TWI Industrial Member Report Summary 20/1976
By M E Wilkinson
The effect of basic welding parameters on tolerance to changes in root gap and travel speed have been assessed for the mechanised vertical dip transfer MIG welding of root runs in steel plate.
The factors examined included wire feed speed, welding direction, wire diameter, voltage, gas-shielded composition, plate preparation and backing systems.
For dip transfer CO2 welding, the tolerance to changes in root gap and travel spced can be optimised by using a deposition rate in the order of 3kg/hr and welding vertically down. Maximum tolerance to changes in root gap and travel speed were achieved with 0.8mm diameter wire, and best tolerance to root mismatch by 1.0mm wire. The use of temporary backing systems gave no advantage with 0.8mm wire, or with 1.0, and 1.2mm at wire feed speeds giving a greater deposition rate than 3.0kg/hr. The use of an Ar/20%CO2 gas mixture was found to give no advantage over CO2 shielding in terms of root run tolerance.