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Now that you've got your new Eastwood MIG welder set up and it is all set up with safety gear, and accessories it's time to learn some techniques. Page 1 was all about the basics, like set up, and now page 2 is all about the execution. MIG is popular now with hobbyists because it doesn't take much practice to learn to make competent weld with it. Follow the tips below and you'll be welding like a pro in no time.
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. At the factory this is done with two prongs that clamp the metal and then arc to weld the metal together. A MIG spot weld is a little different; instead of the two-pronged method, it is simply a single small weld made 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. These are very easy to do, taking less than 1 second to complete. You want to keep the gun stationary while the trigger is pulled. For larger spot welds, use the "C" pattern by moving the tip of the gun in a small "C" shape in the center of the weld puddle to provide a nice, even weld.
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 warping it, and tend to burn-through. 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.
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, 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 - 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 was originally designed for welding aluminum, so it most certainly can be done, just not with a standard MIG welder without the right changes. The issue is the aluminum 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. The biggest problem with a converted MIG welder is that you have to swap wire every time. That is 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. This can lead to feed issues with soft 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.
Not all MIG welders can be used to weld aluminum, even with the spool gun and pure argon as a shielding gas. While some people suggest that 115v volt welders can adequately weld aluminum, many can't weld anything thicker than thin sheet aluminum because they don't have the amperage . A 230v welder does a much better job.
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. Aluminum has an oxidation layer that must be removed before welding. This layer has a higher melt point than the aluminum underneath, which creates all kinds of problems. A stiff stainless steel brush removes the oxidation 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.
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