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| Welding Part 2 |
| Written by David Jackson | ||||||||
| Monday, 28 August 2006 | ||||||||
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Slag in beard = bad
Part 1 - Part 2
This week our focus turns to technique and safety. There is real danger involved with MIG welding, but this can be easily overcome with a little common sense, preparation and correct techniques. Safety Since welding can be dangerous, we'll begin with safety. The most important tool for this job is one you hope to never use: a fire extinguisher. Your extinguisher should be of the A B C type, as these are the most versatile. ABC extinguishers are a combination of these three classes and great to have in your shop and your home. 
Next up, and equally important, is the welding helmet. The light generated by MIG welding is extremely bright. Looking directly at the light generated by MIG welding even for a split second causes arc eye, when the bright flash from the arc burns the cornea. I prefer the kind of helmet that covers your entire face. (burning slag in the beard is the kind of excitement I don't need!) I also like the flip-up, dark glass type. It's easier to keep the torch where you want it without having to flip the whole thing up and down. These are relatively inexpensive, around $20.00 US or about £13 if you are across the pond. 
Since welding is basically melting metal, everything is HOT so welding gloves are a must. Long sleeves and pants help keep the hot slag off and protect from UV burns. Thats right, a few moments of MIG welding is like all day in the sun. Of course you should observe electrical safety. Work only in a dry area, with the welder plugged in to a properly grounded outlet. And to quote a famous Yankee tool man, “Be sure to read, understand and follow all the safety rules that come with your power tools. Knowing how to use your tools properly will help prevent accidents.”Preparation It's tough to weld dirty steel and that says a lot about preperation. If it's not clean, it will be weak when welded. A wire brush on a drill is my preferred method for cleaning the joint to be welded. You need to get the adjoining parts nice and shiny where you intend to weld. You don't have to polish the entire part, just the joining area. While you are at it, go ahead and clean a spot for your ground clamp. Clamps An ample supply of clamps is very helpful. I have been able to get along with a couple of vice-grips, several “C” clamps and occasionally a pipe clamp borrowed from my wood shop. Technique MIG welding either with or without gas is fairly straight forward and you will improve with practice. There is much discussion as to whether to push or pull the torch. I say that whatever you are comfortable with is the right way to weld, and I do both. I prefer to pull, as that seems to keep the torch tip a little cleaner.
This results in good coverage of the parts to be joined, and proper penetration. The illustration above is an exaggerated example of the torch movement There are typically two important settings on a wire feed MIG welder: Amps (sometimes labeled Heat), and wire speed. These are set by running test welds on scrap. A speed setting that is too fast will result in an incomplete arc that does not melt the wire and form the weld pool. Too slow and the weld takes too long and the wire may not arc fast enough, causing a sputtering weld. A proper setting allows a smooth flow and sounds like bacon frying, a steady crackling sound. The procedure for setting up a weld is as follows: prepare scrap the same as you plan to set up your actual weld. Clamp the pieces in place and apply the ground clamp to the larger piece. Clean the joint area with a wire brush. Put on your protective gear and set the wire speed to around 50% and the amp setting to low for thin metal or high for 3/16th or thicker metal. Turn the welder on and hold the torch close to the beginning of the weld. Lower your helmet, and touch the wire to the joint and pull the trigger on the torch. This is called “striking an arc.” Pull the wire to the center of the joint and gently and slowly start the zig-zag movement.
To clarify, you will only be moving the wire back and forth about ¼ to ½ inch.
Move back and forth in the same spot until the weld pool forms. Then start pulling (or pushing) the pool along the joint until you reach the end of your weld. Yes, you can stop to make corrections to settings or just to inspect the weld. Just remember, you need to get the weld pool started again when you return to welding. When you finish your test weld, flip the piece over and look for penetration. This will look like a discoloration of the joint and possibly a melted look to the ends of the metal. Don't expect it to look like the bead on the top; if it does, then you are using too many amps or moving too slow. The photo below shows the weld on the left and the penetration on the right. 
The best advice I can give is “Take your time.” A rushed weld has voids and a “beady” look to it. Oh, and of course, Practice, practice, practice! There are several types of joints you can weld. The butt joint is simply two pieces of metal joined end-to-end or side-to- side. If the metal is thicker it is helpful to bevel the edges with a grinder. This allows the weld to fill the resulting channel and bond the pieces together with a strong joint. a lap joint is when one piece is slightly over lapping the other . For the best strength, a weld can be made on both sides. That about wraps up my somewhat limited experience with MIG welding. I strongly encourage you to visit your local library or do a search for “gasless MIG welding”. There is a lot of information available if you are interested. Give it a try! It's very rewarding and quite easy to pick up. Until next time, Keep Moddin'
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