Gas Metal Arc Welding Equipment and Materials
GMA welding uses a solid welding wire that is fed automatically at a constant speed as an electrode. An arc is generated between the wire and the base metal, and the resulting heat from the arc melts the welding wire and base metal to join the parts together. This is a semiautomatic arc welding process because wire is fed automatically at a constant rate and you provide the gun movement. During the welding process, a shielding gas protects the weld from the atmosphere and prevents oxidation of the base metal. The type of shielding gas used depends on the base material to be welded. This process is often referred to by its original name, MIG, which stands for metal inert gas welding.
The early GMA welding process used only inert gases for shielding, so the name MIG welding applied. Today, there are many different gases used for GMA welding—some are inert, nonreactive under all conditions, and others are reactive and can combine under some conditions. To reflect the addition of reactive gases, the term MAG (metal active gas) has been added to the lexicon of welding terms. The American Welding Society’s standard term is gas metal arc welding (GMAW). However, in some industries the terms MIG and MAG are the most commonly used. The process has had other names through the years such as wire welding, but whatever the name, the process is the same.
The advantages of GMA welding over conventional electrode-type arc (stick) welding are numerous.
Some of the advantages of GMA welding are as follows:
Easy to learn—The typical welder can learn to use GMAW equipment with just a few hours of instruction and practice. More time may be required to master the adjusting of the equipment.
Speed and quality—GMA welding can produce higher-quality welds faster and more consistently than conventional stick electrode welds.
Flexibility—The same size filler metal and type of shielding gas can be used to make welds on thin or thick metal by simply adjusting the welding current.
Low distortion—The faster welding speeds and low currents reduce heat damage to adjacent areas that can cause strength loss and warping. Because there is no flux to remove between weld beads, other techniques, such as producing a series of spot welds or stitch welds, can be used to control distortion.
Weld pool control—The small molten weld pool is easily controlled. This allows GMA welding to tolerate larger gaps and misfits. Gaps can be welded by making several short welds on top of each other. • Out of position—GMA welding can easily be used in all positions because the weld pool is small and the metal is molten for a very short time.
Tack welding—GMA welds are easily started in the correct spot because the wire is not energized until the gun trigger is depressed, so arc strikes outside of the weld groove can be avoided.
Efficient—Some GMA welding procedures have a 98% efficiency of weld metal deposited as compared to shielded metal arc welding (SMAW), which is only 65% efficient under the most ideal conditions.
GMA welding is flexible and can be used for both new construction and repair work. Almost any welding that would be done with either an arc or gas welder can be done faster with GMA welding. In addition, it is possible to weld high-strength steel (HSS), high-strength low-alloy (HSLA), aluminum, stainless steel, and many other metals.