Arc spot welding process
Arc spot welding is an electric arc process where the welding process is carried out at zero arc travel speed. wherein coalescence is produced by heating an electric arc between a tungsten or tungsten alloy electrode and two closely fitted surfaces.
Arc spot welding is basically a TIG welding process where a shielding gas is usually employed and a filler metal can be used depending on the workpiece material. Arc spot welding process performed at zero arc travel speed and produces localized fusion. An arc is struck between a pure tungsten or alloyed tungsten (2% thoriated) electrode and the workpiece using a special arc spot welding gun and ignited under a shielded environment for a fixed period is kept ignited under shielded atmosphere for a definite duration of time during which the upper surface and a portion of the lower surface melt, coalesce and form an integral solid mass after solidification.
The welding gun is pressed against the accessible workpiece to create an arc spot so that the two workpieces come in close contact. The trigger is pulled momentarily. It switches on the power supply and the flow of water when the gas cools. Can be started with the help of an arc. A high-frequency unit or electrode may be advanced to touch the workpiece, moment-to-moment and retracted. A timer in the circuit turns off the power supply and the arc is extinguished after a predetermined time. The timer in the system stops the gas flow after the electrode and the weld pool cool down.
Before welding begins, the top surface and the frying surface must be thoroughly cleaned to remove rust surface dirt, etc. Cleanliness avoids extractions occurring in the pulley and thus produces a sound joint. Surface cleaning can be done by scraping, wire brushing, or chemically.
Since Arc spot welds can be made on (two)pieces kept in lap, butt, fillet or edge types of joints, so no grooving or edge preparation is needed.
Welding parameters of Arc spot welding process
The increasing stream of the arc increases the penetration and fusion area and deepens in the direction of the workpiece thickness. Should be chosen for a good amount of current and for optimal nugget size and joint strength.
Short arc lengths may increase endangering electrode contamination and large arc lengths under caring. In arc spot welding the arc length is usually longer than that placed in TIG welding. Typically, The length of the arc can range from 0.5–2.5 mm.
The diameter of the electrode depends on the thickness of the workpiece, for example, electrodes of about 1 mm, to 1.5 mm are used when thicknesses of 14 to 16 gauge of mild steel, and 14 gauge and above, respectively. Larger electrode diameters are generally preferred to achieve deeper penetration.
Argon, helium carbon dioxide or their mixture, etc. can be used at a flow rate of 1.5 to 3.0 litres/min. Helium produces deeper penetration than argon. Carbon dioxide is cheap and mild steel is very suitable for spot welds.
High quality and reproducible spot welds can only be obtained when the arcing time remains unchanged. Typical welding time is 10 cycles, timer adjustable from 0 to 6 seconds is needy.
Spot welds with large molten pools must be made in a flat position, while thin pieces can be welded in the vertical and overhead positions.