mes - ii, 5.welding

8/4/2019 MES - II, 5.Welding

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Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA

MECHANICAL ENGG. SCIENCE

CHAPTER 5

| WELDING }

By, Akshatha C. Kamath



W ELDING

Welding is a process of joining similar metals by the application of heat with or without the

application of pressure & addition of filler materials.

* Welding rods or Filler rods are used for providing the

extra metal to the weld.

* Flux material is applied to the parts being welded to

prevent the formation of oxides.* Parts being welded are called the base metals or the

parent metals.



TYPES OF W ELDING

Plastic ( Pressure ) Welding I n this process, the piecesof metal to be joined are heated to a very high

temperature i.e. plastic state & then forged together

by external pressure.

Fusion ( Non ± pressure ) Welding I n this process, the

pieces to be joined are heated to a molten state & then

allowed to solidify.



CLASSIFICA T ION

Welding

Pressure Process Fusion Process

Forge Resistance Thermit Arc Gas

Welding Welding Welding Welding Welding

* Spot * Metal Arc

* Butt * Atomic Hydrogen

* Seam * Carbon Arc

* Percussion



ELEC TR IC AR C W ELDING

Slag covering Electrode holder Flux coated AC / DC power supply

electrode Core wire

Weld Electric arc

Gaseous Shield

Job

Crater Molten pool



AR C W ELDING OPE R A T IONS

* Arc Welding Power Source ( AC or DC type )

* Welding Cables

* Electrode Holder * Ground Clamp

* Welding Electrodes

* Helmet or Shield

* Protective Clothing

* Chipping Hammer

* Wire brush



DC PO W E R SOUR CE

DCSP ( Direct Current Straight Polarity )

* Job is connected to + ve terminal & Electrode to ± ve terminal

* 66.66 % ( 2/3 rd ) of heat is supplied to the job.

* 33.33 % ( 1/3 rd ) of heat to the electrode.

* Used of deep penetration.

DCR P ( Direct Current Reverse Polarity )

* Job is connected to - ve terminal & Electrode to + ve terminal

* 66.66 % ( 2/3 rd ) of heat is supplied to the electrode.

* 33.33 % ( 1/3 rd ) of heat to the job.

* Used of less penetration.



AC PO W E R SOUR CE

* There is equal heat distribution at the electrode as

well as at the job.

* No polarity is maintained.

* I t is used for normal penetration.



W EL DING ELEC TR ODES

Consumable Electrodes

* They are made up of materials having a low melting

point.* They are made up of different metals & their alloys.

* When the arc is struck, the electrode melts & transfers

to the job in the form of droplets.



W EL DING ELEC TR ODES

Non ± Consumable Electrodes ( Bare Electrodes )

* They are made up of materials having a high melting

point like Carbon, Tungsten, Graphite««.* Copper coated Carbon or Germanium electrodes are

commonly used.

* The electrodes don¶t melt during welding.

* They maintain an arc which melts the base metals.

* Filler metal addition depends on the plate thickness.



FLUX COA T ING INGR E DIEN T S

* Silicates of Sodium, Magnesium, Al, I ron oxide, Mica produce a slag layer on the molten metal & prevent atmospheric contamination.

* Cellulose, wood, Calcium carbonate form a protective gas shield to prevent combination.

* Calcium carbonate, Potassium silicate add stability tothe arc.

* Coating improves arc penetration & surface finish.* Flux provides a quiet arc & an easily removable slag.

* I t saves the welder from radiations emitted from theelectrodes.

* I t improves metal deposition rates.



W EL DING APPLICA T IONS

The applications of Welding are many. Some of themare as follows :

* I n fabrication & repair work.

* I

n welding metals & their alloys.* I n fabrication of air receiver, boiler, tank, joining

pipes, pressure vessels, building & bridge

construction, automobile & aircraft industry, etc..

mes - ii, 5.welding

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