Patent GB-1235301-A (GB)
Title: Stud welding apparatus
IPC: B23K9/20
Filed: 1968-08-20
Abstract: 1,235,301. Welding by pressure. OMARK INDUSTRIES Inc. 20 Aug., 1968 [21 Aug., 1967], No. 39871/68. Heading B3R. Stud welding apparatus selectively operable in (a) the drawn arc mode, in which the stud initially in contact with the workpiece is withdrawn to strike a pilot arc, a high intensity welding arc is superimposed on the pilot arc and the stud is plunged back towards the workpiece, (b) the initial gap mode, in which the stud having a projection and initially spaced from the workpiece is plunged towards the workpiece and a welding current is discharged upon contact of the projection with the workpiece to disintegrate the projection and heat the stud and workpiece and (c) the initial contact mode in which a stud with a projection is biased into contact with the workpiece and the welding current is discharged through the projection to disintegrate the projection and heat the stud and workpiece, comprises a solenoid for positioning the stud with respect to the workpiece, first circuit means connected to a first power source for applying a first voltage to the solenoid sufficient to cause retraction of the stud, second circuit means connected to a second power source for applying a second voltage to the solenoid sufficient to hold the stud when manully retracted but insufficient to cause retraction of the stud first switching means having switches which are selectively opened in either or both said first and second circuit means, second switching means actuated upon initiation of the welding cycle in the drawn arc mode to simultaneously close contacts in the first circuit means and open contacts in the second circuit means and third switching means for opening contacts in the first circuit means after initiation of the welding cycle. The welding apparatus includes a power source 10 having transformer supplied bridge rectifiers providing a higher voltage supply and a lower voltage supply, a charging circuit 13 maintaining a charge on the welding capacitor 14, a safety circuit 15 and the welding gun having a stud chuck 36 biased towards workpiece 38 by a spring 39 and a solenoid 41. The Figure shows the circuitry arranged for the drawn arc mode. Switches 25, 26, and 30 are closed and switches 27, 28 and 29 are opened, the switches 25, 26 placing the solenoid 41 in circuit with the higher voltage supply and the relay 21 is energized through closed contacts 20-2 so that its contacts 21-1 are closed. The welding cycle is initiated by pressing gun trigger 42 which energizes relay 20 from the lower voltage source. Relay contacts 20-1, 20-3, 20-4 close and 20-2 open. The closing of contacts 20-4 closes the pilot arc circuit across the workpiece and stud from the capacitor 14 via a resistor 61 and the closing of contacts 20-1 completes the energization circuit of the solenoid 41 from the higher voltage source to retract the stud and strike the pilot arc. Opening of contacts 20-2 de-energizes relay 21 after a delay due to capacitor 68 and breaks the solenoid circuit to plunge the stud back towards the workpiece. The closing of contacts 20-3 energizes relay 22 to switch the main welding contacts 22-1 so that the capacitor 14 will discharge across the stud and workpiece. The switching of contacts 22-1 may occur at the same time as, preferably before or even after initiation of the plunge of the stud. To employ the initial gap mode switches 27, 28 and 29 are closed and switches 25, 26, and 30 opened, the operator, after placing the stud in the gun chuck, pushes the latter inwardly where it is held by the solenoid energized from the lower voltage source. The welding cycle is again started by pressing the gun trigger 42. The gun solenoid is deenergized to plunge the stud against the workpiece either before or after the main welding contacts are closed. To employ the initial contact mode all the switches 25-30 are opened, the gun solenoid is removed from circuit and the cycle is again started by pressing the trigger 42. The main welding contacts are closed to discharge the capacitor 14 across the stud and workpiece. The charging circuit 13 employs a unijunction transistor, a Zener diode and a silicon-controlled rectifier 15 provide for charging of the capacitor 14.