A method of TIG welding with alternating current with a welding apparatus (10) which is arranged in such a manner that the polarity of the welding current is controlled by an electronic control circuit (20), which is also arranged so that it continuously registers whether or not the arc is lit, and in that the welding apparatus comprises a controllable inverter (16) and means for re-igniting the arc in the positive period, and arranged so that the length of the positive period is shortened if the arc is not re-ignited in the positive period. The invention also relates to a welding apparatus which can be equipped with a logical circuit or a programmable circuit which instantly ensures that the positive welding period is shortened if the arc is not re-ignited in this period.

Disclosed is an inverter type DC welding machine incorporating constant-power control to assure a high and reliable quality of weld. The pulse width of the high-frequency output of the inverter circuit is controlled at the inverter switching rate by the constant-power control on a feedback loop basis in which the value of a weld power actually supplied to the portion to be welded between electrodes is computed and the computed value is compared with the value of a reference weld power to produce an error signal for controlling the operation of the inverter circuit, so that the actual weld power is maintained constant regardless of variations in the resistance of the portion to be welded during a welding operation.

A control system for an electric arc welder performing a welding process between an electrode and a workpiece, which system comprises: a high speed switching type power supply with a controller operated at a switching frequency of at least about 10 kHz with an input current control signal to adjust the output current of the power supply; a first sensor sensing the actual arc voltage; a second sensor sensing the actual arc current; a first circuit for creating a power signal representing the desired real time power level at progressive times during the welding process; a second circuit for creating a function of the sensed actual voltage and the sensed actual current; and a third circuit for adjusting the current control signal in accordance with the difference between the power signal and the function of the actual voltage and current, preferably arc power.

An a.c. operated arc welding current supply unit comprises a frequency converter of the series capacitor type and operating with a half period which is substantially less than the average duration of the current and voltage transients caused by short circuits through droplets of weld material during welding. The frequency converter is connected to welding electrodes through a transformer in series with a rectifier to provide direct current for the welding electrodes, and the frequency converter is associated with a control device for controlling the operating frequency of the converter in a manner such that it is substantially inversely proportional to the square of the input voltage of the current supply unit, thereby maintaining the power output of said unit substantially unchanged irrespective of changes in load caused by the welding operation and irrespective of variations in said input voltage.

A remote control unit for closing a normally open contactor in response to closing of a normally open gun switch in a portable wirefeed arc welding system having a power source including the contactor, a portable wirefeed unit, a welding gun, a ground cable interconnecting the power source and the work, an electrode power cable interconnecting the power source and the wirefeed unit and gun, and control leads interconnecting the wirefeed unit with the work and the gun; wherein a capacitor in the control unit is operable to place an override current on the ground and electrode power cables in response to closing of the gun switch, and sensing means comprising a sense relay are operable in response to such override current to effect closing of a normally open cycle hold delay relay and the contactor. The cycle hold delay relay, in turn, closes a fourth or rearming delay relay which opens the circuit to the sense relay. So long as welding current is drawn, the first control relay remains closed to hold the cycle hold delay relay closed. An interruption of welding current for two seconds causes the cycle hold delay relay to time out to open the rearming delay relay and the contactor.