Projections (low thermal-mass islands) are one method of insuring proper heat balance in difficult spot-welding applications when there the parts to be welded vary in size by 5:1. By providing a projection on the surface of one of the workpieces, weld current and force can be focused into the small area of the projection to produce heat at the desired weld location. Projection welding can extend electrode life by increasing the electrode contact area and decreasing the current density at the surface of the electrode. Projection welding is effective even if the weldments are thick.
Projection welding differs from spot welding in that one or more projections are attached to one of the two workpieces that are to be joined. The projection forms a defined current conduction point. The parts are placed on top of each other and welded together at this point using large-area electrodes by means of a current pulse under the influence of the electrode force. Several projections can also be welded at the same time.