Explosion bonded laminated face inserts for golf clubs
Laminated striking face inserts for golf clubs are characterized by explosion bonding of the layers of the laminate. The outer layers are of a substantially high strength and density material and the center layer is of relatively lower strength and density material. Explosion bonding results in a laminated face plate or insert in which the yield strength of the laminate is similar to the full strength characteristics of the materials used in the laminate.
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 This application claims the benefit of U.S. provisional application No. 60/358,450 filed Feb. 19, 2002.BACKGROUND OF THE INVENTION
 This invention relates generally to golf club heads and more specifically to golf club heads having inserts in the striking face.
 Golf clubs are designed primarily in separate categories of woods, irons, and putters. The majority of golf club woods at the present time are made of some metal or composite, while most irons are made of varying types of metal. Woods can be constructed of solid metal or can be constructed so as to have recesses in which a face or insert is placed in the striking surface. While most irons are made of metal, some also have recesses for accepting inserts for the striking face.
 It is recognized that advantages are provided by redistributing the weight of golf clubs in both woods and irons so that the weight around the perimeter of the head increases to increase the moment of inertia, thereby increasing head stability, which in turn lessens head rotation that imparts side spin on the ball. This creates either a hook or slice (in the same manner as a gear effect) through impact on off-center hits.
 The present invention relates to laminated inserts and a method for making the same which are configured to redistribute part of the weight of the striking face to the perimeter of the golf club head because the laminated inserts are lighter in weight than metal inserts in order to increase the moment of inertia of the head.BRIEF DESCRIPTION OF THE PRIOR ART
 Laminated inserts for golf club heads are well-known in the patented prior art as evidenced by the Mahaffey et al. U.S. Pat. No. 5,827,131 and the Mahaffey U.S. Pat. No. 6,074,309, both of which are owned by the assignee of the present invention. Both patents disclose inserts formed of outer metal layers and an inner layer, where the outer layers are higher density and stronger than the inner layer. The inserts are connected within a recess in the golf club head by welding, an adhesive, crimping or other method known in the art.
 It is also known in the art to manufacture certain components of a golf club head using explosion bonding. The Ciasullo U.S. patent application publication No. 2002/0187854 discloses a wood type golf club head in which a sole plate and a top plate each include an inner shell of less dense material which is explosion bonded to the respective plates. The components are then welded together to form the golf club head.
 In laminated striking face inserts for golf club heads of the prior art, the bonding strength of the laminate is usually quite low, and it is generally lower than the yield strength of the weakest material. The present invention was developed in order to overcome this and other drawbacks of prior laminated inserts by providing a laminated striking face plate or insert formed by explosion bonding so that the yield strength of the laminate is similar to the full strength characteristics of the materials used in the laminate.SUMMARY OF THE INVENTION
 Accordingly, the present invention relates to a laminated striking face plate or insert for a golf club head including a first outer layer having an outer surface defining a striking face of the club head and an inner layer having a lower strength than the first outer layer. The inner and outer layers are joined by explosion bonding to produce a face plate having a yield strength similar to that of the lower strength material and a higher yield strength than prior laminated face plates.
 According to a preferred embodiment, a second outer layer is provided for the face plate with the inner layer sandwiched between the two outer layers. The second outer layer has a strength which is greater than the inner layer.
 The outer layers are preferably formed of a high strength metal such as titanium and the inner layer is formed of aluminum.
 The invention also relates to a method for forming a laminated striking face plate or insert wherein the layers are bonded via explosion welding.BRIEF DESCRIPTION OF THE FIGURES
 Other objects and advantages of the invention will become apparent from a study of the following specification when viewed in light of the accompanying drawing, in which:
 FIGS. 1 and 2 are sectional views of wood-type and iron-type golf club heads, respectively, having striking face inserts according to a first embodiment;
 FIGS. 3 and 4 are sectional views of wood-type and iron-type golf club heads, respectively, having striking face inserts according to a second embodiment;
 FIG. 5 is an exploded view of a laminated insert according to a first preferred embodiment of the invention;
 FIG. 6 is an exploded view of a laminated insert according to a second embodiment of the invention;
 FIG. 7 is an exploded view of a laminated insert according to a third embodiment of the invention;
 FIG. 8 is a sectional view through a laminated explosion bonded striking face insert according to the preferred embodiment of the invention of FIG. 5; and
 FIG. 9 is a enlarged detail of the sectional view of FIG. 8.DETAILED DESCRIPTION
 FIG. 1 shows a metal wood 11 having a crown 13, a hosel 15, and a sole 23, with a face structure 19 having a recess 17 therein. In this particular configuration, the recess includes a lip surrounding the recess and the insert 21 is configured so as to fit within the recess and be secured therein adjacent the lip. This is commonly referred to as an unsupported insert since the club head does not have a complete surface backing adjacent the major portion of the insert.
 FIG. 2 shows an iron 30 having a sole 31, a top edge 33, and a recess 35. Again, this recess has a lip against which the insert 37 is placed. This also provides an iron with an unsupported face insert.
 FIG. 3 shows a metal wood 40 having a crown 41, a sole 43, and a recess 47 in the face, with the recess terminating in a thin plate member 45 at the interior of the club head. Plate member 45 preferably has a thickness between 0.030 inch and 0.120 inch. Insert 49 is secured within the recess using techniques known in the art and abuts against plate 45.
 FIG. 4 shows an iron 50 having a sole 53, an upper ridge 51, and a cavity 55, with a recess 56 being backed by a thin plate 57. Plate 57 is preferably of a thickness between 0.030 and 0.120 inch. In this type of iron, insert 59 is secured within the recess and abuts against metal layer 57.
 While the inserts of the present invention are of a laminate structure, such structure is not shown specifically in the FIGS. 1-4 for purposes of clarity.
 FIG. 5 shows an insert 60 according to a preferred embodiment of the invention. The insert is a laminate comprised of outer layers 61 and 63 and an inner layer 65. In order to reduce the weight at the center, the outer layers 61 and 63 are of a high strength material such as 6-4 titanium and are of a reduced thickness between 0.025 inch and 0.100 inch, or approximately 1.5 mm. Inner layer 65 is of a less dense material such as aluminum of similar thickness.
 Referring now to FIG. 6, another embodiment of the invention will be described. Shown therein is a laminated insert 70 comprising a face outer layer 71, a rear outer layer 73, and a center layer 75. A second inner or center layer 77 may also be provided. This insert is for use in an iron-type club head without a backing plate such as shown in FIG. 2. The layers are formed of the same materials as set forth above in connection with the insert shown in FIG. 5. However, the rear outer layer 73 contains at least one perforation or through-opening 79 which may have a circular configuration, a rectangular configuration, a square configuration, an oval configuration, or any other suitable geometric configuration which affords visual inspection of the center layer 75. This enables the user to confirm that the club head is in part a laminate because of the visibility of the center layers. The perforations may be hollow or may filled with an epoxy-type material.
 Although the embodiments of FIGS. 5 and 6 illustrate the insert as having two outer layers, the insert can also be manufactured with only a single outer layer as shown in FIG. 7. The outer layer 81 comprises the striking face and the inner layer 85 is formed of a less dense material than the outer layer. This is particularly suitable for an insert which is used in a club head including a backing plate such as shown in FIGS. 3 and 4.
 The layers of the laminated insert are joined by explosion bonding or welding to form the finished insert. According to a preferred embodiment, the layers are initially arranged in spaced relation as shown in FIGS. 5, 6, and 7. In these figures, the outer layers 61, 71 and 81, respectively, would form the striking face of the golf club head, and the outer layers 63 and 73 would form the rear face of the insert. An explosive is applied to the rear surface of the rear outer layers 63, 73 and a detonator is connected with the explosive. When the detonator is activated, the explosive accelerates the rear layer 63 into bonding contact with the inner or center layer 65 which is in turn accelerated into bonding contact with the front outer layer 61, as shown by the arrows between the layers of FIG. 5. Similarly, in the embodiment of FIG. 6, the layer 73 is accelerated into layer 75 which is accelerated into layer 77 which is accelerated into layer 71.
 Explosive bonding provides metal to metal bonding between the layers without generating excessive heat in the layers. In FIG. 8 is shown the explosive bonded layers 61, 63, and 65 of the laminate of FIG. 5.
 The spacing between the layers prior to explosion bonding is a function of the materials being bonded. Typically, the distance is from 0.5 to 4 times the thickness of the layers. When the explosive is ignited, the detonation travels across the surface of the outer layer 63 and the gas expansion of the explosion accelerates the outer layer 63 toward the inner layer 65. Because of the rapid movement of the outer layer toward the inner layer, pressure is created at the opposing surfaces of the layers to remove surface contaminants therefrom, resulting in a metal-to-metal bond between the clean metal surfaces when the outer layer collides with the inner layer. The same occurs between the inner layer 65 and the front outer layer 61.
 As shown in FIG. 9, the interfaces between the explosion bonded layers have a wavy bond morphology. The metallurgical bond results from the interface between the grains of the different metal types of the layers. Although the explosion bonding process generates heat, the heat is not transferred to the metal layers because bonding occurs so quickly. Thus there is no melting or diffusion of the layers. Accordingly, high yield strengths are obtained. Typically, the yield strength of the laminate is similar to the full strength characteristics of the materials used in the laminate.
 The following is a list of examples of further materials which can be used for the layers of the insert: 1 MATERIAL TENSILE YIELD DENSITY 356 Aluminum 40000 27000 0.097 7075 Aluminum 83000 73000 0.101 Forging Brass 55000 20000 0.305 BE-CU 110000 90000 0.297 304 Stainless 85000 35000 0.290 431 Stainless 125000 95000 0.280 17-4 Stainless 150000 110000 0.280 99.0% Titanium 79000 63000 0.163 6-4 Titanium 135000 120000 0.160
 Examples of some of the above materials for construction of the laminate are as follows: 2 FACE LAYER CENTER LAYER BACK LAYER 17-4 Stainless 99.0% Titanium 17-4 Stainless 6-4 Titanium 7075 Aluminum 6-4 Titanium BE-CU 356 Aluminum BE-CU Forging Brass 356 Aluminum Forging Brass 431 Stainless 7075 Aluminum 17-4 Stainless 304 Stainless 356 Aluminum 7075 Aluminum 431 Stainless 7075 Aluminum 431 Stainless
 While the preferred forms and embodiments of the invention have been illustrated and described, it will be apparent to those of ordinary skill in the art, that various changes and modifications may be made without deviating from the inventive concepts set forth above.
1. A laminated striking face plate for a golf club head, comprising
- (a) a first outer layer having an outer surface defining a striking face of the golf club head; and
- (b) an inner layer having a lower yield strength than said first outer layer;
- (c) said inner and outer layers being joined by an explosion bond, whereby the yield strength of said face plate is increased relative to the yield strength of the layers..
2. A laminated striking face plate as defined in claim 1, and further comprising a second outer layer opposite said first outer layer with said inner layer being arranged therebetween, said second outer layer having a higher strength than said inner layer and being joined to said inner layer by said explosion bond.
3. A laminated striking face plate as defined in claim 2, and further comprising a plurality of inner layers.
4. A laminated striking face plate as defined in claim 2, wherein said first and second outer layers are formed of metal and have a greater density than said inner layer.
5. A laminated striking face plate as defined in claim 4, wherein said first and second outer layers are formed of titanium and said inner layer is formed of aluminum.
6. A laminated striking face place as defined in claim 2, wherein said second outer layer contains a plurality of spaced openings.
7. A laminated face plate as defined in claim 2, wherein said plate comprises an insert secured within a recess in a striking face area of the golf club head.
8. A method for manufacturing a laminated striking face plate for a golf club head, comprising the step of explosion bonding a first outer layer to an inner layer, said outer layer having higher yield strength than said inner layer and having an outer surface defining a striking face of the golf club head.
9. A method as defined in claim 8, and further comprising the step of bonding a second outer layer to said inner layer with the same explosion which bonds said first outer layer to said inner layer, said inner layer being arranged between said first and second outer layers, said second outer layer having a higher yield strength than said inner layer.
10. A method as defined in claim 9, and further comprising the step of explosion bonding a plurality of inner layers between said first and second outer layers.
11. A method as defined in claim 9, wherein said first and second outer layers are formed of metal and have a greater density than said inner layer.
12. A method as defined in claim 11, wherein said first and second outer layers are formed of titanium and said inner layer is formed of aluminum.