MIG Welding Part 1: The Basics
The welding method of choice for most car restorers is MIG welding. It is the easiest to learn and the equipment is relatively inexpensive. Because of this, this article will focus on MIG welding.
What is Welding?
Basically, welding is the fusing together of two separate pieces of steel by heating and adding a steel filler. MIG welding (Metal Inert Gas) consists of a consumable wire electrode that creates the arc (which generates the heat) and provides the filler material.
At the same time that the wire electrode is fed through the "torch" or "gun," an inert gas is fed onto the weld zone to shield the weld from contamination from the surrounding atmosphere. One of the primary benefits of MIG welding is that the metal from the wire is deposited at a high rate of speed. This results in the least amount of distortion and the area exposed to the heat is relatively small.
Equipment Used in MIG Welding
A MIG welder is called a Continuous Voltage type power source. It can be a DC rectifier (A rectifier is a device that converts alternating current into direct current.). It can be plugged into a 120 Volt, 220 Volt circuit or the AC power can be supplied by a motor or engine-driven generator.
The relationship between the power supply current and the wire-feed speed is fixed. This means that the amount of current is determined by the wire-feed speed and is controlled by a rheostat (sort of the electrical equivalent of a volume switch.)
MIG welding is done in a controlled atmosphere created by the shielding gas. There are several shielding gases used in MIG welding: pure argon; argon-helium; argon-oxygen; argon-carbon dioxide; and carbon dioxide. You get the greatest weld penetration using carbon dioxide. However, carbon dioxide gives a harsher, more unstable arc, which leads to increased spatter. (Carbon dioxide is not entirely an "inert" gas — one of its components is oxygen). When welding on thin materials, it is preferable to use a 25% argon-75% carbon dioxide mixture.
The gas flow is controlled by a pressure-reducing regulator and flow meter on the gas cylinder. The flow rates vary, depending on the thickness of the material being welded and the design of the weld joint.
As with all the processes used in your car restoration project, safety is of primary importance. Here are some safety considerations:
- Always wear protective clothing. This includes flame-resistant suits or aprons, sleeves, and caps worn under your helmet. Massive amounts of sparks can be flying everywhere when you are welding. You don't want these to land in your hair, on your skin, on your clothes, etc. Keep a wet towel nearby in case something bad happens.
- Always wear heavy flame resistant gloves. These protect your hands from burns, cuts and scratches. While you can obviously get burned from sparks and handling hot steel, any exposed skin is susceptible to ultra-violet induced burning similar to sun burn. The wavelength of the ultra-violet light photons hitting your skin can, over time, cause skin cancers. Welding isn't a good way to get a suntan. Also, when dry, good leather welding gloves can offer some insulation against electric shock.
- Always work in a dry area. Even profusely sweating can increase the potential for electric shock. You must be careful to insulate your body from electrically "live" parts. Do not weld directly on your garage floor. Moisture encapsulated in the concrete can rapidly heat up and can damage your floor.
- Always wear a welding helmet. A helmet gives your face full protection from ultra-violet rays. Exposure to ultra-violet radiation can lead to serious permanent injury to your eyes, especially your retinas. Make sure that your helmet has the proper filter for the welding you are doing. Many welders come with inexpensive (read: not practical) hand-held face shields. We keep these around for any visitors to our garage to use while we are welding. Don't forget to offer your visitors a glove to protect the hand holding the shield from ultra-violate radiation.
- We prefer the auto-darkening welding helmets. The lenses in these let you see what you are doing before the arc forms. As soon as there is an arc, these filters darken, usually in about 1/2000 of a second. You don't have to concern yourself with nodding to get your helmet to fall into place while keeping the welding gun where you want it.
- Electric shock can be deadly. There are two kinds of shock associated with welding. Primary Voltage Shock and Secondary Voltage Shock. Primary Voltage Shock (120, 240, 460 volts) is the greatest hazard because it is shock that comes directly from the power source. You can receive a Primary Voltage Shock if you touch a lead inside the welder with the power switch on, for example, when you are loading a new spool of welding wire. Remember that turning the switch off doesn't turn off the power coming into the welder. The input power cord must be unplugged. Keep all the fixed panels on your welder and never ignore a blown fuse. It's a warning that something is wrong.
A Secondary Voltage Shock occurs when you touch part of the electrode circuit at the same time that another part of your body is touching the metal that you will be welding. To receive a shock, your body must touch both sides of the welding circuit - electrode and work. To prevent this, you must:
- wear dry gloves in good condition when welding;
- Do not touch the electrode or metal parts of the electrode holder with skin or wet clothing
- Keep dry insulation between your body and the metal being welded.
- Keep your welding cable and electrode holder in good working condition.
- Keep your work area clean. Do not have flammable materials around your welding space. Sparks of molten metal can fly as far as 30 feet away and can easily ignite fires. Keep all solvents, paper, wood and other flammables in a safe place. When welding on your car, if possible, put fire-proof shields behind the weld. We make it a habit of working in our garage at least 30 minutes after completion of our welding to be sure that there are no smoldering sparks. And always have a fire extinguisher handy.
- Fumes from welding are hazardous. Depending on the materials you are welding, exposure to these fumes can cause burning of the eyes and skin, dizziness, nausea and fever. Always weld in a well-ventilated area and avoid breathing the fumes. Fumes from welding contain solid particles from the consumables, base metal, and base metal coatings. Depending on the length of exposure most acute effects are temporary. Chronic long-term exposure to welding fumes can lead to siderosis (iron deposits on the lungs) and may affect pulmonary functions. We generally keep a fan blowing (gently) over our welding area to help remove the fumes quickly. Do not aim the fan directly at the piece being welded. It could disrupt the shielding ability of the welding gas.
- Manganese overexposure can affect the central nervous system, resulting in impaired speech and movement. This condition is considered irreversible. Bronchitis and some lung fibrosis also may result from manganese exposure.
- Fumes from the use of stainless steel and other specialized consumables can contain certain compounds of chromium and/or nickel. Some of these compounds are known to have caused lung cancer in processes other than welding.
- Cadmium also requires extra precautions. This toxic metal can be found on steel and steel fasteners as a coating, or in silver solder. Cadmium fumes can be fatal even under brief exposure. It is absorbed through the skin as well, so take care.
- The gases used in the welding process also present a potential hazard. Most of the shielding gases are nontoxic, but as they are released they displace oxygen in your breathing air. If you sit in a low area of the floor it's possible to suffocate due to the heavier-than-air properties of the shielding gas.
Electric and magnetic fields Electric current flowing through any conductor causes local electric and magnetic fields. These fields are created around welding machines and cables and may interfere with some pacemakers. Welders with pacemakers should consult with their physicians before welding. Exposure to electric and magnetic fields may have other health effects that are now not known. All welders should:
- Route the electrode and work (ground) cables together. Secure them with tape when possible
- Never coil the electrode lead around your body
- Do not place your body between the electrode and work cables. If the electrode cable is on your right side, the work cable should also be on your right side.
- Connect the work cable to the work piece as close as possible to the area being welded.
- Do not work next to the welding power source.
While all of this may sound frightening, welding is an intrinsic part to the car restoration hobby and it can be a rewarding experience for the hobbyist. But, probably more than with any other car restoration process, care must be taken to assure your health and safety. Take time to think through what you are doing and take the required precautions. The few minutes required to make sure there are no old rags or paper close to your welding project are certainly a more effective use of your day than trying to put out the fire.