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Percussion Welding - It is a resistance welding process wherein coalescence* is produced simultaneously over the entire area of abutting surfaces by heat obtained from an arc produced by a rapid discharge of electrical energy, with pressure percussively (rapidly) applied during or immediately following the electrical discharge.
Principle of Operation
The following steps are involved in percussion welding.
(i) The workpieces are cleaned by removing grease, dirt, paint, etc.
(ii) The workpieces are clamped into machine or fixture. .
(iii) Light force is applied and the ends or faces of two work-pieces are brought near.
(iv) Arc between the faces of workpieces is struck by using any of the following methods:
(a) Workpieces are brought into light contact to establish a flow of current. The workpieces are then retracted to draw the arc.
(b) A nib of small cross sectional area is formed (by cutting) on one of the pieces. Current as it flows through the nib, explodes the nib and establishes an ionized path for the welding current to flow.
(c) A DC voltage (high enough to jump the gap between the workpieces as they are moved toward each other) when applied, ionizes the air gap between the workpieces and starts the flow of current.
(d) Another method involves superimposing an auxiliary high-frequency, high voltage AC on a low voltage current across the gap between the workpieces. The high frequency AC ionizes the air in the gap and the low voltage DC maintains the arc.

The arc as established above heats the faces of the two work-pieces to be joined to the welding temperature.
(v) At this stage, welding force is applied. It extinguishes the arc find holds parts together while weld cools. Welding force may be: Pneumatic, Electromagnetic, Spring force or Gravity (falling weights).
(vi) Welding force is released.
(vii) Workpieces are unclamped.
Power Supplies for Percussion Welding
(i) Low voltage (10 to 150 volts DC), capacitive storage.
(ii) High voltage (1000 to 6000 volts DC), capacitive storage.
(iii) Electromagnetic or inductive storage.
(iv) Low voltage (10 to 35 volts) AC that uses a transformer to furnish the welding voltage.

Metals Welded
(i) Copper alloys,
(ii) Aluminium alloys
(iii) Nickel alloys,
(iv) Low carbon steels,
(v) Medium carbon steels,
(vi) Stainless steels, and
(vii) Copper to Molybdenum, etc.

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