By: William Walley
This process is called by many names and it basically is a welding process that uses an arc to heat metal that needs to be joined. The welder uses a continuous feed filler metal (a consumable) electrode and this is used on the work-piece. This type of welding also must use a shielding that is provided by a gas or a mixture of gasses.
This type of welding is also called short circuit transfer. In the MIG process, when the wire actually touches the metal to be connected, it lets go of the metal that does the welding. This makes sure that metal doesn’t transfer across an arc so there is no puddling.
Also known as gas metal arc welding, the MIG(GMAW) process uses a metal gun to provide this service instead of a torch so that you get a direct current going to the metal. You can use both constant current and alternating current systems to also produce this method of welding.
GMAW uses four ways to transfer metal. These are:
Globular – this method is difficult and used the least because it has a tendency to spatter because the gun will move to a high heat without warning. This makes the welding surface come out with flaws. This method uses carbon dioxide so the electrode tends to produce a ball of melted metal that cases irregular shapes that are bigger than the electrode. They then drop and falls onto the piece you are working on which causes a spatter. This is difficult to control as you would imagine.
Short circuiting – this uses a smaller current than the globular method but it still uses carbon dioxide. Because of the lower current you can actually weld thinner metals together with this method. This method is similar to the globular method because drops of melted metal from the electrode still forms, but it causes the electrode to short circuit instead of the drops falling on the work. This closes off the arc but comes back again because the surface tension pulls the metal goblet from the tip.
Spray – this was the first method for transfer used with GMAW and used to weld aluminium and stainless steel. The difference with this process is that the electrode metal passes through an electric arc that is stable and goes all the way to the workplace. This stops spattering and you get a weld finish that is higher quality than in other methods. You also will watch as the current and voltage increases so you get small, vaporized steam droplets instead of large globules.
Pulse spray – this last one is a newer way of doing this type of welding that uses a continuous current that pulses and melts the filler wire. In each pulse a small droplet of metal will fall.
This also allows the welder to use a lower current. The welder gets a more stable arc and this stops spatter and the short circuiting process. Because this process is slower, argon gas is used instead of carbon dioxide as the shielding gas.