High Frequency Characteristics Of Low Current Plused TIG Arc

Pulsed TIG welding is an advanced technology on impoving energy density, controlling input energy, welding seam shape and metallurgy quality. It plays a unique and important role in engineering in resent years. However, the knowledge about the pulsed TIG arc plasma is very limited currently for the low pulsing frequency which is below 30KHz. This work focuses on studying the characteristics of pulsed TIG arc plasma and application of them when the pulsed frequency continues to increase in order to promote the development of pulsed TIG welding and deepen the understanding of plused TIG arc plasma.The electrical characteristics of pulsed TIG arc plasma is investigated. After analyzation, a new dynamic model of TIG arc is established, and a transfer function is deduced too. And then, some of the equipment are designed, including main power supply and power amplifier, as well as the platform. The dynamic impedance of TIG arc plasma is obtained through measuring the response voltage when input the different exciting current to the TIG arc plasma. The results show that the electrical characteristics of the low current high frequency TIG arc plasma is not first-order link, but second-order link with an obvious shock. Subsequently, the shock characteristic of TIG arc plasma is investigated under different based values of current and arc length. It is found that the frequency and impedance of resonant point on TIG arc plasma is influenced by base current and arc length. It also shows that the power of pulsed TIG arc is the highest at resonant point.Electron density is one of the most important thermodynamics quantities. The electron density is calculated using Griem's method independent of the assumption of LTE (Local Thermodynamic Equilibrium), and the spectral line width at half maximum is got by Lorentz fitting. The electron density of pulsed TIG arc plasma under different frequency was tested using synchronizer designed on this work to make sure the synchronization of the spectral signal and the signals of arc voltage as well as current. The results show that the base value and fluctuation amplitude of electron density reach the maximum at the resonance point. It keeps a good agreement with the result derived from the arc power calculation. Low current pulsed TIG arc welding technology is studied. After 304-stainless steel is welded, it can be found that the welding penetration depth and bead width are the largest at the resonant frequency point on the pulsed TIG arc plasma. Compared to the DC TIG arc plasma, the weld penetration depth and bead width are increasing relatively, especially the former. It is twice as large as that by DC TIG arc plasma, and grain size is the smallest without directionality at resonant point. The whole study shows that the resonance phenomenon has engineering significance and practical value.