Resistance Spot Welding

In resistance spot welding, you press the electrodes onto the sheets and fire a short, powerful current pulse through the spot. The contact resistance between the sheets heats the material there so much that it melts and forms a lens. Make sure the electrodes are clean and the sheets are bare, otherwise it won't ignite properly. Too much current or pressure gives you a lens that's too thick with sink marks or spatter; too little gives no real bond. Welding time and current must match the material and sheet thickness – you have to feel your way in and make test samples.