Abstract:
A contact tip is provided for wire welding applications. The contact tip includes one or more conductive brushes fitted to a conductive contact tip body. Fibers of the brush extend into a passageway traversed by welding wire in operation. Electrical current is transmitted to the brush assembly and through the brush fibers to the welding wire. The fibers may transmit the current directly and also may enhance contact of the welding wire with one or more walls of the contact tip. Improved electrical contact and weld quality are obtained.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Non-Provisional Application of U.S. Provisional Patent Application No. 60/927,348, entitled “WELDING CONTACT TIP WITH CONDUCTIVE MICROFIBER BRUSH”, filed May 3, 2007, which is herein incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    The present invention relates generally to contact tips for welding applications. 
         [0003]    A range of welding applications and apparatus are known in the field, typically adapted for a particular type of welding operation. For example, in one operation commonly referred to as metal inert gas (MIG) welding, a wire is fed from a spool through a welding torch. An electrical charge is placed on the wire via the torch and, as the wire makes contact with a grounded workpiece, an arc is formed. The arc heats the workpiece as well as the wire, melting the weld location and adding the wire to the weldment. In many such applications, a shielding gas is applied via the torch that at least partially surrounds a progressive weld pool to aide in the formation of the weld and to protect the weld during solidification of the molten metal. 
         [0004]    Various other arrangements and applications exist for wire feed welders. In general, these function similar to the MIG systems described above, but may include wires with a composite structure made of a sheath surrounding a filler material, often disposed in the sheath in a form of a metal powder. Such wires may also include flux cores with materials that protect the weld in lieu of a shielding gas. 
         [0005]    In all of these wire feed welding techniques, a persistent problem exists in maintaining good electrical contact between the wire and the charged portions of the torch. That is, the torch typically includes a series of electrically coupled conductive elements that convey charge to the wire as it passes through the torch. One of these elements is a contact tip, the function of which is to transmit electrical current from the torch to the passing wire. However, because the wire must generally freely pass through the torch as it is driven by a motor and drive mechanism from a spool, less than optimal contact may be made at certain points in the operation. If contact is lost or even temporarily interrupted between the contact tip and the wire, a degraded weld may result, particularly from interrupted or sporadic arcs, re-arcing, less than optimal arcs, and so forth. 
         [0006]    Various arrangements have been devised in attempts to maintain improved contact between elements of welding torches and welding wire. However, these have yet to provide highly reliable contact mechanisms in a range of conditions. Moreover, because certain components of the torch, such as the contact tip, may need to be changed from time to time as they wear or are degraded (such as by weld sputter), certain proposed mechanisms in the art that are not well-suited to the actual conditions present in welding applications or such easy change-out are simply not practical. 
         [0007]    There is a need, therefore, for improved technique for maintaining good electrical contact between a charged welding torch or components of a welding torch and welding wire. 
       BRIEF DESCRIPTION 
       [0008]    The present invention provides a novel approach to this problem designed to resolve certain of these drawbacks in the art. In particularly, the invention provides a contact tip that includes a conductive brush that transmits electrical charge to a welding wire fed through the contact tip. The brush may be inserted in a side aperture of the contact tip and may extend into a pathway traversed by the wire during operation. The brush may transmit electric current to the welding wire directly, but may also urge the welding wire toward a sidewall of the contact tip, insuring even greater electrical contact as the wire traverses the tip. In certain embodiments, more than one such brush may be employed, and these may extend into the passage of the welding wire from different positions around the contact tip. The contact tip may be adapted to conform to a conventional shape or form factor so that it may simply replace existing contact tips already in the field to improve existing welding systems by retrofit. 
     
    
     
       DRAWINGS 
         [0009]    These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
           [0010]      FIG. 1  is a diagrammatical overview of an exemplary wire welding system including a contact tip in accordance with aspects of the present invention; 
           [0011]      FIG. 2  is a side elevation view of an exemplary welding torch including the inventive contact tip; 
           [0012]      FIG. 3  is an exploded view of the end of the torch of  FIG. 2  illustrating the contact tip in place between the torch neck assembly and the torch nozzle; 
           [0013]      FIG. 4  is a partial sectional view through the contact tip, illustrating a conductive brush disposed in the contact tip for maintaining good contact with a welding wire; 
           [0014]      FIG. 5  is a more detailed view of the brush of  FIG. 4  in the contact tip, in contact with a welding wire traversing the contact tip during operation; 
           [0015]      FIG. 6  is a partial sectional view of an alternative configuration for the contact tip including a plurality of conductive brushes; 
           [0016]      FIG. 7  is an elevational view of a brush insert of the type that may be used in the contact tips illustrated in the previous figures; 
           [0017]      FIG. 8  is top view of the brush insert of  FIG. 7 ; and 
           [0018]      FIG. 9  is a sectional view through the brush insert of  FIG. 7  taken along line  9 - 9 . 
       
    
    
     DETAILED DESCRIPTION 
       [0019]      FIG. 1  illustrates an exemplary wire-feed welding system  10  that incorporates a contact tip in accordance with aspects of the invention. The exemplary welding system  10  includes a welding torch  12  and one or more welding resources  14  that may be utilized to perform a welding operation on a workpiece  16 . Placement of the welding torch  12  at a location proximate to the workpiece  16  allows electrical current, which is provided by a power source  18  and routed to the welding torch  12  via a welding cable  20 , to arc from the welding torch  12  to the workpiece  16 . In summary, this arcing completes an electrical circuit that includes the power source  18 , the welding torch  12 , and the workpiece  16 . Particularly, inoperation, current passes from the power source  18 , to the welding torch  12  via the welding cable  20 , to a wire electrode (see, e.g.,  FIG. 5 ), to the workpiece  16 , which is typically grounded. This arcing generates a relatively large amount of heat that causes the workpiece  16  and/or filler metal of the welding wire to transition to a molten state, thereby forming the weld. 
         [0020]    In addition to the power source  18 , the welding resources  14  may include a wire feeder  22  that provides a consumable wire electrode (such as wire  70  shown in  FIG. 5 ), through the welding cable  20  to the welding torch  12 . A wide array of wire electrodes may be used in accordance with the present techniques, including traditional wire electrodes or gasless wire electrodes. As discussed further below, the welding torch  12  conducts electrical current to the wire electrode via a contact tip located in a neck assembly  24  and supported by a securing member or nozzle  26  to facilitate arcing between the egressing wire electrode and the workpiece  16 . 
         [0021]    To shield the weld area from contaminants during welding, to enhance arc performance, and to improve the resulting weld, the exemplary system  10  includes a shielding material source  28  that feeds an inert shielding gas to the welding torch  12  via the welding cable  20 . It is worth noting, however, that a variety of shielding materials for protecting the weld location may be employed in addition to, or in place of, the inert shielding gas, including active gases, various fluids, and particulate solids. Further, other embodiments, such as those employing gasless wire electrodes, may not greatly benefit from a shielding material and, accordingly, may or may not include the shielding material source  28 . 
         [0022]    Referring to an exemplary embodiment of the welding torch, illustrated in  FIG. 2 , advancement of these welding resources (e.g., welding current, wire electrode, and shielding gas) is effectuated by actuation of a trigger  30  secured to a handle  32  of the welding torch  12 . By depressing the trigger  30  of the exemplary welding torch  12 , a switch (not shown) disposed within the trigger is closed, causing the transmission of an electrical signal that commands delivery of the welding resources into the welding cable  20  and to the neck assembly  24 . 
         [0023]    Turning to  FIG. 3 , an exemplary torch assembly is shown, including a contact tip along with other torch components. Notably, the assembly includes a diffuser  34 , a contact tip  36 , and the nozzle  26 . In the exemplary welding system, the diffuser  34  operates to receive the welding current, the wire electrode, and the shielding material. A generally conical seating location  38  of the diffuser  34  corresponds with a mating surface  40  of the contact tip  36 , thereby facilitating the centering and engagement of the contact tip  36  with the diffuser  34 . A shoulder  42  is also formed on the contact tip adjacent to the mating surface  40  for aide in centering the contact tip within the fuser  34  and the nozzle  26 . A wire path  44  extends through the contact tip and accommodates the welding wire as described in greater detail below. It also describes below, a conductive brush extends into this path  44  for aide in transmitting electrical current from the contact tip to the welding wire. A channel or bore  46  is formed in the nozzle  26  and at least partially surrounds the contact tip during operation. The channel and the surrounding nozzle help to guard the contact tip from weld splatter and damage during operation. On an opposite end of the nozzle, a seating surface  48  is formed for receiving the diffuser  34  which, in the illustrated embodiment, is threaded into the nozzle. The illustrated diffuser has a threaded portion  50  that is received in the nozzle for both attaching the nozzle to the diffuser and for capturing the contact tip therebetween. An internal shoulder  52  within the nozzle surrounds the shoulder  42  of the contact tip and further aides in the maintaining the contact tip in alignment and contact with both the diffuser and the nozzle. In operation, welding gas may be transmitted from the diffuser  34  through openings or channels  54  and around the contact tip, through the nozzle to shield welds made by advancing wire fed through the assembly. 
         [0024]      FIG. 4  is a partial sectional view of the contact tip  36  with a conductive brush  56  installed in the contact tip body  58 . As noted above, the body may be contoured and formed to fit within and be retained by the other components of the torch. Any conventional or new shape of contact tip may be accommodated, and the body may be shaped to conform to existing designs, making the contact tip completely retrofitable for improving existing welding torches. Again, the body itself is made of a conductive material, such as copper. In the illustrated embodiment, a side aperture  60  is formed and the brush  56  is disposed in the side aperture. The aperture may be of any form, such as rectangular, oblong, circular, oval, and so forth. In general, the aperture will conform to the outer perimeter configuration of the brush. 
         [0025]    The brush itself includes a holder  62  and a collection of fibers or microfibers  64  held by the holder and extending from the holder through the contact tip sidewall. In a presently contemplated embodiment, the holder may be made of a conductive material such as copper. The microfibers of the brush may be made of any suitable material, such as metal, high temperature plastic, carbon fiber, and so forth. In a presently contemplated embodiment, shoulders  66  are formed in the side aperture  60  and the holder  62  is press-fit into the side aperture until it reaches a final position adjacent to the shoulders. The shoulders keep the brush from protruding further into the aperture and appropriately locate the brush in the contact tip. The holder or the contact tip body, or both, may then be slightly deformed or staked to hold the brush in place. Alternatively, a liquid silver or high temperature solder or weld may be provided to maintain the brush in place in the contact tip. The microfibers themselves may be of any suitable dimensions, with presently contemplated microfibers being between 7 and 150 microns in diameter. Fibers with smaller diameters may provide enhanced performance, such as fibers below about 50 microns in diameter. The microfibers will extend into the passageway through the contact tip. In a presently contemplated embodiment, for example, the microfibers extend approximately to the center line  68  of the passageway through the contact tip, although different extensions may be envisaged. 
         [0026]      FIG. 5  illustrates these structures in operation. In the illustration of  FIG. 5 , a welding wire  70  is being advanced through the contact tip. The passageway through a contact tip is intentionally somewhat larger than the wire to allow the wire to advance relatively freely through the contact tip as it is fed by the wire-feed system. The fibers  64  of the brush  56  contact the wire  70  and pass current from the contact tip body to the wire. Moreover, in the illustrated embodiment, the fibers may exert a lateral force on the wire that drives the wire toward an opposite wall  72  of the contact tip. Both direct contact with the microfibers and enhanced contact with the sidewall of the contact tip improve the transmission of electrical current to the wire. However, it should be noted that sufficient electrical current may be transmitted to the wire by one or more brushes alone, although the additional transmission from the sidewall is contemplated in a present embodiment. 
         [0027]      FIG. 6  illustrates an alternative configuration of the contact tip in which a plurality of brushes  74  are provided at different locations along the contact tip. As in the previous embodiment, the contact tip body has apertures  76  formed therein with shoulders that appropriately position the brushes. The brushes may again be press-fit, staked, or otherwise held in place in the contact tip. The fibers from each brush again extend into the passageway through which the welding wire passes during welding operations. Where multiple brushes are used, these may be placed in a line along the wall of the contact tip, in diametrically opposite locations (as shown in  FIG. 6 ) or at different radial positions around the wire passageway. 
         [0028]      FIGS. 7 ,  8  and  9  illustrate a presently contemplated configuration for a brush insert  78  that can be used for the brushes described above. While the elongated configuration shown in these figures is presently contemplated, and generally conforms to the embodiment illustrated in  FIG. 4 , other configurations, such as generally square, round, oval, elongated, and so forth may be envisaged. As illustrated in  FIG. 7 , the holder  62  may be formed of a casing that is disposed around the fibers  64 . The holder casing may be made of a conductive material, such as copper. As best shown in top view of  FIG. 8 , a central opening  80  is thus formed in the holder and the fibers  64  may be placed in this opening. The holder may then be compressed or crimped as illustrated by the arrows in  FIG. 9  to capture the fibers between side and end panels of the holder. In a presently contemplated embodiment such crimping is sufficient to maintain the fibers in place and to maintain good electrical contact between the holder and the fibers. Alternatively, however, conductive boding materials, solders, and the like may be used either between the fibers or between the holder and the fibers, as well as on top of the fibers, where desired. 
         [0029]    The arrangements described above have been found to provide extremely effective contact between the contact tip and welding wire. The arrangements exhibit negligible wear and operate for long periods, maintenance free. It is estimated that the contact tips described above may provide several times the life expectancy of conventional contact tips that they may replace. Moreover, the contact tips provide for much better electrical contact and, consequently, better weld quality. Moreover, where desired, the same contact tip may be used for multiple wire sizes owing to the extension of the fibers into the passageway of the contact tip. As will be appreciated by those skilled in the art, this might alleviates the need to change the contact tip when different wire sizes are employed as is the case with conventional contact tips. 
         [0030]    While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.