Mathias Lundin

Abstract

In an ongoing project, MAG-welding with the tandem-wire technique is studied.
Reported here are the first parts of the project where butt, fillet and overlap joints were conducted in mild steel. The applications came from industry, all running today with single wire MAG welding (both solid and cored wires depending on the application).

The aim of the project was to evaluate the process by performing a number of application tests. Here, a sufficient joint penetration and quality level should be obtained and possibilities to increase the productivity and cost effectiveness should be explored. Furthermore, the project aimed at gathering more process knowledge. A preceding literature study only resulted in a few hints on how to set the tandem MAG process.

The following applications are reported:
Application No. 1 - Butt weld in 12 mm material thickness (position PA):
Apart from a process performance test, the possibility to exclude the joint preparation should be evaluated (due to a supposed increase in the penetration capacity). A penetration of 70% was obtained with a travel speed of 80 cm/min and no joint preparation. Difficulties experienced in maintaining the quality level were particularly related to spatter. Too large variations in the quality of the cut end surface of the plates were also a contributing factor.
(Comparable single wire data: 40 cm/min with 60 degrees joint preparation - Ferruform)

Application No. 2 - Fillet weld in 12 mm material thickness (position PB):
A 5 mm weld size with sufficient joint penetration of 2,5 mm has been achieved with a travel speed of 100 cm/min. The determined weld quality level was reached. (Comparable single wire data: 47-51 cm/min, position PA - Ferruform)

Application No. 3 - Overlap weld in 2,5 mm material thickness (position PA):
A sufficient weld quality level was achieved with a travel speed of 400 cm/min.
(Comparable single wire data: 108-138 cm/min – Volvo Cars Olofström)

In the conclusions it was stated that for all applications, a substantial increase of the productivity could be reached. The welding speed, the weld quality and the process tolerances must, however, be balanced (evaluated for each case).

In a further optimisation work, it was recommended to focus on a deeper process study. It is essential to improve the process performance in some aspects, such as a reduced spatter level. More work is also needed before recommendations can be given on how to set the tandem MAG welding process.