A high performance transistorised power source for MIG welding.

This research concerns an investigation into the application of Power Electronics to high performance power sources for precise and efficient control of the pulsed-current metal-inert gas (PCM) welding processes. The physical processes of the welding arc are reviewed and the characteristics of a number of power sources are considered prior to preparing the operational specification for the PCM power source. From a number of possibilities the high frequency switching regulator operating in the secondary side of the power transformer was selected for detailed study. The power source was based on the use of state-of-the-art power transistors operating in a switching mode to minimise losses and to give a fast response for good welding performance. The basic operating frequency was chosen to be at the very limit of the audio range. The dynamic behaviour of the transistors and associated protection networks is critical and failure to meet all the operating limits of the transistor can be costly. To assist with the thorough understanding of the circuit behaviour and to predict the transistor switching waveforms a digital computer model was developed. This gave good correlation with experimental results observed with the completed power source. Tests were carried out with the welding power source and showed that there was no discernable difference in the weld quality when compared with those produced by the more expensive series linear regulator power source. As a direct result of the study a new range of power sources meeting exacting standards have been made available to the welding industry.