Gas Metal Arc welding (GMAW), or what is commonly referred to as metal inert gasr (MIG) welding and also metal active gas (MAG) welding. Although MIG is more commonly used compared to MAG. If aren’t familiar with this kind of welding, this is the one wherein an electric arc forms between a consumable wire electrode and the work piece metal or metals. The heat causes this metal or metals to melt and join together. This process can be done automatically or semi-automatically. Here a constant voltage from a direct power source is used. There are four primary methods of metal transfer in GMAW which are called globular, short-circuiting, spray, and pulsed-spray. Each of these methods have their own advantages and limitations.
This has been originally developed for the purpose of welding aluminum and other non-ferrous materials in the year 1940s. After much observation, they noticed that this process was able to provide a faster welding time compared to other welding processes, as a result it was soon applied to steels. The said process was developed even further in the 1950s and 1960s that’s why it has become a highly used industrial process. Today it is preferred by most welders because it is versatile, faster, and there’s an ease of adapting it to the process of robotic automation. Take note however that this process is rarely used outdoors, or in areas of air volatility.
- WELDING GUN AND WIRE FEED UNIT
The welding gun that is used in MIG has common parts which are: a control switch, a contact tip, a power cable, a gas nozzle, an electrode conduit, and a liner. How do you use this? Okay so the first thing to do is to press the control switch or sometimes referred to as the “trigger”, this then initiates the wire feed, electric power, and the shielding gas flow. This causes an electric arc to be struck. Next would be the contact tip, which is normally made out of copper, and it is sometimes chemically treated in order to reduce spatter. This contact tip is then connected to the welding power source through a power cable and through this it is now able to transmit electrical energy to the electrode all the while directing it to the weld area. Note that when doing this, it must be firmly secured and properly sized. You must be able to maintain electrical contact in order to let the electrode pass. In the contact tip, you will notice that the wire is protected and guided by the electrode conduit and liner. This helps in preventing bulking and maintaining uninterrupted wire feed.
Inconsistent flow may not be able to adequately protect the weld area. In some welding areas, it is from a gas hose from the tanks of shielding gas that supplies as tot he nozzle. If you are observant, you may notice that sometimes a water hose is built into the welding gun. The purpose of this is to cool the gun in high heat operations.
It is the wire feed unit which supplies the electrode to work, driving it through the conduit, and on to the contact tip. So what’s the best wire for this?
There are two most popular welding wire in the market today, and we will concentrate on these two today. If you think about it, they won’t be popular if they aren’t any good, right? So both of them are from LINCOLN ELECTRIC. Theser are the SuperArc MIG wire L-50 and L-56. They are both 70,000 lb tensile strength wires that were designed for welding mild and carbon steels. The factor that sets them apart from each other would be the amount of “deodorizers” found in the wires.
L-50 is a great wire to use for general fabrication MIG wire and it usually allows you to make quality welds on a clean steel. If you are into production work, you may switch to 0.035″, and 0.045″. These two are the common diameters used.
If you aren’t welding in what is normally considered as a less than perfect surface conditions, then you should think about getting the L-56 wire. This wire has more deodorizers in it’s chemistry, thus making it have a built-in cleaning action, this usually produces a higher quality weld materials with less than the stellar surface conditions. This wire is chosen by most automotive manufacturers. It also meets the welding performance demands of a sheet metal (24 gauge) to heavy plate welding.
- TOOL STYLE
A semi-automatic air cooled holder is most preferred. Compressed air is able to circulate through it to maintain moderate temperatures. It is often used with lower current levels for welding tap and butt joints.
The next popular one that is use is a semi-automatic but this time, it’s water-cooled. It is used for a high current levels for welding T or corner joints.
- POWER SUPPLY
As I said above, you will need a constant voltage power supply. Any change in arc length results in a large change in heat input and current. If you use a shorter arc length, then this causes a much greater heat input, causing the wire electrode to melt more quickly and restore the original arc length.
In order to select the right electrode, you must base this primarily on the composition of the metal that you are about to weld. The selection process greatly influences the mechanical properties of the weld and is basically the key factor of weld quality. Commercially available electrodes include deoxidizing metals such as silicon, manganese, titanium, and aluminum in small percentages to prevent oxygen porosity. Some contain denitriding metals such as titanium and zirconium to avoid nitrogen porosity.
- SHIELDING GAS
This is necessary for MIG welding in order to protect the welding area from atmospheric gases such as nitrogen and oxygen, which can cause fusion defects, porosity, and weld metal embrittlement if they come in contact with the electrode. The choice of shielding gas depends on several factors but the most important ones in this factor is the type of material to be welded and the process variation being used.