Q. Explain the TIG and MIG systems of arc welding Give the applications of each.

                                                        OR

        Explain briefly the TIG welding techniques with the help of neat sketches.

                                                        OR

        Explain with neat sketches the difference between TIG and MIG welding process.

                                                         OR

        Explain the working principle of TIG and MIG welding with suitable sketches. Discuss the advantages of each one.

Ans. (i) TIG : Inert Gas Tungsten-Arc Welding : It is basically an arc welding process in which the arc is struck between a non-consumable tungsten electrode and the base metal. The electrode is held in a special type of electrode holder which is so designed that apart from holding the electrode, it also carries a passage around the electrode for flow of inert gas to provide the protective shield around the electrode for flow of inert gas to provide the protective shield around the arc. This gaseous shield protects the electrode, molten metal, the arc and adjacent heated areas of base metal from atmospheric contamination. The electrode holder also carries a provision for water cooling or air cooling. This process can be adopted for both manual and automatic operations.

         This process is suitable for welding in all positions. Thin metal foils upto a minimum thickness of 0.125 mm can be easily welded with this process. It is suitable for welding of most metals and alloys except lead and zinc, which have very low melting points.

        (ii) Inert Gas Metal-Arc Welding (MIG Welding)

        This process, popularly known as metal-inert gas (MIG) welding, involves welding of metals using a consumable metal electrode in an inert gas atmosphere. The arc is struck between the metal electrode and workpiece. The electrode is in the form of a continuous wire which is fed into the arc, by an adjustable speed electric motor, of the same speed of which it is melted and deposited in the weld. A specially designed electrode holder is used which, in addition to a passage for wire electrode, also incorporates passages for supply of inert gas for shielding the electrode, molten weld metal, arc and the adjacent not area of base metal from atmospheric contamination. It is possible to weld cast iron, titanium and its alloys, refractory metals, manganese bronze, etc. also it is not suitable for welding of low melting point metals like lead, tin and zinc and also those metals which carry coatings of these low melting point metals.

Advantages of MIG Welding

         1. It is faster than shielded metal arc welding due to continuous feeding of filter metal.

         2. There is no slag formation.

         3. It provides higher deposition rate.

         4. The weld metal carries low hydrogen content.

         5. Deeper penetration is possible.

         6. More suitable for welding of thin sheets.

         7. Welds produced are of better quality.