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MIG Welding Basics
So you finally pulled the trigger and bought one of our Eastwood MIG welders. Now what? As simple as MIG welding is, most hobbyists can't just grab the gun and start laying down beautiful welds that hold together. Getting the most out of your equipment takes time. Practice and understanding the differences in metals, gasses and techniques are the keys to producing top-quality welds. To help you along in your quest of metal fusion, we have put together this guide of tips, tricks and techniques to get it done.
MIG (Metal Inert Gas) welding is a style of GMAW (Gas Metal Arc Welding) electrical welding. Metal filler wire is fed through a handheld gun, providing the arc to melt the metals, welding them together. Most MIG systems use a separate inert gas, most commonly a mix of CO2 and Argon, to shield the arc from contaminants. Non-gas systems use flux-core wire, which has flux in the center of the wire. As the wire melts, so does the flux, releasing the inert gas which shields the weld. MIG welding was originally developed in 1948. Unlike today, its primary use then was welding non-ferrous metals such as aluminum. The advent of carbon dioxide shielding gas made MIG welding a viable (and inexpensive) method of welding ferrous metals too, and today it is the standard by which most welds are made.
The shielding gas is of utmost importance for MIG welding. While flux-core MIG welds certainly work, you can almost always get better results with solid-core wire and shielding gas. Flux core welding produces more slag and coats the weld with residue, much like stick welding. Eliminating that coating and extra slag means less time to clean up the welds and in the end, results in cleaner, better welds. There are several options for shielding gas, each with its own specific use. Flux-core welding certainly has its uses; dirty metal, windy conditions, and thicker metals (such as car frames) are well-suited for flux-core welding because the wire itself carries the shielding, and flux-core runs hotter than solid core wire.
Carbon Dioxide - Pure CO2 is sometimes used for MIG shield gas. It offers deep penetration and minimizes spatter, but is also helps form oxides, which are bad for fresh welds. The weld penetration is so deep that pure CO2 makes welding thin sheet metal difficult.
Argon & Helium - Welding aluminum and other non-ferrous metals requires pure argon or helium. You can use CO2 mixes with aluminum, but the results are very dirty with lots of contamination. The drawback of these pure gasses comes in welding steel. Argon with steel results in shallow penetration, and with helium, encourages spatter and can cause an erratic arc. Argon and helium are sometimes mixed to create a super-inert shielding gas that combines the best of both worlds.
CO2/Argon Mixes - To get the most from your welding experience, Argon and CO2 should be mixed when welding ferrous metals such as steel and stainless steel. The most typical mixes are 75/25 CO2 to Argon and 90/10. The higher the carbon content, the more intense the arc becomes, increasing the energy in the weld. Welding thin sheet metal is easier with a 75/25 mix. Adding hydrogen to the mix is good for welding nickel and stainless steel. The most typical hobbyist use for MIG welding is steel, which means that the standard 75/25 CO2/Argon mix is sufficient. If you want to MIG-weld aluminum, then you need to invest in a second bottle of pure Argon.
Flow rates for MIG welding vary, but most manufacturers suggest starting off with 15-30 cubic feet per hour depending on the materials, your skill level, and the conditions you are welding in. Welding outside or in a garage with the door open creates the opportunity for wind to blow or draft away your shielding gas. If there is not enough shielding gas, your welds will be porous, meaning voids in the middle of the weld. It may look solid on the outside, but inside, it looks like a sponge. Porous welds are very weak, not to mention ugly as sin. If the weld is popping, with lots of spatter, check your flow rate. Too much shielding gas will actually create turbulence, causing outside air to be pulled into the mix, and you get about the same results as you would with too little gas. Aside from your gauges on the tank, your ears are an excellent tool for setting the flow rate. With everything set correctly, you should hear a crackly hiss, no big pops or sputtering.
Wire Size - The wire is the filler material. In general, the thicker the material you are welding, the more filler material you will need. There are 4 common wire sizes for solid-core and 2 sizes for flux-core. To weld thin metal, such as sheet steel, the smaller wire is preferred (0.024"; Eastwood sells 0.023" Solid MIG Wire), as it burns a little cooler and leaves less filler material. 0.030" wire is a good middle-ground wire, and will safely work for 22-gauge up to 1/8" steel in a single pass. The next larger size (0.035") in solid core wire is good for as thin as 18-gauge and up to 1/2". Flux-core wire is available in 0.035" and 0.045" (Eastwood offers 0.030" Flux Core Wire), which is why flux-core wire is more difficult to use on sheet metal. You need to match the wire to the base material; otherwise you will have serious problems.
Aside from the welder itself, there are a few tools that will make welding easier. Some of these you need and some you can live without, but why try?
MIG Pliers - MIG Pliers should be the second tool in your cart after selecting a welder. This multi-tasking tool can be used to clean spatter from the gun tip, pull and cut wire, and aid in the installation of tips and nozzles. Can you use tools you have on hand for these tasks? Sure, but with MIG pliers, you have one tool that is kept on your welding cart and always there when you need it.
Clamps - There are a thousand styles of Clamps, and you really should have a good assortment. If you do sheet metal work, blind clamps (Intergrip Panel Clamps) and Cleco pins are excellent. Locking C-Clamps of various sizes are the welder's best friend; you can never have too many clamps. Eastwood offers just about every clamp you could ever need for any welding project.
Copper Bars - Steel MIG wire doesn't stick to copper, which makes Copper Bars the perfect material for filling holes. With a piece of copper on the backside of a hole, the filler material sticks to the steel but not the copper, leaving a clean backside. There are copper spoons, plates, even magnetic copper bars. Every welding cart should have a few pieces of copper.
Magnets - Sometimes you can't get a clamp where you need it. That's where the magnets come in, at least for ferrous metals. Magnets are good for holding two parts together while you're welding them. Triangle welder's magnets in various sizes provide the help you need. Small magnets are especially handy in sheet metal rust repair, such as holding a small piece of metal inside a hole.
Anti-Spatter Spray - Most welding operations produce spatter, which is small particles of hot metal that bounce off the weld. It's unavoidable unless you are TIG welding, but that's a different subject. While optimum setting and conditions reduce spatter, you will always have some. Coating the tip with Eastwood's Anti-Spatter Spray makes it harder for the spatter to stick to the tip and electrode. That means less cleaning for you, and a clean gun is a better welding gun. The spray should be applied a couple of minutes before welding.
Weld-Thru Coating - Many welding operations leave a section of the weld hidden. Fresh welds are more susceptible to rust and oxidation than just plain steel, so they need to be protected. Weld-thru coatings contain high levels of zinc which, when heated, bonds with the metal and leaves a protective film that keeps the fresh weld from rusting. Sheet metal repairs should always be made with weld-thru coating on the seams before the welds are made. Eastwood offers Self-Etching Weld-Thru Primer, along with After Weld to protect weld beads from corrosion.
Safety - Quality equipment and tools are no good if you can't see to use them. Welding is a dangerous process; high-voltage, blinding light, intense heat, and flying sparks can really ruin your day. Take the necessary precautions so you don't get hurt. See our welding safety products.
Clothing - Sandals and shorts may be comfortable, but drop a hot cherry-red piece of slag on your foot and that dancing sure won't be the Macarena! Wear proper clothing for welding, which means leather shoes or boots, full-length jeans or pants, and long-sleeved shirts. Eastwood's welding jackets are a great addition to any welder's attire.
Gloves - Different welding types require different welding gloves. TIG gloves are thin because you need to be able to manipulate the wire, plus the heat is more concentrated. MIG welding is messy, with lots of flying sparks and slag. MIG gloves are thicker to protect you. Don't buy thin gloves to MIG weld; they will burn up and shrivel. You may consider a welding jacket or welding sleeves.
Helmet - The single most important safety device is the welding helmet. The arc in welding is brighter than the sun, so looking at it unprotected can blind you—this is not a joke. Burning your retinas can occur in just a few minutes, so you must protect your eyes and face with a full-face helmet. The old-school hand-held shield is the bare minimum, but they use a hand that you should really be using for other welding-related tasks, not to mention they don't protect your skin. A traditional flip-up style helmet frees-up your hands, but the biggest problem (aside from whiplash) is that repositioning your torch after the arc has broken means lifting the mask, setting up and dropping it, increasing the time to complete the project. It may not seem like much, maybe 20-30 seconds, but when you are stitch welding, it adds up fast. An auto-darkening welder's helmet is the best bet for any welder, especially the beginner. This lets you see what you are doing wrong or right, without the distraction of resetting the hood all the time. Consider purchasing an adjustable helmet. This allows you to set the hood up for MIG, TIG and plasma cutting (some helmets come pre-programmed for all 3), and includes a "grind" setting. A smart accessory for the helmet is a welder's hat. They may look goofy, but MIG welding is messy, and you might be surprised how often you may find (feel) a hot piece of slag hit your head. You simply cannot get that helmet off fast enough to stop your hair and skin from burning. Be smart—protect yourself.
Sunburns - Welding while your skin is exposed puts you at risk for flash burn. Imagine a bad sunburn, double it, and you get the idea. Skin can burn from welding flash in 10-15 minutes. Protect your skin with clothing or, at the least, heavy sunscreen.
The Motion of the Ocean - There are many ways to weld and they all have their applications. There is no one technique for every MIG welding operation. You have to learn multiple techniques to get the best out of your welder. How you move the gun, as well as the duration of welding time, determines how much heat you put into the metal. As the metal cools down, it contracts, which leads to warping. Your technique can help control the amount of warping, particularly with sheet metal.
Spot Welding - The most basic weld is a spot weld, sometimes referred to as a "tack weld". Most factory body panels are spot-welded in place. This is done at the factory with two prongs that clamp onto the metal and then arc to weld the metal together. A MIG spot weld is a little different. Instead of the two-pronged method, a MIG spot weld is simply a single small weld made in one place without moving the gun. You can use this method to hold parts in position while you fully weld the rest, or to replicate a factory spot weld, such as a body panel. These are very easy to do; a spot weld should take less than 1 second to complete. You want to keep the gun stationary while the trigger is pulled. For larger spot welds, using the "C" pattern provides a nice, even weld. The "C" pattern is performed by moving the tip of the gun in a small "C" shape in the center of the weld puddle.
Stitch Welding - This is best method for welding thin sheet metal, because a long bead would do two harmful things on thin metal: put a lot of heat into the metal, and tend to burn-through the metal. Both of these create more work for you. Stitch welding alleviates those problems by allowing the metal to cool between welds. Stitching is basically a series of small spot welds along a seam. To start, the panel is positioned in place and spot-welded about every 3" to 4". Once the entire panel has been tacked in place, you return to the first weld and repeat with a series of spot welds (using the "C" pattern, connecting each weld ), no more than 1/2" long, then you move to the next section; this is done until the entire panel is fully welded. You can aid cooling by blowing compressed air over the fresh welds. A properly done stitch weld will look like a stack of dimes laid over, much like a TIG weld. CAUTION: stitch welding is only for thin sheet metal, not for thicker structural metal. 14-gauge is the limit for stitch welds; otherwise you may have penetration issues.Push, Pull and Drag - A standard weld bead is made by either pushing or pulling the gun through the weld. Which method you use is determined by the materials you are welding and the amount of penetration needed for the project. The basic weld bead uses the "C" pattern or the "Circle" pattern. Here, the "C" pattern is made with C-shaped motions, where the bottom of one "C" is the beginning of the next. The circle pattern is similar to the C, but instead of open "C" loops, you move the gun in a small complete circle. If you were to replace the MIG gun with a pen, it would look like a stretched-out spring.
The direction of the bead determines the depth of the weld. Pushing the gun through the weld at 10° off perpendicular yields a wide bead with shallow penetration. Holding the gun straight up (90° to the joint) provides a narrower bead than a push, with slightly more penetration. Pulling the gun through the weld yields the narrowest bead, with about the same penetration as a perpendicular bead.
Penetration of the weld is the key to a proper joint. The thicker the metal is, the more penetration you need. A quick spot check for penetration is the color of the metal around the weld. The wider the discoloration is, the more penetration you have. If you can look on the backside of the weld, then you should see full discoloration around the joint. This only works for stainless and mild steel, since aluminum doesn't discolor with heat.
MIG Welding Aluminum - MIG welding was originally designed for welding aluminum, so it most certainly can be done, just not with a standard modern MIG welder. The issue is the welding wire; it's too soft to run through the long line from the machine to the gun. There are two ways to remedy this: modify the machine to be aluminum-wire friendly or use a spool gun.
Modifying a welder is fairly simple; the coiled metal liner must be replaced with a non-metallic (Teflon®, plastic or nylon) liner that won't gall-up the aluminum. The drive roller on the motor must also be changed to a round U-groove; a standard V-groove roller pinches the soft aluminum which causes it to grab the liner and kink. You must also have pure argon for shielding gas. Not all MIG welders can be converted. While some suggest that 115v volt welders can adequately weld aluminum, many do not have the amperage to weld anything thicker than thin sheet aluminum. A 230v welder does a much better job. The biggest problem with a converted MIG welder is that you have to swap wire every time you go back to welding steel. Not just an inconvenience—steel wire is dirty. It tends to leave junk in the liner and even more in the tip of the gun. Steel wire is stiff enough to overcome the dirt, but leads to feed issues with aluminum wire. The best bet is a spool gun, like that included with the Eastwood MIG 175 Welder.
A spool gun is just like it sounds: the wire spool is moved from the machine to the gun. While this makes the gun a little heavier, the wire only has to travel a short distance, so it moves consistently. Most MIG machines can be converted to run a spool gun, and the bigger machines have quick-connect hookups for spool guns, making it easy to go back and forth.
The art of welding aluminum is different than steel. Aluminum does not show heat like steel, it doesn't glow, and it doesn't discolor to show penetration. Aluminum also requires more prep work. The second that fresh aluminum hits the air, it starts to oxidize, but you can't see it. This oxidation must be removed before welding. The oxidized coating has a higher melt point than the aluminum underneath, which creates all kinds of problems. A stiff stainless steel brush removes the coating and makes welding aluminum much easier. You can also use chemical cleaners for this.
When welding aluminum, the wire speed is drastically different. Aluminum wire feeds quickly, which means you have to move the gun faster than you normally would for welding steel. This can be a big adjustment for even experienced MIG steel welders. Practice before you start welding an actual part. Welding aluminum with a MIG welder takes more practice than welding steel.
Once you have the hang of it, MIG welding can be a lot of fun. Creating your own parts, fixing tools and parts, and repairing/customizing your car can be very rewarding. When it comes to welding, practice makes perfect. MIG welding is the easiest form of welding to master and if you have patience and follow the rules, you will be laying down beautiful beads in no time.
Contributed by Eastwood Customer: "Jefferson"