Abstract:
A golf club is manufactured by machining away a portion of the rear surface of a club face blank to form an elliptical central thickened region that tapers through a transition region to a thinner peripheral region. The elliptical central thickened region, transition region and the portion of the peripheral region surrounding the raised portion are formed in a single elliptical pass with a special cutting tool. The cutting tool, or “form cutter” has a conical lateral cutting surface, which forms the sloped transition region and the peripheral region surrounding it in a single operation.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates generally to golf clubs and, in particular, to so-called metal wood drivers.  
         [0002]     Recent developments in golf club design have included improvements in drivers, which are clubs used primarily to strike a golf ball resting on a golf tee. These improvements have resulted in drivers with club heads consisting of a hollow shell usually made of metal, such as steel, aluminum, or titanium. These hollow shells have relatively thin walls including a thin front wall that is used to impact the golf ball. In order to prevent the front wall of these hollow shells from permanently deforming or cracking upon ball impact, it has become necessary to reinforce the front wall. One example of a golf club head consisting of a hollow metal shell with a reinforced front wall is disclosed in U.S. Pat. No. 4,511,145 to Schmidt. The club head disclosed in the Schmidt patent has an arched ridge extending between the heel and toe ends of the front wall. The arched ridge design of the Schmidt provides adequate reinforcement for drivers of moderate head volume, however, in an effort to obtain better and better performance from these hollow metal wood drivers, golf club manufacturers have increased the head volume from the moderate volume of 200 cc&#39;s to over 400 cc&#39;s during the past decade. As head size increases, less and less material is available to reinforce the front wall of the club face within acceptable weight limitations (i.e., around 200 grams mass). Consequently, more exotic materials such as forged or cold rolled titanium faces welded to a cast titanium body have been utilized in these super-oversized drivers. The rear surfaces of the front walls of these super-oversized drivers must be carefully contoured to provide adequate structural strength with a minimum amount of material.  
         [0003]     The most critical region to reinforce, is, of course, the ideal ball impact point of the front wall. Because most golfer&#39;s swings vary somewhat from impact to impact, the reinforced region of the front wall must be distributed around the ideal impact point. However, since variations in a golfer&#39;s swing tend to be more in the heel and toe direction, rather than up or down, the distribution of hits tends to be within a horizontal, elliptical region rather than a circular region centered around the center of the club face. Accordingly, an elliptical, rather than a purely circular reinforcement is preferable. One example of a golf club head having a face with a contoured rear surface is U.S. Pat. No. 6,354,962 to Galloway, et al. The club head disclosed in Galloway has a face plate reinforced with elliptical regions that are formed as part of the forging process of the face plate. For clubs in which the club face is machined from a wrought alloy sheet or other sheet material, forming an elliptical reinforced region presents special problems. The face cannot be machined properly on a lathe because the lathe will produce only a circular reinforced region. One manufacturer is known to use an end mill that makes multiple elliptical passes to machine the reinforced region of the golf club face. This operation is, however, time consuming and unnecessarily costly.  
       SUMMARY OF THE INVENTION  
       [0004]     According to the present invention, a golf club head is manufactured by removing a portion of the rear surface of a face plate to form a central thickened region surrounded by a transition region that tapers to a thinner peripheral region. According to the illustrative embodiment, the face plate is a rolled sheet titanium alloy between 0.130 and 0.180 inches thick, a portion of the transition region of which is machined away to leave the central thickened region and to form the transition region and the thinner peripheral region. Rather than forming the rear surface contour of the face plate by making multiple passes with an end mill, however, the central portion, the transition region and the peripheral region are formed in a single elliptical pass with a special cutting tool. The cutting tool, or “form cutter” has a conical lateral cutting surface, which forms the transition region and the peripheral region in a single operation. Use of this form cutter to machine the transition region and peripheral region in a single operation yields greater uniformity in the rear surface contour of the face plate and saves substantial time and money over prior art multiple pass machining operations. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0005]     The present invention will be better understood from a reading of the following detailed description, taken in conjunction with the accompanying drawing figures in which like references designate like elements, and in which:  
         [0006]      FIG. 1  is a partially cut-away rear perspective view of a golf club incorporating features of the present invention;  
         [0007]      FIG. 2  is a rear cross-sectional view of the golf club of  FIG. 1 ;  
         [0008]      FIG. 3  is a cross-sectional view of the golf club of  FIG. 2  taken along line  3 - 3 ;  
         [0009]      FIG. 4  is a cross-sectional view of the golf club of  FIG. 2  taken along line  4 - 4 ;  
         [0010]      FIG. 5  is a side view of a machining step in the method of forming golf club head in  FIG. 2 ;  
         [0011]      FIG. 6  is a side view of an alternative cutting tool used in the machining step of  FIG. 5 ; and  
         [0012]      FIG. 7  is a side view of another alternative cutting tool used in the machining step of  FIG. 5 . 
     
    
     DETAILED DESCRIPTION  
       [0013]     The drawing figures are intended to illustrate the general manner of construction and are not necessarily to scale. In the description and the in the drawing figures, specific illustrative examples are shown and herein described in detail. It should be understood, however, that the drawing figures and detailed description are not intended to limit the invention to the particular form disclosed but are merely illustrative and intended to teach one of ordinary skill how to make and/or use the invention claimed herein and for setting forth the best mode for carrying out the invention.  
         [0014]     Referring to  FIG. 1 , a golf club  10  includes a head  12 , a hosel  14  and a shaft  16 . Head  12  includes a hollow body  18  made of a metal material such as titanium. Hollow body  18  is formed as a shell  20 , which may be assembled from a series of forged pieces but, in the illustrative embodiment, comprises a titanium investment casting. A face plate  22  is attached by conventional means such as plasma or electron beam welding to a corresponding opening  23  ( FIG. 2 ) in shell  20  to form hollow body  18 . Face plate  22  may be a conventional forged blank but, in the illustrative embodiment, comprises a rolled sheet titanium blank that is machined prior to welding to shell  20  as described more fully hereinafter.  
         [0015]     As noted hereinbefore, because a golfer&#39;s swing tends to vary more in the heel-toe direction than it does up or down, the inventor of the present invention determined that the most efficient reinforcement would be an elliptical thickened region oriented so that the major axis of the reinforced region was substantially horizontal when the club is held in its normal position for addressing the ball. Accordingly, face plate  22  includes a central thickened region  24  that is substantially elliptical in shape with its major axis  26  oriented horizontal when the club is held in its normal address position. In the illustrative embodiment, central thickened region  24  is between 0.130 and 0.180 inches in thickness. Central thickened region  24  is surrounded by a transition region  28  that tapers from the central thickened region  24  to a peripheral region  30 , which in the illustrative embodiment is 0.080 to 0.120 inches thick. Transition region  28  is also elliptical, however, for reasons that are explained more fully hereinafter, the major axis and minor axis of transition region  28  are a fixed amount larger than the respective major and minor axis of central thickened region  24 . Accordingly, the aspect ratio of transition region  28  is lower than the aspect ratio of central thickened region  24  (in other words, transition region  28  is a “fatter” ellipse than central thickened region  24 ).  
         [0016]     With reference to  FIGS. 2-5 , prior to assembly of face plate  22  to shell  20 , the rear contours of face plate  20  are formed by a machining operation shown schematically in  FIG. 5 . The process begins with a blank face plate  32 , which in the illustrative embodiment comprises a blank stamped from a rolled sheet of titanium alloy. The blank face plate  32  has a thickness equal to the final thickness of the central thickened region  24  of the finished face plate  22 , which as noted hereinbefore is from 0.130 to 0.180 inches in thickness. The rear surface of blank face plate  32  is machined by using a cutting tool  34  to remove a portion thereof. The tip of cutting tool  34  has a lateral cutting surface  36  and a lower cutting surface  38 . Lower cutting surface  38  is perpendicular to the axis  40  of cutting tool  34 . Lateral cutting surface  36  is angled upward with respect to lower cutting surface  38  by an angle  42  of from about 5 to 20 degrees, but preferably about 13 degrees such that lateral cutting surface  36  defines a generally inverted conical frustum surface of revolution  44  as cutting tool  34  is rotated about its axis  40 . Lateral cutting surface  36  may have straight edges as shown in  FIG. 5 , or may have edges  36   b  that are concave downward as in the cutting tool  34   b  shown in  FIG. 6 , or may have edges  36   c  that are convex downward as in the cutting tool  34   c  shown in  FIG. 7 . yielding a conical frustum surface of revolution (and corresponding transition regions) having correspondingly curved sides.  
         [0017]     As can be seen from  FIG. 5 , as the lower cutting surface  38  and lateral cutting surface  36  are brought into contact with rear surface  46  of blank face plate  32 , lower cutting surface  38  and lateral cutting surface  36  cooperate to cut a tapered transition region  28  and a flat perimeter region  30  simultaneously in a single pass, thus obviating the need to make multiple passes with an end mill as in the prior art. With particular reference to  FIGS. 2-4 , the major axis  26  of central thickened region  24  is from 0.65 to 1.05 inches in length. The minor axis  48  of central thickened region  24  is 0.25 to 0.45 inches in length. Accordingly, the aspect ratio of central thickened region  24  is between 1.4 and 4.2. In the illustrative embodiment, major axis  26  is approximately 0.85 inches and minor axis  48  is approximately 0.35 inches yielding an aspect ratio of approximately 2.4.  
         [0018]     Major axis  50  and minor axis  52  of transition region  28  are a fixed amount “δ” greater than the respective major and minor axes of central thickened region  24 . In the illustrative example, the major axis  50  and minor axis  52  are approximately 0.86 inches greater than the respective major and minor axes of central thickened region  24 . Thus, major axis  50  in the illustrative embodiment is approximately 1.71 inches in length and minor axis  52  of transition region  28  is approximately 1.21 inches in length. Thus, the aspect ratio of transition region  28  is approximately 1.4 as opposed to the 2.4 aspect ratio of central thickened region  24 . The high aspect ratio central raised portion surrounded by the lower aspect ratio transition region provides optimum distribution of material for improved performance and reliability.  
         [0019]     Although certain illustrative embodiments and methods have been disclosed herein, it will be apparent from the foregoing disclosure to those skilled in the art that variations and modifications of such embodiments and methods may be made without departing from the spirit and scope of the invention. Accordingly, it is intended that the invention should be limited only to extent required by the appended claims and the rules and principals of applicable law.