Welding Terms

Lack of Fusion (LOF) - Also known as cold-lapping or cold shuts, LOF occurs when there is no fusion (melting and mixing) between the weld metal and the base metal. The most common cause of lack of fusion is a poor welding technique. Another cause is the use of a very wide weld joint. If the welding arc is directed down the center of the joint, the molten weld metal will only flow and be solidified and cast against the side walls of the base plate without melting them.

Lack of Penetration (LOP) - A weld defect where the welding process does not reach all the way into the seam between the pieces being welded. Incomplete penetration is usually caused by the use of too low a welding current and can be eliminated by simply increasing the amperage. Other causes can be the use of too slow a travel speed, an incorrect torch angle or too narrow of a gap between pieces.

Gusset - Triangular metal piece added to an interior corner to add strength to the joint.

Fitup - The initial positioning of pieces before welding or fastening.

Fitup Gap - A space or gap between pieces when they are being positioned for welding. The gap may remain after welding or it may be filled by the weld.

Tack Weld - A small, temporary weld placed at intervals along a joint to hold the joint in alignment.

Fillet Weld - A weld of approximately triangular cross section, as used in a lap joint, joining two surfaces at approximately right angles to each other.

Undercut - Undercutting is a defect that appears as a groove in the parent metal directly along the edges of the weld in the weld toe. This type of defect is most commonly caused by improper welding parameters; particularly the travel speed and arc voltage.

Weld Toe - The junction of the weld face and the base metal.

Re-Entrant Angle - The angle formed by the weld and base metal intersection after welding.

Capping Pass - The final pass in welding a joint, sometimes done for cosmetic purposes.