MIG WELDING, METAL INERT GAS

What is MIG WELDING, METAL INERT GAS

An arc is placed between the end of the wire electrode and the workpiece, melting the two to form a weld pool. The wire serves as both the heat source (the tip of the wire through the arc) and the filler metal for the joint.

 The wire is fed through a copper contact tube (contact tip) that turns on the welding current in the wire. The weld pool is protected from the surrounding atmosphere by gas fed through a nozzle around the wire.
The wire is fed from the reel by a motor drive, and the welder moves the welding torch along the joint line. Wires can be solid (ordinary drawn wire) or cored (composites that flow with powder made from a metal sheath or fill liquid). Compared to consumables for other processes, a competitive price is usually determined. The process provides high productivity, as the wire is fed continuously.

speed and wire position is under manual control. When all process parameters are not directly controlled by a welder, the process can also be mechanized but may require manual adjustment during welding. When no manual intervention is required during welding, the process can be referred to as automatic. The process is usually positively charged with a wire and connected to a power source giving a constant voltage. 

The selection of the wire diameter (typically between 0.6 and 1.6 mm) and the wire feed speed determine the welding current, as the burn-off rate of the wire will balance with the feed speed. Metal transfer mode The manner, or mode, in which the metal is moved from the electrode to the weld pool roughly determines the operational characteristics of the process. There are three major metal transfer modes: Short circulating/dip Drop/spray Pulsed Short-circulating and pulsed metal transfer are used for low current operation while spray metal transfer is used only with high welding currents. In short-circuiting or 'dip' transfer, the molten metal formed at the tip of the wire is transferred to the weld pool by wire dipping. This is achieved by setting a low voltage;

 For a 1.2 mm diameter wire, the arc voltage varies from about 17V (100A) to 22V (200A). Care in setting the voltage and inductance concerning the wire feed speed is necessary to reduce the specter. Inductance is used to control the surge in current that occurs when the wire falls into the weld pool. 

Mig welding working

 For droplet or spray transfer, a very high voltage is necessary to ensure that the wire does not make contact i.e. short-circuit, with the weld pool; For a 1.2 mm diameter wire, the arc voltage varies from about 27V (250A) to 35V (400A). The molten metal at the tip of the wire transfers to the weld pool in the form of small droplet sprays (about the diameter of the wire and smaller). However, there is a minimum current level, threshold, below which droplets are not forcibly introduced across the arc. If an open arc technique is attempted to be far below the threshold current level, a low arc force will be insufficient to prevent large drops from forming at the tip of the wire.

 These drops will move irregularly across the arc under normal gravitational forces.to avoid short-circulating and splatter. The transfer of the metal is achieved by applying pulses of current, each pulse having enough force to separate a small droplet. Synergic Pulsed MIG refers to a special type of controller that enables the power source to be set according to the tune (pulse parameter), and wire feed speed, for the wire's structure and diameter. shielding gas In addition to the normal shielding of arc and weld pools, shielding gas performs several important functions: Arc makes plasma The arc on the surface of the material stabilizes the roots Ensures smooth transfer of melted drops from wire to weld pool Thus, 

the shielding gas will have a considerable impact on the stability of the arc and metal transfer and on the behavior of the weld pool, in particular, its penetration. General-purpose shielding of gas for MIG welding consists of mixtures of argon, oxygen, and CO2, and the particular gas mixture may contain helium. Commonly used gases for various materials are: 

Steels: CO2 Argon +2 to 5% 
oxygen Argon +5 to 25% 
CO2 Non-ferrous (such as aluminum, copper, or nickel alloys)

 Argon / Helium Argon-based gases, compared to CO2, are generally more tolerant of parameter settings and produce lower splatter levels with dip transfer modes. However, there is a greater risk of lack of fusion defects