Touch welder general use large transformer + semiconductor silicon controlled conduction time to control welding energy. Anyway is to use a high-power transformer, will become low voltage, one 220V AC current amplification at times; -- Caught up in the workpiece on the electrode, jointing ends tightly, each with a lot of electricity flows through electrode to the work piece, due to welding workpiece in two of the contact surface roughness has micro, causing the surface resistance, according to the contact ohm's law, can produce high metal plastic state to, At the same time between electrodes with proper pressure fluctuation two parts, clamping workpiece materials at each other and together, welding parts.