The GMAW process is a commonly used arc welding process. As all other processes, it has its advantages and limitations.
The gas metal arc welding process, most commonly known as MIG, is one of the most used joining processes in the world today. The process had its beginnings over 60 years ago, but it is still being improved every day. Leading manufacturers in the welding industry spend millions of dollars in research and development to enhance this process. As with many other industries, advancements in manufacturing techniques, reduction of costs, and improved efficiencies have made high-end technology available for the hobby or beginning welder.
First of all a few definitions. The Gas Metal Arc Process is commonly referred to as MIG. MIG stands for Metal Inert Gas. Argon is the gas typically used for this process and it is a non-reactive gas, thus inert gas. However, carbon dioxide is also used either pure or mixed with argon. Carbon dioxide is a reactive gas so the term MAG (Metal Active Gas) should be used when talking about welding with 100% carbon dioxide shielding gas. For simplicity we will refer to GMAW process as MIG.
GMAW, in simple terms, is the joining of two metals by the use of an electric arc and continuously fed filler material. The equipment necessary for this process consists of a constant voltage power source, a wire feeder, a welding gun assembly, a power cable and control cable that run from the power source to the feeder, and ground cable and clamp (properly called work cable assembly).
Advantages of the GMAW Process
As mentioned above, the GMAW process is possible the most widely used process in the United States. This is due to several advantages. Below are listed several of these advantages:
- Low cost equipment – a hobby welder can get a welding machine from a reputable manufacturer such as Lincoln Electric or ITW for less than $600. Add a few dollars for shielding gas and mig wire and you are welding for less than $700.
- Low cost consumables – out of all the process the consumables for mig welding have the lowest cost. You can purchase mig wire from a big box store for less than $3 per pound. Or you can go to a local industrial distributor and get it for closer to $2 per pound.
- High deposition rates – especially when compared to stick welding. With the GMAW process you can deposit up to nearly 10 pounds per hour (deposited weld metal).
- Low hydrogen deposits – since solid does not pick up moisture like flux-cored wires and stick electrodes it consistently deposits welds with low levels of diffusible hydrogen. You can learn more about why this is important by reading “WHY WELDS CRACK”
- Can weld almost all metals – by simply changing your filler wire and at times the shielding gas you can weld from carbon steel, to stainless steel, to nickel alloys and aluminum.
- Low levels of spatter – low spatter can be achieved by selecting the right mode of metal transfer. Spray and pulse welding can provide this benefit.
- Unlimited thickness – this process allows for welding light gage material and up to unlimited thickness by using multiple passes. Higher amperages and proper joint configuration are needed to weld.
- Easy to learn – unlike tig welding or stick welding, mig welding is easy to learn.
- Little clean up – since mig welding is a slagless process it does not require chipping slag, cleaning up flux or discarding unused stick stubs.
- High electrode efficiencies – the GMAW process provides efficiencies of 93-97%. This means that if you buy 100 pounds of mig wire you will be deposition 93 to 97 pounds of weld metal. A process like SMAW (stick welding) has electrode efficiencies of around 65%. This is due to loss due to spatter, slag, and not consuming the entire electrode.
- Input voltages – If you have electric service you can weld. Smaller machines can run on 115 volt input. These machines are limited to about ¼” welding thickness. Some of the newer industrial machines are capable or running anywhere from 208 to 575 input voltage on either single or three-phase circuits. Most mig welding machines can also run off of portable generators.
Despite all these advantages the GMAW process also has some limitations.
Limitations of the GMAW Process
- Sensitive to contaminants – the process can only handle low to moderate levels of surface contaminants such as rust, mill scale, dirt, oil and paint. All these have potential to create problems such as porosity, incomplete fusion, bad bead appearance and even cracking.
- Portability – moving the welding equipment may not be that tough, but you also have to handle the high pressure cylinders that contain the shielding gas. Proper care must be taken.
- Sensitive to wind – the shielding gas used for mig welding can easily be blown away when welding outdoors. Even inside, a fan or a wind draft of as low as 5mph can be enough to cause porosity.
- Lack of fusion – due to the ability to weld at low currents this process has the potential for lack of fusision when running in short circuit mode. Make sure you always use the correct procedure for the thickness of material you are welding. There is a reason why the American Welding Society does not have pre-qualified procedures using the short-circuit mode of metal transfer.
- Open arc process – as with most welding process, GMAW exhibits an open arc. Proper care must be taking to shield the welder and bystanders from the harmful UV rays.