Welded Joints

 A welded joint is a permanent joint which is obtained by the fusion of the edges of the two parts to be joined together, with or without the application of pressure and a filler material. The heat required for the fusion of the material may be obtained by burning of gas (in case of gas welding) or by an electric arc (in case of electric arc welding). The latter method is extensively used because of greater speed of welding.

 Welding is extensively used in fabrication as an alternative method for casting or forging and as a replacement for bolted and riveted joints. It is also used as a repair medium e.g. to reunite metal at a crack, to build up a small part that has broken off such as gear tooth or to repair a worn surface such as a bearing surface.

 

 Advantages and Disadvantages of Welded Joints over Riveted Joints

 Following are the advantages and disadvantages of welded joints over riveted joints.

 Advantages

o   The welded structures are usually lighter than riveted structures. This is due to the reason, that in welding, gussets or other connecting components are not used.

o   The welded joints provide maximum efficiency (may be 100%) which is not possible in case of riveted joints.

o   Alterations and additions can be easily made in the existing structures.

o   As the welded structure is smooth in appearance, therefore it looks pleasing. 

o   In welded connections, the tension members are not weakened as in the case of riveted joints. 

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

o   Sometimes, the members are of such a shape (i.e. circular steel pipes) that they afford difficulty for riveting. But they can be easily welded. 

o   The welding provides very rigid joints. This is in line with the modern trend of providing rigid frames.

 

Disadvantages

·         Since there is an uneven heating and cooling during fabrication, therefore the members may get distorted or additional stresses may develop.

·         It requires a highly skilled labour and supervision.

·         Since no provision is kept for expansion and contraction in the frame, therefore there is a possibility of cracks developing in it.

·         The inspection of welding work is more difficult than riveting work.