Resistance welding machine : The principle of the Resistance welding machine is that press the workpiece between the two electrodes, switch on the current and when the current flows through the surface of the workpiece and its adjacent area, where will generate the electric resistance heating effect and then the workpiece will be melted or in the plastic state and thus forming the combination of metal. The main welding methods are spot welding, slit bonding, projection welding and butt welding.