Process Variables - Linde BOC Smootharc Advance MIG 425R Operating Manual

11.3 Process variables

Process variable
DCEN
Narrow bead,
deep penetration
Nozzle
Ions Electrons
DCEP
Wide bead,
shallow penetration
Nozzle
Ions Electrons
Explanation
When direct-current electrode-negative (straight polarity)
is used:
• Electrons strike the part being welded at a high speed
• Intense heat on the base metal is produced
• The base metal melts very quickly
• Ions from the inert gas are directed towards the
negative electrode at a relatively slow rate
• Direct current with straight polarity does not require
post-weld cleaning to remove metal oxides
The DCEP (reverse polarity) are different from the DCEN in
following ways:
• High heat is produced on the electrode rather on the
base metal
• The heat melts the tungsten electrode tip
• The base metal remains relatively cool compared to sing
straight polarity
• Relatively shallow penetration is obtained
• An electrode whose diameter is too large will reduce
visibility and increase arc instability
BOC Smootharc Advance III MIG 225C & 255C Operating manual
Usage
For a given diameter of tungsten electrode, higher
amperage can be used with straight polarity. Straight
polarity is used mainly for welding:
• Carbon steels
• Stainless steels
• Copper alloys
The increased amperage provides:
• Deeper penetration
• Increased welding speed
• A narrower, deeper, weld bead
• Intense heat means a larger diameter of electrode must
be used with DCEP
• Maximum welding amperage should be relatively low
(approximately six times lower than with DCEN)
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