Welding

OXYACETYLENE WELDING The Process:- Gas welding is a welding process that melts and joins metals by heating them with a flame caused by the reaction between a fuel gas and oxygen. Oxyacetylene welding (OAW), shown in Figure is the most commonly used gas welding process because of its high flame temperature. A flux may be used to deoxidize and cleanse the weld metal. The flux melts, solidifies, and forms a slag skin on the resultant weld metal. Three different types of flames in oxyacetylene welding: neutral, reducing, and oxidizing , which are described next. Advantages and Disadvantages :- The main advantage of the oxyacetylene welding process is that the equipment is simple, portable, and inexpensive.Therefore, it is convenient for maintenance and repair applications. However, due to its limited power density, the welding speed is very low and the total heat input per unit length of the weld is rather high, resulting in large heat-affected zones and severe distortion.The

ELECTROSLAG WELDING The Process :- Electroslag welding (ESW) is a process that melts and joins metals by heating them with a pool of molten slag held between the metals and continuously feeding a filler wire electrode into it, as shown in Figure. The weld pool is covered with molten slag and moves upward as welding progresses. A pair of water-cooled copper shoes, one in the front of the workpiece and one behind it, keeps the weld pool and the molten slag from breaking out. Similar to SAW , the molten slag in ESW protects the weld metal from air and refines it. Strictly speaking, however, ESW is not an arc welding process, because the arc exists only during the initiation period of the process, that is, when the arc heats up the flux and melts it. The arc is then extinguished, and the resistance heating generated by the electric current passing through the slag keeps it molten. In order to make heating more uniform, the electrode is often oscillated, especially when welding thicker

SUBMERGED ARC WELDING The Process :- Submerged arc welding (SAW) is a process that melts and joins metals by  heating them with an arc established between a consumable wire electrode and the metals, with the arc being shielded by a molten slag and granular flux,  as shown in Figure. This process differs from the arc welding processes  discussed so far in that the arc is submerged and thus invisible.The flux is supplied  from a hopper (Figure a), which travels with the torch. No shielding  gas is needed because the molten metal is separated from the air by the molten slag and granular flux (Figure b). Direct-current electrode positive is most  often used. However, at very high welding currents (e.g., above 900A) AC is  preferred in order to minimize arc blow. Arc blow is caused by the electromagnetic  (Lorentz) force as a result of the interaction between the electric  current itself and the magnetic field it induces. In short:- • Fusion Welding Process •Automatic / Semi Auto

PLASMA ARC WELDING The Process:- Plasma arc welding (PAW) is an arc welding process that melts and joins metals by heating them with a constricted arc established between a tungsten electrode and the metals, as shown in Figure 1. It is similar to GTAW , but an orifice gas as well as a shielding gas is used. As shown in Figure 2, the arc in PAW is constricted or collimated because of the converging action of the orifice gas nozzle, and the arc expands only slightly with increasing arc length. Direct-current electrode negative is normally used, but a special variable polarity PAW machine has been developed for welding aluminium, where the presence of aluminium oxide films prevents a keyhole from being established. Fig-1 Plasma arc welding: (a) overall process; (b) welding area enlarged and shown with key holing. Arc Initiation:- The tungsten electrode sticks out of the shielding gas nozzle in GTAW (Figure 1b) while it is recessed in the orifice gas nozzle in PAW (Figure

FLUX-CORE ARC WELDING (FCAW) The Process:- Flux-core arc welding (FCAW) is similar to GMAW , as shown in Figure a. However, as shown in Figure b, the wire electrode is flux cored rather than solid; that is, the electrode is a metal tube with flux wrapped inside. The functions of the flux are similar to those of the electrode covering in SMAW , including protecting the molten metal from air. The use of additional shielding gas is optional. Flux-Core Arc Welding (FCAW) (a) overall process (b) welding area enlarged Advantages of FCAW:- High deposition rates Deeper penetration than SMAW High quality welds Less pre-cleaning than GMAW Slag covering helps with out-of-position welds Self-shielded FCAW is draft tolerant Disadvantages of FCAW:- Slag must be removed Higher fume generation than GMAW and SAW Spatter Equipment is more expensive and complex than SMAW FCAW wire is more expensive Types of continuous wire electrodes:-   Read More abou

GAS–METAL ARC WELDING (GMAW) The Process:- Gas–metal arc welding (GMAW) is a process that melts and joins metals by heating them with an arc established between a continuously fed filler wire electrode and the metals, as shown in Figure. Shielding of the arc and the molten weld pool is often obtained by using inert gases such as argon and helium, and this is why GMAW is also called the metal–inert gas (MIG) welding process. Since non inert gases, particularly CO2, are also used,GMAW seems a more appropriate name. This is the most widely used arc welding process for aluminium alloys. Unlike in GTAW , DCEP is used in MAW. A stable arc, smooth metal transfer with low spatter loss and good weld penetration can be obtained.With DCEN or AC, however, metal transfer is erratic. Gas–metal arc welding: (a) overall process; (b) welding area enlarged. GMAW What Is GMAW ? •A Fusion Welding Process – Semi Automatic •Arc Between Consumable Electrode &Work •Arc Generated by Ele