Short-circuit arc welding with constant beads

Claim 3

A method as claimed in claim 1 wherein the arc is supplied during a constant time interval T b which is the same for successive arc-welding cycles of the welding operation and from a first electric supply source having a no-load voltage which is higher than the arc voltage and having a current-source characteristic, and the short-circuit current is mainly supplied by a second supply source having a voltage which is lower than the arc voltage and a low internal impedance.

Claim 4

A method as claimed in claim 1 comprising the further steps of measuring the presence of arc voltage between welding wire and workpiece for determining the time interval T b and measuring the presence of a voltage which is substantially lower than the arc voltage for determining the moment of short-circuiting.

Claim 5

A short-circuit arc welding apparatus comprising, electric supply source means for supplying welding current between a consumable welding wire and a workpiece, means for feeding the welding wire towards the workpiece, means including said supply source means for applying a voltage between the welding wire and workpiece during a first time interval T b so as to produce a constant power electric arc between the welding wire and workpiece during said first time interval thereby to develop a welding bead of constant size on the welding wire, detector means responsive to the electric condition of the arc gap between welding wire and workpiece for producing first and second control signals indicating the presence of an arc condition and a short-circuit condition, respectively, in said gap, switching means for controlling the supply of electric energy from said supply source means to the welding wire and workpiece, and a control unit controlled by said detector means and including means for developing and supplying further control signals to said switching means for determining the first time interval T b and a second constant time interval T d that begins at the moment of contact between the welding bead and the workpiece and which is indicative of a short-circuit condition therebetween, the control unit supplying a third control signal at the end of the second time interval for operating the switching means to apply a short-circuit current from the supply source means across the welding wire and workpiece so as to separate the welding bead from the welding wire, and wherein said supply source means comprises first and second DC supply sources, said switching means including means connecting the positive terminal of the first supply source to the welding wire by means of a first silicon-controlled rectifier and the positive terminal of the second supply source to the positive terminal of the first supply source by means of a parallel connection of a second silicon-controlled rectifier and a diode of mutually opposite polarity, the control unit being operative after the time interval T b to turn on the second silicon-controlled rectifier and after the second time interval T d turns on the first silicon-controlled rectifier.

Claim 6

A short-circuit arc welding apparatus comprising, electric supply source means for supplying welding current between a consumable welding wire and a workpiece, means for feeding the welding wire towards the workpiece, means including said supply source means for applying a voltage between the welding wire and workpiece during a first time interval T b so as to produce a constant power electric arc between the welding wire and workpiece during said first time interval thereby to develop a welding bead of constant size on the welding wire, detector means responsive to the electric condition of the arc gap between welding wire and workpiece for producing first and second control signals indicating the presence of an arc condition and a short-circuit condition, respectively, in said gap, switching means for controlling the supply of electric energy from said supply source means to the welding wire and workpiece, and a control unit controlled by said detector means and including means for developing and supplying further control signals to said switching means for determining the first time interval T b and a second constant time interval T d that begins at the moment of contact between the welding bead and the workpiece and which is indicative of a short-circuit condition therebetween, the control unit supplying a third control signal at the end of the second time interval for operating the switching means to apply a short-circuit current from the supply source means across the welding wire and workpiece so as to separate the welding bead from the welding wire, and wherein said supply source means comprises first and second DC supply sources, said switching means including means connecting the positive terminal of the first supply source to the welding wire by means of a first silicon-controlled rectifier and the positive terminal of the second supply source to the positive terminal of the first supply source by means of a parallel connection of a second silicon-controlled rectifier and a diode of mutually opposite polarity, the control unit being operative after the time interval T b to turn on the second silicon-controlled rectifier and after the second time interval T d turns on the first silicon-controlled rectifier.

Claim 7

A short-circuit arc welding apparatus comprising, electric supply source means for supplying welding current between a consumable welding wire and a workpiece, means for feeding the welding wire towards the workpiece, means including said supply source means for applying a voltage between the welding wire and workpiece during a first time interval T b so as to produce a constant power electric arc between the welding wire and workpiece during said first time interval thereby to develop a welding bead of constant size on the welding wire, detector means responsive to the electric condition of the arc gap between welding wire and workpiece for producing first and second control signals indicating the presence of an arc condition and a short-circit condition, respectively, in said gap, switching means for controlling the supply of electric energy from said supply source means to the welding wire and workpiece, and a control unit controlled by said detector means and including means for developing and supplying further control signals to said switching means for determining the first time interval T b and a second constant time interval T d that begins at the moment of contact between the welding bead and the workpiece and which is indicative of a short-circuit condition therebetween, the control unit supplying a third control signal at the end of the second time interval for operating the switching means to apply a short-circuit current from the supply source means across the welding wire and workpiece so as to separate the welding bead from the welding wire, and wherein the control unit is connected to the welding wire and the workpiece with one input, and furthermore comprises a first Schmitt trigger circuit which is connected to the input and which has a trigger level which is lower than the arc voltage, a first monostable multivibrator circuit connected to the first Schmitt trigger circuit and to a control input of a controllable semiconductor switch and which determines the time interval T b , a second Schmitt trigger circuit which is connected to the input and which has a trigger level which is substantially lower than the arc voltage, but higher than the short-circuit voltage, and a second monostable multivibrator circuit connected to the second Schmitt trigger circuit and to a control input of a controllable semiconductor switch and which determines the time interval T d .

Claim 8

A short-circuit arc welding apparatus comprising, electric supply source means for supplying welding current between a consumable welding wire and a workpiece, means for feeding the welding wire towards the workpiece, means including said supply source means for applying a voltage between the welding wire and workpiece during a first time interval T b so as to produce a constant power electric arc between the welding wire and workpiece during said first time interval thereby to develop a welding bead of constant size on the welding wire, detector means responsive to the electric condition of the arc gap between welding wire and workpiece for producing first and second control signals indicating the presence of an arc condition and a short-circit condition, respectively, in said gap, switching means for controlling the supply of electric energy from said supply source means to the welding wire and workpiece, and a control unit controlled by said detector means and including means for developing and supplying further control signals to said switching means for determining the first time interval T b and a second constant time interval T d that begins at the moment of contact between the welding bead and the workpiece and which is indicative of a short-circuit condition therebetween, the control unit supplying a third control signal at the end of the second time interval for operating the switching means to apply a short-circuit current from the supply source means across the welding wire and workpiece so as to separate the welding bead from the welding wire, and wherein the control unit is connected to the welding wire and the workpiece with one input, and furthermore comprises a first Schmitt trigger circuit which is connected to the input and which has a trigger level which is lower than the arc voltage, a first monostable multivibrator circuit connected to the first Schmitt trigger circuit and to a control input of a controllable semiconductor switch and which determines the time interval T b , a second Schmitt trigger circuit which is connected to the input and which has a trigger level which is substantially lower than the arc voltage, but higher than the short-circuit voltage, and a second monostable multivibrator circuit connected to the second Schmitt trigger circuit and to a control input of a controllable semiconductor switch and which determines the time interval T d .

Claim 9

A short-circuit arc welding apparatus comprising, electric supply source means for supplying welding current between a consumable welding wire and a workpice, means for feeding the welding wire towards the workpiece, detector means responsive to the electric condition of the arc gap between welding wire and workpiece for producing first and second control signals indicating the presence of an arc condition and a short-circuit condition, respectively, in said gap, switching means for controlling the supply of electric energy from said supply source means to the welding wire and workpiece, said supply source means comprising first and second DC supply sources, means connecting the positive terminal of the first supply source directly to the welding wire for applying a voltage between the welding wire and workpiece during a first time interval T b so as to produce a constant power electric arc between the welding wire and workpiece during said first time interval thereby to develop a welding bead of constant size on the welding wire, means connecting the positive terminal of the second supply source to the welding wire via two silicon-controlled rectifiers which are a part of said switching means and are connected in anti-parallel and which function as welding current switches, means connecting a negative terminal of each supply source to the workpiece, and a control unit controlled by said detector means and including means for developing and supplying further control signals to said switching means for determining the first time interval T b and a second constant time interval T d that begins at the moment of contact between the welding bead and the workpiece and which is indicative of a short-circuit condition therebetween, the control unit being operative to first turn on one silicon-controlled rectifier so that the arc is extinguished and the second supply source consumes the current, the control unit supplying a third control signal at the end of the second time interval T d for turning on the other silicon-controlled rectifier to apply a short-circuit current from the second DC supply source across the welding wire and workpiece so as to separate the welding bead from the welding wire.

Claim 10

A short-circuit arc welding apparatus comprising, electric supply source means for supplying welding current between a consumable welding wire and a workpice, means for feeding the welding wire towards the workpiece, detector means responsive to the electric condition of the arc gap between welding wire and workpiece for producing first and second control signals indicating the presence of an arc condition and a short-circuit condition, respectively, in said gap, switching means for controlling the supply of electric energy from said supply source means to the welding wire and workpiece, said supply source means comprising first and second DC supply sources, means connecting the positive terminal of the first supply source directly to the welding wire for applying a voltage between the welding wire and workpiece during a first time interval T b so as to produce a constant power electric arc between the welding wire and workpiece during said first time interval thereby to develop a welding bead of constant size on the welding wire, means connecting the positive terminal of the second supply source to the welding wire via two silicon-controlled rectifiers which are a part of said switching means and are connected in anti-parallel and which function as welding current switches, means connecting a negative terminal of each supply source to the workpiece, and a control unit controlled by said detector means and including means for developing and supplying further control signals to said switching means for determining the first time interval T b and a second constant time interval T d that begins at the moment of contact between the welding bead and the workpiece and which is indicative of a short-circuit condition therebetween, the control unit being operative to first turn on one silicon-controlled rectifier so that the arc is extinguished and the second supply source consumes the current, the control unit supplying a third control signal at the end of the second time interval T d for turning on the other silicon-controlled rectifier to apply a short-circuit current from the second DC supply source across the welding wire and workpiece so as to separate the welding bead from the welding wire.