For example, in gas tungsten arc (GTA) welding, a nonconsumable electrode welding process, direct
current electrode negative (DCEN) is the polarity used most often. Electrons are easily emitted from
the tungsten electrode (cathode). When the electrons travel through the arc they accelerate to very
high speed. About 70% of the arc heat is released at the workpiece (anode or positive pole) due to
electrons striking the surface at high speed. This produces a weld bead with greater penetration.
When the polarity is reversed (DCEP) the workpiece becomes the cathode. The weld pool cannot
easily emit electrons because the molten pool is at a much lower temperature than the tungsten and
will resist the release of electrons. While DCEP is helpful in cleaning the weld pool by removing the
oxides, about 70% of the arc heat is now generated at the electrode (anode). This reduces the life of
the tungsten electrode and the weld bead has reduced penetration. The use of alternating current
provides arc characteristics that are average of those for DCEN and DCEP (Figure 1.10).