Abstract:
A method for manufacturing an archery bow riser of hollow construction by the tubular hydroforming process and the risers produced by the method.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    There are no related applications.  
         STATEMENTS AS TO RIGHTS TO INVENTION MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT  
         [0002]    The invention disclosed and claimed herein was not made under any federally sponsored research and development program.  
         A. BACKGROUND OF THE INVENTION  
         [0003]    1. Field of the Invention  
           [0004]    This invention concerns a method for manufacturing archery bow risers and the archery bows including such risers produced by the method.  
           [0005]    2. Description of the Prior Art  
           [0006]    Archery bow risers, particular archery bow risers for use with compound bows, are required to be strong enough to withstand the large forces produced by the limbs during firing of the bow. In the past, risers possessing such strength have been manufactured by various processes including the milling of aluminum blocks or billets, the casting of magnesium and aluminum in molds and the extruding of aluminum. A disadvantage of these processes is that the risers so produced are heavy and contribute significantly to the weight of the bow. Users of such bows, for example hunters in the fields, would prefer that the bows be lighter in weight.  
           [0007]    The production of shaped parts by a process referred to as tube hydroforming has become popular in recent times, particularly for parts used in the automotive industry. The process involves placing either a straight metal tube, or a metal tube prebent into the general overall shape of the part to be formed, into a hydraulically activated die. The die cavity is in the shape of the part to be formed. The die parts are then closed and pressurized water is forced into the ends of the tube causing the tube to expand outwardly into the shape of the die cavities. The principal benefit of tube hydroforming is the significant weight saving that is achieved by a hollow component. Other reported benefits of tube hydroforming include part consolidation (i.e., the advantage of using a one piece hollow tube instead of stamping and welding two or more pieces); weight reduction through enhanced control of wall thickness; lower tooling costs; reduced dimensional variations and reduced amount of scrap material. Adding to the popularity of tube hydroforming in recent times has been the advanced software programming which allows more finely tuned movement of the dies and the resultant production of parts to exacting specifications. It is not believed that the tube hydroforming process has been previously utilized to produce archery bow risers.  
         B. SUMMARY OF THE INVENTION  
         [0008]    The present invention is directed to a method for manufacturing an archery bow riser of hollow construction by the tubular hydroforming process and the archery bow risers produced by that method. It is believed that such a hollow construction riser will be able to withstand the significant forces produced by the limbs because most of the riser strength which withstands the limb forces is at the outer edges of the riser and therefore any riser strength lost by the hollow interior construction is not critical.  
           [0009]    The process for manufacturing an archery bow of hollow construction involves prebending a hollow metal tube into the general overall shape of the riser. The riser shape may, for example, include grip attachment surfaces, a bow sight mounting surface, and limb attachment areas. The bent tube is then placed into a cavity in a lower hydraulically activated die. The cavity is in the shape of a first surface of the riser to be formed and includes, for example, the shape of the grip area, arrow shelf and/or bow sight mounting surface. An upper hydraulically activated die includes a cavity in the shape of a second surface of the riser to be formed. The upper and lower dies are closed about the bent tube and water under pressure is forced into the ends of the tube. The combination of the closure of the dies and the internal water pressure in the tube deforms the bent tube into the shape of the cavities in the dies. The dies are then separated and the riser is removed.  
           [0010]    Accordingly, it is an object of this invention to form a light weight archery bow riser by means of a hydroforming process;  
           [0011]    It is a further object of this invention to form a light weight archery bow riser including grip attachment surfaces by means of a hydroforming process;  
           [0012]    It is an additional object of this invention to form a light weight archery bow riser including a bow sight mounting surface by means of a hydroforming process;  
           [0013]    It is a still further object of this invention to form a light weight archery bow riser including limb attachment areas by means of a hydroforming process; and  
           [0014]    It is another object of this invention to form a light weight archery bow riser including a grip portion, an arrow shelf and a bow sight mounting surface by means of a hydroforming process.  
           [0015]    Other objects and attendant advantages of this invention will be readily appreciated as the same becomes more clearly understood by references to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof.  
         C. BRIEF DESCRIPTION OF THE DRAWINGS  
         [0016]    [0016]FIG. 1 is a side elevational view of an archery bow including the riser produced according to the present invention;  
           [0017]    [0017]FIG. 1A is a front elevational view of the archery bow shown in FIG. 1;  
           [0018]    [0018]FIG. 2 is a perspective view of the tubular extrusion from which the riser of the present invention is formed;  
           [0019]    [0019]FIG. 3 is a side view of the tubular extrusion shown in FIG. 2;  
           [0020]    [0020]FIG. 4 is a top plan view of the tubular extrusion shown in FIG. 2;  
           [0021]    [0021]FIG. 5 is a side to side view of the prebent tubular extrusion;  
           [0022]    [0022]FIG. 6 is a front to back view of the prebent tubular extrusion;  
           [0023]    [0023]FIG. 7 is a top plan view of the prebent tubular extrusion;  
           [0024]    [0024]FIG. 8 is a perspective view of the opened dies and the prebent tubular extrusion placed in a cavity of the lower die;  
           [0025]    [0025]FIG. 9 is a perspective view of the closed dies and the prebent tubular extension located in the cavities of the upper and lower die;  
           [0026]    [0026]FIG. 10 is a perspective view of the opened dies and the formed riser removed from the dies; and  
           [0027]    [0027]FIG. 11 is a perspective view of the formed riser after the ends of the limb attachment areas have been further shaped to receive the limb attachment devices. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]    For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing forming a part of this specification and in which similar numerals of reference indicate corresponding parts in all the figures of the drawing.  
         [0029]    In FIG. 1 there is shown an archery bow  2  including a riser  4  of the type produced in accordance with the present invention. Riser  4  includes grip attachment surfaces  6  to which grip  7  having an arrow shelf  8  thereon is secured by, for example, screws or adhesive. Riser  4  includes a bow sight mounting surface  10  and limb attachment areas  9  having angular surfaces  13  at the ends of riser  4 . Riser  4  is connected at one end to an upper limb  12  by a conventional limb attachment device  11  and at the other end by conventional limb attachment device  11  to a lower limb  14 . The riser  4  is connected to the limb attachment devices  11  by bolts  17 . A dual feed cam  15  is mounted on an axle pin which extends through the bottom of lower limb  14 . A concentric pulley wheel  16  is mounted on an axial pin which extends through the top of upper limb  12 .  
         [0030]    A string has a medial portion trained around pulley wheel  16  to form bow string  18  and a secondary return string  20 . The ends of bowstring  18  and secondary return string  20  pass around eccentric peripheral groove portions of the cam  15  and are connected to it, so that when the bow is fired, bow string  18  and return string  20  will be fed out from cam  15 . An anchor cable  22  is anchored at one end to the axle which extends through the top of upper limb  12 . The other end of anchor cable  22  passes around an eccentric peripheral groove portion of cam  15  and is connected to it. In this manner, anchor cable  22  forms a direct connection between the limbs  12  and  14 . While the illustrated bow is a dual-feed single-cam compound bow of the type disclosed in U.S. Pat. No. 5,368,006, it will be understood that the riser produced in accordance with the present invention may be used with other types of bows as well.  
         [0031]    The process for producing riser  4  begins with a tubular extrusion  24  of the type shown in FIGS. 2 through 4. Tubular extrusion  24  which may, for example, be formed of aluminum or steel, includes a hollow interior  26  and openings  23  and  25 . Tubular extrusion  24  may, for example, have a wall thickness of 0.125 inches, a height of 0.75 inches and a width of 1.5 inches. The tubular extrusion  24  is then prebent manually to the shape shown in FIGS. 5 through 7 so that it may fit within a cavity  19  of bottom die  28  shown in FIG. 8. The cavity  19  is in the shape of a first surface of the riser to be formed and includes the area of tubular extrusion  24  which will be formed into the grip attachment surfaces  6  and is shown generally as  6 ′, the area of tubular extrusion  24  which will be formed into the bow sight mounting surface  10  and is shown generally as  10 ′, and the area of tubular extrusion  24  which will be formed into the limb attachment areas  9  is shown generally at  9 ′ in FIGS. 5 and 6.  
         [0032]    In FIG. 8, the tubular extrusion  24  is shown in a cavity  19  in bottom die  28  prior to an upper die  30  and bottom die  28  being brought together and the internal fluid being injected under pressure into both ends of the tubular extrusion  24 . Either upper die  30  may be moved downwardly into contact with lower die  28  or lower die  28  may be moved upwardly into contact with upper die  30 . Upper die  30  includes a corresponding cavity  21  in the shape of a second surface of the riser to be formed. The next step is shown in FIG. 9 wherein upper die  30  and lower die  28  are brought into contact and internal fluid is injected into openings  23  and  25  of tubular extrusion  24  in the direction of the arrows. The pressure exerted by die  28  on tubular extrusion  24  may, for example, be in the range of 40,000 to 60,000 pounds per square inch and the pressure of the internal fluid injected into tubular extrusion  24  may be in the range of 20,000 to 30,000 pounds per square inch. During this step, the combination of the upper die  30  and the bottom die  28  being closed on tube extrusion  24  and the internal fluid being injected into openings  23  and  25  of tube extrusion  24  forces the external surfaces of tube extrusion  24  to conform to the surface of cavity  19  in bottom die  28  and cavity  21  in upper die  28 . In the next step shown in FIG. 10, the bottom die  28  and the upper die  30  of die  28  are separated and the riser  4  is removed. The angular surfaces  13  of limb attachment areas  9  are then further shaped by, for example, machining or cold sawing to enable the angular surfaces  13  to receive the limb attachment devices. A perspective view of the finished riser  4  is shown in FIG. 11.  
         [0033]    This invention has been described above with reference to presently preferred embodiments of the invention; such description has not been presented as a catalog exhaustive of all forms which this invention may take. Accordingly, workers skilled in the art to which this invention pertains will readily appreciate that variations, alterations or modifications in the structures, procedures and arrangements described above may be practiced without departing from the scope of this invention. Thus, the foregoing description should not be read as limiting the scope of this invention to less than the fair scope of the appended claims.