The following tests, as specified by EWM, were carried out to compare EWM-forceArc® with conventional MIG/MAG welding;
- Butt weld using spray transfer in the PA position with 20mm plate and a machined V-prep of 60°
- Butt weld using EWM-forceArc® in the PA position with 20mm plate and a machined V-prep of 40°
- Butt weld using EWM-forceArc® in the PA position with 20mm plate and a machined V-prep of 30°
- Fillet weld using spray transfer in the PB position with 10 mm plate
- Fillet weld using EWM-forceArc® in the PB position with 10 mm plate.
Butt welds were made using a backing bar and a root opening of 3.5mm. Welding conditions were chosen by the EWM welder who carried out the welding tests. TWI documented the welding procedure. Each weld was examined visually and a macro-section taken to assess bead shape and penetration in accordance with EN1321:1997. A hardness survey was also carried out in accordance with EN1043:1996. In addition the following mechanical tests were carried out on the butt welds:
- Two transverse tensile tests in accordance with EN 895:1995.
- Four transverse bend tests in accordance with EN 910:1996.
- Two sets of Charpy v-notch impact tests at -20oC in accordance with EN 875:1995.
The welding parameters showed that very similar welding conditions were used for all the welds. The wire feed speed was set at 10m/min for all the welds, apart from the butt weld with the narrow preparation of 30o, for which a wire feed speed of 11m/min was set for the first three passes. Consequently, a similar welding current of 269-318A was measured for most passes.
Differences in current are attributed to variations in contact tip to work piece distance (CTWD) rather than transfer mode. Arc voltage was also similar, being in the range 29.7 to 31.2v. This was slightly surprising, as the manufacturer's information about the process suggests that lower voltages are used with EWM-forceArc®.
However, in these trials, particularly with a narrow preparation angle, the CTWD was longer, which would lead to a reduced current and a higher voltage (due to the stick-out) for a given wire feed and voltage setting, as recorded for like-for-like passes at 10m/min wire feed speed for two of the welds.
The reduction in joint volume, by using a narrower preparation angle, is seen to provide significant benefits in the number of passes required to fill the joint, and consequently on the joint completion rate.