A gas metal arc welding process variation in which the consumable electrode is deposited during repeated short circuits.
A short circuiting arc is a method of metal transfer in gas metal arc welding (GMAW). This process is sometimes referred to as short arc or dip transfer. It can be used with most metals, providing the welding wire, which is a consumable electrode, has a good burn off characteristic, and the correct shielding gas and welding machine are used.
Short circuiting GMAW has gained wide acceptance in industry for welding thin materials in all positions, and some heavier gauges in the vertical and overhead positions. It has proven useful for applications that require welding large gaps.
Short circuiting metal transfer is most widely used in welding carbon steels and low-alloy steels. Stainless steels and light gauge aluminum are also being welded with this process, but to a lesser degree. Short circuiting metal transfer is done at low currents, generally from 50 to 225 amperes, and low voltage, 12 to 22 volts, using small diameter wires, usually with 0.8, 0.9 and 1.1 mm (0.030,0.035, and 0.045 in.) diameters.
The outstanding characteristic of the short circuiting arc is the frequent shorting of the wire to the workpiece. All metal transfer takes place when the arc is extinguished. This happens at a steady rate from 20 to over 200 times a second. This results in a very stable arc of low energy and heat input. The low heat input minimizes distortion and metallurgical effects.
The arc voltage and arc current patterns during a typical short circuiting welding cycle are traced by means of an oscillograph. Each short circuit should produce a definite controlled current surge sufficient to recreate the arc without an undesirable high surge or blast.
Special machines of the constant potential type are used for this welding method. They have appropriate induction or voltage-ampere slope control, or both, for producing the specific current surges needed to implement short circuit metal transfer for its full range of most metals.
Equipment- Short circuit metal transfer can be accomplished on basic GMAW equipment. The wire feed system should be of a constant speed design, using either a mechanical or an electronic governor. A wire feed range of 12 to 340 m d s (50 to 800 in/min) will make it adequate for nearly all applications. The welding machine should be a direct-current type designed for short circuiting metal transfer, usually with a 200-or 300-ampere capacity.
The GMAW torch may be either air cooled or water cooled, with a straight or curved nozzle. The curved nozzle is the most popular design for welding in the short circuiting metal transfer mode.
Shielding Gases- Many of the shielding gases react favorably with short circuiting metal transfer.Pure argon and helium, or mixtures of both, are used on thin aluminum. For carbon and low-alloy steels, the gases generally used are carbon dioxide, or mixtures of argon and carbon dioxide, or argon and oxygen.
Shielding gas flow rates range from 7 to 12 L/min (15 to 25 cfh). This is less than required for spray arc welding, because a much smaller weld puddle is involved. See also FINE WIRE WELDING and DIP TRANSFER.