This method is also known as Shielded Inert Gas Metal Arc (SIGMA) welding or Metal Inert Gas (MIG) welding or Gas Metal Arc Welding (GMAW).
It uses a shielded arc struck between a bare metal electrode and the work piece.
It is based on the principle of developing weld by melting faying surfaces of the base metal using heat produced by a welding arc established between base metal and a consumable electrode.
Welding arc and weld pool are well protected by a jet of shielding inactive gas coming out of the nozzle and forming a shroud around the arc and weld.
The metal electrode is provided in the form of a wire reel.
Metal inert gas process is similar to TIG welding except that it uses the automatically fed consumable electrode thus it offers high deposition rate and then it suits for good quality weld joints.
Effectiveness of shielding in two processes is mainly determined by two characteristics of the welding arc namely stability of the welding arc and length of arc besides other welding related parameters such as type of shielding gas, flow rate of shielding gas, distance between nozzle and work-price.
During welding consumption of the electrode slightly decreases the stability of the arc.
Torch is controlled either manual or automatically when consumable electrode is fed automatically.
It is suitable for thicker plates of reactive metals.
CHARACTERISTICS OF THE MIG WELDING PROCESS
Uses a consumable wire electrode during the welding process that is fed from a spool, Provides a uniform weld bead, Produces a slag-free weld bead.
Uses a shielding gas, usually – argon, argon - 1 to 5% oxygen. argon - 3 to 25% CO2 and a combination argon/helium gas.
It is a semi-automatic welding process.
It allows welding in all positions.
It requires less operator skill.
It allows long welds to be made without starts or stops.
SHIELDING GAS
The shielding gas forms the arc plasma stabilizes the arc on the metal being welded shields the arc and molten weld pool and allows smooth transfer of metal from the weld wire to the molten weld pool.
The primary shielding gasses are
Argon
Argon - 1 to 5% Oxygen
Argon - 3 to 25% CO2
Argon/Helium
CO2 is also used in its pure form in some MIG welding processes.
ADVANTAGES :
Less operator skill required
Minimal post weld cleaning is required
All position capability
Higher deposition rates than SMAW
Long welds can be made without starts and stops
MIG weld is not considered as clean as TIG weld
DISADVANTAGES :
Unstable arc
Irregular wire feed
Heavily oxidized weld deposit
Porosity
Difficult arc starting
Kommentare