TWI Industrial Member Report Summary 936/2009
V Kumar and C Peters
Background
Metal active gas (MAG) welding is often employed for joining thin sections due to its high productivity, however, the high heat input associated with the process can be a limiting factor, especially when the joint fit-up is poor. The heat input in MAG welding depends on the metal transfer mode employed by the process, which can be classified as short-circuit, pulsed and spray transfer. Operating parameters such as the arc voltage, current, shielding gas and electrode wire feed rate control the transfer mode. Short-circuit transfer takes place at relatively low values of current and voltage, hence the heat input is low, however, conventional short-circuit transfer is associated with excessive spatter. Spray transfer occurs at relatively high values of arc voltage and current and hence is associated with high heat input.
Developments in inverter-based power supplies with microprocess control now provide greater power over metal transfer modes, not possible with earlier conventional power sources. This has led to the development of a number of MAG welding process variants such as electronically controlled short-circuit transfer, electronically controlled modulated wire feed short-circuit transfer, pulsed transfer with greater dynamic response, etc suitable for thin sheet welding. This report, investigates some of these developments with respect to their productivity and tolerance to joint gap in thin steel sheet welding.
Objectives
Compare the maximum welding speed, the associated heat input, and tolerance to variations in the joint fit-up at the maximum welding speed, of the following MAG welding process variants:
- Conventional spray transfer (Process A).
- Pulsed current metal transfer (Process B).
- Electronically controlled short-circuit transfer (Process C).
- Electronically controlled modulated wire feed short-circuit transfer (Process D).
a) Cold rolled steel;