Introduction
Incomplete
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Undercutting
Fusion
Porosity
Cracking

 

 

 

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5 UNDERCUTTING As shown in Figure 10-3, undercutting is a defect that appears as a groove in the parent metal directly along the edges of the weld. It is most common in lap fillet welds, but can also be encountered in fillet and butt joints. This type of defect is most commonly caused by improper welding parameters; particularly the travel speed and arc voltage. When the travel speed is too high, the weld bead will be very peaked because of its extremely fast solidification. The forces of surface tension have drawn the molten metal along the edges of the weld bead and piled it up along the center. Melted portions of the base plate are affected in the same way. The undercut groove is where melted base material has been drawn into the weld and not allowed to wet back properly because of the rapid solidification. Decreasing the arc travel speed will gradually reduce the size of the undercut and eventually eliminate it. When only small or intermittent undercuts are present, raising the arc voltage or using a leading torch angle are also corrective actions. In both cases, the weld bead will become flatter and wetting will improve. Continued on next page... Figure 10-3 – Examples of Undercutting