Abstract:
An apparatus and method for securing one or more workpieces before welding in a weld head unit. The apparatus includes a welding collet which incorporates a cantilevered, flexible spring “finger” or beam to support the workpiece. The finger is adapted to more uniformly distribute bending stresses along the clamping portions of the collet.

Description:
RELATED APPLICATIONS  
       [0001]     This application is a continuation-in-part of co-pending U.S. application Ser. No. 11/008,663, filed on Dec. 9, 2004, entitled “High Production Welding Fixture” which claims the benefit of U.S. Provisional Application Ser. Nos. 60/481,760, filed Dec. 9, 2003, entitled “High Production Welding Fixture” and 60/560,931, filed Apr. 9, 2004, entitled “High Production Welding Fixture” and further claims the benefit of the filing date of U.S. Provisional application Ser. No. 60/613,770, filed Sep. 28, 2004, entitled “Cantilevered Welding Collet,” which are incorporated by reference in their entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present application relates to welding collets.  
       BACKGROUND OF THE INVENTION  
       [0003]     It is known to use orbital weld heads to weld tubes and tube fitting elements. A fixture, such as a collet or clamp, is used to hold the workpieces that are to be welded.  
         [0004]     Prior wire cut work piece holders for orbital weld heads are disclosed by the following patents: U.S. Pat. No. 4,973,823, U.S. Pat. No. 5,136,134, and U.S. Pat. No. 6,325,366.  
       SUMMARY OF THE INVENTION  
       [0005]     One aspect disclosed in the present application relates to an apparatus and method for securing one or more workpieces before welding in a weld head unit. The apparatus includes a welding collet which incorporates a cantilevered, flexible spring “finger” or beam to support the workpiece. The finger is adapted to more uniformly distribute bending stresses along the clamping portions of the collet. Other embodiments may include a collet having a tapered beam dimensioned to provide compliance for varying outside diameter (O.D.) tolerances of tubing.  
         [0006]     In another aspect, the present application discloses an improved apparatus and method of securing one or more workpieces before welding in a weld head unit. The apparatus includes a welding collet which incorporates a pair of cantilevered, flexible spring “fingers” or beams to support the workpiece. The fingers are adapted to more uniformly distribute bending stresses along the clamping portions of the collet.  
         [0007]     In another aspect, the present application discloses a welding system including an orbital weld head and a welding collet. The welding collet includes a pair of cantilevered, flexible spring “fingers” or beams to support the workpiece. The fingers are adapted to more uniformly distribute bending stresses along the clamping portions of the collet. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     FIG. A is an isometric of a first embodiment of a cantilever collet;  
         [0009]     FIG. B is a finite element analysis (FEA) representation of the collet of FIG. A in an unclamped condition;  
         [0010]     FIG. C is an FEA representation of the collet of FIG. A in a clamped condition;  
         [0011]     FIG. D is an FEA representation of another embodiment of the invention;  
         [0012]      FIG. 1  is a side elevational view of the fixture that is a first embodiment of the invention, showing the handles and the clamps in the open or load position.  
         [0013]      FIG. 2  is a side elevational view of the fixture, showing the handles and the clamps in the closed position.  
         [0014]      FIG. 3  is a side elevational view of the fixture, showing the handles and the clamps in the tool change position.  
         [0015]      FIG. 4  is a front elevational view of the fixture.  
         [0016]      FIG. 5  is a top plan view of the fixture.  
         [0017]      FIG. 6  is a side elevational view of the fixture shown in a tilted position.  
         [0018]      FIG. 7  is a sectional view through a portion of the fixture showing the splined connections of the hubs and barrels that transmit rotational force from the handles to the clamps.  
         [0019]      FIG. 8  is an exploded perspective view showing the left clamp and left barrel, the right clamp and right barrel, and the screw.  
         [0020]      FIGS. 9-11  are perspective views of a fixture in accordance with a second embodiment of the invention;  
         [0021]      FIG. 12  is a top plan view of the fixture of  FIG. 9 ;  
         [0022]      FIGS. 13 and 14  are elevational views of the fixture of  FIG. 9 ;  
         [0023]      FIG. 15  is a sectional view of a clamp drive assembly that forms part of the fixture of  FIG. 9 ;  
         [0024]      FIGS. 16-19  are additional views of the fixture of  FIG. 9 ;  
         [0025]      FIG. 20  is an exploded perspective view of parts of the clamp drive assembly of the fixture of  FIG. 9 ;  
         [0026]      FIG. 21  is a perspective view of a workpiece support system usable with a welding fixture;  
         [0027]      FIG. 22  is another perspective view of a workpiece support system of  FIG. 22 ;  
         [0028]      FIG. 23  is a schematic view of a workpiece support turret that forms part of the workpiece support system of  FIG. 22 ;  
         [0029]      FIG. 24  is a partial elevational view of the workpiece support system of  FIG. 22 ;  
         [0030]      FIG. 25  is a perspective view of a welding fixture similar to the fixture shown in  FIG. 9 , with parts removed;  
         [0031]      FIG. 26  is another perspective view of the welding fixture of  FIG. 25 ;  
         [0032]      FIG. 27  is an elevational view of a side plate that forms part of the welding fixture of  FIG. 25 ; and  
         [0033]      FIG. 28  is an elevational view of a movable clamp plate that forms part of the welding fixture of  FIG. 25 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0034]     The collet  10  includes one or more wire cut “fingers” that act as a cantilever beam  12  to stabilize the welding work piece. The fingers are designed to deflect a known distance based on tubing O.D. to generate a desired reaction force. The height of the beam cross-section tapers from a relatively short section  14  at the tip of the beam  12  to a taller section  16  at the base of the beam  12 . This effectively creates a beam where the bending stiffness (a function of the moment of inertia of the cross-section) is proportional to the applied bending moment over the length of the beam. The result is a uniform distribution of bending stresses over the length of the beam  12 , which eliminates concentrated stresses at the base of the cantilever. The elimination of concentrated stresses at the base of the cantilever increases the fatigue life of the component. This application relates to welding fixtures for supporting workpieces in a welding process, such as orbital welding. The invention is applicable to fixtures of various differing constructions, some of which are shown herein as exemplary embodiments. As one example, FIG. A illustrates a fixture  10  that is a first embodiment of the invention.  
         [0035]     The tips  18  of the tapered beam  12  are shaped to conform to nominal size tubing in the deflected state, while also allowing to hold the entire tolerance range for the welding work piece. In order to accommodate the range of diameters, the tips of the tapered beam  12  are shaped with an offset nominal diameter such that when deflected, the contact points of the tip  18  conform to a nominal size workpiece, maximizing the contact area with a nominal workpiece. Furthermore, this offset of the curved tip  18  allows for contact with the minimum diameter workpiece (within tolerance) while giving enough deflection in the tapered beam to provide sufficient force, while minimizing the deflection necessary to support a workpiece of maximum outside diameter tolerance.  
         [0036]     The welding collet may be further provided with opposing termination holes at the base of the cantilevered beams, which minimize the areas of high stress at the base of each beam.  
         [0037]     The collet concepts can be incorporated into different welding heads. The disclosure that follows below, is made in pending U.S. nonprovisional patent application Ser. No. 11/008,664 filed on Dec. 9, 2004, entitled “High Production Welding Fixture,” and is substantially duplicated below and disclosed in  FIGS. 1-28  of the present application. The collet concepts of the present invention may be used in place of the work piece holders such as the clamp plates described in detail below. However, the invention may be incorporated into systems such as described in the above noted patents, and other systems as needed.  
         [0038]     Referring now to  FIG. 1 , the fixture  10  includes a base  12  that supports a left clamp  14  and a right clamp  16 . The terms left and right are used herein to designate the positions of the clamps  14  and  16  as seen from the front end of the assembly  10 , for example, as viewed in  FIG. 4 . The left and right clamps  14  and  16  are disposed on opposite sides of a welding plane  17 , which is the plane in which a welding electrode of a weld head  60  rotates about an axis to effect welding of the two workpieces along the welding plane. Each one of the left and right clamps  14  and  16  holds a respective one of the two workpieces to be welded together, against a fixed jaw  18 .  
         [0039]     A right handle  20  has a manually graspable end portion in the form of a knob  22 . The lower end of the handle  20  is formed as a base plate  24 . Connected with the base plate  24  are an extension spring  26  and a push rod  28 . The opposite end of the extension spring  26 , and the opposite end of the push rod  28 , are connected with a right hub  30 . The right hub  30  is supported for rotation about an axis  32 . The right hub  30  has external splines that mate with internal splines on a left barrel  34 . The left barrel  34  is thus rotatable with the right hub  30 . The left clamp  14  is fixed for movement with the left barrel  34 . Thus, upon movement of the right handle  20 , the right hub  30  and the left barrel  34  are rotatable with each other about the axis  32 , to pivot the left clamp  14 .  
         [0040]     A left handle  40  has a manually graspable end portion in the form of a knob  42 . The lower end of the left handle  40  is formed as a base plate  44 . Connected with the base plate  44  are an extension spring  46  and a push rod  48 . The opposite end of the extension spring  46 , and the opposite end of the push rod  48 , are connected with a left hub  50 . The left hub  50  is supported for rotation about the axis  32 . The left hub  50  has external splines that mate with internal splines on a right barrel  54 . The right barrel  54  is thus rotatable with the left hub  50 . The right clamp  16  is fixed for movement with the right barrel  54 . Thus, upon movement of the left handle  40 , the left hub  50  and the right barrel  54  are rotatable with each other about the axis  32 , to pivot the right clamp  16 .  
         [0041]     The splined connection between the left hub  50  and the right barrel  54  is spaced axially from the splined connection between the right hub  30  and the left barrel  34 . The two barrels  34  and  54  are rotatable independently of each other about the axis  32 . A screw  56  extends through the left barrel  34  and the right barrel  54  and is screwed into the right hub  30 .  
         [0042]     Each one of the clamps  14  and  16  has three basic positions relative to the weld head  60 . Movement and positioning of the left clamp  14  is similar to movement and positioning of the right clamp  16 , and so only the movement and positioning of the left clamp is described herein.  
         [0043]     A first position, i.e., a closed position, is shown in  FIG. 2 . In this position, the left clamp  14  is holding the workpiece against the fixed jaw  18 . The spring force of the spring  26  acts through the right hub  30  and the left barrel  34  to hold the left clamp  14  against the workpiece. The right handle  20  engages a stop bar (not shown) to provide a positive stop that limits pivoting movement of the right handle  20  in the closing direction. The base plate  24  on the right handle  20  is in a first over center position relative to the pivot axis of the right handle. The force of the spring  26  holds the left clamp tightly closed.  
         [0044]     A second position, i.e., an open or load position, is shown in  FIG. 1 . In this position, the left clamp  14  is moved away from the closed position, to enable a workpiece to be removed from, or put into position against, the fixed jaw  18 .  
         [0045]     To move the left clamp  14  from the closed position to this open position, the right handle  20  is grasped manually and caused to pivot about its axis. The right handle  20  acts through the push rod  28  and the spring  26  to rotate the right hub  30  about the axis  32 . Rotation of the right hub  30  acts through the splined connection to transmit rotational force to the left barrel  34  and thence to the left clamp  14  itself. The left clamp  14  pivots about the axis  32  to the open position.  
         [0046]     During this movement of the left clamp  14  from the closed position to the open position, the base plate  24  on the right handle  20  moves over center relative to its axis so that the spring  26  also holds the pieces in this position.  
         [0047]     A third position, i.e., a tool change position, is shown in  FIG. 3 . In this position, the left clamp  14  is located even farther away from the closed position, to enable the left clamp to be removed from the fixture  10  in order to, for example, put on a clamp of a different size.  
         [0048]     In order for the left clamp  14  to be moved into the tool change position, a tool change lever  70  is first moved from the position shown in  FIGS. 1 and 2  to a tool change position (not shown). This movement of the tool change lever  70  moves a cam or hard stop  72  ( FIG. 25 ) away from a projection on the right hub  30 . This movement of the stop  72  allows the right hub  30  to rotate past the open position to the tool change position, under the influence of force applied to the right handle  20 .  
         [0049]     Thus, to move the left clamp  14  from the open position to the tool change position, the tool change lever  70  is first pulled forward, allowing the handles to be moved farther back. The right handle  20  is grasped manually and caused to pivot farther about its axis. The right handle  20  acts through the push rod  28  and the spring  26  to rotate the right hub  30  even farther about the axis  32 . This additional rotation of the right hub  30  transmits rotational force to the left barrel  34  and thence to the left clamp  14  itself. The left clamp  14  pivots about the axis  32  to the tool change position.  
         [0050]     During movement of the left clamp  14  from the open position to the tool change position, the base plate  24  on the right handle  20  moves even farther over center with respect to its pivot axis. The handle  20  stops at the shortest spring distance of overcenter action, so that the spring  26  holds the pieces in this position.  
         [0051]     It can be seen that right handle  20  moves the left clamp  14 , and the left handle  40  moves the right clamp  16 . This arrangement of parts enables the operator to use the operator&#39;s right hand to grasp the workpiece that is being held by the right clamp  16 , while grasping its operating handle, the left handle  40 , with the operator&#39;s left hand. Similarly, the operator uses the operator&#39;s left hand to grasp the workpiece that is being held by the left clamp  14 , while grasping its operating handle, the right handle  20 , with the operator&#39;s right hand. As a result, the operator need not reach across the fixture  10  to put both hands on the same side of the weld head  60  or fixture  10 , when dealing with workpieces, moving them either onto or off of the fixture.  
         [0052]     When the fixture  10  is in the tool change position, the left and right clamps  14  and  16  are spaced apart from the closed position (and from the fixed jaw  18 ) by a distance that is significantly more than when the clamps are in the open position. This extended positioning of the left and right clamps  14  and  16  enables them to be clear of the weld head  60 . The left and right clamps  14  and  16  can then be changed out simply by removing the single screw  56  and sliding the clamps (along with their attached barrels  34  and  54 ) axially or laterally out of the fixture  16 , to the right as viewed in  FIG. 4 . Thus, to change the clamps  14  and  16 , the weld head  60  does not have to be removed, nor any other parts of the fixture  10  at all, other than the one screw  56 .  
         [0053]     The operator normally needs to move the right handle  20  only between the open and closed positions, which is not a large distance. The tool change position is substantially farther away from the closed position. In addition, it should be noted that the handles can be operated, or the clamp plates otherwise actuated, via something other than manual force—e.g., pneumatic or electric.  
         [0054]     The knobs  22  and  42  on the handles  20  and  40  are spaced apart from the two clamps  14  and  16  by a large distance, even when the clamps are in the open position. In one fixture  10  constructed in accordance with the invention for welding workpieces having a diameter in the range of from about one quarter inch to about one half inch, the knobs  22  and  42  are six inches to a foot away from the clamps  14  and  16 . To move the clamps  14  and  16 , the operator does not need to touch the clamps or the weld head  60  or any of the metal pieces near the clamps or the welding area, only the handles  20  and  40 . Thus, the actual clamping portions of the fixture itself, i.e., the movable clamps  14  and  16 , the fixed jaw  18 , or any other nearby piece, does not need to be touched by the operator. This is advantageous especially if the fixture  10  is hot from welding. Because the actuation force for the fixture operation is applied at a location remote from the clamps  14  and  16 , the operator&#39;s hands are disassociated from the location at which the fixture  10  grasps the workpieces.  
         [0055]     The fixture clamping mechanism includes an arc cover  80  for shielding the user from the light energy of the welding process. The arc cover  80  is supported for sliding movement on a longitudinal rail  82  of the base  12 , in-line with the weld head  60 , with its motion being restricted in all other directions. Therefore, the arc cover  80  can slide toward and away from the weld head  60 , along the longitudinal rail  82 , but cannot move to either side of the weld head. The arc cover  80  does not move laterally off the rail  82 , thus keeping the areas to the sides of the rail, where the workpieces would be located, unobstructed.  
         [0056]     An upper arc cover pin  84  and a lower arc cover pin  86  extend from the inner sidewall of the arc cover  80 . One end of an arc cover return spring  88  is connected to the upper arc cover pin  84 . The other end of the arc cover return spring  88  is connected to the base  12 . As the arc cover  80  slides away from the weld head  60 , the spring  88  stretches. The spring tension that is created helps to return the arc cover  80  to the closed position over the weld head  60  when other forces on the arc cover, tending to move the arc cover away from the closed position, are released.  
         [0057]     The lower arc cover pin  86  is connected to a rotatable plate  96  via a slotted link  92  and a connector link  94 . The slotted link  92  receives the lower arc cover pin  86  so as to allow the pin to slide within the slot. The distal end of the slotted link  92  is pivotally connected to the connector link  94 . At an intermediate position along the length of the slotted link  92 , the slotted link is pivotally mounted on the base  12  so as to allow the slotted link to rotate about its intermediate point relative to the base.  
         [0058]     The opposite end of the connector link  94  is pivotally connected to the rotatable plate  96 . An intermediate portion of the rotatable plate  96  is pivotally mounted on the base  12 . One end of the rotatable plate  96  has a handle follower pin  100  that extends perpendicularly from the plate and is in the path of movement of the handles  20  and  40 . The handle follower pin  100  is located behind both of the handles  20  and  40 . Because of the force of the return spring  88 , the pin  100  remains in contact with whichever handle  20  or  40  is in the rear most position (or both if both are in that position).  
         [0059]     The combination of the arc cover  80  being connected to the arc cover spring  88  as described, and connected to the rotatable plate  96  and follower pin  100  as described, has several advantages. First, as mentioned, the follower pin  100  remains in contact with whichever one of the handles  20  or  40  is in the rear most position. Therefore, when the arc cover  80  is in the closed position as shown in  FIG. 2 , the arc cover will slide away from the welding head  60 , into the load position, when either handle  20  or  40  is pushed away (back). This makes the welding area visible to the operator during positioning of either clamp  14  or  16  with its associated handle  20  or  40 . Conversely, when the arc cover  80  is in the load position as shown in  FIG. 1 , the arc cover will slide back to the closed position only when both handles  20  and  40  have been pulled forward, keeping the welding area visible to the operator.  
         [0060]     Second, the arc cover  80  can be manually slid away from the weld head  60 , against the bias of the return spring  88 , without moving either one of the handles  20  or  40 . This manual operation allows the user quickly to check work piece alignment, without moving the handles  20  and  40 .  
         [0061]     In accordance with another feature of the invention, the fixture  10  has two separate base plates, a top base plate  102  and a bottom base plate  104 . The top base plate  102  is connected to the bottom base plate  104  via a hinge  106  positioned at the front of the two base plates. The other parts of the fixture  10  clamping mechanism are mounted on the top base plate  102 . The hinged connection allows the top base plate  102  to be pivoted upward and forward from the bottom base plate  104  about the axis of the hinge  106 . An adjustment knob  108  is mounted onto the fixture clamping mechanism  10  for travel along a slotted guide  112  when the top base plate  102  and fixture clamping mechanism  10  pivot relative to the bottom base plate  104 . The adjustment knob  108  is positioned so as be tightenable against the slotted guide  112  to secure the fixture clamping mechanism  10  in a desired position of tilt. Rotating the adjustment knob  108  in the opposite direction releases the fixture clamping mechanism  10 , allowing it to be repositioned by the user. In this way, the user may adjust the line of sight required to view the weld joint during the welding operation.  
         [0062]      FIGS. 9-20  illustrate a fixture  200  that is a second embodiment of the invention. The fixture  200  is usable in a manner similar to the manner of use of the fixture  10 , to weld together two pieces that are releasably clamped adjacent a weld head. Many parts of the fixture  200  are similar in construction and operation to parts of the fixture  10 , and such parts are described only briefly here.  
         [0063]     The fixture  200  includes a base  202 . The base  202  includes side plates  206  ( FIG. 9 ) and a bottom plate  208  preferably formed as one piece, such as by milling from an L-shaped aluminum extrusion.  
         [0064]     A clamp drive assembly  210  of the fixture  200  includes a shaft  212  ( FIG. 15 ) supported on the two side plates  204  and  206  for rotation about an axis  214 . A first handle, or outer handle,  216  is connected with the shaft  212  through a linkage mechanism  218  that is similar in construction and operation to the linkage mechanism shown in the first embodiment of the invention. As a result, when the outer handle  216  is pivoted, the shaft  212  rotates about the axis  214 .  
         [0065]     The shaft  212  extends for substantially the entire width of the clamp drive assembly  210  of the fixture  200 . The shaft  212  is not splined but instead has a smooth, cylindrical outer surface. An outer end portion  220  ( FIG. 20 ) of the shaft  212  includes two radially outward opening notches  222  formed in the outer end face of the shaft.  
         [0066]     The clamp drive assembly  210  of the fixture  200  also includes a sleeve  230  that is supported on the shaft  212  for rotation about the shaft and thus about the axis  214 . The sleeve  230  is larger in diameter than the shaft  212 . A second handle, or inner handle,  232  is connected with the sleeve  230  through a linkage mechanism  234  that is similar in construction and operation to the linkage mechanism shown in the first embodiment of the invention. As a result, when the inner handle  232  is pivoted, the sleeve  230  rotates about the axis  214 .  
         [0067]     The sleeve  230  for its entire length extends about the shaft  212 , so that the outer end portion  220  of the shaft  212  projects axially outward of the sleeve. The sleeve  230  is not splined but instead has a smooth, cylindrical inner surface. Two radially outward opening notches  236  ( FIG. 20 ) are formed in the outer end of the sleeve  230 . The notches  236  in the sleeve  230  are farther apart than the notches  222  in the shaft  212 .  
         [0068]     The clamp drive assembly  210  of the fixture  200  also includes a hub  240 . The hub  240  is an axially short, annular member that is designed to fit on the end of the shaft  212  and replicate the end of the sleeve  230 . The hub  240  has two radially inwardly extending tabs  242  that fit into the outwardly opening notches  222  on the outer end portion  220  of the shaft  212 . When this is done, the hub  240  becomes rotatable with the shaft  212 . The hub  240  also has two radially outward opening notches  244  that are identical in configuration and radial location to the notches  236  on the sleeve  230 . The hub  240  in this aspect thus replicates, on the outer end portion of the shaft  212 , the outer end portion of the sleeve  230 .  
         [0069]     The fixture  200  includes a first clamp plate, or inner clamp plate,  250  and a second clamp plate, or outer clamp plate,  252 . In the fixture  200 , the two clamp plates  250  and  252  are physically the same as each other, to reduce manufacturing cost and complexity.  
         [0070]     The two clamp plates  250  and  252  are disposed on opposite sides of a welding plane  253  ( FIG. 15 ), which is the plane in which a welding electrode of the weld head  60  rotates to effect welding of the two workpieces.  
         [0071]     On a first side, or outer side, of the fixture, that is, to the left (as viewed in  FIG. 15 ) of the welding plane  253 , there is located the second clamp plate  252 . On a second side, or inner side, of the fixture, that is, to the right (as viewed in  FIG. 15 ) of the welding plane  253 , there is located the first clamp plate  252 . The first and second handles  216  and  232  are both located on the second side of the fixture.  
         [0072]     Each one of the clamp plates  250  and  252  has an annular hub portion  254  with two radially inward extending tabs  256 . The tabs  256  are sized and located to fit into the radially outward opening notches on the hub or into the radially outward opening notches  236  on the sleeve  230 . Thus, either one of the two clamp plates  250  or  252  can be fitted on the sleeve  230  or on the hub  240 .  
         [0073]     The clamp drive assembly  210  of the fixture  200  is assembled by, first, placing the inner clamp plate  250  over the projecting outer end portion  220  of the shaft  212  and into engagement with the sleeve  230 . The tabs  256  of the inner clamp plate  250  fit into the notches  236  on the sleeve  230 . As a result, the inner clamp plate  250  is pivotable upon rotation of the sleeve  230 .  
         [0074]     A thrust roller bearing shown schematically at  258  is then placed over the shaft  212 . The hub  240  is then placed over the outer end portion  220  of the shaft  212 . The tabs  242  of the hub  240  fit into the notches  222  on the outer end portion  220  of the shaft  212 . As a result, the hub  240  is rotatable with the shaft  212 .  
         [0075]     The outer clamp plate  252  is placed onto the hub  240 . The tabs  256  of the outer clamp plate  252  fit into the notches  244  on the hub  240 . As a result, the outer clamp plate  252  is pivotable upon rotation of the hub  240  and the shaft  212 .  
         [0076]     The fixture  20  includes a side plate or fixed jaw  260  ( FIG. 9 ) that is removably mounted to the base  202 . The fixed jaw  260  is mounted to the base  202  after the weld head  262  is affixed. The weld head  262  is secured with two socket head screws extending through a horizontal rail portion of the base  202  and into the weld head. The fixed jaw  260  is then slipped down over the weld head  262 , being aligned with a pin on the base  202  that fits into a hole on the underside of the fixed jaw. The fixed jaw  262  has a horizontal surface (not shown) that rests on a horizontal surface of the weld head  262  to set the vertical position of the fixed jaw relative to the weld head. A spring clamp  272  then is engaged with a projecting button  274  on the fixed jaw  260 , to retain the fixed jaw in position on the weld head  262 . The fixed jaw  260  supports the workpieces being welded, in position on the weld head  262 , with the workpieces being releasably held down on the fixed jaw by the movable clamp plates  250  and  252 . (The fixed jaw may be held on the base  202  by other means than the spring clamp  272 , for example, one or more screws.)  
         [0077]     To move the first or outer clamp plate  252 , the first or outer handle  216  is pivoted between its open position as shown in  FIGS. 16 and 17  and its closed position as shown in  FIGS. 9-12 . Pivoting movement of the outer handle  216 , which takes place on the second side of the fixture  200 , causes the shaft  212  to rotate about the axis  214 . Rotation of the shaft  212 , which extends across the welding plane  253 , causes the hub  240  to rotate, thereby pivoting the outer clamp plate  252  on the first side of the welding fixture. The outer clamp plate  252  is thereby movable relative to the fixed jaw  260  between an open position and a closed position. (It should be noted that the handles can be operated, or the clamp plates otherwise actuated, via something other than manual force—e.g., pneumatic or electric.)  
         [0078]     The second or inner clamp plate  250  is pivotable independently of the outer clamp plate  252 , because the two handles  216  and  232  and their respective linkages  218  and  234  are separately movable. To move the second or inner clamp plate  250 , the second or inner handle  232  is pivoted, on the second side of the welding fixture  200 , between an open position (not shown) and a closed position as shown in  FIGS. 12-15 . Pivoting movement of the inner handle  232  causes the sleeve  230  to rotate about the axis  214 . Rotation of the sleeve  230 , which occurs on the second side of the welding fixture, causes the inner clamp plate  250  to pivot (also on the second side of the welding fixture) between its open and closed positions relative to the fixed jaw  260 .  
         [0079]     When the clamp plates  250  and  252  rotate between their open and closed positions, they stay within the envelope of the weld head  262  (as seen or projected laterally, along the direction of the axis  214 ). This aspect of the fixture  200  is beneficial in that it minimizes the operating space needed for the fixture itself, thus making it possible to work with larger or differently shaped workpieces. This beneficial effect is a result of the configuration of the clamp plates  250  and  252  and of their relatively small pivoting arc of movement.  
         [0080]     Another beneficial aspect of the fixture  200  as thus described is the relative simplicity of the clamp drive assembly  210 , which can be easier and less costly to manufacture than the corresponding assembly of the fixture  10  with its splined fittings. In addition, the configuration of the clamp drive assembly  210  that allows for identical inner and outer clamp plates  250  and  252  helps to reduce cost and to simplify assembly. Specifically, the hub  240  allows the clamp plates  250  and  252  to be the same as each other—and to allow the plates not to be welded to the sleeve or shaft.  
         [0081]     In the fixture  200 , the inner and outer handles  216  and  232  are shorter and smaller than the handles of the fixture  10 . In addition, the inner and outer handles  216  and  232  do not extend laterally outward of the plane of the outside face of the weld head  262 , as can be seen from  FIG. 12 , for example (to the top as viewed in  FIG. 12 ). This aspect of the fixture  200  again has the benefit of enabling welding of workpieces that extend away from the weld head  262  in a direction along the length of the fixture, that is, generally toward the handles  216  and  232 , or to the left as viewed in  FIG. 12 . Further, as with the first embodiment, the right (outer) handle  216  moves the outer clamp plate  252 , while the left (inner) handle  232  moves the inner clamp plate  250 . This again enables the improved ease of operation discussed above with reference to the first embodiment of the invention.  
         [0082]     The fixture  200  includes an arc shield, or arc cover,  280  for shielding the user from the light energy of the welding process. The arc cover  280  is a U-shaped member that is replaceably mounted on an arc cover support  282 . The cover support  282  has an annular hub portion  284 , similar to the hub portions  254  of the clamp plates  250  and  252 . The hub portion  284  of the cover support  282  is rotatably fitted over the hub  240 . The cover support  282  is thus rotatable relative to the shaft  212 . A torsion spring  286  ( FIG. 18 ) acts to bias the arc cover  280  toward a closed position as shown in  FIGS. 9 and 10 .  
         [0083]     The cover support has two parallel support arms  288  that end outward from the hub portion  284  and that terminate in a cross bar  290 . The arc cover  280 , itself, is clipped onto the cross bar  290  and against the support arms  288  and is thereby self-retaining on the cover support  282 .  
         [0084]     The support arms  288  of the arc cover support  282  are spaced apart from each other by a distance that is equal to the distance between the inner clamp plate  250  and the outer clamp plate  252 . The cover support  282  is positioned axially on the shaft  212  such that the support arms  288  of the cover support  282  are radially outward of (behind) the clamp plates  250  and  252 ; the clamp plates are interposed between the cover support and the axis  214 . As a result, when either one of the clamp plates  250  and  252  is pivoted away from its closed position, it engages a support arm  288  of the cover support  282 , and the arc cover  280  is pivoted out of the closed position. Thus, the arc cover  280  is always opened as soon as the first clamp plate  250  and  252  of the fixture  200  is opened. Similarly, if both clamp plates  250  and  252  are in the open position, and one is then closed, the remaining (open) clamp plate holds the arc cover  280  in its open position. The arc cover  280  does not move back to its closed position until both clamp plates  250  and  252  are pivoted closed.  
         [0085]     The arc cover support  282  includes a manually engageable arm  292  that projects axially from the hub portion  284 . The arm  292  is engageable to enable manual pivoting of the arc cover  280  between the closed position and the open position, without moving either of the clamp plates  250  and  252 . In this manner, the work area can be viewed without disturbing the clamping of the workpieces.  
         [0086]     The direct actuation of the arc cover support  282  by the clamp plates  250  and  252 , enables the fixture  200  to do without the more complex actuation mechanism found in the fixture  10  of the first embodiment. In addition, the fixture  200  does not need structure corresponding to the longitudinal rail  82  of the base  12  of the fixture  10 . As a result, more space is available for workpieces being welded in the fixture.  
         [0087]     We therefore claim as part of our invention, among other aspects, the weld fixture having opposite handles for actuating the two movable clamp plates; the pivoting base assembly; the clamp drive assembly with coaxial shaft and sleeve for the two clamp plates; the sliding or pivoting arc cover with actuating mechanism; and the configuration of the parts as described that maximizes the space available for workpieces.  
         [0088]      FIGS. 21-24  illustrate portions of an exemplary workpiece support system  300  that can be used with, or as part of, a welding fixture of the present invention. The system  300  is shown as associated with a fixture  302 ; the system can be used with, or as a part of, other welding fixtures.  
         [0089]     If a workpiece is other than a short tube, it can be too heavy to be supported in a correctly aligned position at the welding location without the use of one or more external supports. The workpiece support system  300  is designed to support one or both of the workpieces being welded at a welding location  316  on the fixture  302 . In  FIGS. 21-24 , the system  300  is shown supporting a short tube  304  on the left side of the fixture  302 , coaxial with the welding axis  306 , and a long tube  308 , at an angle to the welding axis, on the right side of the fixture.  
         [0090]     The system  300  includes an exemplary assembly  310  shown supporting the short tube  304 . The assembly  310  includes a pair of rails  312  that are screwed into the base  314  of the fixture  302 . The rails  312  project outward from the left side of the fixture, below the welding location  316 . The rails  312  support a pillow block  320  that is movable along the rails in a direction toward and away from the base  314 . The pillow block  320  can be secured in a selected position along the rails  312  by two thumbscrews  322 .  
         [0091]     The pillow block  320  has a vertically extending slot  324  that receives a thumbscrew connector  326  for a support member  328 . The support member  328  has a V-notch  330  on one end for supporting a tubular workpiece. The opposite end (not shown) of the support member  328 , which is the lower end in  FIG. 25 , is flat for supporting a differently configured workpiece. The support member  328  can be secured in either vertical orientation with respect to the pillow block  320 , so that either the V-notch  330  or the flat end portion is uppermost. The support member  328  is then fixed in position vertically with the thumbscrew connector  326 .  
         [0092]     The combination of the rails  312  and the pillow block  320  and the support member  328  provides a support for the workpiece  304  on the left side of the fixture  302 , which is vertically adjustable and also adjustable inward or outward in a direction parallel to the welding axis  306 .  
         [0093]     The support system  300  also includes structure  334  for supporting the workpiece  308  on the other side of the welding location  316 . The structure  334  includes another set of rails  336  that extend laterally from the right side of the fixture base  314 . The rails  336  support a pillow block  340  whose position on the rails can be adjusted and set with the use of two thumbscrews  342 . The pillow block  340  supports in a vertically adjustable manner one end portion  344  of a bar  346 , along the welding axis  306 . The other end portion  348  of the bar  346  is located adjacent the welding location  316  and is supported by a foot  350  on top of the shroud  352  of the fixture  302 . The bar  346  supports the inner end of the long tube  308 .  
         [0094]     The outer end of the long tube  308  is supported by another pillow block assembly  354 . This pillow block assembly  354  is located on two rails  356  that extend from the side of the pillow block  340 , in a direction transverse to the rails  336  and transverse to the welding axis  300 . The location of this pillow block  354  is settable and lockable by two thumbscrews  358 . The pillow block  354  supports a vertically adjustable block  360  that has a V-notch on its upper end portion. The block  360  is oriented at an angle to the welding axis  306  so that it can properly support the outer end portion of the long tube  308 , which is itself oriented at an angle to the workpiece axis in this particular configuration. The workpiece support system  300  with this angular feature shown is merely illustrative; a workpiece support system in accordance with the invention can include one or more units arranged in differing configurations, on one or both sides of the fixture.  
         [0095]      FIGS. 23 and 24  illustrate schematically another portion of the system, specifically, a turret  370  that can support a plurality of tubes of different sizes (diameters). The turret  370  has a generally disc shaped configuration with a central mounting portion  372  that is adapted to be connected with the pillow block  310 . When so connected the turret  370  is rotatable on the pillow block  310 . Its rotational position can be set by detents  373 . The vertical position of the turret  370  can be set with the thumbscrew adjuster mechanism  326  of the pillow block  310 .  
         [0096]     A one hundred eighty degree sector of the circumference of the turret  370  has a scalloped configuration including a plurality of arcuate notches  374 . The notches  374  are of differing diameters. Each one of the notches  374  is defined by a respective arcuate surface  376  centered on an imaginary circle  378  that is itself centered on the welding axis  306 . As a result, each one of the notches  374  is adapted to receive and support a tubular workpiece that is centered on the welding axis  306 , without having to move vertically either the workpiece or the turret  370 . The opposite one hundred eighty degree sector of the circumference of the turret  370  has two flats  380  for supporting planar or other non-tubular workpieces.  
         [0097]      FIGS. 25-28  illustrate portions of another exemplary welding fixture  400  that includes several components that are configured differently from corresponding components in the welding fixtures described above. The components shown in  FIGS. 25-28  are usable separately or in combinations with any welding fixture of the present invention.  
         [0098]      FIGS. 25 and 26  are perspective views, from opposite sides, of the welding fixture  400 . The arc shield  402  in the fixture  400  is differently configured and constructed than the arc shield shown in  FIGS. 9-20 . Specifically, the arc shield  402  includes a one piece metal shield member  404  that is secured by four screws  406  to a hub  408 . The shield member  404  is removable and replaceable as one piece. The hub  408  is supported for rotation about an axis  410 . A finger tab  412  on the hub  408  is manually engageable to enable the arc shield to be manually retracted from its closed position (shown in  FIGS. 25 and 26 ) covering the welding location, to its open position. A spring tab  414  on the hub  408  receives one end of a coil spring  416 . The coil spring  416  extends into a slot  418  in the base  420  and has its opposite end fixed to the base. The coil spring  416  acts between the arc shield  402  and the base  420  to bias the arc shield into the closed position.  
         [0099]     In the fixture  400 , the movable clamp plates  422  are differently configured than the movable clamp plates  250  and  252  shown in  FIGS. 12-24 . Specifically, each movable clamp plate  422  has an inner edge  424  that is substantially straight as compared to the recessed inner edge of the clamp plates  250  and  252 . Thus, the width across the clamp plate  422  from its inner edge  424  to its outer edge  426  is greater, and the clamp plate  422  can be more rigid and stronger.  
         [0100]     In the fixture  400 , the side plate  430  is attached to the base  420  in a different manner. Specifically, the side plate  430 , which forms the fixed jaw or fixed clamp plates on both sides of the welding plane, has two through holes  432  which can receive fasteners (not shown), such as screws or bolts, that extend parallel to the welding axis  406 , for fastening the side plate to the base  420 . The fasteners secure the side plate  430  in the selected position relative to the base  420 . That position is set by an angled clamp  434  that acts between the base  420  and the lower outside corner  436  of the side plate  430 , to pull the side plate simultaneously both down and laterally into the proper position relative to the weld head.