Research On The Variable Polarity Inverter TIG Welding Supply

In order to satisfy the special technological demands of welding of aluminum and aluminum alloys, the development of aluminum AC TIG welding experienced three stages such as the sine wave AC TIG welding, the square wave AC TIG welding and the variable polarity TIG welding. As a special square-wave AC power supply, the variable polarity power TIG welding can be adjusted separately including the output current frequency, duty cycle and current amplitude. In the welding of the aluminum alloy, it not only can guarantee clean-up role of the cathode, but also can minimize the damage of tungsten electrode, so it become the best approach for TIG welding. Because of this reason, the variable polarity inverter TIG welding supply was designed in this paper. Then, the power system was debugged and the waveforms of the actual welding process were tested.Full-bridge dual inverter structure was used in the main circuit. IGBT was chosen as switch component to perform energy transfer and power conversion. The main circuit was made up of rectifier, filter, the first inverter, high-frequency transformer and the latter inverter. Each part of the elements involved in the main circuit was designed and selected. The working process of the second inverter circuit was also analyzed.TIG welding control circuit was designed according to the characteristics of the variable polarity inverter TIG welding supply. The pulse width modulation (PWM) regulating mode was used in the first inverter to control the value of the output current. Then, the sampling result of the output current was input to the op-amp LM324. Finally, the output of PI regulator was sent into the TL494 modulating IC. A two-way non-overlapping pulse was trigged. The pulses were used to trigger IGBTs after they were magnified by EXB841, and DC output was achieved. The second inverter part was designed based on circuit 555 which can output square wave. The reversed-phase circuit, the dead zone control circuit, and positive and negative half-wave amplitude adjustment circuit were also designed. Two ways of pulses were used to trigger the switch components of the second inverter after they were magnified. The waveforms of the current can meet the requirements of variable polarity welding. The protection circuits which were used to solve the problem of the over-heat and over-current protection for the IGBT were also designed.Through the debugging, waveforms were attained and analyzed. The experiments results showed that following parameters of the power supply can be adjusted separately including the output current frequency, duty cycle and current amplitude. The structure design was rational, the devices worked reliably, the control system run well and the expected goal can be achieved. Finally, the metallographic structure of the test specimens, appearance of welds, tungsten electrode ablating were investigated. The experiment results showed that the welding source can not only meet the requirements of negative-pole atomization effects but also reduce tungsten electrode ablating and welding defect under suitable welding parameters.