Abstract:
A method for chemically etching a forged striking plate for a golf club to uniformly remove 0.002 inch to 0.015 inch of material therefrom. The forged striking plate is placed in an acidic bath to uniformly remove material from all surfaces of the striking plate. The forging process, conducted prior to etching, involves multiple heating and pressing of a metal bar to obtain a final face member configuration. The heating of the metal bar is performed at temperatures below 1000° C. for less than twenty minutes. The final face member configuration has a striking plate with regions of variable thickness. The metal bar is preferably composed of a forged titanium material.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The present application is a continuation-in-part application of co-pending U.S. patent application Ser. No. 09/431,982, filed on Nov. 1, 1999, for A Golf Club Head With A Face Composed Of A Forged Material. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for processing a striking plate for a golf club head. More specifically, the present invention relates to a method for chemical etching a forged metal striking plate for a golf club head to achieve proper thickness uniformly. 
     2. Description of the Related Art 
     When a golf club head strikes a golf ball, large impacts are produced that load the club head face and the golf ball. Most of the energy is transferred from the head to the golf ball, however, some energy is lost as a result of the collision. The golf ball is typically composed of polymer cover materials (such as ionomers) surrounding a rubber-like core. These softer polymer materials having damping (loss) properties that are strain and strain rate dependent which are on the order of 10-100 times larger than the damping properties of a metallic club face. Thus, during impact most of the energy is lost as a result of the high stresses and deformations of the golf ball (0.001 to 0.20 inches), as opposed to the small deformations of the metallic club face (0.025 to 0.050 inches). A more efficient energy transfer from the club head to the golf ball could lead to greater flight distances of the golf ball. 
     The generally accepted approach has been to increase the stiffness of the club head face to reduce metal or club head deformations. However, this leads to greater deformations in the golf ball, and thus increases in the energy transfer problem. 
     Some have recognized the problem and disclosed possible solutions. An example is Lu, U.S. Pat. No. 5,499,814, for a Hollow Club Head With Deflecting Insert Face Plate, discloses a reinforcing element composed of a plastic or aluminum alloy that allows for minor deflecting of the face plate which has a thickness ranging from 0.01 to 0.30 inches for a variety of materials including stainless steel, titanium, KEVLAR®, and the like. Yet another Campau invention, U.S. Pat. No. 3,989,248, for a Golf Club Having Insert Capable Of Elastic Flexing, discloses a wood club composed of wood with a metal insert. 
     Although not intended for flexing of the face plate, Viste, U.S. Pat. No. 5,282,624 discloses a golf club head having a face plate composed of a forged stainless steel material and having a thickness of 3 mm. Anderson, U.S. Pat. No. 5,344,140, for a Golf Club Head And Method Of Forming Same, also discloses use of a forged material for the face plate. The face plate of Anderson may be composed of several forged materials including steel, copper and titanium. The forged plate has a uniform thickness of between 0.090 and 0.130 inches. 
     Another invention directed toward forged materials in a club head is Su et al., U.S. Pat. No. 5,776,011 for a Golf Club Head. Su discloses a club head composed of three pieces with each piece composed of a forged material. The main objective of Su is to produce a club head with greater loft angle accuracy and reduce structural weaknesses. 
     The typical forging process for metal golf club faces involves heating the metal bar at a temperature in excess of 1000° C. for longer than twenty minutes, pressing and then repeating the process. The forged face is then milled or ground to obtain the proper face thickness. Thus, all current golf club forged face plates undergo a post-forging milling or grinding step to achieve a proper thickness, and proper bulge and roll. However, this milling and grinding of forged face plate cannot achieve a uniform reduction in thickness. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides a method for chemically etching a forged face member for golf club head to achieve a relatively thin striking plate in a uniform manner. The thin striking plate allows for greater compliance of the striking plate with a golf ball during impact. A more compliant striking plate provides for lower energy loss and a higher coefficient of restitution. 
     One aspect of the present invention is a method for chemically etching a finished forged striking plate for a golf club head. The method includes forging a face member with a striking plate to a final configuration having predetermined thickness. Next, the forged face member with the striking plate is chemically etched in an acidic bath to uniformly remove 0.002 inch to 0.015 inch from the forged face member with the striking plate. Preferably, 0.003 inch each surface of the forged face member with the striking plate. 
     The forging process may include heating a metal bar to a temperature less than 1000° C. for less than 20 minutes, and then pressing the heated metal bar into an L-shape metal bar. Next, the L-shape metal bar is again heated to a temperature less than 1000° C. for less than 20 minutes, and then pressed into an intermediate shape face member. Next, the intermediate shape face member is coated with a glazing compound. Next, the coated intermediate shape face member is heated to a temperature less than 1000° C. for less than 20 minutes, and then pressed into a final face member configuration. 
     The method may also include additional heating and pressing at even lower temperatures and at a lowered pressure to finalize the bulge and roll of a striking plate of the final face member configuration. The preferred metal is titanium, and most preferably alpha-beta-titanium. The multiple heating and pressing provides a thin face with greater durability. 
    
    
     Having briefly described the present invention, the above and further objects, features and advantages thereof will be recognized by those skilled in the pertinent art from the following detailed description of the invention when taken in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a front view of a golf club produced according to the method of the present invention. 
     FIG. 1A is a front view of an alternative embodiment of a golf club produced according to the method of the present invention. 
     FIG. 2 is a top plan view of golf club head of FIG.  1 . 
     FIG. 2A is a top plan view of an alternative embodiment of a golf club produced according to the method of the present invention. 
     FIG. 3 is a top plan isolated view of the face member of a golf club head produced according to the method of the present invention with the crown in phantom lines. 
     FIG. 4 is a side plan view of a golf club head produced according to the method of the present invention. 
     FIG. 4A is a side plan view of an alternative embodiment of a golf club head produced according to the method of the present invention. 
     FIG. 5 is a bottom view of a golf club head produced according to the method of the present invention. 
     FIG. 6 is a front view of the golf club head produced according to the method of the present invention illustrating the variations in thickness of the striking plate. 
     FIG. 7 is an isolated top view of the striking plate illustrating the variable face thickness. 
     FIG. 8 is a flow chart of the method of the present invention. 
     FIG. 8A is a flow chart of the forging process of the present invention. 
     FIG. 9 is an exploded view of the components of a golf club head produced according to the method of the present invention. 
     FIG. 10 is an isolated view of the face member of FIG.  9 . 
     FIG. 11 is an exploded view of the crown and the connected sole and face member. 
     FIG. 12 is a side view of a golf club head produced according to the method of the present invention immediately prior to impact with a golf ball. 
     FIG. 13 is a side view of a golf club head produced according to the method of the present invention during impact with a golf ball. 
     FIG. 14 is a side view of a golf club head produced according to the method of the present invention immediately after impact with a golf ball. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is directed at a method for uniformly chemically etching a forged face member for a golf club head. The face member has a relatively thin striking plate thereby allowing for greater compliance of the striking plate during impact with a golf ball. The compliant striking plate allows for a high coefficient of restitution thereby allowing for greater distance of a golf ball hit with the golf club head of the present invention. The coefficient of restitution (also referred to herein as “COR”) is determined by the following equation:        e   =         v   2     -     v   1           U   1     -     U   2                                
     wherein U 1  is the club head velocity prior to impact; U 2  is the golf ball velocity prior to impact which is zero; ν 1  is the club head velocity just after separation of the golf ball from the face of the club head; ν 2  is the golf ball velocity just after separation of the golf ball from the face of the club head; and e is the coefficient of restitution between the golf ball and the club face. The values of e are limited between zero and 1.0 for systems with no energy addition. The coefficient of restitution, e, for a material such as a soft clay or putty would be near zero, while for a perfectly elastic material, where no energy is lost as a result of deformation, the value of e would be 1.0. The present invention provides a club head having a striking plate or face with a coefficient of restitution approaching 0.93, as measured under conventional test conditions. 
     As shown in FIGS. 1-5, a golf club is generally designated  40 . Such a golf club is described in greater detail in co-pending U.S. patent application Ser. No. 09/431,982, filed on Nov. 1, 1999, for A Golf Club Head With A Face Composed Of A Forged Material, which is hereby incorporated by reference in its entirety. The golf club  40  has a golf club head  42  with a body  44  and a hollow interior, not shown. Engaging the club head  42  is a shaft  48  that has a grip  50 , not shown, at a butt end  52  and is inserted into a hosel  54  at a tip end  56 . An O-ring  58  may encircle the shaft  48  at an aperture  59  to the hosel  54 . 
     The body  44  of the club head  42  is generally composed of four sections, the hosel  54 , a face member  60 , a crown  62  and a sole  64 . The club head  42  may also be partitioned into a heel section  66  nearest the shaft  48 , a toe section  68  opposite the heel section  66 , and a rear section  70  opposite the face member  60 . 
     The face member  60  is generally composed of a single piece of forged metal, and is preferably composed of a forged titanium material. The face member  60  generally includes a striking plate (also referred to herein as a face plate)  72  and a face extension  74  extending laterally inward from the perimeter of the striking plate  72 . The striking plate  72  has a plurality of scorelines  75  thereon. A more detailed explanation of the scorelines  75  is set forth in co-pending U.S. patent application Ser. No. 09/431,521, filed on Nov. 1, 1999, entitled Contoured Scorelines For The Face Of A Golf Club, and incorporated by reference in its entirety. The face extension  74  generally includes an upper lateral extension  76 , a lower lateral extension  78 , a heel wall  80  and a toe wall  82 . 
     The upper lateral extension  76  extends inward, toward the hollow interior  46 , a predetermined distance to engage the crown  62 . In a preferred embodiment, the predetermined distance ranges from 0.2 inch to 1.0 inch, as measured from the perimeter  73  of the face plate  72  to the edge of the upper lateral extension  76 . Unlike the prior art which has the crown engage the face plate perpendicularly, the present invention has the face member  60  engage the crown  62  along a substantially horizontal plane. Such engagement enhances the flexibility of the striking plate  72  allowing for a greater coefficient of restitution. The crown  62  and the upper lateral extension  76  are secured to each other through welding or the like along the engagement line  81 . As illustrated in FIG. 2A, in an alternative embodiment, the upper lateral extension  76  engages the crown  62  at a greater distance inward thereby resulting in a weld that is more rearward from the stresses of the striking plate  72  than that of the embodiment of FIG.  2 . 
     The uniqueness of the present invention is further demonstrated by a hosel section  84  of the upper lateral extension  76  that encompasses the aperture  59  leading to the interior hosel  54 . The hosel section  84  has a width w 1  that is greater than a width w 2  of the entirety of the upper lateral extension  76 . The hosel section  84  gradually transitions into the heel wall  80 . The heel wall  80  is substantially perpendicular to the striking plate  72 , and the heel wall  80  covers the interior hosel  54  before engaging a ribbon  90  and a bottom section  91  of the sole  64 . The heel wall  80  is secured to the sole  64 , both the ribbon  90  and the bottom section  91 , through welding or the like. 
     At the other end of the face member  60  is the toe wall  82  which arcs from the striking plate  72  in a convex manner. The toe wall  82  is secured to the sole  64 , both the ribbon  90  and the bottom section  91 , through welding or the like. 
     The lower lateral extension  78  extends inward, toward the hollow interior  46 , a predetermined distance to engage the sole  64 . In a preferred embodiment, the predetermined distance ranges from 0.2 inches to 1.0 inches, as measured from the perimeter  73  of the striking plate  72  to the end of the lower lateral extension  78 . Unlike the prior art which has the sole plate engage the face plate perpendicularly, the present invention has the face member  60  engage the sole  64  along a substantially horizontal plane. This engagement moves the weld heat affected zone rearward from a strength critical crown/face plate radius region. Such engagement enhances the flexibility of the striking plate  72  allowing for a greater coefficient of restitution. The sole  64  and the lower lateral extension  78  are secured to each other through welding or the like, along the engagement line  81 . The uniqueness of the present invention is further demonstrated by a bore section  86  of the lower lateral extension  78  that encompasses a bore  114  in the sole  64  leading to the interior hosel  54 . The bore section  86  has a width w 3  that is greater than a width w 4  of the entirety of the lower lateral extension  78 . The bore section  86  gradually transitions into the heel wall  80 . 
     The crown  62  is generally convex toward the sole  64 , and engages the ribbon  90  of sole  64  outside of the engagement with the face member  60 . The crown  62  may have a chevron decal  88 , or some other form of indicia scribed therein that may assist in alignment of the club head  42  with a golf ball. The crown  62  preferably has a thickness in the range of 0.025 to 0.060 inch, and more preferably in the range of 0.035 to 0.043 inch, and most preferably has a thickness of 0.039 inch. The crown  62  is preferably composed of a hot formed or “coined” material such as a sheet titanium. However, those skilled in the pertinent art will recognize that other materials or forming processes may be utilized for the crown  62  without departing from the scope and spirit of the present invention. 
     The sole  64  is generally composed of the bottom section  91  and the ribbon  90  that is substantially perpendicular to the bottom section  91 . The bottom section  91  is generally convex toward the crown  62 . The bottom section has a medial ridge  92  with a first lateral extension  94  toward the toe section  68  and a second lateral extension  96  toward the heel section  66 . The medial ridge  92  and the first lateral extension  94  define a first convex depression  98 , and the medial ridge  92  and the second lateral extension  96  define a second convex depression  100 . A more detailed explanation of the sole  64  is set forth in U.S. Pat. No. 6.007,433, filed on Apr. 2, 1998, for a Sole Configuration For Golf Club Head, which is hereby incorporated by reference in its entirety. The sole  64  preferably has a thickness in the range of 0.025 to 0.060 inch, and more preferably 0.047 to 0.055 inch, and most preferably has a thickness of 0.051 inch. The sole  64  is preferably composed of a hot formed or “coined” metal material such as a sheet titanium material. However, those skilled in the pertinent art will recognize that other materials and forming processes may be utilized for the sole  64  without departing from the scope and spirit of the present invention. 
     FIGS. 6 and 7 illustrate the variation in the thickness of the striking plate  72 . The face plate or striking plate  72  is partitioned into elliptical regions, each having a different thickness. A central elliptical region  102  preferably has the greatest thickness that ranges from 0.110 inch to 0.090 inch, preferably from 0.103 inch to 0.093 inch, and is most preferably 0.095 inch. A first concentric region  104  preferably has the next greatest thickness that ranges from 0.097 inch to 0.082 inch, preferably from 0.090 inch to 0.082 inch, and is most preferably 0.086 inch. A second concentric region  106  preferably has the next greatest thickness that ranges from 0.094 inches to 0.070 inch, preferably from 0.078 inch to 0.070 inch, and is most preferably 0.074 inch. A third concentric region  108  preferably has the next greatest thickness that ranges from 0.090 inch to 0.07 inch. A periphery region  110  preferably has the next greatest thickness that ranges from 0.069 inch to 0.061 inch. The periphery region includes toe periphery region  110   a  and heel periphery region  110   b . The variation in the thickness of the striking plate  72  allows for the greatest thickness to be distributed in the center  111  of the striking plate  72  thereby enhancing the flexibility of the striking plate  72  which corresponds to a greater coefficient of restitution. 
     Additionally, the striking plate  72  of the present invention has a smaller aspect ratio than face plates of the prior art. The aspect ratio as used herein is defined as the width, “w”, of the face divided by the height, “h”, of the face, as shown in FIG.  1 A. In one embodiment, the width w is 78 millimeters and the height h is 48 millimeters giving an aspect ratio of 1.635. In conventional golf club heads, the aspect ratio is usually much greater than 1. For example, the original GREAT BIG BERTHA® driver had an aspect ratio of 1.9. The face of the present invention has an aspect ratio that is no greater than 1.7. The aspect ratio of the present invention preferably ranges from 1.0 to 1.7. One embodiment has an aspect ratio of 1.3. The face of the present invention is more circular than faces of the prior art. The face area of the striking plate  72  of the present invention ranges 4.00 square inches to 7.50 square inches, more preferably from 4.95 square inches to 5.1 square inches, and most preferably from 4.99 square inches to 5.06 square inches. 
     The club head  42  of the present invention also has a greater volume than a club head of the prior art while maintaining a weight that is substantially equivalent to that of the prior art. The volume of the club head  42  of the present invention ranges from 175 cubic centimeters to 400 cubic centimeters, and more preferably ranges from 300 cubic centimeters to 310 cubic centimeters. The weight of the club head  42  of the present invention ranges from 165 grams to 300 grams, preferably ranges from 175 grams to 225 grams, and most preferably from 188 grams to 195 grams. The depth of the club head from the striking plate  72  to the rear section of the crown  62  preferably ranges from 3.606 inches to 3.741 inches. The height, “H”, of the club head  42 , as measured while in striking position, preferably ranges from 2.22 inches to 2.27 inches, and is most preferably 2.24 inches. The width, “W”, of the club head  42  from the toe section  68  to the heel section  66  preferably ranges from 4.5 inches to 4.6 inches. 
     FIG. 8 is a flow chart of the method of the present invention, generally designated  190 . At block  192 , a metal bar is forged into a final face member configuration. The final face member configuration preferably has a striking plate with variable face thickness as described above. The final face member configuration has a thickness that ranges from 0.050 inch to 0.250 inch. Preferably, the striking plate  72  has a thickness that is slightly greater than that described in reference to FIG.  6 . At block  194 , the final face member configuration is dipped into a bath of acid for chemical etching to uniformly remove from 0.002 inch to 0.015 inch from the final face member configuration. Preferably, 0.003 inch is uniformly removed from each surface of the final face member configuration. Thus, an interior surface of what will be the striking plate  72  has 0.003 inch chemically etched and an exterior surface has 0.003 inch chemically etched for a total removal of 0.006 inch from the final face member configuration. The acid bath is preferably hydrofluoric acid, nitric acid, hydrochloric acid or a mixture thereof. The final face member configuration is placed within the acid bath for a predetermined time depending on the strength of the acid in order to remove the necessary thickness of material. 
     At step  196 , a hot set operation is begun to ensure that the striking plate  72  of the final face member configuration has a proper bulge and roll. At step  196 , the final face member configuration is heated in a furnace at a temperature less than 600° C. for less than 20 minutes. Preferably, the final face member configuration is heated in a furnace at a temperature of 250° C. to 520° C. for 15 to 20 minutes, and most preferably to a temperature of 300° C. At step  198 , the heated final face member configuration is immediately placed in a low pressure press for ensuring the proper bulge and roll of the striking plate  72 . After step  198 , the face member  60  has finished the forging process, and is ready for assembly with the other components of the golf club head  42 . 
     FIG. 8A is more detailed explanation of the forging process  192 . The forging process  192  commences at block  202  with a metal bar being provided for forging into a face member  60 . The metal bar preferably has a diameter of 1.8 centimeters and is preferably 10 centimeters in length. The metal bar is preferably composed of titanium, and most preferably alpha-beta titanium. At step  204 , the metal bar is heated in a furnace at a temperature less than 1000° C. for less than 20 minutes. Preferably, the metal bar is heated in a rotary furnace at a temperature between 900° C. and 970° C., most preferably 920° C., for between 10 and 17 minutes, preferably 15 minutes. At step  206 , the heated metal bar is pressed immediately after removal from the furnace into an L-shape bar. The L-shape bar, has a smaller portion that is pressed at substantially a right angle to a larger portion of the metal bar. The pressing is performed in a conventional press at conventional pressures. 
     At step  208 , the L-shape metal bar is again heated in a furnace at a temperature less than 1000° C. for less than 20 minutes. Preferably, the L-shape metal bar is heated in a rotary furnace at a temperature between 900° C. and 970° C., most preferably 920° C., for between 10 and 17 minutes, preferably 15 minutes. At step  210 , the heated metal bar is pressed immediately after removal from the furnace into an intermediate shape face member. 
     At step  212 , the intermediate shape face member is placed in a tumbler for tumbling to improve the surface condition of the intermediate shape face member. At step  214 , the tumbled, intermediate shape face member is placed in an acidic bath for a light chemical etching to remove dirt and other particles on the surface. The acidic bath is preferably composed of a nitric acid, a hydrochloric acid, or a mixture of both. At step  216 , the etched, intermediate shape face member is coated with a conventional glazing compound to provide lubrication during the final full pressure pressing to form the final configuration. 
     At step  218 , the coated, intermediate shape face member is heated in a furnace at a temperature less than 1000° C. for less than 20 minutes. Preferably, the coated, intermediate shape face member is heated in a rotary furnace at a temperature between 900° C. and 970° C., most preferably 920° C., for between 10 and 17 minutes, preferably 15 minutes. At step  220 , the heated, intermediate shape face member bar is pressed immediately after removal from the furnace into a final face member configuration. The final face member configuration preferably has a variable face thickness as set forth in FIGS. 6 and 7. Further, the final face member configuration has the face extension with the upper lateral extension  76 , the lower lateral extension  78 , the heel wall  80  and the toe wall  82 . 
     FIGS. 9-11 illustrate a preferred assembly of the different components of the golf club head  42 . Essentially there are four main components, the face member  60 , the crown  62 , the sole  64  and the interior hosel  54 . Sub-components include two weight members  122  and  123  and a decal  88 . The face member  60  is formed in the forging process  200  to create the striking plate  72  and face extension  74  with the upper lateral extension  76 , the lower lateral extension  78 , the heel wall  80  and the toe wall  82 . The aperture  59  is drilled in the hosel section  84  of the upper lateral extension  76 , after forging, and the drilling continues downward to the bore section  86  where the bore  114  is created in the bore section  86 . 
     Next, as shown in FIG. 10, the interior hosel  54  is welded to the hosel section  84  and the bore section  86  in alignment with the aperture  59  and the bore  114 . In a preferred embodiment, a sold cylinder is welded to the hosel section  84  and the bore section  86  in alignment with the aperture  59  and the bore  114 , and then the solid cylinder is reamed to create the hollow interior  118  of the interior hosel  54 , as defined by the hosel wall  120 . In an alternative embodiment, the interior hosel may be pre-reamed prior to welding to the face member  60 . Those skilled in the pertinent art will recognize that methods similar to welding may be employed for attachment of the hosel  54  to the face member  60  without departing from the scope and spirit of the present invention. Next, the sole  64  is welded to the face member  60  (with attached hosel  54 ) as shown in FIG.  11 . The weight members  122  and  123  are attached on the bottom section  91  of the sole  64 , and then the crown  62  is welded to the face member  60  and the ribbon section  90 . 
     As shown in FIGS. 12-14, the compliance of the striking plate  72  allows for a greater coefficient of restitution, in the range of 0.83 to 0.93 under test conditions such as the USGA test conditions specified pursuant to Rule 4-1e, Appendix II of the Rules of Golf for 1998-1999. At FIG. 12, the striking plate  72  is immediately prior to striking a golf ball  140 . At FIG. 13, the striking plate  72  is engaging the golf ball, and deformation of the golf ball  140  and striking plate  72  is illustrated. At FIG. 14, the golf ball  140  has just been launched from the striking plate  72 . Thus, unlike a spring, the present invention increases compliance of the striking plate to reduce energy losses to the golf ball at impact, while not adding energy to the system. 
     From the foregoing it is believed that those skilled in the pertinent art will recognize the meritorious advancement of this invention and will readily understand that while the present invention has been described in association with a preferred embodiment thereof, and other embodiments illustrated in the accompanying drawings, numerous changes, modifications and substitutions of equivalents may be made therein without departing from the spirit and scope of this invention which is intended to be unlimited by the foregoing except as may appear in the following appended claims. Therefore, the embodiments of the invention in which an exclusive property or privilege is claimed are defined in the following appended claims.