Principle of Capacitor Discharge welding (CD welding)
During CD welding the required welding energy is taken from previously charged capacitors. This energy is transferred via a thyristor and a welding transformer. Charging times are typically between 0.5 and 2 seconds; weld times between 3 and 10 milliseconds.
The capacitors are typically loaded at a voltage of 1500 V for maximum usage of them. These high charging voltages allow high turns ratios. Doing so high weld currents are achieved as well as relatively high secondary voltages.
This effect gives advantages in designing machines and fixtures. Through the short circuit like discharging of the capacitors the energy maximum is reached very quickly. The resistance maximum is reached also very quickly due the fixture and advance preparations.
This extremely fast temperature raise in the welding zone heats it up before the heat can dissolve. This prevents the heat to reach other parts of the part. Just after a few milliseconds the weld is finished without heating up the surrounding area. This effect is responsible for all advantages and possibilities of the CD welding.
Grace to the high energy density on the heated volume the efficiency factor of a CD weld is higher than 90%. So CD welding is a very economical weld application. Additionally there is a low requirement on the mains supply. The combination of both makes CD welding very attractive.
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