Arc welding definition can be described as:
“Arc welding (AW) is a fusion welding process in which heat produced with the help of electric arc between the electrode and workpiece to join metal parts”.
An electric arc is the discharge of electric current through a gap in a circuit (a gap between workpiece and electrode). To initiate the arc, the electrode brought in contact with the workpiece. After that, the electrode quickly separated from the workpiece through a short distance. Thus, electric energy from arc produces a temperature of 55000C (10,0000F) or higher. This produced arc enough to melt any metal. A pool of molten metal formed with the help of high-temperature arc. A pool of molten metal consists of base metal (workpiece) and filler metal.
Filler metal added during the arc welding process to increase the strength and volume of the weld joints. Filler materials must be selected to match the base metal with respect to properties or alloy composition. After making of the molten metal pool, electrode moves relative to the workpiece with a controlled rate. Movement of electrode carried out through human welding or manual welding. Mechanical methods for electrode movement can also use. These mechanical methods are machine welding, automatic welding or robot welding.
Arc welding Diagram:
The time during which an arc is maintained in making an arc weld is called arc welding. An arc time also called arc on time. Arc on time is the proportion of hours worked that arc welding being accomplished.
Arc time= time arc is on/ hours Worked
This definition can be applied to an individual welder or to a mechanized work station. For manual welding, usually, arc time is 20%. This arc time increases up to 50% with the help of machine, automatic and robotic welding.
Arc Welding Equipment:
- AC or DC welding machine
- Electrode holder
- Chipping hammer
- Wire brush
- Cables connector
- Earth clamps
- Asbestos hand Gloves
- Safety goggles
The electrode produces an electric arc and plays a very important role in arc welding. An arc welder without electrode cannot perform arc welding (AW). Electrode used in AW classified as a consumable electrode and non-consumable electrode.
Consumable electrodes provide filler metal during the welding process to fill the joint. These consumable electrodes have a melting point below the temperature of the arc. Electrodes are available in two forms, rod, and wire. Electrode rods also called sticks. Welding rods are normally 225 to 450 mm (9 to 18 inch) long and 9.5 mm or less in diameter. Consumable welding rods periodically change, thus reducing the arc time of the welder in production welding.
On the other hand, consumable weld wire continuously fed into the weld pool from spools that contain the long length of wire. Thus, using an electrode wire avoid frequent interruptions that occur during welding rod electrodes. In both wire and rod electrodes, during welding electrode continuously consumed to fill the metal joints.
To maintain the stable arc and other satisfactory conditions for welding, the electrode moved toward the workpiece at a controlled as well as constant rate. Manual arc welding mostly performed with shielded electrodes. A continuous bare-metal wire can be used as an electrode in semi-automatic or automatic welding. Following welding processes used consumable electrodes.
- Shielded Metal (SMAW)
- Flux Cored Arc (FCAW)
- Gas Metal Arc (GMAW)
- Submerged (SAW)
A non-consumable electrode made with tungsten or sometimes made with carbon. Tungsten electrode provides resistance to melt the electrode through an arc. Relatively slow vaporization occurs in non-consumable electrodes. In non-consumable electrode welding, a separate metal wire feed into the weld pool as filler metal. Gas tungsten arc welding (GTAW) uses the non-consumable electrode.
At high temperature in arc welding, joined metals chemically reactive to hydrogen, oxygen, and nitrogen in the air. The mechanical properties of weld joints degraded due to these chemical reactions. Therefore, shielding of an arc is necessary to prevent the arc from environmental air. To achieve arc shielding, cover the electrode tip, arc and molten weld pool with a blanket of flux or gas or both.
Argon and helium commonly used gases for arc shielding. These both gases are inert. During welding of ferrous metals, Oxygen and carbon dioxide in combination with argon or helium used to produce an oxidizing atmosphere or to control weld shape.
A flux also used for arc shielding. The flux prevents the formation of oxides and unwanted contaminations or dissolves them and facilitates removal. During the welding, the flux melts and develops a liquid slag. This liquid slag covers the welding operation and protecting the molten weld metal. Slag hardens after cooling of the weld joint. Chipping or brushing used to remove hardens slag. Flux performs the following main functions:
- Provide a protective atmosphere for welding (Provide shielding)
- Reduce spattering/ splashing
- Stabilize the arc
Arc Welding Power Supply Source:
Direct current (DC) and Alternative Current (AC) is used in this welding process. Arc welding current varies from 1 amp to 4000 amps. Usually, 100 to 1000 amps used for the arc welding process. Voltages use generally in the range of 20 to 50V.
If Direct Current (DC) used in arc welding and electrode made negative than this condition called straight polarity (SPDC) or direct current electrode negative (DCEN). In straight polarity, electrons attracted to the positive workpiece while ionized atoms move toward the negative electrode. Meanwhile, ions are far more massive than the electrons; the heat of the arc is more concentrated at the electrode. Direct current electrode negative (DCEN) process characterized as fast melting of electrode and a shallow molten pool on the workpiece (weld penetration).
If the workpiece made negative and electrode positive, this condition called reverse polarity (RPDC). Direct current electrode positive (DCEP) is the other name of reverse polarity condition. In this condition, positive ions impinge on the workpiece, breaking up any oxide film and giving deeper penetration. The molten deposition rate is lower in DCEP as compared to DCEN.