Preparing for GMAW, back to basics: All about setup

Details matter when preparing to weld

By Todd Bridigum
September 1, 2009
Article
Arc Welding

Of all the welding processes, gas metal arc welding is the easiest to learn. However, setting up a GMAW system isn't quite so straightforward. The wire feed process is all about setup, really, and improper setup can lead to some major problems.

If machine settings are incorrect, the welder pulls the trigger and produces an obviously bad weld, or wire doesn't feed at all. That's the best scenario. The worst scenario: An inexperienced welder starts welding with an improperly set up machine--and doesn't know it. Incomplete fusion or other weld discontinuities are detected in inspection or, worse, in service.

Often a brief check of the wire, contact tip, gun, machine settings, and other basic elements is all that's needed. It's analogous to a commuter versus a race car driver. The commuter usually opens the door, turns the key, and drives off. The race car driver and his team go through a list to ensure all systems are go, not only before a race but before every practice run as well.

The same holds true in GMAW, and paying attention to the little things matters.

Jelly and Spray

You'll always get some spatter with most GMAW applications, but to reduce spatter buildup on gun components you can use jelly or spray. Spray is convenient and fast, and sometimes used more to reduce spatter sticking to the base metal, especially when using short-circuit transfer (see Figure 1).

Jelly is cheap and lasts forever, if used properly. Try not to stick the nozzle in cold; otherwise, the jelly tends to clump up inside the gun. Instead, run a few test beads to heat up the gun components, and then dip the nozzle in the jelly.

Removing Spatter

The gun is the "business end" of GMAW, where the arcing process occurs. So before a shift, take the nozzle off and check it for spatter, especially if the welder working the prior shift was welding out-of-position. Spatter can lodge itself between the diffuser and nozzle, and the arc can actually melt the diffuser, turning a small issue into a big problem. Also, ensure the insulator is in the proper location and not covering the diffuser holes (see Figure 2).

Dents or chips in the nozzle are likely from people banging the side of the nozzle against the worktable to remove spatter--not good for the gun components and nozzle, especially a gooseneck gun. Those nozzle dents may even cause weld problems, because they can alter the delivery of your shielding gas. Your weld pool may change slightly and cause weld issues.

Instead, try removing spatter with a rat-tail file, as long as the nozzle and insulator are separate pieces. If the nozzle and insulator are one piece, a rat-tail file can ruin the threads. So in this case, try using welpers--a specialized tool that's especially helpful in GMAW and flux-cored arc welding (FCAW). The welpers' ends are square, so you can stick them into the nozzle, give them a turn, and effectively clean out your nozzle. Welpers also have notched openings designed for easy gripping of contact tips and nozzles, which help when it comes time to inspect, maintain, or replace these components.

Figure 2 A small rat-tail file works for removing spatter (left) only when the nozzle and insulator are separate pieces. Welpers (right) are a good alternative for cleaning the nozzle, especially if the nozzle and insulator are one piece.

Contact Tips

The contact tip, or tube, is a critical component of GMAW. The arc emanates from it. And it's cheap, only about 50 to 75 cents a pop, depending on your system. So be sure to inspect it and replace it regularly. Just like people keep driving on bald tires that are almost shot, an inexperienced welder may keep working with a bad contact tip, even though he could work more efficiently and produce a better weld if he just took a few seconds during setup to replace it (see Figure 3).

While inspecting the tip, look at the orifice. Are there gaps around the wire? Take it off the wire and look at it. Is it out of round or melted in any way? If the hole looks too big for the wire, check the size. Usually the wire needs to fit inside the contact tip like a glove, if you're performing conventional short-circuit transfer on mild steel. If, say, you're using spray transfer with aluminum, you may want to use a contact tube one size larger than the diameter of the wire, because the aluminum wire expands slightly when heated.

Also, make sure the contact tube setback is correct, which is something beginners often overlook. A contact tube recessed too far into the nozzle essentially increases stickout, or electrode extension, so the welder "corrects" for it by dialing in different, less-than-optimal machine settings.

Finally, check that the contact tip is centered in the nozzle and tightened. A loose contact tip can cause an erratic arc and affect weld quality significantly.

Cables

Make sure the cable isn't wrapped tightly or kinked, which can put excessive wear on or damage your liner. Also, welding cables in general can really get out of hand, particularly in multiprocess workcells. Cables strewn all over a floor coated in steel dust can create a serious tripping hazard. Use the cables you need and organize the rest. Some shops even put welding cables and wire feeds on booms, to clear floor space and improve welder access to large workpieces (see Figure 4).

Inlet/Outlet Guides

Directly in front of the wire feed's drive rolls is a set of inlet/outlet guides, which align the wire coming into and going out of the drive rolls. Check the holes and O-rings at the end of the gun cable to ensure the end connects solidly with the inlet/outlet guides. If the gun cable is loose or not pushed in all the way, gas will not be able to get from the solenoid in the welding machine to the gun cable. A bad connection or bad O-rings can lead to gas flow restrictions or atmospheric contamination and, ultimately, weld porosity (see Figure 5).

Drive Rolls

Check for correct drive roll tension. Small systems usually have a single set of drive rolls that push the wire into the gun cable; larger machines have dual drive roll systems with two sets of rollers in line with each other. Some systems use a feed in which rolls mounted in the gun pull wire through the gun cable. Still others use a push-pull system, handy for aluminum or other soft wire grades (see Figure 6).

Regardless of the type of feeder, wire tension matters. If the tension is set too low, the wire can slip, leading to an intermittent welding arc. If the wire is too tight, the wire can be gouged or flattened, which can cause feeding clearance issues through the contact tip. If contact tips are wearing out quickly, check the drive roll tension, especially if you're using ribbed or grooved rollers.

Shielding Gas

Safety first. Make sure your cylinder is chained before the regulator is installed. Ensure tight connections to prevent gas leakage. Also, make sure the cylinder isn't positioned against a metallic structure (like a metal worktable) that could put it in an electrical circuit.

Check the flowmeter to ensure it has the proper CFH (cubic feet per hour). An inexperienced welder might think "more is better," but this isn't the case. You want to have enough to shield the pool but not too much, or you'll waste gas and create turbulence that distorts or even aspirates air into the molten metal in the weld pool.

Figure 3 The worn, spatter-filled contact tip on the left should be replaced (at right) with a new contact tip that's the correct size for the wire being used.

The higher the voltage and larger wire you use, the more CFH you need. So if you are using pulse or spray transfer with a 0.052-in. wire, 40 to 45 CFH may suffice. For a short-circuit, smaller-wire application, anywhere between 25 and 35 CFH is often just fine. Of course, exact settings depend on the gas mixture, stickout, nozzle diameter, and other factors.

Electrode Extension

To start with the proper electrode extension, or stickout, welders sometimes point the gun at the edge of the worktable, pull the trigger, and melt a bit of wire. This is just sloppy work practice and a nuisance, leaving wire nubs sticking up on the table. This often happens because tools, including the wire clippers, are unorganized and hard to find. During setup, ensure tools are organized and in their place so you can find the clippers quickly and cut the wire to the correct length. As an added benefit, cutting the welding wire at a 45-degree angle will promote a faster arc start and wire burn-off as well.

Machine Settings

If the previous shift involved jobs with different base metals or thicknesses, the machine settings may have been changed. Don't just turn on the machine and assume that it's set at the correct voltage and wire feed speed for your job.

Also, consider the age of the welding machine. An older, well-used machine set at 20 volts and 190 IPM may work well, but if you move to a newer (and more accurate) machine, those same settings may cause some weld problems.

Mentally Prepare

Part of setup involves mental preparation. If it's a new job, take the time to digest the blueprint, welding procedure specification (WPS), and the essential variables. Welders often face the unfortunate problem of incomplete or inaccurate welding symbols and WPSs, so they need to develop those "soft" communication skills. Some issues should send up a red flag and spur the welder to ask a supervisor. "Why does the WPS call for 5356 aluminum wire, and I've got 4043 on the machine?" Maybe it's called out for a specific reason, and often you can't be sure without checking.

Another big welding symbol issue is the use of the designation for typical (TYP) in the tail of the welding symbol. AWS A2.4, "Standard Symbols for Welding, Brazing, and Nondestructive Examination," addresses the issue: "Misuse of the TYPICAL designation has caused many instances of confusion and fabrication errors by failing to completely identify all applicable joints or by joints that might be similar but not identical."

Companies rely on the welder's knowledge and experience to fabricate parts correctly. So, for example, even if the print or procedure does not call for a root opening, the welder may know that for the joint geometry at hand, complete penetration isn't possible without a root opening, so he will put one in.

Will adding that root change the design? Probably not, but the risk is there. Besides, leaving a required root opening out of the WPS certainly doesn't abide by the AWS standard. The foreword of A2.4 states: "Welding cannot take its place as a fabricating tool unless means are provided for conveying information. Statements such as 'to be welded throughout' or 'to be completely welded' in effect transfer design responsibility from the designer to the welder, who cannot be expected to know design requirements."

That really says it all, but unfortunately it may not spur organizational changes overnight. You may have heard professional engineers say, "Just weld it," which according to the AWS is completely unacceptable--but it happens. So as part of a "mental" setup, you must know how to read a WPS and welding symbols, and know when to ask questions. Some questions are valid, but you can reach the point where you're picking everything apart and wasting people's time. It's a fine line. But by being mentally engaged when setting up, you can ensure you have the information you need to perform the weld correctly the first time.

Todd Bridigum is a welding instructor at Minneapolis Community and Technical College, 1501 Hennepin Ave. S., Minneapolis, MN 55403. He is also author of How To Weld, published by MBI Publishing Co. and available at major booksellers, including Amazon.com, as well as through the American Welding Society, www.aws.org. Photos, taken by Monte Swann, are from How To Weld and are reprinted with permission.