Welding

ELECTRON BEAM WELDING The Process:- Electron beam welding (EBW) is a process that melts and joins metals by heating them with an electron beam. As shown in Figure 1a, the cathode of the electron beam gun is a negatively charged filament.When heated up to its thermionic emission temperature, this filament emits electrons. These electrons are accelerated by the electric field between a negatively charged bias electrode (located slightly below the cathode) and the anode. They pass through the hole in the anode and are focused by an electromagnetic coil to a point at the workpiece surface. The beam currents and the accelerating voltages employed for typical EBW vary over the ranges of 50–1000mA and 30–175kV, respectively. An electron beam of very high intensity can vaporize the metal and form a vapour hole during welding, that is, a keyhole, as depicted in Figure 1b. 1  Electron beam welding: (a) process; (b) keyhole. Modified from Arata Figure 2 shows that the beam diameter...

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:- • Fus...

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 ...

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...

GTAW The Process Gas–tungsten arc welding (GTAW) is a process that melts and joins metals by heating them with an arc established between a non consumable tungsten electrode and the metals, as shown in Figure. The torch holding the tungsten electrode is connected to a shielding gas cylinder as well as one terminal of the power source, as shown in Figure a . The tungsten electrode is usually in contact with a water-cooled copper tube, called the contact tube, as shown in Figure b , which is connected to the welding cable (cable 1) from the terminal. This allows both the welding current from the power source to enter the electrode and the electrode to be cooled to prevent overheating.The workpiece is connected to the other terminal of the power source through a different cable (cable 2). The shielding gas goes through the torch body and is directed by a nozzle toward the weld pool to protect it from the air. Protection fro...

SMAW The Process:- Shielded metal arc welding (SMAW) is a process that melts and joins metals by heating them with an arc established between a sticklike covered electrode and the metals, as shown in Figure below. It is often called stick welding . The electrode holder is connected through a welding cable to one terminal of the power source and the workpiece is connected through a second cable to the other terminal of the power source (Figure a). The core of the covered electrode, the core wire, conducts the electric current to the arc and provides filler metal for the joint. For electrical contact, the top 1.5 cm of the core wire is bare and held by the electrode holder. The electrode holder is essentially a metal clamp with an electrically insulated outside shell for the welder to hold safely. The heat of the arc causes both the core wire and the flux covering at the electrode tip to melt off as droplets (Figure b ). The molten metal collects in the weld pool and solidifies ...

Overview Fusion welding processes- Fusion welding is a joining process that uses fusion of the base metal to make the weld. The three main type of the fusion welding are as follows: 1. Gas Welding :                             Oxyacetylene welding (OAW) 2. Arc Welding :                             Shielded metal arc welding (SMAW)                             Gas-tungsten arc welding (GTAW)                             Plasma arc welding (PAW)                             Gas-metal arc welding (GMAW)                             Flux-cored arc welding (FCAW)  ...

Welding :- Welding is process of joining of two similar or dissimilar materials by the application of heat and with or without the application of pressure and with or without application of filler materials. On Cooling the molten edges fuse together to form a strong joint. A filler material is added to the molten parent metal. Welding (GMAW) In simple words-           Process of joining metals/alloys           The process performed by Heat with or without Pressure           Filler metal may or may not be used           The joint will be homogeneous Classification of Welding :-           Pressure Welding-           With Heat & Pressure           Fusion Welding -              With Heat & mostly with Filler ...