Pulse Welding, Pulse-On-Pulse Gmaw-Pp | Lincoln Electric IM845-A

B-5	OPERATION	B-5

PULSE WELDING

Pulse welding procedures are set by controlling an overall "arc length" variable. When pulse welding, the arc voltage is highly dependent upon the waveform. The peak current, back ground current, rise time, fall time and pulse frequency all affect the voltage. The exact voltage for a given wire feed speed can only be predicted when all the pulsing waveform parameters are known. Using a preset voltage becomes impracti- cal, and instead the arc length is set by adjusting "trim".

Trim adjusts the arc length and ranges from 0.50 to 1.50, with a nominal value of 1.00. Trim values greater than 1.00 increase the arc length, while values less than 1.00 decrease the arc length.

All pulse welding programs are synergic. As the wire feed speed is adjusted, the Power Wave will automati- cally recalculate the waveform parameters to maintain similar arc properties.

The Power Wave utilizes "adaptive control" to com- pensate for changes in electrical stick out while weld- ing. (Contact to Work Distance is the distance from the contact tip to the work piece.) The Power Wave wave forms are optimized for a 0.75" (19mm) stick- out. The adaptive behavior supports a range of stick- outs from 0.50" (13mm) to 1.25" (32mm). At very low or high wire feed speeds, the adaptive range may be less due to reaching physical limitations of the welding process.

Arc Control, often referred to as wave control, in pulse programs usually adjusts the focus or shape of the arc. Wave control values greater than 0.0 increase the pulse frequency while decreasing the background cur- rent, resulting in a tight, stiff arc best for high speed sheet metal welding. Wave control values less than

0.0decrease the pulse frequency while increasing the background current, for a soft arc good for out-of-posi- tion welding.

FIGURE B.3

CURRENT WAVE FORM (PULSE)

Current

Time

PULSE-ON-PULSE™ (GMAW-PP)

Pulse on Pulse™ is a Lincoln process specifically designed for use in welding relatively thin, less than 1/4"(6.4mm) thick aluminum (See Table B.3). It gives weld beads with very consistent uniform ripple.

In Pulse on Pulse modes, two distinct pulse types are used, instead of the single pulse type normally used in GMAW-P. A number of high energy pulses are used to obtain spray transfer and transfer metal across the arc. Such pulses are shown in Figure B.4. After a number "N" of such pulses, depending on the wire feed speed used, an identical number "N" of low ener- gy pulses are performed. These low energy pulses, shown in Figure B.4, do not transfer any filler metal across the arc and help to cool the arc and keep the heat input low.

FIGURE B.4

"N" PULSES	"N" PULSES
HIGH HEAT	LOW HEAT
PULSES	PULSES
PEAK
AMPS
BACKGROUND
AMPS
	TIME

The Peak Current, Background Current, and Frequency are identical for the high energy and low energy pulses. In addition to cooling the weld down, the major effect of the low energy pulses is that they form a weld ripple. Since they occur at very regular time intervals, the weld bead obtained is very uniform with a very consistent ripple pattern. In fact, the bead has its best appearance if no oscillation of the welding gun ("whipping") is used.(See Figure B.5)

FIGURE B.5

When Arc Control is used in the Pulse on Pulse modes, it does the same things it does in the other pulsed modes: decreasing the Arc Control decreases the droplet transfer and weld deposition rate. Increasing the Arc Control increases the droplet trans- fer and weld deposition rate. Since Arc Control varies weld droplet transfer rate, the Arc Control can be used to vary the ripple spacing in the weld bead.

POWER WAVE 355M

OPERATION