There are many types of work which require engineering materials to be joined by welding, for example:
Pressure vessels
Bridges
Oil rigs
Earth moving equipment
Aero-engines
Pressure vessels require welds which can withstand the stresses and high temperatures experienced in operation.
Bridges must take into account the effect of differing vehicle loads and wind loading.
Oil rigs are designed to withstand the effect of wave formation and wind loads
Earth moving equipment has to accommodate differences in terrain and earth conditions and is subject to fatigue loading.
Welds in food processing plants must withstand corrosion by hot acidic liquors.
Welding is the process of joining different materials. Weld is a localized coalescence of metals with or without application of pressure and filler metal.
Classification Of Welding
Based on mode of energy transfer.
Electrical to heat energy – Arc
Mechanical to heat energy – friction welding
Chemical to heat energy – Gas
Light to heat energy – lazer welding
Sound energy – ultrasonic welding
Type Of Interaction
Fusion welding : Liquid / liquid
Solid state welding: solid / solid
Fusion welding: Base metal is fused. Do Not require application of pressure.
Welding is performed with / without addition of filler metal.
Solid state welding: In this method, two sides of a joint are brought in to intimate atomic contact either by mechanical deformation or by atomic diffusion or combination of both.
Pressure butt welding is used to join tube ends by the action of heat generated by electric arc or electric resistance across the joint.
Mode Of Welding
Manual: welding operation is performed and controlled by hand. Two movements are involved ie. feed of electrode and weld speed.
Semi automatic: Instead of stick electrode, wire electrode is used. Wire electrode is drawn and fed by a motorized wire feeder into the torch. Wire feeding is automatic. Welding speed is manual. ( MIG welding).
Mechanized welding: Motors control both wire feeding and welding speed. Loading and unloading of work is manual. Example: SAW
Automatic Welding: Entire welding operation is performed without constant observation and adjustment of controls by an operator.
Soldering: Joining of different materials by the action of heat. Filler is used. Filler metal, melting temperature should be less than 450 ° C
Brazing: Joining of different materials by the action of heat. Filler is used. Filler metal, melting temperature should be more than 450 ° C
Types Of Weld:
Butt Weld
Fillet weld
Edge Weld
Spot Weld
Type Of Joint:
Butt
Tee
Corner
Lap
Different Positions:
Flat
Horizontal
Vertical
Overhead
Inclined
Flux:
To protect from atmospheric contamination
Arc stabilization
To add alloying elements
To increase metal deposition
To improve penetration and surface finish
To limit spatters
To prevent cracking.
To remove impurities
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