WELDING METHOD AND APPARATUS

Abstract: A welding operation is monitored by causing a formed weld pool to vibrate, directing radiation, and preferably light, into the weld pool and collecting the modulated radiation reflected from the surface thereof, converting the collected radiation into an electrical signal, and processing the electrical signal to obtain details of parameters of the weld pool. Such method has the advantage that only the surface of the weld pool has to be accessible and that there will be no contamination of the weld pool as can occur if a probe is used.

Description: WELDING METHOD AND APPARATUS This invention relates to a welding method and apparatus . When two pieces of metal are joined by welding it is generally preferred to obtain a fully fused weld that has an even penetration, the welding operation being controlled in order to avoid under-penetration or blow-through. A skilled welder can manually effect the necessary control of the welding operation, but it is also known to use automatic control in dependence upon details of parameters of the welding operation. Known automatic welding operation controllers use radiation reflected from the backface of a weld being produced, that is the bottom of the weld pool formed during the welding operation, in order to control the weld penetration depth. However, such controllers cannot be used when the backface of the weld is inaccessible. Other known controllers use an ultrasonic probe which is contacted with the workpiece near the weld pool to measure weld penetration. However, such controllers have the disadvantage that the probe is generally covered in grease in order to ensure good acoustic coupling, and this grease can contaminate the weld pool. Another known controller operates by determining weld pool vibration by measuring changes in the arc voltage of the welding apparatus. However, this controller requires the use of a high quality welding power supply in order to maintain a short stable arc and thus ensure an adequate signal to noise ratio in the arc voltage. According to this invention a method of welding includes the steps of forming a weld pool; causing the weld pool to vibrate; directing radiation into the vibrating pool surface; collecting modulated radiation reflected from the vibrating pool surface; converting the collected radiation into an electrical signal; and processing the electrical signal to obtain details of parameters of the weld pool. Also according to this invention there is provided welding apparatus comprising means to Eoπα a weld pool; vibrating means to cause the weld pool to vibrate; radiation source means to direct radiation onto the vibrating pool surface; collection means to collect modulated radiation reflected from the vibrating pool surface; conversion means to convert the collected radiation into an electrical signal; and processing means to process the electrical signal to obtain details of parameters of the weld pool. The radiation used can be light derived ' , for example, from a laser or from the welding apparatus used to form the weld pool, or any other suitable radiation from a source thereof. The method and apparatus of this invention have the advantages that access is required to only the front surface of the weld pool which should always be accessible, that the weld pool will remain uncontaminated, and that a relatively cheap welding power supply can be used. This invention will now be described by way of example with reference to the drawings, in which: - Figure 1 is a diagrammatic block diagram of welding apparatus according to the invention; Figures 2A and 2B illustrate the lowered frequency vibrations possible set up in a penetrated weld pool and an unpenetrated weld pool respectively; and Figures 3A and 3B illustrate the frequency response of weld pools as shown in Figures 2A and 2B respectively. Figure 1 shows welding apparatus comprising a welding power supply 1 and a welding torch 2 being used for welding together two pieces of metal 3 and 4. Light from the torch 2 is reflected from the surface of the weld pool formed by the torch 2 and is collected by an optical fibre collector 5 and transmitted thereby to processing means in the form of a computer 6. The light collected by the optical fibre 5 is converted to an electrical signal by a photodiode arrangement in the processing means 6, the signal then being processed to obtain details of parameters of the weld pool. The weld pool is excited and caused to vibrate by supply of a short high intensity pulse of electric current. Otherwise vibration can be caused by a short reduction in the electric welding current, or by a short pressure pulse in any gas being used in the welding operation. The vibration of the weld pool is characteristic of parameters thereof, for example mass and depth, and the light collected by the optical fibre 5 and the electrical signal obtained therefrom contain these characteristics. The processing means ascertains details of these characteristics and produces a control signal which is used to control the apparatus and thus effect the welding operation as required. Although in the apparatus described above the light collected by the optical fibre 5 derives from the torch 2, an independent light source, for example in the form of a laser, can otherwise be provided. Further, although in the apparatus described above visible light is used, it will be appreciated that radiation at any other suitable frequency can otherwise be used. Figures 2A and 2B illustrate the type of vibration set up in a weld pool 7 which has completely penetrated the work pieces 3 and 4, and which has not completly penetrated the work pieces 3 and 4, respectively, while Figures 3A and 3B illustrate the associated frequency response characteristics of the pools of Figures 2A and 2B respectively, from which characteristics the processing means 6 produces the control signal for the power supply 1.

Claims: CLAIMS 1. A method of welding including the steps of forming a weld pool; causing the weld pool to vibrate; directing radiation onto the vibrating pool surface; collecting modulated radiation reflected from the vibrating pool surface; converting the collected radiation into an electrical signal; and processing the electrical signal to obtain details of parameters of the weld pool. 2. A method as claimed in Claim 1, in which the weld pool is caused to vibrate by exciting the pool with a short high intensity pulse of electric current. 3. A method as claimed in Cla-im 1, in which the " weld pool is caused to vibrate by a short reduction in the electric welding current. 4. A method as claimed in Claim 1, in which the weld pool is caused to vibrate by a short pressure pulse in gas being used in the welding operation. 5. A method as claimed in any preceding claim, in which the radiation directed onto the pool surface is light. 6. A method as claimed in Claim 5, in which the light directed onto the pool surface is from a laser. 7. A method as claimed in Claim 5, in which the light directed onto the pool surface is from the welding apparatus used to generate the weld pool. 8. A method as claimed in Claim 5, Claim 6, or Claim 5 in which the reflected light is collected using an optical fibre. 9. A method as claimed in any one of Claims 5 to 8, in which the collected light is converted to an electrical signal using a photodiode. 10. A method as claimed in any preceding claim, in - which the electrical signal is processed using a computer. 11. A method as claimed in any preceding claim, in which the electrical signal is processed to determine the mass of the weld pool and/or the depth of the weld pool. 12. - A method as claimed in any preceding claim, in which the details obtained from processing the electrical signal are used for automatic control of the welding operation. 131 A method of welding, substantially as hereinbefore described with reference to the drawings. 14. Welding apparatus comprising means to form a weld pool; vibrating means to cause the weld pool to vibrate; radiation source means to direct radiation onto the vibrating pool surface; collection means to collect modulated radiation reflected from the vibrating pool surface; conversion means to convert the collected radiation into an electrical signal; and processing means to process the electrical signal to obtain details of parameters of the weld pool. 15 Apparatus as claimed in Claim 14, in which the vibrating means comprises a source providing a short high intensity pulse of electric current with which the weld pool is excited. 16. Apparatus as claimed in Claim 14, in which the vibrating means comprises means to produce a short reduction in the electric welding current. 17. Apparatus as claimed in Claim 14, in which the vibrating means comprises means to produce a short pressure pulse in gas being used in the welding operation. 18. Apparatus as claimed in any one of Claims 14 to 17, in which the radiation source means is a laser. 19. Apparatus as claimed in any one of Claims 14 to 17, in which the radiation source means is the apparatus used to form the weld pool. 20. Apparatus as claimed in Claim 18 or Claim 19, in which the collection means comprises an optical fibre. 21. Apparatus as claimed in any one of Claims 18 to 20, in which the conversion means comprises a photodiode arrangement. 22. Apparatus as claimed in any one of Claims 14 to 21, in which the processing means comprises a computer. 23. Apparatus as claimed in any one of Claims 14 to 22, including control means operative to effect automatic control of the operation of the apparatus in dependence upon the output of the processing means. 24. Welding apparatus substantially as hereinbefore described with reference to the drawings. 0 15 2.0 25 30 35

Inventors: DEAM ROWAN THOMAS, SALTER ROBERT JOHN, DEAM, ROWAN, THOMAS, SALTER, ROBERT, JOHN
Applicants: CENTRAL ELECTR GENERAT BOARD, CENTRAL ELECTRICITY GENERATING BOARD
Application year: 1988
Main classification: B23K9
IPC codes: B23K9