Welding Machines

Metal Inert Gas (or MIG) Welding machines are the machines that utilize a continuous consumable wire electrode and a shielding gas in the welding process. MIG Welding is an arc welding process which is a subtype of Gas Metal Arc Welding (GMAW). In MIG Welding process, the arc which is created melts both the work pieces and the electrode wire. The fused electrode material gets deposited on the weld pool and joins the pieces together. The electrode is continuously fed automatically and hence the overall process is semi-automatic. It is called semi-automatic because the operator still has to control the torch positioning and speed.
The equipments in a MIG Welding machine are: welding gun and wire feed unit, electrode, shielding gas and a power supply unit.
The welding gun in a MIG Welding machine has the following parts: an electrode conduit and liner, a gas hose, a gas nozzle, a power cable, a contact tip and a control switch. First, the operator presses the control switch which initiates the power, the wire feed and shielding gas flow and cause the arc to be created. Next, the contact tip which is usually made of copper and which is connected to the power source through the power cable transmits the electrical energy to the electrode which directs it to the weld area.
The wire is protected by an electrode conduit and liner just before the contact tip which prevents the buckling up of the wire feed. The gas nozzle makes sure that the shielding gas has a consistent flow over the weld area as any inconsistency can hinder the protection of the weld area. The gas hose supplies the gas to the nozzle. The wire feed unit is responsible for driving the wire through the conduit over to the contact tip.
The choice of the electrode in a MIG welding machine depends on the surface conditions of the material and the joint design but it is usually based on the composition of the metal being welded. The electrode wire has composition similar to that of the parent metal. Commercially available electrodes have a little percentage of deoxidizing agents like silicon, zirconium, manganese, etc which helps to prevent the porosity caused by oxygen and nitrogen.
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Using a shielding gas in a MIG Welding machine is very important as it plays a very important role of protecting the weld from getting contaminated by atmospheric gases like nitrogen and oxygen. These gases cause the metal embrittlement, porosity and fusion defects. Inert gases like argon and helium are usually used as shielding gases in the welding process of non-ferrous metals.
The power supply used has to be constant voltage power supply. The arc length is directly related to the voltage and any change in the arc length causes large changes in the heat and current. A D.C. power source is usually used but some designs may also use A.C. power source.
MIG Welding Machine has the advantages that no slag formation takes place and a continuous weld may be produced. But there are certain disadvantages also. The most important being that the outdoor application of MIG welding machine is very limited since the wind can cause the dispersion of shielding gas. Also this welding machine is very expensive and non-portable.