Transcript GMAW Fundamentals

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 shielding gas.
 GMAW is also known as MIG (Metal Inert Gas).
 Produces high-quality welds
 Yields high productivity
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
TYPES 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)
 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
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
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
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
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
GMAW COMPONENT DIAGRAM
WIRE CONTROL
&
WIRE FEED
MOTOR
POWER SOURCE
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
GAS DIFFUSER
NOZZLE
TRIGGER
CONTACT TIP
INSTALLED
COMPONENTS
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
WIRE FEEDER
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
POSITIVE
TERMINAL
NEGATIV
E
TERMINA
L
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
FLOW METER
CFH PRESSURE
ADJUSTMENT
KNOB
CYLCINDER
PRESSURE
GAUGE
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).
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
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.