TROUBLESHOOTING MIG BEFORE AND AFTER YOU WELD

Today?s MIG welders have become so easy to use that when a weld doesn?t turn out as expected, or the equipment starts acting differently, it can confuse the operator and leave him searching for an answer. This article will look at some of the most common equipment and technique issues that crop up and how to solve them. Be sure to consult your manual for your specific machine?s set up and operation. Many companies post their manuals on-line.

EQUIPMENT ISSUES

Often, the complaint is heard that a welder was working perfectly and then suddenly the operator started experiencing problems with arc stability, burnbacks or porosity in the weld. If this happens, after changing wire or gas, the new spool of wire or cylinder of gas should be checked first.

Shielding Gas: Make sure you?re using the right shielding gas. When welding steel, a 75 percent Ar ? 25 percent CO2 mixture is usually recommended. If you were to inadvertently use 100 percent argon on steel, the weld will have low penetration and produce excessive spatter. Similarly, if instead of using the 100 percent argon usually recommended for aluminum, you use a 75/25 mix, the weld will turn black, and you will observe tiny aluminum ?BBs? on the weld surface. Turning up the amperage to compensate will only cause melt-thru.

If you were achieving satisfactory welds before changing gas, use a cylinder you know to be good and see if that corrects the problem.

Electrode wire: Exposed to moisture in the air or environment, welding wire not used for a period of time can develop an oxide layer. If feeding or arc instability problems occur after changing wire, examine the spool to make sure the wire is in good condition. If you?re not planning on using a spool of wire immediately, make sure to store it in a plastic bag in a dry environment, preferably with small packages of desiccant.

Wire feeding issues can affect performance; good welds require a consistent wire feed supply. One way to test if wire is feeding smoothly is to feed wire against a block of wood and watch for continuous smooth wire coil up, which implies there is no obstruction to wire feed. If the wire does not coil smoothly, there is a problem somewhere in the wire feed process.

Cable liners: A kinked, worn, wrong size or partially plugged liner can easily lead to burnback or arc instability issues. Removable liners can be blown out with compressed air if dirty or replaced if worn or kinked.

Wire feeder drive rolls: The drive rolls are designed to feed the electrode wire smoothly from the wire spool into the gun cable. However, if drive roll tension is set too tightly, the drive rolls not only can deform the wire (i.e., take on shape of drive roll grooves) ? causing it to wear down the liner and contact tube ? but also cause rough wire feeding, which can lead to arc instability or burnback. Too little tension can lead to wire slipping. Follow your owner?s manual?s instructions.

Wire feeder spool brake: The electrode wire spool is mounted on a support arm equipped with a hub brake that prevents the spool from ?free-wheeling? when the arc stops. Operators should set the brake with just enough tension to prevent freewheeling; too much tension will impede smooth wire feed through the drive rolls and gun cable, leading to arc instability, inconsistent wire feeding or burnback.

MIG gun: Welders may find that issues with liners and contact tips are the source of most problems (arc instability, wire stubbing, burnback) related to the arc and electrode wire. Make sure that you match contact tip size with the wire size you?re using. In addition, liners that are too small or too large can cause poor wire feeding. MIG guns are never intended to be used as a pry bar or hammer; abuse can damage the MIG gun?s internal components and cause wire feed and shielding gas malfunctions.

Shielding gas: Shielding gas protects the molten weld pool from the surrounding atmosphere, which would otherwise contaminate the weld. Figure 1 shows how the lack of shielding gas can cause porosity (pinholes) in the weld bead are formed in the face and weld interior in the absence of shielding gas. Check that there are no gas flow problems in the MIG gun (e.g., tear or hole in gas hose) and that the MIG gun o-rings are in good condition. Make sure the valve is turned on and supplying gas at the specified flow rate. If all of these checkpoints are OK, determine if a fan or breeze is blowing away the flow of shielding gas around the arc.

Work connection: Arc stumbling can occur if there is a poor connection between the workpiece or workbench and the welding machine output stud. Make sure the clamp is in good working condition and the work lead?s cable lug is making good contact. Grind off rust or paint and ensure that the work clamp is connected as close to the work area as possible.

VOLTAGE AND WIRE FEED SPEED (WFS) SETTINGS

Increasingly, welding equipment manufacturers are developing MIG welders that simplify parameter settings with automatic features. Our Auto-Set?, for example, enables users to set wire diameter and material thickness onlythen Auto-Set automatically sets WFS and voltage to achieve optimal welding results. In addition, most commercially available MIG welders today come with parameter charts that specify the proper voltage and WFS (amperage) settings for optimum welding performance.

Manual setting is still available for broader applications, but the use of parameter charts is highly recommended and usually are available for download from provider web sites. When manually setting parameters, here?s what to look for:

? Voltage Too High: Too much voltage is marked by poor arc control, inconsistent penetration, and a turbulent weld pool that fails to consistently penetrate the base material (see Figures 2a, 2b).

? Voltage Too Low: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 (see Figure 3).

? Wire Feed Speed/Amperage Too High: Setting the wire feed speed or amperage too high (depending on what type of machine you're using) can cause poor arc starts and lead to an excessively wide weld bead, burn-through and distortion (see Figure 4).

? Wire Feed Speed/Amperage Too Low: A narrow, oftentimes convex bead with poor tie-in at the toes of the weld marks insufficient amperage (see Figure 5).

OPERATOR ISSUES

Operators are under complete control of travel speed and gun angle, so they can affect welding results with variations in their individual techniques.

Travel speed: Excessively fast travel speed can lead to insufficient penetration because the arc does not stay in one place long enough to build up sufficient heat. This results in a narrow, convex bead with poor toe tie-in (see Figures 6a, 6b).

Too-slow travel speed may produce a large weld with excessive heat input resulting in heat distortion and possible burnthrough (see Figures 7a, 7b). In most cases, proper travel speed is when the arc is on the leading edge of the puddle.

Gun travel angle: If your welds tend to have more spatter and less penetration and there is general arc instability, check your travel angle. Normal welding conditions in all positions specify a travel angle of 5 to 15 degrees for good weld puddle control. Excessive torch angle can cause limited penetration and not enough can result in poor gas coverage.

PRACTICE, PRACTICE, PRACTICE

With practice and good equipment care, many welders reach a point at which their technique and welding equipment enable them to create perfect welds on the first pass. Until that time comes, however, sound knowledge of troubleshooting steps can help operators ascertain equipment issues quickly or correct technique errors after the weld.

One sure way to ?short-circuit? the troubleshooting process, however, is to practice the weld on scrap metal ? taking note of welding parameters and travel speed, access to the weld and the ability to make needed position changes, in addition to weld appearance.

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Chris Roehl is a product manager for Miller Electric Mfg. Co., 1635 West Spencer Street, P.O. Box 1079, Appleton, WI 54912-1079, 920-734-9821, www.millerwelds.com.