METAL INERT GAS WELDING – METAL ACTIVE GAS WELDING

METAL INERT GAS / METAL ACTIVE GAS WELDING

      MIG / MAG welding are also called as Gas Metal Arc Welding Process (G.M.A.W). This process uses Constant Voltage Power Supply (or) Flat Characteristic and Polarity used in this Process is D.C.E.P. In this process an arc is struck between the end of a wire electrode and the work piece, melting both to form a weld pool. The metal wire serves as the source of heat and filler metal for the joint. The wire is fed through a copper contact tube which conducts welding current into the wire. The weld pool is protected from the surrounding atmosphere by a shielding gas fed through nozzle surrounding the wire which can be inert or active. Inert gas is used for weldig non-ferrous material whereas Active gas is used for welding ferrous material.              

The wire is fed from a reel by a motor drive, and the welder moves the gun or torch along joint line. The MIG / MAG process uses Semi-automatic, Mechanized or Automatic equipment.this is a continous process.

PROCESS VARIABLE:

• • Welding current& voltage.
  • Wire feed speed
  • Tip to work piece distance
  • Nozzle to work piece distance
  • Inductance
  • Shielding gas nozzle
  • Electrode orientation

EQUIPMENT REQUIREMENT:

• • A transformer / rectifier
  • Power & power return cable
  • An inert or active or mixed shielding gas
  • Gas hose, flow mete & gas regulator
  • MIG torch with nose, liner, diffuse, contact tip & nozzle.
  • Wire feed unit
  • Correct visor / helmet, all safety clothing & good extraction. 

TYPICAL WELDING IMPERFECTION:

• SILICA INCLUSION
• Lack of fusion
• Surface porosity
• Burn through

ADVANTAGES:

• • High productivity
  • Easily automated
  • All position of welding can be done
  • Continuous electrode
  • High input
  • Low hydrogen potential process

DIS-ADVANTAGES:

• • LACK OF FUSION
  • SMALL RANGE OF CONSUMABLES
  • Protection for site working
  • Complex equipment
  • High ozone level.

TYPES OF METAL TRANSFER:

• 1. Dip transfer
  2. Spray Transfer
  3. Pulsed Transfer
  4. Globular Transfer.

DIP TRANSFER:

• • Used for positional welding
  • Risk of lack of fusion
  • Used for thin sheets above 0.8mm and less than 3-2mm.

SPRAY TRANSFER:

• • Also known as Free flight Metal Transfer.
  • High heat input
  • Used for steel above 6mm
  • Used only for flat, horizontal & vertical position.

PULSED TRANSFER:

• • Also known as free flight droplet transfer
  • Very low spatters
  • It is used for all steel thickness above 1mm

GLOBULAR TRANSFER:

• • Also known as irregular metal transfer.
  • High risk of spatter
  • It is used for steel thickness 3-6mm in flat position.

MCQ IMPORTANT POINTS

• 1. Argon + 1% – 5% oxygen is used for welding stainless steel.
  2. Argon + 3% – 5% hydrogen I used for welding Austenitic Stainless Steel
  3. Argon + 3% nitrogen is used for welding Duplex Stainless Steel.
  4. 100% carbon-di-oxide is used for welding Low Carbon Steel
  5. Argon + 15% – 25% co2 is used for FLUX CORED ARC WELDING of Stainless steel.
  6. Inert gasses like Argon & Helium are used for welding non-ferrous material using MIG WELDING PROCESS.
  7. Active gasses like oxygen, carbon-di-oxide & nitrogen are used for welding ferrous material using MAG WELDING PROCESS.
  8. Inductance is used to reduce spatters.
  9. Argon is 1.4 times heavier than air.
  10. MIG cannot be used for welding carbon steel.