What is welding? Types of Welding I Welding symbols

Welding is usually preferred to melt the separate pieces of metal or alloys by heat or pressure to be welded together and fuse into a single seamless piece. The metal parts that are melted together are called base metal, additional metal called filler is often added to the process.Types of Welding
Ancient and traditional welding process includes soldering and braze welding, more modern techniques to have a good fusion and composition of metals are
  • Oxyacetylene welding,
  • Gas-metal arc welding or MIG
  • Gas-tungsten arc welding or TIG
  • Shielded-metal arc welding or STICK
  • Energy beam and  plasma arc welding. 
There is not such an area in the metallurgical industry where welding is not used. In airplane and automobile industry, oil and gas, machine tools, heavy industry welding techniques are practiced extensively.
Before going to the welding types, let’s be familiar with some of the essential facts that needs to be uncovered.


Different types of metals have different types of characteristics that effect the welding capabilities and precision's. Base metal of the same type is welded together and filler is added. For this accomplishment, the base metal and filler must have the same characteristics and melting point.  The amount of carbon in the steel and alloys results in applying various welding techniques.

A chart reflecting welding techniques and melting point of some metal is given below

Welding joint types

The basic founding joints in welding are butt joint, lap joint, corner joint (open and closed corner joint), T-joint, edge joint and saddle joint.Now let’s be clear about the joint types:

Butt joint

The butt joint is where two pieces of base metal is placed side by side each other in the same plane or in parallel. When the surface is beveled groove weld is used.

Lap joint

Two metal pieces are overlapped in the same plane over each other. Fillet weld is used in lap joint.

Corner joint

Forms when two metal parts are welded together at the corner at a right angle. And forms letter“L”.

T Joint 

Two metal pieces placed together in 90° angle to form”T” shape .

Welding symbols

Welding blueprints uses symbol to indicate welding types and locations. The specification is consisted of arrows and a reference line that denotes in where the weld is located.Some of the symbols are:
(Welding area is indicated by red color)

Types of Welding

  1. Oxyacetylene welding.
  2. Shielded metal arc welding.
  3. Gas-metal arc welding.
  4. Gas-tungsten arc welding.
  5. Plasma arc welding.

Oxyacetylene welding

Oxy-fuel welding with acetylene is called oxyacetylene welding but widely known as gas welding. It is the process that uses the relevant heat from a gas flame to melt down the base metal and cause it to join together. The gas flame can be generated from fuel gases like acetylene, propane, butane, natural gas and MPS (methyl acetylene propa-dine). The combustion temperature of the relative fuel is around 5000-6300° F. it is less expensive and can weld any thickness of metal.

Equipment: oxygen and acetylene cylinder, regulators, gauges, torch, tips, hose.

Shielded metal arc welding or STICK

In this welding process the base metal is heated to a proximate welding temperature by the electric arc. The arc is covered with a shielding flux and provide necessary shielding for the welding process. It is expensive, easier to carry used in construction, repair work etc. 

Equipment: knob, lead electrode, electrode holder, ground clamp, power supply. The electrode should be changed frequently.

Gas-metal arc welding

Gas- metal arc welding is also be called as metal inert gas or MIG. In this technique a consumable electric wire is used that acts like the filler, the wire doesn’t contain or is coated with any flux. To protect the molten puddle from reacting shielding gas (argon, carbon dioxide) is simultaneously supplied during the operation. It is smooth, clean and relatively cool.

Equipment: power supply, torch, electrode, gas cylinder, gas flow meter.

Gas-tungsten arc Welding

Gas-tungsten arc welding is also be called as tungsten inert gas (TIG). In this process a non-consumable tungsten electrode is used, to protect the welding area from atmospheric contamination shielding inert gas is supplied during the operation. It differs from MIG because the electrode is non-consumable and doesn’t act as a filler. It is much cleaner and versatile process.

Equipment: constant power supplier, torch, clamp, electrode, inert gas cylinder and regulators.

Plasma arc welding (types of welding)

In plasma arc welding process welding is performed by consumable tungsten electrode, high temperature-high velocity ionized plasma gas is being delivered throughout the copper nozzle during the operation. It is familiar to the TIG welding but is more versatile in speed, distortion, deeper penetration and considerably steady arc.

Equipment: laser torch, power supply, filler, plasma console, water cooled liquid, gas cylinder.

Energy source for welding operation

Since there is a variety of arc welding available so does the energy source during the welding operation.
  • In oxyacetylene welding technique the oxygen and acetylene must be kept in a pressurized cylinder and should be kept in upright position.
  • In STICK welding DC current supply must be preferred because of wide range of advantages like wide welding area, thickness position and penetration.
  • In MIG welding DC power supply should be recommended for having a steady arc. One can also adjust the voltage, polarity and wire rate feed.
  • In TIG welding metals like aluminum, magnesium that are used for welding requires AC current but when dealing with stainless steel DC polarity is required.
  • Plasma arc welding requires a compressed air source and a constant high voltage DC power supply unit to deliver high intensity plasma gas to the torch.


It is extremely important to follow the basic welding safety rule and manufacture’s safety guidelines. Keep in mind that your dealing with very high voltage arc and pressurized cylinder.
Some of the safety equipment:
  1. Safety glasses.
  2. Leather seal boots.
  3. Low-profile respirator mask.
  4. Welding helmet.
  5. Welding gloves.
  6. Welding cap.
  7. Heat reductant jacket.

Types of welding

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