MIG/GMAW 101: Setting the Correct Parameters
Unless you weld for a living, it is often difficult to know if your MIG welder is setup for optimal performance. If you find yourself asking questions such as "Am I using the proper voltage? Do I have too much or too little wire? Am I traveling at the right speed?" this article is for you! First we will touch on the basics of properly setting up your welder, and then look what your weld bead is telling you.
Good equipment makes gas metal arc welding easier. Poor equipment can cost you dearly in frustration and weld quality.
Recent technology advancements, such as some welding machines' ability to set optimal parameters automatically based on material thickness and wire diameter, allow you to focus on proper technique while achieving smooth, spatter-free starts, a common problem area for occasional welders; however, not all welding machines have this capability.
To determine which welding machine and technology suit you the best, find a local welding supply distributor that has an on-site welding lab or will allow you to test-drive a machine before buying one.
Getting the Most from Your Machine
Regardless of your power source choice, read your owner's manual. It contains important information about proper operation and safety guidelines. Most companies offer their manuals online.
The following basic guidelines are for welding steel with solid wire. Aluminum and flux-cored welding require separate discussion. Joint design, position, and other factors affect results and settings. When good results are achieved, record the parameters.
1. Material thickness determines amperage. As a guideline, each 0.001 inch of material thickness requires 1 amp: 0.125 in. = 125 amps.
2. Select proper wire size, according to amperage. Since you don't want to change wire, select one for your most commonly used thicknesses.
* 30-130 A: .023-in.
* 40-145 A: 0.030 in.
* 50-180 A: 0.035 in.
* 75-250 A: 0.045 in.
3. Set the voltage. Voltage determines height and width of bead. If no chart, manual or specifications are available for setting the correct voltage, you can try this: while one person welds on scrap metal, an assistant turns down the voltage until the arc starts stubbing into the work piece. Then, start welding again and have an assistant increase the voltage until the arc becomes unstable and sloppy. A voltage midway between these two points provides a good starting point.
There is a relationship between arc voltage and arc length. A short arc decreases voltage and yields a narrow, "ropey" bead. A longer arc (more voltage) produces a flatter, wider bead. Too much arc length produces a very flat bead and a possibility of an undercut.
4. Set the wire feed speed. Wire speed controls amperage, as well as the amount of weld penetration. A speed that's too high can lead to burn-through. If a manual or weld specification sheet is not available, use the multipliers in the following chart to find a good starting point for wire feed speed. For example, for 0.030-in. wire, multiply by 2 in. per amp to find the wire feed speed in inches per minute (IPM).
Examining the Beads
One way to check your parameters is by examining the weld bead. Its appearance indicates what needs to be adjusted.
Good Weld (Figure 1)-Notice the good penetration into the base material, flat bead profile, appropriate bead width, and good tie-in at the toes of the weld (the edges where the weld metal meets the base metal).
Voltage Too High (Figure 2)-Too much voltage is marked by poor arc control, inconsistent penetration, and a turbulent weld pool that fails to consistently penetrate the base material.
Voltage Too Low (Figure 3)-Too little voltage results in poor arc starts, control and penetration. It also causes excessive spatter, a convex bead profile, and poor tie-in at the toes of the weld.
Travel Speed Too Fast (Figure 4)-A narrow, convex bead with inadequate tie-in at the toes of the weld, insufficient penetration, and an inconsistent weld bead are caused by traveling too fast.
Travel Speed Too Slow (Figure 5)-Traveling too slow introduces too much heat into the weld, resulting in an excessively wide weld bead and poor penetration. On thinner material it may also cause burn through.
Wire Feed Speed/Amperage Too High (Figure 6)-Setting the wire feed speed or amperage too high (depending on what type of machine you're using) can cause poor arc starts, lead to an excessively wide weld bead, burn-through, excessive spatter, and poor penetration.
Wire Feed Speed/Amperage Too Low (Figure 7)-A narrow, oftentimes convex bead with poor tie-in at the toes of the weld marks insufficient amperage.
No Shielding Gas (Figure 8)-A lack of or inadequate shielding gas is easily identified by the porosity and pinholes in the face and interior of the weld.
(For more GMAW guidelines, download "Guidelines for Gas Metal Arc Welding" at http://millerwelds.com/resources/improving-your-skills/mig/.)