GMAW (MIG/MAG Welding )

MIG / MAG WELDING 

Definition:- It is arc welding process wherein coalescence is produced by heating the job with an electric arc established between a continuously fed metal electrode and the job. No flux is uses but the arc and molten metal are shielded by an inert gas, which may be argon, helium, carbon dioxide or a gas mixture.

    If the shielding gas used in this process is an inert gas or mixture of inert gases, then it is termed as Metal Inert Gas (MIG welding) . When the shielding gas used contain active constituents eg. carbon dioxide or oxygen , then it is termed as Metal Active Gas ( MAG welding).

Principle of Operation:- Before igniting the arc, gas and water flow is checked. Proper current and wire feed speed is set and the electrical connections are ensured. The arc is struck by any one of the two methods. In the first method, current and shielding gas is switched on and the electrode is scratched against the job as usual practice for striking the arc. In the second method, electrode is made to touch the job, is retracted and then moved forward to carry out welding but before striking the arc shielding gas and current is switched on. About 15mm length of the electrode is projected from the torch before striking the arc. During welding, torch remains about 10-12 mm away from the job and arc length is kept between 1.5 to 4 mm. Arc length is maintained constant by using the principles of self-adjusted arc, and self controlled arc in semi- automatic and automatic welding sets respectively.

 

Advantages:-  

   * It is the only consumable electrode process that can be used to weld all commercial metals and alloys.

   * MIG/MAG welding overcomes the restriction of limited electrodes length encountered with manual metal arc welding.

   * welding can be done in all positions, a feature not found in submerged arc welding .

   * deposition rates are  significantly higher than those obtained with manual metal arc welding .

   * welding speeds are higher than those with MMAW because of the continuous electrode feed and higher filler metal deposition rates.

   * because the wire feed is continuous, long welds.

   * be deposited without stops and starts.

   * when spray transfer is used, deeper penetration is possible than with MMAW, which may permit the use of small size fillet welds for equivalent strength.

   * minimal post weld cleaning is required due to the absence of a heavy slag.

   * the arc and weld pool is visible which aids  correct placement of weld.

   * possible to have a control over heat input as the welding speed is higher. 

   * wide range of currents can be employed for a given diameter wire.

   * it produces low hydrogen types of weld deposit on steels.

   * thinner materials can be easily welded.

   * minimum quantity of smoke and fumes provides better work atmoshphere.

   * large gap can be bridged easily because of high deposition rate.

   * high utilisation of filler metal.

   * distortion is less due to number of passes and high welding speeds.