Real-time Measurement of Weld Pool Oscillation Frequency in GTAW-P Process

Real-time measurement and controlling the degree of weld penetration is a key issue in developing intelligent welding machines. To a certain extent, these welding machines can perform in a manner similar to that of a skilled human welder. The oscillation frequency of weld pool is closely related to weld penetration. However, traditional methods, such as arc voltage and arc light, lack the fundamentals to measure the oscillation frequency accurately. To solve this problem, a real-time sensing system based on photoelectric conversion is proposed for pulsed gas tungsten arc welding process. This sensing system consists of an illumination laser and a photoelectric conversion chamber. The illumination laser with five-line pattern is projected onto the whole possible pool surface and its reflection is captured by the photoelectric conversion chamber. By observing and analyzing the variation of voltage from the photoelectric conversion chamber, we found that the voltage variation is strongly related to the weld pool oscillation. Several experiments with different penetration for stationary and traveling weld pool were conducted, and the oscillation frequency was extracted. Experimental results show that the weld pool oscillation frequency can be measured in real time using this method. In comparison with the image-laser-vision method proposed in our previous work, the laser-photoelectric-conversion method has the advantages of high sampling rate, high processing speed, device simplicity, and ability to completely meet the requirement of real-time measurement in actual welding process. The oscillation frequency of partial penetration is considerably higher than the oscillation frequency of full penetration and that an abrupt transition occurs. This abrupt transition in oscillation frequency can be used for monitoring and in-process control of the weld penetration.