Welding machines and welding processes operating in the 50 kHz to 3 MHz frequency range. High frequency power sources are used for arc initiation, arc stabilization and gas ionization with the gas tungsten arc welding (GTAW) process.
Arc Initiation. By ionizing a gas path between the electrode and the workpiece, high-frequency power helps bridge the physical distance for making non-touch starts. Non-touch starts are preferable in GTAW, since they minimize the possibility of electrode contamination, as well as weld metal contamination, which would result from touching the tungsten electrode to the workpiece. High-frequency voltage is considered relatively safe for the operator to use in making non-touch starts. While the voltage is high, the current is in milliamperes.
Arc Stabilization. Arc stabilization is considered the most important function of high-frequency power in welding. When welding with an a-c welding power source connected to a 60 Hz power system, there is an arc outage each 1/120 of a second. The time of the arc outage will depend somewhat on the re-initiation characteristics of the welding machine. When high frequency is a part of the welding circuitry system, it provides the stable re-initiation effect necessary to maintain a steady arc.
Gas Ionization. In GTAW, the open circuit voltage of the welding machine is insufficient to ionize the shielding gases; consequently, a direct arc path is not readily established. This can be overcome by imposing high frequency voltage on the arc voltage, producing a high frequency voltage in the range of 20 000 volts at the electrode tip. Since the ionization potentials of the two commonly used shielding gases, argon and helium, are relatively low, the high-frequency voltage creates an ionized path for the welding current to follow.