3
The contact tip-to-work distance, because
of its effect on the wire extension, affects the welding current
required to melt the wire at a given
feed speed. Fig. 7-3 shows the extent to which the welding current
requirement can vary with tip-to-work
distance. Basically, as the tip-to-work distance is increased, the
amount of I2R
heating increases and the welding current required to melt the wire is decreased.
The converse is
also true. Controlling
tip-to-work distance is important. Long extensions result in excess weld metal
being deposited with
low arc heat. This can cause poor bead shape and low penetration. In addition,
as the tip-to-work distance
increases, the arc becomes less stable. For short arc welding 3/8 in. (9.6mm)
tip-to-work distance is
recommended. It is very important that the wire extension be kept as constant
as possible during the welding
operation. In view of the substantial effect on the welding operation, it is always
wise to record not only
current and voltage, but also the wire-feed speed. Figure
7-3 – Effect of Tip-To-Work Distance on Welding Current
