Abstract:
A wire conveying mechanism, preferably for a welding, cladding or additive manufacturing apparatus, with a slip clutch mechanism connectable to a motor.

Description:
[0001]    The present disclosure generally relates to wire feeders. More particularly, the disclosure relates to wire feeders used in metalworking applications such as welding, cladding and additive manufacturing applications. 
       BACKGROUND 
       [0002]    Wire feeders are used in various welding or cladding applications to feed wire to the welding or cladding spot. Such wire can be referred to as filler wire, additive wire or consumable wire. 
         [0003]    Hot wire welding/cladding is a process where a metal filler wire is resistively heated, typically, to a softened/plastic/semi-liquidus state, usually by passing an electrical current through it. This reduces the amount of added heat from another high-power energy source needed for the base metal of a workpiece to which the heated wire is applied. Beneficially, heating up the wire rids it of moisture, so when it enters the welding/cladding puddle it&#39;s free of porosity, it&#39;s clean and the quality is significantly better than cold wire. The wire is typically fed in front of or behind a high-power energy source such as a laser or plasma that further melts the wire material or the wire material along with the base metal of the workpiece to produce a weld or clad. In TIG welding, the wire is fed to the TIG arc. 
         [0004]    In arc welding processes, such as gas metal arc welding or flux-cored arc welding, an electrode wire is used to produce the weld. An arc created between the electrode and the base metal of the workpiece is used to melt a portion of the workpiece to form a molten puddle that when solidified creates a weld. 
         [0005]    In both cases, the wire is fed into or near the puddle. This way, when a workpiece is moved relative to the welding arrangement (with either the workpiece moved or the welding equipment moved), the puddle can be maintained to create a continuous weld or cladding layer. 
         [0006]    In hot wire welding, the start of wire feeding is sequenced very precisely to prevent arcing, or overfeeding of the wire before the process can stabilize and be in a steady state. Commonly, first the wire feed is initiated. Second, the wire contacts the workpiece. Third, heating power (e.g., electrical current applied through the wire, which has some resistance) is applied to the wire. Fourth, the wire heats to a plastic/semi-liquidus phase at the weld/clad spot, namely the weld/clad puddle. Fifth, feeding and sustained high-power energy heating of the wire occurs in the steady state. 
         [0007]    The use of hot wire welding, such as tungsten inert gas welding, tends to be more part-related and industry-related. For example, hot wire TIG is used extensively in the transportation and power generation industries. It&#39;s big in shipbuilding, and for rebuilding turbine shafts for large power plants. Hot wire TIG also is used in cladding very large valve welds such as those for oil industry in which welders clad the inside of the valve weld with high-performance alloys. 
         [0008]    Additionally, wire feeders can be used in additive manufacturing, sometimes referred to as 3D printing. In additive manufacturing, wire is melted to make a three-dimensional object. To that end, successive layers of melted wire are laid down under computer control. These objects can be of almost any shape or geometry, and can be produced from a 3D model or other electronic data source. 
       SUMMARY 
       [0009]    Overfeeding of wire can be problematic in many applications, and especially in welding and cladding applications. In some applications, if the wire feeding is restricted near the weld area, the wire can buckle and coil or bunch up and form a so-called bird&#39;s nest. In arc welding, the wire can contact the weld spot and stick to the welding contact tip. This is called “burnback.” Further, the wire can fuse to the workpiece and the continuous feeding of the electrode wire and will also cause the wire to bunch up and form a bird&#39;s nest. 
         [0010]    In  FIG. 1 , there is illustrated in perspective view a wire feeder in which wire has been overfed. Wire  100 , is frictionally engaged by a wheel pair comprised of upper wheel  102  and lower wheel  104  to be conveyed relative to the wheels. In this figure, the wire  100  is conveyed from left to right. The wire  100  is feed into a nozzle or welding gun  106 , which is only partially shown. In  FIG. 1 , the wire  100  has encountered obstruction and buckled prior to the gun  106  and formed a coil or bird&#39;s nest  108 . 
         [0011]    The present disclosure describes one or more inventions relating to torque limiter or slip clutch mechanisms for wire feeders. Such mechanisms serve to reduce or end wire feeding in response to the wire fed by the feeder encountering resistance beyond a threshold. In hotwire welding, this enables the wire feeding to momentarily stop or slow until the wire again softens to the point that the set torque level is no longer exceeded. In either hotwire or arc welding, it can prevent the coiling or bunching up of the wire and the formation of bird&#39;s nests. 
         [0012]    As used herein, a slip clutch also means a torque limiter clutch and/or a safety clutch, as those terms are understood in the mechanical arts. In such clutches, a first moving part and a second moving can be frictionally engaged for cooperative movement. However, the first moving part is allowed to slip relative to the second moving part when the first moving part encounters a higher than a threshold resistance. Usually the movement is rotational movement. For consistency, the term slip clutch is used herein. 
         [0013]    As used herein, the term wire feed gun means any welding gun, cladding gun, additive manufacturing gun, or the like used to guide wire to an application. The wire feed gun may emit welding shielding gas in addition to the wire. The wire feed gun is positioned downstream of a wire feeding mechanism which performs the action or actions to convey the wire. 
         [0014]    Unless specifically noted otherwise, the term metalworking apparatus is used generically to mean any welding apparatus, any cladding apparatus, any additive manufacturing apparatus and any arc welding apparatus. The term hotwire metalworking apparatus means any metalworking apparatus employing a wire that is subjected to heating prior to application of a high energy heat source. 
         [0015]    As used herein, a high energy heat source means a laser or welding arc (which encompasses plasma). 
         [0016]    In an embodiment, the disclosure provides a wire feeder with a slip clutch that stops, slows or limits wire feeding whenever the wire experiences a resistance above a threshold resistance. 
         [0017]    In an embodiment, the slip clutch threshold is selectable in discrete increments. 
         [0018]    In an embodiment, the slip clutch threshold is selectable along a continuum. 
         [0019]    In an embodiment, the wire feeder is part of a metalworking apparatus. 
         [0020]    In an embodiment, the wire feeder is part of a welding apparatus. 
         [0021]    In an embodiment, the wire feeder is part of a cladding apparatus. 
         [0022]    In an embodiment, the slip clutch is a push-type friction clutch in which the first moving part is a rotating disc and the second moving part comprises friction members mounted on a rotating member. 
         [0023]    In an embodiment, the rotating disc is fixed relative to a rotating shaft and the rotating member rotates freely relative to the rotating shaft. 
         [0024]    In an embodiment, the second moving part includes a gear. 
         [0025]    In an embodiment, the wire feeder includes one or more wheels that frictionally engage with the wire to cause the wire to be conveyed, each such wheel including a gear meshed with the gear of the second moving part. 
         [0026]    In an embodiment, the second moving part is mounted on the rotating shaft and is retained on the shaft by means of an adjustable spring mechanism. 
         [0027]    In an embodiment, the adjustable spring mechanism includes a nut threadingly received on an end of the shaft and a helical spring between the nut and the rotating member. 
         [0028]    In an embodiment, adjustable spring mechanism includes a bearing between the spring and the rotating member. 
         [0029]    In an embodiment, the second moving part includes a friction pad disc to which are secured friction pads and a gear to which the friction pad disc is secured. 
         [0030]    In an embodiment, the first moving part includes a driving disc mounted on and keyed to the rotating shaft and a slip surface disc secured to the driving disc. 
         [0031]    In an embodiment, the wire feeder includes four wheels disposed in two wheel pairs, each wheel frictionally engaging the wire to convey the wire relative to the wheels, the wire being gripped between the wheels of each wheel pair, each wheel having a gear meshed with the gear of the second moving part. 
         [0032]    In an embodiment, a metalworking apparatus includes one of the foregoing slip clutches. 
         [0033]    In an embodiment, a metalworking apparatus includes one of the foregoing wire feeders with one of the foregoing slip clutches. 
         [0034]    These and other features are described below in greater detail with reference to the accompanying drawings. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0035]      FIG. 1  illustrates in perspective view a wired feeder in which excessive wire has been fed by the wire feeder. 
           [0036]      FIG. 2  illustrates in general a hotwire welding or cladding arrangement. 
           [0037]      FIG. 3  illustrate in side view a wire feeder using in a welding or cladding arrangement. 
           [0038]      FIG. 4  illustrates in exploded view a push-type slip clutch mechanism that can be used in a wire feeder. 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    The present disclosure is herein described in detail with reference to embodiments illustrated in the drawings, which form a part hereof. Other embodiments may be used and/or other changes may be made without departing from the spirit or scope of the present disclosure. The illustrative embodiments described in the detailed description are not meant to be limiting of the subject matter presented herein. 
         [0040]    Reference will now be made to the exemplary embodiments illustrated in the drawings, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Alterations and further modifications of the inventive features illustrated herein, and additional applications of the principles of the inventions as illustrated herein, which would occur to one skilled in the relevant art and having possession of this disclosure, are to be considered within the scope of the present disclosure. 
         [0041]    In  FIG. 2  there is illustrated a hotwire laser welding/cladding arrangement/process in which one or more of the present inventions can be used. As illustrated, a metallic workpiece  10  and wire feeding gun or torch  12  are positioned for relative travel between them. The workpiece  10  is representative of a base metal of any suitable workpiece. The direction of travel of the wire feeding gun  12  relative to the workpiece  10  is indicated by arrow  14 . 
         [0042]    Note that the relative direction of travel is not necessarily linear. The workpiece  10  could rotate about a horizontal axis, for example a pipe rotation about its cylindrical axis, or it could rotate about a vertical axis, for example, a wheel mounted in a horizontal plane. The workpiece might also be moved three dimensionally, as with multi-axis robotic welding. 
         [0043]    In process steady-state, wire  16  is feed out of the wire feed gun  12  toward a molten pool or puddle  18 . At the same time, the molten pool is subject to heating by a high energy source, in this case a focused laser beam  20 , that further melts the wire  16  and, if a welding process, a portion of the metallic workpiece  10  (i.e., the base metal) to form the puddle  18 . 
         [0044]    Since the workpiece  10  is moving relative to wire feed gun  12  and the high energy source  20 , the molten metal comprised of molten wire and, if a welding process, molten workpiece metal, exiting the incidence area of the high energy  20  cools and solidifies to form a clad layer, an additive layer, or if a welding process, a weld,  22 . 
         [0045]    In this illustrative process, shielding gas  24  is also provided via the wire feed gun  12 . 
         [0046]    In  FIG. 3 , there is illustrated in side view a wire feeding mechanism suitable for feeding the wire  16  through the wire feed gun  12 . In a housing  30 , there are provide upper wheels  32   a  and  32   b  and lower wheels  34   a  and  34   b . The wheels are paired such that wheels  32   a  and  34   a  form one pair and wheels  32   b  and  34   b  form another pair. The each wheel pair frictionally engages the wire  16  so at to convey the wire  16  between the upper and lower wheels. In this figure, the wire  16  is feed from right to left. 
         [0047]    As can be seen, the wheels are provided with respective gears  36   a ,  36   b ,  38   a  and  38   b . The gears  36   a  and  38   a  are intermeshed so that driving of wheel  34   a  also drives wheel  32   a  in the known way. Similarly, gears  36   b  and  38   b  are intermeshed so that driving of wheel  34   b  also drives wheel  32   b  in the known way. 
         [0048]    Positioned between wheels  32   b  and  34   b  is a driving gear  40  which is intermeshed with the gears  36   b  and  38   b  in the known way. 
         [0049]    In  FIG. 4 , there is illustrated in exploded view, a slip clutch mechanism  42  including the gear  40 . As illustrated, the slip clutch  42  includes a rotating shaft  44  that is driven by a motor. Secured to the rotating shaft  44  is a first moving part  46  that includes a driving disc  48 , that includes a keyway  49  that accommodates a key  44   a  on the shaft  44  so that the driving disc  48  rotates with the shaft  44 . 
         [0050]    A slip surface disc or pressure plate  50  is positioned against the driving disc  48  for rotation therewith due to an inner periphery profile that mates with a raised profile on the driving disc  48 . The specifics of the way in which the discs  50  and  48  engage each other, if at all, are not material, so long as an appropriate or sufficient slip or pressure surface facing a second moving part  52 , described below, is provided. 
         [0051]    The second moving part  52 , the components of which are described below, is also received on the rotating shaft  42 . However, the second moving part  52  is not secured to the shaft  42  and is free to rotate relative to the shaft  42 . 
         [0052]    The second moving part  52  includes the gear  40 . Secured to the gear  40  is a clutch pad part  54  that includes three friction material shoes or pads  56   a - 56   c  mounted on brackets  58   a - 58   c , respectively. The clutch pad part  54  is secured to the gear  40  by means of three bolts  60 . The clutch shoes/pads  56   a - 56   c  face the slip/pressure surface of the slip surface disc  50 . 
         [0053]    The gear  40  is received on one end of the shaft  44  but does not include any keying arrangement so that it is free to rotate relative to the shaft  44 . The gear  40  is held on the shaft  44  by means of a nut  62 . Between the nut  62  and the gear  40  is a pressure spring  64  and bearing  66 . By adjusting the nut  62  it is possible to adjust the amount of pressure of the shoes/pads  56   a - 56   c  against the slip surface. As can be appreciated, with less pressure, the shoes/pads  56   a - 56   c  will experience less friction on the slip/pressure surface, and thus be able to slip relative to the slip surface. In turn, the gear  40  will slip relative to the rotation of the shaft  44 . 
         [0054]    Conversely, suitable tightening of the nut  60  will cause the spring  64  to exert more pressure against the bearing  66  and the gear  40 , so that the shoes/pads  56   a - 56   c  in turn exert more pressure against the slip/pressure surface. Thus the pads  56   a - 56   c  will experience greater friction and be caused slip less relative to the slip/pressure surface, and thus the gear  40  will be caused to rotate more in concert with the rotation of the shaft  44 . 
         [0055]    The foregoing slip clutch mechanism uses what is referred to as an axial pressure plate mechanism or a push type mechanism. Alternatively, a radial pressure plate mechanism or centrifugal clutch mechanism might be used in which friction pads are positioned in a flywheel mechanism on a driving rotating part so with increasing rotation and centrifugal force, the pads exert increasing radial force. Such types of clutches are well known and come in many designs. Also, the slip/pressure surface is a cylindrical surface on the driven rotating part within which the friction pads rotate, as would be understood by those of ordinary skill in this art. The pressure of the pads would be adjustable by known adjustment mechanisms that would impede or facilitate the ability of the pads to extend radially due to rotation of the shaft. Other clutches use radial spring pressure to the same effect. 
         [0056]    Regardless of the type of slip clutching mechanism, the pressure or resistance needed for the friction pads to not slip is a function of, among other things, the size of the wire, and the material of which the wire is made. Thinner wire which tends to be flimsier, requires less pressure to feed it through the feeding assembly. Similarly, softer metals require more delicate handling and thus lower pressures to feed it through the feeding assembly. 
         [0057]    It can be appreciated that the above describe axial pressure adjustment mechanism provided by the nut  62  and the spring  64 , is a form of a continuously variable adjustment mechanism in that the nut can be tightened or loosening at virtually, if not actually, infinite positions along a continuum between completely disengaged to fully tightened. However, other mechanisms that can be used include incremental adjustment mechanisms in which the tightening unit includes discrete positions. An example is a spring loaded nut with detents. 
         [0058]    In one method for determining a suitable resistance threshold for the wire, and thus the pressure for the pressure applying mechanism, as an initial set-up, the wire is fed through the feeding mechanism under cold conditions under the control of the drive gear  40 . However, the pressure is adjusted so that the clutch barely does not slip so that the feeding is very slow. Then the pressure is adjusted to an increased level until the desired feeding speed is reached. At this point, any further resistance encountered by the wire causes the wire to resist feeding by the wheels  32   a ,  32   b ,  34   a  and  34   b  and, in turn, the gear  40  to slip relative to the shaft  44 . 
         [0059]    It can be appreciated that a structure such as the foregoing enables the momentary stop of the wire by means of mechanical slippage of a clutch mechanism. However, the feed wheels maintain pressure between the wire and the workpiece, but will not move the wire until it is soft enough to plastically deform, melt and flow. 
         [0060]    It is possible to measure this resistance using a load cell or some other suitable device so that the pressure setting can be repeated by simply referring to the measured values. 
         [0061]    In a typical hotwire welding arrangement, the load of the wire will be about 20-30 lbs. of force at steady state. Thus, the threshold setting for the slip clutch will typically fall within this range. 
         [0062]    At the same time, the feed rate of the wire will typically be about 400 inches per minute (ipm) at steady state. During start-up, the feed could be slow, e.g. 50 ipm. Feed speeds up to 700 ipm are also contemplated. 
         [0063]    Also, it typically takes about 1.0 to 1.5 seconds to reach steady state. The first 0.75 second or so is spent for the wire to heat up to the semi-liquidus state. 
         [0064]    In addition to the above described four driven wheel arrangement of  FIG. 3 , the two driven wheel arrangement of, e.g.,  FIG. 1  can be similarly be adapted with a suitable clutch mechanism. Other numbers and arrangements of driven wheels can also be used with similar slip clutch mechanisms. 
         [0065]    The preceding description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined here may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown here but is to be accorded the widest scope consistent with the following claims and the principles and novel features disclosed here.