GB1559833A

GB1559833A - Automatic welding

Info

Publication number: GB1559833A
Application number: GB3237875A
Authority: GB
Original assignee: BOC Ltd
Current assignee: BOC Ltd
Priority date: 1976-07-28
Filing date: 1976-07-28
Publication date: 1980-01-30

Description

(54) AUTOMAC WELDING (71) We, BOC LIMITED, of Hammersmith House, London, W6 9DX, England, an English company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to the welding of workpieces along a seam.

In the past, where long seams have had to be welded, although coarse control of the traversing of the welding torch along the seam has been effected automatically, it has usually been necessary to use an operator to effect additional control of the direction of the torch with respect to the line of weld while the weld metal is being deposited.

Attempts have been made to automate this aspect of the welding operation, by the use of mechanical guide mechanisms, but the use of these has been subject to various imperfections preventing their large-scale adoption.

The present invention aims at enabling an automatic welding machine to follow the seam to be welded with sufficient precision to eliminate the need for an operator to guide the movement of the welding torch relative to the workpiece.

According to one aspect of the present invention an apparatus for welding workpieces along a seam comprises a heat source capable of making the weld, means for automatically controlling the movement of the heat source relative to the seam during a pass along the seam, and means providing a refernce path which, in use, duplicates the path of the seam to be welded the controlling means being responsive to signals generated from the reference path, and the reference path means being provided with timing indicia, means being provided for using the indicia to indicate the speed with which the heat source moves relative to the seam during a pass along the seam.

Preferably, the heat source is an electric arc welding torch (MIG TIG, plasma etc), but other heat sources could conceivably be used, e.g. electron beam of a laser beam.

In accordance with a further aspect of the present invention, a method of welding workpieces along a seam comprises the steps of automatically controlling the movement of a heat source capable of making the weld relative to the seam during a pass along a seam by means of signals generated from a reference path, which reference path duplicates the path of the seam, and controlling the speed with which the heat source moves relative to the seam during the pass along the seam by means including timing indicia provided on the reference path.

The present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic view of one form of welding apparatus of the present invention, and Figure 2 is a diagrammatic view of the apparatus shown in Figure 1 used for welding two tubular workpieces together.

The welding apparatus shown in Figure 1 consists of an MIG welding torch 2 mounted on a movable carriage 4 and having connected to it a flexible conduit 6 for a consumable electrode, a conduit 8 for shielding gas, and a conductor 10 from an electric arc welding power source 16 which is capable of supplying a high voltage output for the welding torch pilot arc as well as the main current for the welding arc.

The conduit 6 is connected to an electrode reel and feed motor 12; and conduit 8 to a cylinder 14 of inert of other shielding gas, such as argon.

The carriage 4 is supported by a platform 18 secured to a support 20. The carriage 4 is movable relatively to platform 18 in the plane of the drawing, for reasons which will be discussed. below.

Attached to platform 18 is a photoelectric line follower 22 which can operate with normal light or with a coherent laser beam.

The signals from this line follower are used to control the position of torch 2 relative to the two tubular workpieces 24 which are to be welded together.

In one process of the present invention a self-adhesive tape 26 is secured to the outer surface of one of the workpieces at a distance spaced by a known and fixed amount from the respective portion of the seam 28 to be welded. The tape 26 is of aluminium or other material which presents a high visual contrast to the normal surface of the tubular workpiece 24 as seen by the line follower. Because of this, the follower 22 can follow one edge of the tape, or in some cases, it might be preferred to arrange for the follower to trace a line drawn on the tape and likewise arranged. parallel with the seam 28 to be welded.

The tape 26 can be laid down manually on the respective workpiece 24, or it may be preferable for a machine to be used which follows either the seam to be welded, or a workpiece edge before they are abutted, and which lays down tape on the surface of one of the workpieces at a chosen distance from the seam. As such a tape-laying machine does not form part of the subjectmatter of the present invention, it will not be described in any further detail in this specification The apparatus shown in Figure 1 is arranged so that the welding torch 2 moves relatively to the workpieces, the torch is forced to follow the seam to be welded by the line follower 22. In that the tape 26 represents a duplicate of the path to be followed by the torch, the torch is constrained to follow the seam accurately.

After a root weld has been made, i.e.

after a single welding pass, the position of carriage 4 on platform 18 is adjusted either manually or automatically so as to alter the spacing between the line follower and welding torch. As the follower continues to track the same edge of tape 26, this adjustment results in the torch 2 laying down a deposit to one side of the root weld. The deposition process is repeated as many times as is necessary with different and controlled positions of the welding torch 2 so as to build up successive weld deposits in a chosen sequence so as completely to fill the edge preparation along the seam 28 to be welded.

The tape 26 may have on it a mark aligned with the start of the welding process.

Each time the line follower detects the mark a special signal can be generated either to adjust the position of torch 2 relative to line follower 22 automatically or to warn the operator that the adjustment is necessary.

Figure 2 shows one method of mounting the welding torch so that it is able to effect a peripheral weld between two tubular workpieces. In Figure 2, those parts which are the same as shown in Figure 1 has been given the same references. For clarity, some of the parts shown in Figure 1 have been omitted from Figure 2.

It can be seen that the tubular workpieces 24 are mounted on a workholder 30 having driven support and positioning rollers 32 which are able to rotate the tubular workpieces about their common axis.

Associated with workholder 30 is a column 34 carrying the support 20 which the platform 18 is secured. The support 20 is movable along its length by chosen increments, or at chosen speeds, by means of electric motors associated with the column 34 but which have been omitted from the drawing for clarity.

Although the movement of the support 20 perpendicular to the plane of the drawing which would be necessary to allow the torch to follow the welding seam under the control of the line follower could be effected by mounting the column 34 so that it is movable perpendicularly to the plane of the drawing, this would not be a preferred arrangement. This is because it would be almost impossible to prevent the whole of the welding apparatus and line follower from vibrating if the column 34 and its associated apparatus were to be moved bodily. It would therefore normally be preferred to keep the support 20 fixed against movement perpendicularly to the plane of the drawing, and instead to mount the platform 18 on it in such a way that the platform is movable in this direction under the control of suitable electric motors, which are not shown. Because both the line follower 22 and torch 2 are movable with platform 18, selective energisation of the respective motors, under the control of line follower 22, is effective to cause the torch to follow the seam.

The welding apparatus would normally include a height sensor 36. This would either measure directly the distance between the sensor and the workpiece, and to control it accordingly so as to keep the distance between the electrode of the welding torch 2 and the seam a constant length, or it could be one which operates in response to changes in the voltage across the welding arc with variations in height. Whatever form of height sensor is use, it is designed so as to keep the arc of substantially-constant length. Thus as the different weld deposits are built up, which would otherwise reduce the effective arc length the height sensor detects this reduction in height and moves the welding apparatus away from the workpieces by a distance sufficient to keep the arc length constant. In the form of apparatus shown in Figure 2, the height sensor can be used to control the motors for raising or lowering the support 20 relative to column 34.

In operation, the motor or motors controlling the rollers 32 is or are energised so as to cause the tubular workpieces to rotate at a speed such that the workpieces traverse past the relatively-stationary torch at a speed appropriate for the welding process.

Because tubular workpieces are rarely completely circular, a fixed speed of rotation of rollers 32 can result in variations in the speed with which the workpieces move past the torch. This latter speed has to be controlled relatively accurately in order to lay down the required deposit.

Accordingly, the tape 26 is provided with timing indicia, and appropriate sensing apparatus is associated with the welding apparatus. The indicia are detected by the line follower 22 or other device, and they produce signals which indicate the actual relative speed of the torch 2 and workpieces 24. When this speed becomes too high or too low, adjustments are made so as to keep it within the preferred narrow range of operating speeds. Whereas in some forms of the present invention it might be sufficient to control the speed of rotation of rollers 32, their speed can be controlled only relatively coarsely. It might be preferable in some instances to control movement of the support 20 along its length so that the torch is moved along the welding seam at a speed related to the speed of rotation of the workpieces 24 such that the actual speed of movement of torch 2 over the surface of workpieces 24 is within the desired range of operating speeds.

Obviously, there are limits to the range of movement of the support 20 in order to bring about this desired movement of torch 2 along the length of the welding seam.

Means can therefore be provided for adjusting the speed of rotation of rollers 32 in relatively-coarse steps, and in the appropriate direction, when necessary, when the support 20 is nearing one or other of its effective limits of operation, so that the direction and speed of movement of the support 20 can be altered to give the same desired relative operating speed to the torch despite the change in rotational speed of workpieces 24.

WHAT WE CLAIM IS: 1. An apparatus for welding workpieces along a seam comprising a heat source capable of making the weld, means for automatically controlling the movement of the heat source relative to the seam during a pass along the seam, and means providing a reference path which, in use, duplicates the path of the seam to be welded, the controlling means being responsive to signals generated, from the reference path, and the reference path means being provided with timing indicia, means being provided for using the indicia to indicate the speed with which the heat source moves relative to the seam during a pass along the seam.

2. An apparatus as claimed in claim 1, in which the reference path means is in the form of a tape stuck to one of the workpieces and in which a photoelectric line follower is provided which is adapted to scan the tape, the photoelectric line follower and the heat source being mounted on a platform which, when the apparatus is in use, is capable of moving transversely across the seam to be welded, the position of the heat source being adjustable relative to the photoelectric line follower so as to permit the production of a multi-pass weld between the workpieces.

3. An apparatus as claimed in claim 2, in which the platform is secured to a horizontal support mounted on an upstanding column, the support being movable along its own length and being able to be raised or lowered along the upstanding column.

4. An apparatus as claimed in claim 1, 2 or 3, in which a height sensor is provided for measuring the distance between the height sensor and the workpieces, thereby to control the heat source so as to keep a constant distance between the heat source and the seam.

5. An apparatus as claimed in claim 4, in which the heat source is in the form of an arc welding electrode, the height sensor operating in response to changes in the voltage across the welding arc with variations in the length of the arc.

6. An apparatus as claimed in claim 4 or 5, in which the height sensor is used to control motors for raising or lowering the support relative to the column.

7. Apparatus as claimed in any one of claims 1 to 6, in which a work holder is provided for tubular workpieces, the work holder having a driven support and positioning rollers which are able to rotate the tubular workpieces about their common axis.

8. An apparatus as claimed in claim 7, including means for controlling the movement of the support along its length so that the heat source is moved along the seam at a speed related to the speed of rotation of the workpieces such that the actual speed of movement of heat source over the surface of the workpieces is within a predetermined range.

9. An apparatus as claimed in claim 8, including means for adjusting the speed of rotation of the said rollers in the appropriate direction, when necessary, when the support

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the welding apparatus away from the workpieces by a distance sufficient to keep the arc length constant. In the form of apparatus shown in Figure 2, the height sensor can be used to control the motors for raising or lowering the support 20 relative to column 34. In operation, the motor or motors controlling the rollers 32 is or are energised so as to cause the tubular workpieces to rotate at a speed such that the workpieces traverse past the relatively-stationary torch at a speed appropriate for the welding process. Because tubular workpieces are rarely completely circular, a fixed speed of rotation of rollers 32 can result in variations in the speed with which the workpieces move past the torch. This latter speed has to be controlled relatively accurately in order to lay down the required deposit. Accordingly, the tape 26 is provided with timing indicia, and appropriate sensing apparatus is associated with the welding apparatus. The indicia are detected by the line follower 22 or other device, and they produce signals which indicate the actual relative speed of the torch 2 and workpieces 24. When this speed becomes too high or too low, adjustments are made so as to keep it within the preferred narrow range of operating speeds. Whereas in some forms of the present invention it might be sufficient to control the speed of rotation of rollers 32, their speed can be controlled only relatively coarsely. It might be preferable in some instances to control movement of the support 20 along its length so that the torch is moved along the welding seam at a speed related to the speed of rotation of the workpieces 24 such that the actual speed of movement of torch 2 over the surface of workpieces 24 is within the desired range of operating speeds. Obviously, there are limits to the range of movement of the support 20 in order to bring about this desired movement of torch 2 along the length of the welding seam. Means can therefore be provided for adjusting the speed of rotation of rollers 32 in relatively-coarse steps, and in the appropriate direction, when necessary, when the support 20 is nearing one or other of its effective limits of operation, so that the direction and speed of movement of the support 20 can be altered to give the same desired relative operating speed to the torch despite the change in rotational speed of workpieces 24. WHAT WE CLAIM IS:

1. An apparatus for welding workpieces along a seam comprising a heat source capable of making the weld, means for automatically controlling the movement of the heat source relative to the seam during a pass along the seam, and means providing a reference path which, in use, duplicates the path of the seam to be welded, the controlling means being responsive to signals generated, from the reference path, and the reference path means being provided with timing indicia, means being provided for using the indicia to indicate the speed with which the heat source moves relative to the seam during a pass along the seam.

is nearing one or other of its effective limits of operation, so that the direction and speed of movement of the support can be altered to give the desired operating speed to the heat source despite the change in rotational speed of the workpieces.

10. A method of welding workpieces along a seam comprising the steps of automatically controlling the movement of a heat source capable of making the weld relative to the seam during a pass along a seam by means of signals generated from a reference path, which reference path duplicates the path of the seam, and controlling the speed with which the heat source moves relative to the seam during the pass along the seam by means including timing indicia provided on the reference path.

11. A method as claimed in claim 10, in which the reference path is provided by positioning a guide member along side and parallel with the seam to be welded, the guide member being arranged to control the subsequent movement of the heat source relative to the workpieces.

12. A method as claimed in claim 11, in which the guide member takes the form of a tape able to be stuck to one of the workpieces, the tape either presenting a visual contrast with its background whereby one edge of the tape is able to be scanned photoelectrically by a line follower controlling the movement of the heat source relative to the workpiece, or the tape having a line thereon which is able to be scanned by the said line follower.

13. A method as claimed in any one of claims 10, 11 or 12, in which the reference path has on it a mark aligned with the start of the path of the seam to be welded, so that each time the mark is detected by a detector, a signal is generated either to adjust automatically the position of the heat source relative to the reference path or to warn an operator that adjustment of the heat source is necessary.

14. A method as claimed in any one of claims 10 to 13, in which the heat source is a MIG, TIG or plasma torch or other electric arc welding torch.

15. A method as claimed in any one of claims 10 to 13, in which the heat source is an electron beam or laser beam.

16. A method of welding workpieces along a seam substantially as hereinbefore described with reference to the accompanying drawings.

17. An apparatus for welding workpieces along a seam, constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the Figures of the accompanying drawings.