Capacitor discharge (CD) welding is a form of resistance welding that relies on energy stored in a large capacitor bank instead of drawing directly from a power distribution network. Because of this ability to rely on stored energy, CD welders have welding times that are short and concentrated, around 12 milliseconds, as opposed to about 100 milliseconds on a typical resistance welder. For mass production, such small time savings can really add up.

CD welders have many advantages. Weld nugget formation takes place during the first few milliseconds. CD welders release energy extremely fast, with large peak currents. More of the energy goes into weld formation and less into heating surrounding material. The heat-affected zone, where the properties of the metal have been changed from rapid heating and cooling, is localized to a small area around the weld.