Percussion Welding | Advantages and Disadvantages

It is one type of resistance butt-welding process. The parts to be welded are clamped in copper jaws of the welding machine in which one clamp is fixed and other one is movable. The movable clamp is backed up against the pressure from a heavy spring. The jaws act as
electrodes. Heavy electric current is connected to the workpieces. Now, the movable clamp is released rapidly and it moves forward at high velocity. When the two parts are approximately 1.6 mm apart, a sudden discharge of electrical energy is released thereby causing an intense arc between two surfaces. The arc is extinguished by the percussion blow of the two parts coming together with sufficient force to complete in 0.1 second. No upset or flash occurs at the weld. This method is primarily employed to join dissimilar metals. This method is limited to small areas of about 150 to 300 mm2.

Welding energy, E = 1/2 CV2

where
E = energy in watt-seconds (Joules)
C = capacitance in farads
V = voltage.

Amount of energy required to make joint depends on the following factors.
(i) Cross-sectional area of joint
(ii) Properties of work metal or metals
(iii) Depth to which metal is melted on workpieces.

Advantages of Percussion Welding:

1. The time cycle involved is very short.
2. Shortness of arc limits melting and heating.
3. Heat-treated and cold worked materials can be welded without annealing.
4. No filler metal is required.
5. No cast structure is produced at interface.
6.Charging rate is low and controlled.
7. It can tolerate some contamination on faying surface.
8. Welding of dissimilar metal and copper to steel is possible.
9. These welders have a long wear life for welding jaws due to very short relatively low current welding pulse.
10. Welding of metals with high melting point such as tungsten, molybdenum etc. are possible by this method.

Limitations of Percussion Welding:

1. The welding process is limited to butt joints.
2.Total area is limited.
3. Similar metals can usually be joined more economically by other processes.
4.The process is usually confined for joining of dissimilar metals not normally considered weldable.
5. Welding is typically dirtier and less smooth than resistance welding.
6. With nib start precussive arc welding, a starting nib must be cut onto workpieces.
7. The workpieces must be free of oil or dirt.