Welding

Welding

Welding is a process of joining similar and dissimilar metals or other material by application of heat with or without application of pressure and addition of filler material.”
Or
“Welding is a fabrication process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing fusion.”

Welding is distinct from lower temperature metal-joining techniques such as brazing and soldering, which do not melt the base metal. It is used as permanent fasteners. Welding is essential process of every manufacturing industries such as computer industries, mechanical industries, petroleum industries, chemical industries etc.


Need of Welding

1. It is a permanent joint that provided adequate strength as per the requirement.
2. Welding done in a organized way will provide leak-proof joint.
3. Components of thicker dimensions can be joined through welding in a convenient way.
4. From cars to planes and bridges to buildings, welding keeps our economy moving.

Classification of Welding

Welding process can also be classified as follows:
1. Gas Welding
(i) Oxy-Acetylene Welding
(ii) Oxy-Hydrogen Welding
(iii) Pressure Gas Welding
(iv) Air-Acetylene Welding

2. Arc Welding
(i) Carbon Arc Welding
(ii) Shield Metal Arc Welding
(iii) Submerged Arc Welding
(iv) Metal Inert Gas Welding (MIG or GMAW)
(v) Tungsten Inert Gas Welding (TIG or GTAW)
(vi) Electro Slag Welding
(vii) Plasma Arc Welding
(viii) Electro-gas Arc Welding
(ix) Stud Arc Welding

3. Resistance Welding
(i) Spot Welding
(ii) Projection Welding
(iii) Resistance Butt Welding
(iv) Seam Welding
(v) Flash Butt Welding
(vi) Percussion Welding
(vii) High Frequency Resistance Welding

4. Solid State Welding
(i) Forge Welding
(ii) Cold Welding
(iii) Friction Welding
(iv) Explosive Welding
(v) Diffusion Welding
(vi) Ultrasonic Welding

5. Thermo-Chemical Welding
(i) Thermit Welding
(ii) Atomic H2 Welding

6. Radiant Energy Welding
(i) Electron Beam Welding
(ii) Laser Welding

On the basis of joining process-

1. Homogeneous Process- In this process filler rod or electrode are used & two same metal is joining no pressures is applied. For Example- Gas Welding.

2. Heterogeneous Process- In this process filler metal is soluble in both the parent metal which themselves are soluble in each other. For Example – TIG Welding, MIG Welding etc.

3. Autogeneous process- In this type of welding no filler rod is used but pressure is extremely used. For Example- Resistance welding, Forged Welding, Friction Welding, Diffusion Welding etc.

Base Metal of Welding

1. Ferrous Metal – It’s contain the iron as a main constituent.
  • Wrought Iron.
  • Cast Iron.
  • Carbon Steels ( Low, Medium & High).
  • Cast Steel.
  • Alloy Steels.
  • Stainless steels.
2. Non-ferrous Metal – It’s not contain iron.
  • Aluminium & it’s alloys.
  • Copper & it’s alloys.
  • Magnesium & it’s alloys. etc.
Advantages of Welding

1. As no hole is required for welding, hence no reduction of area. So structural members are more effective in taking the load.
2. In welding filler plates, gusseted plates, connecting angles etc. are not used, which leads to reduced overall weight of the structure.
3. Welded joints are more economical as less labor and less material is required.
4. The efficiency of welded joint is more than that of the riveted joint.
5.The welded joints look better than the bulky riveted/butted joints.
6. The speed of fabrication is faster in comparison with the riveted joints.
7. Complete rigid joints can be provided with welding process.
8. The alternation and addition to the existing structure is easy.
9. No noise is produced during the welding process as in the case of riveting.
10. The welding process requires less work space in comparison to riveting.
11. Any space of joint can be made with ease.

Disadvantages of Welding

1. Welded joints are more brittle and therefore their fatigue strength is less than the members joined. 
2. Due to uneven heating & cooling of the members during the welding, the members may distort resulting in additional stresses. 
3. Skilled labor and electricity are required for welding. 
4. No provision for expansion and contraction is kept in welded connection & therefore, there is possibility of racks. 
5. The inspection of welding work is more difficult and costlier than the riveting work. 
6. Defects like internal air pocket, slag inclusion and incomplete penetration are difficult to detect.
7. Jig and fixture are generally required to hold & position the part to be weld.
8. Edge preparation of the work piece is generally required welding them.
9. Welding heat produces metallurgical changes. The structure of the welded joint is not the same as that of parent metal.

Applications of Welding

1. Automobile Industries.
2. Aircraft Industries.
3. Building Construction.
4. Bridge Construction.
5. Pressure Vessel & Tank.
6. Railroad Industries.
7. Pipeline Industries.
8. Petrochemical Industries.
9. Earth moving Equipment & Machinery.
10. Shipbuilding Industries.
11. Truck & Trailers.
12. Machine tool frame, cutting tools & dies.

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