Introduction
Incomplete
Penetration
Lack of
Longitudinal
Undercutting
Fusion
Porosity
Cracking

 

 

 

Variations-
Metal
Transfer
Equipment
Power
Supply
Shielding
Gases
Wire
Electrodes
Safety
Welding
Techniques
Welding
Conditions
Economics
Weld
Defects
Mig Spot
Welding
Tables

 

3 Continued on next page... LACK OF FUSION Lack of fusion, also called cold lapping or cold shuts, occurs when there is no fusion between the weld metal and the surfaces of the base plate. This defect can be seen in Figure 10-2. The most common cause of lack of fusion is a poor welding technique. Either the weld puddle is too large (travel speed too slow) and/or the weld metal has been permitted to roll in front of the arc. Again, the arc must be kept on the leading edge of the puddle. When this is done, the weld puddle will not get too large and cannot cushion the arc. Another cause is the use of a very wide weld joint. If the arc is directed down the center of the joint, the molten weld metal will only flow and cast against the side walls of the base plate without melting them. The heat of the arc must be used to melt the base plate. This is accomplished by making the joint narrower or by directing the arc towards the side wall of the base plate. When multipass welding thick material, a split bead technique should be used whenever possible after the root passes. Large weld beads bridging the entire gap must be avoided. Lack of fusion can also occur in the form of a rolled over bead crown. Again, it is generally caused by a very low travel speed and attempting to make too large a weld in a single pass. However, it is also very often caused by too low a welding voltage. As a result, the wetting of the bead will be poor. When welding aluminum, the common cause of this type of defect is the presence of aluminum oxide. This oxide is a refractory with a melting point of approximately 35000F (19270C). It is also insoluble in molten aluminum. If this oxide is present on the surfaces to be welded, fusion with the weld metal will be hampered.