GB1568934A - Welding apparatus - Google Patents

Description

(54) WELDING APPARATUS (71) I, EDWARD GEORGE SPISAK, a Citizen of the United States of America, of 35700 Oakwood Lane, Westland, Michigan 48185, United States of America, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to welding apparatus and particularly to welding apparatus for accurately positioning and welding workpiece portions to each other.

In the repeated welding of like workpieces in manufacturing processes it is necessary that the workpiece portions be accurately positioned relative to each other and to a welding head during the welding process.

It is particularly difficult to accurately align adjacent edges of workpiece portions so that they can be welded by plasma type welders. With such welding apparatus it is necessary that the edges to be welded be brought together very accurately and, once the weld begins, that the workpiece portions remain stationary relative to each other, as opposed to some forms of butt welding in which the edges actually are forced against each other to displace some of the metal which is melted during the welding process.

It is an object of the invention to provide welding apparatus by which adjoining edges of workpiece portions are accurately positioned relative to each other and to a welding head.

According to the present invention there is provided apparatus for welding adjoining workpiece portions together comprising: gauge means movable between a first and a second position; two clamp means capable of clamping respective workpiece portions, the two clamp means being disposed at opposite sides of the first position of the gauge means and each clamp means having a support member and a clamp member movable relative to the support member to engage opposite surfaces of the respective workpiece portion and hold said portion in engagement with the gauge means when the gauge means is in its first position so that in a clamping condition the clamp means align the workpiece portions on opposite sides of the gauge means; means capable of moving the two clamp means relatively towards each other a distance greater than the thickness of the gauge means, when the gauge means is in its second position remote from the workpiece portions, to move the aligned workpiece portions towards each other into tight abutting relationship with each other; and a welding head supported for movement in close proximity to the abutting workpiece portions to weld the portions to each other; and wherein each clamp means is operative to initially engage the opposite surfaces of the respective workpiece portion at a first location spaced from the gauge means in its first position and to subsequently engage and clamp the workpiece portion at a second location between the first location and the gauge means, whereby when the workpiece portions are engaged by the clamp means only at their first locations, if one or each workpiece portion is not in engagement with its respective support member at the second location, movement of the respective clamp member to clamp the workpiece portion at the second location will exert a force on the workpiece portion having a component towards the first position of the gauge means thereby urging the workpiece portion into firm engagement with the gauge means in its first position.

Further according to the present invention, there is provided a workpiece when welded on apparatus substantially as de scribed in the immediately preceding para @@@@@@ present invention it is possible to a@@@@@@ @@y high the workpiece portions @@@@@@@ @@@ gange means and then to move @@@@@@@ @@i@o@ portions into accurate abht @@@@@@ @@@@@ship when the gauge means is @@@@@@ @@ns second position. The gauge @@@@ @@@ conveniently be used to subse quently eject the welded workpiece portions from the apparatus. The apparatus of the present invention is particularly applicable where the workpiece portions comprise the opposed ends of a hoop to be welded where the curvature of the hoop may otherwise cause difficulties in accurately aligning the opposed ends with the gauge means and with each other.

Since clamp elements of the clamp mem bers, which engage the workpiece portions at the second locations, are likely to lie close to the welding path, it is preferred that the clamp elements be capable of absorbing heat generated during welding, and conveniently they are replaceable.

As the two clamp means are capable of moving relatively towards each, other a dis tance greater than the thickness of the gauge means, one of the clamp means may be adapted to permit slip of the associated clamped workpiece portion when the work piece portions are in abutting relationship with each other and the two clamp means are moving relatively towards each other, to force the workpiece portions into their right abutting relationship. Each of the clamp means may comprise a fluid cylinder opera tively associated with the respective clamp member to move the clamp member relative to the respective support member, and the fluid cylinder of the one clamp means may be adapted to apply a smaller force to the respective, clamp member than the force applied by the fluid cylinder of the other clamp means to permit the sliding move ment of the associated workpiece portion.

Conveniently only a first of the clamp means is displaced during the relative movement of the clamp means towards each other, and where the aforementioned slip of one of the workpiece portions is permitted, it is preferably in said first clamp means.

Conveniently, the initial engagement by the clamp means of the workpiece portions at the first location, and subsequently at the second location is permitted by a rocking action of the clamp members, and m a preferred embodiment the clamp members are supported by respective pin and toggle arrangements in which a relatively loose fit permits a small amount of rocking action.

One embodiment of apparatus in accord- ance with the present invention will now be described by way of example only, with reference to the accompanying drawings, in which.

Figure 1 is a side elevation of the welding apparatus embodying the invention with portions thereof shown schematically; Figure 2 is a front elevation of the welding apparatus seen in Figure 1; Figure 3 is a view of a portion of the welding apparatus taken generally on line 3-3 in Figure 1; Figure 4 is a highly schematic view of a portion of the welding apparatus seen in Figure 2 but at an enlarged scale and show ing a different condition of operation; Figure 5 is a schematic view showing the electrical control circuit and the various associated components of the welding apparatus; Figure 6 is a view of the portion of the welding apparatus seen in Figure 2 but at an emerged scale and illustrating in grossly exaggerated manner the initial positioning of workpiece portions to be welded together; Figure 7 is a view similar to Figure 6 showing a subsequent condition of opera tion in which the workpiece portions are clamped; Figure 8 is a view similar to Figure 7 showing another condition of operation, and Figure 9 is a view similar to Figure 8 showing the workpiece portions in position for welding.

Referring to the drawings welding apparatus embodying the invention is desig nated at 10 and includes a welding head 12, a clamp assembly 14, and a gauge member 16, all of which are supported on a frame structure 18. The welding apparatus 10 is particularly adapted for welding together the abutten ends 20 of a strip of metal which has been performed into a general circular hoop 22, and will be described hereinafter with that use in mins.

As shown schematically in Figure 2, the clamp assembly 14 includes a left clamp sub-assembly 24 and a right clamp sub assembly 26 which are used to hold the respective ends 20 of the hoop 22 during the welding operation. The left clamp sub assembly 24 includes a stationary work sup port 28 mounted in a stationary position relative to the frame 18 and a generally vertically movable clamp member 30 which can be moved generally vertically relative to the work support 28 by means of a hydraulic cylinder 32.

The right clamp subassembly 26 includes a work support 34 which is supported rela tive the frame 18 for generally horizontal movement relative to the work support 28.

The work support 34 has a bracket member 36 extending upwardly to support a hy draulic cylinder 38, the rod end of which is provided with a clamp member 40. The cylinders 32 and 38 are operated simul tarieously from a common hydraulic source not shown and are disposed at a light an to the vertical so that the clamp mem bers@@@ and @@@@@@ @@@verb generally radially @@ lbs he @@@@@gel @@@@@@@@ to @@@@ end 20b during champings andouz@@@@@@ing of the hoop 22 in @@working portions. The clamp member 40 together w@@@@@ the cylinder 38 and the bracket 36 @@@ slide generally horizontally as a@@@@@@@ with the work support 34. Such movement is acomplis@ed by a hydraulic a@ne@ 41 @@@hich @@tracts @@@@@@@@@@@ the assem@@@@ the left in Figure 3 and which extends to move the slider @@@@@@ b@@@@@@the right The gang me @@@@@@ 163 isnsupporthed@@@ the 0 @@@ahres @@@ forednosvements generally hori zontally shown inqdull line daird @nokerg line position show in @@@@ id broken line positions perspectively in Figure 1 @@@ the enterred first @@ @@@@@@@@@@ galuge member 16 indisposed between right and left clamp subassed @@ lies 24 and 26 when the lattemare in spaqeds @@ @@@@@ relationship as @@@@@@@ Figure 4. Movementioned gauge member @@ @@@@@@@@@plis@@@@ oby @@ hydraulic cylinder 4 supported in generally horizontal posi tion run other frame 18 at the mean whit be apparatus @@@@@ The hoop 22 displaded in position in the wtiling apparatus 10 when the clamp sub- asser@@@@ 24 and 26 care in spaced apart relationship gasgsedm in Figure 4. This is accomplished placing the ends 20 on the left @@@@ support 28 and the right work support 34 with the end 20 in substantially abutting relationship with the gauge mem ber 16. Thereafter the clamps 30 and 40 are moved downwardly by the hydraulic cylinders 32 and 38 @@@@ engagement with the ends 20 to clamp quesh against the re spective supports 28 and 34, as described in greater detail hereinafter.

The welding head 12 is support relative to an verhead track structure 48 forming part of the frame 18 for movement loni tudinally of the track structure. The weld ing head assembly 1 includes a welding nougle 52 which is the preferred embodie ment of invention is a nozzle of the plasma type welder morti fullyridisclosed in U.S. patent 2,806,124. The welding nozzle 52 nachdes genered vertically extending @@@@@ag portion 53 through which the arc and arc gases pass. The nozzle 52 is mounted on a guide bracket 54 for movement here with. The guide bracket 54 is pivotally mounted for swinging movement about an axis indicated at 56 relative to a movable mounting structure or trolley 58 As seen in Figure 2, the trolleyl 58 is con nected @@@@@@ upper @@@@ to grooved member so which blidably receives a tongue member 62 @@@@ tongued member 62 is @@@@@ted rigidly right @@@@@ structure 48 of frame 18 and has a generally V shaped configura tion which receives a longitudinally extending screw 66. As seen in Figure 1, the screw 66 is connected by means of a coupler 68 to a direct current motor 70 which is reversible and of variable speed Rotational movement of the reversible motor 70 is transmitted by way of a Aupler 68 to a screw 66 which is threadedly engaged with a drive portion 72 (Figure 2) forming pair of the grooved meniber 60. Consequently rotationaly movement of the motor 70 causes sliding movement of other grooved member 60 on the tongue member 62 and movement of the welding nozzle 52. Movement of the welding nozzle 52 is used to actuate electrical switches in a control circuit be dis cussed later.

In addition to movement longitudinally of the track structure 50, the nozzle 52 may be pivoted about the axis indicated at 56 between the full line and the broken line positions shown in Figure 1. A tension spring 74 is interposed between the guide bracket 54 and the trolley assembly 58 so that the welding nozzle 52 is continuously urged towards its vertical position seen in Figure 1.

A limit stop 78 is mounted in the path of movement of the welding nozzle 52 so that as the welding head 52 moves from left to right as viewed in Figure 1, the guide bracket 54 engages stop 78 and causes the welding nozzle 52 and the support bracket 54 to pivot to the full time position.

At a forward portion of frame 18, welding apparatus 10 is provided with a gate 80 which is mounted to slide vertically between open and closed positions. The gate 80 is balanced by a counterweight 81 so that manual movement is required by the oper ator to move the gate to its closed position.

Closing the gate serves to bring it into engagement with a latch mechanism 82 to maintain it in its closed position and opening of the gate is achieved electrically by actuation of a splenoid forming part of the latch 82. The purpose of teh gate 80 is to shield an operator of the apparatus from the operator of the welding nozzle 52.

Also located at a forward part of the apparatus 10 is a guide block 84 which as seen in Figure 3 has a V-notch 85 to receive the forward tapered end 86 of the gauge member 16 to ensure that the gauge member is accurately aligned in parallel relationship to the track structure 48 and therefore to the path of the welding head when in its first position. When the tapered end 86 is disposed in the V-notch 85 the gauge member 16 is accurately aligned and it is at this time that the end 20 of the workpiece are placed into abutting relationship therewith to ac@@rately gauge the ends 20 of the workpiece 22 .

In the @@@@@ 1 initial condition of the welding apparatus 10, the left and right clamp subassemblies 24 and 26 will be spaced apart horizontally with the gauge member 16 disposed therebetween as best seen in Figure 4. The left and right clamp members 30 and 40 will be in their open position with the hydraulic cylinders 32 and 38 retracted. At the same time the welding nozzle 52 will be in its fully tilted position with the guide bracket 54 in engagement with the stop member 78 so that the welding head 52 is disposed at an angle to the vertical with the end of the nozzle 52 above the path of movement of the gauge member 16.

Under the above conditions, an operator utilizing the apparatus locates an elongated strip of material which may have been preformed into the generally circular hoop 22 in the clamp assembly 14 with the end 20 generally on the work supports 28 and 34 so that the ends 20 abut the gauge member 16 at its opposite sides. When the strip of material to be welded is relatively thin and flexible it is unnecessary to preform the material into the generally circular hoop 22 since the material can be easily flexed by the operator to place the opposite ends 20 in abutment with the gauge member 16. The opposed surfaces 75 of the gauge member 16 are accurately formed to be parallel to each other so that, as seen in Figure 6, when the ends 20 of the workpiece portions are placed in engagement with the surfaces 75, they also are parallel. Moreover, whether or not the workpiece is preformed, but particularly where the end portions are allowed to remain planar, the workpiece portions may not engage the full surface of the supports 28 and 34, as seen in Figure 6.

When the workpiece portions do not engage the full support surface of the work supports 28 and 34, tight abutting relationship between the ends 20 of the workpiece portions and the respective surfaces 75 of the gauge member 16 is provided by the means described immediately hereafter.

The clamp members 30 and 40 are attached to the respective hydraulic cylinders 32 and 38 by means of a pin and toggle arrangement, and a small amount of rocking of each clamp member relative to the respective hydraulic cylinder is afforded in the embodiment illustrated by ensuring that there is a relatively loose fit in the pin and toggle arrangement. Such rocking action of the clamp members 30 and 40 may however clearly be afforded by means other than a relatively loose fit in a pin and toggle arrangement.

The rocking action of the clamp members 30 and 40 permits a heel 76 of each to initially engage and grip the respective workpiece portion at a first location spaced from the gauge member 16 when the clamp members are moved towards the respective work supports 28 and 34 upon actuation of a manual control such as a foot switch 90 (Figure 5) to extend the hydraulic cylinders 32 and 38. This initial gripping action holds the workpiece portions off part of the respective work support as shown in grossly exaggerated manner in Figure 6. In practice, it is doubtful that the relatively loose pin and toggle arrangement, or the fact that the angle the workpiece portions make with the respective surfaces 75 of the gauge member is not a right-angle, would be immediately apparent.

Subsequent extension of the hydraulic cylinders 32 and 38 causes additional movement of the clamp members 30 and 40 to bring clamp elements 77 thereof into engagement with the top surface of the workpiece portions at a second location between the first location and the gauge member 16 in its first position. Additional increments of movement of the hydraulic cylinders 32 and 38 cause each clamp member to rock or pivot about its heel 76 and bend the workpiece portions downwardly towards the respective work support. Such downward movement exerts a force on the workpiece portions in the direction of the gauge member 16 and thereby ensures tight engagement of the ends 20 with the opposite surfaces 75 of the gauge member until the workpiece portions and gauge member assume the relative position shown in Figure 7, when the adjacent end regions of the workpiece portions are disposed on the whole support surface of the work supports 28 and 34 in a common plane as well as at right angles to the surfaces 75.

With the workpiece or hoop 22 firmly gripped by the clamp subassemblies 24 and 26 the operator pulls down the gate 80 from its elevated position. As the gate 80 reaches its lower position it is automatically latched in a closed position by the latch 82 and actuates a switch 92 controlling the hydraulic actuator 46 so that the latter is retracted and causes the gauge member 16 to move toward the right as viewed in Figure 1. As the gauge member 16 approaches its extreme right position, that is, its second retracted position, a switch 94 (seen in Figure 5) is energized causing the motor 70 to begin rotation so that the welding head 12 with the nozzle 52 is advanced toward the left in Figure 1. Initial leftward movement brings the guide bracket 54 out of engagement with the stop 78 so that the spring 74 is effective to swing the welding head together with the nozzle 52 is a generally vertical position.

As the welding head is moving to its generally vertical position the guide bracket 54 disengages from switch 96 causing hydraulic actuator 41 to move the right clamp subassembly 26 toward the left as viewed in Figure 2 to occupy the gap once occupied by the gauge member 16. Such generally horizontal movement of the right clamp subassembly 26 is for a greater distance than the thickness of the gauge member 16, that is, greater than the original spacing of the ends 20 of the workpiece portions. Since the workpiece portions were originally aligned in the same plane and at opposite sides of the gauge member 16 movement of the clamp subassembly 26 initially brings the ends 2Q of the hoop 22 into abutting engagement with each other. After the parts are in abutting engagement the clamp assembly 26 is moved an additional amount during wfiich time the associated workpiece portion slips between the clamp member 40 and work support 34. This forces the ends 20 tightly against each other to the abutting relationsnip in which they are held during the welding operation. To facilitate this tight abutting relationship of the ends 20, the hydraulic actuator 38 applies a lesser degree of pressure to the right clamp member 40 than is applied by the hydraulic actuator 32 to the left clamp member 30.

This may be accomplished by ensuring that cylinder 38 has a smaller internal diameter than cylinder 32 or by limiting the hydraulic pressure delivered to cylinder 38. In an actual embodiment of the invention the gauge member has a thickness of approximately five-eights of an inch so that after removal of the gauge member and movement of the clamp subassembly 26 the latter moves a distance of five-eights of an inch to absorb the space once occupied by the gauge member as seen in Figure 8. The subassembly 26 continues to move an additional amount of approximately one quarter of an inch which requires the workpiece portion held by the subassembly 26 to slip that amount before the clamp subassembly comes to a stop as determined by the full stroke of cylinder 41 or a stop 79 as seen in Figure 9. Once the workpiece portions reach this position they are held in tight engagement with each other but no additional force is applied to press the ends 20 against each other.

When the clamp subassembly 26 reaches a final position as seen in Figure 9, the clamp elements 77 are spaced apart only sufficiently to allow the welding nozzle to have access to the abutting edges 20 for conducting the welding process. In this position the clamp elements 77 support the workpiece portions and also tend to absorb heat generated by the weld and dissipate it to the clamp members 30 and 40 to prevent distortion of the clamp elements to ensure a uniform, smooth weld. However, in view of the substantial amount of heat to be absorbed by the clamp elements 77, they are replaceably mounted on the respective clamp members.

During the time that the right clamp subassembly moves to close the gap left by the gauge member 16, leftward movement of the welding head 12 (Figure 1) continues until the nozzle 52 reaches the beginning of the area to be welded at which time a limit switch 98 seen in Figure 5 is engaged by the moving trolley 58 to initiate the welding process. The welding head 52 travels the length of the seam formed by the abutting ends 20 and is in alignment with the original location of the left surface 75 of the gauge member 16. At the end of the weld, another switch 100 is engaged by the trolley 58 to discontinue the welding operation. Simultaneously with the actuation of the switch 100 to discontinue the welding operation, the hydraulic actuators 32 and 38 are retracted to release the clamp subassemblies 24 and 26 and the right clamp subassembly 26 moves horizontally to the right as viewed in Figure 1. During this latter movement the counterweighted door 80 is unlatched so that it is permitted to move upward to an open position.

After discontinuation of the weld the welding nozzle 52 travels an additional amount so that the trolley 58 engages another limit switch 102 which reverses the rotation of the motor 70 and returns the welding head assembly 12 to the right in Figure 1. Reversal of direction of welding head serves to actuate the hydraulic cylinder 46 so that it is extended causing the gauge member 16 to move to the left as viewed in Figure 1. The left end of the gauge member will enter the gap between the right and left clamp subassemblies 24 and 26 and engage the welded hoop 22 and eject it from the work supports 28 and 34.

At the same time the left end of the gauge member 16, which is formed with the cam surface at 84, engages the lower end of the guide bracket 54 to tilt the welding head 52 about the pivot 58. Thereafter the welding nozzle 52 is moved to the right at an angle in elevated relation to its welding path with the guide bracket 54 in engagement with the top of gauge member 16. As the guide bracket 54 engages the stop member 78, the welding head and bracket 54 are tilted an additional amount to engage switch 96 and the motor 70 is deenergized to terminate further rightward movement of the welding head 12. At this point in the operation, the welded hoop 22 has been ejected from the apparatus in condition to receive the next workpiece to be welded.

In the interest of clarity the electrical circuit by which switches 90 through 102 are actuated is shown in Figure 5 in association with schematically represented components of the welding machine 10.

Switch 90 is connected to a source of power 104 and is operated by the foot of the operator to close a circuit to a control 91 which simultaneously actuates solenoid valves extending the clamp cylinders 32 and 38. Switch 92 which also is connected to the source of power 104 is closed in response to closing of the gate 80 to actuate a solenoid valve associated with cylinder 46 to retract gauge member 16. Retraction of the gauge member 16 by cylinder 46 actuates a switch 94 closing the circuit between the source of power 104 and a reversible control on the motor 70 to move the welding head 12. Switch 96 is normally held in an open position by the tilted welding nozzle 52. Movement of the welding head 12 permits the nozzle 52 to move to a vertical position so that switch 96 closes the circuit between the power source 104 and a solenoid controlled valve associated with cylinder 41 to retract the latter and close the right clamp subassembly 26 relative to the left clamp subassembly 24. Continued forward movement of welding head 12 actuates switches 98, 100 and 102 in succession. Switch 98 is normally open and switch 100, which is connected to the source of power 104 is normally closed and as the welding head 12 engages switch 98 the latter is closed to complete the circuit through the switch 100 and from the power source 104 to initiate the welding process. When the welding head 12 engages the switch 100 it opens it to discontinue the welding step and simultaneously releases a solenoid associated with latch 82 to permit the gate 80 to move upwardly to an open position.

At the same time switch 100, which also is connected to the control 91 and to the cylinder 41, causes cylinders 32 and 38 to simultaneously retract to open the clamp subassemblies 24 and 26 and causes cylinder 41 to extend to move the clamp subassembly 26 horizontally to an open position. Continued movement of the welding head 12 actuates the switch 102 which is connected to the control on the motor and serves to reverse the direction of rotation and at the same time is connected to actuate the solenoid controlled valve on the cylinder 46 to extend the gauge member 16. When the welding head moves rearwardly it reengages the switch 96 to open the circuit between the power source 104 and the motor 70 so that the latter stops its rotation.

The circuit is such that, with the clamp subassemblies 24 and 26 in closed position in response to actuation of the valve 90, subsequent closing of the gate 80 and switch 92 serves to automatically actuate each of the remaining control switches 94 through 102 in sequence to bring about automatic control of the various devices.

Although the preferred embodiment of the invention utilizes hydraulic cylinders 32, 38, 41 and 46 it will be understood that various forms of linear actuators and fluid motors may be used.

Welding apparatus has been provided for automatically welding abutting ends of a workpiece such as in a ring formed of a strip of material in which the ends are accurately aligned by a gauge member which moves out of position to permit the ends to be moved into accurate position relative to each other and in tight engagement for welding. After welding the welded workpiece is ejected from the apparatus and the apparatus is placed in condition for receiving the next workpiece and the movements of gauging, holding, welding and ejecting the workpiece occur in timed sequence.

Claims (10)

WHAT I CLAIM IS:

1. Apparatus for welding adjoining workpiece portions together comprising: gauge means movable between a first and a second position; two clamp means capable of clamping respective workpiece portions, the two clamp means being disposed at opposite sides of the first position of the gauge means and each clamp means having a support member and a clamp member movable relative to the support member to engage opposite surfaces of the respective workpiece portion and hold said portion in engagement with the gauge means when the gauge means is in its first position so that in a clamping condition the clamp means align the workpiece portions on opposite sides of the gauge means; means capable of moving the two clamp means relatively towards each other a distance greater than the thickness of the gauge means, when the gauge means is in its second position remote from the workpiece portions, to move the aligned workpiece portions towards each other into tight abutting relationship with each other; and a welding head supported for movement in close proximity to the abutting workpiece portions to weld the portions to each other; and wherein each clamp means is operative to initially engage the opposite surfaces of the respective workpiece portion at a first location spaced from the gauge means in its first position and to subsequently engage and clamp the workpiece portion at a second location between the first location and the gauge means, whereby when the workpiece portions are engaged by the clamp means only at their first locations, if one or each workpiece portion is not in engagement with its respective support member at the second location, movement of the respective clamp member to clamp the workpiece portion at the second loca tion will exert a force on the workpiece portion having a component towards the first position of the gauge means thereby urging the workpiece portion into firm engagement with the gauge means in its first position.

2. Apparatus as claimed in claim 1 in which the clamp members comprise olamp elements which are engageable with the workpiece portions at the second locations and which are capable of absorbing heat generated during welding, and wherein the clamp elements are replaceable.

3. Apparatus as claimed in claim 1 or claim 2 in which one of the clamp means is adapted to permit slip of the associated clamped workpiece portion when the workpiece portions are in abutting relationship with each other and the two clamp means are moving relatively towards each other.

4. Apparatus as claimed in claim 3 in which each clamp means comprises a fluid cylinder operatively associated with the respective clamp member to move the clamp member relative to the respective support member, and wherein the fluid cylinder of said one clamp means is adapted to apply a smaller force to the respective clamp member than the force applied by the fluid cylinder of the other clamp means, to permit the sliding movement of the associated workpiece portion.

5. Apparatus as claimed in any one of the preceding claims in which a first of the clamp means is displaced towards the second clamp means during the relative movement of the clamp means towards each other, while said second clamp means remains stationary.

6. Apparatus as claimed in claim 5 when dependent from claim 3 or claim 4 in which said first clamp means comprises the one clamp means in which slip of the associated clamped workpiece portion is permitted.

7. Apparatus as claimed in any one of the preceding claims in which the initial engagement by the clamp means of the workpiece portions at the first location and subsequently at the second location is permitted by a rocking action of the clamp members.

8. Apparatus as claimed in claim 7 in which the clamp members are supported by respective pin and toggle arrangements and wherein a relatively loose fit in each pin and toggle arrangement permits the rocking action of the clamp members.

9. Apparatus as claimed in claim 1 and substantially as herein described with reference to Figures 6 to 9 of the accompanying drawings.

10. A workpiece which has been welded on apparatus as claimed in any one of the preceding claims.