Page 63 - CITS - Welder - Trade Theory

WELDER - CITS

3 Porosity
4 Lack of fusion (LOF)
5 Lack of penetration (LOP)

6 Craters
7 Melt – through
8 Spatter
9 Arc Strikes (Arc burns)
1 Undercut: A groove melted into the base metal adjacent to the toe or root of a weld and left unfilled by weld
metal.
Undercutting is a defect that appears as a groove in the parent metal directly a long the edges of the weld. It
is most common in lap fillet welds, but can also be encountered in fillet and butt joints.
Causes
1 Improper welding parameters; particularly the travel speed and arc voltage.
2 Excessive welding currents.

3 Slag inclusion: Non metallic solid material entrapped in weld or between weld metal and base metal.
4 Porosity: Cavity-type discontinuities formed by gas entrapment during solidification.
Porosity is gas pores found in the solidified weld bead. These pores may vary in size and are generally distributed
in a random manner. However, it is possible that porosity can only be found at the weld centre. Pores can occur
either under or on the weld surface.

The most common causes of porosity are atmosphere contamination, excessively oxidized work piece surfaces,
inadequate deoxidizing alloys in the wire and the presence of foreign matter.
Atmospheric contamination can be caused by:

1 Inadequate shielding gas flow.
2 Excessive shielding gas flow. This can cause aspiration of air into the gas stream.
3 Severely clogged gas nozzle or damaged gas supply system (leaking hoses, fittings, etc.)
4 An excessive wind in the welding area. This can blow away the gas shield.

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CITS : C G & M - Welder - Lesson 12&13