Presentation on theme: "Instructables.com. MIG WELDING MIG welding was developed in the 1940's and 60 years later the general principle is still very much the same. MIG welding."— Presentation transcript:
MIG WELDING MIG welding was developed in the 1940's and 60 years later the general principle is still very much the same. MIG welding uses an arc of electricity to create a short circuit between a continuously fed anode (+ the wire-fed welding gun) and a cathode ( - the metal being welded). The heat produced by the short circuit, along with a non-reactive (hence inert) gas locally melts the metal and allows them to mix together. Once the heat is removed, the metal begins to cool and solidify, and forms a new piece of fused metal. A few years ago the full name - Metal Inert Gas (MIG) welding was changed to Gas Metal Arc Welding (GMAW) but if you call it that most people won't know what your talking about - the name MIG welding has certainly stuck. MIG welding is useful because you can use it to weld many different types of metals: carbon steel, stainless steel, aluminum, magnesium, copper, nickel, silicon bronze and other alloys.
About MIG Welding: The Basics Technically called Gas Metal Arc Welding, or GMAW, MIG welding is also referred to as “wire welding.” MIG welding creates an arc between the work piece and a continuously fed wire filler metal, which also functions as the electrode. An external source of shielding gas protects the molten weld puddle from atmospheric contamination (When oxygen is present, it burns and that burning can contaminate the weld); it also contributes to welding characteristics and total heat input. The shielding gas and wire are both fed through a MIG gun. When the operator squeezes the gun trigger, three things happen: 1) The solenoid valve controlling the shielding gas engages and allows gas to flow; 2) The drive roll motors that feed the wire feed move at a speed pre-set by the operator; 3) The welder supplies current and voltage to the wire electrode, with the electrical pick-up point occurring at the contact tip of the MIG gun. Stick and TIG welding are manual processes where operators need to focus on feeding the electrode into the weld puddle. Whereas MIG welding is called a semi- automatic process because the wire feed system takes care of continuously feeding the electrode while the operator directs the electrode into the weld puddle. It is much like caulking a joint. A MIG welder can weld most common steel, stainless and aluminum alloys, giving the owner a large degree of versatility.
The Good, Bad and The Ugly Here are some advantages to MIG welding: The ability to join a wide range of metals and thicknesses All-position welding capability A good weld bead A minimum of weld splatter Easy to learn Here are some disadvantages of MIG welding: MIG welding can only be used on thin to medium thick metals The use of an inert gas makes this type of welding less portable than arc welding which requires no external source of shielding gas Produces a somewhat sloppier and less controlled weld as compared to TIG (Tungsten Inert Gas Welding) Credit:
Comparing The Most Common Weld Types Stick Weld Technically called Shielded Metal Arc Welding, or SMAW, Stick welding is the simplest of all welding processes. It requires nothing more than a welder, a work clamp and an electrode holder that clamps onto the electrode, or “Stick rod.” If you hear veteran welders refer to “arc welding,” they’re talking about Stick welding. TIG Weld Technically called Gas Tungsten Arc Welding, or GTAW, TIG welding uses a non- consumable tungsten electrode and a shielding gas that protects the welding area from contamination. The welding arc comes off the point of the tungsten to melt the base metal, while the operator manually adds filler wire in a method similar to oxy-fuel welding or brazing. MIG Weld Technically called Gas Metal Arc Welding, or GMAW, MIG welding is also referred to as “wire welding.” MIG welding creates an arc between the work piece and a continuously fed wire filler metal, which also functions as the electrode. An external source of shielding gas protects the molten weld puddle from atmospheric contamination; it also contributes to welding characteristics and total heat input.
Selecting the Right Gas… Argon is essentially inert to the molten weld metal and therefore will not react with the molten weld metal. When CO 2 is mixed with Argon, the reactivity of the gas is reduced and the arc becomes more stable. But, Argon is more expensive. In production welding, selecting the perfect shielding gas can be a science of its own. Attributes such as material thickness, welding position, electrode diameter, surface condition, welding procedures and others can affect results. Common gas mixes for the home hobbyist and small fabricator would be: 100% CO 2 -Lowest price, generally greatest penetration, and higher levels of spatter. Limited to short circuit and globular transfer. 75% Argon - 25% CO 2 -Higher price, most commonly used by home hobbyist and light fabricator, lower levels of spatter and flatter weld bead than 100% CO 2. Limited to short circuit and globular transfer. 85% Argon - 15% CO 2 -Higher price, most commonly used by fabricators, with a good combination of lower spatter levels and excellent penetration for heavier plate applications and with steels that have more mill scale. Can be used in short circuit, globular, pulse and spray transfer. 90% Argon - 10% CO 2 - Higher price, most commonly used by fabricators, with a good combination of lower spatter levels and good penetration for a wide variety of steel plate applications. Can be used in short circuit, globular, pulse and spray transfer. TRY C-25 SHIELDING GAS (75% Argon, 25% CO 2 )
TIPS Years of welding and teaching welding have given me insight into the most often asked questions about MIG welding. The following tips may answer your questions. You'll find additional information in the resources at the end of the article. If you're teaching yourself, surf all the Net sites, read all the manuals, and watch all the videos you possibly can. Remember, no one is there to correct you if you are doing something wrong. Along with practice, practice, practice, remember safety, safety, safety! You can MIG weld mild steel, stainless, and aluminum, although you will need a special adapter for aluminum. MIG is great for welding motorcycle frames and race car frames. And although it keeps the heat-affected zone concentrated, remember to be careful with the amount of heat used. MIG isn’t worth a dang on paint, dirt, rust, oil, and grease. Use nozzle dip or antispatter spray to keep your gun nozzle from getting clogged with spatter (molten welding droplets that solidify and stick to the inside of the nozzle, obstructing shielding gas flow). Use a pad with cleaner where the wire feeds into the liner to prevent the liner from clogging up with dirt. Most solid-steel MIG wire has a tensile strength (ability to resist being pulled apart) of 70,000 lbs. per square inch. A good general-use wire diameter for the hobbyist is in. Make sure your machine is set to direct current electrode positive (DCEP)—what used to be called reverse polarity. Commonly used in MIG welding, DCEP gives the best penetration in steel. Remember to use the right amp fuse where you plug in your machine. Make sure your wiring is sufficient to carry the current. A 75/25 shielding gas (75 percent Argon / 25 percent carbon dioxide) is perfect for the hobbyist. A good general flow rate for your shielding gas is 20 cubic feet per hour (CFH) unless specified otherwise on your regulator. Although you cannot have air blowing around because it displaces your shielding gas, make sure you have some ventilation. Do not inhale the shielding gas. Inhaling argon can cause you to wake up dead! Put the work clamp as close as possible to the work piece. That way you'll have a better circuit, which will give you a better weld. Although most manuals recommend wire stick out (from nozzle to steel) of 1/8-in. to 1/4-in., I recommend using as little stick out as possible. When filling in a big gap or hole, I allow up to 1/2-in. of stick out. When welding thin gauge, allow more wire stick out—even up to 3/4-in. Use the push, or forehand, method because you don't want very much penetration. Forehand welding allows you to see better with shallow penetration. Although difficult to see because of the nozzle, backhand welding is smooth and gives the best penetration. Relax your hand and watch the puddle. Watch your travel speed, gun angle, and temperature (heat, or amps, which are controlled by the wire feed speed). The thinner the steel, the faster the travel speed. Skip weld—weld a couple of inches at the beginning, middle, end, and then come back—when you want to control distortion. If you weld a long seam all at once, you are likely to warp the steel. Make sure you are getting good penetration into the steel. Your machine should sound like bacon frying when it is set right on short circuit. The more you burn, the more you'll learn. Do it right the first time. Cutting corners usually results in problems that have to be corrected. Check around when buying equipment. Prices vary big-time.
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