March 24, 2009
Getting comfortable and attaining a clear view of the arc can make gas metal arc welding a lot easier.
Welders of the world have a secret: Gas metal arc welding really isn't that difficult, if you have the correct equipment setup, if you can see the wire feeding into the weld, if you move smoothly, and if you're comfortable. Of course, those if aren't all easy, but once they're achieved, learning how to lay down a bead, in or out of position, gets a lot easier.
When troubleshooting a welding problem, don't start with welding technique. Instead, tackle the easy fixes first by making sure your equipment is set up correctly. Take a look at your gun. Is your contact tip worn? Is it loose? Make sure all components are tight, the contact tip is the right size, and that it isn't worn. Pay attention to your setback, and make sure the contact tip is centered in the nozzle. Next, look at the machine itself. Are the controls dialed in correctly? Is the ground/work clamp properly secured, or is it loose or connected to a rusty or painted surface? Are the volts and wire feed speed (amps) set high enough for the metal thickness? Not having enough heat for the material thickness and joint design is arguably one of the most common mistakes beginners make. Last, don't forget the shielding gas flow rate. Setting it too high can be just as bad as setting it too low.
If you can't see the wire going into the weld pool, you have little chance of being able to follow the root of the joint. This is simple logic. To weld well, you need to see what you're doing. If you work in a comfortable position with a clear view of the wire feeding into the joint, you'll have a better chance of producing a good weld.
Use a welding lens as dark as practical, within a range that welding safety standards specify, but no darker. If you have poor eyesight, or you use a too dark lens shade, you may have problems. Next, analyze your physical position when welding. If your head is at the wrong angle, the gas nozzle will block your view of the wire and arc as you run it down the joint. Whenever possible, change your head position, not the gun angle. If you do make a gun angle change, do it only to ensure you're directing the arc to both sides of the joint—not just because you need to see the joint.
It's instinct to stay away from something dangerously hot, so if you're welding for the first time, you may have a tendency to hold the gun at arm's length. Stiff, extended arms produce jerky moves that can result in terrible welds. Making smooth weld beads requires you to move closer and get comfortable. You need to be close enough to see what's happening at the arc. Avoid rapid movements by bracing your elbow or upper arm against something. This steadies your hand motions just as a tripod steadies a camera lens for long exposures. Your elbows likely will be positioned tight against your body, with either your elbows or forearms resting against a tabletop or another solid surface.
Typically, backhand will result in deeper joint penetration and a narrow, convex weld bead. Welding forehand will give you a wider bead with less penetration. Generally speaking, try using forehand for metals less than 1/8 in., backhand for thicker metals.
Which direction you weld also depends on the metal transfer you're using, as well as the weld position. Consider the flat and horizontal positions using short-circuit GMAW. You may be able to see the wire feed into the joint better if you're pulling the gun, a position that may give you a bit more endurance for longer weld beads.
Here's why. If you're right-handed, you hold the gun with the right hand, or both hands; to get a better view you can move your shoulders and head to the left. As you pull the weld gun, your arms become less extended as the weld progresses. True, you may be a bit uncomfortable as you start the weld, but as the weld progresses you move into a more comfortable position. Typically, your body is more fatigued at the end of a long weld, so you may be better off ending a weld comfortably rather than starting a weld in an easy position and straining near the end.
Now say you're welding vertically, downhill, with short-circuit GMAW. If you're right-handed, try positioning your head slightly to the left of the joint—nothing radical, but just enough so you can see the joint below the gun. Then pull the gun downhill, paying attention to the weld pool, which, thanks to the intermittent arc of short-circuit transfer, should solidify quickly. If you weld using your left hand, try positioning your head to the right instead. (It's not a bad idea, in fact, to practice welding both left- and right-handed.)
During short-circuit GMAW in the horizontal position, gravity becomes a factor, which means you need to be precise in setting up your machine. It's true that the horizontal position may require higher wire feed speeds. But that means you also have to move faster, or you'll have too much liquid metal built up in one spot. The wire feed speed shouldn't be too high, either, because you'll put too much heat into the joint, so the pool will become too fluid and sag from gravity, producing undercut on the top side of the weld and overlap on the bottom. You can compensate by changing your gun angle slightly, perhaps by 10 degrees, pointing the wire to the high end of the joint. But the gun angle shouldn't change too radically. The key is getting the wire feed speed just right—not too low, not too high—to get that optimum weld bead. Use guidelines like the 1-to-6 ratio (1 volt of every 6 amps to burn off the wire properly) and the manufacturer's specifications to get started. Once you find a setting that works well, write it down. Next time you encounter that weld, it will be easy to set the machine.
If you're welding a square groove on sheet metal downhill, at or near vertical, gravity causes the weld pool to "follow" you a bit—think of a tiny, fast-moving lava flow as the weld bead solidifies behind the gun. But if you're using short-circuit transfer, the weld metal solidifies very quickly, avoiding a weld metal "lava slide."Any time molten metal gets in front of the welding arc, incomplete fusion likely will result.
In vertical-up welding, the molten pool fights gravity. The pool wants to go down, while your welding gun directs the arc upward. The result: It becomes very easy to put too much heat into your weld and burn through. If you're welding material more than 1/8 in. thick with short-circuit transfer GMAW, consider welding vertical-up only when no other welding position is practical. And even then, consider changing your process to flux-cored arc welding (FCAW) or, if the power source is available, pulsed GMAW. Whenever possible, try to avoid welding vertical-up for material thinner than 1/8 in.
Welding overhead isn't as difficult as it looks. In fact, considerations for overhead welding are similar to flat welding. True, there can be gravitational pull on the molten metal, so you may need to raise your heat input (wire speed) and your travel speed a bit. But otherwise, everything overhead works about the same as it does in the flat position. The hard part is getting comfortable with the idea of welding in the position, both physically and mentally.
Before starting to weld overhead, be sure you're suited up for it. Even with GMAW, sparks will fly in your direction. Also note that "overhead"doesn't necessarily mean "over your head."If possible, try to position the joint as close to eye level as you can. The more you extend your elbows away from your body, the more unsteady you'll be, and the harder it will be to weld, particularly for long joints. Just like for any other welding position, get comfortable. Try to brace yourself against a table, wall, or some other sturdy (and safe) object. The more comfortable and steady you are, the easier it will be to weld.
Like in the flat position, you may want to pull your weld (backhand). If you're right-handed, position your body to the left, so the joint is to your right, and weld toward yourself, making sure you can see the wire going into the joint at all times. If you're welding thin material, about 1/16 in. or less, try pushing the gun (forehand). Otherwise you risk melting through the metal.
All welders learn to lay stringer beads. They're arguably the easiest way for you to produce good welds, free of defects. When laying down stringers, don't hurry during the critical root pass. If you have a clear view of the joint, and can see the wire going directly into the root of the joint, you should have no problems. Issues arise when you either can't see the root or you jerk the wire and arc away from it during the critical first pass.
Weaving, on the other hand, sparks debate in welding circles. Some organizations will tell you to weave, while other organizations forbid it. A weave bead allows you to deposit more weld metal in less time, with fewer passes. However, the overall heat input per pass is larger, which can affect weld quality, depending on the base and filler metals used.
To determine which technique to use, first refer to welding procedures for the job. On metals thicker than 1/4 in., weaving may make sense, because thicker metals require more heat for complete penetration—but for thinner metals, weaving can cause problems. Weaving has a tendency to produce a larger heat-affected zone (HAZ) around the joint, which could be detrimental to the material's microstructure. For mild steels, a larger HAZ may not matter. But alloy steels can be very sensitive to a larger HAZ, so a weave may not be a good choice, no matter how tight your weave is.
If you choose to do a weave, make your motion—in an overlapping crescent or triangle shape along the joint—as tight as possible to ensure complete fusion. A loose weave produces a wide HAZ and a potentially weak weld. This can be somewhat counterintuitive for beginners, who think a wider weave is like painting with a larger brushstroke, giving greater coverage in less time. But, in fact, just the opposite is true. Think of it as if you're climbing a ladder. Going one rung at a time gives you the most stability. If you skip a rung (that is, have a too loose weave), you'll have incomplete fusion staggered throughout the joint.
A better (and perhaps less controversial) option might be to perform a slight wiggle motion, which can either be very small circles, U's, or some variation. These aren't weaves, but depending on the joint, they can be just as effective in depositing more metal in one pass.
Welding is called an art for a reason. It's not really art, but like an artist, your hand in the finished weld can easily be seen, for good or bad. And even though welding is based on metallurgy and physics, everyone welds a little differently.
First, get set up for success by following specified techniques in welding procedures and company policies. But exactly how you weld—forehand, backhand, uphill, downhill, and so on—largely depends on experience and preference. Ultimately, what matters is that you weld in a timely manner, achieve complete joint fusion without weld defects, and obtain good bead appearance.
The FABRICATOR® is North America's leading magazine for the metal forming and fabricating industry. The magazine delivers the news, technical articles, and case histories that enable fabricators to do their jobs more efficiently. The FABRICATOR has served the industry since 1971. Print subscriptions are free to qualified persons in North America involved in metal forming and fabricating.