Welding-Definition, Classification in details (Arc, Gas and Resistance Welding), Advantages, Disadvantages and Application, PDF


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Welding process

  • Welding is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpiece and adding a filler material from a pool of molten material that cools to become a strong joint, but Sometimes the pressure is used in conjunction with heat, or by itself, to produce the weld. This is in contrast with soldering and brazing which involves melting a lower-melting-point material between the workpiece to form a bond between them, without melting the workpiece. Another definition is,
  • The welding process is a material joining process which process, which produces coalescence of Material by heating them to suitable temperature with or without application of pressure or by the application of pressure alone and with or without the use of filler materials.

Types of Welding Process:

Welding Processes and their Letter designation:

Group Welding Process Letter designation


Arc welding

  • Carbon Arc
  • Flux cored Arc
  • Gas Metal Arc
  • Gas Tungsten Arc
  • Plasma Arc
  • Shielded Metal Arc
  • Stub Arc
  • Submerged Arc
  • Atomic hydrogen
  • CAW
  • FCAW
  • GMAW
  • GTAW
  • PAW
  • SMAW
  • SW
  • SAW
  • AHW

Oxyfuel Gas

  • Oxyacetylene
  • Oxyhydrogen
  • Pressure gas welding
  • OAW
  • OHW
  • PGW


  • Flash welding
  • High-frequency Resistance
  • Percussion 
  • Projection
  • Resistance-seam
  • Resistance-spot
  • Upset welding
  • FW
  • HFRW
  • PEW
  • RPW
  • PEW
  • RESW
  • UW


Solid state and

  • Cold 
  • Diffusion
  • Explosion
  • Forge
  • Friction
  • Hot pressure
  • Roll
  • Ultrasonic Welding
  • CW
  • DFW
  • EXW
  • FOW
  • FRW
  • HPW
  • ROW
  • USW

Another welding process

  • Electron Beam
  • Electroslag
  • Induction
  • Laser beam and
  • Thermit welding
  • EBW
  • ESW
  • IW
  • LBW
  • TW

The above table represents the classification of welding. I know there are a few types of welding you might not hear about it but don’t worry I will explain only those welding process which you have to study in details. If you want all the welding process in details just comment down I will provide you the link. So let’s start,

Arc welding :

  • Arc welding is a welding process that is used to join metal to metal by using electricity to create enough heat to melt metal, and the melted metals when the cool result in a binding of the metals. Or
  • Arc welding is one of several fusion processes for joining metals. By applying intense heat, metal at the joint between two parts is melted and caused to intermix directly, or more commonly, with an intermediate molten filler metal. Upon cooling and solidification, a metallurgical bond is created. Since the joining is an intermixture of metals the final weldment potentially has the same strength properties as the metals of the parts.
  • A problem that arises in arc welding is contamination of the metal with elements in the atmosphere (O, H, N, etc). There can also be a problem with the surface that is not clean. 
  • The solution to this Includes,
    1. Gas shields: An inert gas is blown into the weld zone to drive away other atmospheric gases.
    2. Flux: A material that is added to clean the surface this may also give off a gas to drive away unwanted gases.

Let’s understand by an Arc welding circuit diagram:

Arc welding circuit diagram:

  • An AC or DC power sources, fitted with whatever controls may be needed, is connected by work cable to the workpiece and by an electrode cable to electrode holder of some type, which makes electrical contact with the welding electrode.

ARC Welding process

  • An arc is created across the gap when the energized circuit and the electrode tip touches the workpiece and is withdrawn yet still within close contact. The arc produces a temperature of about 6500-degree centigrade at the tip. This heat melts both the base metal and the electrode producing a pool of molten metal sometimes called a creator. The creator solidifies behind the electrode as it is moved along the joint. This result is a fusion bond.

Advantages of Arc welding:

  • The process gives high deposition rates.
  • Welding speed is high.
  • Wire consumption is low.
  • The consumption of electrical energy is low, as a maximum of 97 % of heat energy can be utilized.
  • Any length can be welded without any interruption.
  • High-quality Welds are achieved with no fusion defects, no porosity and slag inclusions.

Disadvantages of Arc welding:

  • Arc is invisible, it can be controlled only by measuring arc voltage and current.
  • It can be used only in the down hand welding position.

Gas welding:

  • Gas welding is a type of liquid state welding process, in which fuel gases burns to generate heat.
  • This heat is used to melt interface surfaces of welding plates which are held together to form a joint.
  • In this welding process, mostly oxy-acetylene gas is used as working fuel gas.
  • This process can be done with or without the help of filler material.

Main component or Equipment of Gas Welding:


Oxygen and acetylene are stored under pressure in a steel cylinder. They are seized by the amount of oxygen or acetylene that they hold. Cylinders should always be secured and used in the upright position. When a cylinder is not being used the valve cap should always be in place.

Oxygen cylinders:

These cylinders are made of Steel and are usually painted green. They contain compressed oxygen at presses that can be as high as 2200 PSI. All cylinders have valves and are fitted with a screw on steel cap that protects the cylinder valve when the cylinder is not in use.

Acetylene cylinders:

These cylinders contain acetylene under pressure are painted black made of steel and have cylinder valves. The cylinders contain a porous filler material which is fitted with acetone that allows the acetylene to be safely be contained in the cylinder at 250 PSI. Acetylene should never be used at a pressure that exceeds 15 PSI as it becomes highly unstable which depending upon the condition could cause it to decompose and explode.

Pressure regulator:

Both oxygen and fuel gases are filled in the cylinder at high pressure. These gases cannot use at this high pressure for welding works, So a pressure regulator is used between the flow. It supplies oxygen at a pressure about 70 – 130 Kn/m2 and gas at 7 – 103 Kn/m2  to the welding torch.


The torch assembly consists of the handle Oxygen and fuel gas valves and the mixing chamber. Welding tips or cutting attachment can be used with the handle the allowing it to be used for welding, heating and cutting operations. Oxygen and fuel gas flow through tubes inside the handle which blend in the mixing chamber or tip. it is at the tip that the mixed gas is ignited.

Goggles and Gloves:

These two Goggles and Gloves are used for safety purpose. Goggles protect eyes and Gloves protects the hand from radiation and flame of fire.

Types of Flames:

Neutral Flame:

Welding process

Welding is generally carried out using the neutral flame sitting which has equal quantities of oxygen and acetylene.

Oxidizing Flame:

Welding process

The oxidizing flame is obtained by just increasing the oxygen flow rate.

Carburising or Reducing Flame:

Welding process

The carburizing or reducing flame is achieved by increasing acetylene flow in relation to oxygen flow. Because steel melts at a temperature of 1500 degree centigrade the mixture of Oxygen and acetylene is used as it is the only gas combination with enough heat to weld Steel. However other gases such as propane hydrogen and coal gas can be used for joining lower melting point of metals and for brazing and silver soldering.

Gas welding working:GAS Welding process

As the figure shows all the equipment are set carefully and now the gas cylinder and oxygen cylinder connected to the welding torch through pressure regulators. Now the regulate pressure of gas and oxygen supplied to the torch where they properly mixed. The flame is ignited by a striker. Take care the tip of a torch is pointing downward. Now the flame is controlled through valves situated in the welding torch. The flame is set at the natural flame or carburizing flame or oxidizing flame according to the welding condition. Now the welding torch moved along the line where joint to be created. This will melt the interface part and join them permanently.

3 Types of technique in gas welding:

  • Leftward technique:

The leftward technique is used almost exclusively and is Ideally suited for welding butt, fillet, and lap joints in sheet thickness up to approximately 5 mm.

  • Rightward technique:

The rightward technique finds an application on plate thickness above 5 mm for welding in the flat and horizontal-vertical position.

  • All positional rightward technique:

The all positional rightward method is a modification of the rightward technique and is ideally suited for welding steel plate and in particular pipework where positional welding (vertical and overhead) has to be carried out.

Advantages of Gas welding:

  • Process is versatile
  • Adapted too many different jobs
  • Equipment is relative to low cost
  • Portable
  • Self-sufficient
  • Independent from the availability of external energy sources.

Disadvantages of Gas welding:

  • Welders skill required in manipulating the torch, the flame, and the filler Rod.
  • Flux required for most materials other than low Carbon Steel.
  • Reactive or refractory metals are unsuited to gas welding.
  • Slow metal joining rate.

Application of Gas welding:

  • For joining thin materials.
  • For joining most ferrous and nonferrous materials.
  • Used in automatic and aircraft industries and sheet metal fabrication.

Resistance Welding:

  • Resistance welding is one of the oldest of the electric welding process is used by industry today. The weld is made by the combination of the heat, pressure and time.
  • All resistance welding spot welding, seam welding, projection welding, etc. are worked on the same principle of heat generation due to electric resistance.

  • When a current passes through an electric resistance, it produces heat. This is the same principle which is used in the electric coil. The amount of heat produced depends on the resistance of the material, surface conditions, a current supplied, time duration of current supplied etc. This heat generation takes place due to the conversion of electric energy into thermal energy.  The current is the same in the whole circuit. Heat is proportional to the product of resistance by the square of the current and by time. therefor The heat generation equation is  (H=I2Rt). 
  • Where H=Heat generated in joules.
    I=Current in amperes. 
    R=Resistance in omes. 
    T=flow time of the current in seconds.
    The highest Heat is developed where the resistance is at its maximum, exactly where it is needed for this process.

Resistance Welding Equipment:

  • The main requirement of the process is the low voltage and high current power supply. This is obtained by means of a step-down Transformer with a provision to have different tapping on the primary side, as required for different materials. The secondary windings are connected to the electrodes which are made of copper to reduce their electrical resistance. The time of the Electric Supply needs to be closely controlled so that the heat released is just enough to melt the joint and the subsequent fusion takes place due to the force (Forge welding) on the joint. The force required can be provided either mechanically, hydraulically or pneumatically as shown in the figure. To precisely control the time sophisticated electronic timers are available.

RESISTANCE Welding process

  • The critical variable in the resistance welding process is the contact resistance between the two workpiece plates and their resistance themselves. The contact resistance is affected by the surface finish on the plate since the rougher surface has higher contact resistance. The contact resistance also will be affected by the cleanliness of the surface. Oxides or other contaminants if present, should be removed before attempting resistance welding.

Defects, Advantages, and Disadvantages of Resistance Welding:

Defects in Resistance Welding:

  • Cracks
  • Electrode deposit on work
  • Porosity or cavities
  • Pinholes
  • The electrode indentation
  • Improper weld penetration

Advantages of Resistance Welding:

  • Capable of a high degree of process control
  • Capable of a high degree of mechanization
  • Good Mechanical properties
  • high-speed welding
  • Easily automated
  • Suitable for high rate production
  • Economical

Disadvantages of Resistance Welding:

  • High equipment and tooling costs.
  • Limitation of joint design requirements
  • Initial equipment costs
  • Lower tensile and fatigue strength
  • Irregularly shaped welds

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