Projection Welding

Projection Welding

Projection Welding -
Definition
Projection welding is a resistance welding process wherein coalescence is produced by the heat obtained from resistance to electric current flow through the work parts held together under pressure by electrodes. The resulting welds are localized at predetermined points by projections, embossments or intersections.
Principle of Operation
Projection welding is similar to spot welding except that
(i) The electrodes, instead of being tips as in spot welding, are flat and relatively large in surface area. Electrodes are cooled as in spot welding.
(ii) Since a number of welds are made at each operation, both the electrical power (kVA) and mechanical pressure must be correspondingly greater, as compared with a spot welder.

The success of projection welding depends on the surface preparation of the work-pieces to be welded. Projections, small deformations that will touch the surface of the material to be welded are formed on the weld areas by embossing, stamping, casting or machining.
These projections serve to concentrate (localize) the welding heat at these areas and facilitate fusion without the necessity of employing a large current.
(i) The projection in the upper piece is held in contact with the lower piece under electrode pressure.
(ii) The current flows and being localized to the region around the projection, heats the metal in that area to the plastic state.
(iii) The heated and softened projection collapses under the pressure of the electrodes thereby forming the weld.

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