Introduction to Welding

The process of joining similar metals by the application of heat is called "welding'. It is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence. It is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint.

Welding can be obtained with or without application of pressure and with or without addition of filler metal. During welding, the edges of these metal pieces are either melted or brought to the plastic condition.

The welding process is used for making permanent joints which are obtained by homogenous mixture of two materials. The heat may be developed in several ways for welding operation. A good welded joint is as strong as the parent metal.

Nowadays, welding finds wide spread applications in almost all branches of engineering industries. Welding is extensively employed in the fabrication and erection of steel structure in industry and construction e.g. structural joints of bridges and buildings, pipelines etc. It is also used in various industries such as aircraft frame works, railway wagons, furniture, automobile bodies, ship building etc. depending upon their applications.

1. Advantages of Welded Joints

1. Complete rigid joints can be provided with welding process.

2. Welded joints are more economical as less labor and less material are required.

3. A welded joint has a great strength. Often, a welded joint has the strength of the parent metal itself.

4. The efficiency of welded joint is more than the riveted joint.

5. The welded joints look better than bulky riveted/butted joints.

6. As no hole is required for welding, there is no reduction of area. So, the structural members are more effective in taking the load.

7. In welding filler plates, gusseted plates, connecting angles etc., are not used which lead to reduced overall weight of the structure.

8. The speed of fabrication is faster in comparison with the riveted joints. 

9. No noise is produced during welding process similar to riveting process. 

10. The welding process requires less work space in comparison to riveting. 

11. Any space of joint can be made with ease.

12. Welded structures are smooth in appearance. Therefore, it looks pleasing.

2. Disadvantages of Welded Joints

1. Welded joints are more brittle and therefore, their fatigue strength is less than members joined.

2. Since the joint is made permanent, it is not easy to modify the structure, once welding is done.

3. Due to uneven heating and cooling of the members during welding, the members may distort which results additional stresses.

4. Skilled labour is required for welding.

5. Electricity is required for welding. Therefore, welding is not possible in remote locations.

6. No provision for expansion and contraction is kept in welded connection. Therefore, there is a possibility for the formation of cracks.

7. The inspection of welded joints is more difficult and costlier than riveted joints.

8. Defects such as porosity, slag inclusion and incomplete penetration are difficult to detect.