Patent Publication Number: US-7584531-B2

Title: Method of manufacturing a golf club head with a variable thickness face

Description:
This is a division of application Ser. No. 11/194,958 filed Aug. 1, 2005, now U.S. Pat. No. 7,338,388. 

   BACKGROUND OF THE INVENTION 
   This invention relates generally to golf equipment and, in particular, to a golf club head with a variable thickness face and a method of manufacturing the same. 
   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. 
   The most critical region to reinforce the ideal ball impact point of the front wall. Because most golfers&#39; 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. In addition, removing portions of the club face using a cutter in an elliptical pattern may result in a face that is prone to fatigue cracks. 
   SUMMARY OF THE INVENTION 
   According to a first aspect of the present invention, a golf club head is manufactured by removing a portion of the inner 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 with a portion of the face plate being machined away to form the transition region and the thinner peripheral region. 
   The method for manufacturing a golf club face plate includes locating a ball end mill revolving about an axis generally normal to the inner surface of the face plate at an initial location on a first circumferential intersection between the outer edge of the central thickened region and the transition region. The inner surface of the face plate is machined by moving the revolving ball end mill in a radial direction outwardly toward and through the transition region and the peripheral region to machine the inner surface of the face plate creating a tool channel having a width as the ball end mill traverses the transition region and the peripheral region and thereby vary the thickness of the face insert in the tool channel. The ball end mill is then raised in a direction normal to the surface of the face plate and relocated to a subsequent location on the first circumferential intersection adjacent to the previous tool channel. The steps of machining, raising and relocating the ball end mill are repeated until the end mill has traversed the entire circumference of the circumferential intersection. In preferred embodiments, the machining step may vary the thickness of the transition region from the first thickness to a second thickness. The ball end mill may traverse the transition region along a variable path, which may be a straight line, a curved line, or any other suitable path. 
   According to another embodiment of present invention, a golf club head including a face plate arranged for impacting a golf ball may be formed. The face plate preferably varies in thickness and includes a central thickened region surrounded by a transition region tapering from the central thickened region to a thinner peripheral region, and a circumferential intersection between the central thickened region and the transition region. The inner surface of the face plate preferably includes a plurality of tool channels formed therein, the plurality of tool channels extending radially outward from the circumferential intersection to an outer edge of the peripheral region. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a partially cut-away front view of a golf club head having a machined face plate manufactured according to the present invention; 
       FIG. 2  is a rear cross-sectional view of the golf club head of  FIG. 1 ; 
       FIG. 3  is a cross-sectional view of the golf club head taken along lines  3 - 3  in  FIG. 2  showing the machined face plate; 
       FIG. 4  is a cross-sectional view of the golf club head of taken along line  4 - 4  in  FIG. 2  showing the machined face plate, and  FIG. 4A  is a cross-sectional view similar to  FIG. 4  showing a blank face plate prior to machining; 
       FIG. 5  is a another rear cross-sectional view of the golf club head of  FIG. 1 ; and 
       FIG. 6  illustrates the use of a milling machine in a preferred method of the present invention. 
   

   DESCRIPTION OF THE INVENTION 
   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. 
   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 a thickened region that is preferably elliptical and oriented so that the major axis of the reinforced region was substantially horizontal when the club head is held in its normal position for addressing the ball. Accordingly, face plate  22  includes a central thickened region  24  that is preferably 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 preferably 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 ). 
   With reference to  FIGS. 2-6 , prior to assembly of face plate  22  to shell  20 , the rear contours of the inner surface of face plate  20  are formed by a machining operation shown schematically in  FIG. 6 . The process begins with a blank face plate  32  shown in  FIG. 4A , 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 or inner surface  33  of blank face plate  32  is machined by using a ball end mill  34  to remove a portion thereof. A revolving ball end mill  34  is located normal to the rear surface  33  of the blank face plate  32  at an initial location on a first circumferential intersection  36  between the outer edge of the thickened region  24  and the transition region  28 . As can be seen from  FIG. 6 , as the lower cutting surface  38  of the ball end mill  34  is brought into contact with rear surface  33  of blank face plate  32 , the lower cutting surface  38  begins to cut into rear surface  33  of the blank face plate  32 . A tool channel  40  having a width equivalent to the width of the lower cutting surface  38  of the ball end mill  34  is machined into the inner rear surface  33  of the blank face plate  32  by moving the revolving ball end mill  34  in a radial direction outwardly toward and through the transition region  28  and the peripheral region  30 . As the ball end mill  34  traverses the transition region  28 , the lower cutting surface  38  is gradually moved closer to the rear surface  33  of the blank face plate  32  to thereby vary the thickness of the transition region  28  in the tool channel  40 . Preferably, upon reaching a second circumferential intersection  42 , located at the intersection of the transition region  28  and the peripheral region  30 , the ball end mill  34  does not increase its depth of penetration into the blank face plate  32 , thus forming the peripheral region  30  having a constant thickness. The ball end mill  34  may traverse the transition region  28  along various paths including a straight or curved path. Upon reaching the peripheral region  30 , the revolving ball end mill  34  is raised in a direction normal to the rear surface  33  of the face plate  32  and moved to a location on the outer edge of the thickened region  24  adjacent to the previous tool channel  40 . The process of machining a tool channel  40 , raising the ball end mill  34 , and relocating the revolving ball end mill  34  to a subsequent location on the elliptical outer edge of the thickened region  24  adjacent to the previous tool channel  40  is repeated until the entire face plate  22  is formed. The movement of the ball end mill  34  during formation of the face plate  22  may be computer controlled. In a preferred embodiment, the process of forming the face plate  22  results in about 95% of the surface area of the rear surface  33  of the blank face plate  32  being machined, with about 25% of the volume of the blank face plate  32  removed. 
   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. 
   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. 
   The use of a ball end mill to surface machine the inner surface of the face plate by creating tool channels in a radial direction improves the fatigue strength and promotes better face durability because the tool channels are perpendicular to the direction that a fatigue crack generally forms. 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.