Arc Welding Power Supply Research Articles

Influence of GMAW-P current waveforms on heat input and weld bead shape

Manufacturers use different, proprietary pulse current programming algorithms in their synergic 'one knob control' pulsed gas metal arc welding (GMAW-P) power supplies. Since the different pulse waveforms produced by these supplies can produce somewhat different welding characteristics, inconsistent results can be obtained when transferring welding procedures between different GMAW-P power supplies. A primary objective of this work was to characterise the differences in welding heat input and weld bead shape that could be produced by the pulsed current waveforms from four different commercial supplies. To eliminate the affects of subtle differences in electrical characteristics and to ensure that the exact shape of all waveforms was fully known, the comparison was also done by simulating the waveforms generated by three of the four power supplies on the fourth supply, which was equipped with waveform programming capability. Then, the four waveforms were used to create 'bead on plate' welds over a range of wire feed speed settings, and corresponding heat inputs were calculated from current and voltage samples recorded by a computer data acquisition system during welding. Welds were also done at the same wire feed speed setting using a constant voltage supply. All welds were then cross-sectioned for penetration and dilution measurements. In general, all of the waveforms produced good metal transfer and weld quality. However, the heat input and beads shapes varied noticeably. The heat inputs for the four pulse waveforms and constant voltage welds differed by as much as 150 J mm−1 (17% of the maximum heat input) at the highest wire feed speed of 212 mm s−1. The weld penetration differed by 1 mm (22% of the maximum penetration) at a wire feed speed of 169 mm s−1 and the dilution differed a maximum value of 6.5% dilution (22% of the maximum dilution) at a wire feed speed of 169 mm s−1 .

Series-parallel load-resonant converter for controlled-current arc welding power supply

An arc welding power supply requires the ability to limit the load current under short circuit conditions and limit the load voltage under open circuit conditions. The series–parallel load-resonant converter is a circuit configuration which can achieve this. The potential for high frequency operation in these converters minimises the size of the magnetic components in the converter and reduces output current ripple. The paper presents the theoretical and practical aspects of the design and construction of a series–parallel load-resonant converter, for use as a controlled current arc welding power supply. A converter with an output voltage of 25 V and output current of 200 A operating at 85 kHz is designed and constructed. A novel method of control of the resonant converter is described. Output power control is achieved by using an active rectifier modulating the DC supply voltage to the converter. Practical results of the converter in operation supplying 200 A to a low inductance load are presented.