Arc And Power Control For DC Pulse Welding

Among the welding methods, TIG welding has been widely used for the advantages of wide range of welding suitability and stable welding electric arc and so on. In TIG welding, DC pulse TIG welding adopts pulse current welding, which can reduce the average value of the current and get enough welding depth with a lower heat input. In addition, it can also reduce the welding heat affected zone and welding deformation, so it is suitable for thin plate welding. When the pulse frequency increased, arc pressure for the welding pool and arc stiffness are increased, welding depth is increased and welding width becomes narrow, which is advantage to the welding process. Many advantages make pulsed TIG welding an irreplaceable position in welding field.Based on some technical characteristics of pulsed TIG welding, this paper designs the power control system of DC pulsed TIG welding. Power control system includs power switch control system, frequency adjustable digital control system, MOSFET and IGBT drive system. The designed power control system in a time base circuit free divider, outputing pulse frequency ranging from 1 Hz to 111 kHz, frequency and pulse width ratio can be calculated by adjustable, which suits for the DC pulse TIG welding pulse frequency and pulse width adjustment. Drive circuit controls voltage conversion, making MOSFET output voltage between +12V and-6V in a fast conversion, IGBT output drive voltage between +15V and-8V in a fast conversion. It can reduce the function of the device and suit for the requirements of the chopper control for the short conversion time. The comparison test proved that the IGBT power switch is a reasonable choice for this design.Lots of experiments had been done for the power control system of DC pulse TIG welding. The pulse current frequency can reach 20 kHz, and current is stable. Arc pressure is measured at a different pulse current frequency when the pulse current frequency changed and other parameters kept constant in welding parameters. The results show that arc pressure increases gradually with the increase of the pulse current frequency. When the frequency reaches a certain value, arc pressure keeps constant. The welding formation is good in the welding of Q235 thin plate of 0.8mm for the pulse current frequency ranging from 1 kHz to 20 kHz. The measurement of width and depth and metallographic test were carried out for the welding seam. The results show that heat input and welding deformation decreases, welding formation coefficient becomes lower, grain size of the welding is fine and grains distributed uniform with the frequency of the welding increased. Experimental results show that the design of DC pulse TIG welding power system can run stably and meet the design requirements.