Patent Publication Number: US-2015087440-A1

Title: Golf club head

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 13/960,677, filed Aug. 6, 2013, which is a continuation of U.S. patent application Ser. No. 13/741,286, filed Jan. 14, 2013, which is a divisional of U.S. patent application Ser. No. 12/763,014, filed Apr. 19, 2010, which claims the benefit of U.S. Provisional Patent Application No. 61/214,487, filed Apr. 23, 2009, all of which are incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to a golf club head. More specifically, the present disclosure relates to a golf club head made of multiple pieces that are welded together. 
     BACKGROUND 
     A golf set includes various types of clubs for use in different conditions or circumstances in which a ball is hit during a golf game. A set of clubs typically includes a “driver” for hitting the ball the longest distance on a course. A fairway “wood” can be sued for hitting the ball shorter distances than the driver. A set of irons are used for hitting the ball within a range of distances typically shorter than the driver or woods. 
     An iron has a flat face that normally contacts the ball whenever the ball is being hit with the iron. Irons have angled faces for achieving lofts ranging from about 18 degrees to about 60 degrees. 
     Every club has a “sweet spot” that represents the best hitting zone on the face for maximizing the probability of the golfer achieving the best and most predictable shot using the particular club. Most golfers strive to make contact with the ball inside the sweet spot to achieve a desired trajectory. 
     In order to withstand repeated ball impacts, the face plate of a golf club has traditionally been made thick enough to prevent mechanical failure. 
     SUMMARY OF THE DESCRIPTION 
     The present disclosure describes a golf club head comprising a heel portion, a toe portion, a crown, a sole, and a face. 
     The foregoing and other objects, features, and advantages of the invention will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures. 
     According to one aspect of the present invention, an iron-type golf club head is described having a first piece including at least a portion of an iron-type face. A second piece including a heel portion, a sole portion, a toe portion, a top-line portion, a hinge region, and a front opening for receiving the first piece is also described. A first contact surface of the first piece is connected with a second contact surface of the second piece at a contact interface. A continuous weld extends along the contact interface attaching the first and second pieces together at the contact interface. The continuous weld includes a fusion zone occurring substantially on the iron-type face outside the hinge region of the club head. 
     In one example, a rear weld bead is exposed on a rear surface of the iron-type face. 
     In another example, the rear weld bead is substantially covered by a third piece. 
     In yet another example, a front weld bead is removed from a front surface of the iron-type face and a weld centerline axis is offset from a rear wall portion by a distance of at least 1 mm. 
     In one example, a total face area is about 2,700 mm 2 -5,000 mm 2  and a thin face area is about 450 mm 2 -2,020 mm 2 . 
     In another example, a thin face thickness is about 1.5-2.5 mm or a thin face thickness is in a range of less than 2.0 mm. 
     In yet another example, a thin face area percentage is about 13-70% and an inverted cone region is about 230 mm 2  to about 2,000 mm 2 . 
     In one example, a first piece rear surface area is about 300 mm 2  to about 4,000 mm 2  and a coefficient of restitution is greater than about 0.8. 
     In another example, the first piece is forged of a steel selected from the group consisting of maraging steels, maraging stainless steels, and PH stainless steels. The stainless steel is C455 or 17-4 stainless steel. 
     In yet another example, the fusion zone is substantially located in a relatively low impact stress region of the front striking surface. 
     According to another aspect of the present invention, a golf club head is described having a front striking surface, a rear face surface located behind at least a portion of the front striking surface in a cavity region, a first piece including at least a portion of the front striking surface, and a second piece including a heel portion, a sole portion, a toe portion, a top-line portion, a hinge region, and a front opening on the front striking surface for receiving the first piece. A first contact surface of the first piece is connected with a second contact surface of the second piece at a contact interface. A continuous weld extends along the contact interface attaching the first and second pieces together at the contact interface. The continuous weld includes a fusion zone creating a weld bead on at least the rear face surface. A third piece is configured to be inserted into the cavity region and attached to the rear face surface. The third piece substantially covers the weld bead on the rear face surface. 
     According to another aspect of the present invention, a method is described including placing a continuous weld located on the face of a cavity back iron-type golf club head. The weld extends continuously on a front striking surface of the face creating a front and rear weld bead. The weld is located at least partially on a contact interface between a first piece and a second piece. A method of removing a front weld bead from the front striking surface of the face and covering the rear weld bead located on a rear surface of the face with a badge is described. The rear weld bead is obscured by the badge in the cavity back iron-type golf club head. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements. 
         FIG. 1A  is an exploded view of an embodiment of a golf club head according to the present disclosure. 
         FIG. 1B  is an assembled view of the golf club head of  FIG. 1A . 
         FIG. 2  is an illustration of a golf club head and an impact area. 
         FIG. 3A  is a cross-sectional view of the golf club head taken along section lines  3 A- 3 A in  FIG. 1B . 
         FIG. 3B  is a magnified view of a weld zone. 
         FIG. 3C  is a magnified view of a weld zone. 
         FIG. 4  is a cross-sectional view of a golf club head according to an embodiment. 
         FIG. 5  is a cross-sectional view of a golf club head according to an embodiment. 
         FIG. 6  is a cross-sectional view of a golf club head according to an embodiment. 
         FIG. 7  is a cross-sectional view of a golf club head according to an embodiment. 
         FIG. 8  is a toe perspective view of a golf club head. 
         FIG. 9  is a cross-sectional view of the golf club head taken along section lines  9 - 9  in  FIG. 8 . 
         FIG. 10  is a cross-sectional view of a golf club head according to an embodiment. 
         FIG. 11  is a cross-sectional view of a golf club head according to an embodiment. 
         FIG. 12A  is an isometric view of a golf club assembly. 
         FIG. 12B  is an isometric view of an assembled golf club head. 
         FIG. 13  is a flow chart of a golf club assembly operation. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments and aspects of the inventions will be described with reference to details discussed below, and the accompanying drawings will illustrate the various embodiments. The following description and drawings are illustrative of the invention and are not to be construed as limiting the invention. Numerous specific details are described to provide a thorough understanding of various embodiments of the present invention. However, in certain instances, well-known or conventional details are not described in order to provide a concise discussion of embodiments of the present inventions. 
       FIG. 1A  illustrates a golf club head  100  including a first piece striking plate  118  and a second piece  126 . The first piece striking plate  118  is a portion of a front striking surface. The second piece  126  is attached to the first piece  118  to form the golf club head  100 . 
       FIG. 1A  further illustrates the first piece striking plate  118  being a portion of the front striking surface of the golf club head  100  and having a first piece front surface  120 . The first piece front surface  120  includes grooves  124  in accordance with The Rules of Golf issued by the United States Golf Association (USGA). The first piece striking plate  118  also includes a first contact surface  122  extending away from a perimeter of the front surface  120 . 
     The second piece  126  includes a hosel  102 , a hosel axis  104 , a sole portion  106 , a toe portion  108 , a heel portion  110 , a top-line portion  112 , a cavity back wall  113 , a front opening  114 , and a second contact surface  116 . 
       FIG. 1B  illustrates the golf club head  100  after the first piece striking plate  118  is inserted into the second piece  126  and welded. In one embodiment, a front weld bead  128  is formed from a continuous laser weld or plasma weld that extends along a contact interface between the first contact surface  122  and second contact surface  116 . In certain embodiments, the welding occurs on the front striking surface of the golf club head  100  while creating a front weld bead  128  on the front striking surface and a rear weld bead on the rear face surface located behind a portion of the front striking surface. 
       FIG. 1B  shows the front weld bead  128  created immediately after a welding operation and prior to finishing. In one embodiment, the weld contour matches the outer profile contours of the top-line portion, the toe portion, and the sole portion. In one embodiment, the weld contour can enclose the set of grooves  124  that are machined or cast into the front piece striking plate  118 . In another embodiment, the grooves  124  can be added after the welding operation and can overlap with the weld contour in certain locations. 
       FIG. 2  shows a golf club head  200  with a front weld contour  216  and the weld contour  216  placement with respect to an impact area. In defining the impact area, a center line axis  206 , a toe offset axis  208 , a heel offset axis  210 , a top-line axis  202 , a top-line offset axis  204 , a sole axis  214 , and a sole offset axis  212  are shown to be coplanar across the striking face  218  of the golf club head  200 . The center line  206  passes through an ideal center striking point  220 . The toe offset axis  208  and heel offset axis  210  are parallel and coplanar with the center line axis  206 . The toe offset axis  208  is offset from the center line axis  206  by a distance, d1. The heel offset axis  210  is offset from the center line axis  206  by a distance, d2. 
     The top-line axis  202  is parallel with the top-line edge. In cases where the top-line edge is non-linear, the top-line axis  202  is tangent to the outermost top-line edge while remaining primarily parallel with the top-line edge. The top-line offset axis  204  is coplanar, parallel, and offset from the top-line axis  202  by a distance, d3. Similarly, the sole axis  214  is tangent and primarily parallel with the sole edge. The sole offset axis  212  is coplanar, parallel, and offset from the sole axis  214  by a distance, d4. 
     In one embodiment, the impact area is defined as the part of the front striking face  218  that lies within 0.80 inches (20 mm, dimensions d1,d2) on either side of a vertical center line  206  of the face  218 , but excluding strips that are 0.25 inches (6.35 mm, dimensions d3,d4) wide from the top and bottom edges of the club head. In other words, the impact area is defined by the top-line offset axis  204 , the toe offset axis  208 , the heel offset axis  210 , and the sole offset axis  212  within a striking face plane. 
       FIG. 2  further shows the weld contour  216 , in one embodiment, extending at least partially into the impact area. In certain embodiments, the weld contour  216  can be located entirely within the impact area or entirely outside of the impact area. 
       FIG. 3A  shows a cross-sectional view along cross-section lines  3 A- 3 A (passing through a face center point) in  FIG. 1B .  FIG. 3A  illustrates a cross-sectional profile  300  including a cavity back wall  113  forming a cavity with the first piece striking plate  118 . A weld is created by a welding device  302 , such as a laser or plasma weld. In one embodiment, the weld is applied on the front face of the golf club head  300  from a frontward to rearward direction. A top weld line  304  including a top weld axis  306  is shown. The weld axis  306  is co-axial with the direction that the weld is applied (in the case of laser welding). In addition, a bottom weld line  308  including a bottom axis  310  is shown. In one embodiment, it is understood that the top weld line  304  and bottom weld line  308  can be part of the same continuous weld line or can be two separate and distinct weld lines. The weld can be any type of weld including (but not limited to) bead, groove, fillet, surfacing, tack, plug, slot, friction, and resistance welds. 
       FIG. 3A  shows a butt weld made by a laser that includes a narrow and deep fusion zone and a narrow heat affected zone flanking the fusion zone, as will be discussed in further detail. The interface surface between the first  122  and second  116  contact surfaces is perpendicular to the plane of the face. The depths of these weld zones extend along respective weld axes  306 , 310  that are parallel to the direction of load in a face-normal direction. 
     Compared to TIG welding and other welding techniques, laser welding can be advantageous by concentrating more energy at the weld site. Laser welding also produces a more localized melt, less material interdiffusion, and reduced material fatigue during subsequent use. 
     In one example, a laser weld operation is performed on the contact interface surface while the first piece  118  and second piece  126  are held together using a clamp or fixture to ensure a gap between the first  122  and second  116  contact surfaces is minimized. 
       FIG. 3A  further shows the top weld line  304  having a front weld bead  320  and a rear weld bead  318  prior to finishing. In addition, the bottom weld line  308  also includes a front weld bead  312  and a rear weld bead  314 . 
       FIG. 3A  also shows a cross-sectional profile of a variable thickness across the first piece striking plate  118 . The thickest portion of the first piece striking plate  118  has a thickness, t1. The thinnest portion of the first piece striking plate  118  has a thickness, t3. A transition region between the thinnest and thickest portions has a thickness, t2, that is thinner than the thickest portion, t1, but thicker than the thinnest portion, t3. The thicknesses t1,t2,t3 described above contribute to a particular profile of an inverted cone region, as will be described in further detail. 
       FIG. 3A  illustrates an upper return wall  322  and a lower return wall  324 . The upper and lower return walls  322 , 324  extend away from the first piece striking plate  118  toward a rear portion of the club head  100 . In other words, the upper and lower return walls  322 , 324  extend in a general direction normal to the face. It is understood that the return walls  322 ,  324  may not be perfectly perpendicular to the face plane in certain embodiments. In one embodiment, the upper and lower return walls  322 , 324  define a portion of the cavity  344  located behind the first piece striking plate  118 . The upper return wall  322  can be defined as the portion of a return wall that is above a horizontal plane  342  that is perpendicular to the face plane (parallel with the score-lines) passing through a center point  340 . Subsequently, the rear lower return wall  324  can be defined as any return wall portion below the horizontal plan  342  (toward the sole portion). 
     The upper and lower return walls  322 ,  324  can be one single continuous return wall that extends from the rear surface of the striking plate or two or more separate return wall portions. In other words, the entire return wall including an upper wall  322  and a lower wall  324  can extend 360° about the perimeter of the cavity  344 . In another embodiment, the entire return wall only extends around the perimeter of the cavity  344  about 270° (relative to the center face) while excluding all or part of the upper wall  322  portion. 
     Both the top weld line  304  and bottom weld line  308  are located inwardly away from the upper and lower return walls  322 ,  324  toward the center point  340  of the front striking surface of the golf club head  300 . In one embodiment, the top weld line  304  includes the weld axis  306  that is inwardly offset from the upper return wall  322  by a distance, a1 (described in further detail below). Similarly, the bottom weld line  308  includes the weld axis  310  that is inwardly offset from the lower return wall  324  by a distance a1. In one embodiment, the offset distance a1 is the same for the upper return wall  322  and lower return wall  324 . In other embodiments, the offset distance, a1, can vary around a perimeter of the striking plate  118 . In one embodiment, the offset distance a1 can be between about 1-5 mm, 1-10 mm, 1-15 mm, 1-20 mm, or at least 1 mm. In certain embodiments, the weld axes  304 , 308  are equally offset from the upper and lower return walls  322 , 324  by the offset distance a1 at all points around a periphery of the striking plate  118 . 
       FIG. 3B  is an enlarged view of the bottom weld line  308  after the front weld bead  312  (and front bead  320 , not shown) has been removed by machining or polishing to create a smooth front surface.  FIG. 3B  provides a clear view of the heat-affected zone  326  and the fusion zone  328  previously mentioned. The fusion zone  328  and heat affected zone  326  tend to be wider at the front surface and progressively narrower with increasing depth of the weld. The width of the weld zone including the heat affected zone  326  and fusion zone  328  is relatively narrow compared to a conventional weld. 
     At all locations around the 360° circumference of the contact interface, the respective weld axes and fusion zones extend substantially parallel to the direction of the ball impact force that is applied to the face during use. In one embodiment, all the weld axes are in the plane of the contact interface to provide a sufficient butt weld. The entire weld is located on the face of the club head and away from the return wall  322 , 324 . In other words, the entire weld is located within the cavity  344  back portion of the golf club head and does not extend beyond any return wall  322 , 324  or into any hinge region. 
     In one embodiment, the first piece striking plate  118  is fitted to and aligned with the second piece  126  and is moved relative to the laser  302 . It is understood that the laser can move relative to the assembly or both the laser and the assembly can move. In one embodiment, the laser is a CO 2  cw laser and has an adjustable output power in the range of 1350-2000 W. The welding can begin near the hosel and continue around the contact interface forming the front and rear weld bead. In one embodiment, the laser can move relative to the surface within the range of 40 to 80 cm/min. 
     After completion of the welding, the club head is subjected to a heat treatment for aging. The post-weld heat treatment is generally at 480-540° C. for four hours. The club head is also machine finished as required, such as grinding, polishing, or sandblasting, to smooth and topologically blend the surface of the weldment into the face plane. Finish machining is desirably followed by passivation. After completing finish-machining, it may be desirable to apply a suitable surface treatment of the club head, such as plating, painting, coating, or the like. Plating may be performed to produce a surface plating layer that protects against corrosion and is strong, durable, relatively inert, and aesthetically pleasing. Exemplary materials for forming a plating layer are Cr, Ni, and Cu. Exemplary techniques for forming the plating layer are electrode plating, electroless plating, physical vapor deposition (PVD), chemical vapor deposition (CVD), ion plating, and ion-beam-enhanced diffusion. An intermediate sublayer can be applied prior to the plating layer such as soft nickel, soft copper, and oxides. 
       FIG. 3B  illustrates the weld penetrating 100% through the first piece striking plate  118 . In one embodiment, the weld penetration is at least about 1 mm deep or at least 90% (of the thickness of the material) penetration to maintain sufficient strength and durability. In another embodiment, the weld penetration is between about 1-4 mm depending on the thickness of the material. In certain embodiments, the width of the fusion zone is about 2 mm to 3 mm wide (as measured in a plane parallel to the face plane). In one embodiment, the welding is not performed at a constant power or speed. The output of the laser and the progression rate of the laser around the circumference are controllably adjusted as required to apply more power for a longer time in regions where a deeper weld is desired. 
       FIG. 3B  further shows a hinge region  330  or transition region located between the front striking surface  338  of the club and a lower return wall  324 . For clarity, only the lower return wall  324  is shown in  FIG. 3B  although it is understood that a hinge region  330  can extend around the all or part of the periphery of the front striking surface  338 . For example, a hinge region  330  can extend between the upper return wall  322  and front striking surface  338  as well. In one embodiment, the front striking surface  338  includes the first piece striking plate  118  in addition to a portion of the second piece  126  that is within the striking surface plane  336 . In another embodiment, the fusion zone  328  can be located at the very edge of the front striking surface  338  just outside of the hinge region  330  (i.e. inward and away from the hinge region  330 ). Therefore, in certain embodiments, the front striking surface  338  can be entirely comprised of the first piece striking plate  118 . 
     Locating the fusion zone  328  outside of the hinge region  330  allows for greater dimensional uniformity in the hinge region  330  during casting or forming of the second piece. The hinge region  330  is formed as a portion of the second piece  126 . 
     Placing the fusion zone  328  outside of the hinge region  330  prevents any unintentional deformation of material within the hinge region  330  ensuring consistent mechanical characteristics and performance during impact in the hinge region  330 . The mechanical characteristics (such as strength, bending stiffness, shear force, stress, strain, ductility etc.) of the hinge region  330  can be negatively impacted by the presence of a fusion zone  328  within the hinge region  330 . The presence of a fusion zone  328  in the hinge region can create unwanted stress concentrations which may lead to mechanical failures. 
     A front striking surface plane  336  extends across the entire front striking surface  338  while being co-planar with the front striking surface  338  (excluding grooves).  FIG. 3B  further shows a face-hinge boundary line  332  which identifies the edge of the front striking surface  338  and the hinge region  330 . The face-hinge boundary line  332  is generally perpendicular or normal to the front striking surface plane  336  around a periphery of the front striking surface  338 . The face-hinge boundary line  332  is located at the point where the front striking surface  338  ends and a face contour or profile is no longer coplanar with the front striking surface plane  336 . 
     The hinge region  330  is further defined by the hinge-rear wall boundary  334 . The hinge-rear wall boundary  334  indicates the location where the hinge region  330  ends and the rear wall  324  begins. The hinge-rear wall boundary  334  is a plane parallel with the front striking surface plane  336  offset in a rearward direction toward the back of the club head  300 . In one embodiment, the hinge-rear wall boundary  334  is offset from the front striking surface plane  336  by a distance, a2. In certain embodiments, the offset distance a2 is about 2-5 mm or about 2-20 mm toward the rear portion of the club head  300  depending on the thickness of the striking plate  118 . 
     In one embodiment, the hinge-rear wall boundary  334  is primarily defined as a 1 mm offset from a rear surface plane  346 . The rear surface plane  346  is a plane that is generally coplanar with the rear surface of the striking plate  118  having a relatively constant and thin thickness immediately outside and adjacent to the hinge region  330 . In some embodiments, the rear surface plane  346  is generally perpendicular to the face-hinge boundary line  332 . The hinge-rear boundary  334  is parallel with the rear surface plane  346  and offset by a distance, a4. In a preferred embodiment, the hinge-rear boundary  334  is offset from the rear surface plane  346  by at least about 1 mm. In certain embodiments the offset distance, a4, is about 1 mm. 
     In addition, the face-hinge boundary line  332  is offset a minimum distance, a3, from the weld line axis  310  measured across the striking surface plane  336 . In one embodiment, the offset distance a3 is about 1 mm while still remaining outside the hinge region  330 . In certain embodiments, the offset distance a3 is between about 1-10 mm, and preferably between at least about 1-5 mm or at least 1 mm. In embodiments where the weld bead  314  does not follow the peripheral contour of the face-hinge boundary line  332 , the a3 offset distance can vary for different shaped face welds. A weld having a distance, a3, of zero would be located directly on the face-hinge boundary line  332  and would therefore undesirably create a weld in the hinge region  330 . 
     In some embodiments, the a3 offset distance (related to face-hinge boundary  332 ) and the a1 offset distance (related to rear wall) may be equal depending on the construction. The weld axes  310 , 306  should always be placed outside of the hinge region and inward (toward the center) of any return wall that may be present. 
       FIG. 3C  illustrates a magnified hinge region according to another embodiment similar to  FIG. 3B . However, the lower return wall  324  is located inwardly toward the center of the club face and above the face-hinge boundary  332 . A return wall plane  348  is shown to be located a certain distance, a5, above the face-hinge boundary  332 . The distance a5 can be any distance depending on the location of the rear wall  324  with respect to the face-hinge boundary  332 . The return wall plane  348  is normal and perpendicular to the striking surface plane  336  and the hinge-rear wall boundary  334 . The hinge-rear wall boundary  334  intersects with a return wall profile at an intersection point  350 . The return wall plane  348  intersects with the hinge-rear wall boundary  334  at the intersection point  350 . Subsequently, the weld axes  310 , 306  are offset by the offset distance a1 from the return wall plane  348 . In one embodiment, the offset distance, a1, is about 1 mm or more, as described herein. 
     The location of the weld bead  314  and fusion zone  328  with respect to the hinge region  330  is critical to achieving a high COR (coefficient of restitution), thin face, cavity back iron having consistent hinge region performance while saving mass in the face to be allocated to other regions of the golf club head. In some embodiments, the COR is greater than 0.790. Preferably, the COR is at least 0.80 as measured according to the USGA Rules of Golf. The COR can even be as high as 0.83. 
     In certain embodiments, the first piece striking plate  118  can be forged maraging steel, maraging stainless steel, or precipitation-hardened (PH) stainless steel. In general, maraging steels have high strength, toughness, and malleability. Being low in carbon, they derive their strength from precipitation of inter-metallic substances other than carbon. The principle alloying element is nickel (15% to nearly 30%). Other alloying elements producing inter-metallic precipitates in these steels include cobalt, molybdenum, and titanium. In one embodiment, the maraging steel contains 18% nickel. Maraging stainless steels have less nickel than maraging steels but include significant chromium to inhibit rust. The chromium augments hardenability despite the reduced nickel content, which ensures the steel can transform to martensite when appropriately heat-treated. In another embodiment, a maraging stainless steel C455 is utilized as the first piece striking plate  118 . In other embodiments, the first piece striking plate  118  is a precipitation hardened stainless steel such as 17-4, 15-5, or 17-7. 
     The first piece striking plate  118  can be forged by hot press forging using any of the described materials in a progressive series of dies. After forging, the first piece striking plate  118  is subjected to heat-treatment. For example, 17-4 PH stainless steel forgings are heat treated by 1040° C. for 90 minutes and then solution quenched. In another example, C455 stainless steel forgings are solution heat-treated at 830° C. for 90 minutes and then quenched. 
     In one embodiment, the second piece  126  is made from carbon steel (e.g., 1020, 1030, or 1040 carbon steel), chrome-molybdenum steel (e.g., 4140 Cr—Mo steel), Ni—Cr—Mo steel (e.g. 8620 Ni—Cr—Mo steel), austenitic stainless steel (e.g., 304, N50, or N60 stainless steel (e.g., 410 stainless steel). 
     The second piece  126  can include various features such as weighting elements, cartridges, and/or inserts or applied bodies as used for CG placement, vibration control or damping, or acoustic control or damping. For example, U.S. Pat. No. 6,811,496, incorporated herein by reference in its entirely, discloses the attachment of mass altering pins or cartridge weighting elements. 
     After forming the first piece striking plate  118  and the second piece  126 , the first  122  and second  116  contact surfaces can be finish-machined to ensure a good interface contact surface is provided prior to welding. In one embodiment, the first  122  and second  116  contact surfaces are planar for ease of finish machining and engagement. 
     It is possible that an alignment aid can be used to ensure the first piece striking plate  118  engages with the second piece  126 . In one embodiment, an alignment aid can include an edge, lip, pin, nubbin, male-female detents, or similar aides that ensure the interface surfaces are brought into mating engagement. Moreover, the interface surfaces can have complex complementary contours. 
       FIG. 4  illustrates another embodiment including a club head  400 , a first piece striking plate  402 , a top line weld  404 , a top rear weld bead  418 , a top weld axis  406 , a striking face plane  436 , a bottom line weld  408 , a bottom rear weld bead  414 , a bottom weld axis  410 , and a face-hinge boundary line  432 , as similarly described above. 
       FIG. 4  further shows a weld axis convergence point  440  where the top weld axis  406  and the bottom weld axis  410  intersect or converge. In the embodiment shown, the convergence point  440  occurs behind the striking face plane  436  in a rearward direction relative to the club head  400 . It is understood that the top weld axis  406  and bottom weld axis  410  would form a weld axis plane as the weld is created about the periphery of the first piece striking plate  402 . The weld axis angle  442  is created between both weld axis  406 , 410  and the first piece striking plate  402 . In one embodiment the weld axis angle  442  is between about 90° to about 180°. For example, the weld axis angle  442  can be about 135°. In certain embodiments, the weld axis angle  442  is at least less than about 180°. 
       FIG. 5  illustrates yet another embodiment including a club head  500 , a first piece striking plate  502 , a top line weld  504 , a top rear weld bead  518 , a top weld axis  506 , a striking face plane  536 , a bottom weld  508 , a bottom rear weld bead  514 , a bottom weld axis  510 , and a face-hinge boundary line  532  as similarly described above. 
       FIG. 5  further shows a weld axis convergence point  540  where the top weld axis  506  and the bottom weld axis  510  intersect or converge. In the embodiment shown, the convergence point  540  occurs in front of the striking face plane  536  in a forward direction relative to the club head  500 . In one embodiment the weld axis angle  542  is between about 0° to about 90° relative to the first piece striking plate  502 . In certain embodiments, the weld axis angle  542  is less than 90°. 
       FIG. 6  illustrates another embodiment including a golf club head  600  having a lap joint created between the first piece striking plate  602  and the second piece  612 . The golf club head  600  includes a top line weld  604 , a bottom line weld  608 , a top weld axis  606 , and a bottom weld axis  610  as similarly described above. The lap joint created includes a front edge  616  located around a periphery of the striking plate  602  and a rear edge  614 . In one embodiment, both the front edge  616  and the rear edge  614  are parallel with the weld axes  606 , 610 . The weld axes  606 , 610  are aligned with the front edge  616  so that a weld is primarily created at the interface between the front edge  616  and the second piece  612 . It is understood that in some embodiments, the front edge  616  and rear edge  614  may be non-parallel with the weld axes  606 , 610 . In one embodiment, the maximum radial diameter of the front edge  616  across the face plane is less than the maximum radial diameter of the rear edge  614  across the face plane. 
       FIG. 7  illustrates another embodiment including a golf club head  700  having a lap joint. The golf club head  700  further includes a first piece striking plate  702 , a second piece  712 , a top line weld  704 , a bottom line weld  708 , a top weld axis  706 , a bottom weld axis  710 , a front edge  716 , and a rear edge  714 . In one embodiment, the maximum radial diameter of the front edge  716  is larger than the maximum radial diameter of the rear edge  714  across the face plane. The weld axes  706 , 710  are aligned and parallel with the front edge  716  to create a weld at the front edge  716  interface with the second piece  712 . 
       FIG. 8  illustrates a toe view of a golf club head  800  having a hosel  802 , a hosel axis  804 , a sole portion  806 , a toe portion  808 , a heel portion  810 , and a top-line portion  812 . 
       FIG. 9  is a cross-sectional view of the golf club head  800  taken along the cross-sectional lines  9 - 9  in  FIG. 8 , according to one embodiment.  FIG. 9  illustrates a first piece striking plate  902  and rear second piece  904 . The first piece striking plate  902  includes “inverted cone technology”  906  (hereinafter, “ICT”), a thin face area  908 , a inverted cone region edge  912 , center point  914 , and a rear weld bead  910 . The ICT region  906  can be considered a sweet spot where an ideal impact can occur at the center point  914 . Variable thickness configurations or inverted cone configurations are discussed in, for example, U.S. Pat. Nos. 6,800,038, 6,824,475, 6,904,663, and 6,997,820, all incorporated herein by reference. 
     The inverted cone region  906  is an ellipse (of which the major axis is nearly horizontal), including a central zone  906   a  and a surrounding ridge  906   b . In one embodiment, the thin face area  908  has a nominal thickness of about 1.8 mm. The ridge  906   b  can have a thickness of about 2.0 mm. In the region located between the ridge  906   b  and the ICT region edge  912 , the thickness of the face tapers down to a thickness of about 1.8 mm. In other embodiments, various profile thicknesses in the range of 1.6 mm to less than 2.5 mm are possible. In some embodiments, the thin face thickness is less than 2.0 mm. The thickness profiles and low thickness values can be achieved during forging of the first piece striking plate  902 . 
     In one embodiment, a 0.5 mm to 1.0 mm machine stock plate can be added to the first piece striking plate  902  to increase tolerance control. After forging, the first piece striking plate  902  can be slightly milled and engraved with score-lines. A key advantage of being able to forge such a thin face is the freeing up of discretionary mass (up to about 20 g) that can be placed elsewhere in the club head (such as the rear piece) for manipulation of the moment of inertia or center of gravity location. 
     The thickness of the first piece striking plate  902  in the thin face area  908  is generally consistent in thickness and non-variable. Of course, manufacturing tolerances may cause some variation in the thin face area  908 . The thin face area  908  and the ICT region  906  can be considered the “unsupported” face area of the striking face because the thickness dimensions are relatively thin in those areas. 
       FIG. 9  further shows the weld bead  910  being offset by a distance a1 (previously described in  FIG. 3A ) all along a perimeter of the return wall  916 . Exemplary club head geometries for representative club heads are described in Tables 1-9 below. The exemplary club heads (examples 1-9) in Tables 1-9 are similar to the embodiment of  FIG. 9  in that the weld bead  910  axis is offset from the return wall  916  by a minimal a1 distance in the range of about 1-5 mm or at least 1 mm. In some embodiments, the a1 distance is between about 1-4 mm. 
     The tabulated values in Tables 1-9 are total face area, thin face area, thin face thickness, thin face area %, Inverted Cone Technology (ICT) region, and the First Piece Striking Plate Surface Area (FPSPSA). 
     The “total face area” is defined as the area of face contained within a face plane on a front striking portion of the club head. The “thin face area” is defined as the portion of the first piece striking plate that is generally unsupported, constant in thickness, and thin. For example, the thin face area  908  shown in  FIG. 9  illustrates an exemplary unsupported thin face area. The thin face area  908  excludes the inverted cone region and any region that is located outside of the weld bead  910 . The “thin face thickness” is the nominal thickness of the first piece striking plate in the thin face area  908  as shown as dimension t3, in  FIG. 3A . The “thin face area %” is the percentage of the total face area that includes a thin face area having the thickness, t3 (excluding the ICT region). The thin face area percentage is the thin face area divided by the total face area multiplied by 100. The “inverted cone region” is the surface area contained by the variable thickness region  906  or inverted cone area. Furthermore, the “First Piece Striking Plate Surface Area” is the rear surface area of the first piece striking plate  902  contained within the continuous weld bead  910  (including an ICT region). 
     Example 1 
       
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Total 
                 Thin Face 
                 Thin Face  
                 Thin  
                 ICT 
                   
               
               
                 Club  
                 Face Area  
                 Area 
                 Thickness  
                 Face 
                 Region 
                 FPSPSA 
               
               
                 head 
                 (mm 2 ) 
                 (mm 2 ) 
                 (mm) 
                 Area % 
                 (mm 2 ) 
                 (mm 2 ) 
               
               
                   
               
             
            
               
                 3-iron 
                 2,825 
                 1,633 
                 2.1 
                 57 
                 541 
                 2,175 
               
               
                 6-iron 
                 2,964 
                 1,735 
                 2.1 
                 58 
                 541 
                 2,276 
               
               
                 9-iron 
                 3,116 
                 1,553 
                 2.1 
                 49 
                 541 
                 2,094 
               
               
                 Wedge 
                 3,452 
                 1,804 
                 2.1 
                 52 
                 541 
                 2,345 
               
               
                   
               
            
           
         
       
     
     Example 2 
       
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Total 
                 Thin Face  
                 Thin Face 
                 Thin  
                 ICT 
                   
               
               
                 Club  
                 Face Area 
                 Area 
                 Thickness 
                 Face 
                 Region 
                 FPSPSA 
               
               
                 head 
                 (mm 2 ) 
                 (mm 2 ) 
                 (mm) 
                 Area % 
                 (mm 2 ) 
                 (mm 2 ) 
               
               
                   
               
             
            
               
                 3-iron 
                 2,824 
                 1,876 
                 2.4 
                 66 
                 527 
                 2,403 
               
               
                 6-iron 
                 2,962 
                 1,945 
                 2.4 
                 65 
                 527 
                 2,473 
               
               
                 9-iron 
                 3,113 
                 1,717 
                 2.4 
                 55 
                 527 
                 2,245 
               
               
                 Wedge 
                 3,451 
                 2,012 
                 2.4 
                 58 
                 527 
                 2,540 
               
               
                   
               
            
           
         
       
     
     Example 3 
       
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                   
                 Total 
                 Thin Face 
                 Thin Face 
                 Thin  
                 ICT 
                   
               
               
                 Club  
                 Face Area 
                 Area 
                 Thickness 
                 Face 
                 Region 
                 FPSPSA 
               
               
                 head 
                 (mm 2 ) 
                 (mm 2 ) 
                 (mm) 
                 Area % 
                 (mm 2 ) 
                 (mm 2 ) 
               
               
                   
               
             
            
               
                 3-iron 
                 2,792 
                 1,242 
                 2.5 
                 44 
                 388 
                 1,631 
               
               
                 6-iron 
                 2,965 
                 1,219 
                 2.5 
                 41 
                 388 
                 1,608 
               
               
                 9-iron 
                 3,151 
                 1,208 
                 2.5 
                 38 
                 388 
                 1,597 
               
               
                 Wedge 
                 3,304 
                 1,130 
                 2.5 
                 34 
                 388 
                 1,519 
               
               
                   
               
            
           
         
       
     
     Example 4 
       
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                   
                 Total 
                 Thin Face 
                 Thin Face 
                 Thin  
                 ICT 
                   
               
               
                 Club  
                 Face Area 
                 Area 
                 Thickness 
                 Face 
                 Region 
                 FPSPSA 
               
               
                 head 
                 (mm 2 ) 
                 (mm 2 ) 
                 (mm) 
                 Area % 
                 (mm 2 ) 
                 (mm 2 ) 
               
               
                   
               
             
            
               
                 3-iron 
                 2,796 
                 1,313 
                 2.2 
                 46 
                 247 
                 1,560 
               
               
                 6-iron 
                 2,934 
                 1,281 
                 2.2 
                 43 
                 247 
                 1,529 
               
               
                 9-iron 
                 3,084 
                 1,232 
                 2.4 
                 39 
                 247 
                 1,479 
               
               
                 Wedge 
                 3,421 
                 1,464 
                 2.4 
                 42 
                 247 
                 1,711 
               
               
                   
               
            
           
         
       
     
     Example 5 
       
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 5 
               
               
                   
               
               
                   
                 Total 
                 Thin Face 
                 Thin Face 
                 Thin  
                 ICT 
                   
               
               
                 Club  
                 Face Area  
                 Area 
                 Thickness 
                 Face 
                 Region 
                 FPSPSA 
               
               
                 head 
                 (mm 2 ) 
                 (mm 2 ) 
                 (mm) 
                 Area % 
                 (mm 2 ) 
                 (mm 2 ) 
               
               
                   
               
             
            
               
                 3-iron 
                 2,763 
                 1,906 
                 2.4 
                 68 
                 314 
                 2,220 
               
               
                 6-iron 
                 2,974 
                 1,892 
                 2.4 
                 63 
                 314 
                 2,206 
               
               
                 9-iron 
                 3,376 
                 1,926 
                 2.4 
                 57 
                 314 
                 2,240 
               
               
                 Wedge 
                 3,421 
                 1,741 
                 2.4 
                 50 
                 314 
                 2,055 
               
               
                   
               
            
           
         
       
     
     Example 6 
       
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 6 
               
               
                   
               
               
                   
                 Total 
                 Thin Face 
                 Thin Face 
                 Thin  
                 ICT 
                   
               
               
                 Club  
                 Face Area  
                 Area 
                 Thickness 
                 Face 
                 Region 
                 FPSPSA 
               
               
                 head 
                 (mm 2 ) 
                 (mm 2 ) 
                 (mm) 
                 Area % 
                 (mm 2 ) 
                 (mm 2 ) 
               
               
                   
               
             
            
               
                 3-iron 
                 2,790 
                 1327 
                 2.5 
                 47 
                 239 
                 1,567 
               
               
                 6-iron 
                 2,958 
                 1426 
                 2.5 
                 48 
                 292 
                 1,719 
               
               
                 9-iron 
                 3,150 
                 1313 
                 2.5 
                 41 
                 308 
                 1,621 
               
               
                 Wedge 
                 3,301 
                 1314 
                 2.5 
                 39 
                 313 
                 1,627 
               
               
                   
               
            
           
         
       
     
     Example 7 
       
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 7 
               
               
                   
               
               
                   
                 Total 
                 Thin Face 
                 Thin Face 
                 Thin  
                 ICT 
                   
               
               
                 Club  
                 Face Area  
                 Area 
                 Thickness 
                 Face 
                 Region 
                 FPSPSA 
               
               
                 head 
                 (mm 2 ) 
                 (mm 2 ) 
                 (mm) 
                 Area % 
                 (mm 2 ) 
                 (mm 2 ) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 3-iron 
                 3,153 
                 1459 
                 1.9 
                 46 
                 1,136 
                 2,595 
               
               
                 6-iron 
                 3,104 
                 1118 
                 2.2 
                 36 
                 1,134 
                 2,253 
               
               
                 9-iron 
                 3,150 
                 920 
                 2.5 
                 29 
                 969 
                 1,889 
               
               
                 Wedge 
                 3,348 
                 922 
                 2.5 
                 27 
                 1,017 
                 1,939 
               
               
                   
               
            
           
         
       
     
     The tabulated values are representative and other configurations can be provided as described herein. It should be noted, in the above examples, that the larger the thin face area percentage and thin face area, the more mass savings can be achieved in the first piece striking plate. In addition, the first piece striking plate rear surface area surrounded by the weld bead can be an indication of how much mass savings is achieved. A balance is achieved by the FPSPSA to achieve mass savings while also locating the weld bead in an advantageous position away from a hinge area and return wall to achieve a reliably high COR with a thin face. Also, locating the weld bead away from the hinge region will reduce the possibility of corrosion and rust in the hinge region over time. 
       FIG. 10  illustrates another embodiment having similar characteristics of the embodiment shown in  FIG. 9 . A golf club head  1000  includes a first piece striking plate  1002 , a rear piece  1004 , an ICT region  1006 , a center point  1014 , a return wall  1016 , a thin face area  1008 , and a weld bead  1010 . The weld bead  1010  is strategically located in a low stress zone located within the thin face area  1008 . In one embodiment, a zone having the lowest stress is identified in order to place the weld  1010  in such a zone. Strategically placing the weld  1010  in a low stress zone reduces the likelihood that the weld will mechanically fail upon impact.  FIG. 10  further shows the weld  1010  being non-conforming with the peripheral contour of the return wall  1016 . In other words, the weld contour  1010  across the face plane is independent of the return wall contour. The same thin face area and thin face thickness dimensions of Tables 1-7 can be achieved. 
       FIG. 11  illustrates yet another embodiment of a golf club head  100  including a first piece striking plate  1102 , a second piece  1104 , a thin face area  1108 , a weld bead  1110 , a center point  1114 , and a rear wall contour  1116 . The inverted cone region is no longer present and the thin face area  1108  is a constant flat thickness (with some manufacturing tolerance variation) across the entire surface of the first piece striking plate  1102 . The weld bead  1110  is offset from the rear wall contour  1116  by a distance, a1, as similarly described above. 
     The exemplary golf club heads (examples 8-9) in Tables 8 and 9 below are similar in construction to the embodiment shown in  FIG. 11 . The ICT Region is not applicable since the first piece striking plate  1102  is a constant thickness. Therefore, the thin face area and the first piece striking plate area surrounded by the weld bead are the same. 
     Example 8 
       
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 8 
               
               
                   
               
               
                   
                 Total 
                 Thin Face 
                 Thin Face 
                 Thin  
                 ICT 
                   
               
               
                 Club  
                 Face Area  
                 Area 
                 Thickness 
                 Face 
                 Region 
                 FPSPSA 
               
               
                 head 
                 (mm 2 ) 
                 (mm 2 ) 
                 (mm) 
                 Area % 
                 (mm 2 ) 
                 (mm 2 ) 
               
               
                   
               
             
            
               
                 3-iron 
                 2,918 
                 1,205 
                 2.1 
                 41 
                 NA 
                 1,205 
               
               
                 6-iron 
                 3,068 
                 1,216 
                 2.1 
                 40 
                 NA 
                 1,216 
               
               
                 9-iron 
                 3,220 
                 1,091 
                 2.1 
                 34 
                 NA 
                 1,091 
               
               
                 Wedge 
                 3,440 
                 1,067 
                 2.1 
                 31 
                 NA 
                 1,067 
               
               
                   
               
            
           
         
       
     
     Example 9 
       
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 9 
               
               
                   
               
               
                   
                 Total 
                 Thin Face 
                 Thin Face 
                 Thin  
                 ICT 
                   
               
               
                 Club  
                 Face Area  
                 Area 
                 Thickness 
                 Face 
                 Region 
                 FPSPSA 
               
               
                 head 
                 (mm 2 ) 
                 (mm 2 ) 
                 (mm) 
                 Area % 
                 (mm 2 ) 
                 (mm 2 ) 
               
               
                   
               
             
            
               
                 3-iron 
                 2,782 
                 672 
                 2.0 
                 24 
                 NA 
                 672 
               
               
                 6-iron 
                 2,958 
                 681 
                 2.0 
                 23 
                 NA 
                 681 
               
               
                 9-iron 
                 3,159 
                 576 
                 2.0 
                 18 
                 NA 
                 576 
               
               
                 Wedge 
                 3,354 
                 489 
                 2.0 
                 14 
                 NA 
                 489 
               
               
                   
               
            
           
         
       
     
     In the examples provided in Tables 1-9, a total face area can be in a range of about 2,700 mm 2  to about 3,500 mm 2 . The FPSPSA can be in a range of about 300 mm 2  to about 4,000 mm 2 , or preferably 450 mm 2  to about 2,600 mm 2 . The thin face thickness can be in a range of about 1.0 mm-3.0 mm, preferably 1.5-2.5 mm, and also preferably in a range of about 1.6-2.0 mm. In certain embodiments, the thin face thickness is less than about 2.0 mm. The thin face area percentage can be in a range of about 13-70%. In embodiments having an ICT region, the ICT region surface area can range from about 230 mm 2  to about 2,000 mm 2 . 
       FIG. 12A  illustrates a cavity back golf club head  1200  including a club head portion  1202  and a badge  1204  (or third piece). The club head portion  1202  includes the entire welded club head assembly having a rear weld bead  1204 , as similarly described above. The front weld bead has been removed and polished according to the operations described above. However, the rear weld bead  1204  is not removed or polished and remains exposed in the cavity and visible to a user prior to the attachment of a badge  1204 . Instead of incurring addition manufacturing cost in removing the weld bead  1204 , the badge  1204  is adhesively bonded to the rear surface of the striking face of the club head  1200 . The badge obscures the weld bead  1204  so that no visual difference can be observed by the user. Applying the badge  1204  allows a weld to be placed on the face of the iron with minimal cost. Furthermore, the badge  1204  can have desirable effects on sound and vibration dampening upon impact with a golf ball. 
       FIG. 12B  illustrates an assembled view of the golf club head  1200  where the badge  1204  has been adhesively applied with epoxy or any known adhesive. For example, an epoxy such as 3M® DP460 can be used. It is possible for the badge  1204  to be mechanically attached to the club head portion  1202 . 
       FIG. 13  illustrates a series of operations  1300  that are accomplished in utilizing a badge to cover a rear face weld bead. Initially, a weld is placed on the face of an iron-type golf club in the first operation  1302 . A weld bead likely occurs on the front face portion and within the rear cavity portion of the golf club head. The weld bead or weld marks are removed from the front face of the golf club head while allowing the rear weld bead to remain intact in a second operation  1304 . Finally, the rear exposed weld that is visible in the cavity is covered by an adhesively or mechanically attached  1306  badge thereby reducing the cost of manufacturing and additional processing operations. 
     It is understood that the rear exposed weld can be partially covered by a badge or part of the rear piece (or second piece) so that at least a portion of the weld is visible within the cavity region. In some embodiments, 50% or more of the rear weld bead may be exposed or visible (while 50% or less is covered) in the cavity back region without departing from the scope of the present invention. 
     At least one advantage of the embodiments described is that dimensional uniformity is achieved in the hinge region of the golf club head. Therefore, the likelihood of a “wall blowout” or failure in the hinge region is avoided. Also, the weld is capable of being placed in a high stress location (such as on the face) due to the use of high strength materials which provide additional stability to the weld line. 
     At least another advantage of the embodiments described is that the weld bead being located away from the hinge region and on the face of the golf club head allows a badge to be placed in the cavity region of the club head with minimal or no manufacturing processing. 
     At least another advantage of the embodiments described is that a thin face and high COR golf club can be achieved by providing further dimensional stability in the hinge region. 
     The components of the above described components disclosed in the present specification can be formed from any of various suitable metals or metal alloys. 
     In addition to those noted above, some examples of metals and metal alloys that can be used to form the components of the connection assemblies include, without limitation, carbon steels (e.g., 1020 or 8620 carbon steel), stainless steels (e.g., 304 or 410 stainless steel), PH (precipitation-hardenable) alloys (e.g., 17-4, C450, or C455 alloys), titanium alloys (e.g., 3-2.5, 6-4, SP700, 15-3-3-3, 10-2-3, or other alpha/near alpha, alpha-beta, and beta/near beta titanium alloys), aluminum/aluminum alloys (e.g., 3000 series alloys, 5000 series alloys, 6000 series alloys, such as 6061-T6, and 7000 series alloys, such as 7075), magnesium alloys, copper alloys, and nickel alloys. 
     In view of the many possible embodiments to which the principles of the disclosed invention may be applied, it should be recognized that the illustrated embodiments are only preferred examples of the invention and should not be taken as limiting the scope of the invention. It will be evident that various modifications may be made thereto without departing from the broader spirit and scope of the invention as set forth. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.