Metal Inert Gas Welding or MIG welding, also known as GMAW (Gas Metal Arc Welding) is a very complicated welding process. Many men and women work in this trade with great happiness and success. It is complicated because there are so many variables that a welder needs to be aware of to perform and create a solid quality weld. Just a few variables include volts, amperes, type of metal being welded, type of weld joint, various welding positions, type of filler metal being added, type of gas used, power source used during the welding process, environmental variables such as temperature, wind, and moisture, and most importantly, weld profile. Four MIG welding processes exist, while three are most commonly used. MIG uses a constant voltage power supply to maintain a stable arc while welding. This means that the power source is designed to create constant voltage while allowing the welder to adjust the voltage and amperes to perform the applicable weld process.
This may sound daunting but do not worry; I am a professional. The arc welding of metals began in the 1800s with the discovery of the electric arc. The MIG welding process was not a practical use until 1948. However, it was not until 1953 that a gas shielding was used to maintain a stable arc. Today, it is the most versatile and efficient weld process used. For beginning welders there are several tools available to assist in eliminating some of the variables that make this process so difficult. Many welding supply stores carry literature like pocket welding guides and welding calculators. Pocket welding guides are invaluable to the beginning welder because they have illustrations showing what a good weld looks like and the most common weld defects with suggestions on how to remedy the defect. They also have charts that show the type of metal, metal thickness, and filler metal to use. With these charts, they easily give a point of reference on where one might set volts and wire speed to achieve the proper amount of amperes allowing for a stable arc during the welding process. This stable arc is often described as sounding like crackling sizzling bacon. Most seasoned welders are able to set their machines by this sound alone. The four main welding positions are flat, horizontal, vertical, and overhead; these are ordered from easiest to most difficult.
Earth’s atmosphere contains many types of gasses to make it allowable for human inhabitance; a shielding gas is required to help protect the arc because of this. The most common gas is called 75/25 or C25. It contains 75% Argon and 25% CO2. Argon is an inert gas, meaning it will not chemically react with other elements. CO2 is a reactive gas. This means that the term Metal Inert Gas Welding is a bit of a misnomer because today in welding practices both inert and reactive gases are used for different reasons. For example, the gas Argon has a cooling effect and it allows for a smaller heat affected zone. On the other hand, CO2 causes more heat to be applied to the weld allowing for deeper weld penetration into the base metal. Argon is more expensive while CO2 is less expensive. If there is a smaller heat affected zone, this is the area outside the actual weld that is heated, there is have less chance of distortion in our finished work. If the metal heats and cools unevenly, then all we have is a warped piece of metal.
MIG is not ideal for welding outside because windy conditions disrupt the gas shield that protects the arc; however, MIG welding is great for production welding because it is often in a shop and allows for high weld deposition. This process can be used with a variety of metals. These metals are carbon steel, stainless steel, and aluminum. The type of metal and thickness determines which weld process that is to be applied. The four types of weld process are short-circuit transfer, spray transfer, spray-pulse transfer, and globular transfer. Short-circuit uses low volts and amps, generally less than 20 volts and 200 amperes and is often used on thinner metals. It is possible to weld in all positions in short-circuit transfer. While using short-circuit, 75/25 is the optimal shielding gas.
Spray transfer should be used for thicker metals because it has a higher penetration rate. It should only be used in flat and horizontal positions only because the weld puddle is very fluid. If one might try to weld in say the overhead position; speaking from experience, they would find themselves with a pool of molten metal in their lap. To achieve spray transfer, high voltage and amperage must be applied. To maintain spray transfer stability, your shielding gas must have at least 80% Argon. Spray-pulse has the high deposition rate and penetration like spray, but it can be used in all positions like short-circuit. The pulsing action allows your weld puddle enough time to cool down. Globular transfer is a weld process that is not very commonly used; in fact, in my welding career I have never had to use it.
Joint type and fit-up also play a key role in the quality of your weld. There are several types of joints. For example, butt joint, T-joint, bevel groove joint, lap joint, and corner joint are just a few. Butt joints are two pieces of metal put tightly together. A T-joint is exactly how it sounds, it resembles the letter “T.” Lap joints and corner joints are as they sound as well. Lap, as in overlap is when to pieces of metal are overlapping one another. A corner joint is when two pieces come together and form a corner.
Welding, like any other art takes practice and exposure. In today’s job market, welding is becoming an industry where many positions are open across the country. The baby-boomers, hard working men and women are coming to the age of retirement. That is, if they have not left the trade already due to accident or injury. Welding is a skilled trade that takes time and patience to master. While difficult, with the right aptitude and perseverance anyone man or woman can learn this art. Many community colleges and trade schools offer programs ranging from associates degrees to qualification certificates. It’s important when choosing a program that you look for a program that teaches both practical and text book knowledge. Do you have what it takes to be a welder?