Pulsed DC Welding
Pulsed DC involves the repetitive variation in arc current from a background (low) value to a peak value. Adjustments of the pulse current time, background current time,peak current level & background current level can be made to provide a current output wave form suited to a fixed application. Generally, pulse frequencies are ranges from 0.5 to 20 pulses per second. Pulsed DC is usually applied with the negative electrode (DCEN). In pulsed DC welding, the pulse current level is typically set at 2 to 10 times the background level of current. This combines the driving, forceful arc characteristics of high current with the low heat input of low current. The pulse current achieves good fusion and penetration, while the background current maintains the arc and allows the weld area to cool.
There are several advantages of pulsed current. For a given average current level, greater penetration can be obtained than with steady current, which is useful on metals sensitive to heat input and minimises distortion. Very thin metals can be joined with pulsed DC. In addition, one set of welding variables can be used on a joint in every positions, like circumferential weld In a horizontal pipe. Pulsed DC is also useful for bridging gaps in open root joints.