MIG Welding FAQ
(Words and Photos: By MattM, Eastwood.com, December 2014)
MIG Welding FAQ
What does MIG stand for? – MIG stands for Metal Inert Gas Welding. It is also sometimes called Gas Metal Arc Welding (GMAW), or just wire feed welding. A metal electrode/filler wire is fed through the machine, and inert shielding gas is released from an attached tank.
What metals can I weld with MIG? – A vast assortment. MIG is most often used on mild steel, but with the right wire spool and gas it can be used for stainless steel, aluminum, magnesium and more.
What are the advantages of MIG welding? – It can be used on a large variety of common metals. It’s easy to learn. You can weld in any position. It’s a strong durable weld.
What are the disadvantages? – MIG is not as good as stick welding, or flux core welding at welding thicker materials, or welding outside in a dirty, windy environment. It is also not as precise or attractive as TIG welding for thinner and more delicate welding.
How does shielding gas affect the quality of the finished weld? - For most MIG welding, CO2 is fine, but for a flatter bead profile, less spatter or better wetting action, an Argon-CO2 mix is better. 100% CO2 is the lowest priced and will give the greatest weld penetration, but it also causes the most spatter. 75% Argon - 25% CO2 costs more, but offers lower levels of spatter and flatter weld bead than CO2. Other mixes are available, but those two are the most common.
How important is a good ground in MIG welding? – A good ground is very important for all types of electrical arc welding. Without a good ground your weld maybe inconsistent and of low quality, even though you do everything else right. Be sure the ground clamp is mounted securely to the work, and not clamped onto an overly rusted, or heavily painted surface. The ground clamp must have good electrical continuity for you to get good quality, consistent welds.
Is the contact tip of the MIG gun important to my weld quality? – Yes, a worn tip can cause an erratic arc due to the inconsistent electrical contact between the wire and the tip. The hole in the end should be just a little bigger than the wire, and perfectly round. Holes usually wear into an oval shape with use. A good rule of thumb is to replace the tip after every 100lbs of wire.
What safety gear do I need for MIG welding? – At the very least you need a tinted welding helmet and leather gloves. It’s not a bad idea to wear a leather welding jacket and leather shoes too. Hot sparks and metal will fly everywhere when you weld. Besides not offering any protection t-shirts and non-leather shoes will quickly get holes in them from sparks burning through. Weld in an area with proper ventilation too, the fumes that come off many metals are really bad for you, especially galvanized steel. It’s also a good idea to have a fire extinguisher handy too.
How much gas flow do I need? – A starting point is with 20 cubic feet per hour of gas for shielding. If you are welding thinner materials at lower power you can turn the gas down. If you are welding at a higher setting you should turn it up. If you aren’t using enough gas your welds will be sloppy, splattered and brown looking. If you use too much gas you are just wasting money.
What setting do I use? – This will be different for every welder and project. As a rule though, if you are burning holes through the metal you are trying to weld you have too much power. If the bead ends up lumpy and bumpy, chances are you have too much wire being fed. If the welds are happening in fits and spurts you likely don’t have enough wire being fed. When MIG welding is being done properly you should be able to hear it. It will sound similar to the crackle of bacon frying, or a large angry bee buzzing.
What do I need to weld aluminum with MIG equipment? – Because aluminum wire is so much softer than steel, you typically need a spool gun that mounts the wire just inches from the end of the gun. Typically for aluminum the gun is connected to the positive side of the welder. Instead of CO2, Argon gas is the preferred shielding gas for aluminum welding. Then it is just a matter of learning to deal with the different thermal properties of the metal and how it welds.
How do I weld stainless steel with MIG? – You can weld stainless the same way you weld mild steel, but you will lose its corrosion resistance is you don’t use the correct wire and shielding gas. Typically a tri-mix gas of Helium, Argon and CO2 is used. Using a gas with much more than 2% Oxygen or CO2 can lead to the weld eventually rusting, even though you use stainless steel filler wire.
Can I weld cast iron with MIG? – Not really. Some people have had limited success welding a little at a time and peening the weld with a chipping hammer as it cools. The important thing is to put as little heat into the iron as possible. There are always new filler materials being developed though, so cast iron repairs with MIG may become common one day.
Do I need 220v, or will a 110v unit be good enough? – If you do a lot of welding or if you already have a shop wired for 220v the higher powered unit is the way to go. If you don’t have a shop wired for 220v, or want to be able to weld literally out in the field (of your farm), or in the pits of the racetrack, the 110v unit is the way to go. A 220v unit is going to have a longer duty cycle for a given amount of power being used, but it’s still going to be able to weld at all the low powers you would set the 110v welder at. The 110v unit is going to be much easier to run off a generator, an extension cord (be sure to use a heavy duty one that can handle the amps), or just about any 110v outlet you can find. A 110v MIG welding unit is still powerful enough to weld frames, roll cages and other structural components too, it just may need to be rested more frequently.
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