Modular resistance weld gun

A resistance welding gun is provided that includes an arm assembly having spaced apart plates. First and second spaced apart blocks interconnect the plates and extend between the plates in a first direction. The first and second blocks are machined to provide a desired spacing between the plates. An electrode arm is arranged between the plates and blocks and supports an electrode end having a replaceable cap in one example. A clamping device applies a clamping load in a second direction transverse to the first direction to secure the electrode arm between the blocks. Lateral alignment between opposing electrode ends is achieved by a movable adjustment assembly on one of the arm assemblies. A pivot pin interconnects the block and electrode arm for permitting rotation of the electrode arm relative to the block. In one example, the adjustment assembly includes an adjustment member that is rotated to laterally move the electrode arm about the pivot pin in a desired position.

BACKGROUND OF THE INVENTION

This application relates to resistance welding guns. More particularly, the application relates to arm assemblies that support electrode arms.

Resistance welding guns are used in the automotive industry, for example, for spot welding a workpiece. Opposing arm assemblies are actuated to engage the workpiece with electrode arms provided on the arm assemblies. Numerous resistance welding guns are typically employed to spot weld a vehicle body, for example. However, the welding guns must be customized to reach the area to be spot welded, which results in many unique parts for the arm assemblies.

A modular design approach previously has been applied to resistance welding guns. This design approach focused on mass producing the welding gun body, which includes the actuator, transformer and arm assemblies (excluding the electrode arms). The electrode arms were unique to reach the area to be spot welded. The electrode arms are commonly made of high strength copper or aluminum alloys that are very expensive and may be difficult to fabricate into complex shapes. This is particularly problematic since the electrode arms are perishable due to the mechanical and thermal loads to which they are subjected during welding operations. As a result, while the cost of the welding gun bodies has dropped, the high cost of the electrode arms has offset the gains.

Furthermore, prior art modular resistance welding guns have been expensive in that they have utilized many high tolerance machined components to ensure alignment between opposing electrode ends. In the event of a misalignment of the electrode ends in the field, for example due to a crash, time consuming and costly repairs in the field must be employed to restore electrode alignment.

What is needed is improved modular resistance welding guns that reduce the overall cost of the gun assembly. Moreover, a modular welding gun is needed that provides improved alignment between the electrodes while reducing the high tolerance machining typically required of the gun components.

SUMMARY OF THE INVENTION

A resistance welding gun is provided that includes an arm assembly having spaced apart plates, which are shaped to provide electrodes access to area to be welded. First and second spaced apart blocks interconnect the plates and extend between the plates in a first direction. The first and second blocks are machined to provide a desired spacing between the plates. An electrode arm is arranged between the plates and blocks and supports an electrode end having a replaceable cap, in one example. The electrode arm has a quadrilateral cross-section in a plane including the first and second directions.

A clamping device applies a clamping load in a second direction transverse to the first direction to secure the electrode arm between the blocks. In one example arrangement, the clamping device is provided by a wedge assembly. In another example arrangement, a movable block is secured about the electrode arm using clamping fasteners supported by a fixed block.

In one example arrangement, a cradle is arranged between and interconnected to the plates. The cradle supports an actuator by trunnion pins extending into the actuator. In one example, the plates include a notch having a flat wall. The trunnion pins are received in the notches and include a flat that cooperates with the flat wall to prevent rotation of the trunnion pin relative to the plates. In this arrangement, the notch in the plate also acts to retain the trunnion pin.

Lateral alignment of the opposing electrode arms is provided. In one example, this is achieved by a simple clamping arrangement. In the other example, the electrode arm adjustment is achieved in a controllable fashion by a movable adjustment assembly. A pivot pin interconnects the block and an electrode arm for permitting rotation of the electrode arm relative to the block about the pivot pin. The adjustment assembly includes an adjustment member that is rotated to turn the electrode arm about the pivot pin and laterally move an end of the electrode arm to a desired position.

These and other features of the application can be best understood from the following specification and drawings, the following of which is a brief description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Example resistance welding guns are shown at10,210,310, respectively, inFIGS. 1a-1c. Similar components between the Figures are referenced using numerals in multiples of 100.FIG. 1illustrates a large pinch-style welding gun.FIG. 1billustrates a small modular pinch-style welding gun.FIG. 1cillustrates a modular scissor-style welding gun.

Referring toFIG. 1a, the welding gun assembly10includes upper and lower arm assemblies12,14. The use of the terms “upper” and “lower” are exemplary only and are not intended to be limiting. An actuator16actuates the upper and lower arm assemblies12,14relative to one another about a common pivot A to move opposing electrode ends26into engagement with a work piece to be welded. The electrode ends26typically include replaceable welding caps. The actuator16can be a hydraulic or pneumatic cylinder, or a servo-electric actuator, for example.

A bracket20is supported by a transformer18in the example shown. The bracket20pivotally supports the upper and lower arm assemblies,12,14at the common pivot A in the example. In one example, the actuator16is pivotally supported by the lower arm assembly14at an actuator pivot B. The actuator16includes a portion, in one example a rod68(FIG. 5), pivotally supported at an axis C provided by the upper arm assembly12. In operation, the rod68is extended to close the upper and lower arm assemblies12,14about the work piece for the example shown.

The upper and lower arm assemblies12,14include upper and lower electrode arms22,24. In the example, the upper and lower electrode arms22,24are relatively small and of simple construction as compared to the prior art. The upper and lower electrode arms22,24can be cut and machined from a wrought copper bar stock or plate, for example, and may have dimensional variation or distortion that would not be acceptable in the prior art. The adjustment provided in the design of the arm assemblies thus enables a reduction in the cost of replacing the electrode arms over the welding gun's life. In one example, the electrode arms22,24have a quadrilateral cross-section in a plane P. Of course, the electrode arms could have any desired cross-section and may incorporate a more complex shape, if desired on some applications.

Shunts28electrically connect the transformer18to the upper and lower electrode arms22,24to transmit current to the electrodes ends26. In one example, a stabilizing cylinder30is interconnected between the lower arm assembly14and the bracket20to stabilize the position of the upper and lower arm assemblies12,14during operation of the welding gun10. The equalizing cylinder30is used to position the lower arm assembly14between fixed and floating points that allow the electrode ends26to engage the workpiece, which may be mislocated or moved during the welding operation.

Should the equalizing cylinder30not be required for a particular resistance welding application, a single fastener can be used in place of the equalizing cylinder30rod mount, to rigidly connect the lower arm assembly14to the bracket20. In one example, the equalizing member can be a fastener rigidly securing the plate74to the bracket20, as shown inFIG. 10. In this adaptation, a spacer33is provided with a thickness that corresponds to the gap between the lower arm assembly14and the bracket20. The equalizing member31is received in a hole in the plate74and extends into the bracket20. The spacer33corresponds to the width or gap between the plate74and bracket20. Thus, both methods of operation are supported with the same configuration of the lower arm assembly14and bracket20, and the change can be made easily by the addition of removal of the equalizing cylinder.

The example modular welding guns can incorporate relatively simple, inexpensive upper and lower electrode arms22,24. The flexibility is provided, in part, by simple, flat side plates that support the electrode arms and by blocks used to precisely space the side plates. By comparison, the material and machining costs of the side plates and blocks relative to prior art electrode arms is much cheaper. As a result, a significant cost savings can be realized when using the example welding guns while achieving a flexible, modular design.

The example upper arm assembly12, as illustrated inFIG. 1a, is shown in more detail inFIGS. 2a-2b. The upper arm assembly12includes spaced apart side plates32that are cut in a desired shape for the particular application. In one example, the side plates are cut from metal sheets using laser, plasma or waterjet cutting, for example.

A block34is machined to a desired width to accommodate the upper arm22and achieve a desired spacing between the side plates32. However, the upper electrode arm22does not have to be accurately machined, which will be appreciated relative to the clamping devices discussed below. The side plates32include holes36for receiving fasteners40threadingly received in apertures in the block34to secure them to one another in a first direction J. In one example, washers42are arranged between the fasteners40and side plates32. Dowels38are used to locate the side plates32relative to the block34. An isolator bushing46is received in an aperture47in the upper electrode arm22. A dowel44locates the upper electrode arm22in a transverse direction L relative to the block34while still permitting the electrode end26to be repositioned in the lateral direction J.

Insulator sheets48are used to electrically isolate the upper electrode arm22relative to the side plates32and block34. The insulator sheets48may be affixed to upper electrode arm22with adhesive or other suitable means to ensure they remain in place, since compressive forces may not be present due to the relatively loose tolerances between the upper electrode arm22and the side plates32. The insulator sheets48can be constructed from micarta, fiberglass or any other suitable material.

A wedge assembly49provides a clamping device that is used to clamp and lock the upper electrode arm22in a second direction K once in a desired position relative to the side plates32and block34. A first wedge portion50is secured to the side plates32in a similar manner to that described above relative to block34. The first wedge portion50provides desired spacing between the side plates32. A second wedge portion52is arranged between the first wedge portion50and the upper electrode arm22. The first and second wedge portions50,52include complimentary inclined surfaces54. Clearance is provided between the second wedge portion52and the side plates32to permit sliding movement of the second wedge portion52.

In operation, a face56on the second wedge portion52is loaded in a third direction L using shoulders58of fasteners secured to the first wedge portion50. In one example, the first, second and third directions are approximately 90 degrees apart. The fasteners are tightened to move the second wedge portion52along the inclined surface54on the first wedge portion50to clamp the upper electrode arm22between the block34and the first wedge portion50. In this manner, the height of upper electrode arm22need not be accurately machined and can be secured in place once a desired orientation is achieved.

Referring toFIG. 2a, the upper arm assembly12includes a first portion60that is secured to a recessed area63of a pivot block64(FIG. 3) using fasteners (not shown). The pivot block64is supported by and rotates relative to bracket20about the common axis A. A second portion62is secured to a portion of the actuator16, best shown inFIG. 5, using fasteners (not shown).

The lower arm14is shown inFIGS. 4a-4b. A fixed block76is secured between opposing side plates74using fasteners40in the first direction J. A movable block78provides a clamping device and is arranged between the side plates74. The lower arm24is arranged between the fixed and movable blocks76,78and is clamped in place. The side plates74include slots77that receive the fasteners40which are secured to the movable block78. Clamping fasteners80extend through the fixed block76on either side of the lower arm24and are threadingly received in the movable block78and secured in the second direction K.

In operation, to retain the lower electrode arm24in a desired position, the clamping fasteners80are tightened to apply a clamping load in the second direction K to the lower electrode arm24. The slots77permit vertical movement of movable block78(in the orientation shown). Once the lower electrode arm24is clamped in a desired position by the fixed and movable blocks76,78, the fasteners40within the slot77can be tightened to retain the movable block78in its position.

Similar to the upper arm assembly12, insulators48are arranged about the lower electrode arm24to electrically isolate the lower electrode arm24relative to the side plates74and fixed and movable blocks76,78. Again, the lower electrode arm24does not need to be precisely machined when using the clamping device.

Referring toFIG. 5, an end83of the actuator16is supported in a U-shaped cradle82, in one example. The cradle82provides desired spacing between the side plates32and is secured thereto by fasteners (not shown). The end83is pivotally supported by the trunnion pins84extending inserted into opposing sides of the end83to provide the axis B. The cradle82ensures alignment of the two trunnion pins84irrespective of the machining accuracy or alignment of the side plates. Optimum alignment contributes to smooth closing and minimizes the requirements for maintenance of the trunnion pins or actuator bushings. The end83supports the rod68, which is extended when the actuator16is actuated to close to the electrode end26about the work piece.

An upper portion of each side plate74includes a notch88that receives an end of the trunnion pin84. A flat wall90provided by the notch88cooperates with a flat86in the trunnion pin84to prevent its rotation, which would create wear between the side plates74and the trunnion pins84. Moreover, the trunnion pins84cannot back out of the end83and free the actuator16. Thus, supplemental components commonly used to retain such trunnion pins, such as retainer plates and fasteners, are not required.

In one example, spacers70are arranged about an end of the rod68between the side plates32of the upper arm12. A pin (not shown) supports the rod end relative to the upper arm assembly12. Caps72are secured to the side plates32to capture the pin.

In one example, the lower electrode arm24can be laterally adjusted relative to the upper electrode arm22to provide alignment between the electrode ends26. The adjustment assembly91is best illustrated inFIGS. 6-8. The lower electrode arm24is located relative to the fixed block76by a pivot pin45and isolator bushing47received in a corresponding hole95of the lower electrode arm24. The lower electrode arm24can be rotated about the pivot pin45at a desired angle X (FIG. 7). An adjustment pin92is received in a corresponding hole97in the lower electrode arm24. An isolator bushing94is received in a hole in the fixed block76. An adjustment member96receives an end of the pin92and is arranged within the bushing94.

Referring toFIG. 7, the adjustment member96includes an eccentric, cam-like slot98that may be elongated (shown) or arcuate, for example. The adjustment member96includes flats99that can be manipulated by a tool to rotate the adjustment member96to achieve a desired angle X for the lower electrode arm24. The orientation of the flats99can provide a visual indication of the adjusted position of the lower electrode arm24.

In operation, the clamping fasteners80and fasteners40secured to the movable block78would be loosened to permit adjustment of the lower electrode arm24using the adjustment member96. The angle X corresponds to a distance Y at the electrode end26, which corresponds to the lateral adjustment of the lower electrode arm24to achieve alignment of opposing electrode ends26. A securing member100, such as a threaded fastener, is supported by the fixed block76to clamp the adjustment member96to the fixed block76once the desired arm adjustment has been achieved. Afterwards the movable block78can be tightly secured relative to the side plates74and fixed block76. An isolator washer (not shown) is arranged between the securing member100and adjustment member96.

Another example of securing the lower electrode arm24is shown inFIG. 9. The fixed block76includes an arcuate slot110that receives an insulator bushing104. The insulator bushing104is received in a hole in the lower electrode arm24. A fastener108, such as a bolt, is received in the insulator bushing104and threadingly secured to the lower electrode arm24within the corresponding hole. An insulating washer106is arranged between the fastener108and fixed block76. The arcuate slot110accommodates lateral repositioning of the lower electrode arm24. In the example, the fastener108provides a securing member that clamps the lower electrode arm24in a desired position.