GB2160138A - Cold pressure butt welding - Google Patents

Abstract

Apparatus for end to end welding of two workpieces in a repeated cycle of operations comprises two carriers (10) each having a pair of jaws (D) for clamping around a respective workpiece and a drive mechanism (80-90) which reciprocates the carriers towards and away from each other. After the jaws grip each workpiece and the carriers move the workpieces together for butting pressure, detainers (40) acted on by a lost motion mechanism operated by the drive mechanism obstruct the movement of the jaws with the carriers when the carriers begin to move apart and a keyed connection thereupon moves the jaws of each pair apart transversely only to release the workpieces before the jaw pairs begin to retract axially with the carriers. Gates prevent return movement of the released workpieces but can be opened, as also can the jaws, to remove the welded workpieces and to insert fresh workpieces, by an additional retraction movement of the carriers. Operation of the drive mechanism is via a hand lever cranks and levers (18,87) or by fluid cylinders and levers. <IMAGE>

Description

SPECIFICATION Welding apparatus and method This invention relates to apparatus for and a method of cold-pressure butt welding.

The welding of two workpieces end-to-end by cold pressure butt welding is effected by multiple upsetting of the ends of the workpieces to bring them repeatedly into contact under high pressure. It is used to join together two lengths of corresponding cross-section wire or rod or other elongate workpieces and has the advantage that no special weld preparation is necessary because the frictional forces as the ends of the workpieces are brought together repeatedly has the effect of displacing surface contamination away from the faces that are eventually welded together.

Known apparatus (e.g. US 3098018 and 3 106013) for such a process employs a die set comprising two pairs of jaws, that are reciprocated towards and away from each other. Each pair of jaws has registering semi-circular recesses that provide a circular cross-section passage in which the workpiece is held when the jaw parts are closed together, the die set being mounted so that the apertures are coaxial whereby short projecting lengths from each pair of jaws are pressed against each other essentially end to end as the two pairs of jaws are brought together. As the pairs of jaws are moved apart, their grip on the workpieces is relaxed and the cycle of movement is then repeated.During the first few cycles of operation, any contamination on the contacting surfaces is removed as the abutment pressure causes material displacement at the end of the workpieces. Welding of the contacting faces occurs as the operating cycle is continued, and once the welding adherence is sufficient to resist the gripping force of the dies, the retracting jaws slide on the workpieces. Subsequent cycles feeding more material to the weld region increase the welded area and produce a bead at the interface that is subsequently removed e.g. by means on the die set (GB 2 107 224A).

According to one aspect of the present invention, there is provided a cold pressure butt welding apparatus comprising respective carriers for two pairs of jaws in which respective workpieces to be welded are gripped, said carriers being reciprocable along a common axis to move the pairs of jaws towards and away from each other in the direction of said axis to bring the ends of the workpieces together under pressure, and means for displacing the jaws of each pair relative to their carrier trans tersely to said axis to grip and ungrip the workpieces, drive means for operating a mechanism for said movement of the carriers and jaws in the direction of said axis comprising a pair of levers attached to the carriers and being pivotable in a plane containing or parallel to said common axis, said mechanism and said pairs of jaws being arranged to operate in a sequence comprising the steps of (i) gripping the workpieces, (ii) moving the two workpieces together to bring their ends into contact under pressure, (iii) releasing the grip on the workpieces, and (iv) retracting the carriers the workpieces ungripped.

According to another aspect of the invention, there is provided a cold pressure butt welding apparatus comprising means for holding pairs of jaws for respective elongate workpieces, drive means for displacing the holding means with the pairs of jaws to bring the ends of said workpieces into engagement under pressure, first control means acting on the jaws to urge the jaws of each pair apart, guide means for acting between the holding means and the pairs of jaws when the jaws are displaced relative to the holding means by said control means to cause the jaws of each pair to close together to grip the associated workpiece, further control means acting on said pairs of jaws to urge them together, means inhibiting the operation of said further control means until the pairs of jaws approach a fully closed position, said further control means exerting a force on said pairs of jaws sufficient to overcome the action of said first control means, the arrangement being such that in the fully open position of the pairs of jaws, said first control means act to cause the jaws to grip their respective workpieces, whereupon the drive means are operable to displace the holding means together with the gripping pairs of jaws to force the ends of the workpieces into abutment, the further control means then restraining return movement of the pairs of jaws with the holding means, whereby in said return movement of the holding means said guide means act to open the jaws of each pair, said further control means then being rendered inoperative to cause the opened pairs of jaws to be moved apart with the remaining displacement of the holding means and to be displaced by said first control means to regrip the workpieces as a first step in a repeat cycle of operations.

The invention will be described in more detail with reference to the accompanying drawings, in which; Figures 1,2 2 and 3 are front, side and top plan views of a first form of apparatus according to the invention.

Figure 4 is a detail view of a vertical cross-section on the axis X-X in Figure 3, showing the jaws in the fully open position on the left and in a fully closed position on the right, Figure 5 is a detail view in the direction V in Figure 2 with the casing cover plate removed, Figure 6 is a top plan view showing further details of the carriers of the apparatus, with the die set removed, Figure 7 is a similar plan view showing the carriers in the fully opened position, Figure 8 is a sectional view on the line Y-Y in Figure 6, Figures 9, 10, 1 and 12 are schematic views illustrating some modifications of the apparatus of Figures 1 to 8, Figures 9, 10 and 11 being respectively a longitudinal axial section, a plan view, and a transverse axial section, and Figure 12 being a view onto the detainer cam in the direction X, Figures 13, 14 and 15 are front, side and top plan views of another form of apparatus according to the invention, Figure 16 is a detailed illustration of the fulcrum joint of the carrier levers of the apparatus shown in Figures 13-15.

Referring to Figures 1 to 8 of the drawings, the apparatus shown comprises a main casing 2, on the top wall 4 of which is arranged a guidance and drive mechanism for a replacable die set D consisting of two pairs of jaws, the mechanism on the top wall being symmetrically arranged with respect to a central vertical transverse plane. The die set is of generally conventional form with two pairs of mating faces having rearwardly tapering side faces and mating faces of the jaws of each pair of jaws having matching recesses that together define a circular cross-section die passage P of a size appropriate to the cross-section of wire or other workpiece being processed. The centre line of the passage lies on an axis X-X perpendicular to a transverse plane of symmetry of the mechanism.The die set is mounted such that the pairs of jaws are displaceable towards and away from each other in the direction of the axis X-X, and in addition the two jaws of each pair are able to move towards and away from each other transversely to that axis so as to grip a wire releasably in the die passage P.

Each pair of jaws is held in a respective channelshaped carrier 10 the lower regions of which rest in a parallel-sided trough 12 that extends axially across the top of the casing. Guide plates 14 secured to the trough sides project inwards to locate in slots 16 in the sidewalls of the carriers 10 so that the carriers are prevented from moving in any other direction but the axial direction X-X. For this movement each carrier is connected to a pair of links 18 of a driving linkage that will be described in more detail below.

Each pair of jaws is located in a forward region of its carrier between side walls 20 in this region having oblique faces conforming to the tapering side faces of the jaws. A key plate 22 is secured to the base of the carrier in this same region and has integral keys 24 which run parallel to the adjacent side walls 20 and which are located in complementary slots in the underface of the jaws.

Blocks 26 fixed to the guide plates 14 project above the carriers on opposite sides of the trough 12 in its central region. Retaining plates 28 are adjustably held on the blocks to be slidable towards and away from each other by wing-headed bolts 30 passing through elongated slots in the plates. When the plates are advanced towards each other so that they extend over the carrier channels in which the die set is held, as is shown in Figure 3, they prevent the jaws lifting from the carriers. They can also be slid apart when the bolts are loosened, to give access to the recesses when the die is to be replaced.

The blocks 26 also provide housings for transversely slidable plungers 32 the axes of which coincide with the transverse plane of symmetry of the guidance and drive mechanism. The plungers (only one of which is shown in Figure 6) are urged into the path of the jaws by coil springs 34 to a distance determined by the abutment of collar 36 at the rear end of the plunger on the shoulder of a counterbore 38 in which it slides. Each plunger has a cone or wedge-shaped nose that engages chamfers on the forward outer corners of the jaws so that when the carriers have advanced the pairs of jaws towards each other the spring load on the plungers will urge the two pairs of jaws apart, whereby in the absence of any other influence the jaws slide backwards and, guided by the key plates 22, the jaws of each pair are closed together, as will be further described.The plungers can be retracted manually by using the pins 32a.

The pairs of jaws are also engagable by respective detainers 40 each comprising a lower slide portion 42 displaceable in the direction X-X in a guide space 44 formed between the top face of the casing and the carriers, and a contact limb 46 projecting upwards through a clearance space 48 in its associated carrier to lie behind the rear face of the pair of jaws mounted thereon. A spring or springs 50 acts on each detainer to urge it towards its associated pair of jaws and each contact limb, the lower face 52 of which is inclined obliquely towards the jaws, can be acted on by a wedge member 54 that is displaceable vertically to engage that sloping face. Under pressure from the wedge member, therefore, each detainer 40 can be moved back, against the bias of its spring or springs 50.When the spring force is allowed to hold its detainer in contact with the pair of jaws, as in the fully closed position shown on the right of Figure 4, the biasing force of the spring or springs 50 on the jaws is greater than the spring biasing force of the transverse plungers; in this condition, therefore, the pairs of dies are prevented from moving apart in the X-X direction. The wedge members which withdraw the detainers from the jaws to allow the action of the plungers to be released are operated in synchronism with the main drive for the carriers by means still to be described.

In fixed positions rearwards of and above each of the carriers are respective T-plates 56 on each of which is mounted a gate 58 through which a workpiece passes. Each gate is composed of two main members supported on the top of the T-plate.

The first of these members takes the form of a block 60 secured to the plate by a clamping screw 64 that passes through a slot 66 in the block that allows the block to be adjusted towards and away from the path of the workpiece, to which it presents a serrated face.

The second member 62 is in the form of a lever mounted on a pivot 68 intermediate its length so that a curved forward face can swing towards and away from the opposed, serrated face of the block 60. The lever forward face is normally urged towards the block by a coil spring 70 mounted on its pivot, thereby to grip the workpiece between the lever and the block so as to prevent it moving rearwards, while permitting it to be fed forwards. The adjustment of the block 60 allows different thicknesses of workpiece to be accomodated and by way of illustration Figures 6 and 7 show (to the left) larger and (to the right) smaller diameter workpieces.

The drive for the carrier is provided by a hand lever 80 mounted on head 81 of a boss 82 that is rotatably mounted in a bore 83 in the casing, in which it is located axially by the head 81 and an end plate 84 secured to the main end of the boss.

Adjustably mounted on a flange 85 concentric with the boss 82 is an adjustment ring 86 for setting the limits of rotation of the boss, as will be described below. At diametrically opposite positions on the boss 82 a pair of links 87 are attached through pivots 88, one located in the upper half of the boss, the other in the lower half. The pivots 88 are provided by bolts that also secure the end plate 84 to the boss 82.

The opposite ends of the links are pivoted on the lower ends of levers 90 journalled on bearings 92 in the casing, and the upper ends of the levers are in their turn attached to the pivot links 18 engaging the carriers 14. Figure 1 shows this mechanism with the hand lever in a lowermost position L1 and the jaw pairs closed together. In the illustrated example a return spring 94 connected between extensions 96 of the pivot links 87, as shown, or of the levers 90 urges the mechanism to its opposite end position, but such a return spring may be omitted without disadvantage.

Also attached to the drive disc through the upper of the two pivots 88 is a further pivot link 98 connected at its upper end to a mounting plate 100 from which the two wedge members 54 project. A light spring (not shown) acts between the casing and the plate urging it upwards to keep the members 54 in contact with the detainers 40. As can be seen from the detail view in Figure 5, the pivot for the lower end of the link 98 extends through an elongated slot 102 in the link, providing a lost-motion connection by allowing the link a limited relative movement at the pivot.

In welding operations, the adjusting ring 86 is fixed to the casing by screws 104 passing through arcuate slots 106 in the ring into tapped holes in the casing. The boss carries a spring-loaded plunger 108 engaged in a further arcuate slot 110 in the ring 86 to limit its range of movement, and therefore the pivoting of the levers 90, in particular to limit the opening movement of the dies.

For the initial setting of the apparatus to suit a particular set of dies, the plunger 108 is lifted from its slot 110 so that the hand lever 80 can be swung to the position L3, this position being determined by the abutment of the lower ends of the levers 90 against fixed stops (not shown) within the casing. A large opening is thereby created between the jaws and resulting from that opening movement the two jaws of each pair also have a considerable space between them. The adjustment ring fixing screws 104 are slackened to allow the ring to be turned sufficiently for the plunger 108 to be reinserted in its slot 110. The ring is then rotated, taking the boss 82 with it, to bring the dies closer together and as a consequence also bringing the two jaws of each pair closer to each other.When the jaws are nearly in contact at the diametrical dividing plane, the screws 104 are tightened again to fix the ring with the result that an end limit is set to the opening of the jaws by the engagement of the plunger with the end of its slot 110. It is thus ensured that the operating lever has a repeatable end position in which the jaws of each pair are at a very small gap to each other, sufficient to allow the workpieces to be fed freely through the cylindrical passages but so small that they cannot slip from the passages and be trapped between the opposed faces of the jaws when the jaws close.

With this initial adjustment made, the hand lever 80 has a relatively small angular operating movement, e.g. in Figure 1 the closed and open positions are represented by the positions L1 and L2 some 250 apart. When it is required to open fully the space between the jaws of each pair (as shown in Figure 7) e.g. in order to remove the welded workpieces of to replace a set of dies, the plunger 108 can be lifted, as already described, and the hand lever swung upwards to bring the lower ends of the levers against the stops within the casing, the lever 80 then lying at position L3. Any readjustment of the lever end position L2 to suit a replacement die set can be readily made using the procedure described above.

After the initial adjustment of the apparatus, the workpieces to be joined are fed through the gates 58 and the cylindrical passages P, as already described, to have short lengths projecting from the front of each jaw pair. The hand lever 80 is now swung downwards from L2 to L1, clamping the wires in the jaw pairs and pushing the jaw pairs towards each other so that the wires are brought into end-to-end abutment under pressure.

At the start of this operation, while the lever 80 is at L2, the wedge members 54 hold the detailers 40 away from the jaws (left-hand side of Figure 4).

Because the pivot 88 lies at the upper end of the slot 102 in the link 98, during the initial movement of the hand lever the detainers are still retracted as the carriers 10 begin to move together. The jaw pairs are not entrained with the carriers as they are held back by the transverse plungers 32. However, because of the key connection between the jaws and their carriers, the movement of the carriers brings the two pairs of jaws together, clamping the workpieces. As the movement of the lever 80 continues the link 98 is lowered to retract the wedge members 54 and the detainer springs 50 are able to push the detainers onto the jaws and urge them forwards against the bias ofthetranverse plungers.Soon after this the jaws are contacted by the inclined faces of the advancing carriers and the wires are forced into abutting end-to-end contact as the hand lever completes its movement to L1.

When the hand lever begins its return movement from the end position L1 the detainers 40 remain in their extended positions holding the jaw pairs together while the carriers begin to retract away from each other. The reverse relative movement between the jaws and the carriers opens the jaws of each pair to release the grip on the wires while the jaw pairs remain stationary in the direction X-X. As the lost motion in the operation of the pivot link 98 is taken up and the link rises, so the wedge members too are raised to retract the detainers. The jaw pairs can now slide away from each other on their carriers, under the influence of the plungers 32, to be brought into abutment with the inclined faces of the carriers again and grip the wires at a position rearwards of the previous gripping position.The procedure is repeated until continued upsetting pressure between the ends of the two wires welds them together.

During upsetting operations, the gates 58 engage the workpieces continuously, acting as one way clutches holding the workpieces stationary while they are released by the jaws. When the welded workpieces are to be removed and further workpieces inserted, or the die set is to be replaced, the carriers are moved further rearwards by swinging the lever 80 to its upper position L3. The gap between the carriers is thus fully opened, the position of the mechanism being as shown in Figure 7, and an oblique rear face 114 on each carrier then engages curved face 116 on the rear end of the adjacent lever 62 to pivot the forward face of the lever away from the axis X-X so as to leave the path of the workpiece clear.At the same time, the rearwards movement of the carrier brings a projecting portion 118 of the fixed member 60 of the gate against the rear of one of each pair of jaws so that the die set is prevented from participating in the final part of the opening movement of the carriers. The two jaws of each pair being connected to move together forwards and rearwards and being engaged by the key plate, the final movement of the carrier therefore opens the jaws. With both the gates and the jaws open, an ample clearance is left for removing a welded pair of workpieces and for inserting furtherworkpieces.

It will be noted that in the butt welding process the sequence of operations of the apparatus is (i) gripping of the workpieces in their respective pairs of jaws (ii) feeding the workpieces into end-to-end contact to apply an upsetting pressure between them (iii) release of the grip of the jaws on the workpieces, (iv) return movement of the jaws to grip the workpieces again in preparation for feeding the wires further forwards. Because the workpieces are released before the jaws make their return move ment there is no tension applied to the workpieces once they begin to be attached together, so that the formation of a satisfactory pressure weld is unimpeded.

The form of apparatus illustrated has further features that lead to the effort on the hand lever to be used to best effect. For example, it is to be noted that the direction of workpiece feed and abutment is along the axis X-X, the same direction as that in which the force from the hand lever is applied through the levers 90. It will also be seen from Figure 1 that the links 87 approach an in-line position when the jaw pairs are brought together so that they act in the manner of a toggle mechanism, giving a very high mechanical advantage and so allowing high upsetting pressures to be applied.

As already mentioned, the die sets themselves can be of conventional form and preferably they are arranged with the front faces of their respective jaws staggered, in the manner described in US 3340 596, to make the welding flash more easily removable.

Some possible modifications of the apparatus described above are shown in Figures 9 and 10, those parts of the apparatus not illustrated there being substantially in the form already described.

In Figure 9 can be seen an alternative to the wedge-controlled detainer mechanism for determin ing some of the movements of the die set. The carriers (not shown) are mounted on the top wall 4a of the main casing similarly to the first example with the pairs of jaws and their key plates. The retainers are now in the form of plates 120 held in grooves 121 in the walls of the casing, their front faces 122 serving as before to engage the rear faces of the jaws when return movement of the pairs of jaws is to be prevented. Towards their rear an aperture 123 is formed through each retainer to receive the upper end of a control lever 124 mounted on a pivot 125 in the casing top wall.At their lower ends the levers carry follower rollers 26 that bear against a cam disc 127 mounted on a spigot 82a extending co-axially from the boss 82 which, with the main drive levers 90 are constructed and operated essentially in the manner already described. The control levers are spring-loaded against the cam disc, e.g. by a tension spring 124a connected between them. Also because the central axial plane of the apparatus contains the main drive levers and their links, the cam disc is offset from that central plane and the control levers are cranked below their pivots 125.

When the cam disc is rotated, each roller will bear alternatively on a smaller radius 127a, which is the case when the jaws are in their retracted starting positions and the detainers 120 are also retracted as shown on the left of Figure 9, and on a larger radius 127b when the levers 124 are pivoted to advance the detainers, as shown on the right of Figure 9. The cam disc is rotated by the rotation of the boss 82, through driving pins 128, 128a mounted on the boss, which locate on arcuate slots 129 in the disc and thereby provide a lost-motion connection between the boss and the levers.

The sequence of operation of the detainers is thus as follows, beginning from the starting position in which the workpieces have been mounted in the jaws, the operating lever 80 (not shown) is in the raised position L2 and the control levers 124 bear on the smaller radius 127a of the cam disc to hold the detainers clear of the dies. The initial movement of the lever first causes the jaws to close onto the workpieces to grip them, in the manner already described, and the jaws are moved forwards. As pressure to upset the workpieces against each other begins to be exerted, the lever rollers 126 each meet a respective rise on the cam disc between the smaller and larger radius portions and the detainers 120 begin to follow the jaws forwards. When the upset has been completed the rollers have reached the larger radius 127b and the detainers have advanced to positions where they block return movement of the pairs of jaws.

When the operating lever is raised for the return movement, the lost-motion connection between the pin 128 and the slot 129 in the cam disc leaves the control levers 124 stationary; the jaws therefore cannot retract and are instead opened by the movement of the key plates underneath them as the carriers are drawn back, and so the grip on the workpieces is released. After the initial stage in which the lost-motion is taken up, the control levers are retracted by the rotation of the cam disc, so that the detainers are withdrawn and the jaws are forced back to their starting positions by the plungers 32 (not shown).

As will be apparent from the steeply stepped cam profile, the movement of the detainer control levers 124 is arranged to be relatively abrupt. In order to reduce shock loads, the follower rollers 126 are held against the cam disc by springs 130 which can therefore yield to limit the force transmitted through the levers. In addition, the cam disc is provided with a damping means to eliminate unwanted disturbances. In the example shown in Figure 9, the damping means comprises a housing 132 having a pivotal mounting 134 with the main casing 2. A round rod 136 passes axially through the housing and is itself pivoted to the cam 127 at 138. Inside the housing 132 and co-axial with the rod 136 there is held an O-ring 140 or similar elastomeric element.

This can be urged under an adjustable degree of compression against the rod by a shouldered cap 142 through which the rod extends and which is adjustably screwed into the housing 132. An adjustable friction force is thus applied to the rod to give the required degree of damping to the rotation of the cam 127.

In order to extend the range of dies that can be employed in the apparatus, means may be provided for changing the amount of lost motion in the operaton of the control levers. Such means may conveniently take the form of a blocking member that can be inserted into a cam disc slot when required, so altering the amount of free movement allowed for the driving pin 128 in the slot. One example of such a member is illustrated in Figures 11 and 12, in which a blocking member 146 is to be seen, fixed to a cross plate 148 on the end of an operating rod 150 to project towards the cam slot.

The operating rod is mounted centrally to the boss 82 which provides an axial guide for it, and one cam slot pin 127a is elongated to provide a parallel guide for the cross plate. By means of a hand knob 152 on the operating rod the rod can be slid axially of the boss, so that the blocking member is displaceable between the position shown in Figure 11 and a position in which it lies in the opposed cam slot 129, side by side with the pin 127a, so reducing the possible arcuate movement between the cam disc 127 and the boss 82. To hold the blocking member stably in the chosen axial position while allowing it to follow the rotation of the cam, a friction force is applied to the operating rod by a resilient ring 154 that is adjustably compressed by a screwed cap 156.

In describing the operating sequence with the modified detainer mechanism no reference has been made to the workpiece gates which are also shown in a modified form in Figures 9 and 10. These gates comprise a pair of levers 160 symmetrically mounted on fixed pivots 162 each side of the workpiece path and having pins 164 projecting from their undersides near inner, rounded noses to engage each in a slot 166 in a gate slide 168 displaceably mounted in an elongate recess 170 in the detainer and urged by a spring 172 towards the rear of the detainer. Biassing springs (not shown) urge both gate leves against an inserted workpiece to grip it, preventing rearward movement but permitting forward movement, the right-hand side of Figure 10 showing in the individual levers how they adapt to different thicknesses of workpiece.When the workpiece path is to be fully opened, to remove the welded workpieces or to insert fresh workpieces, or when the die set is to be replaced, the links 18 move further rearwards and pins 174 projecting from their upper edges engage the outer ends of the gates levers, so pivoting them clear of the workpiece path.

The only restriction in the cross-sectional size of the elongate workpieces to be joined together by the apparatus described above lies in the force needed to produce the required upsetting pressure intensity for welding to occur. In a further embodiment of apparatus according to the invention illustrated in Figures 13to 16, operation is powered by fluid pressure cylinders so that considerably thicker workpieces can be cold-pressure butt welded.

As in the first embodiment, the mechanism has a central plane of symmetry transverse to a longitudinal axis X-X along which the two workpieces to be welded are fed. On a top plate 240 of a main casing 14 of this second embodiment are secured coaxial support sleeves 244 in which cylindrical carriers 246 are guided to be displaceable towards and away from each other. Attheirforward ends projecting from the sleeves the carriers have bearing stubs 248 each serving as a common pivot for a pair of gripper levers 250,252. In the shorter arms of the levers projecting above the stubs, a die set 'D' composed of two pairs of jaws is mounted, each jaw being secured in a mating recess 254 in its lever arm by a bolt 256. It will be noted that in this instance the pairs of jaws have a circular cross-section.

The levers have pivoted to their lower arms, which depend within the casing, two links 258 through which each pair of arms is connected to a cross-head 260 of a piston rod 262 of a pneumatic pressure cylinder 264. Extension of the piston rod spreading the lower arms of the levers to the position illustrated in Figure 14 closes the jaws of each pair of jaws to grip a workpiece, and conversely contraction of the cylinder releases the workpiece. The complete assembly of each pressure cylinder 264, the gripper levers 250, 252 and the connecting linkage therebetween is suspended from the stub 148 and can swing somewhat in a plane transverse to X-X. Transverse stop members (not shown) are provided to ensure that the two pairs of jaws are held in alignment with each other and so to ensure the correct alignment of the elongate members to be welded together.

The carriers 246 are connected at their rear ends through links 266 to further levers 268 having pivot connections 270 with blocks 272 fixed to the casing and depending within the casing in a vertical plane containing the axis X-X to be attached to the piston rods 274 of respective pneumatic pressure cylinders 276, the casings of which have pivotal supports 278 on the casing.

As in the first-described embodiment, respective gates 280 are mounted in fixed positions on the sleeves 244 so as to retain the workpieces stationary when they are not held by the jaws of the die set D.

The gates 280 are substantially of the same form as the gates of the first embodiment.

In operation, with the workpieces to be joined inserted in the respective pairs of jaws, the pneumatic cylinders operate in a sequence determined by a pneumatic control circuit. In the position illustrated the jaws have completed an upsetting stroke, both pairs of pneumatic cylinders thus being extended.

Under the control of the sequencing circuit, the cylinders 264 of the gripping levers 250,252 are first contracted while leaving the carrier cylinders 276 extended, so that the grip on the workpieces is relaxed before the cylinders 276 are contracted to withdraw both carriers 246 rearwards while the workpieces are held stationary by the gates 280. The gripper lever cylinders 264 are then extended again to regrip the workpieces, and finally the carrier cylinders 276 are extended to apply an upsetting force to the workpieces. This sequence is repeated until a satisfactory welded joint is obtained.

In the sequence of operations described, the opening of the jaws of each pair must be limited as already explained, to ensure that the workpieces cannot be displaced tranversely from their passages in the pairs of jaws, whereas a greater spacing is required for removing the welded workpieces and so on. Adjustable stop means are therefore provided for the operation of the gripper lever cylinders 264.

Mounted on the lower end of the body of each cylinder, and therefore forming part of the assembly suspended from the associated stub 248, is a mounting plate 284 on which a control shaft 286 is rotatably mounted. A stop arm 288 is keyed to the lower end of the shaft and a hand lever 290 is mounted on its other end to project through an opening 292 in the casing. By manipulating the levers the shafts 286 are rotated to bring the stop arms into and out of the path of the cross-heads 260 on the piston rods 262 of the respective cylinders 264. Thus, when in the path of the cross-heads each stop arm blocks the movement of the rod after a limited displacement, corresponding to that required simply to release the grip on the workpiece, whereas when the stop arms are out of the path of the cross-heads the cylinders 264 can contract fully so opening the jaws of each pair of jaws more widely.

It is alternatively possible to rotate the shafts 286 by additional pneumatic cylinders (or other drive means) which are arranged to incorporate the movement of the gates 280 into an automatic welding sequence. In such an automatic sequence the pneumatic control circuit can be provided with a first counter which is adjustable to set the number of upsetting strokes to be performed to weld together two workpieces. The completion of the preset number of upsetting strokes brings a flash trim cycle into operation in which the pressure in one of the gripper cylinders is reduced and a second counter sets a further number of strokes, typically 2-3, during which the welded workpieces are displaced axially for the weld flash to be cut off by one pair of jaws. In the final closing stroke of this cycle, the stop arms are withdrawn by the additional pneumatic cylinders, so that in the final retraction stroke of the sequence the jaws open fully. The welded workpieces can then be removed, fresh workpieces inserted, and the cycle be repeated.

Claims (21)

1. A method of cold pressure butt welding two elongate workpieces by multiple upsetting the ends of the workpieces in a repeated cycle of operations, comprising the steps of (i) gripping the workpieces in respective pairs of jaws, (ii) moving the two pairs of jaws together to bring the ends of the workpieces into contact under pressure, (iii) opening the jaws of each pair to release their grip on the workpieces, (iv) moving the pairs of jaws apart independently of the workpieces, and (v) repeating said steps until the ends of the workpieces are welded together.

2. A cold pressure butt welding apparatus comprising respective carriers for two pairs of jaws in which respective workpieces to be welded are gripped, said carriers being reciprocable along a common axis to move the pairs of jaws towards and away from each other in the direction of said axis to bring the ends of the workpieces together under pressure, and means for displacing the jaws of each pair relative to their carrier transversely to said axis to grip and ungrip the workpieces, drive means for operating a mechanism for said movement of the carriers and jaws in the direction of said axis comprising a pair of levers attached to the carriers and being pivotable in a plane containing or parallel to said common axis, said mechanism and said pairs of jaws being arranged to operate in a sequence comprising the steps of (i) gripping the workpieces, (ii) moving the two workpieces together to bring their ends into contact under pressure, (iii) releasing the grip on the workpieces, and (iv) retracting the carriers with the workpieces ungripped.

3. Apparatus according to claim 2 wherin detainers are arranged to engage the jaws to restrain their return movement after the ends of the workpieces have been pressed together, said levers returning the carriers while said detainers are operative to cause said transverse displacement means to open the jaws and release their grip on the workpieces and the detainers thereafter permitting the retraction of the carriers.

4. Apparatus according to claim 3 wherein for said operation of said detainer means said mechanism comprises a lost-motion means whereby the levers are displaced by the drive means to cause the workpiece to be gripped while the lost motion is being taken up preparatory to the pairs of jaws being moved towards each other with their gripped workpieces, and said lost motion also allowing the jaws of each pair to be opened before the pairs of jaws are returned to their starting positions.

5. Apparatus according to claim 4wherein means are provided to vary the amount of lost motion.

6. Apparatus according to claim 4 or claim 5 wherein the lost motion means comprises a rotary cam member having a slot-and-pin connection with the drive means, and cam follower means provide said detainers.

7. Apparatus according to any one of claims 4to 6 wherein control means act on the pairs of jaws to urge them apart while said lost motion is effective, thereby causing said displacement of the jaws of each pair to grip the workpiece, the levers causing forwards displacement of the jaws and gripped workpieces against said control means when the lost motion has been taken up.

8. Apparatus according to claim 7 wherein resiliently biased members provide said action urging the pairs of jaws apart, said members being set between the pairs of jaws and being displaceable transversely to said common axial plane.

9. Apparatus according to any one of claims 3 to 8 wherein spring means act between the detainers and the drive means to permit movement of the detainers apart the drive means when an overload is applied to the detainers.

10. Apparatus according to any one of claims 3 to 9 wherein damping means act on the driving connection to the detainers.

11. Apparatus according to any one of claims 2 to 10 wherein means are provided for setting predetermined retraction positions for the mechanism comprising a first position in which the jaws of each pair are opened sufficiently to disengage their grip on the workpieces but to retain the workpieces in channels in opposed faces of the jaws of each pair, and an alternative position in which the jaws are further opened to permit the removal of the welded workpieces

12. Apparatus according to claim 11 wherein end stop means are provided for setting alternative retracted positions of the levers, in one of which the workpieces are ungripped but are retained in the pairs of dies and in the other of which the dies of each pair are open sufficiently to permit the welded workpieces to be removed between their opposed faces.

13. Apparatus according to any one of claims 2 to 12 wherein gate means are provided to hold the ungripped workpieces against withdrawal when the jaws are retracted.

14. Apparatus according to claim 13 wherein said gate means are arranged to be maintained open and clear of the workpiece path when the carrier movement mechanism is in said alternative retraction position.

15. Apparatus according to any one of claims 2 to 14 wherein the levers are connected by pivot links to a rotary drive member and the links extend close to a radial position with respect to the drive member rotary axis when the pairs of jaws are brought together.

16. A cold pressure butt welding apparatus comprising means for holding pairs of jaws for respective elongate workpieces, drive means for displacing the holding means with the pairs of jaws to bring the ends of said workpieces into engagement under pressure, first control means acting on the jaws to urge the jaws of each pair apart, guide means for acting between the holding means and the pairs of jaws when the jaws are displaced relative to the holding means by said control means to cause the jaws of each pair to close together to grip the associated workpiece, further control means acting on said pairs of jaws to urge them togeher, means inhibiting the operation of said further control means until the pairs of jaws approach a fully closed position, said further control means exerting a force on said pairs of jaws sufficient to overcome the action of said first control means, the arrangement being such that in an open position of the pairs of jaws, said first control means act to cause the jaws to grip their respective workpieces, whereupon the drive means are operable to displace the holding means together with the gripping pairs of jaws to force the ends of the workpieces into abutment, the further control means then restraining return movement of the pairs of jaws with the holding means, whereby in said return movement of the holding means said guide means act to open the jaws of each pair, said further control means then being rendered inoperative to cause the opened pairs of jaws to be moved apart with the remaining displacement of the holding means and to be displaced by said first control means to regrip the workpieces as a first step in a repeat cycle of operations.

17. Apparatus according to claim 16 wherein said first control means comprise members urged by springs against the jaws.

18. Apparatus according to claim 16 or claim 17 wherein said further control means comprise members displaceable to an operative position in which they restrain said return movement of the jaws, a mechanism for said displacement being connected to said drive means for coordinated operation therewith.

19. Apparatus according to claim 16 wherein sequencing means are provided to coordinate the operation of the drive means and the first and further control means.

20. A method of cold pressure butt welding two elongate workpieces by multiple upsetting the ends of the workpieces in a repeated cycle of operations, substantially as described herein with reference to the accompanying drawings.

21. A cold pressure butt welding apparatus constructed and arranged for use and operaton substantially as described herein with reference to the accompanying drawings.