Electrode welding is one of several processes of welding for joining metals
The basic principle of operation is that the arc created by passing of a high current through an electrode, creates intense at the point of the weld, which results in the melting of metal, thereby causing fusion. Very often, intermediate molten filler metal is used and due to the intermixing of metals a metallurgical bond is created.
The electrode can be of two types; one, which simply provides the current to form the arc or, it, may also be of a special type that also provides the filler metal in addition to providing the current for the arc.
The source of power to the electrodes is AC or DC power, and is connected by a wire or cable to the work piece. Another cable, also known as a "hot" cable, runs from the source to the electrode through some type of a holder. When the live electrode touches the work piece and is withdrawn slightly, an electric arc is created between the electrode and the work piece. This arc produces a very high temperature, as much as 6500 degrees Fahrenheit at the tip of the electrode.
This very intense heat melts the metal at the base of the electrode, and the electrode itself. This creates a pool of molten metal. It is also called as crater. As the electrode is moved along the joint, the metal solidifies behind the electrode resulting in the bond caused by the fusion of metals.
At high temperatures, metals will react chemically with atmospheric elements such as oxygen and nitrogen. If this is allowed to happen, the bond will be greatly compromised by the natural oxidation and formation of nitrides in the welding process. To prevent this from occurring a form of shielding is provided through a supply of inert gases such as helium or argon, or of vapor or slag. This improves the strength of the bond.
The physics of the electric arc that is key to the welding process presents and intriguing phenomenon. It is nothing but an electric current between the electrode and the work piece through an ionized column of gas. The arc not only performs the all important function of providing the heat for melting the metal, but is also provides the transport mechanism for the molten metal from the electrode to the work piece
If the electrode is of a consumable type, the tip of the electrode provides the metal filler. Molten droplets from the tip of the electrode are transported though the arc to the work piece. In cases where the electrode simply provides the arc and does not provide the filler, a separate filler metal is provided.
Since a larger amount of heat is provided to the weld pool though consumable electrodes, this method is considered more thermally efficient. It also localizes heat delivery to a smaller area. The choice of power may be direct (DC) or alternating current (AC). This will depend on the type of metal being bonded, the arc atmosphere and the type of electrode.