Welding power source

Claim 2

Metal arc welding apparatus for use in a welding process in which short circuits occur or may occur between a consumable electrode and a workpiece in a welding circuit, the apparatus including: a first D.C. power supply circuit connected to the welding circuit to supply a restricted current to the welding circuit for maintaining an arc between said consumable electrode and said workpiece; a first short-circuit detector operative to produce a short circuit signal in response to signals derived from the welding circuit and resulting from the onset of a short-circuit condition; a second substantially inductance-free D.C. power supply circuit; and a control circuit, including delay means responsive to said short-circuit signal to connect said second power supply circuit to the welding circuit, after a period determined by said delay means, and thereby to apply an increased current to the welding circuit, said delay means being adjustable to permit variation in the period between the onset of the short circuit condition and the increase in current flow to the welding circuit.

Claim 3

Metal arc welding apparatus in accordance with claim 1, in which said short-circuit detector includes a differentiating circuit connected to receive the arc voltage during an arcing period.

Claim 4

Apparatus in accordance with claim 1, in which the first and second power supply circuits include independent power sources for supplying electric current to the welding circuit.

Claim 5

Apparatus in accordance with claim 3, in which the second power supply circuit includes a solid-state power control circuit.

Claim 6

Apparatus in accordance with claim 4, in which the solid-state power control circuit is adjustable to permit the supply to the welding circuit of successive currents of different amplitudes during a single short-circuit period.

Claim 7

Apparatus in accordance with claim 4, in which the solid-state power control circuit includes a number of different current-conducting sections and means for selecting different comBinations of the said current-conducting sections to provide different levels of current for the welding circuit.

Claim 8

Apparatus in accordance with claim 6, in which each current-conducting section includes a transistor or a group of parallel-connected transistors.

Claim 9

Apparatus in accordance with claim 1, including further control means for reducing the arc current after a predetermined period has elapsed from the rupture of the short circuit, whereby the next short circuit is encouraged to occur at the reduced current level.

Claim 10

Apparatus in accordance with claim 8, in which the arcing current, prior to its reduction in level, consists of a series of impulses.

Claim 11

Apparatus in accordance with claim 1, in which the control means includes a pulsing circuit arranged to supply the additional current from the second power supply circuit as a train of pulses.

Claim 12

Apparatus in accordance with claim 1, including a third power source of high open circuit voltage but capable of supplying only a small current, connected to be operative during arcing periods to assist in stabilising the arc.

Claim 13

Metal arc welding apparatus for use in a welding process in which short circuits occur or may occur between a consumable electrode and a workpiece in a welding circuit, the apparatus including: a first D.C. power supply circuit connected to the welding circuit to supply a restricted current to the welding circuit for maintaining an arc between said consumable electrode and said workpiece; a first short circuit detector operative to produce a short circuit signal in response to signals derived from the welding circuit and resulting from the onset of each short circuit condition; a second detector including means responsive to a predetermined change in each short circuit condition indicative of an impending rupture of the short circuit to produce a rupture-indicating signal; a second substantially inductance-free D.C. power supply circuit; and a control circuit, including delay means, operative in each period of short-circuiting to connect said second power supply circuit to the welding circuit after a period determined by said delay means in response to said short-circuit signal from said first detector and thereby to apply and increased current to the welding circuit for an ensuing portion of the period of short circuiting, and to reduce or cut off the flow of current from the second power supply circuit to the welding circuit, prior to the termination of the said short-circuiting condition, in response to said rupture-indicating signal from said second detector.

Claim 14

Metal arc welding apparatus for use in a welding process in which short circuits occur or may occur between a consumable electrode and a workpiece in a welding circuit, the apparatus including: a first D.C. power supply circuit connected to the welding circuit to supply a restricted current to the welding circuit for maintaining an arc between said consumable electrode and said workpiece; a first short circuit detector operative to produce a short circuit signal in response to signals derived from the welding circuit and resulting from the onset of each short circuit condition; a second detector including means responsive to a predetermined change in each short circuit condition indicative of an impending rupture of the short circuit to produce a rupture-indicating signal; a second substantially inductance-free D.C. power supply circuit; and a control circuit, including delay means, operative in each period of short-circuiting to connect said second power supply circuit to the welding circuit after a period determined by said delay means in response to said short-circuit signal from said first detector and thereby to apply and increased current to the welding circuit for an ensuing portion of the period of short circuiting, and to reduce or cut off the flow of current from the second power supply circuit to the welding circuit, prior to the termination of the said short-circuiting condition, in response to said rupture-indicating signal from said second detector.

Claim 15

Apparatus in accordance with claim 12, in which said second detector includes means for detecting an increase in voltage between the consumable electrode and the workpiece during a short-circuit condition, the said increase indicating the impending rupture of the short circuit.

Claim 16

Metal arc welding apparatus for use in a welding process in which short circuits occur or may occur between a consumable electrode and a workpiece in a welding circuit, the apparatus including: a first D.C. power supply circuit connected to the welding circuit to supply a restricted current to the welding circuit for maintaining an arc between said consumable electrode and said workpiece; a first short-circuit detector operative in response to signals derived from the welding circuit and resulting from the onset of a short-circuit condition; a second detector including means responsive to a predetermined change in the short-circuit condition indicative of an impending rupture of the short circuit; a second substantially inductance-free D.C. power supply circuit; a first control circuit, including delay means, responsive to operation of said first detector to connect said second power supply circuit to the welding circuit, after a period determined by said delay means, and thereby to apply an increased current to the welding circuit, said delay means being adjustable to permit variation in the period between the onset of the short circuit condition and the increase in current flow to the welding circuit; and a second control circuit responsive to a signal from the second detector to reduce or cut off the flow of current from the second power supply circuit to the welding circuit prior to the rupture of the short circuit.

Claim 17

Metal arc welding apparatus for use in a welding process in which short circuits occur or may occur between a consumable electrode and a workpiece in a welding circuit, the apparatus including: a first D.C. power supply circuit connected to the welding circuit to supply a restricted current to the welding circuit for maintaining an arc between said consumable electrode and said workpiece; a first short-circuit detector operative in response to signals derived from the welding circuit and resulting from the onset of a short-circuit condition; a second detector including means responsive to a predetermined change in the short-circuit condition indicative of an impending rupture of the short circuit; a second substantially inductance-free D.C. power supply circuit; a first control circuit, including delay means, responsive to operation of said first detector to connect said second power supply circuit to the welding circuit, after a period determined by said delay means, and thereby to apply an increased current to the welding circuit, said delay means being adjustable to permit variation in the period between the onset of the short circuit condition and the increase in current flow to the welding circuit; and a second control circuit responsive to a signal from the second detector to reduce or cut off the flow of current from the second power supply circuit to the welding circuit prior to the rupture of the short circuit.

Claim 18

Apparatus as defined in claim 14, in which the second power supply circuit includes a solid-state power control circuit.