Patent Publication Number: US-2021178504-A1

Title: Return Current Roller For Automatic Welder

Description:
RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 62/948,412 filed on Dec. 16, 2019, the entire disclosure of which is hereby expressly incorporated by reference. 
    
    
     FIELD 
     The present disclosure relates generally to automatic electric welding machines, more particularly to automatic arc welding machines, and even more particularly to return current techniques in automatic arc welding machines. 
     BACKGROUND 
     Automatic electric welding machines (hereinafter, simply “welding machines”) are widely used in industrial fabrication to join metal workpieces where the relative disposition of the workpieces and the configuration of the seam to be welded are sufficiently simple so as not to require the skill of a human welder. For example, automatic welding machines are widely used to join abutting flat panels which form a generally linear seam. 
     In some configurations, the panels are laid flat on a supporting surface to form seams to be welded. A welding head of the welding machine is suspended above the panels. The welding head and panels are moved relatively such that the welding head traverses the seam. For example, the welding head may be supported by a frame which is movably mounted to a gantry or rail. Alternatively, the welding head may be fixed, while the supporting surface of the panels is movable. In either case, the welding head and panels may be moved relatively to cause the welding head to travel along the seam, so as to enable welding along a length of the seam. 
     For example, U.S. Pat. No. 9,012,809 to Melin et al. teaches a welding device and a central element configured with sensor members to register geometric properties of a spacing between the work pieces. An auxiliary sensor means registers a vertical distance between the welding head and a bottom surface of the spacing between the work pieces. The auxiliary sensor means has a roller member attached to the central element including a lever-type design allowing the auxiliary sensor means to pivot around a pivoting point, to maintain contact between the roller member and the bottom surface during transport of the device along an operating direction. It is not taught, however, how the welding device is grounded. 
     In some configurations, the workpiece edges are overlapped. For example, in U.S. Pat. No. 5,726,410 to Fukushima et al, overlapping edge portions of the workpieces to be welding are squeezed together by roller electrodes with a welding current being applied between the roller electrodes. The roller electrodes are thus provided on opposite sides of the plate-like workpieces. 
     It remains commercially desirable to develop further improvements and advancements in automatic electric welding, to overcome shortcomings of known techniques, and to provide additional advantages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments will now be described, by way of example only, with reference to the attached Figures. 
         FIG. 1  is a front perspective view of a welding apparatus including an electrically conductive return current roller. 
         FIG. 2  is a side perspective view of the welding apparatus of  FIG. 1 . 
         FIG. 3  is a side elevation view of the welding apparatus according to  FIGS. 1-2 . 
         FIG. 4  is a front perspective view of a return current roller assembly according to  FIG. 3  in isolation. 
         FIG. 5  is a front elevation view of a return current roller assembly as disclosed herein including an enlarged view of a return current roller having a circumferentially tapered V-shaped rim in conforming contact with an unwelded seam of a workpiece. 
         FIG. 6  is a side elevation view of two return current rollers according to  FIG. 5 , rolling in electrically conductive conforming contact with a workpiece. 
         FIG. 7  is a figurative side elevation view of a welding apparatus having a welding torch electrically connected by a welding current lead to a welding current terminal of a current source, and return current roller rollers electrically connected by a return current lead to a return current terminal of the current source. 
     
    
    
     Throughout the drawings, sometimes only one or fewer than all of the instances of an element visible in the view are designated by a lead line and reference character, for the sake only of simplicity and to avoid clutter. It will be understood, however, that in such cases, in accordance with the corresponding description, that all other instances are likewise designated and encompassed by the corresponding description. 
     DESCRIPTION 
     Techniques for providing a return current path for an automatic electric welding apparatus are disclosed herein. In particular, disclosed herein are techniques for a welding apparatus  100  for use in performing any suitable welding, including but not limited to, electrical welding, including arc welding, including shielded metal arc welding, gas metal arc welding, flux-cored arc welding, gas tungsten arc welding, plasma arc welding, or automatic welding. 
       FIGS. 1 and 2  illustrate perspective views of a welding apparatus  100  according to an embodiment herein. The welding apparatus  100  includes a frame  102 , a return current roller assembly  116 , and a welding torch  170  for welding an unwelded seam  162  of a workpiece  160 . At least one roller  110  is rollably mounted in the return current roller assembly  116 . At least one such roller  110  is an electrically conductive return current roller  111  as further disclosed herein.  FIGS. 1 and 2  are illustrative of a two roller embodiment. Other embodiments disclose single roller embodiments including a welding apparatus  100  comprising a welding torch  170  and a single roller  110  rollably mounted in the current roller assembly  116 . This arrangement enables rolling engagement between the at least one roller  110 , including the return current roller  111 , and the workpiece  160 . In an embodiment, the welding apparatus  100  is actuated or driven to move in rolling engagement with a stationary workpiece  160 . For example, the frame  102  may be mounted to or include a rail  138  whereby a motor (not shown) drives movement of the rail  138 , and by extension, movement of the welding apparatus  100  over the workpiece  160  while the workpiece  160  remains stationary. In another embodiment, the welding apparatus  100  is stationary and the workpiece  160  moves relative to the welding apparatus  100 , for rolling engagement therewith. In another embodiment, at least one of the welding apparatus  100  and the workpiece  160  are actuated or driven to enable relative rolling engagement between the welding apparatus  100  and the workpiece  160 . 
     A welding torch  170  may be electrically connected by a welding current lead  122  to a welding current terminal  192  of a current source  190  (shown in  FIG. 7 ). Accordingly, when using the welding torch  170  to weld an unwelded seam  162  of a workpiece  160 , a welding current conducts along a source current path  195  from the current source  190  and draws into the workpiece  160  at a welding point  178  of a welding torch tip  171  of the welding torch  170  and the workpiece  160 . The welding point  178  is understood to generally encompass a point where a weld pool is formed through application of heat from the welding torch tip  171 . The weld pool, formed at the welding point  178 , subsequently forms a weld through cooling and fusion of metals. In particular, the welding point  178  may not require direct contact between the welding torch tip  171  and the workpiece  160 , in particular in methods of welding including but not limited to, electrical welding, arc welding, shielded metal arc welding, gas metal arc welding, flux-cored arc welding, gas tungsten arc welding, plasma arc welding, or automatic welding. In such welding techniques, and other similar and related welding techniques, the welding current draws into the workpiece  160 , from the welding torch tip  171 , at the welding point  178 . 
     Techniques known in the art for providing a return current path include providing a workpiece clamp, sometimes called a “ground clamp”, fixed to an end of the workpiece  160 . The workpiece clamp may form part of a return current path to the current source, for example, by operatively connecting the workpiece clamp to a return current terminal of the current source. Such techniques however suffer the disadvantage of a variable return current path length through the workpiece, inasmuch as the welding torch tip  171  advances along the unwelded seam  162 , current drawn into the workpiece  160  conducts over a varying distance to the workpiece clamp as a result of the changing distance between the welding torch tip  171  and the workpiece clamp. Such variability in return current path length degrades welding conditions, resulting in lower quality welds. 
     Thus, at least one roller  110  is an electrically conductive return current roller  111 . The return current roller  111  is formed of a durable, conductive material, such as a conductive metal or alloy, which may be brass, copper alloy, aluminum, or any other suitable conductive material. The return current roller  111  is electrically connectable to a return current terminal  194  of a current source  190 , such as by a return current lead  121  as shown in  FIG. 7 . Thus, the return current roller  111  functions as a return current electrode in a return current path  196  for welding current entering the workpiece  160  from the welding torch tip  171 , and then exiting the workpiece  160 . 
     As shown especially in  FIG. 5 , the return current roller  111  may be sized and shaped for conformable contact with the unwelded seam  162  of the workpiece  160  for rolling in conforming engagement with the unwelded seam  162  sufficiently to maintain electrically conductive contact with the unwelded seam  162 . The return current roller  111  sized and shaped for conformably rolling contact with the unwelded seam  162  may provide the further advantage of restricting rolling engagement of the return current roller  111  to within the unwelded seam  162 , thereby laterally restricting and aligning movement of the welding apparatus  100  to the unwelded seam  162  as it rollingly engages the workpiece  160 . The restricted movement of the welding apparatus  100  may be operative to position the welding torch  170  in alignment with the unwelded seam  162 . Thus, as the welding apparatus  100  moves in rolling engagement with the workpiece  160 , the welding torch  170  may be aligned to move along and weld the unwelded seam  162  as the welding torch  170  passes thereover. Alignment of the welding apparatus  100  with the unwelded seam  162  may be achieved at least in part by restricting rolling movement of the return current roller  111  to the unwelded seam  162 . The return current roller  111  may be circumferentially tapered to form a V-shaped rim  114 , as shown in  FIG. 5 . Generally, the profile of the rim of the return current roller  111  may be matched to a profile of the unwelded seam  162 , including shapes other than a V-shape. For example the return current roller may have a rim circumferentially profiled in a circular shape, a semi-circular shape, an elliptical shape, or a semi-elliptical shape. 
     As shown particularly in  FIGS. 1-3 , the welding torch  170  and the return current roller  111  may be mounted relative to one another in a substantively fixed spatial relationship for disposition of the welding torch tip  171  a substantively fixed distance from the return current roller  111 , or each return current roller  111 , as the case may be. In some embodiments, a first electrically conductive return current roller  112  and a second electrically conductive return current roller  113  are rollably mounted in a return current roller assembly  116  relative to the welding torch  170 , wherein the first and second return current rollers  112 ,  113  are respectively mounted first and second substantively fixed distances apart from welding torch  170 . A contact point between the one or more electrically conductive return current rollers  111  and the unwelded seam  162  enables current to exit the workpiece  160  through the respective return current roller  111  (shown in  FIG. 7 ), which thus functions as a return current electrode in a return current path. Accordingly, a return current path through the workpiece  160  (arrows  197 ) may be maintained at a substantively fixed length, or variability of such length may be minimized, thereby minimizing or at least decreasing variability in the electrical impedance of the return current path, thereby minimizing or at least decreasing variability in the welding current flowing into the workpiece  160  at the welding point  178  in the unwelded seam  162  where the welds are formed, and thereby maximizing, or at least improving, a quality of the welds thus formed. In an embodiment, the return current roller  111  is mounted to a frame  102  a substantially fixed distance apart from welding torch  170 . 
     In an embodiment, a return current roller assembly  116  may include an A-frame assembly  117  mounted to a strut  120 . A-frame assembly  117  may have three legs  118   a ,  118   b , and  118   c , as shown particularly in  FIGS. 1-4 . An orientation of the A-frame  117 , such as a pitch of the A-frame assembly  117 , is pivotably variable relative to the strut  120 . In this manner, pivotably varying an orientation of the A-frame assembly  117  may advantageously maintain at least one roller  110  in rollingly conforming contact with an unwelded seam  162  as the rollers  110  traverse undulations and other deviations of the unwelded seam  162 . In an embodiment, the A-frame assembly  117  is pivotable about a pin  119  by which the pivot leg  118   a  of the A-frame assembly  117  is mounted in the strut  120 . The pivotable A-frame assembly  117  may include two electrically conductive return current rollers  111 , which may leverage advantages of pivotably varying an orientation of the A-frame assembly  117 . 
     Pivoting and by extension varying an orientation of the A-frame assembly  117  may rotatably displace a position of the rollers  110  relative to the strut  120 . For example, as the return current rollers  111  conductively contact an unwelded seam  162 , undulations or other deviations in the unwelded seam  162  may urge the return current rollers  111  to displace in a particular direction, causing the A-frame assembly  117  to correspondingly vary its orientation, for example by pivoting in a clockwise or counter clockwise direction. Undulations causing the A-frame assembly  117  to pivot in a counter-clockwise direction may result in a first return current roller  112  breaking electrically conductive contact with the unwelded seam  162  while concurrently transferring weight to a second return current roller  113 , thereby exerting greater pressure on the second return current roller  113  to maintain electrically conductive contact with the unwelded seam  162 . Conversely, undulations causing A-frame return current roller assembly  116  to pivot in a counter clockwise direction may result in the second return current roller  113  breaking electrically conductive contact with the unwelded seam  162  while concurrently increasing pressure on the first return current roller  112 , thereby exerting greater pressure on the first return current roller  112  to maintain electrically conductive contact with the unwelded seam  162 . As described herein, a return current roller assembly  116 , such as an A-frame return current roller assembly  117 , may advantageously pivot in response to the additional weight bearing on either the first return current roller  112  or the second return current roller  113 , thereby maintaining at least one return current roller  111  in electrically conductive contact with the unwelded seam  162 . 
     As an example, current drawn into the workpiece  160  may initially exit the workpiece  160  through the first return current roller  112 , and subsequently exit the workpiece  160  through the second return current roller  113  in the event that the first return current roller  112  breaks electrically conductive contact with workpiece  160 . As such, the return current path in the workpiece (arrows  197 ) distance may experience some minor variance in length based on whether current drawn into the workpiece  160  exits through the first return current roller  112  and thus travels a first return current path in the workpiece (arrow  198 ) or the second return current roller  113  and thus travels a second return current path in the workpiece (arrow  199 ). Such variance in the return current path length may however be maintained at a substantively fixed length, or variability of such length may be minimized, thereby minimizing or at least decreasing variability in the electrical current flowing into the workpiece  160 . For example, the first return current roller  112  and the second return current roller  113  may be mounted in the return current roller assembly  116 , relatively close together, to minimize variance in the return current path length between the return current rollers  112 ,  113 . Additionally, or alternatively, a distance between the first return current roller  112  and the second return current roller  113  may be proportionally small compared to the respective distances between the first return current roller  112  and the second return current roller  113 , on the one hand, and the welding torch  170 , on the other hand, such that the proportional change in return current path length resulting from changing of contact of the first return current roller  112  and the second return current roller  113  with the workpiece  160  is likewise proportionally small. Accordingly, a multi-roller pivotable return current roller assembly  116  may thus advantageously maintain at least one return current roller  111  in electrically conductive conforming contact while minimizing variance in the return current path length that may arise from one return current roller  111 , or the other, breaking from electrically conductive contact with the unwelded seam  162 . Other embodiments as disclosed herein further provide for varying an orientation or position of the return current roller assembly  116 , such as by varying a heading or elevation of the return current rollers  111  relative to the frame  102 , providing additional responsiveness to undulations, deviations, and other topographic features of the workpiece  160  and the unwelded seam  162 . 
     As shown in  FIG. 3 , the welding apparatus  100  may include return current rollers  111  rollably mounted to the A-frame assembly  117  which is pivotably mounted to a strut  120  which is in turn mounted to the frame  102 . In particular, a bracket  137  may support the strut  120 , and may be supported in turn a rail  138 . The welding torch  170  may be mounted to a welding torch mounting assembly  172 , and the welding apparatus  100  may further have a filler rod feeder  180  mounted to a filler rod feeder mounting assembly  182 . Each of the return current roller assembly  116  and welding torch mounting assembly  172  may be mounted to the frame  102  to maintain a substantially fixed distance between them, minimizing variability in welding conditions, as the welding apparatus  100  rollingly engages with and welds an unwelded seam  162  of a workpiece  160 . In this way, a return current path length, including a distance travelled by the current in the workpiece  160  from the welding torch tip  171  and exiting the workpiece  160  through the return current rollers  111 , may be substantially fixed when the welding apparatus  100  is in operation. 
     The welding torch  170  may be mounted to the frame  102  of the welding apparatus  100  by means of the welding torch mounting assembly  172 . Alternatively, the welding torch  170  may be mounted directly to the frame  102 . Regardless, the welding torch  170  may be mounted in such fashion as to remain spaced a substantively fixed distance from each respective return current roller  111 . This establishes a return current path having a substantively fixed length based on a substantively fixed distance between where current enters the workpiece  160  from the welding torch tip  171  and where the current exits the workpiece  160  through the return current rollers  111 . 
     In particular, the welding torch mounting assembly  172  may comprise a mounting arm  173  having a mounting arm slot  174 , a mounting bracket  175 , and a welding torch bracket  176  pivotally mounted to the mounting bracket  175 . The welding torch  170  may be mounted to the welding torch bracket  176  which may pivot relative to the mounting bracket  175  for varying a position and/or orientation of the welding torch  170 . Accordingly, the welding torch bracket  176  may be pivotable to position and orient the welding torch tip  171  relative to the workpiece  160 , to locate the welding torch tip  171  in a position suitable for welding an unwelded seam  162  of a workpiece  160 . A position of the welding torch  170 , and by extension the welding torch tip  171 , may be further varied by adjusting a position of the mounting bracket  175  within the mounting arm slot  174  of the mounting arm  173 . For example, the mounting bracket  175  may affix to the mounting arm  173  using fasteners, or other adjustable mechanical coupling mechanisms and mounting techniques known in the art. A position of the mounting bracket  175  relative to the mounting arm  173  may be slidably adjusted by loosening the fastening or other coupling mechanism which engages the mounting bracket  175  with the mounting arm slot  174 , and then sliding the mounting bracket  175  to a different position within the mounting arm slot  174 . Once moved to a new position, the mounting bracket  175  may be reaffixed to the mounting arm  173 , to maintain a fixed position relative to the mounting arm  173 . Accordingly, the mounting bracket  175  and the welding torch bracket  176  may cooperate to provide the welding torch  170 , and by extension welding the torch tip  171 , at a desired elevation, position, and orientation relative to workpiece  160 . Once fixed in position, and by virtue of the welding torch mounting assembly  172  being fixedly attached to the frame  102 , the spatial relationship between the welding torch  170  and the respective return current rollers  111 , is maintained a substantively fixed distance apart. 
     The welding apparatus  100  may include other welding equipment, including a filler rod feeder  180  for providing a filler rod  181 . The filler rod feeder  180  may be mounted to a filler rod feeder mounting assembly  182 , as shown for example, in  FIG. 3 . The filler rod feeder mounting assembly  182  may comprise a filler rod feeder bracket  183  fastened or otherwise mechanically coupled to a mounting bracket  175 , a filler rod feeder mounting arm  185  extending from the filler rod feeder bracket  183 , and wherein the filler rod feeder  180  is pivotally attached to a filler rod feeder mounting arm  185 . In an embodiment, the filler rod feeder mounting assembly  182  further comprises a welding shield  186  attached to the filler rod feeder mounting arm  185  for disposing the welding shield  186  between the filler rod feeder  180  and the welding torch  170 . Similar to the welding torch mounting assembly  172 , the filler rod feeder mounting assembly  182  may be operative to vary or adjust a position, elevation, and/or orientation of the filler rod feeder  180  relative to the workpiece  160 , for locating the filler rod feeder  180  at a desired position. For example, a position or elevation of the filler rod feeder bracket  183  may be adjusted by fastening or mechanically coupling the filler rod feeder bracket  183  to the mounting bracket  175  at a desired location within the filler rod feeder bracket slot  184 . Similarly, the filler rod feeder  180  may pivot relative to the filler rod feeder mounting arm  185 , to vary a position or orientation of the filler rod feeder  180 . In this manner, a position, orientation, and/or elevation of the filler rod feeder  180 , may be varied or adjusted as desired. 
       FIG. 4  further shows a front perspective of the return current roller assembly  116  in isolation. The strut  120  may include a strut rod  132  and a suspension device  134 . The strut rod  132  may be coupled to the suspension device  134  for sliding movement of the strut rod  132  relative to the suspension device  134 , which may be in-and-out of the suspension device  134 . The suspension device  134  may be configured to urge the strut rod  132  out of, and away from, the suspension device  134 , and may also include damping means. For example, the suspension device  134  may include a coilover (coil-over shock absorber), or may alternatively include a spring in a housing. The A-frame assembly  117  may be mounted to the strut rod  132 , whereby an orientation or position, including an elevation of the A-frame roller assembly  117 , may vary relative to the bracket  137 , and thus the frame  102 , by movement of the strut rod  132 . For example, an orientation or position of the A-frame assembly  117  may vary by extension or retraction of the strut rod  132  in-and-out of the suspension device  134 . As indicated above, the strut rod  132  may be urged outwardly to extend from the suspension device  134 , towards the workpiece  160 . In this manner extendedly urging the A-frame assembly  117  towards the workpiece  160  applies pressure between the return current rollers  111  and the workpiece  160 . Constant application of pressure acting on the return current rollers  111  assists in maintaining the return current rollers  111  in electrically conductive conforming rolling contact with the unwelded seam  162 . The suspension device  134  may be configured to permit retraction of the strut rod  132 , thereby enabling movement of the A-frame assembly  117  toward the suspension device  134 , and thus the frame  102 . In this way the A-frame assembly  117  and return current rollers  111  may be configured to intimately track vertical undulations and other elevation changes in the unwelded seam  162 . The A-frame assembly  117  may be mounted to the strut rod  132 , or the strut rod  132  may be mounted to the suspension device  134 , in such a way as to permit rotation of the A-frame assembly  117  about a longitudinal axis of the strut rod  132 , to vary a heading of the A-frame roller assembly  117  and return current rollers  111 . In this way the A-frame assembly  117  and return current rollers  111  may also be configured to intimately track lateral undulations in the unwelded seam  162 . 
     As discussed herein, the return current roller  111  may have a circumferential rim sized and shaped for conforming contact with the unwelded seam  162 . As shown particularly in  FIG. 5 , the return current roller assembly  116  may include the A-frame roller assembly  117  and return current roller  111  having a circumferentially tapered V-shaped rim  114 . The V-shaped rim  114  may be tapered to conformingly roll in electrically conductive contact with the unwelded seam  162  having a similarly V-shaped cross-section. Tapering the rim  114  to a shape or contour of the unwelded seam  162  advantageously yields constant and reliable contact between the return current roller  111  and the unwelded seam  162 , producing consistent welding conditions. A return current roller  111  having a rim  114 , such as a circumferentially tapered V-shaped rim, sized and shaped for conformably rolling contact with the unwelded seam  162 , may provide the further advantage of restricting rolling engagement of the return current roller  111  to the unwelded seam  162 , thereby laterally restricting and aligning movement of the welding apparatus  100 , including particularly the welding torch  170 , and even more particularly the welding torch tip  171 , to the unwelded seam  162  as it rollingly engages the workpiece  160 . 
       FIG. 6  shows a side elevation view of the return current roller assembly  116 , including the A-frame assembly  117 , and illustrates how lateral movement of the welding apparatus  100  may be restricted by the return current rollers  111  having circumferentially tapered V-shaped rims  114 , or other rims sized and shaped for rolling in conforming contact with the unwelded seam  162 . As shown in  FIG. 6 , a side portion  204  of the rim  114  of each of the first return current roller  112  and the second return current roller  113  extends beneath a top surface  161  of the workpiece  160 . Accordingly, any lateral force exerted against the return current rollers  111  causes the side portion of the rim  114  beneath the top surface  161  of the workpiece  160  to abut against a side of the unwelded seam  162 . Such contact may prevent or restrict lateral movement of the return current rollers  111  relative to the unwelded seam  162 , thereby restraining the return current rollers  111  to roll in conformably rolling electrically conductive contact along the unwelded seam  162 . 
       FIG. 7  shows the welding apparatus  100  which may include a current source  190  having a current source terminal  192 , and a return current terminal  194 . A current source lead  122  electrically connects the current source terminal  192  and the welding torch  170 , and conducts current from the current source  190  to the welding torch  170 . A return current lead  121  electrically connects the return current terminal  194  and the return current rollers  111 , and conducts current exiting the workpiece  160  through the return current rollers to the current source  190 . Accordingly, a return current path is established whereby current entering the workpiece  160  from welding torch tip  171  subsequently returns to the current source  190 . As disclosed herein, the spatial relationship between the welding torch  170  and the respective return current rollers  111  is maintained at a substantively fixed distance apart, thereby, a return current path is established having a substantively fixed return current path distance, for maintaining consistent electrical parameters and thereby maintaining consistent welding conditions and improving a quality of weld. 
     The embodiments illustrated in  FIGS. 1-7  depict a single welding apparatus  100 , however, the disclosure herein is not so limited. Other aspects of the disclosure include a welding apparatus system having a plurality of welding apparatus  100  as disclosed herein. Each welding apparatus  100  may be mounted to a common element or structure, such as a linear rail. For example, in an embodiment, a plurality of welding apparatus  100  may be mounted to a linear rail which rides on an overhead track, extending above a corresponding plurality of unwelded seams situated amongst one or more workpieces. A motor, or the like, may be used to drive or actuate movement of the linear rail, for correspondingly driving movement of each individual welding apparatus, to simultaneously move in relation to the workpiece(s) and weld each corresponding unwelded seam. 
     A common element or object, such as the linear rail, may further provide a common surface for ground and power lines to run along for each of the plurality of welding apparatus. Such comingling of lines however may give rise to cross-interference, cross-inductance, and other undesirable effects between the plurality of welding apparatus. Accordingly, the set of power and ground lines for each welding apparatus may be run within a steel sheath further contained within a non-conductive wrap, thereby minimizing cross-contamination effects with other welding apparatus. Each sheath of wires may be further isolated using plastic IGUS™ cable trays, further spaced with coolant lines in between each sheath of wires. Moreover, each steel sheath may be electrically bonded to machine ground only at a power source of the steel sheath. 
     The following are non-limiting embodiments according to the disclosure herein. 
     Embodiment 1. A welding apparatus, comprising: a welding torch mounted to a frame and electrically connectable in a source current path of a welding current source, and an electrically conductive return current roller rollably mounted to the frame a substantially fixed distance from the welding torch, the return current roller electrically connectable in a return current path of the welding current source, the return current roller having a rim sized and shaped to roll in electrically conductive contact with an unwelded seam of a workpiece. 
     Embodiment 2. The welding apparatus according to Embodiment 1, wherein the return current roller is circumferentially tapered to form a V-shaped rim. 
     Embodiment 3. The welding apparatus according to Embodiment 1 or 2, wherein a profile of the return current roller rim matches a profile of the unwelded seam of the workpiece. 
     Embodiment 4. The welding apparatus according to any one of Embodiments 1 to 3, wherein, when the welding apparatus is in use, the substantially fixed distance is between a contact point of the return current roller with the unwelded seam and a welding point of a welding torch tip of the welding torch in the unwelded seam. 
     Embodiment 5. The welding apparatus according to any one of Embodiments 1 to 4, wherein, when the welding apparatus is in use, the return current roller is operative as a return current electrode in the return current path between the welding torch and the welding current source. 
     Embodiment 6. The welding apparatus according to Embodiment 1, wherein the return current roller is a first electrically conductive return current roller, the welding apparatus further comprising: a return current roller assembly mounted to the frame, wherein the first return current roller is rollably mounted in the return current roller assembly a first substantially fixed distance from the welding torch; and a second electrically conductive return current roller rollably mounted in the return current roller assembly a second substantially fixed distance from the welding torch, wherein the first return current roller and the second return current roller are each electrically connectable in the return current path of the welding current source. 
     Embodiment 7. The welding apparatus according to Embodiment 6, wherein, when the welding apparatus is in use: the first return current roller is operative as a first return current electrode in a first return current path between the welding torch and the welding current source; and the second return current roller is operative as a second return current electrode in a second return current path between the welding torch and the welding current source. 
     Embodiment 8. The welding apparatus according to Embodiment 7, wherein: the first return current path has a first substantially fixed return current path length based on the first substantially fixed distance; and the second return current path has a second substantially fixed return current path length based on the second substantially fixed distance. 
     Embodiment 9. The welding apparatus according to any one of Embodiments 6 to 8, wherein: the first return current roller has a first rim sized and shaped to roll in electrically conductive contact with the unwelded seam of the workpiece; and the second return current roller has a second rim sized and shaped to roll in electrically conductive contact with the unwelded seam of the workpiece. 
     Embodiment 10. The welding apparatus according to Embodiment 9 wherein: a first profile of the first return current roller rim matches a profile of the unwelded seam of the workpiece; and a second profile of the second return current roller rim matches the profile of the unwelded seam of the workpiece. 
     Embodiment 11. The welding apparatus according to any one of Embodiments 6 to 10, wherein the return current roller assembly comprises a pivotable A-shaped frame wherein an orientation of the return current roller is pivotally variable. 
     Embodiment 12. The welding apparatus according to Embodiment 10, wherein the return current roller assembly comprises a pivotable A-shaped frame wherein an orientation of the return current roller is pivotally variable, and when the welding apparatus is in use, the orientation of the return current roller assembly is pivotally variable to maintain at least one of the first and second return current rollers in electrically conductive contact with the unwelded seam. 
     Embodiment 13. The welding apparatus according to any one of Embodiments 6 to 12, wherein the first return current roller is circumferentially tapered to form a first V-shaped rim, and the second return current roller is circumferentially tapered to form a second V-shaped rim. 
     Embodiment 14. The welding apparatus according to any one of Embodiments 6 to 13, wherein, when the welding apparatus is in use: the first substantially fixed distance is between a first contact point of the first return current roller with the unwelded seam and a welding point of a welding torch tip of the welding torch in the unwelded seam; and the second substantially fixed distance is between a second contact point of the second return current roller with the unwelded seam and the welding point. 
     Embodiment 15. The welding apparatus of any one of Embodiments 6-14, wherein the return current roller assembly is mounted to a strut, wherein the strut is mounted to the frame, and the strut is operative to vary a position of the return current roller assembly. 
     Embodiment 16. The welding apparatus of Embodiment 15, wherein the strut comprises a suspension device comprising a strut rod, wherein the strut is mounted via a bracket to the frame, wherein the strut rod is coupled for sliding moving relative to the suspension device, to vary the position of the return current roller assembly. 
     Embodiment 17. The welding apparatus according to Embodiment 16, wherein the suspension device is operative to urge extension of the strut rode from the suspension device. 
     Embodiment 18. The welding apparatus according to Embodiment 16 or 17, wherein the suspension device comprises a coilover. 
     Embodiment 19. The welding apparatus according to any one of Embodiments 6-18, wherein the return current roller assembly is rotatably mounted to the frame for varying an orientation of the return current roller assembly. 
     Embodiment 20. A welding system comprising a plurality of welding apparatus according to any one of Embodiments 1-19 wherein the frame corresponding to each of the plurality of welding apparatus is coupled to a moveable rail. 
     In the preceding description, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the embodiments. However, it will be apparent to one skilled in the art that these specific details are not required. In particular, it will be appreciated that the various additional features shown in the drawings are generally optional unless specifically identified herein as required. The above-described embodiments are intended to be examples only. Alterations, modifications and variations can be effected to the particular embodiments by those of skill in the art. The scope of the claims should not be limited by the particular embodiments set forth herein, but should be construed in a manner consistent with the specification as a whole.