MIG Welding Basics: Safety, Metal Prep and Laying Your First Beads
When you’re putting together a project car, you’re going to run into instances where you’re going to need to attach two pieces of metal. You could drill and bolt them, but for replacing floor pans or repairing body rust with patch panels that’s not going to work. There are a variety of welding processes you can use but MIG welding is one of the easiest, versatile and most forgiving methods to learn. It’s a good skill to have in your back pocket because it comes in handy on just about every build and can turn into a source of side income.
Although our guide will help you along with getting started and keeping you out of the emergency room, it’s no substitute for actually having a piece of metal in front of you with a torch in your hands and putting in the required time.
1. Safety First
Remember, when you’re MIG welding, you’re working with inert gases, which are gases that displace oxygen. Also, you’re working with high voltages and very high temperatures. The arc that allows the welding to occur can cause you to go blind, so there are some precautions you need to take as well as some pieces of equipment you need:
- Work in a well-ventilated area: Welding and grinding produce metal vapors which can include aluminum alloy, zinc fumes, chromium from stainless steel, ozone and more which are poisonous. Repeated exposure can cause metal poisoning also known as “welding shivers” which manifests itself as flu-like symptoms that lasts a few days. While professional settings use extraction fans, a good DIY approach is to leave the garage door open and wear a mask.
- Make sure the areas around your workspace are clean and free of exposed combustibles: Molten metal and grinding sparks can fly several feet so keep your surroundings tidy. With all your safety gear on and darkened welding helmet, flames won’t be bright enough to notice until it’s too late.
- Use welding gloves and long sleeves: Not only does welding produce a lot of heat, it’s also common for molten metal to splatter off your work piece. In addition, the UV light produced by the process can burn your skin like the sun so be sure to cover up and protect all skin from exposure.
- Wear a welding mask or at least goggles, preferably the auto-darkening kind: The light produced by welding is extremely bright and looking directly at even for a short time can burn your cornea, causing “arc eye”. It’s like getting sun burn on your eyes which will definitely keep you up at night. The advantage of auto-darkening masks or helmets is that it frees your hand from having to pull it up and down manually as you work.
- Keep a fire extinguisher handy, just in case: CO2 is best for welding and having a bucket of sand nearby isn’t a bad idea either. Don’t use foam extinguishers or water to put out fire near your welder …for obvious (electrical) reasons.
- When performing overhead welding jobs, wear a welder’s smock: Hot metal will fall straight down onto your body so a leather smock will give you the best protection. Besides leather, cotton is the next best material because it won’t melt like polyester and rayon. The same rule applies to footwear – wear leather, boots or simply cover your shoes with non-flammable or heat-resistant material over sneakers which have plastic. Molten metal + plastic = hot plastic goo that will burn your toes!
- Wear safety glasses under your helmet: As the weld cools, slag can pop off and fly onto you. This is especially important when you have your shield raised and are inspecting your welds.
2. Set Up Your Welder
Thicker metals requires a thicker welding wire, while thinner metals require a thinner wire. A happy medium for wire is .030″ thick, solid-core. You want the shielding gas flowing at about 15 – 30 cubic feet per hour. It’s usually in a tank behind your welder and is either 100% argon or a mix of CO2 and argon. This protects your weld from the atmosphere and contamination. The voltage and wire feed speed will depend on the thickness of the metal you’re welding. Most quality welders will have charts on the inside of the wire roll compartment with recommended settings. These will get you in the ballpark and then you can adjust from there. You want the contact tip on your welding gun to stick out about 1/4-inch, but no more than 3/8-inch. Make sure the welder’s ground clamp is securely attached to clean metal.
3. Prepare the Metal for Welding
This is probably the most important part of being able to make a successful weld. You can’t reliably weld two pieces of dirty, rusty metal with paint in the weld area. Ideally, you’d be able to chemically wash the pieces and then give them a nice acid dip to eat off all of the contaminants and rust. However, most people don’t have that luxury, so they’re going to have to clean the metal another way. Use a wire wheel on a drill to clean all of the major rust and contaminants from the metals. Next, take a piece of 150 grit sandpaper and do all of the fine cleaning to get what the wire wheel missed. When you’re butt-welding thicker metals bevel the edges that you’ll be joining to allow for better penetration and puddling. When the beveled edges of each of the metal pieces are brought together they create a valley that helps the puddle penetrate the metal deeper while yielding a stronger, flatter bead.
4. Practice Laying a Bead
With your welder set up and your metal prepped, it’s time to start doing some actual welding. Whenever possible, practice a little with similar pieces of metal prior to doing your actual “production welds”. Use scrap pieces of metal to lay a few beads and fine tune your settings before moving on to joining two pieces of metal together. MIG welding isn’t hard, but there are tricks in how you hold and move the gun that take practice to master.
Gun Position
Since the wire and gas are fed through the MIG torch according to your settings, the trick is to maintain a consistent position and orientation between the gun and metal surface for a stable arc. Hold the gun at about a 45 degree angle and try to maintain the same arc length (distance between the torch and the metal surface) while moving with a constant speed. This can be hard at first since the wire electrode is constantly melting down.
Starting the Weld
Press the trigger and strike an arc by tapping the gun tip to the metal surface to complete the circuit and pull away. The electricity jumps from the wire tip to the metal surface. Once you get a stable arc, you’ll notice a pool of molten metal start to form near the tip. Stay there for a second or two to build a good pool and then start moving. Rather than moving in a straight line, make small circles, c-shapes or zig-zags with your tip as you push the weld pool across the metal. This will give you better penetration and a flatter bead when you move onto joining two pieces of metal. Think of it as a sewing motion where you’re stitching two pieces of metal together. A good general guideline is that you want to use about an inch of electrode wire for each inch of weld. Pushing the torch (away from you) rather than pulling it (towards you) is a good habit to get into because you get better shielding gas coverage, but there will be certain welding positions where the “pull” technique will give you better visibility so get comfortable with both movements.
Make your practice beads about one or two inches long and then stop and move to another area on the metal. If you make your beads too long, that area of the metal heats up too much and begins to warp. When working on your car or truck move from spot to spot as you complete your weld to keep heat build-up to a minimum.
Fine Tuning Your Settings
The charts on the inside of the wire-feed door will get you in the ballpark but you’ll often find the need to make some fine adjustments from there. Too much voltage/current, and you’re going to burn through the metal. Wire feed not fast enough, and you’re going to have spotty welds. Wire feed too fast or voltage/current too low and you’re not going to have enough penetration. Gas flow too low, and you’re going to have a plain ugly weld with porosity. Once your piece has cooled, it’s a good idea to take a look at the back to see what kind of penetration you’re getting.
Other than visually inspecting your welds, another great indicator of correct settings is the sound you hear while welding. You want a consistent sizzling sound like bacon gently frying in a pan. If you’re hearing erratic spits and pops then your wire speed is too fast.
5. Practice. Then Practice Some More.
Don’t worry if you’re having problems in the beginning. It pays to practice on scrap metal until your technique produces consistently good results before moving onto the panels of your prized car or truck. Nothing beats getting a MIG gun in your hands and spending a bit of time working on some pieces of metal. Get to know your local welding fabricators because they are often happy to sell scrap metal from their bins and share their years of experience with you. Or hit up your local junkyard. Select a few different thicknesses. With a few hours of dedicated practice you’ll go from a booger-welding novice to a relatively capable metal sticker.
Photo credit: noahw
About the Author
Gearhead Diva Purveyor of the illest car stuff on the net, decreaser of stance and performance suck world-wide, proud superfan of mods and now recommended by 4 out of 5 people that recommend things.