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Gas Metal Arc Welding

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GMAW FUNDAMENTALS Gas Metal Arc Welding (Metal Inert Gas) (MIG) INTRODUCTION GMAW is defined as arc welding using a continuously fed consumable electrode and a ... – PowerPoint PPT presentation

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Title: Gas Metal Arc Welding


1
GMAW Fundamentals
  • Gas Metal Arc Welding
  • (Metal Inert Gas)
  • (MIG)

2
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

3
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

4
Types of Metal Transfer
  • The basic GMAW process includes three
    distinctive process techniques
  • Short Circuit (Short Arc)
  • Globular Transfer
  • Spray Arc Transfer

5
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

6
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

7
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

8
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

9
GMAW Components
  • DC or Direct Current power supply
  • Electrode or wire feed controller
  • Wire drive roller assembly
  • Shielding gas source (cylinder) regulator
  • Manually held Gun ground clamps
  • Wire reel

10
GMAW component diagram
11
WIRE CONTROL WIRE FEED MOTOR
POWER SOURCE
12
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

13
GAS DIFFUSER
NOZZLE
TRIGGER
CONTACT TIP
INSTALLED COMPONENTS
14
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

15

WIRE FEEDER
16
(No Transcript)
17
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

18
POWER SOURCE
POSITIVE TERMINAL
NEGATIVE TERMINAL
19
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

20
FLOW METER
CFH PRESSURE ADJUSTMENT KNOB
CYLCINDER PRESSURE GAUGE
21
Shielding Gas
  • Air in the welding zone is displaced by inert gas
    to Shield the molten weld pool and prevent it
    from contamination from Oxygen, Nitrogen and
    Water present in the atmosphere.
  • Insufficient gas flow will not displace the
    atmosphere resulting in porosity or voids in
    the deposited weld.
  • Flow is measured in CFH (Cubic Feet per Hour).

22
Insufficient Shielding Gas coverage
  • Gas not turned on
  • Flow rate not properly adjusted
  • Leaks in the hose supplying the shielding gas to
    the machine
  • GMAW / MIG Gun loose at wire drive connection
  • Spatter buildup on gas cup
  • Windy environment

23
Excessive Gas coverage
  • Will cause porosity.
  • The turbulence caused by the rapid flow of
    shielding gas exiting from the gas cup will draw
    the surrounding atmosphere into the stream of
    gas.
  • It will reduce weld pool temperatures causing
    decreased penetration.
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