Arc welding is a process utilizing the concentrated heat of an electric arc to join metal by fusion of the parent metal and the addition of metal to joint usually provided by a consumable electrode. Either direct or alternating current may be used for the arc, depending upon the material to be welded and the electrode used.
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Let us go to the types of Arc Welding
Gas Metal-Arc Welding (GMAW), also called Metal Inert Gas (MIG) welding, shields the weld zone with an external gas such as argon, helium, carbon dioxide, or gas mixtures. Deoxidizers present in the electrode can completely prevent oxidation in the weld puddle, making multiple weld layers possible at the joint.
GMAW is a relatively simple, versatile, and economical welding apparatus to use. This is due to the factor of 2 welding productivity over SMAW processes. In addition, the temperatures involved in GMAW are relatively low and are therefore suitable for thin sheet and sections less than ¼ inch.
GMAW may be easily automated, and lends itself readily to robotic methods. It has virtually replaced SMAW in present-day welding operations in manufacturing plants.
Shielded-Metal Arc Welding (SMAW) is one of the oldest, simplest, and most versatile arc welding processes. The arc is generated by touching the tip of a coated electrode to the workpiece and withdrawing it quickly to an appropriate distance to maintain the arc. The heat generated melts a portion of the electrode tip, its coating, and the base metal in the immediate area. The weld forms out of the alloy of these materials as they solidify in the weld area. Slag formed to protect the weld against forming oxides, nitrides, and inclusions must be removed after each pass to ensure a good weld.
The SMAW process has the advantage of being relatively simple, only requiring a power supply, power cables, and electrode holder. It is commonly used in construction, shipbuilding, and pipeline work, especially in remote locations.
Fluxed-Core Arc-Welding (FCAW) uses a tubular electrode filled with flux that is much less brittle than the coatings on SMAW electrodes while preserving most of its potential alloying benefits.
The emissive fluxes used shield the weld arc from surrounding air, or shielding gases are used and nonemissive fluxes are employed. The higher weld-metal deposition rate of FCAW over GMAW (Gas Metal Arc Welding) has led to its popularity in joining relatively heavy sections of 1" or thicker.
Another major advantage of FCAW is the ease with which specific weld-metal alloy chemistries can be developed. The process is also easily automated, especially with the new robotic systems.
Gas Tungsten-Arc Welding (GTAW), also known as Tungsten Inert Gas or TIG welding, uses tungsten electrodes as one pole of the arc to generate the heat required. The gas is usually argon, helium, or a mixture of the two. A filler wire provides the molten material if necessary. http://tristate.apogee.net/et/graphics/ftjgtw01.gif
The GTAW process is especially suited to thin materials producing welds of excellent quality and surface finish. Filler wire is usually selected to be similar in composition to the materials being welded.
Atomic Hydrogen Welding (AHW) is similar and uses an arc between two tungsten or carbon electrodes in a shielding atmosphere of hydrogen. Therefore, the work piece is not part of the electrical circuit.
Plasma arc cutting can increase the speed and efficiency of both sheet and plate metal cutting operations. Manufacturers of transportation and agricultural equipment, heavy machinery, aircraft components, air handling equipment, and many other products have discovered its benefits.
Plasma cutters are used in place of traditional sawing, drilling, machining, punching, and cutting. The high-temperature plasma arc cuts through a wide variety of metals at high speeds. Although plasma arc cutting can cut most metals at thicknesses of up to 4 to 6 inches, it provides the greatest economical advantages, speed, and quality on carbon steels under 1 inch thick, and on aluminum and stainless steels under 3 inches thick.
Plasma arc cutting has gained approval in both hand-held and automated cutting operations. Some of the most impressive results are achieved in automated systems. Advances in computer numerical controls (CNC), robots, and other automation techniques have offered manufacturers higher cutting speeds achieved through plasma arc cutting. Improved torch designs and more efficient power supplies have made plasma arc cutting increasingly popular.
New areas of technology in plasma arc cutting systems include non-transferred arc plasma, which allows plastics and other nonconductive materials to be cut. Research on cutting plastics is continuing and at least one commercial process is currently available.