GAS METAL ARC WELDING (GMAW)

What is GMAW An arc welding process that uses an arc between a continuous filler metal electrode and the weld pool to produce a fusion (melting) together of the base metal The process is used with a shielding gas supplied from an external source without pressure.

Also Known AS Wire Feed MIG = Metal Inert Gas MAG= Metal Active Gas Inert Gas= Inactive gas that does not combine chemically with base or filler metal MAG= Metal Active Gas Active Gas= Gas will combine chemically with base or filler metal

Advantages Disadvantages Variety of Metals All Position Welding Quality Welds Little to No Slag Low Spatter Disadvantages Cost Portability Outdoor Welding Clean Base Material

GMAW Safety Cover all skin to prevent Radiation burns Cover hair to prevent sparks setting hair on fire Wear ear plugs to protect from noise and burning ear drums with sparks Use a 14 shade welding helmet to protect eyes Wear safety glasses at all times Make sure pants pockets are empty

GMAW Equipment Power Supply Wire Feeder Direct Current Electrode Positive (DCEP) (Electrons flow from – to +) Wire Feeder Electrical mechanical device that feed required amount of filler material at a constant rate of speed

GMAW Equipment (Cont) Welding filler electrode Shielding Gas Small diameter consumable electrode that is supplied to the welding gun by the roller drive system Shielding Gas Gas used to protect the molten metal from atmospheric contamination 75%Argon (inert gas) & 25% Carbon Dioxide most common gas used for GMAW

Principles of the GMAW Process

GMAW Set UP Plug ground wire into (Neg) Terminal Plug Wire Feeder into (Pos) Terminal Select CV-Wire mode Hot start is not used Set Arc Control to “-5” -10= soft arc (for use with inert gases) +10= crisp arc (for use with CO2) (See Next Slide)

Min. Arc Control Max Arc Control Soft Arc Thicker Materials Deeper Penetration More Fluid Weld Pool Flatter / Smoother Weld Reduce Spatter Stainless Steels Max Arc Control Crisp Arc Thin Materials Arc Stability On Open Gaps Convex Weld Bead Increased Spatter Colder Arc Improved Weld Pool Control 12

GMAW Set Up (Cont) Set Volts Set Wire Speed Set gas flow See Chart for proper setting Set Wire Speed Increase wire speed = Increase amps Decrease wire speed = Decrease amps Set gas flow Pull trigger to get gas flowing then adjust regulator

Running a Bead Hold tip 1/16” to 1/8” from work piece Angle of tip should be 10-15° Can push or pull bead Pull (preferred) More stable arc Less Spatter Deeper penetration Push More spatter Less penetration Good cleaning action

Bead Formation

Wire Burnback Possible Causes Corrective Actions * Drive Rolls in Poor Condition *Tighten, Clean, or Replace Drive Rolls * Excessive Welding Voltage * Reduce Voltage * Insufficient Electrical Stickout * Increase Contact Tip to Work Piece Distance * Contact Tip in Poor Condition * Clean or Replace Contact tip * Spatter on Contact Tip * Remove Spatter

Burnthrough Possible Causes Corrective Actions * Excessive Amperage *Reduce Amperage * Improper Travel Angle * Use a Push Angle *Travel Speed Too Low * Increase Travel Speed * Insufficient Electrical Stickout * Increase Contact Tip to Work Distance

Incomplete Penetration Possible Causes Corrective Actions * Insufficient Amperage *Increase Amperage * Improper Travel Angle * Use Less of a Drag angle * Excessive Electrical Stickout * Decrease Contact Tip to Work Piece Distance * Weld Joint Too Narrow * Increase the Opening of the Weld Joint

GMAW Process Parameters Steel Material .035” wire Short-Arc Mode Thickness Gas 75%AR-25%CO2 Amps Wire Speed Volts 1/8” 18-19 140-150 280-300 23-24 3/16” 160-170 320-340 24-25 1/4” 21-22 180-190 360-380 5/16” 200-210 400-420 25-26 3/8” 220-250 420-520 26-27