GMAW Fundamentals

GMAW FundamentalsGMAW Fundamentals

Gas Metal Arc Welding

Metal Inert Gas

By: Wanda Sue Benton

ESAB University & Florence-Darlington Technical College

IntroductionIntroduction

GMAW is defined as arc welding using a continuously fed consumable electrode and a shielding gas.

GMAW is also known as MIG (Metal Inert Gas).

Produces high-quality weldsYields high productivity

AdvantagesAdvantages

Large gaps filled or bridged easilyWelding can be done in all positionsNo slag removal requiredHigh welding speedsHigh weld qualityLess distortion of work piece

Types of Metal TransferTypes of Metal Transfer

The basic GMAW process includes three distinctive process techniques:

1. Short Circuit (Short Arc)

2. Globular Transfer

3. Spray Arc Transfer

Short Circuit (Short Arc)Short Circuit (Short Arc)

Operates at low voltages and welding current

Small fast-freezing weld puddle obtainedUseful in joining thin materials in any

position, as well as thick materials in vertical and overhead positions

Metal transfer occurs when an electrical short circuit is established

Globular TransferGlobular Transfer

Welding current and wire speed are increased above maximum for short arc

Droplets of metal have a greater diameter than the wire being used

Spatter present Welding is most effectively done in the flat

position when using globular transfer

Spray Arc TransferSpray Arc Transfer

Occurs when the current and voltage settings are increased higher than that used for Globular Transfer

Used on thick sections of base material, best suited for flat position due to large weld puddle

Spatter is minimal to none

Manual GMAW EquipmentManual GMAW Equipment

Three major elements are :

1.) Welding torch and accessories

2.) Welding control & Wire feed motor

3.) Power Source

GMAW equipment can be used either manually or automatically

WIRE CONTROL&

WIRE FEED MOTOR

POWER SOURCE

Welding Torch & AccessoriesWelding Torch & Accessories

The welding torch guides the wire and shielding gas to the weld zone.

Brings welding power to the wire alsoMajor components/parts of the torch are the

contact tip, shielding gas nozzle, gas diffuser, and the wire conduit

TRIGGER

INSTALLED

COMPONENTS

NOZZLE

CONTACT TIP

GAS DIFFUSER

Welding Control & Wire Welding Control & Wire Feed MotorFeed Motor

Welding control & Wire feed motor are combined into one unit

Main function is to pull the wire from the spool and feed it to the arc

Controls wire feed speed and regulates the starting and stopping of wire feed

Wire feed speed controls Amperage

WIRE FEEDER

Power SourcePower Source

Almost all GMAW is done with reverse polarity also known as DCEP

Positive (+) lead is connected to the torchNegative (-) lead is connected to the work

pieceProvides a relatively consistent voltage to the

arcArc Voltage is the voltage between the end of

the wire and the work piece

POSITIVETERMINAL

NEGATIVETERMINAL

Shielding GasesShielding Gases

Purpose of shielding gas is the protect the weld area from the contaminants in the atmosphere

Gas can be Inert, Reactive, or Mixtures of both

Gas flow rate is between 25-35 CFHArgon, Helium, and Carbon Dioxide are the

main three gases used in GMAW

FLOW METER

CYLCINDERPRESSUREGAUGE

CFH PRESSURE ADJUSTMENT KNOB