GB2288138A - Cold pressure butt welders - Google Patents

Abstract

In cold pressure butt welding machines of the type in which a pair of wires, rods or sections are gripped in a pair of split dies and brought together under an axial upset pressure such that the yield stress of the parent metal is exceeded. The layout of gripping and upsetting components is such that the lines of action of these forces all converge at a point, eliminating undesirable bending moments on the mechanism. The dies are carried by pivoted arms actuated by a piston cylinder assembly (Fig. 1, not shown). Upsetting pressure is applied by piston/cylinders 7, 8 operating parallel to and either side of the welding axis. <IMAGE>

Description

Improvements In Or Relating To Apparatus For the Cold Pressure Butt Welding Of Non-Ferrous Wires Rods And Sections The present invention relates to cold pressure welding machines ofthe type in which a pair of wires, rods or sections are gripped in a pair of split dies and brought together under an axial upset pressure such that the yield stress of the parent metal is exceeded. The welding machines according to the invention are designed to weld up to 25 mm. diameter copper workpieces or up to 30 mm. diameter of pure aluminium. This induces an outward radial flow of metal from the weld zone. By a succession of such upset movements - typically 5 - 10 though the number of upsets may be outside these limits - the whole of the oxidised material on the respective cross sections is swept aside. This action enables the material ofthe respective wires, rods or sections to enter into a molecular relationship without allowing access of free air which would reoxidise the material. Under these "oxygen free" conditions a weld takes place which under metalographic andlor mechanical test condition is indistinguishable from a weld produced by thermal methods and which exhibits the same strength relationship between weld metal and parent metal.

The primary objective ofthe invention is to achieve cold pressure butt welds of rods, wires or sections of cross sectional areas greater than has in the past normally been the case although the principles ofthe invention are applicable to a wide range of cross sectional areas.

The problems to be overcome with the cold pressure welding and joining small cross sections, for example thin wire using hand held machines are somewhat different to the cold pressure and welding ofthicker rods. Thus the invention is directed more particularly to improvements in floor mounted machines a) to accommodate the considerable forces involved b) to reduce wear leading to backlash and the replacement of parts c) to produce consistentlv acceptable weld d) to reduce finishing operations and e) to reduce scrap. One of the major problems with cold pressure welding and joining end to end rods of a larger cross sectional area is concentricity and forms of misalignment. Clearly if the rod is to be further drawn down after joining any lack of concentricity or misalignment will cause further problems as the cross sectional area is reduced. Thus the machine features which provide initial alignment and maintain this alignment during welding are extremely important as is the maintenance of acceptable alignment during a production cycle and from cycle to cycle. In addition rods may varv from batch to batch regards size and external shape and the machine according to the invention is required to handle these variations with little adjustment by the operator.

Accordingly the invention provides in one aspect a cold pressure welding machine for joining two elongate workpieces together end to end including means to repeatedly force the ends of said workpieces together to form a weld dies adaptable to be clamped around the workpieces on opposite sides ofthe abutting surfaces when the said force is being applied to form an upset of workpieces in the region of the abutting surfaces and workpiece holding means operable to maintain alignment ofthe workpieces between successive applications of force in which machine the clamping dies and the force providing means are arranged so that the resolution of forces converge at a point corresponding to a position where the weld is beginning to form due to the upsetting pressure.

The means for repeatedly forcing the ends ofthe workpieces together preferably comprises a pair of pistons and cylinder assemblies on eitherside of the workpieces the axes ofthe assemblies being positioned parallel to one another and to the workpieces axes such that the axes of the assemblies are in the same horizontal plane as the workpicces and the said dies adaptable to be clamped around the workpieces comprise a split die and lever system for each workpiece, operable to grip the material ofthe workpieces under pressure on either side ofthe workpieces upsetting region.

The split dies maybe closed into position around the workpieces on either side ofthe abutting ends thereof for the application of an upsetting force by clamping units operable to move towards each other along a shaft Mien the closing pressure applied to the piston and cylinder assemblies during an upsetting stroke the clamping units having rods extending between them operable to compensate for any mismatch of workpiece ends.

Conveniently each clamping unit comprises a pair of pivotally mounted levers for closing the split dies around the workpieces when upset pressure is applied to the workpieces and the compensating rods extend between equivalent levers on opposite sides of the abutting ends of the workpieces.

The compensating rods may have a part of larger diameter at one end and a part of reduced diameter at the other end the smaller end of one rod being attached to a lever on one side ofthe abutting ends by a ball joint and the smaller end ofthe other rod being attached by a ball joint to the equivalent lever on the opposite side ofthe abutting ends while the other compensating rod is connected between equivalent pairs of levers on opposite sides of the abutting ends in the reverse direction as regards the reduced and increased diameter thereof The reduced and increased diameters of each compensating rod maybe eccentric with regard to each other in such a way that rotation ofthe rod will offset a lever connected to the rod by a ball joint.

Additional flexible restraints maybe incorporated to assist the appropriate alignment of the workpiece holding means between successive applications of upsetting force and to restrain movement ofthe clamping dies around the shaft along which they slide.

The invention will now be described by way of example only with reference to the accompanying diagrammatical drawings: Figure 1 shows in schematic form important elements ofthe cold forming apparatus including a part in cross section but leaving out for reasons of clarity other elements associated with such forms of machinery, Figure 2 shows in more detail features ofthe machine particularly relating to alignment, Figure 3 shows a diagram relating to how the forces are resolved in a machine according to the invention to maintain alignment and reduce distortion ofthe machine due to the high upsetting forces involved in the cold pressure welding machine and Figure 4 indicates the possible variation of diameter or profile ofthe rods from batch to batch which need to be accommodated by the machine without adjustment.

As shown in Figure 1 workpieces 1 and 2 are required to be joined by pressure welding. The workpieces 1 and 2 are placed respectively in split dies 3 and 4. A gripping mechanism 5 is associated with split die 3 and a gripping mechanism 6 is associated with split die 4. The upsetting force is provided by two separate power cylinders 7 and 8 which pulls the grip mechanism 6 towards the grip mechanism 5 by piston rods only one of which 9 is shown in Figure 1. The closing force of gripping mechanism 6 towards gripping mechanism 5 is in the direction shown by arrow A in a direction parallel to the axis ofthe workpieces 1 and 2. Hydraulically powered gates or clamps 10 and 11 operating on the workpieces 1 and 2 respectively are provided to maintain the workpieces in the required juxtaposition at certain times in the welding process. The upset of metal during formation ofthe weld is indicated at 12 as the gripping arms 5 and 6 are repeatedly brought together by power cylinders 7 and 8. A main control shaft 13 is provided for the gripping arms 5 and 6 to slide along when cold pressure welding is taking place and the arms 5 and 6 are being brought together by the power cylinders 7 and 8.

As is shown in Figure 1 a pair of bars extend between the gripping arms 5 and 6 into openings formed therein. Only one bar 14 is shown having one end 15 of larger cross section than the other end 16. It is to be understood that the other bar of the pair is identical but is reversed in position. The reduced cross section end 16 terminates in one of the ball joints ofthe pair 19. These bars are very important for the maintenance of concentricity and alignment of the workpieces during welding as will be referred to later.

Furthermore the reduced cross sectional ends 16 and 18 are formed to be slightly eccentric with respect to their larger ends. The arrangement ofthe bars.

ball ends is shown more clearly in Figure 2.

The gripping arms 5 and 6 force the split dies 3 and 4 around the workpieces 10 and 11 respectively during the upsetting process. Thus each of the arms 5 and 6 consist oftwo levers of which only one pair.20 is shown. The levers are pivoted on the shaft 13 so as to close the split dies around the workpiece and to retract and release the workpieces. A cylinder 21 fixed at 22 and 23 between the levers 19 and 20 is operated to close or open the die. It is to be understood that a further cvlinder is provided for the levers for grip arm 6 but not shown.

The cycle of operations during the formation of a weld will now be described with reference to Figure 1 and 2. The workpieces 1 and 2 are placed in abutting relationship and held by the clamps 10 and 11. The split dies 3 and 4 are closed around the workpieces 1 and 2 by the levers ofthe gripping mechanisms 5 and 6 by the operation of cvlinder 21. The clamps 10 and 11 are relaxed. The upset cylinders 7 and 8 are operated and the gripping mechanism brought together to force the ends ofthe workpieces 1 and 2 together and begin to upset and form a weld. The gripping mechanisms 5 and 6 are released from the workpieces by the cylinder 21 and the power cylinders 7 and 8 operated to return the gripping mechanisms 5 and 6 to the position ready for the next upset. While the weld is being formed by the application of an upset force on the workpieces the clamps 10 and 11 are relaxed. In between the applications of an upsetting force the clamps 10 and 11 are in operation to maintain the alignment ofthe workpieces until the weld has fully formed by the repeated applications of an upsetting force. The clamps 10 and 11 not only provide continued alignment when the gripping mechanisms 5 and 6 are relaxed and retreated to their position ready for the next application of force but prevent backward movement ofthe workpieces as the gripping mechanisms are retracted.

The clamps 10 and 11 thus effectively prevent backward movements of the workpieces as the gripping mechanisms 5 and 6 are retracted ready for another upset action. This prevents access of air to the workpiece cross sections at a time when the weld has not vet formed and thus avoids the possibility ofthe grip arms moving "backwards" and "forwards" while allowing the workpieces to part company sufficiently to allow re-oxidisation ofthe cross sectional material. It will be appreciated that once a weld has formed - or partly formed - the function ofthe clamps 10 and 11 becomes far less critical and indeed after this point the gates could, in principle be turned off. In practice however the sequence is not modified until the full number of upsets, e.g. about 5 to 10. has been completed due to the fact that it is impossible to predict how manv upsets need to be completed to be sure that enough strength has been attained to allow the welding process to continue without reintroducing oxygen into the weld zone.

It is necessary for succeeding lengths of wires, rods or sections (which may originate from different batches or rollings) to be butt welded in a concentric manner. In this way a smooth progressions ofthe butt weld through the subsequent reductions - for example through dies. will be achieved. Fig. 4 illustrates this problem and one objective ofthe invention is to achieve perfect or near perfect concentricity as illustrated at 4.1 rather than the eccentric alignment illustrated at 4.2. It will also be noted from this figure that succeeding lengths of sections - which may have to be welded together, may be supplied with a non-uniform profile as illustrated (for a nominally circular section) at 4.3. It is clearly desirable that welds should be performed with perfect concentricity as illustrated at 4.1 and an objective of the invention is to ensure that within reasonable limits. this does occur. To this ends features are incorporated in the design ofthe butt welding machine to accommodate the following sources of error: (a) Variations in effective die or ruling dimension ofthe workpiece sections from one length to the next.

(b) The effects of tolerance build up and backlash in the various elements ofthe machine.

The basic mechanism bv which this is achieved is illustrated in Fig. 2, from which it will be seen that lying between the two gripping mechanisms 5 and 6 are disposed two bars 14 and 1 4at The synchronising bars constitute an equal and opposite pair and each is provided with a large diameter section 15 and a reduced diameter section 16. The reduced diameter sections 16 and respectively located in the grip arm 5 or 6 by a "ball end" bearing 19. The "ball end" bearings provide a termination for their respective synchronising bars 14 and 14A. These "ball ends" form hinged terminations for the reduced diameter sections ofthe synchronising bars 14 and 1 4A, the whole arrangement constituting an equal and opposite pair. A further feature of the design of the synchronising bars 14 and 14A is that there is a small eccentricity between the large diameter sections and the small diameter sections. Thus rotation ofthe enlarged ends ofthe synchronising bar 14 and 1 4A produces a lateral adjustment of the respective small ends. This enables the dies 3 and 4 to be brought into correct alignment relative to the two sections of workpiece 1 and 2. Assuming this action is completed without producing any deflection ofthe reduce diameter ends ofthe svnchronising bars 14 and 14A, this adjustment has the effect of eliminating the results of any tolerance build up in the components of the respective grip arms 5 and 6 and sets the machine correctly to receive workpieces 1 and 2 of nominally identical diameter. If it is now assumed that one workpiece say 1 is substituted for one of larger diameter than 2, it will be understood that it will not be possible for the levers 19 and 20 ofthe grip arm assembly 5 to close as far as the levers of grip arm assembly 6. Assuming the spring properties ofthe reduced diameter sections ofthe respective synchronising bars 14 and 1 4A are identical this will result in the two reduced diameter sections deflecting an identical mount and the two sections of the workpiece 1 and 2 being presented to each other as shown at 4.1 of Fig. 3 rather than 4.2.

A further feature ofthe synchronising system is also shown in Fig. 2, a rotating lever arm 24 and tie bars 25. This sub-system is founded a a central pivot point 26 attached to the frame of the butt welder. Upon this point 26 the lever arm 24 is free to rotate and at each end ofthe lever 24 is attached a tie bar 25 one end of which is in turn attached to a point on the respective grip mechanism 5 and 6 at points 27. The connections between these points are made via ball joints similar in principle to 19. It will be appreciated that.

although the two grip arms 5 and 6 are correctly related to each other by the svnchronising bars 14 and 1 4A the whole assembly could, in principle. rotate about the main central support spindle 13. This action, if it occurred, would not influence the alignment between the two sections of the workpiece 1 and 2 since this alignment is controlled by the svnchronising bars 14 and 14A, however. it would have an influence on the relationship between the workpiece 1 and 2 and other components ofthe butt welder such as the clamps 10 and 11.

The system 24 - 27 controls axial alignment ofthe clamps 10 and 11 relative to the actual positions ofthe grip arms 5 and 6 and their levers. It will be understood that said rotational relationship is defined as rotation about the main central support spindle 13 and that the two grip arm assemblies 5 and 6 slide axially along this spindle when an upset is being performed. It will be understood that the function of the clamps 10 and 11 is to grip the workpieces 1 and 2 when an upset has been performed. Thus there is no tendency for the workpieces 1 and 2 to part company after the first upset has been completed.

This effect, if allowed to happen would result in permitting access of air (and therefore oxygen) to the cross sections of the workpieces. This might have the effect of inhibiting the welding action and a weld would in all probability never form.

Figure 4 shows how the clamping forces units 5 and 6 and upset forces from power cylinders 7 and 8 are resolved to a point B where a weld is to be formed which reduces undesirable bending moments on the machine, on completion of a set number of upsetting operations. One set of clamping units 5 or 6 remains in a clamping position while the other is relaxed from clamping.

The now joined workpiece held in the die bv the clamping unit is pushed through the other die, thus shearing off or deflashing the build up of material caused by the upsetting. This deflashing may be automatic at the completion of a weld.

Claims (7)

1. A cold pressure welding machine forjoining two elongate workpieces together end to end including means to separately force the ends of said workpieces together to form a weld die adaptable to be clamped around the workpieces on opposite sides ofthe abutting surfaces when the said force is being applied to form an upset of workpieces in the region ofthe abutting surfaces and workpiece holding means operable to maintain alignment ofthe workpiece between successive applications of force, in which machine the clamping dies and the force providing means are arranged so that the resolution of forces converge at a point corresponding to a position where the weld is beginning to form due to the upsetting pressure.

2. A cold pressure welding machine as claimed in Claim 1, in which the means for repeatedly forcing the ends of the workpiece together preferablv comprises a pair of piston and cylinder assemblies on either side of the workpiece the axes of the assemblies being positioned parallel to one another and to the workpiece axes such that the axes ofthe assemblies are in the same horizontal plane as the workpiece and the said dies adaptable to be clamped around the workpiece comprise a split die and lever system for each workpiece operable to grip the material of the workpiece under pressure on either side of the workpiece upsetting region.

3. A cold pressure welding machine as claimed in Claims 1 and 2, in which the split dies are clamped into position around the workpieces on eitherside of the abutting ends thereof for the application of an upsetting force by clamping units operable to move towards each other along a shaft when the closing pressure applied by the piston and cylinder assemblies during an upsetting stroke the clamping units having rods extending between them operable to compensate for any mismatch of workpiece ends.

4. A cold pressure welding machine as claimed in Claim 3, in which each clamping unit comprises a pair of pivotally mounded levers for closing the split dies around the workpieces when upset pressure is applied to the workpieces and the compensating rods extend between equivalent pairs of levers on opposite side ofthe abutting ends ofthe workpiece.

5. A cold pressure welding machine as claimed in Claim 4, in which the compensating rods may have a part of larger diameter at one end and a part of reduced diameter at the other end, the smaller end of one rod being actuated to a lever on one side ofthe abutting ends by a ball joint and the smaller end of the other rod being attached by a ball joint to the equivalent lever on the opposite side of the abutting ends while the other compensating rod is connected between equivalent levers on opposite sides ofthe abutting ends in the reverse direction as regards the reduced and increased diameters thereof.

6. A cold pressure welding machine as claimed in Claim 5 in which the reduced and increased diameters of each compensating rod are eccentric with regard to each other in such a way that rotation ofthe rod will offset a lever connected to a rod by a ball joint

7. A cold pressure welding machine as claimed in Claim 3. in which an additional flexible restraints maybe incorporated to assist the appropriate alignment of the workpiece holding means between successive applications of upsetting force and the restrain movement of the clamping dies around the shaft along which they slide.