GMAW Fundamentals

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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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WIRE FEEDER
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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