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Chapter: Mechanical : Manufacturing Technology : Metal Joining Process

Welding and Types of welding

Types of welding 1)GAS Welding 2)ARC Welding



Welding is a materials joining process which produces coalescence of materials by heating them to suitable temperatures with or without the pplication of pressure or by the application of pressure alone, and with or without the use of filler material. Welding is used for making permanent joints. It is used in the manufacture of automobile bodies, aircraft frames, railway wagons, machine frames, structural works, tanks, furniture, boilers, general repair work and ship building.


Types of welding


GAS Welding


ARC Welding




Sound weld is obtained by selecting proper size of flame, filler material and method of


moving torch

The temperature generated during the process is 33000c.


When the metal is fused, oxygen from the atmosphere and the torch combines with molten metal and forms oxides, results defective weld


Fluxes are added to the welded metal to remove oxides


Common fluxes used are made of sodium, potassium. Lithium and borax. Flux can be applied as paste, powder, liquid. solid coating or gas.




1. Gas Cylinders Pressure


Oxygen  125 kg/cm2 Acetylene  16 kg/cm2


2. Regulators


Working pressure of oxygen 1 kg/cm2 Working pressure of acetylene 0.15 kg/cm2


Working pressure varies depends upon the thickness of the work pieces welded.

3. Pressure Gauges

4. Hoses

5. Welding torch


6. Check valve

7. Non return valve




Three basic types of oxyacetylene flames used in oxyfuel-gas welding and cutting operations:


(a) neutral flame;  (b) oxidizing flame; (c) carburizing, or reducing flame.


Addition of more oxygen give a bright whitish cone surrounded by the transparent


blue envelope is called Neutral flame (It has a balance of fuel gas and oxygen) (32000c)

•        Used for welding steels, aluminium, copper and cast iron


oxygen give a bright whitish cone surrounded by the transparent

blue envelope is called Neutral flame (It has a balance of fuel gas and oxygen) (32000c)

•  Used for welding steels, Aluminium, copper and cast iron.



Oxygen is turned on, flame immediately changes into a long white inner area (Feather)


surrounded by a transparent blue envelope is called Carburizing flame (30000c)


Advantages of Gas welding.


1.Simple Equipment 2.Portable 3.Inexpensive

4.Easy for maintenance and repair


Disadvantages Of Gas welding


1.Limited power Density 2.Very low welding speed.


3.High total heat input per unit length 4.Large Heat affected Zone

5.Severe Distortion

6.Not recommended for welding reactive metals such as titanium and Zirconium.


Difference between Gas Welding and Arc Welding





1. Heat is produced by the Gas Flame

2. The Flame temperature is about 3200oC

3. Separate Filler rod introduced

4. Suggested  for thin materials

5. Gas welded parts do not have much strength

6. Filler metal may not be the same parent metal

7. Brazing and soldering are  done using gas





1. Heat is produced by Electric Arc

2. The temperature of Arc is about 4000oC

3. Arc Producing as well as filler rod material is the  electrode.

4. Suggested for medium and thick materials

5. Arc welded parts have very high strength

6. Filler metal must be same or an alloy of the parent  metal

7. Brazing and soldering can’t be carried out by electric arc.






Uses an electric arc to coalesce metals

Arc welding is the most common method of welding metals


Electricity travels from electrode to base metal to ground



1.Arc welding Equipments

• A welding generator (D.C.) or Transformer (A.C.)


      Two cables- one for work and one for electrode


     Electrode holder




     Protective shield




     Wire brush


     Chipping hammer







Electrode is a thin rod made up of same as that of parent material. Flux is coated over the electrode to avoid oxidation. It is mostly connected to the negative polarity.


Two Basic Types of AW Electrodes

Consumable  consumed during welding process Source of filler metal in arc welding


Nonconsumable  not consumed during welding process


Filler metal must be added separately


Consumable Electrodes

Forms of consumable electrodes


        Welding rods (a.k.a. sticks) are 9 to 18 inches and 3/8 inch or less in diameter and must be changed frequently


        Weld  wire  can  be  continuously  fed  from  spools  with  long

lengths  of  wire, avoiding frequent interruptions


In both rod and wire forms, electrode is consumed by arc and added to weld joint as filler metal.


Nonconsumable Electrodes

Made of tungsten which resists melting


Gradually depleted during welding (vaporization is principal mechanism) Any filler metal must be supplied by a separate wire fed into weld pool




A substance that prevents formation of oxides and other contaminants in welding, or dissolves them and facilitates removal


Provides protective atmosphere for welding Stabilizes arc


Reduces spattering





      Prepare the edges to be joined and maintain the proper position


      Open the acetylene valve and ignite the gas at tip of the torch


      Hold the torch at about 45deg to the work piece plane


      Inner flame near the work piece and filler rod at about 30  40 deg


        Touch filler rod at the joint and control the movement according to

the flow  of the material



Most efficient way to join metals


Lowest-cost joining method


Affords lighter weight through better utilization  of materials


Joins all commercial metals


Provides design flexibility



•  Manually applied, therefore high labor cost.


      Need high energy causing danger


      Not convenient for disassembly.


      Defects are hard to detect at joints.



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