The High Frequency Welding Machine produces high frequency voltage

HF (High Frequency Welding Machine) TIG welding units are Always Required

Whether AC or DC is used for TIG welding, a high frequency (HF) unit must be built into the machine, or a portable one must be attached to it.
The high frequency unit produces high frequency voltage (several thousand volts) at a frequency of several million cycles per second.

The current in the high frequency circuit is only a fraction of an ampere.
Because of the high voltage and frequency, the current is carried on the surface of the conductor rather than penetrating throughout the conductor.

When TIG welding with DC current, the high frequency unit must be on
in order to start the arc. Once the arc is stabilized, the high
frequency unit is turned off.

On DC machines using an add-on portable high frequency unit, the high frequency circuit will need to be turned off manually.

On AC machines TIG welders with high frequency units are used to stabilize the arc and to ionize gases in the arc zone.

The ionized gases HF Welding Machine make the arc easier to maintain when the current changes directions.