Patent Publication Number: US-9884231-B2

Title: Multi-material iron type golf club head

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present invention is a Continuation-in-Part of U.S. patent application Ser. No. 14/585,688, filed on Dec. 30, 2014, which is a Continuation-in-Part of U.S. patent application Ser. No. 14/512,270, filed on Oct. 10, 2014, which is Divisional of U.S. patent application Ser. No. 13/894,660, filed on May 15, 2013, now U.S. Pat. No. 8,870,683, which is a Continuation of U.S. patent application Ser. No. 13/043,985, filed on Mar. 9, 2011, now U.S. Pat. No. 8,454,453, the disclosure of each incorporated by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to an iron type golf club head that utilizes different materials to improve the performance of the golf club head. More specifically, the present invention relates to a golf club head that utilizes different materials to construct different portions of the iron type golf club head in order to reduce weight from undesirable portions of the golf club head; all while maintaining the strength and durability characteristics typically associated with a golf club head that is formed out of a unitary material. Because the performance of a golf club head is so dependent upon the Center of Gravity (CG) location as well as the Moment of Inertia (MOI) of the golf club head itself, saving weight from undesirable portions of the golf club head creates more discretionary weight, which can be placed at strategic locations that improves the CG and MOI characteristics of the golf club head. Hence, the golf club head in accordance with the present invention achieves both of the objectives mentioned above by increasing the amount of discretionary weight to improve performance while maintaining the solid feel generally associated with a solid unitary golf club. 
     BACKGROUND OF THE INVENTION 
     In order to continually improve the performance of a golf club, golf club designers are constantly searching for new and innovative ways make a golf club perform better. Although what constitutes better performance for golf club is debatable, the great popularity of the game of golf has required golf club designers to create a golf club that performs better for your average everyday golfer, who may not have the perfect golf game day in and day out. 
     It is worthwhile to recognize here that when your average golfer swings a golf club, he or she may not always have a replicable golf swing; often resulting in the golf club impacting the golf ball at different locations on the golf club face. Needless to say, it is difficult for any golf club to achieve consistent result when the impact between the golf club and the golf ball isn&#39;t consistent. Although this specific problem with impact consistency decreases with an increase in experience and skill level, it is something that even the best golfer will inevitably struggle with from time to time. Hence, in order to address this issue of inconsistency of impact that can lead to inconsistent performance, golf club designers need to come up with golf clubs that can minimize the undesirable effects from such off-center impact. U.S. Pat. No. 5,395,113 to Antonious provides one example of one of the earlier attempt to address this issue by providing an iron type golf club with a weight configuration that utilizes peripheral weights that extend around a rear surface of the club head. Without going into too much physics about the MOI of a golf club head as well as the CG location, the shifting of these weights shown by U.S. Pat. No. 5,395,113 address the problem of inconsistent impact by prohibiting the golf club head from twisting when it is struck off center. 
     U.S. Pat. No. 7,789,772 to Sukman provides another example of a methodology used to minimize the adverse effects of inconsistent impact by adjusting the thicknesses of various portions of the golf club head. More specifically, U.S. Pat. No. 7,789,772 discloses a golf club head comprising of a sink portion having a variation in heel-to-toe contour while maintaining a low-order front-to-rear contour resulting in an iron type golf club having a unique weighting distribution. 
     Although the above mentioned attempts to improve the performance of the golf club in terms of manipulating the thicknesses at various portions of the golf club head are admirable, they fail to take in consideration of the performance gains that are possible by using alternative materials having different densities that could accentuate the weighting affects. Recent golf club designers, in order to further improve the performance of a golf club head, have recognized the performance advantages that could be achieved using alternative materials by experimenting with materials having different densities. U.S. Pat. No. 6,814,674 to Clausen et al. illustrates one of the more recent attempts that incorporate different components to construct a golf club head. More specifically, U.S. Pat. No. 6,814,674 discloses three different components, a periphery member, a central member, and a face plate; all made out of different materials to improve the CG and MOI of the golf club head by creating more discretionary weight than previously possible. 
     Although these recent attempts at utilizing multiple materials having different material properties can dramatically increase the amount of discretionary weight, it does so at the expense of sacrificing the feel of a golf club head. Feel of a golf club head, although a difficult criteria to quantify, generally results from the capability of a golf club to feel solid upon impact with the golf ball. This type of solid feedback is generally achieved by having the golf club head formed out of a unitary solid structure, as the structural integrity of this type of unitary solid structure clubs allows the energy of the impact to be felt by a golfer in a consistent manner. 
     Hence, it can be seen from above, there exists a need for a golf club to provide a more even balance between forgiveness and feel. More specifically, there is a need in the field for a golf club head that utilizes a substantially uniform material throughout the body portion of the golf club head to maintain the feel that is generally associated with a solid golf club; all while pushing the boundaries of performance by creating the maximum discretionary weight that can be used to improve the MOI and CG location of the golf club head. 
     BRIEF SUMMARY OF THE INVENTION 
     One non-limiting embodiment of the present technology includes an iron type golf club head comprising: a blade portion located near a terminal end of said iron type golf club head, said blade portion defining a striking face adapted for striking a golf ball and a rear surface, wherein over 50% of said blade portion is made out of a first material; a hosel portion located near a proximal end of said iron type golf club head, wherein over 50% of said hosel portion is made out of a second material; and a bifurcation plane defined as a plane that is perpendicular to said striking face positioned at a distance of 30 mm heel-ward along an X-axis from a face center of said iron type golf club head, said bifurcation plane separating said blade portion from said hosel portion; wherein said first material has a yield strength greater than about 570 MPa; wherein said second material has a yield strength less than about 570 MPa. 
     In an additional non-limiting embodiment of the present technology over 70% of said blade portion is made out of a first material and wherein over 70% of said hosel portion is made out of a second material. 
     In an additional non-limiting embodiment of the present technology over 90% of said blade portion is made out of a first material and wherein over 90% of said hosel portion is made out of a second material. 
     In an additional non-limiting embodiment of the present technology said first material comprises greater than 0.10% carbon content by weight and wherein said second material comprises less than 0.10% carbon content by weight. 
     In an additional non-limiting embodiment of the present technology said first material comprises greater than 0.10% carbon content by weight and wherein said second material comprises less than 0.10% carbon content by weight. 
     In an additional non-limiting embodiment of the present technology said first material is 17-4 stainless steel and said second material is 304 stainless steel. 
     In an additional non-limiting embodiment of the present technology said first material is 17-4 stainless steel and said second material is 304 stainless steel. 
     An additional non-limiting embodiment of the present technology includes an iron type golf club head comprising: a blade portion located near a terminal end of said iron type golf club head, said blade portion defining a striking face adapted for striking a golf ball and a rear surface, wherein over 50% of said blade portion is made out of a first material; a hosel portion located near a proximal end of said iron type golf club head, wherein over 50% of said hosel portion is made out of a second material; and a bifurcation plane defined as a plane that is perpendicular to said striking face positioned at a distance of 30 mm heel-ward along an X-axis from a face center of said iron type golf club head, said bifurcation plane separating said blade portion from said hosel portion; wherein said blade portion has an average Brinell HB hardness greater than about 275; wherein said hosel portion has an average Brinell HB hardness less than about 275. 
     In an additional non-limiting embodiment of the present technology said hosel portion has an average Brinell HB hardness less than about 250. 
     In an additional non-limiting embodiment of the present technology said hosel portion has an average Brinell HB hardness less than about 225. 
     In an additional non-limiting embodiment of the present technology said hosel portion has an average Brinell HB hardness less than about 200. 
     In an additional non-limiting embodiment of the present technology said hosel portion has an average Brinell HB hardness less than about 175. 
     In an additional non-limiting embodiment of the present technology said hosel portion has an average Brinell HB hardness less than about 150. 
     In an additional non-limiting embodiment of the present technology said hosel portion has an average Brinell HB hardness less than about 125. 
     An additional non-limiting embodiment of the present technology includes a method of forming an iron type golf club head comprising: providing a blade portion in the form of a rod, said blade portion made out of greater than 50% of a first material having a first yield strength; providing a hosel portion in the form of a rod, said hosel portion out of greater than 50% of a second material having a second yield strength; welding said blade portion together with said hosel portion into a pre-form billet; forging said pre-form billet into a desired shape for said iron type golf club head; wherein said first yield strength is greater than about 570 MPa; wherein said second yield strength is less than about 570 MPa; wherein the separation between said blade portion and said hosel portion is defined by a bifurcation plane, defined as a plane that is perpendicular to a striking face of said iron type golf club head, positioned at a distance of 30 mm heel-ward along an X-axis from a face center of said iron type golf club head; 
     In an additional non-limiting embodiment of the present technology over 70% of said blade portion is made out of a first material and wherein over 70% of said hosel portion is made out of a second material. 
     In an additional non-limiting embodiment of the present technology over 90% of said blade portion is made out of a first material and wherein over 90% of said hosel portion is made out of a second material. 
     In an additional non-limiting embodiment of the present technology said blade portion in the form of a rod further comprises a first locating feature and wherein said hosel portion in the form of a rod further comprises a second locating feature, wherein said first locating feature is configured to cooperate with said second locating feature to locate said blade portion relative to said second portion during welding. 
     An additional non-limiting embodiment of the present technology includes rotating said blade portion in the form of a rod relative to said hosel portion in the form of a rod, locking said blade portion to said hosel portion. 
     An additional non-limiting embodiment of the present technology includes welding around the perimeter of the intersection of said blade portion in the form of a rod and said hosel portion in the form of a rod. 
     An additional non-limiting embodiment of the present invention includes a method of forming an iron type golf club head comprising of the steps of partially forging a blade portion of said golf club head with a cavity near a bottom sole portion of said blade portion, partially forging a hosel portion of said golf club head, and joining said blade portion to said hosel portion to create a partially forged golf club head before forging said partially forged golf club head into said golf club head. 
     An additional non-limiting embodiment of the present invention includes an iron type golf club head comprising a blade portion including a heel muscle region, made out of a first material, located near a terminal end of the iron type golf club head, the blade portion defining a striking face adapted for striking a golf ball, a hosel portion, made out of a second material, located near a proximal end of the iron type golf club head, and wherein the blade portion including the heel muscle region is forged from a unitary piece of material, and wherein the first material has an average Brinell HB hardness greater than 375. 
     These and other features, aspects and advantages of the present invention will become better understood with references to the following drawings, description and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features and advantages of the invention will be apparent from the following description of the invention as illustrated in the accompanying drawings. The accompanying drawings, which are incorporated herein and form a part of the specification, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. 
         FIG. 1  shows a perspective view of a golf club head in accordance with an exemplary embodiment of the present invention; 
         FIG. 2  shows a perspective view of a pre-form billet used to create a golf club head in accordance with an exemplary embodiment of the present invention; 
         FIG. 3 a    shows a perspective view of a pre-form billet used to create a golf club head in accordance with an alternative embodiment of the present invention; 
         FIG. 3 b    shows a perspective view of a pre-form billet used to create a golf club head in accordance with an alternative embodiment of the present invention; 
         FIG. 4  shows an exploded perspective view of a golf club head in accordance with an exemplary embodiment of the present invention; 
         FIG. 5  shows a frontal view of a golf club head in accordance with an exemplary embodiment of the present invention that defines a coordinate system; 
         FIG. 6  shows a perspective view of a golf club head without a sole insert in accordance with an exemplary embodiment of the present invention; 
         FIG. 7  shows an exploded perspective view of a golf club head in accordance with an exemplary embodiment of the present invention; 
         FIG. 8  shows a frontal view of a sole insert in accordance with an exemplary embodiment of the present invention. 
         FIG. 9  shows a frontal view of a golf club head in accordance with an exemplary embodiment of the present invention 
         FIG. 10  shows a perspective view of a pre-form billet used to create a golf club head in accordance with an exemplary embodiment of the present invention; 
         FIG. 11A  shows a perspective view of a blade portion in the form of a rod and a hosel portion in the form of a rod in accordance with an exemplary embodiment of the present invention; 
         FIG. 11B  shows a perspective view of a pre-form billet used to create a golf club head in accordance with an exemplary embodiment of the present invention; 
         FIG. 12A  shows a perspective view of a blade portion in the form of a rod and a hosel portion in the form of a rod, each including a locating feature, in accordance with an exemplary embodiment of the present invention; 
         FIG. 12B  shows a perspective view of a pre-form billet used to create a golf club head in accordance with an exemplary embodiment of the present invention; 
         FIG. 13A  shows an exploded perspective view of a partially forged components of a golf club head in accordance with an alternative embodiment of the present invention; 
         FIG. 13B  shows a perspective view of the golf club head in accordance with an alternative embodiment of the present invention before the final forging step; 
         FIG. 14  shows a perspective view of a finished golf club head in accordance with the alternative embodiment of the present invention; 
         FIG. 15  shows a rear exploded perspective view of the finished golf club head in accordance with an alternative embodiment of the present invention; and 
         FIG. 16  shows a frontal exploded view of the finished golf club head in accordance with an alternative embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims. 
     Various inventive features are described below that can each be used independently of one another or in combination with other features. However, any single inventive feature may not address any or all of the problems discussed above or may only address one of the problems discussed above. Further, one or more of the problems discussed above may not be fully addressed by any of the features described below. 
       FIG. 1  of the accompanying drawings shows a perspective view of a golf club head  100  in accordance with an exemplary embodiment of the present invention. More specifically,  FIG. 1  shows a golf club head  100  comprising out of three separate and distinct metallic alloy parts. First, the golf club head  100  shown in the current exemplary embodiment of the present invention may comprise a blade portion  102  located near a terminal end of the golf club head, wherein the blade portion  102  is made out a lightweight iron-aluminum alloy material to save weight from the blade portion  102  of the golf club head. Secondly, the golf club head  100  may comprise a hosel portion  104  located near a proximal end of the golf club head, wherein the hosel portion  104  is made out of a conventional carbon steel material to preserve the traditional performance needs of a sturdy hosel portion. Finally, golf club head  100  may have a sole insert  106  located near a bottom of the golf club head, wherein the sole insert  106  is made out of a heavy tungsten alloy material to shift the discretionary weight saved from the blade portion  102  to a location that can be controlled using the heavier denser material. It should be noted that the materials discussed above for the various components are only illustrative and shouldn&#39;t be construed as exhaustive; other materials may be used in other embodiments of the present invention without departing from the scope and content of the present invention so long as it meets the density requirements below. 
     Blade portion  102  of the golf club head  100 , as shown in the current exemplary embodiment, may generally be comprised out of a first material that has a first density of less than about 7.10 grams/cc, more preferably less than about 7.05 grams/cc, and most preferably less than about 7.00 grams/cc. In one exemplary embodiment, this first material may be a lightweight iron-aluminum material for its lightweight property; however, numerous other lightweight metallic materials may be used to achieve the same weight savings without departing from the scope and content of the present invention. Hosel portion  104  of the current inventive golf club head  100  may generally be comprised out of a second material having a second density of between about 7.75 grams/cc to about 7.95 grams/cc, more preferably between about 7.80 grams/cc to about 7.90 grams/cc, and most preferably about 7.85 grams/cc. In one exemplary embodiment, this second material may be a standard carbon steel for its strength and malleable characteristics, however, numerous other materials may be used without departing from the scope and content of the present invention so long as it has a second density in the ranges described above. Sole insert  106  of the golf club head  100  may generally be comprised out of a third material having a third density of greater than about 11.00 grams/cc, more preferably greater than about 11.50 grams/cc, and most preferably greater than about 12.00 grams/cc. In one exemplary embodiment, this third material may be a tungsten alloy for its heavy density characteristics; however, numerous other materials may be used without departing from the scope and content of the present invention so long as it has a third density in the range described above. 
     Although the current exemplary embodiment is illustrated using three different materials to create the blade portion  102  of the golf club head  100 , additional materials may be used without departing from the scope and content of the present invention. More specifically, the blade portion  102  may be constructed out of four different materials, five different materials, six different materials, or any number of different materials without departing from the scope and content of the present invention. 
     It is worth noting here that the first, second, and third material used in this current exemplary embodiment of the present invention may all generally be a metallic type material that can be easily welded to one another. This ability of the various components to be easily welded to one another provides great performance advantage because it allows the finished product to maintain a consistent solid feel; something that is difficult to accomplish when contrasting materials such as a metal and a plastic are combined to form a golf club head. In a current exemplary embodiment of the present invention shown in  FIG. 1 , the blade portion  102  and the hosel portion  104  may generally be forged from a single pre-form billet is spin welded together from two individual rods, allowing the finished product to achieve the solid structural integrity generally associated with a golf club formed from a uniform material. Once the pre-form billet is forged into its desired shape, a sole cavity may cut out using a cutter to create space for the sole insert  106 ; which itself may be welded into its final resting place within the golf club head  100 . 
       FIG. 2  of the accompanying drawings shows a perspective view of a pre-form billet  200  used to form the golf club head  100  shown in  FIG. 1 . Per-form billet  200 , as shown in  FIG. 2  may generally have a blade portion  202  and a hosel portion  204  separated by a bifurcation plane  203 . The blade portion  202  and the hosel portion  204  are generally spun welded together using traditional friction welding techniques. Friction welding, as discussed in this current application, may generally refer to a solid-state welding process that generates heat through mechanical friction between a moving workpiece and a stationary component, with the addition of a lateral force called “an upset” to plastically displace and fuse the materials together. Although actual no melting of the material occurs, this process is commonly known as friction welding due to the fact that it is capable of combining two materials together. Preferably, spin welding techniques that uses traditional friction welding is used in this current exemplary embodiment, however, other attachment techniques can be used without departing from the scope and content of the present invention so long as it is capable joining two different materials into a pre-form billet  200 . 
       FIG. 3 a    of the accompanying drawings shows a pre-form billet  300  in accordance with an alternative embodiment of the present invention that can be used to achieve the same weight savings by pre-form billet  200  shown in  FIG. 2  using a different construction. More specifically, pre-form billet  300  in this alternative embodiment of the present invention, may have a lightweight material  320  being wrapped around by a denser material  322  to create the pre-form billet  300  that is capable of achieving the same lightweight properties needed by the golf club head  100  (shown in  FIG. 1 ). In this current exemplary embodiment of the present invention the lightweight material  320  may have a density of less than about 7.10 grams/cc, more preferably less than about 7.05 grams/cc, and most preferably less than about 7.00 grams/cc; while the denser material  322  may have a density of between about 7.75 grams/cc to about 7.95 grams/cc, more preferably between about 7.80 grams/cc to about 7.90 grams/cc, and most preferably about 7.85 grams/cc. 
       FIG. 3 b    of the accompanying drawings shows a further alternative embodiment of the present invention wherein the pre-form billet  300  could have dense materials  322  placed at strategic locations within the pre-form billet  300  that is substantially constructed out of a lightweight material  320 . In this current exemplary embodiment of the present invention, the golf club head  300  could be formed in a way to allow for strategic adjustment of the weighting characteristics of a golf club head without the need for post operations. In the embodiment shown in  FIG. 3 b    the placement of the dense materials  322  within the pre-form billet  300  may coincide with the a lower heel and lower toe portion of a golf club head to increase the moment of inertia of the finalized product without departing from the scope and content of the present invention. Although the current exemplary embodiment utilizes dense materials  322  embedded within a lightweight material  320 , the actual densities of the relative components could be adjusted to meet the weighting needs of a golf club head without being restricted to the drawing provided in  FIG. 3   b.    
       FIG. 4  of the accompanying drawings showing an exploded view of golf club head  400  with the sole insert  406  shifted out from the body of the golf club head  400  to provide a clearer illustration of the relationship of the various components. More specifically  FIG. 4  of the accompanying drawings shows the golf club head  400  having the same blade portion  402 , the same hosel portion  404 , and the same sole insert  406  as previously discussed; however, the exploded view of the golf club head  400  shown in  FIG. 4  allows the sole cavity  405  to be shown. Sole cavity  405 , as shown in the current exemplary embodiment, may generally be cut out from the forged blade portion  402  and the hosel portion  404  spanning across both of these portions to cover a significant portion of the golf club head  400 . Because Blade portion  402  and the hosel portion  404  are generally spun welded together to form a pre-form billet, the golf club head  400  may generally be created using a forged process to maintain the separation of the two different components. However, in alternative embodiment of the present invention, golf club head  400  may be formed using different process such as a casting process if alternative methodologies allow the separation between the blade portion  402  and the hosel portion  404  to be maintained without departing from the scope and content of the present invention. 
     The exploded view of golf club head  400  shown in  FIG. 4  also allows the sole profile of the golf club head  400  to be shown as it relates to the sole insert  406 . More specifically, sole insert  406 , in accordance with the current exemplary embodiment of the present invention, may generally have an outer surface that has a shape being congruent with the external curvatures of the sole of the golf club head. Alternatively speaking, the outer sole surface of the sole insert  406  has a shape that compliments the contour of the perimeter of the sole cavity  405 . 
     In addition to illustrating the sole cavity  405  more clearly,  FIG. 4  of the accompanying drawings is also capable of showing the size, shape, and geometry of the sole insert  406 . At first glance, it is apparent that the shear volume of the sole insert  406  is significantly greater than prior art dense sole inserts due to the amount of weight that can be saved from the remainder of the golf club head  400  via the usage of the lightweight first material in the blade portion  402 . More specifically, the volume of the sole insert  406 , as shown in this current exemplary embodiment of the present invention, is generally greater than about 7.50 cubic centimeters, more preferably greater than about 7.6 cubic centimeters, and most preferably greater than about 7.69 cubic centimeters. This type of increased volume for the sole insert  406 , combined with the heavier third material used to create the sole insert  406 , may generally yield a sole insert with a total weight of greater than about 90 grams, more preferably greater than about 91 grams, and most preferably greater than about 92 grams. 
     Because the overall weight of an iron type golf club head  400  is generally kept consistent at about 240 grams to about 250 grams, the ability to achieve a sole insert  406  in the weight ranges discussed above must be accompanied by a significant weight reduction at alternative locations of the golf club head  400 . Recognizing this, it is worthwhile to explain that the present invention achieves this weight reduction by minimizing the weight of the blade portion  402  of the golf club head  400  via a lightweight first material for the entire blade portion of the golf club head  400 . More specifically, the present invention utilizes a low density iron-aluminum alloy material as one way achieve this significant amount of weight reduction; however numerous other types of material may be used to reduce the overall weight of the blade portion  402  of the golf club head  400  without departing from the scope and content of the present invention. 
     In order to further explain the ability of the current inventive golf club head  400  to incorporate a blade portion  402  that is made out of a first material while maintaining a hosel portion  404  that is made out of a second material,  FIG. 5  is presented here showing a frontal view of a golf club head  500  in accordance with an exemplary embodiment of the present invention allowing the blade portion  502  and the hosel portion  504  to be more clearly defined. 
     Golf club head  500  in accordance with the exemplary embodiment of the present invention shown in  FIG. 5  may generally show a “face center”  508  as well as a bifurcation plane  503 . “Face center”  508 , as defined in the current application, does not actually refer to the geometric center of the striking face itself, but in reality refer to an easily replicable location based off the scorelines on the striking face of the golf club head  500 . More specifically, “face center”  508 , as referred to in the current application, is located on the striking face plane at a location that is at the midpoint along the length of the scorelines along the X-axis of the coordinate system  501  and at a point that is 15 mm away from the ground  510  along the Y-axis of the coordinate system  501 . The location of this “face center”  508  is crucial in the current invention because the bifurcation plane  503  that separates the blade portion  502  from the hosel portion  504  is defined based off this “face center”  508 . Bifurcation plane  503 , as defined in the current application, may generally refer to a plane that is perpendicular to the striking face plane and located at a distance d 1  of exactly 30 mm heel-ward from the “face center”  508  of the golf club head  500  along the X-axis. 
     Because the bifurcation plane  503  is defined by the “face center”  508 , whose exact location could differ when different scoreline patterns are used, the exact separation between the two portions are not necessarily captured by the bifurcation plane  503 . However, the bifurcation plane  503  is useful in determining the amount of weight that can be removed from the blade portion  502  of the golf club head  500  by utilizing the lightweight first material discussed earlier. More specifically, a ratio of the weight of the blade portion  502 ; defined by the portion of the golf club head  500  that is toe-ward from the bifurcation plane  503 , divided by the weight of the hosel portion  504 ; defined by the portion of the golf club head  500  that is heel-ward from the bifurcation plane  503 , is generally less than about 2.0, more preferably less than about 1.90, and most preferably less than about 1.80. In order to achieve the ratio above, the weight of the blade portion  502  may generally be less than about 110 grams, more preferably less than about 105 grams, and most preferably less than 100 grams; while the weight of the hosel portion  504  may generally be greater than about 55 grams, more preferably greater than about 55.25 grams, and most preferably greater than about 55.5 grams. 
     It should be noted here that in this current exemplary embodiment of the present invention, the ratio of the weights of the blade portion  502  relative to the hosel portion  304  excludes the weighted sole insert  506 . Despite the clear concise definition given above for the boundaries between the blade portion  502  and the hosel portion  504 , the boundaries of the sole insert  506  to be excluded from the relative weight above is less obvious. Hence, in order to provide a clearer definition about the boundaries of the sole insert  506 , the present invention provides several different methodologies; which can all be used interchangeably to define the boundaries of the sole insert  506 . 
     In one exemplary embodiment of the present invention, the boundaries of the sole insert  506  can be defined as portion of the golf club head that is made out of a third material having a density of greater than 10.0 grams/cc. Under this current definition the boundary of the sole insert  506  from the remainder of the body of the golf club head  500  is easily identifiable because they are formed from two very distinct materials having very different densities. Alternatively, in another exemplary embodiment of the present invention, the boundaries of the sole insert  506  can be defined by using geometric shapes defined using the sole cavity (shown in  FIG. 4 ). In order to provide a clearer view of the sole cavity in a way that allows it to be easily defined geometrically,  FIG. 6  is provided to show the boundaries of the sole cavity  605 . 
       FIG. 6  of the accompanying drawings shows a perspective view of a golf club head  600  in accordance with an exemplary embodiment of the present invention oriented in a way to illustrate the boundaries of the sole insert  506  (shown in  FIG. 5 ) through the sole cavity  605 . More specifically,  FIG. 6  shows how the sole cavity  605  can be defined geometrically by the amount of offset from the planar striking face  610  of the golf club head. Alternatively speaking, sole cavity  605  can be formed by a cut that is offset by a distance d 2  of 2.8 mm away from the striking face  610  of the golf club head  600 . In order to maintain a consistent thickness at the frontal portion and the rear portion of the golf club head  600 , the cut used to form the rear surface of the sole cavity  605  may also be offset by a distance d 2  of 2.8 mm away from the rear surface  612  of the golf club head  600 . It is worth recognizing that in this current exemplary embodiment of the present invention the rear surface  612  of the golf club head  600  may be a curved surface, hence sole cavity  605  may have a curved surface near the rear surface  612  to match. Finally, the depth of the cut of the sole cavity  605  within the current embodiment may generally be defined by a distance d 3  of 34 mm, measuring from the top surface of the sole onto the bottom surface of the sole cavity  605 . 
     The view of the golf club head  600  provided in  FIG. 6  provides another interesting feature of the present invention in creating the sole cavity  605  in a unique shape that sandwiches the sole insert (not shown) between the striking face  610  and the rear surface  612 , both of which are substantially planar. The ability of the golf club head  600  to create this sandwich structure is important to maintaining the solid feel of a golf club head  600  that is built from one material, but still be capable of incorporating a significant amount of discretionary weight within the sole insert (not shown) to improve the performance of the golf club head  600 . 
     In summary, the present invention provides a golf club head that is made out of preferably three different materials to achieve the most discretionary weight without sacrificing the solid feel generally associated with a golf club head that is formed using a unitary material. In order to provide a comprehensive view of the three different materials,  FIG. 7  is provided showing an exploded view of all three different of the components that have the different materials. More specifically,  FIG. 7  shows an exploded perspective view of a golf club head  700  in accordance with an exemplary embodiment of the present invention. Here, it can be seen that the blade portion  702  may be separated from the hosel portion  704  at the bifurcation plane  703  to create two different components with different density characteristics. Because the blade portion  702  may be joined together with the hosel  704  using friction welding techniques such as spin welding, the materials are not easily separated, but are exploded from each other in this view for ease of identification. The exploded view of the golf club head  700  shown in  FIG. 7  also allows the sole insert  706  to be shown in its natural state before being assembled into the golf club head  700 . It is worthwhile to note here that the sole insert  706  in accordance with the current exemplary embodiment of the present invention may be where the majority of the weight of the golf club head  700  is focused, as the discretionary weight saved by the blade portion  702  opens up a significant amount of design space for the shape and geometry of the sole insert  706 . Sole insert  706  in accordance with the current exemplary embodiment of the present invention may generally be welded to the blade portion  702  and hosel portion  704  of the golf club head  700 ; however numerous other attachment methods such as swaging, gluing, or even using screws may be used without departing from the scope and content of the present invention. 
       FIG. 8  of the accompanying drawings shows an enlarged perspective view of the sole insert  806  in accordance with an exemplary embodiment of the present invention. This enlarged view of the sole insert  806  illustrates how the discretionary weight saved from the remainder of the golf club head could be used at strategic locations near the bottom of the golf club head to improve the performance of the golf club head. More specifically,  FIG. 8  shows not only an increase in the size of the sole insert  806 , but also the unique geometric shape of the sole insert  806  that indicates the strategic placement of the discretionary weight. Sole insert  806  may generally have a heel portion  832 , a central portion  834 , and a toe portion  836  of varying thicknesses to help not only create a lower CG, but also to increase the MOI of the golf club head. The increase in MOI of the golf club head can be achieved by increasing the thickness of the heel portion  832  and the toe portion  836  relative to the central portion  834 , which in turn, makes the golf club head less susceptible to twisting when it is struck off center. It is also worth recognizing here that because significant amount of weight can be saved from the remainder of the golf club head, the toe portion  836  of the sole insert  806  is capable of extending higher into the toe of the body of the golf club head to provide extreme toe weighting to counteract the weight already designed into the hosel of the golf club head. 
       FIG. 9  of the accompanying drawings shows a front view of a golf club head  900  in accordance with an exemplary embodiment of the present invention. More specifically,  FIG. 9  shows a golf club head  900  comprising a blade portion  902 , and a hosel portion  904 , separated by a bifurcation plane  903 . Additionally,  FIG. 9  illustrates face center  908  of the face of the golf club head  900 . Face center  908 , as referred to in the current application, is located on the striking face plane at a location that is at the midpoint along the length of the scorelines along the X-axis of the coordinate system and at a point that is 15 mm away from the ground  910  along the Y-axis of the coordinate system. The bifurcation plane  903 , as defined in the current application, may generally refer to a plane that is perpendicular to the striking face plane and located at a distance d 9  exactly 30 mm heel-ward from the face center  908  of the golf club head  900  along the X-axis. 
     It can be preferable to manufacture the blade portion  902  and the hosel portion  904  out of different materials, in order to maximize the performance characteristics of the golf club head  900 , while also allowing the golf club head  900  to be modified to fit golfer&#39;s requirements. For example, the hosel portion  904  of the golf club head may need to be bent to alter lie angle or loft. Therefore, it is preferable for the hosel portion  904  of the club head  900  to yield without using extreme force and without cracking. It has been found that it is preferable for the hosel portion  904  to be comprised of a material having a yield strength less than about 570 MPa, to allow for adjustment of lie and loft angle without the use of excessive force. It is preferable however to construct the blade portion  902  out of a high strength material to achieve maximum performance characteristics. Thus, in accordance with an exemplary embodiment of the present invention, the blade portion  902  is made of a first material, and the hosel portion  904  is made of a second material. Additionally, it is preferable that the first material has a higher yield strength than the second material. In some embodiments, the first material has a yield strength greater than about 570 MPa and the second material has a yield strength less than about 570 MPa. In some embodiments, the first material has greater than 0.10% carbon content by weight and the second material has less than 0.10% carbon content by weight. 
     In some embodiments, over 50% of the blade portion  902  is made of a first material and over 50% of the hosel portion  904  is made of a second material. In other embodiments, over 70% of the blade portion  902  is made of a first material and over 70% of the hosel portion  904  is made of a second material. In additional embodiments, over 90% of the blade portion  902  is made of a first material and over 90% of the hosel portion  904  is made of a second material. In additional embodiments, over 95% of the blade portion  902  is made of a first material and over 95% of the hosel portion  904  is made of a second material. 
     Hardness is an additional indication of the strength of different materials, and thus of different portions of the golf club head  900 . Hardness can be tested after a golf club head has been forged. To achieve an average hardness of each portion of the golf club head, greater than 3 tests are completed at random locations around each portion of the golf club head, and then averaged. In some embodiments, as a function of the different materials, the blade portion  902  can have an average Brinell HB hardness greater than about 275. The hosel portion  904  can have an average Brinell HB hardness less than about 275. In other embodiments, hosel portion  904  can have an average Brinell HB hardness less than about 250. In other embodiments, hosel portion  904  can have an average Brinell HB hardness less than about 225. In other embodiments, hosel portion  904  can have an average Brinell HB hardness less than about 200. In other embodiments, hosel portion  904  can have an average Brinell HB hardness less than about 175. In other embodiments, hosel portion  904  can have an average Brinell HB hardness less than about 150. 
     A new and innovative method for forming such a golf club head  900  as illustrated in  FIG. 9  has been developed.  FIG. 10  illustrates a perspective view of a pre-form billet  1000  used to form the golf club head  900 . Pre-form billet  1000  may generally have a blade portion  1002  and a hosel portion  1004  separated by a bifurcation plane  1003 . The blade portion  1002  and hosel portion  1004  can be welded together. In some embodiments, as illustrated in  FIGS. 11A and 11B , blade portion  1102  can be welded together around the perimeter of the bifurcation plane  1103 . In other embodiments they can be spin welded together as described above. In an additional embodiment, as illustrated in  FIGS. 12A and 12B , the blade portion  1202  and the hosel portion  1204  can each incorporate a locating feature  1212 ,  1214 , configured to cooperate with one another and located said blade portion  1202  relative to said hosel portion  1204  during welding. The first locating feature  1212  can comprise a bore and the second locating feature  1214  can comprise a protrusion. These roles can be reversed in another embodiment. As illustrated in  FIG. 12B , the second locating feature  1214  can be coupled to the first locating feature  1212 , and the blade portion  1202  can be welded to the hosel portion  1204 . Subsequently, the pre-form billet  1000 ,  1100 ,  1200  can be forged into a desired shape for the iron type golf club head  900 . In another embodiment, the first locating feature  1212  and second locating feature  1214  could each include threads to further lock the blade portion  1202  to the hosel portion  1204 . Additional mechanical locking features are possible as well. 
     The following is a list of example materials from which the first material could be selected: steel, managing steel, high strength steel, ultra high strength steel, stainless steel, low alloy steel, chrome moly steel, precipitation hardened stainless steel, 17-4, 15-3, 4340, 4140, 4130, Allvac® VascoMax® C300 Specialty Steel, Custom 455® Stainless, Custom 465® Stainless, Custom 475® Stainless, K301 steel etc. (Allvac® is a registered trademark of Vanadium-Alloys Steel Company located in Latrobe Pa.; VascoMax® is a registered trademark of Allvac Metals Company located in Monroe, N.C.; Custom 455®, Custom 465®, and Custom 475® are registered trademarks of Carpenter Technology Corporation located in Reading, Pa.) 
     The following is a list of example materials from which the second material could be selected: steel, stainless steel, plain carbon steel, 304, 431, 1025, 1018, 1020, etc. 
       FIGS. 13A and 13B  shows an alternate embodiment of the present invention wherein the blade portion  1302  and the hosel portion  1304  are pre-forged into shapes that more closely resemble their ultimate shape before they are joined together using the methods discussed above. Ultimately, after the blade portion  1302  and the hosel portion  1304  are joined together, they form a partially forged golf club head that can then be forged again to create the end product without departing from the scope and content of the present invention. Referring to  FIG. 13A , the blade portion  1302  may be partially forged into a shape that more closely resembles the ultimate shape of the striking face of the golf club while the hosel portion  1304  may be also be partially forged into a shape that more closely resembles the ultimate shape of the upper end of the hosel of the golf club. It should be noted that in this intermediary phase of the alternate construction methodology, both the blade portion  1302  and the hosel portion  1304  may have a significant amount of excess material around the perimeter of the forged component. This excess material, generally known as “flash”  1351  may generally need to be trimmed off before the next phase of the manufacturing process. 
     It should be noted that the blade portion  1302  in this current exemplary embodiment may have a cavity  1352  already forged in the lower heel side of the golf club head  1300  to create space for a weight member made out of a dense material. Finally, and most importantly, it should be noted that the blade portion  1302  in this embodiment includes the heel muscle region  1354  that is made out of the same material. This material may generally be a high strength steel having a hardness of greater than Brinell HB greater than 375, because the hosel portion  1304  has been isolated from the blade portion  1302 . Having the blade portion  1302  include the heel muscle region  1354  is critical to the present invention because it allows a significant portion of the striking face portion to be forged out of the same high strength steel material without the need for any welding on the contact surface. 
       FIG. 13B  shows the next step of the manufacturing process in accordance with this alternative embodiment of the present invention. More specifically,  FIG. 13B  shows that the flash  1351  has been trimmed from the blade portion  1302  and the hosel portion  1304 , and those pieces are joined together at the jointed section  1352 . In the figure shown in  FIG. 13B  the location of the jointed section  1352  is only provided as a reference, as the exact location of the jointed section  1352  may shift relative to the blade portion  1302  and the hosel portion  1304 , as the jointed golf club head may need to be subjected to a final forging step that could shift the flow of material. In one preferred embodiment of the present invention, the blade portion  1302  may be joined to the hosel portion  1304  by welding the two pieces together, however, numerous other joining methods such as a threaded attachment, spin welding, mechanical lock, or any other types of joining mechanism may be used without departing from the scope and content of the present invention so long as it is capable of joining the two pieces of material together. 
     Although the concept of using different materials with different material properties at different portions of the golf club head has already been discussed above, the present embodiment provides a method to more easily implement the technology. More specifically, due to the fact that the present embodiment allows both the blade portion  1302  and the hosel portion  1304  to be partially forged, it is easier to control the separation of the materials when compared to when the materials are joined at the billet stage. In addition to the benefit of being able to more easily control the separation of material, the present embodiment also provides an additional benefit of allowing more complicated construction methods to be utilized. 
     In summary, it can be said that in this alternative embodiment of the present invention, a golf club may be created by first partially pre-forging a blade portion  1302  and a hosel portion  1304  independently of one another. In this embodiment, the blade portion  1302  may be created out of higher strength steel as discussed previously, while the hosel portion  1304  may be created out of softer steel as discussed previously as well. The softer steel used at the hosel portion  1304  may allow more ease of bending of the final golf club head to accommodate the fitting needs of the end golfer. It should also be noted that the blade portion  1304  of the golf club head  1300  may also contain a cavity  1353  located at a bottom heel portion of the golf club head  1300  created during the pre-forging process. Subsequent to the independent formation of the blade portion  1302  and the hosel portion  1304 , the two pieces are joined together using one of the joining methods discussed above. Once the blade portion  1302  and the hosel portion  1304  are joined together to form a partially forged golf club head. This unitary piece of partially forged golf club head will now be forged again to the final desired shape. During this final forging step, additional weights may be added to the cavity  1353  and sealed with cap if such weighting is desired. 
       FIG. 14  shows the finished golf club head  1400  in accordance with this alternative embodiment of the present invention described in  FIG. 13A  and  FIG. 13B . In this finished golf club head, it can be seen that after the final forging step, the blade portion  1402  and the hosel portion  1404  have been joined together to produce an end product that may look identical externally when compared to a conventional golf club head. However, underneath the cosmetics, it can be seen that the material used at the hosel portion  1404  may generally be softer than the material of the blade portion  1402 , allowing a high performing golf club head to have a soft bendable hosel. It should be noted that this specific embodiment of the present invention may be able to incorporate more complex construction methods, allowing a backing piece  1458  and a medallion  1460  to be used to create a potentially hollow golf club head  1400 . In order to illustrate the components of this embodiment of the present invention,  FIGS. 15 and 16  are provided with exploded views of the different components of the present invention. 
       FIG. 15  of the accompanying drawings shows an exploded back view of a golf club head  1500  in accordance with this alternative embodiment of the present invention illustrating all the components associated that can be used with this construction method. The blade portion  1502  and the hosel portion  1504  are attached to one another after each has been individually forged. It can be seen in this embodiment that the blade portion  1502  may have a cavity  1553  already forged into its geometry to accept the weight member  1554 , which will be encased by the cover  1556 . At the toe portion of the golf club head another weight member  1554  is placed near the bottom of the golf club head  1500 , and that weight is encased by the backing piece  1558 . Finally, this alternative embodiment of the present invention may have a medallion  1560  attached to an external portion of the backing piece  1558 . 
       FIG. 16  provides a similar exploded view of the golf club head  1600  in accordance with this alternative embodiment of the present invention. This frontal exploded view of the golf club head  1600  provides a different angle to show the different shapes of the components used to create the golf club head  1600 . More specifically, this frontal exploded view allows the cavity  1653  near the heel side of the sole of the golf club head  1600  to be shown. In addition to the above, this frontal view also allows internal components of the backing piece  1658  to be shown more clearly. Finally  FIG. 16  also shows that the weight member  1654  could be placed at the heel portion and the heel portion together. 
     Other than in the operating example, or unless otherwise expressly specified, all of the numerical ranges, amounts, values and percentages such as those for amounts of materials, moment of inertias, center of gravity locations, loft, draft angles, various performance ratios, and others in the aforementioned portions of the specification may be read as if prefaced by the word “about” even though the term “about” may not expressly appear in the value, amount, or range. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. 
     Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting form the standard deviation found in their respective testing measurements. Furthermore, when numerical ranges of varying scope are set forth herein, it is contemplated that any combination of these values inclusive of the recited values may be used. 
     It should be understood, of course, that the foregoing relates to exemplary embodiments of the present invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.