An arc welding process variation in which the current is pulsed to utilize the advantages of the spray mode of metal transfer at average currents equal to or less than the globular to spray transition current.
Also known as pulsed arc welding, pulsed spray welding is a direct-current welding system in which a pulsing current is superimposed on a constant voltage d-c background current. It can be used for either gas metal arc welding (GMAW) or gas tungsten arc welding (GTAW), but is generally associated with GMAW.
Pulsed arc welding is a modified form of gas metal arc spray transfer welding, which produces a controlled and periodic melting off of droplets which are projected across the arc. This process allows spray transfer welding at average currents which are considerably lower than the steady-state current necessary for spray transfer welding. The pulsed current process allows welding of thin sheet which would be melted through by the standard GMAW process. In the pulsed arc process the filler wire is heated by the background current and the end may start to melt into a drop.
When the high current pulse occurs, the drop melts completely and is propelled, by the arc pinch effect, directly from the wire to the weld pool. One or more drops may be propelled across the arc during each pulse. The pulsed arc mode of gas metal arc welding produces deeper penetration and better root fusion than the dip transfer, or short circuiting mode, of GMAW. For this reason, pulse arc welding is particularly suited to welding the thinner materials.
Initially, pulsed arc power supplies consisted of a standard three phase d-c power rectifier and a 60 cycle half-wave rectifier. The 60 cycle half-cycle pulse was superimposed on the direct current to provide the pulsating dc. With the introduction of solid state devices and computers, pulse current power supplies are designed so that the pulsing rate can be varied over a wide range, and the width of the pulse can be varied independently of the pulsing rate. The magnitude of the background and pulse current levels can be adjusted independently of one another.
Pulsed arc welding can also be useful for gas tungsten arc welding (GTAW) applications, particularly for autogenous welding of tubing in a fixed position, where satisfactory penetration and weld face contours can be maintained. The high current pulse produces full penetration quickly, but does not remain at this high level long enough to cause excessive melting. The lower background current maintains the arc between pulses.Compared with the steady arc, the pulsing arc increases the penetration, with less heat input into the joint; however, welding speeds are reduced by 20 to 40%.
Generally the pulsation rate can be adjusted from 1 to over 100 pulses per second, and with some equip- ment, to over 1000 pulses per second. When a programmed weld is made involving current upslope and downslope, pulsation starts at the beginning of upslope there both the peak and background current increase to the beginning of main weld current and continue to pulse at those values for the remainder of weld time. At this time, both peak and background current start to diminish to a final current at the end of the downslope time. This type of weld program is often used for girth welding pipe or tubing by the automatic GTAW process.