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GMAW Fundamentals. Gas Metal Arc Welding Metal Inert Gas By: Wanda Sue Benton ESAB University & Florence-Darlington Technical College. Introduction. GMAW is defined as arc welding using a continuously fed consumable electrode and a shielding gas.

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Gmaw fundamentals l.jpg

GMAW Fundamentals

Gas Metal Arc Welding

Metal Inert Gas

By: Wanda Sue Benton

ESAB University & Florence-Darlington Technical College


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Introduction

  • 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 welds

  • Yields high productivity


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Advantages

  • Large gaps filled or bridged easily

  • Welding can be done in all positions

  • No slag removal required

  • High welding speeds

  • High weld quality

  • Less distortion of work piece


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Types of Metal Transfer

The basic GMAW process includes three distinctive process techniques:

  • Short Circuit (Short Arc)

  • Globular Transfer

  • Spray Arc Transfer


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Short Circuit (Short Arc)

  • Operates at low voltages and welding current

  • Small fast-freezing weld puddle obtained

  • Useful 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


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Globular 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


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Spray 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


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Manual 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


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WIRE CONTROL

&

WIRE FEED MOTOR

POWER SOURCE


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Welding Torch & Accessories

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

  • Brings welding power to the wire also

  • Major components/parts of the torch are the contact tip, shielding gas nozzle, gas diffuser, and the wire conduit


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GAS DIFFUSER

NOZZLE

TRIGGER

CONTACT TIP

INSTALLED

COMPONENTS


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Welding Control & Wire Feed 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



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Power Source

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

  • Positive (+) lead is connected to the torch

  • Negative (-) lead is connected to the work piece

  • Provides a relatively consistent voltage to the arc

  • Arc Voltage is the voltage between the end of the wire and the work piece


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POWER SOURCE

POSITIVE

TERMINAL

NEGATIVE

TERMINAL


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Shielding 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 CFH

  • Argon, Helium, and Carbon Dioxide are the main three gases used in GMAW


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FLOW METER

CFH PRESSURE

ADJUSTMENT

KNOB

CYLCINDER

PRESSURE

GAUGE


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