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The Basics of MIG Welding - You Can Do It
The Basics of MIG Welding
From the November, 2004 issue of Sport Truck
By Mike Finnegan
Photography by Mike Alexander, Mike Finnegan
If you've never fabricated anything for your truck but would like to, you can learn the most basic skill necessary, MIG welding, to build most anything for your ride. This article will give you the basic knowledge to safely operate a MIG welder. Once you have the basics down, the sky is the limit - and so is the level of performance of your truck. Gas Metal Arc Welding is commonly referred to as MIG welding. The MIG welding process was developed in the late 1940s as an alternative to Gas Tungsten Arc Welding, which uses a nonconsumable tungsten electrode and is a much slower welding process. MIG welding is preferred in many applications because it is easy to learn, has a high deposition rate, and creates minimal weld slag. A wire-feed MIG welder outfit consists of the welder itself and several "consumable" items. These consumables include the electrode, welding wire, and shielding gas. A MIG welder is capable of welding ferrous metals such as steel, aluminum, and stainless steel, depending on what type of shielding gas you use and the diameter and type of the weld wire. Since our trucks are built from steel, we'll concentrate our efforts toward making good welds on steel from sheetmetal up to 3/16-inch steel plate. A MIG welder welds steel together by heating the metals with an electric arc. The arc is generated between the electrode in the welding gun and the metalwork piece. This arc is shielded from contaminants in the atmosphere by the shielding gas. The most common shielding gas that is readily available at welding supply houses is a mixture of 75 percent argon and 25 percent CO2. This mix helps produce welds with little slag and excellent penetration. There is a multitude of electrode-wire types available for welding different types of metal. The wire we'll use in conjunction with the shielding gas will have a steel core with a copper coating and a diameter of 0.035 inch. This wire will be suitable for welding steel with a thickness between 1/6 and 3/8 inch. Should we ever decide to weld sheetmetal with a smaller thickness, we can switch electrodes in our welding gun and then switch to a smaller diameter wire, such as 0.023 inch. MIG welding is one of the easiest welding processes to learn as well as the most inexpensive. A basic MIG-welding outfit can be purchased for less than $500 and requires only a small amount of time to competently operate. Here is a look at a typical MIG welding setup as well as what a good weld looks like and why a bad weld occurs.  1. The argon/CO2 shield gas...  1. The argon/CO2 shield gas mixture is regulated to 25 psi with this regulator. The bottle is turned "off" between welding sessions.  2a. In this article, we'll...  2a. In this article, we'll be welding 1/8-inch mild steel plate, which is a common metal thickness used for suspension mounting points, body mounts, framerails, and so on. Wire with a diameter of 0.035 inch is suitable for this application and is inserted into a Millermatic 210 wire-feed welder.  2b.  3. After the wire is fed into...  3. After the wire is fed into the driver roller, the welder is turned on and the trigger is pulled on the gun. The drive roll activates and feeds the wire into the liner of the gun. Drive tension is adjusted until the wire feeds smoothly through the gun without "bird nesting." The wire is then cut off 3/16 inch away from the tip of the gun. It's a good idea to cut the small section of old wire off the end before you begin to weld because it will lessen the initial "pop" from the welder at the beginning of the weld.  4a. Protective clothing should...  4a. Protective clothing should be worn to prevent hot sparks from contacting your skin. Especially when you're first learning, there will be plenty of hot sparks that can light clothing on fire or burn your skin. Protection should include leather welding gloves, sleeves, and the appropriate shield helmet. We suggest one of Miller Electric's auto-darkening shields, which offer excellent visibility without having to flip the shield up and down whenever you stop and start welding.  4b.  4c.  5. Before you begin to weld,...  5. Before you begin to weld, you must first ground the welder to a metal work surface that the part can sit on, or connect the ground clamp directly to the part you'll be welding.  6. On the inside cover of...  6. On the inside cover of all Miller MIG welders you'll find a handy chart that will tell you what settings the wire feed and voltage the welder should be set to for welding different metal types, depending on what kind of shielding gas and wire diameter you are using. Follow the setting instructions and you'll have a better shot at producing a good weld.  7. The front of the welder...  7. The front of the welder is where you'll find the on/off switch and controls. In the upper-left-hand corner there is a dial marked wire speed. This dial controls the rate at which wire is fed into the gun. The dial on the right marked voltage controls the amount of voltage coming from the welder. The more voltage is applied, the hotter the arc coming out of the gun will be, and the thicker the material the weld will penetrate into. There is a direct correlation between voltage and wire speed. Consequently, the hotter the weld, the quicker the wire must be fed into the puddle.  8. Once the welder is set...  8. Once the welder is set up properly, grab some scrap steel to practice welding on. In this picture, we have set two pieces of 1/8-inch steel plate next to each other. The gun should be positioned at a 45-degree angle with the contact tip approximately 3/8 inch away from the surface of the steel. Use one hand to hold the gun and the other hand to steady it. It's important that this gap and angle be maintained as the gun is moved along the surface of the metal. To begin welding, the trigger on the gun is pulled, which turns on the shielding gas, wire feed, and voltage, simultaneously. If the gun is held steadily enough, you'll see a small puddle of weld form on the metal, which you can either drag toward you or push away from you. Typically, pushing the weld along the steel will yield a less-desirable weld with less heat penetration than dragging the weld puddle along the steel.  9. Your first few attempts...  9. Your first few attempts at MIG welding will most likely not yield a very effective or good-looking weld. You'll find that a steady hand is one of the most important parts of making a good weld. In this photo, we see that although the welder is set correctly and the weld is penetrating the metal (look at the heat marks around the weld area), the weld is not a good one. As the gun was moved from left to right, the puddle started out with good penetration and coverage on both pieces of steel. But as the puddle was dragged to the right, the operator moved the puddle too quickly, which decreased the amount of penetration.  10. Here is a much better...  10. Here is a much better weld. As you can see, there is an equal amount of heat penetration on both pieces of steel and the weld is equally distributed as well. A good technique for distributing the puddle across both parts being welded is to make curlicue or small-letter C welds as you go.  11. On the left, we see another...  11. On the left, we see another good example of a good weld. Again, the operator dragged the puddle while moving the gun in the shape of the letter C. Aside from looking at it, you can tell a good weld from a bad one by the way it sounds. You'll hear a continuous buzzing noise when you are making a good weld. A bad weld will make popping noises and a lot of sparks.  12. What does a bad weld look...  12. What does a bad weld look like? This photo illustrates what happens to a weld when insufficient voltage is supplied from the welder. The arc is not hot enough to penetrate the steel adequately, and as such, the weld has a tall, fat appearance with little or no heat penetration marking around the weld. Turning the voltage up to the recommended level will cure this situation. In this case, where we are welding 3/16-inch steel plate, setting our Millermatic 210 welder wire speed to 60 and the voltage to 6 will yield a good penetrating weld.  13. Whenever you are welding...  13. Whenever you are welding together two pieces of steel that have different thicknesses, set the welder for the thickest material and start the weld on that material, dragging the puddle onto the thinner material. This will concentrate the heat onto the thicker material to ensure good penetration, while allowing you to drag the weld onto the thinner material, without burning a hole.  14.  15. One of the tougher positions...  15. One of the tougher positions to weld in is overhead or downward. Whenever you must weld downward, start at the top of the part and drag the weld down. The weld should look like this.  16. If you try to drag the...  16. If you try to drag the puddle uphill by starting at the bottom of the part, the weld will look like this - not too good.  17. Here's a good example...  17. Here's a good example of what happens when you move the gun too quickly across the work area. Moving the gun too quickly breaks up the puddle, and you'll know you're screwing up by the sparks and prominent popping noise you'll hear.  18. Moving the gun too slowly...  18. Moving the gun too slowly will yield a weld that is too wide and sloppy-looking, and will put too much heat into the part.  19. Once you've mastered MIG-welding...  19. Once you've mastered MIG-welding steel with your welder, you can then move on to new materials, such as aluminum. Certain models of welders, such as the Millermatic 210, offer optional spool guns that have their own wire supplies built into the gun. Switch out the bottle of argon/Co2-mix shield gas for straight argon and you can easily MIG-weld aluminum together. But that's another story altogether and something we can cover in another article.
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