Pulsed MIG welding settings for trim

Q: We use the pulsed-spray-transfer GMAW process in our shop. When setting weld voltage, we can adjust the trim between 0.5 and 1.5. What do those numbers mean, and how do they relate to weld voltage?

A: Pulsed-spray-transfer welding equipment has challenged the conventional wisdom we’ve picked up over the years from using a good old constant-voltage (CV) GMAW machine. With typical CV equipment, you select a voltage and wire feed speed (WFS) combination, possibly a percentage of slope, and inductance.

Most GMAW-P machines run on preset programs. You select the type of wire, the wire diameter, possibly a base material, and the shielding gas. Using this information, the equipment looks at the WFS and calculates the optimal weld voltage. Of course, this voltage may need some type of adjustment depending on what you need.

Settings to Use for Pulsed MIG Welding

For example, the best voltage to lay a 3/8-inch fillet weld at 475 IPM in the flat position (1F) may not be the best voltage for laying a root pass in a horizontal groove (2G) at the same WFS. With this in mind, power source manufacturers have built in a voltage adjustment feature. Think of it as a percentage of optimal voltage.

Some power sources may give you a 0.50 to 1.50 range, while others a 0 to 50 range. This adjustment range is the trim. Using the 0.50 to 1.50 range as an example, 1.00 is considered the optimal 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 increase trim to 1.15, you’ve increased arc length and therefore increased weld voltage.

This is similar to what you were doing all along on that old CV GMAW 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 still applies.

What’s different is that a trim of 1.00 for a given electrode 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 you’ve stopped welding. This feature helps you to monitor compliance to the weld procedure specification (WPS).