Gas Metal Arc Welding (GMAW)

GMAW

• Gas Metal Arc Welding

• MIG ( Metal Inert Gas )

• MAG (Metal Active Gas)

• Wire Welding

Proper Attire

What is GMAW?Gas Metal Arc Welding• MIG - MAG Welding– MIG = Metal Inert Gas– MAG= Metal Active Gas

• Solid Wire with ExternalShielding Gas

• DCEP (DC+) Polarity

ADVANTAGES:

• All Position Welding • Quality Welds • Little to No Slag• Low Spatter• Variety of Metals• Various Material Thickness • High Efficiency • High Radiated Heat

LIMITATIONS:

• Cost• Portability • Outdoor Welding • Clean Base Material• Potential for Cold Lap • Potential for Undercut• High Radiated Heat

Identify Major Components• Power Source, Wire Feeder, Shielding Gas,

Electrode Wire, Gun

Power Source

• Converts Primary ( Outside ) Power To Secondary ( Useable ) Power

• DCEP Direct Current Electrode Positive / Reverse Polarity

• DCEP = Lower spatter levels, Deeper Penetration levels

Wire Feeder

• Delivers Wire To The Weld Pool At A Very Constant Speed

• Wire Feeder starts gas flow, current, wire feed• Wire Speed Is Measured In Inches Per Minute

Shielding Gas• To Shields The Weld Pool Form Contaminants

That are In The Atmosphere• Stabilize The Arc• Helps Regulate Penetration• Argon 75% - CO2 25% (C-25)

Mig GUN• Trigger• Liner• Contact Tip• Diffuser• Nozzle

Electrode WIRE

ER70S-6• ER = ELETRODE ROD• 70,000 TENSILE STRENGTH• S = SOLID WIRE• 6 = CHEMICAL COMPOSITION

• Wire Diameter Range (.025” - .125”)• Copper coated vs. non-coated wire

Starting the Arc

Electrode Stick Out - ESOSheet ESO = 3/8 - 1/2 inch

Plate ESO = ¾ - 1 inch

Bead Initiation

Bead Manipulation

Travel Angle

Bead Termination

Modes of Metal Transfer

1. Short Circuiting (Short Arc)2. Globular3. Spray

The welding machine automatically selects mode of transfer dependent upon settings & variables.– Type/mix of shielding gas– Electrode diameter– Voltage– ESO

Short Circuiting

• Droplet Forms• Droplet Shorted• Metal Transfers• Fuse Forms• Arc Re-established• Low Cost• Deep Penetration • Less Spatter• More Fluid Weld Pool

Globular• Arc Initiated

• Large Droplet Forms

• Projected into weld pool

GlobularAdvantages • Deep Penetration• High Deposition• Low Cost Gas

Limitations • Excessive Spatter• Flat / Horizontal

Position Only

Spray• Arc Initiated• Point Forms on End of

Electrode Wire• Numerous tiny Drops

Form the Weld Pool• 100% Argon

SprayAdvantages • Smooth Weld Bead

• Deep Penetration

• High Deposition

• Little to No Spatter

Limitations• Potential Undercut

• Higher Shielding Gas Cost

• Flat / Horizontal Position Only

• High Radiated Heat

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” 18-19 160-170 320-340 24-25

1/4” 21-22 180-190 360-380 24-25

5/16” 21-22 200-210 400-420 25-26

3/8” 23-24 220-250 420-520 26-27

Determining IPM without readout

• Cut shielding gas• Pull trigger & count to 6• Measure length of wire• Multiply x 10

Wire welds itself to the tip

Possible Causes Corrective Actions* Drive Rolls in Poor Condition *Tighten, Clean, or Replace 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

Wire Burnback

Hole burns through base metal

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 Distance

Burnthrough

Repairing Burn through

• Turn voltage slightly down• Extend ESO to ¾” • Small tack welds in a “star pattern”• Allow metals to cool sufficiently

• Toes should tie into metal • 1/8 bead height max

Possible Causes Corrective Actions* Insufficient Amperage *Increase Amperage * Improper Travel Angle * Use Less of a Drag angle* Excessive Electrical Stickout * Decrease Distance* Weld Joint Too Narrow * Increase joint opening

Incomplete Penetration

Lincoln V350 Setup - GMAW

• Plug ground wire into (-) Terminal• Plug Wire Feeder into (+) 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)