A constant potential single phase A.C. power welding source is connected to a thyristor network and an energy storing inductor to create a square wave welding current that is adjustable in height, and is further adjustable to allow either half-cycle to be wider than the other, the sum of two adjacent half-cycles always equaling 360°. The welding current is forced to reverse rapidly by a substantial voltage to insure conduction when the welding load is an arc to an aluminum work piece, and the aluminum tends to rectify. The heights of the positive and negative half-cycles are simultaneously adjustable in response to manual control and feedback signals. In addition, the ratio of the heights of the positive and negative half-cycles can be other than 1:1 by selectively enabling a conduction path through a different number of turns on the inductor during the negative and positive half-cycles, such enabling being either continuous or on an adaptive feedback basis as a function of arc length as determined by arc voltage. The height difference is effective in a step fashion since the total ampere-turns must remain constant. The thyristor network may also be re-connected for full-wave rectification for D.C. welding.

Asymmetrical a.c. welder

Disclosed is a variable polarity power supply for arc welding that quickly switches between polarities in order to more easily re-establish the arc. The variable polarity power supply includes a current-limited boost circuit for providing increased open circuit voltage to re-establish the arc, while limiting the re-establishment current. The variable polarity power supply is particularly suitable for computer-controlled welding applications because it periodically restarts the arc in either direction without using high frequency radiation, and provides quick switching times along with a low reverse current to reduce the heat in the torch, thereby increasing the longevity of the torch.

Variable polarity power supply for welding

There is provided a method and apparatus for electric-arc welding, in which an alternating current of positive and negative pulses is supplied to produce an electric arc between a welding electrode and a workpiece. The ratio of the durations of the positive and negative pulses of welding current is arranged to be changed in response to a signal from a sensing device adapted to sense a change in a characteristic of the electric arc so as to provide optimum welding current for changed welding conditions. The ratio of the amplitudes of the positive and negative pulses may also be varied in response to a signal from a sensing means.

Electric arc welding processes and apparatus therefor

In a method for high frequency pulse welding and an apparatus therefor, a highly directive arc can be obtained by eliminating the effect of the inductance of the welding cable, which tends to make the high frequency electromagnetic pinch force large. In a method and an apparatus for high frequency pulse arc welding which is performed by generating an arc between an inconsumable electrode or a consumable electrode arranged near a portion of a base metal to be welded and the base metal with main pulse current, when the main pulse current is shifted from ON to OFF, a reverse pulse current having a polarity opposite to the polarity of the main pulse is supplied between the electrode and the base metal to improve the stiffness (directivity) of the arc by making the rising and falling edges of the pulses steeper. A rail-car and a nuclear power plant obtained by the method are also provided.

Method of high frequency pulse arc welding and apparatus therefor

An consumable electrode AC pulsed arc welding is performed by repeatedly executing a cycle of supplying a peak current Ip in an electrode positive polarity, then supplying an electrode negative current Ien in an electrode negative polarity and finally supplying a base current Ib in the electrode positive polarity. During a base current supply time, the rate of increase dVb/dt of the base voltage Vb is detected. Should the base voltage increase rate dVb/dt detected be larger than a predetermined determining value ΔVu, it means that the arc interruption is likely to occur and, therefore, since that timing, the peak current Ip for the subsequent cycle is supplied to thereby prevent the arc interruption from occurring.

Method of controlling the AC pulsed arc welding and welding power supply apparatus therefor

A reversing polarity arc-welding technique, wherein a welding current waveform has alternate ''''straight-polarity'''' portions and ''''reverse-polarity'''' portions; the reverse-polarity portion being desirable for its ionic cleaning, but being undesirable for its electron bombardment of the welding electrode. This disclosure teaches the advantages of reducing the welding current during the reverse-polarity interval; and discloses electronic circuitry for achieving this result.

Donald R Lien

Papers

Control for reverse-polarity welding