Miller Multimatic 220 Owner's Manual page 75

Distortion - contraction of weld metal during welding that forces base metal to move.
Illustration: Base metal moves in the direction of the weld bead.
Possible Causes Corrective Actions
Excessive heat input. Use restraint (clamp) to hold base metal in position.
Make tack welds along joint before starting welding operation.
Select lower amperage for electrode.
Increase travel speed.
Weld in small segments and allow cooling between welds.
OM-281426 Page 71