The Basics of MIG Welding

By Chet Hastings

For over a hundred years arc welders were used for fusing pieces of metal together to produce various products. With many innovations this system has proved to be very practical. But as modern production methods demanded a faster more economical welding method that did not require extremely qualified welders became necessary. The basic arc welding system uses electricity to produce an arc between a coated welding rod and the metal to be welded. Although a simple enough process in detail it actually required a fairly competent welder to produce satisfactory welds at an economical rate. The process also has other faults.

The welding rods are short in length, 12 to 16 inches, to make it possible to properly handle them. Because they are consumed as the welding progresses the welder needs to stop every couple of minutes to load a new rod. He also needs to adjust the distance from the metal as the rods are consumed and become shorter while at the same time maintaining the proper arc distance. This requires practice. In addition the coating on these rods which is used to shield the weld puddle from the atmosphere leaves a coating on the finished weld called slag. In most cases this slag must be chipped off and wire brushed before the welding can continue. This can be a slow tedious job.

To solve these problems an arc welding machine called a MIG, (metal inert gas), has appeared. While the welding is performed by producing an arc between the welding torch and the metal as in standard arc welding, the actual process is vastly different. First and very important a MIG welder uses pressurized gas to shield the weld puddle. This system leaves a clean weld without slag which means that the welder no longer has to spend time cleaning each weld before he starts the next one.

Instead of a short consumable welding rod the MIG system uses a large coil of bare welding wire which can be fed through the welding torch at a controllable rate. While doing so the welder can maintain the arc by holding the welding torch in the same position at all times. The welding torch has a trigger which when pulled feeds the wire and starts the electrical current needed to produce the welding heat. The shielding gas is also turned on as the wire is fed and shields the weld puddle without leaving an residue which would need to be cleaned. This system allows the welder to work for long periods of time on long welds without stopping to replace his welding rod.

About once per shift or less the welder will replace the empty wire coil with a new roll of wire and perhaps will need to replace the gas bottle. Other than these chores he is free to spend his time completing welds at a very economical rate. Any fairly competent person with normal eye site and standard mechanical can be taught to be a production welder in a short time.

The MIG welding machine has allowed many manufacturers to greatly reduce their welding costs. This system also works very well for welding aluminum which is extremely difficult to do with the standard arcwelding system.

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