Percussion or Percussive welding is similar to flash welding except that the arc is produced by the rapid discharge of stored electrical energy across an air gap between the ends of the work pieces to be welded. It belongs to a family of joining techniques generically referred to as percussion or stud welding. The weld is affected by the heat produced by the arc with pressure percussively (rapidly) applied immediately following the electric discharge.
The pieces to be welded are held in two clamps as for flash welding. One of the clamps in stationery while the other is mounted in a slide and backed up against a heavy spring. When the movable clamps is released it advances rapidly towards the fixed clamp carrying the work piece.
As the distance between the ends of the work pieces reduces to less than about 1.5 mm, then the stored electric energy causes intense arcing over the surfaces raising the temperature. As the two parts come together the arc is extinguished due to the percussion blow.
The energy required for causing the discharge may be built up either by the electrostatic method using a capacitor or by the electromagnetic method using a collapsing magnetic field linking the primary and secondary windings of an inductive device or transformer. A Protective gas shield around the weld may be provided when welds of very high quality are desired. The process is used in the butt welding of bars, rods, tubes and pipes. Theses welding machines are built for automatic operation and have pre-set controlled parameters at each stage of the cycle.
History of Percussion Welding:
Percussive arc welding has been around for years, but it’s only recently that technology capability and commercial demand have converged to expose some genuine component production advantages. Percussion welding has the best features of 19th century technology. It is a “heat it and beat it” method that can be readily automated using straight forward electromechanical tooling.
Welding force may be applied by:
3. Spring force or
4. Gravity (falling weights).
Power Supplies for Percussion Welding:
(i) Low voltage (10 to 150 volts DC) / High voltage (1000 to 6000 volts DC).
(ii) Electromagnetic, Capacitive storage or Inductive storage.
(iii) Low voltage (10 to 35 volts) AC that uses a transformer to furnish the welding voltage.
Advantages of Percussion Welding:
1. The action takes place in a very little time, usually less than 0.1 Seconds
2. It causes very little damage to material close to the weld.
3. Hardened surfaces may be welded without any danger of annealing.
4. As the heat is concentrated at the ends of the work pieces heat balance is not much of a problem.
5. Parts with different thermal conductivities or different masses can be easily welded.
Disadvantages of Percussion Welding:
1. The process cannot be used for welding heavy sections larger than 600 mm2.
2. The process is limited to butt welded joint only
Applications of Percussion Welding:
1. Welding of satellite tips to tools
2. Welding of Steel to Cast Iron
3. Welding of Zinc to Steel
4. Welding of Copper to Aluminium etc.,
5. Welding of Studs
6. Join a stranded wire directly to a component pin on axis