Abstract:
A golf club head having a defined internal cavity, and a golf club head containing a bi-material weight having a nonhomogeneous structure is disclosed herein. A method to add the bi-material weight to the golf club entails heating, vibration and cooling to produce the nonhomogeneous structure is also disclosed herein.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This patent application is a divisional application of co-pending U.S. patent application Ser. No. 09/330,292, filed on Jun. 11, 1999. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to golf clubs and, more specifically, a golf club head and weighting method to provide better performance, greater weighting flexibility and lower production costs. 
     2. Description of the Related Art 
     The location and distribution of weight within a golf club is an important factor in the performance of the golf club. In particular, weight placement at the bottom of the golf club head provides a low center of gravity to help propel a golf ball into the air during impact, and weight concentrated at the toe and heel of the golf club head provides a resistance to twisting, or high moment of inertia, during golf ball impact. Both the low center of gravity and high moment of inertia are important performance variables which affect playability and feel of the golf club. Alternative designs have resulted in many innovations for varying the weight location and distribution in a golf club head portion. Among these designs is a combination of high and low density materials within the golf club head, and associated methods for combining these materials. 
     One example of multiple materials used in the construction of the golf club head is a high density material attached to a lower density material golf club head. A high density block or contoured shape is attached, via mechanical means such as friction fit, fasteners or screws, to a reciprocal recess in the golf club head, as shown in U.S. Pat. No. 5,776,010, issued to Helmstetter et al. Although supplying the desired performance enhancements, the high density block and the reciprocal recess must be machined to precise tolerances, involving high production costs. 
     Another example of weighting the golf club is pouring a high density fluid into a reservoir within the golf club. This ensures an exact placement of the weighting material within the golf club, as the fluid will conform to the internal shape of the reservoir without the need for mechanical or an adhesive bonding. One drawback of this type of processing is the requirement that one must operate below the melt or softening temperature of the club head material. In addition, as processing temperatures increase the associated costs will increase to accommodate higher energy use and high temperature equipment. The limitations for a low melt temperature, yet high density, material restricts the available options for this type of process. 
     To overcome the limitations associated with a single material, the advent of multi-component weighting systems makes use of the high density materials in combination with a carrier fluid, such as a polymer. A particulate form of the high density material is mixed with the carrier fluid and poured into the reservoir in the golf club, wherein the carrier fluid is allowed to solidify to form a composite weighting material. Readily available materials include a thermoset polymer carrier fluid, such as epoxy, which allows ambient temperature processing and solidification of the high density material and epoxy mixture. A thermoplastic polymer carrier fluid, such as polypropylene, requires heat to obtain a fluid state and cools to a solid at ambient temperatures, with the capability to be re-heated to the fluid state, in distinction to the epoxy. A disadvantage of the multi-component weighting system is the low density associated with the carrier fluid, typically 1 g/cm 3 , thus requiring a high ratio of the weighting material to the carrier fluid to obtain the desired high density for a bi-material weight. The carrier fluid also acts as a binder for the weighting material to ensure the bi-material weight forms a solid block. 
     A drawback to the multi-component weighting system is the need to use small amounts of carrier fluid relative to the weighting material, leading to entrapped air or voids and incomplete binding in the bi-material weight. Incorporating larger amounts of the carrier fluid promotes better mixing within the bi-material weight in conjunction with an attendant decrease in density. Therefore, it is desirable to provide a bi-material weight containing a higher density carrier fluid to provide greater weighting flexibility for allocating weight within a golf club head in conjunction with lower cost production. It is further desirable to provide a golf club head to accommodate the bi-material weight and enable a variable location of the bi-material weight. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the problems of the golf industry by providing a bi-material weight and a golf club head that when used in combination result in a golf club that provides a low center of gravity, and superior feel and playability. A distinctive feature of the bi-material weight of the present invention is the use of vibrational energy to provide complete contact between the high density material and the lower density material. This embodiment reduces or eliminates voids associated with mixing dissimilar density materials, and promotes migration, or orientation, of the high and lower density materials to the preferred location within the golf club head. 
     In a preferred embodiment, the bi-material weight is a nonhomogeneous mixture composed of a high density metal material forming a discontinuous phase, and a lower density metal material forming a continuous phase. The choice of metal materials is advantageous for their high density, metal to metal compatability, availability and for many alloys good long term environmental stability. Among the choices for the high density metal material are copper metals, brass metals, steel and tungsten metals; wherein the lower density metals afford a low melt temperature and include several types of solder. In a most preferred embodiment, a plurality of tungsten spheres comprises the high density metal forming the discontinuous phase, and a bismuth-tin solder comprises the lower density metal forming the continuous phase. An important operation in achieving the nonhomogeneous mixture is providing the lower density material in a liquid state, followed by imparting vibrational energy to diminish or eliminate voids and permit migration of the high density metal material to a preferred location within the golf club head, followed by solidification of the lower density material. 
     A preferred embodiment of the present invention is generally descriptive of a class of golf clubs known as irons. Within this class is a type of iron referred to as a cavity back iron, and well known to those of ordinary skill in the art, which contains a continuous ribbon, or flange, of material at the outer periphery of the rear face of the iron. This construction yields an open cavity, or first cavity, in the rear or back of the iron and yields a larger “sweet spot” in the front or striking face of the iron to provide a wider margin of error in striking the golf ball. The ribbon of material located below the open cavity, extending between the heel and toe and adjacent the bottom periphery of the golf club head, contains an internal cavity, also referred to herein as a second cavity or weight pocket, for accepting a weighting material. This cavity contains at least one inlet into an interior volume, or interior space, of the internal cavity, having a vertical dimension between a ceiling wall, or top wall, and a bottom wall, and a horizontal dimension between a toe region and a heel region of the golf club head. In a preferred embodiment, the internal shape, or configuration, of the internal cavity allows weight to be located in the toe region or heel region to help a golfer open or close the golf club head relative to the intended target line. Specifically, weight located in the toe region helps to open the golf club head, and weight located in the heel region helps to close the golf club head. In addition, an expanded center volume portion of the internal cavity allows for a vertical density transition zone in the bi-material weight, resulting in a more satisfying feel during golf ball impact. 
     In a preferred embodiment, an undercut recess is located rearward of a front face of the golf club, as discussed in U.S. Pat. No. 5,282,625, issued to Schmidt et al., which is hereby incorporated by reference. The purpose of the undercut recess is to help expand the “sweet spot”, in conjunction with “sweet spot” improvement inherent in the cavity back iron, by moving weight to a rearward peripheral region of the golf club head. In addition, the rearward location of the bi-material weight improves playability by helping propel the golf ball into the air during impact with the golf club. 
     Accordingly, it is an object of the present invention to provide a bi-material weighting system for golf clubs to allow a greater flexibility in locating the center of gravity and providing better feel. 
     It is another object of the present invention to impart vibrational energy to a bi-material weighting system for golf clubs to allow better mixing and orientation between the weighting materials to form a continuous phase and a discontinuous phase. 
     A further object of the present invention is to provide a golf club head containing an internal cavity having an expanded vertical dimension in the center of the cavity, thereby allowing greater precision in locating high density material in the center of the golf club head. 
     Another object of the present invention is to provide a cavity-back titanium alloy iron golf club head with a cavity containing a plurality of tungsten alloy spheres and a bismuth-tin solder. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a rear view of a golf club head of an embodiment of the present invention showing an internal cavity arrangement with a contoured rear face. 
     FIG. 2 is a front perspective view of the golf club head of an embodiment of the present invention. 
     FIG. 3 is a rear perspective view of the golf club head of an embodiment of the present invention. 
     FIG. 4 is a front view of the golf club head of an embodiment of the present invention. 
     FIG. 5 is a top view of the golf club head of an embodiment of the present invention. 
     FIG. 6 is a bottom view of the golf club head of an embodiment of the present invention. 
     FIG. 7 is a toe view of the golf club head of an embodiment of the present invention. 
     FIG. 8 is a heel view of the golf club head of an embodiment of the present invention. 
     FIG. 9 is a cut-away view along line  9 — 9 , as shown in FIG. 4, of the golf club head of an embodiment of the present invention. 
     FIG. 10 is a cut-away view along line  10 — 10 , as shown in FIG. 1, of the golf club head of an embodiment of the present invention. 
     FIG. 11 is a rear perspective view of FIG. 10 of the golf club head of an embodiment of the present invention. 
     FIG. 12 is a cut-away view of the golf club head and the first weight material of an embodiment of the present invention. 
     FIG. 13 is a top perspective view of the golf club head within a fixture of an embodiment of the present invention. 
     FIG. 14 is a heel view of the golf club head during addition of the second weight material of an embodiment of the present invention. 
     FIG. 15 is a top perspective view for clamping the golf club head of an embodiment of the present invention. 
     FIG. 16 is a cut-away view of the golf club head containing the bi-material weight of an embodiment of the present invention. 
     FIG. 17 is a table to obtain a specific weight for various empty weights for the golf club head for an embodiment of the present invention. 
     FIG. 18 is a front view of an alternative embodiment of the golf club of the present invention showing a wood club head. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in FIGS. 1-8 a golf club of the present invention is generally designated  12 . The golf club head  12  comprises a heel section  14 , a bottom section  16 , a toe section  18 , a top section  20  and a hosel  22 . The heel, toe, bottom and top sections,  14 ,  18 ,  16  and  20  respectively, are meant to describe general sections of the golf club head  12  and may overlap one another. The golf club  12  further comprises an inset wall  24 , an entry  26 , an internal cavity  28 , a cavity flange  30 , a rear face  32  and a series of contour lines  34  extending generally from the heel section  14  to the toe section  18 . The internal cavity  28  is located within the rear flange  30 , and generally extends adjacent the bottom section  16  from the heel section  14  to the toe section  18 . In a preferred embodiment, a heel wall  44  (shown in phantom in FIG. 1) and a toe wall  52  (shown in phantom in FIG. 1) defines the lateral extent of the internal cavity  28 . The internal cavity  28  has a volume from 5 cm 3  to 25 cm 3 , and in a most preferred embodiment from 9 cm 3  to 15 cm 3 . The length and volume of the internal cavity allow for flexibility in the placement of the bi-material weight of the present invention to control the location of the center of gravity in order to improve the feel during impact of the golf club head with the golf ball. 
     The golf club head  12  further comprises a hosel inlet and a hosel exit,  36  and  40  respectively, for accepting the distal end of a golf shaft (not shown), a face  38  for impacting the golf ball (not shown) and a set of scorelines  40 . 
     As shown in FIGS. 9-11 the golf club of the present invention is generally designated  12 . The golf club  12  further comprises the heel wall  44 , a floor wall  45 , a lower face thickness  46 , an undercut recess  47 , a front wall  48 , a ceiling wall  49  and an upper face thickness  50 . In a preferred embodiment the boundaries of the internal cavity  28  are defined by the lower face thickness  46 , the upper face  48 , the ceiling wall  49 , the floor wall  45 , the inset wall  24 , the heel wall  44  and the toe wall  52  (as shown in FIG.  10 ). The distance between the floor wall  45  and the ceiling wall  49  is defined by a gap  51  having a first minimum at the heel wall  44  and a second minimum at the toe wall  52  (as shown in FIG.  10 ). The volume of the internal cavity  28  near the heel and the toe wall,  44  and  52  respectively, can be reduced because the effectiveness of weight placed at these locations is higher than that an equal weight placed in the center of the internal cavity  28 . In a preferred embodiment the gap  51  reaches a maximum between the heel wall  44  and the toe wall  52  (as shown FIG. 10) to produce a vertical density transition zone producing better feel during golf ball impact. The lower face thickness  46  is less than upper face thickness  50  to lighten the golf club head  12 , allowing more weight to be moved to the internal cavity  28  yet ensuring adequate structural strength for the lower face thickness  46 . In a preferred embodiment, the entry  26  for the internal cavity  28  is located on the inset wall  24  and is covered by a medallion (not shown). In a preferred embodiment the golf club head  12  is made of a titanium alloy. 
     A preferred method for adding weight material to the golf club head  12  involves a bi-material weighting operation. FIG. 12 is a cut-away view of the golf club head  12  of a method embodiment of the present invention. The golf club head  12  is weighed and a predetermined, or specific, weight of a first weight material  54  is added to the internal cavity  28 . In a preferred embodiment the first weight material  54  occupies 10% to 40% of the internal cavity  28 . In a more preferred embodiment a metal material forms the first weight material  54  and exhibits a high density, good compatibility with structural metals such as titanium and steel, high environmental stability and good commercial availability. Available choices for the first weight material  54  are copper metals, brass metals, steel and tungsten metals. In a preferred embodiment the density of the first weight material  54  is greater than 12 g/cm 3 , more preferred is between 12 g/cm 3  and 20 g/cm 3 . In a most preferred embodiment, the first weight material  54  comprises tungsten alloy spheres, with approximately 18 g/cm 3  density and having a diameter greater than 3 mm, dispensed into the internal cavity  28  of the golf club head  12 . The requirement for a diameter in excess of 3 mm is to provide an effective fluid path between the spheres and ensure a fully dense weight block. The golf club head  12  and the first weight material  54  are raised to a temperature sufficient to maintain a second weight material  60  (as shown in FIG. 14) in a fluid or liquid phase. In a preferred embodiment, a continuous oven is used to raise the temperature of the golf club head  12  and the first weight material  54  to at least 350° F. Although several heating methods are available, in a preferred operation the golf club head  12  containing the tungsten alloy spheres is placed upon a heated conveyor moving at 5.5 inches/minute through a 24 inch heat zone. 
     After exiting the heating operation the golf club head  12  containing the tungsten alloy spheres is secured in a fixture  56 , as shown in FIG.  13 . The second weight material  60  is then poured into the cavity  28  in the golf club head  12 , as shown in FIG.  14 . In a preferred embodiment the density of the second weight material  60  is less than 14 g/cm 3 , more preferred is between 6 g/cm 3  and 10 g/cm 3 . In a most preferred embodiment, the second weight material  60  is a bismuth-tin solder, with approximately 8.6 g/cm 3  density, heated to a liquid phase of at least 350° F. The weighting method may include any number of combinations associated with heating the golf club head  12  and the first and second weight materials  56  and  60  to form a finished product. Attached to the fixture  56  is a scale  58  to measure the total weight of the golf club head  12  during addition of the second weight material  60 . In a preferred embodiment, the scale  58  is used throughout the weighting method to ensure that the proper amount of the first and the second weight material  54  and  60  have been added to the golf club head  12 . 
     The golf club head  12  is forced against the fixture  56  and a mounting pad  64  via a clamp  62 , as shown in FIG.  15 . The mounting pad  64  is used to tilt the golf club head  12  to any desired orientation allowing the first weight material to migrate to the lowest point in the internal cavity  28  under the influence of vibrational energy. Vibrational energy treatment of the golf club  12  and a bi-material weight  70  (as shown in FIG. 16) may be accomplished by a mechanical device, ultrasound, radiation, or any other means of imparting vibrational energy. In a preferred embodiment, a mechanical vibration device supplies a small amplitude vibration to the golf club head  12 . The timing for starting and stopping the vibration is an important factor in obtaining the benefits of the present invention. The second weight material  60  should be in a liquid phase while exposed to vibration energy to prevent the first weight material  54  from creating voids or migrating out of the second weight material  60 . In a preferred embodiment, the vibrational energy is sustained for approximately 20 seconds. Following termination of the vibrational treatment, the golf club head  12  is cooled to allow the second weight material  60  to solidify. Cooling of the bi-material weight  70  may be accomplished by refrigeration, immersion in a cold fluid such as water, or simply allowing the golf club head  12  to cool naturally to ambient temperature. In a preferred embodiment, an air nozzle  68  supplies cooling air to the golf club head  12 . 
     FIG. 16 shows the golf club head  12  containing the bi-material weight  70  comprising the first weight material  54  and the second weight material  60 . The golf club head  12  may have a range of initial weights reflecting variability in manufacturing the golf club head  12 . To accommodate this variability the specific weight for the golf club head  12  is illustrated in FIG. 17, which lists the ratio of the first and second weight material  56  and  60  used in a  5  iron of the present invention. 
     An alternative embodiment of the present invention is a wood configuration for the golf club head  12 , as illustrated in FIG. 18, containing the internal cavity  28  and the bi-material weight  70 . The location of the internal cavity  28  is not limited to that illustrated in FIG. 18, but can be placed in various locations within the golf club head  12  to adjust center of gravity affecting feel and playability. 
     It is understood that various modifications can be made to the golf club head  12  and method of weighting, both outlined above, and remain within the scope of the present invention. For example, the golf club head  12  can be a wood-type golf club, a putter or an iron-type golf club, and can be made from various materials including metals and non-metals. 
     While preferred embodiments have been discussed and illustrated above, the present invention is not limited to these descriptions or illustrations, and includes all such modifications which fall within the scope of the invention and claim language presented below.