TWI Industrial Member Report Summary 56/1978
By J A Street and W Lucas
The effects, on mechanised bead-on-plate runs, of modulating the feed rate in MIG-welding from a spray condition to virtually zero feed are examined for 1mm diameter mild steel wire in Ar/5%CO2. The durations of the high and low levels range from 0.1 to 0.5sec with spray current levels from 250 to 400A and a nominally constant low or background current of 25.4. A low-inertia printed-armature motor was used for the feed, together with a transistor regulator for the power supply. Enhanced intermittent penetration is obtained, which becomes virtually continuous for the shorter durations, and for constant deposition (10:1 ratio of mean wire feed speed to traverse rate) the penetration profile is some 50% deeper than that for short circuiting MIG at the same average current. At 150A average current the pulsed wire feed spray MIG gives full penetration of a 1.5mm root face, zero root gap preparation, in a root pass without requiring any backing bar. Potential extensions of the system are discussed including the use of synergic pulse control of metal transfer.