Projections (low thermal mass islands) are one method of ensuring proper heat balance in difficult spot welding applications when a 5:1 size difference exists between the parts to be welded. 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 elements 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 with large-area electrodes by a current pulse under the influence of the electrode force. Several projections can also be welded at the same time.