TWI Industrial Member Report Summary 128/1980
By E W L Norman
An investigation has been carried out to explore the problems associated with the operation and control of the MIG spot welding process on aluminium alloys, particularly arc initiation and inconsistent weld penetration and properties. Experimental work, including high speed cinephotography, indicated that the
fundamental process problem was associated with the arc and weld pool behaviour as the top sheet was penetrated. Arc initiation could be satisfactorily controlled for 1.2mm diameter filler wires by a reduced wire approach speed and increased short-circuit current level.
Oxygen, when up to 2% was added to the argon shielding gas greatly improved the consistency of penetration on unbacked 1mm 5182 sheets, without affecting the shear values obtained. With or without oxygen additions there was an inherent risk of undisturbed-oxide films at the interface. This risk was
reduced by the higher currents and longer weld times possible when copper backing was used. Both push and push-pull manual systems could be used to produce acceptable results providing the filler wire type and diameter necessary for the sheet alloy type and thickness was suitable for the wire feed system.