1. Gas Metal Arc Welding (Metal Inert Gas) (MIG)
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

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 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.