Saturday, November 21, 2009

Pulsed Welding Equipment

Cory G. from Norther Iowa asks:

"We use the Pulsed GMAW process with Lincoln equipment. When setting weld voltage the Trim can be adjusted between 0.5 and 1.5
What do those numbers mean and how to they relate to weld voltage?"

Pulsed welding equipment can challenge the conventional wisdom we’ve picked up over the years using a good ol’ constant voltage (CV) GMAW (Mig) welder. With typical CV equipment, the Welder will select a voltage and wire feed speed (WFS) combination, possibly a percentage of slope and/or inductance and then be ready to weld. Today’s pulsed Mig equipment changes most of that.

Most pulsed Mig welders run on pre-set programs. The Welder will select the type of wire, the wires diameter, possibly a base material and the shielding gas used. From this information the equipment will look at the WFS selected and do a calculation as to what the optimum weld voltage should be.

Of course, this optimum voltage may need some type of adjustment depending on the needs of the Welder. Example: The optimum weld voltage to weld a flat position, 3/8 inch fillet (1F) at 475 ipm may not be optimum to weld a root pass in a horizontal groove (2G) at the same WFS. Understanding that, each manufacturer of this equipment has built-in, an adjustment for voltage. Think of it as a percentage of optimum voltage.

Manufacturers may give you a 0.50 to 1.50 range, or a 0 to 50 range, or something similar. All will call this “Trim”. Using the 0.50 to 1.50 range as an example, 1.00 would be considered the optimum setting. When you reduce your Trim from 1.00 to 0.85, you have reduced arc length and, in doing so, reduced weld voltage. Similarly, when you increased Trim to, say 1.15, you’ve increased arc length and, in doing so, increased weld voltage.

This is very similar to what you were doing all along on that old CV Mig equipment. When you reduced voltage, you were reducing arc length. Even with this new fancy equipment the age-old understanding that “Weld voltage has a direct relationship to arc length” doesn’t change.
What’s different is that a Trim of 1.00 for a given electrode (type/dia.) will give you a completely different weld voltage when you change electrode, shielding gas or WFS.

Most of today’s pulsed equipment will display average weld voltage as the equipment is welding, and some will continue to display it for a short period (seconds) after welding has stopped. This feature helps the welder monitor compliance to the weld procedure (WPS).


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