Patent GB-1172322-A (GB)
Title: Arc Welding System and Process
IPC: B23K9/09
Filed: 1967-11-22
Abstract: 1,172,322. Welding by fusion. GENERAL DYNAMICS CORP. 22 Nov., 1967 [22 Nov., 1966], No. 53214/67. Heading B3R. [Also in Division H2] A process of non-consumable electrode pulsed arc welding includes the steps of maintaining the solidification of the weld puddle in a continuous wave marked by accelerating and decelerating portions, and accelerating and decelerating the solidification in a predetermined periodic manner. A pulsed arc automatic welding system comprises a carriage (Fig. 4) movable along the workpiece, a motor 42 (Fig. 1) for moving the carriage, a motor travel control circuit 20, a non-consumable electrode 28 carried by the carriage, a current control circuit 14 for periodically varying the level of the weld current, a device for applying shielding gas to the electrode at the workpiece and a timing control circuit 12 for operating the current supply, the current control circuit, the gas supply device and the motor control circuit in accordance with a predetermined pattern. Operation.-Depression of a start switch on control panel 10 energizes valve-actuating solenoids (84, 86) (Fig. 2C, not shown) to feed cooling water and inert gas to the welding torch 30. After a 5-10 sec. delay an H.F. control circuit 18 generates a high voltage signal which is applied between electrode and workpiece in the form of a spark to ignite the arc. At the same time the control winding (104) of a magnetic amplifier power supply 16 saturates to produce a large output current to the arc and to energize a relay (38) which initiates a welding cycle timer. After a delay of ¢ sec., the control winding (104) desaturates and is connected to the weld current control circuit 14. After a 6-10 sec. delay, for attainment of the proper welding temperature, the welding torch motor travel control circuit 20 and an (optional) wire feed motor control circuit 22 are energized to move the carriage 160 and feed wire 46. A pulse generator (114) (Fig. 2B, not shown) feeds pulses, which rise as A(l-e-<SP>(t+to)/RC</SP> ) and fall as B + De-t/Rc (where t is the time from to, the beginning of the use or fall, RC is the time constant of the controlling pulse source, and A, B, D are constants), to the control winding (104) to periodically vary the level of current supplied to the electrode, and a feedback shunt (40) feeds part of the output to the electrode back to the current control circuit to adjust the output of this circuit for spurious changes in welding current. At the end of the cycle the wire feed stops and a slope amplifier (150) supplies a negative ramp function in opposition to the pulses from the generator (114) to gradually reduce the level of the output to the electrode until the arc extinguishes. The timing initiation relay (38) de-energizes through lack of welding current and causes motor 42 to stop. Finally, the water and gas supply ceases, a predetermined time after the current supply stops. During operation the motors 42, 44 can be momentarily impulsed to drive the welding torch momentarily clockwise or counter-clockwise and to momentarily feed the wire into or take the wire up from the arc, depending on the setting of forward-reverse switches (120, 122) in the motor control circuits. The pulse generator (114) includes a unijunction transistor multivibrator arrangement for generating rectangular pulses which are integrated by a capacitor (115). The arc may be pulsed manually or automatically during all or part of the welding cycle by appropriate adjustment of a contact (64a) (Fig. 2A, not shown) of a timer circuit (64) and a current step switch (140). If it is necessary to decrease the level of current supplied to the magnetic amplifier power supply 16 during the cycle, the slope amplifier (150) can be actuated, but a potentiometer (146) must be adjusted to preclude reduction of the welding current to a value below that necessary to sustain energization of the relay (38) which initiates the cycle timing. The weld.-The nature of the pulses from the generator is determined by the requirements of the welding process. For continuity of solidification of the weld puddle the current to the arc must rise and fall periodically to permit acceleration and deceleration of the solidification of the weld, and the solidification of the weld puddle thus proceeds in a continuous wave marked by accelerating and decelerating portions, the latter occurring on the rise of the current pulses.  The carriage.-The welding carriage 160 is provided with positioning screws 162 for clamping the workpiece, e.g., a pipe 32, with the torch 30 positioned over the junction of the pipe with another pipe to be welded. The carriage mounts a split gear 164 rotated by a worm gear driven by motor 42. A clamp 166 mounted on the split gear 164 carries the torch 30 and wire feed motor 44.