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Low Voltage Short Circuiting-GMAW

Print Date: 1/27/2009 8:26:47 AM
M.J. Houle
January 1985
Category: Design/Fabrication
Summary: The following article is a part of National Board Classic Series and it was published in the National Board BULLETIN. (3 pages)
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The National Board has been frequently asked to give some guidance to gas metal arc welding (GMAW or commonly called MIG) when welding in the low voltage short circuiting (GMAW-S) mode.
GMAW-S is normally a solid wire (ASME SFA-5.18) gas shielded welding type process which uses semiautomatic or automatic equipment. It is similar to the spray arc or globular arc transfer GMAW processes, the flux-cored arc welding (FCAW) process, and is closely related to the submerged arc welding (SAW) process. Although, the GMAW-S has unique features.
All of the related processes are very high-energy processes which transfer weld metal across a continuous electric arc and generally carry a large molten weld puddle. GMAW-S is a low energy process which also generates its heat from an electric arc but the weld metal is transferred only partially across an arc and partially when the filler metal touches the base metal and the arc is short circuited. This short-circuiting occurs 20 to 200 times per second which results in a small molten weld puddle.
When the arc is short circuited, the molten weld puddle is able to freeze more quickly than when welding with a continuous arc. This gives GMAW-S a unique ability to weld out of position, to weld thin base metals and to weld open butt root passes without backing and without "blowing through." One bad characteristic, however, is that the quick freeze puddle has a tendency to "cold lap" when not carefully deposited with the correct technique by a skilled welder. This bad characteristic is often why the process is written out of purchase specifications.
Because of the