Working Principle of Resistance Projection Welding (RPW)
In resistance projection welding (RPW), small projections are formed on one or both pieces of the base metal to obtain contact at a point which localize the current flow and concentrate the heat. Under pressure, the heated and softened projections collapse and a weld is formed. Projection on the upper component is pressed against the lower component by electrode force. The projection collapses and a fused weld nugget are formed with the application of current. This technique is of special value in mounting attachments to surfaces of which the back side is inaccessible to a welding operator.
Advantages of resistance projection welding
- Simultaneous operation can be done i.e. more than one welds can be made.
- Projection welding has this advantage that it can weld metals of thickness which is not suitable for spot welding.
- Projection welding electrodes have a longer life when compared to spot welding electrodes. Its because projection welding electrodes have to withstand less wear and less heating.
- Resistance projection welding is not limited to sheet to sheet joints.
- Projection welding can be done in specific points which are desired to be welded.
- In difficult welding work projection welding gives a better heat balance.
- Projection welding saves electricity because it needs less current to produce heat. So it reduces the shrinkage and distortion defects.
Disadvantages of RPW
- All types of metals cannot be welded using projection method. Metal thickness and composition is a big question.
- All the metals are not strong enough to support the projections. Some brasses and coppers cannot be welded satisfactorily using projection welding.
- There is an extra operation which is called forming of projection.
- Projections need to have same heights for a appropriate welding.
- Resistance Projection welding is used in Automobile sector.
- Projection welding is used in refrigeration works ( mass production of condensers, gratings, racks etc.)
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