TWI Industrial Member Report Summary 274/1985
M G Murch
The variability found in arc formation time with conventional short-circuit initiation in MIG spot welding, particularly as related to thin sheet aluminium alloys, has necessitated the development of an alternative arc ignition system. To ignite the arc without the need for the wire to make contact with this sheet, the potential benefits of an auxiliary d.c. voltage applied across the electrode gap at the onset of wire feeding was investigated. The amplitude of a single pulse of rising voltage required for gap breakdown and initiation was determined over a series of initial electrode-workpiece displacements from 1 to 10mm in argon, helium, argon/1% oxygen and helium/20% argon gas compositions for 5183 and 4043A aluminium wire.
The results demonstrated that, for all the above combinations of wire and gas composition, the voltage breakdown and arc establishment occurred when the electrode approached closely to the workpiece. Arc initiation was obtained without a short-circuit at less than 2.2kV even for initial electrode gaps of up to 10mm. With a 1mm electrode gap only 0.7kV was needed in helium/20% argon and 0.95kV in argon/1% oxygen gas shield on a 5183 electrode wire. For the 4043A wire 1.3kV was necessary for a 3mm initial electrode gap in argon/1% oxygen shielding gas.