Abstract:
A pinch type weld gun wherein a shunt is fixedly secured at one end thereof to a gun electrode and fixedly secured at another end thereof to the gun transformer. The shunt is formed of a plurality of elongated strips of flexible copper material which are arranged in stacked configuration whereafter the end portions of the stack are electrically welded to fuse the end portions together to form solid unified end portions. The strips are unsecured intermediate the unified end portions to form a flexible intermediate portion extending between the transformer and the electrode. The solid end portion of the shunt for securement to the transformer is thereafter machined to form intersecting longitudinal and transverse bores to define a passage for delivery of a coolant fluid to the transformer coolant passage system through the solid end of the shunt.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 10/298,818 filed Nov. 10, 2002. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to weld guns and more particularly to weld guns especially suitable for use in industrial automotive applications.  
         BACKGROUND OF THE INVENTION  
         [0003]    Weld guns are common usage in many industrial applications and in particular in automotive applications. Where a myriad of weld gun designs have been proposed and/or utilized commercially, there is still a need for a simpler weld gun design, providing a less expensive cost of assembly; for a weld gun design that is easier to service, thereby reducing servicing costs; and for a weld gun design that provides a longer life, thereby reducing replacement costs. Specifically, there is a need for a weld gun having an improved coolant system for the weld gun transformer.  
         SUMMARY OF THE INVENTION  
         [0004]    This invention is directed to the provision of an improved weld gun.  
           [0005]    More specifically, this invention is directed to the provision of a weld gun design that is simple, inexpensive and durable.  
           [0006]    The weld gun of the invention is of the type including a frame structure, a weld arm mounted on the frame structure, an electrode mounted on the weld arm and including an electrode cap at one end of the electrode, a transformer, and a shunt secured at opposite ends thereof to another end of the electrode and to the transformer.  
           [0007]    According to an important feature of the invention, the transformer includes a coolant passage system; the transformer end of the shunt includes a coolant passage; and the transformer coolant passage system and the shunt coolant passage are aligned and communicate so that a cooling fluid may be passed through the shunt coolant passage and into the transformer coolant passage system. This arrangement provides a ready and convenient means for delivering a coolant fluid to the transformer and eliminates the need for shunt adapters.  
           [0008]    According to a further feature of the invention, the transformer end of the shunt is secured to an end face of the transformer and the shunt coolant passage includes a transverse bore extending through the transformer end of the shunt parallel to the transformer end face and a longitudinal bore intersecting the transverse bore and communicating with the transformer coolant passage system. This arrangement provides a convenient means of accessing the coolant passage in the shunt to facilitate delivery of the cooling fluid to the transformer.  
           [0009]    According to a further feature of the invention, the weld arm comprises a first weld arm; the electrode comprises a first electrode; the shunt comprises a first shunt; the weld gun further includes a second weld arm mounted on the frame structure, a second electrode mounted on the second weld arm and including an electrode cap at one end of the second electrode, and a second shunt fixedly secured at one end thereof to another end of the second electrode and fixedly secured at another end thereof to the transformer at a location on the transformer spaced from the transformer end of the first shunt; the transformer coolant passage system includes an inlet end and an outlet end; the coolant passage in the transformer end of the first shunt communicates with the inlet end of the transformer coolant passage system; and the transformer end of the second shunt includes a coolant passage communicating with the outlet end of the transformer coolant passage system. This arrangement allows for delivery of a cooling fluid to the transformer coolant passage system through the transformer end of the first shunt and allows the discharge of the cooling fluid from the transformer coolant passage system through the transformer end of the second shunt.  
           [0010]    According to a further feature of the invention, the transformer ends of the first and second shunts are secured in spaced relation to an end face of the transformer and the inlet and outlet ends of the transformer coolant passage system open in the end face of the transformer proximate the transformer ends of the first and second shunts respectively. This arrangement provides a convenient means of packaging the shunt ends with respect to the transformer coolant passage system.  
           [0011]    According to a further feature of the invention, the shunt is formed of a plurality of strips of electrically conductive material; the strips are fixedly secured at their opposite end portions to form rigid unified shunt end portions but are unsecured intermediate the unified end portions to form a flexible intermediate portion between the unified end portions and; the unified end portion of the shunt for securement to the transformer includes a shunt coolant passage which, with the shunt end portion secured to the transformer, is aligned with and communicates with the transformer coolant passage system so that a cooling fluid may be passed through the shunt coolant passage and into the transformer coolant passage system.  
           [0012]    According to a further feature of the invention, the strips are fixedly secured together in an electric welding process to form solid fused together end portions which are thereafter machined to form the shunt coolant passage. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein:  
         [0014]    [0014]FIG. 1 is a perspective view of a weld gun according to the invention;  
         [0015]    [0015]FIG. 1A is a perspective view of a coolant distributor assembly for the weld gun;  
         [0016]    [0016]FIG. 2 is a side elevational view of the weld gun;  
         [0017]    [0017]FIG. 3 is an end view of the weld gun;  
         [0018]    [0018]FIG. 4 is a cross-sectional view taken on line  4 - 4  of FIG. 2;  
         [0019]    [0019]FIG. 5 is a perspective view of the basic skeletal structure of the weld gun;  
         [0020]    [0020]FIGS. 6, 7 and  8  are elevational, end, and perspective views of a first shunt utilized in the weld gun;  
         [0021]    [0021]FIG. 6A is a detail view taken within the circle  6 A of FIG. 6;  
         [0022]    [0022]FIGS. 9, 10,  11  and  12  are elevational, front end, rear end, and perspective views of a second shunt utilized in the weld gun;  
         [0023]    FIGS.  13 - 16  are detail views of component parts of the weld gun;  
         [0024]    [0024]FIG. 17 is a fragmentary cross-sectional view taken within the circle  17  of FIG. 3;  
         [0025]    [0025]FIG. 18 is a detail view showing a transformer/shunt interface of the weld gun; and  
         [0026]    [0026]FIG. 19 is a cross-sectional view of a portion of the coolant distributor assembly seen in FIG. 1A. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0027]    The weld gun  10  of the invention, broadly considered, includes, a transformer  12 , a cage or cradle assembly  14 , an outer weld arm structure  16 , an inner weld arm structure  18 , an upper electrode assembly  20 , a lower electrode assembly  22 , a power cylinder assembly  24 , a balancing cylinder assembly  26 , an upper shunt  28 , a lower shunt  30 , and a coolant distributor assembly  31 .  
         [0028]    Transformer  12  (FIGS. 1, 2 and  18 ) is of known form and has a monolithic rectangular configuration including a top face  12   a ,side faces  12   b , a rear end  12   c , and a front face  12   d . Transformer  12  in known manner includes a coolant passage system  13  to facilitate the delivery of coolant to the transformer.  
         [0029]    Cage or cradle  14  (FIGS. 1, 2 and  5 ) is arranged to straddle the transformer and includes side plates  32 , cross bars  34  and  36 , and a front shield  37 . Cage  14  fits around the transformer with forward bracket arm portions  32   a  of the side plates extending forwardly beyond the front face  12   d  of the transformer. Shield  37  is fixedly secured to and extends between the front ends of bracket portions  32   a . Bolts  38  fixedly secure cross-bars  34 ,  36  to side plates  32  and set screws  39  fixedly mount the cage on the transformer.  
         [0030]    Outer weld structure  16  (FIGS. 1, 2,  5 ,  13  and  14 ) includes a pair of spaced arcuate side arms  40  and a holder block  42  fixedly positioned between the lower ends  40   a  of the side arms  40  via bolts  43 . A pair of spacer plates  44  are positioned between the opposite faces of block  42  and the respective confronting inner faces of side arm lower end portions  40   a.    
         [0031]    Side arms  40  are pivotally secured to the bracket arm portions  32   a  of the side plates of the cage via a clevis or pivot pin  46  passing through aligned apertures  32   b  (FIG. 4) in bracket arm portions  32   a  and through apertures  40   b  in the respective side plates. A ball bearing assembly  47  is positioned between each aperture  40   b  and the main body portion of  46   a  of the clevis pin  46 . Each bearing assembly  47  includes an inner race  48  fixedly secured to pivot pin main body portion  46   a , an annular dielectic member  49  (formed of a suitable insulative material such as nylon) fixedly positioned within the respective aperture  40   b  and having an inwardly facing cup shaped configuration in cross-section; an outer race  50  fixedly secured within the annular cup defined by annular member  49 , and a ball run  51  rollably positioned between inner and outer races  48  and  50 .  
         [0032]    Inner weld arm structure  18  (FIGS. 1, 2,  5  and  15 ) has a clevised upper configuration defined by spaced arm portions  18   a  and a monolithic lower main body portion  18   b  defining a lower cross bore  18   c  receiving pivot pin  46 . The lower end  18   b  of arm  18  is pivoted on pivot pin  46  via spaced ball bearing assemblies  52  (FIG. 4) each including an inner race  53  fixedly secured to a respective portion of pivot pin main body portion  46   a , an outer annular insulative member  54  fixedly positioned within bore  18   c  and having an inwardly facing cup shaped cross-sectional configuration, an outer race  56  fixedly positioned within the annular cup defined by annular member  54 , and a ball race  58  rollably positioned between the inner and outer races.  
         [0033]    An annular spacer  60  is positioned between the inner face of each bracket side arm portion  32   a  and the inner race of a respective bearing assembly  47 ; an annular spacer  62  is positioned between the inner races  53  of the respective bearing assemblies  50 ; and annular spacers  64  are positioned between the inner race of each bearing assembly  47  and the inner race of the respective bearing assembly  52 . Insulative annular shims  66  are positioned between the inner faces of bracket arm portions  32   a  and the respective side arms  40  and further insulative annular shims  68  are positioned between the inner face of each side arm  40  and a respective outer face of inner arm  18 . Bearings  47  and  52 , in coaction with spacers  60 ,  62  and  64  and shims  66  and  68  will be seen to provide a robust journaling of the outer arms  40  and the inner arm  18  on the pivot pin  46  while providing effective electrical insulation between the arms and the cage structure.  
         [0034]    Upper electrode assembly  20  (FIGS. 1, 2 and  17 ) includes an electrode  70 , a hex adapter  72  secured to the free front end  70   a  of the electrode, a cap adapter  74  connected to hex adapter  72 , an electrode cap or weld tip  76  connected to cap adapter  74 , and a central coolant tube  80  positioned concentrically in a central axial passage  70   b  in electrode  70 . Coolant tube  80  coacts with passage  70   b  to define concentric axially extending coolant fluid passages including a central inner passage defined within tube  80  and an annular outer passage  81  defined between passage  70   b  and tube  80 . It will be understood that, in known manner, the concentric coolant fluid passages extend through hex adapter  72 , and cap adapter  74  whereby to deliver coolant fluid to weld tip  76  and return coolant fluid from the tip. For example, coolant fluid may be delivered via inner tube  80  and return flow may be provided via annular outer passage  81 .  
         [0035]    The rear end  70   c  of electrode  70  is clampingly received in a bore  18   d  defined in arm  18  with clamping accomplished via a split  18   e  in the arm coacting with suitable fasteners passing through and interconnecting the sides of the arm on opposite sides of the split. An angled fitting  82  is threadably received in a reduced diameter rear portion  70   c  of electrode  70 .  
         [0036]    Lower electrode assembly  22  (FIGS. 1 and 2) includes an electrode  83 , a hex adapter  84  connected to the free front end  83   a  of electrode  83 , a cap adapter  86 , an electrode cap or weld tip  88  connected to cap adapter  86 , and a central coolant tube  89  positioned concentrically in a central axial passage  83   b  in electrode  83 . Coolant tube  89  coacts with passage  83   b  to define concentric axially extending coolant fluid passages including a central inner passage defined within tube  89  and an annular outer passage  90  defined between passage  83   b  and tube  89 . It will be understood that, in known manner, the concentric coolant fluid passages extend through hex adapter  84  and cap adapter  86  whereby to deliver coolant fluid to weld tip  88  and return coolant fluid from the tip. For example, coolant fluid may be delivered via inner tube  89  and return flow may be provided via an annular outer passage  90 . The rear end  83   c  of electrode  83  is clampingly received in an aperture  42   a  in holder  42  with a split  42   b  in the lower end of the holder coacting with fasteners  43  to effect the clamping action. An angled fitting  91  is threadably received in a reduced diameter rear portion  83   d  of electrode  83 .  
         [0037]    Power cylinder assembly  24  (FIGS. 1, 2 and  16 ) includes a cylinder main body  92  clampingly positioned between end plates  94  via tie rods  96 , a mounting block  98  provided on the front face of front end plate  94 , a piston rod  100  connected in known manner with a piston received within the cylinder body  92 , and a cylinder rod end  102 . The front end  100   a  of piston rod  100  is clampingly received in a bore  102   a  in the rear face of cylinder rod end  102  and a bore  102   b  in the forward end of rod end  102  receives a pivot pin  103  passing through apertures  18   f  in spaced clevis upper arm portions  18   a  of inner arm  18  to pivotally mount the front end of the piston rod to the upper end of the inner arm  18 . Power cylinder assembly  24  may for example comprise a hydraulic cylinder assembly. The upper ends  40   c  of outer arms  40  define trunnions  40   d  (FIGS. 3 and 5) which are journaled in suitable sockets in cylinder mounting block  98  to pivotally connect the upper ends of arms  40  to the power cylinder assembly  24 .  
         [0038]    Balancing cylinder assembly  26  (FIGS. 1, 2,  3  and  5 ) may comprise, for example, an air cylinder and includes a cylinder body  104  pivotally mounted by a pin  106  on a bracket portion  36   a  of cage cross bar  36 , a piston rod  106  suitably connected to the piston within cylinder  104 , and a clevis  108  fixedly secured t the upper free end of a piston rod  106  and carrying a cross rod  110  jounaled at its opposite ends in suitable apertures in spaced arms  40  whereby to pivotally mount the upper end of piston rod  106  with respect to arms  40 .  
         [0039]    Upper shunt  28  (FIGS. 1, 2,  5 ,  6 ,  6   a ,  7 ,  8 ,  17  and  18 ) has a serpentine or “S” configuration and has a laminated copper construction whereby to provide a flexible electrical interconnection between the transformer and upper electrode assembly  20 . Shunt  28  is formed of a plurality (for example 95) of elongated strips of copper  112  which are suitably fixedly secured together at their opposite ends  28   a  and  28   b  but are unsecured intermediate the unified ends so that they are free to flex between the unified ends. Shunt  28  is produced by arranging the copper strips in a stacked configuration, positioning U-shaped copper clips  114  and  116  over the opposite ends  28   a  and  28   b  of the stacked copper strips, and electrically welding the end portions  28   a  and  28   b  with the clips in place to form fused together, solid unified end portions  28   a  and  28   b . Care is taken during the welding operation to ensure that the intermediate shunt portion  28   i  between the unified ends is not welded so that the intermediate portion is free to flex. Care is also taken to ensure that the extreme inboard portions  114   a / 116   a  of the clips  114 / 116  are not welded to the copper strips so that, following the welding operation, the outboard ends  117   a  of insulative fabric strips  117  may be positioned under the inboard ends  114   a / 116   a  of the clips and the inboard ends  114   a / 116   a  of the clips may be crimped to fixedly clamp the outboard ends of  117   a  of the insulative strips under the inboard ends of the clips. The fabric strips  117  are positioned loosely above and below the copper strips in a sandwich configuration and serve to protect the copper strips and preclude inadvertent electrical contact between the copper strips and other elements of the weld gun. Following the crimping of the fabric strips  117 , unified end  28   a  is subjected to a bending operation to import a curvilinear configuration to the end portion. The particular curvilinear configuration imparted to the end portion  28   a  may allow the end portion to assume a “hook” configuration. Shunt end  28   b  is machined to provide a clevis configuration and defines a partially circular opening  28   c  adapted to be clampingly secured to the reduced diameter portion  70   c  of electrode  70  utilizing suitable clamping bolts passing through bores  28   d . Shunt end  28   a  is provided with suitable bolt apertures  28   e  to fixedly secure the shunt end to the front face  12   d  of the transformer and is further provided with a coolant passage  28   f  communicating with a cross bore  28   g . Passage  28   f  in turn communicates with an inlet/outlet end  13   a  of transformer coolant passage system  13  whereby to facilitate the delivery of a suitable cooling fluid to the transformer coolant system via cross-bore  28   g  and passage  28   f . The delivery of a suitable cooling fluid to the transformer coolant passage system through the end of the shunt is illustrated by the arrow  119  in FIG. 8. It will be understood that clips  114  and  116  are suitably formed and apertured to conform to and accommodate the form and apertures of the corresponding ends of the shunt.  
         [0040]    Lower shunt  30  (FIGS. 1, 2,  5 ,  9 ,  10 ,  11 ,  12  and  18 ) has a generally U-shaped configuration and is formed of a plurality (for example 95) of elongated copper strips  112  which are suitably fixedly secured together at their opposite ends  30   a  and  30   b  but are unsecured intermediate the unified ends so they are free to flex between the unified ends. Shunt  30  is produced by arranging the copper strips in a stacked configuration, positioning U-shaped copper clips  118  and  120  over the opposite ends  30   a  and  30   b  of the stacked copper strips, and electrically welding the end portions  30   a  and  30   b , with the clips in place, to form fused together solid unified end portions  30   a  and  30   b . Care is taken to insure that the intermediate shunt portion  30   i  between the unified ends is not welded so that the intermediate portion is free to flex. Care is also taken to insure that the extreme inboard end portions  118   a ,  120   a  of the clips  118 ,  120  are not welded to the copper strips so that, following the welding operation, the outboard ends  121   a  of insulative fabric strips  121  may be positioned under the inboard ends  118   a ,  120   a  of the clips and the inboard ends of the clips may be crimped to fixedly clamp the outboard ends  121   a  of the insulative strips under the inboard ends of the clips. The fabric strips  121  are positioned loosely above and below the copper strips in a sandwich configuration and serve to protect the copper strips and preclude inadvertent electrical contact between the copper strips and other elements of the weld gun. Unified end  30   a  is machined to provide a clevis configuration defining a partially circular opening  30   c  whereby to facilitate the clamping engagement of the end  30   a  to the reduced diameter portion  83   d  of electrode  83  utilizing a clamping bolt passing through bores  30   d . End  30   b  is provided with a pair of vertically spaced cross-bores  30   e  and  30   f . Upper cross-bore  30   e  communicates with a coolant passage  30   g . End  30   b  is secured to the front face  12   d  of the transformer immediately below the end  28   a  of the upper shunt utilizing suitable fasteners passing through apertures  30   h.  Thus positioned, cooling passage  30   g  communicates with an inlet/outlet end  13   b  of transformer coolant passage system  13  so that a cooling fluid may be circulated through bore  28   g  of the upper shunt, through passage  28   f  to coolant system inlet/outlet  13   a , routed in cooling fashion around the transformer through coolant system  13 , returned via inlet/outlet  13   b  to passage  30   g  of lower shunt  30 , and discharged through cross bore  30   e  of the lower shunt, whereby to provide a continuous flow of cooling fluid to and through the transformer and to the electrical interfaces between the shunts and the transformer. If desired or required, further cooling fluid flow may be provided through cross bore  30   f  communicating with passage  30   g . It will be understood that clips  118  and  120  are suitably formed and apertured to conform to and accommodate the form and apertures of the corresponding ends of shunt  30 . A suitable coolant fitting  123  (FIG. 5) may be provided to communicate with cross-bore  30   e  and a suitable coolant fitting (not shown) may be provided to communicate with cross-bore  28   g.    
         [0041]    Coolant distributor assembly  31  (FIGS. 1, 2,  17  and  19 ) includes a mounting plate  122 , a distributor block  124 , and concentric tubing assemblies  126  and  128 .  
         [0042]    Mounting plate  122  has a rectangular configuration and is sized to be fixedly mounted via suitable fastener devices on top of cradle  14  in overlying relation to transformer  12 . The plate may extend for example from the rear top cross bar  34  to the front top cross bar  36  and may provide a notch  122   a  to accommodate the bracket portion  36   a  of cage cross bar  36 .  
         [0043]    Distributor block  124  has a monolithic configuration and is mounted on the top face of mounting plate  122  proximate the rear edge  122   b  of the plate. Block  124  defines parallel transverse bores  124   a  and  124   b , parallel axial bores  124   c  and  124   d , and further parallel axial bores  124   e  and  124   f  in respective axial alignment with bores  124   c  and  124   d.    
         [0044]    Threaded fittings  130  and  132  communicate with one end of transverse passages  124   a  and  124   b  respectively and receive hoses  134  and  136  which extend to suitable inlet and outlet ports of a source  138  of cooling liquid. This arrangement allows cooling liquid to be supplied for example from source  138  to passage  124   b  and returned to the source  138  via passage  124   a.    
         [0045]    Concentric tubing assembly  126  includes a fitting  140 , a hose  142  and a central tube  144 .  
         [0046]    Fitting  140  is threadably received in a front face  124   g  of block  124  with its inner diameter  140   a  coextensive with bore  124   c . Hose  142  is received at one end  142   a  over the barbed end  140   b  of fitting  140  and extends forwardly to a front end  142   b  which is fitted over the barbed, angled end  82   a  of fitting  82 . Central tube  144  is press fit at a rear end  144   a  thereof in passage  144   e  and extends forwardly across passage  124   a , through passage  124   c , and through the central passage of the fitting  140  whereafter it extends forwardly and concentrically within and through hose  142  to its forward end  144   b  which is fitted concentrically within fitting  82  and which connects telescopically at the extreme forward end  144   c  thereof with the rear end  80   a  of tube  80 . Tube  144  is spaced radially from fitting  82  to define an annular passage  118  between the tube and the fitting and is spaced radially from fitting  140  to define an annular passage  148  between the tube and the fitting.  
         [0047]    It will seen that a coolant flow passage is thereby established between coolant liquid source  138  and welding tip  76  via hose  136 , fitting  132 , passage  124   b , tube  144  and tube  80  and that a continuous return flow passage is established between weld tip  76  and source  10  via annular passage  81 , annular passage  146 , the annular space between hose  142  and tube  144 , annular passage  148 , passage  124   c , passage  124   a , fitting  130  and hose  134 .  
         [0048]    Concentric tubing assembly  128  includes a fitting  150 , a hose  152 , and a central inner tube  154 .  
         [0049]    Fitting  150  is threadably received in the front face  124   g  of distributor block  124  with the inner diameter  150   a  of the fitting coextensive with passage  124   d ; one end  152   a  of hose  152  is fitted over the barbed end  150   a  of fitting  150 ; the other end  152   b  of the hose is fitted (FIG. 2) over the barbed end  91   a  of angle fitting  91 ; and the rear end  154   a  of tube  154  is press fit in passage  124   f  and extends forwardly across passage  124   a , through passage  124   d , through fitting  150 , and concentrically within hose  152  to a front end (not shown) which is telescopically coupled to the rear end of tube  89 . As with the tubing assembly  126 , central tube  154  is spaced radially throughout its length from the surrounding hardware so as to define a continuous annular passage between weld tip  88  and source  138  and define a continuous central passage between source  138  and weld tip  88  whereby to allow the provision of recirculating flow of coolant fluid from the source to the weld tip. As with the concentric tubing assembly  126 , the flow from the source  138  to the weld tip  88  may be through passage  124   b , central tube  154 , and central tube  89 , and the return flow may be via the annular passageways defined around central tube  89  and central tube  154  and finally via passage  124   a  and hose  134  to source  138 .  
         [0050]    In a typical operation of the invention welding gun, the gun is attached to a robot (for example by attaching the robot to the cage  14 ); gross adjustment of the overall welding gun is performed utilizing the robot; and the upper and lower electrode caps are moved against opposite faces of a workpiece to be welded by simultaneous actuation of power cylinder  24  and air cylinder  26 .  
         [0051]    The weld gun of the invention provides many important advantages as compared to prior art weld guns. Specifically, the use of a shunt incorporating built in cooling passages for delivery of coolant to the transformer simplifies the construction of the gun and reduces the cost of the gun; the use of a shunt having a unified end portion bent into a curvilinear configuration facilitates the compact and relaxed routing of the shunt; the use of an electrically insulated ball bearing at the central pivot of the gun provides a more robust construction as compared to prior art sleeve bushing constructions while yet providing the required electrical insulation between the electrodes and the main frame of the gun; the gun design allows the ready interchange of the power cylinder with a servo motor of known configuration; the use of a distributor block at a location remote from the electrodes in combination with concentric tubing extending from the distributor block in the electrodes minimizes the volume of tubing required to provide the cooling function and thereby simplifies the gun both structurally and operationally; the use of identical side plates to establish all of the critical dimensions of the components of the gun insures that tolerances will be maintained on all of the critical dimensions and at all of the critical point; and the use of identical side plates further simplifies reconfiguration of the gun since the shape and the configuration of the side plates may be changed to accommodate a different welding requirement while continuing to utilize much of the same componentry of the welding gun in the new configuration.  
         [0052]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.