Its name derives from the term metal inert gas, which is really a misnomer. After all, so-called TIG welding for tungsten inert gas is also a metal-inert-gas welding process. Now, please forgive me, while I continue to use the vernacular terms, MIG and TIG, for no better reason than that everyone uses and understands them.
In the MIG process, a welding wire is continuously fed into the weld area the puddle as it is drawn along the weld seam. The wire carries current, and is surrounded at the weld, by an inert shielding gas that is fed there through the welding hose and gun, along with the wire.
C is the most common gas used for sheetmetal welding, in a percent CO2 and percent argon mixture. The gas acts like the heat-vaporized rod coating in stick welding. It shields the weld puddle and the cooling weld from most of the oxidation corrosion that would occur if the weld was made and cooled in a normal air environment. The actual MIG process involves a cycle. As the mechanically fed wire contacts the puddle, it creates a direct short circuit with the grounded work piece.
However, it is quickly reestablished, as more wire is fed into the puddle, creating the short arc cycle that is the basis of MIG welding.
The most-often botched aspect of MIG welding is fit-up, the distance between the edges of the metal pieces that are being joined. In lap and offset lap joints, fit-up is not an issue because the joints are overlaps.
But in butt welding, it is critical to leave adequate fit-up distance between butted edges. This space is consistently in the range between the thickness of a dime and a nickel. It may sound more difficult to carry a weld puddle down such a gap than down two more closely fitted edges. However, this is not the case. What is beyond difficult, in fact all but impossible, is to get a good MIG butt weld when edges are fitted up too closely or in actual contact with each other.
This is because the expansion from welding heat inevitably distorts too-closely-fitted metal edges so badly that it is very hard to weld them. It is also very difficult to straighten out panels welded that way. Today, MIG welding is the mainstay of most autobody welding. It is relatively easy to learn this technique. It is being used here to fill weak spots in a sheetmetal floor. There are several issues to master in order to do good MIG welding.
You need to figure out ideal gas flow for your work. This is set with a regulator as the volume of shielding gas delivered. Try to use a two-stage regulator that employs a volume indicator in its second stage. About 10 to 20 CFM at atmospheric pressure is a good range in which to work when you are welding body metal with. Practice and experimentation are your best guides in this matter. Amperage settings are critical when MIG welding sheetmetal.
Amperage is set by setting the wire feed speed. Different wires and different thicknesses of metal require different speeds. Manufacturers supply recommendations for this setting with their machines. It is, however, rough data, and you should plan to modify it for your own situations and according to your own experience.
Voltage settings are also critical. The best MIG machines have continuous voltage settings, while less-expensive ones rely on step settings. In either case, the voltage setting in MIG welding is somewhat analogous to how long an arc you hold in stick welding. It controls the format of the weld bead and thus its height, shape, and, to some degree, its penetration. Somewhere between your general experience and getting frequent practice, you will get the hang of setting wire speed and voltage properly for MIG welding.
Some machines set one, or even both, of these variables automatically. While many welds do not allow for practice, some do. If you can duplicate the conditions of a difficult weld with scrap metal that is similar to the material in the sections that you will be welding, and practice your difficult weld, it would be to your advantage to do so. Some MIG welding machines have fine controls for things like stitch welding, that is, weld time on and time off, and burnback control, which is the time that the wire electrode remains energized after the gun trigger is released.
These are handy features that can improve the convenience and quality of work, but they are not essential to doing good MIG welding.
One thing that is essential is to use good wire. MIG welding wire varies in quality. Some wires are junk, barely good enough to weld with, while others are a pleasure to use. Today, most of the major wire brands perform well. Still, different wires often have different features and advantages. For example, one wire may produce welds that are easier to grind, while another may lay down more uniform beads.
Again, these are things with which you should experiment. Other variables, like torch approach forehand or backhand , distance from work, position, and angle, are best dealt with in manuals and other sources that are specifically devoted to MIG welding instruction.
This is probably the most skill-intensive type of welding, but presents an odd dichotomy. It can be understood in very complex and technical terms, but it can be performed beautifully with little knowledge of its technical aspects. Here is an example: Back in the age when TIG welders did not have the modern sophistication of solid-state-generated square-wave forms and slope control, they relied on carbon bundle frequency generators for superimposed high-frequency currents to keep their arcs from stalling at the AC wave turnover point.
I knew a man who operated one of those primitive TIG machines. He would not have understood much of the technical sentence above, but with the equipment of that period, he could deposit a uniform and well-penetrated weld bead on the business edge of a razor blade.
It was no small feat. He understood little of TIG technology, but knew how to weld with it, instinctively and superbly. The point is: You can interpret TIG welding in many ways and at many levels, comprehending and mastering as much or as little of the underlying technical issues as the spirit grabs you.
Some people revel in the complexities of TIG waveforms and the possible adjustments to them. Others almost intuitively know or remember how to make the best choices in these matters.
TIG welding is probably the most difficult welding technology to master. However, it pays the reward of being the best way to join sheetmetal pieces and panels, when quality is the prime objective. Gas welding is difficult to master, due to the many operator variables involved in its performance. Note the extreme torch angle and the use of filler rod to add metal to the puddle and, sometimes, to shield it from excessive heat.
Also note the distortion in this example. TIG is the most individualistic welding format that exists. Some operators prefer air-cooled torches; others prefer liquid-cooled units. The merits of each are often debated for jobs that involve the same materials and similar welds. Foot controls versus thumb wheels, and so forth, are hot topics. Also, there is specialization in TIG welding particular metals and alloys.
Unfortunately, is not possible to offer instruction in TIG welding in this book. However, if you are interested in doing ultimate-quality welding work on a variety of metals, from stainless and common steel to aluminum, TIG welding provides the best results.
It takes some considerable commitments of money for equipment and of time to learn to use it, but you should at least consider making those commitments if ultimate welding quality is your objective. You do not have to understand it in technical detail to make great welds in a variety of situations. As with your personal computer, you can operate a TIG welder without a deep understanding of how it works. A good welding course at a vocational school will have you started down the path of mastering TIG techniques.
In most cases they will prove inferior, in one or more of several ways, to electric welding approaches. But there are times when you may find uses for torch welding and brazing techniques.
The oxy-acetylene flame, generated by mixing oxygen and acetylene gases to fuel a torch, is infernally hot about 6, degrees F at the cone tip of a neutral flame. A neutral flame has a perfect, combustible mixture of oxygen and acetylene for complete combustion of each gas, with no excess of either in the mix. Obviously, follow the procedures dictated by the specific, relevant OEM and wire manufacturer when you do your own welding.
Oxidation begins immediately and thickens over time — particularly under warm or humid conditions, according to Lincoln Electric. After that, spools should be chucked, it said. Hiser also warned against using the wrong tips when squeeze-type resistance spot welding. He said his longtime former employer GM specifies tip size and type, as do other automakers. They might need to be changed every welds, sometimes more frequently, sometimes less, he said.
Check with the welder manufactuer, he said. Pro Spot training development manager Ryan Swanson, another panelist, said the tip dressing and replacement schedule might vary between tip type, vehicles or welder brand.
Olson suggested shop owners in the audience check on how many tips they were buying when they return home. It can happen if you start with a higher power setting right from the beginning! According to WeldingHubs , you need to make sure the metals are adequately cleaned to prevent the formation of oxide layers.
All the metals must be cleaned off before you even start the welding process. Otherwise, all your sweats and times will go in vain. If the sheet metals are not measured accurately, then there is a chance there will be holes created during the welding process.
You might not even realize before you are finished. That is why it is necessary to get proper joint and other measurements right before you start welding auto body sheet metals? Otherwise, it might feel challenging to fit the joints or not able to do it at all.
Do not compromise with wearing proper safety gear like the welding hood and gloves to avoid getting nasty shocks to the eye or the whole body. It is better not to be too cocky around those sheet metals and welders and forget to wear those. Even a second bright splash or exposure to the toxic fumes are enough to ruin your eye for life.
Last but not least, you should never in an area which does not have proper ventilation.
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