8 
               
               
                 Width W (mm) 
                 1 
                 1.0/1.0 
                 1 
                 1 
                 1 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 Rate of 
                 0.5 
                 0.5 
                 0.5 
                 0.5 
                 0.5 
                 65 
                 77.2 
                 23.4 
                 48.9 
                 51.6 
               
               
                 occurrence of 
               
               
                 dent (%)