Abstract:
A chisel-type broadhead comprises a threaded ferrule laser welded to multiple blades. The blades are welded from both sides. The blades are welded to each other and to the ferrule. The ferrule and blades are configured to provide maximum impact strength to the broadhead. An optional feature enabling the broadhead ferrule threads to be tightened to the arrowshaft is provided. An improved method of welding the blades to the ferrule is provided.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Provisional Application 60/878,951, filed Jan. 5, 2007 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to archery hunting equipment. More particularly, the invention relates to a broadhead arrow point for an arrow, and a method of manufacturing the same. 
     BACKGROUND OF THE INVENTION 
     Typically, a broadhead arrow point, or simply broadhead, is an assembly of blades arranged around a central axial shaft or ferrule for attachment to an arrowshaft to form a complete arrow for use in target archery or hunting. The broadhead may be detachable for replacement in case it becomes dull or damaged. 
     The broadhead applies a large force to the target upon striking it and so must be as strong as possible within the constraints of mass and aerodynamic shape. Existing design broadheads frequently break upon impact with the target so there is a need for an improved stronger broadhead. 
     Detachable broadheads can become loose from the arrowshaft, or can become detached from the shaft entirely, leading to erratic flight performance or disintegration in flight, which would render the arrow ineffective or lead to something other than the targeted object being impacted, so there is a need for a more secure attachment between the broadhead and the arrowshaft. Additionally, broadheads comprising multiple parts that are inserted together and held by screws or clamps may become loose or fall in handling or in use and parts may be lost rendering the broadhead useless. Broadheads with moving parts, such as cams and swivels may not operate correctly in field conditions outside in weather and mud. Broadheads with separate removable ferrules, sometimes referred to as modular broadheads, may become loose in handling. So there is a need for a unitary broadhead with minimum or no moving parts. 
     Broadheads are costly to manufacture, and there is constant market pressure to produce an effective high performance broadhead with reduced manufacturing costs. 
     There have been many broadhead designs developed over the years, yet there are none previously known that optimally combine strength, reliability, and cost. Prior art designs have had detachable blades, multiple threaded ferrules with caps, two piece ferrules, slotted blades, or other features that added to the expense or detracted from the strength and reliability of the broadhead. 
     For example, Muller in US Published Patent Application 20050181898 Unitary Broadhead Blade Unit discloses an injection molded modular blade unit with separate ferrule which requires a pair of threaded connections; one between the ferrule and the arrowshaft and another between the blade unit and the ferrule. By requiring the blades to be molded, either as an assembly of blades or separably molded and then fused together, and then mated to the ferrule, the configuration results in a design that has several unnecessary potential points of weakness, since sintered metal typically sacrifices some strength compared to sheet or foil stock. 
     Similar disadvantages exist in U.S. Pat. No. 6,726,581, also to Muller, which also specifies a separate ferrule, and U.S. Pat. No. 6,290,903 to Grace, Jr et al which specifies a molded blade unit of sintered powder. 
     Thus there is a need for an improved broadhead. The object of the present invention is to overcome these shortcomings and present a strong, economical, and rugged broadhead. 
     SUMMARY OF THE INVENTION 
     In accordance with a preferred embodiment of the invention, a broadhead includes a threaded ferrule portion permanently attached to multiple blades. At the distal end of the broadhead, the blades are permanently attached directly together. At the proximal end of the blades, the blades are permanently attached to the ferrule portion. Between the proximal and distal ends, the blades are further permanently attached to the ferrule portion and to each other. 
     In the discussion to follow, “ferrule” will refer to the separate ferrule piece part before assembly into the broadhead, and “ferrule portion” will refer to the portion of the broadhead arrowpoint (after assembly) comprising the ferrule. 
     Preferably, the ferrule portion has a proximal end with a threaded portion to receive the mating portion of the arrowshaft for attachment to the shaft. Typically, an arrowshaft comprises an elongated shaft with fletches or vanes at the proximal end and a threaded distal end attachable to the broadhead. Distally of the threaded portion of the ferrule portion there may be one or more conical or spherical contacting portions to receive the blades for permanent attachment. The conical or spherical portions help transmit the axial load imposed by the blades upon the shaft at target impact. By using a conical or spherical portion, the load is transmitted partially by compression between the blades and ferrule portion resulting in a stronger unit than if the load were transmitted by only shear at the blade to ferrule weld attachment. 
     Typically, the ferrule portion diameter is selected to a predetermined value at various points along its length to achieve a predetermined design value for mass for the broadhead. Typically, the desired mass is about 100 grams, but other design values may be desirable for different applications. 
     Preferably in accordance with the invention, each blade is formed of stainless steel, preferably 400 Series stainless steel, which may be heat treated for hardness before or after attachment to the ferrule. Preferably the blades are stamped from 416 or 420 series stainless steel. The edges of the blades are beveled where they are attached together to reduce the gap which may be filled upon attachment. Preferably, the blades are individually heat treated to achieve the desired strength and hardness before attachment to the ferrule. 
     In the preferred embodiment, there are three blades attached symmetrically at intervals around a threaded ferrule portion. The blades are welded to the ferrule portion and to each other by laser welding techniques which are well known in the art. Preferably the welds would be applied at the distal end, where the three blades join together directly, at the blade proximal end where each blade contacts the ferrule portion, and in a middle zone where the blades contact each other and also contact the ferrule portion. In accordance with the invention, the welding laser energy is applied to both sides of a given blade. Preferably the welds may be done to both sides simultaneously. Preferably the laser welds are a series of spot welds which overlap to create a nearly continuous weld along each weld zone. 
     In accordance with the invention, the ferrule portion has a threaded proximal portion, a proximal shaft extension portion, a proximal conical or spherical portion, a distal shaft extension portion, and a distal conical or spherical portion. The threaded proximal portion may be male or female threads, but is preferably a male thread and the thread on the arrowshaft is preferably female. The threaded portion of the broadhead is threaded into the mating threaded portion of the arrowshaft with sufficient tightening torque to remain firmly attached in use. The proximal conical or spherical portion may have a planar or annular portion contacting the corresponding distal portion of the arrowshaft. 
     In an optional embodiment, the proximal conical or spherical portion may have a square or hexagonal feature, or opposed flats to enable engagement with a tool to aid in fixing the broadhead securely to an arrowshaft with reduced chance of injury to the person assembling the broadhead to the arrowshaft while simultaneously allowing increased tightening torque to be applied to the arrowshaft-to-broadhead connection. 
     In accordance with the method aspects of the invention, the method includes stamping the blades from 400 series stainless steel sheet, fixturing them on a rotatable mandrel with a ferrule, spot welding them with a laser of approximately 1200 nM wavelength with peak power of 3 KW with a pulse duration of 3.3 milliseconds on one side of each blade to form welds of approximately 0.030 inches diameter. Tack welds are applied initially to hold the blade assembly and ferrule together for subsequent handling during welding. The blade unit is rotated to bring the next desired weld area under the working range distance of the laser so that the blade assembly may be similarly tack welded on each blade. The blade unit is then welded with power settings and pulse duration as above with a series of spot welds overlapping by 60 to 70 percent. Then the assembly is rotated on the mandrel one third of a turn (in the case of a three bladed broadhead) and welded again in similar fashion. Then it is rotated a further one third of a turn and welded again. Then in further accordance with the invented method, the welded assembly is removed from the mandrel, heat treated for 1.5 hours at 1800 degrees Fahrenheit in an inert atmosphere comprising Argon to harden them to approximately Rc 56, and stress relieved for 15 minutes at 900 degrees Fahrenheit in an Argon comprising inert atmosphere. Optionally the heat treatment may be in an oxidizing atmosphere to achieve a black oxide finish which would be advantageous in an application requiring camouflaging the user. The blades are sharpened by grinding at an angle of 60 degrees, and then lapped by conventional means, and then the broadhead is cleaned and packaged. 
     Optionally in addition the distal point of the broadhead may be welded from both sides of each blade simultaneously. In the case of a three bladed broadhead all three blades are welded together at the tip with welds directed from one, two or three directions as will be explained in detail later. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view of an arrow with arrowshaft and broadhead. 
         FIG. 2  is a ferrule used in the invented broadhead. 
         FIG. 3  is an optionally used ferrule in the invented broadhead. 
         FIG. 4  is a side view of a ferrule used in the invented broadhead 
         FIG. 5  is a blade of the invented broadhead. 
         FIG. 6  is a side view of the invented broadhead 
         FIG. 7  is a detail of the distal end of the invented broadhead. 
         FIG. 8A  is a schematic representation of the invented welding method. 
         FIG. 8B  shows details of the blade assembly configured prior to welding. 
         FIG. 8C  shows a detail of the preferred blade bevel. 
         FIG. 9  is a schematic representation of an invented alternate welding method. 
         FIG. 10  is an end view illustrating the invented method. 
         FIG. 11  is an end view of the invented broadhead 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, in  FIG. 1  the invented broadhead  1  is shown in relation to an arrowshaft  2 . Threads  6 , shown as preferably male in broadhead  1  engage with threads  19  shown as preferably female of arrowshaft  2  to form arrow  20 . Broadhead  1  comprises multiple blades  10  which form a blade assembly  33  which is attached to ferrule  3 . Broadhead  1  comprises cutting edges  36 . Arrowshaft  2  comprises fletches  34 .  FIG. 2  more clearly shows ferrule  3  which is conventional and known in the art and is optionally used in the invented broadhead  1 . 
       FIG. 3  shows an optional ferrule  4  with tightening feature  5  which may optionally be used in the invented broadhead  1 . Tightening feature  5  may be a hexagonal nut feature (as shown) or a pair of opposed flats or similar features that allow a tool to be used to apply a tightening torque encouraging engagement of threads  6  to engage threads  19  in secure assembly of the broadhead  1  to arrowshaft  2  to form arrow  20 . 
       FIG. 4  shows a side view of optional ferrule  21  which features cone  7  which provides a site for attachments  15 . Threads  6  are shown at proximal end of ferrule  21 . Cone  7  may optionally be replaced by a hemisphere (not shown). Attachments  15  are preferably laser welds as described later. We have found optimized cone angle  20  of proximal cone or sphere  7  to be preferably 30 degrees to 60 degrees, and more preferably 40 degrees to 50 degrees for best strength and flight characteristics of the broadhead. Ferrule  21  also has a shaft distal portion  8  with portion length  22  and diameter  23  which may be adjusted during ferrule fabrication to achieve the target mass for the ferrule  21 . Distal cone or sphere  9  provides a site for welds  16 . Distal cone or sphere  9  may vary from cone or spherical shape. For example a bullet nose or ellipsoid shape may optionally be used. 
     Various alternative embodiments of the invention may use ferrules  3 ,  4 , or  21 . Blade  10  is shown in detail in  FIG. 5 . Blade  10  is preferably made of metal, preferably stainless steel, preferably 400 series stainless steel. In the most preferred embodiment, blade  10  is made of 420 Stainless Steel. Blade  10  includes proximal attachment zone  12 , which attached to proximal cone or sphere  7  in the broadhead  1 . Blade  10  also includes intermediate attachment zone  13  and distal attachment zone  14 . Both intermediate attachment zone  13  and distal attachment zone  14  are preferably beveled with bevel  24  to enhance the attachment to the corresponding zones of adjacent blades  10  when assembling multiple blades  10  with ferrule  21  or ferrule  3  to fabricate broadhead  1 . Bevel  24  is preferably formed by coining but can also be formed by machining and results in bevel angle  11  which is preferably about 45 degrees. Bevel  24  is coined with a coining punch (not shown) using techniques well known in the art. Any resulting flash may be trimmed off with a trimming die (not shown.) Blade edge  35  is initially formed dull and will be ground to cutting surface  36  after the blades  10  are welded to ferrule  3 ,  4 , or  21  to form broadhead  1 . 
     As shown in  FIG. 6 , blades  10  are attached to ferrule  3 , preferably by laser welding, at attachment zones  15  and  16 , and are attached to each other at attachment zone  17 . Optionally, ferrule  3  or ferrule  4  (not shown) may be used instead of the preferred ferrule  21 . At attachment zone  16 , the blades  10  are preferentially welded to each other as well as to ferrule  3 , ferrule  4 , or ferrule  21  at distal cone or sphere  9 . 
       FIG. 7  shows a detail of attachment zone  17 . The welds  18  may be spaced at intervals or preferably overlap to form a series of overlapping welds  19  that have minimum or no space between welds. Preferably, the overlap is 60 to 70 percent overlap between adjacent welds. 
     The same overlap is preferably applied at attachment zones  15  and  16  (detail not shown). 
     As shown in  FIG. 8A , corresponding to the view A-A of  FIG. 6 , bevel  24  allows optimal gap  27  between the blades. In the preferred embodiment, details of which are shown in  FIG. 8B , gap  27  is about 0.012 inches and weld channel angle  38  is about 30 degrees. Weld channel angle  38  permits radiant energy  28  to be applied simultaneously to gap  27  and along bevel  24  to bevel contact point  39  enhancing the strength of welds  18 , or  19 . These preferred dimensions are achieved when blade  10  is coined with bevel  24  chosen to be about 45 degrees and remaining unbeveled stock depth  37  (shown in  FIG. 8C ) is about 0.008 inches. Laser  25  applies radiant energy  28  through fiber optic lines  26  to apply radiant energy  28  to both sides of blades  10  at gap  27  to create a weld  18  (shown in  FIG. 7 ) or series of overlapping welds  19  to blades  10 . 
     Optionally, as shown in  FIG. 9 , one or more additional fiber optic lines  26  may be employed to simultaneously apply energy  28  to both sides of blade  10  at once. The simultaneous welding is achieved in a staggered manner to avoid excessive heat buildup. In the preferred embodiment, optional simultaneous welding of both sides of blade  10  would be done at attachment zones  15 ,  16 , and  17  by welding attachment zone  15  on one side of blade  10  while the other side of blade  10  would be simultaneously welded at attachment zone  16 . Then while the first side of blade  10  is being welded at attachment zone  16 , the other side would be being welded at attachment zone  17 , and the first side of blade  10  is welded at attachment zone  17  while the opposite side is being welded at attachment zone  15 . 
       FIG. 10  shows details of the invented method of  FIG. 8  whereby the assembly of blades  10  and ferrule  21  (not shown) is mounted on a mandrel (not shown) and then welded along one line of overlapping welds  19  ( FIG. 10   a ) rotated 120 degrees, welded again ( FIG. 10   b ), rotated 120 degrees, and welded ( FIG. 10   c ). An end view of the welded assembly is shown in  FIG. 10   d.    
       FIG. 11  shows another end view of invented broadhead  1  with angle  28  preferably 120 degrees and bevel angle  29  being preferably 30 degrees so that bevel  30  of blade  10  is thereby coplanar with bevel  31  of adjacent blade  10  thus allowing broadhead  1  to be sharpened on a flat honing stone (not shown.) 
     Broadhead  1  is a modular assembly of blades and ferrule portion which is easier to handle in field (hunting) conditions than a prior art assembly of numerous small easily lost pieces. There are no moving parts to lose. It may be easily sharpened in the field while mounted to the arrowshaft because the three blades are permanently deployed in a 120 degree arrangement so that each blade edge is in a plane with its adjacent blade&#39;s edge leading to ease of sharpening with a flat stone. The blades are preferably welded to the ferrule portion on both sides as seen in  FIG. 10 . The welded tips  17  provide mutual support resulting in a strengthened impact point  32  as well as cut on contact. Cut on contact is a design feature well known in the art and means ability to cut the target animal&#39;s flesh immediately upon impact. The impact strength is further increased by the unitary ferrule portion designed for maximum axial (impact) load support and then further being welded to the blades. The welded assembly is resistant to deformation which could result in asymmetrical flight or wobble. The ferrule portion may be selected from a different species of steel (preferably 416 SST) from that of the blades (preferably 416 or 420 SST) allowing optimum material selection choices for both. 
     In the method aspects of the invention, as shown in  FIG. 10 , the blades  10  are welded by radiant energy  28  applied by laser  25  to create welds  18  or preferably overlapping welds  19 . Initially the welds are tack welds to hold the blades and ferrule in their correct alignment for further welding.  FIG. 10  shows the view taken along sightline A-A in  FIG. 6 . In the invented method, the welds are created by a series of overlapping spot welds along gap  27 . The fiber optic line  26  is passed along the length of the area to be welded, attachment zones  15 ,  16 , and  17  in turn, applying an appropriate amount of laser energy to fuse the blades  10  together in attachment zone  17  or to fuse the blades  10  to the ferrule  3 ,  4 , or  21  at attachment zone  15 , or to both blades  10  and ferrule  3 ,  4 , or  21  at attachment zone  16 . Typically, a 1200 nM wavelength laser beam with a peak power of 3 KW with a pulse duration of 3.3 milliseconds and focused spot size of 0.025 inches is used to accomplish the laser welding. After all the welds along a series of welds are completed, the broadhead is rotated on the mandrel and the next series is welded as shown in  FIG. 10   b  and repeated as shown in  FIG. 10   c . The resulting weld series results in both sides of each blade being welded to both an adjacent blade and the ferrule. 
     While various dimensions in the drawings have been specifically shown, it is not intended that these dimensions be limiting in any way since many other dimensions can be used as desired. 
     While these embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications will be made without departing from the invention in its broader aspects. The aim of the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.