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Chapter: Mechanical : Manufacturing Technology : Metal Joining Process

Special Welding Process

1.Submerged arc welding 2.Laser Beam Welding (LBW) 3.Electron Beam Welding (EBW) 4.PLASMA ARC WELDING 5.THERMIT WELDING 6.TIG& MIG WELDING 7.RESISTANCE WELDING



1.Submerged arc welding


     Weld arc is shielded by a granular flux , consisting of silica, lime,


manganese oxide,

calcium fluoride and other compounds.

•             Flux is fed into the weld zone by gravity flow through nozzle




Thick layer of flux covers molten metal


•             Flux acts as a thermal insulator ,promoting deep penetration of heat into the work




      Consumable electrode is a coil of bare round wire fed automatically through a tube


Power is supplied by 3-phase or 2-phase power lines



2.Laser Beam Welding (LBW)


Fusion welding process in which coalescence is achieved by energy of a highly concentrated, coherent light beam focused on joint

Laser = "light amplification by stimulated emission of radiation" LBW normally performed with shielding gases to prevent oxidation


Filler metal not usually added


High power density in small area, so LBW often used for small parts






The laser WELDING system consists of a power source, a flash lamp filled with Xenon, lasing material, focusing lens mechanism and worktable. The flash tube flashes at a rate of thousands per second. As a result of multiple reflections, Beam power is built up to enormous level.


The output laser beam is highly directional and strong, coherent and unicromatic with a wavelength of 6934oA. It goes through a focusing device where it is pinpointed on the work piece, fusion takes place and the weld is accomplished due to concentrated heat produced. Laser beam welding process is shown in the figure.




1.Wide variety of metals can be welded. 2.Thermal damage is minimum.

3.Weld metal is purified.


4.Good ductility and mechanical properties. 5.Welds are vaccum tight.

6.filler metal is not used.

7.No effect on heat treated components.




1.Low welding Speed.


2.Limited to thickness of 1.5mm. 3.Materials like Mg cannot be welded.




Radio Engineering and




3.Electron Beam Welding (EBW)


Fusion welding process in which heat for welding is provided by a highly-focused, high-intensity stream of electrons striking work surface

Electron beam gun operates at:


High voltage (e.g., 10 to 150 kV typical) to accelerate electrons Beam currents are low (measured in milliamps)


Power in EBW not exceptional, but power density is





The Kinetic energy of the electrons is converted into intense heat energy when the electrons are absorbed by the metal piece over a small area of the weld, producing deep penetration weld with a depth/width ratio as high as 15. This results in a narrow, almost parallel weld with very little distortion and a small width of the heat affected zone. There is no possibility of contamination by atmospheric gases because process is carried out in vaccum.



High-quality welds, deep and narrow profiles


Limited heat affected zone, low thermal distortion High welding speeds


No flux or shielding gases needed



High equipment cost


Precise joint preparation & alignment required Vacuum chamber required


Safety concern: EBW generates x-rays


Comparison: LBW vs. EBW


No vacuum chamber required for LBW No x-rays emitted in LBW


Laser beams can be focused and directed by optical lenses and mirrors


LBW not capable of the deep welds and high depth-to-width ratios of EBW

Maximum LBW depth = ~ 19 mm (3/4 in), whereas EBW depths = 50 mm (2 in)






Plasma Arc welding is a constricted arc process. The arc is constrained with the help of a water cooled small diameter nozzle which squeezes the arc, increases its pressure, temperature and heat intensely and thus improves stability, arc shape and heat transfer, characteristics


There are two methods of Plasma Arc Welding


(A) Transferred Arc

(B)Non- Transferred Arc.


(a)Transfered Arc


Here the electrical circuit is between the tungsten electode and the work piece. Work piece acts as anode and the tungsten electrode as cathode. The arc is transferred from the electrode to the work piece and hence the term transferred. Here the arc force is directed away from the plasma torch and into the work piece, hence capable of heating the work piece to a higher temperature.


(b)NON-Transferred Arc.


In Non-transferreed type, power is directly connected with the electrode and the torch of nozzle. The electrode carries the same current. Thus ,ionizing a high velocity gas that is strewing towards the workpiece. The main advantage of this type is that the spot moves inside the wall and heat the incoming gas and outer layer remains cool. This type of plasma has low thermal efficiency.




1.Ensures arc stability. 2.Produces less thermal distortion


3.The process is readily automated.




1.Excessive noise is produced. 2.Equipment is complicated and expensive.

3.Large amount of ultraviolet and infrared rays are emitted.





FW process in which heat for coalescence is produced by superheated molten metal from the chemical reaction of thermite


Thermite = mixture of Al and Fe3O4 fine powders that produce an exothermic reaction when ignited


Also used for incendiary bombs


Filler metal obtained from liquid metal


Process used for joining, but has more in common with casting than welding


Fig: Thermit welding: (1) Thermit ignited; (2) crucible tapped, superheated metal flows into mold; (3) metal solidifies to produce weld joint.


joining of railroad rails


Repair of cracks in large steel castings and forgings


Weld surface is often smooth enough that no finishing is required




Inert Gas Welding


For materials such as Al or Ti which quickly form oxide layers, a method to place an inert atmosphere around the weld puddle had to be developed


Metal Inert Gas (MIG)


      Uses a consumable electrode (filler wire made of the base metal)


      Inert gas is typically Argon


Gas Tungsten Arc Welding (GTAW)

Uses a non-consumable tungsten electrode and an inert gas for arc shielding

Melting point of tungsten = 3410 C (6170 F) A.k.a. Tungsten Inert Gas (TIG) welding


In Europe, called "WIG welding" Used with or without a filler metal


When filler metal used, it is added to weld pool from separate rod or wire

Applications: aluminum  and stainless steel most common



High quality welds for suitable applications No spatter because no filler metal through arc


Little or no post-weld cleaning because no flux



Generally slower and m ore costly than consumable electrode AW processes




Resistance Welding (RW)


A group of fusion weldin g processes that use a combination of heat and pressure to accomplish coalescence


Heat generated by electrical resistance to current flow at junction to be welded Principal RW process is res istance spot welding (RSW


Components in Resistance Spot Welding

Parts to be welded (usually sheet metal) Two opposing electrod es


Means of applying pressure to squeeze parts between electrodes


Power supply from wh ich a controlled current can be applied for a specified time duration



No filler metal required


High production rates p ossible


Lends itself to mechanization and automation Lower operator skill le vel than for arc welding


Good repeatability and reliability.

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