1. Basic equipment setup and welding procedures
GMAW / Mig Welding
Basic equipment setup and welding procedures

2. Gas Metal Arc Welding
Versatile technique suitable for both thin and thick sheet,
Is a process where a continuously fed metal electrode ( Wire ) contacts the base metal and produces heat . The arc is shielded by an inert gas ,
high productivity and economical.

3. 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

4. GMAW component diagram

5. Gas Metal Arc Welding Principles
Gas metal arc welding is generally used due to the high efficiency of filler metal that can be deposited per hour.
GMAW is approximately 92% - 98% efficient
GMAW requires a shielding gas

6. Gas Metal Arc Welding Principles
The GMAW process is performed using DCEP ( Direct Current Electrode Positive)
Alternating current is never used for GMAW
DCEN is used only for a specialized process using emissive electrodes

7. GMAW Advantages Welding can be done in all positions
No slag removal required
High efficiency(automatic regulation of arc length, high deposition rate )
Less work piece distortion
Large gaps bridged easily , Good for poor fitup
High Weld Quality
Low hydrogen potential process

8. GMAW Disadvantages No independent control of filler addition,
Difficult to set up optimum parameters to minimise spatter levels,
Risk of lack of fusion when using dip transfer on thicker weldments,
Lower heat input can lead to high hardness values,
Higher equipment cost than MMA,
Etc.

9. Typical Setup for voltage
The GMAW machine is a “Constant Voltage” power supply. This is set using the voltage dial
This setting can be monitored by the “Volt” meter on the front panel of the welder
Ideal voltage settings can be found in the wire manufactures data book

10. Typical Setup for Wire speed
The wire feed rate or speed is set using the dial on the wire controller This setting increases or decreases current or “Heat”. This setting is measured in AMPS or IPM (inches per minute )
Ideal settings can be monitored by the “Amp” meter on the front panel of the welder. Note : Some machines display “Current” (Same as AMPS) or IMP
Ideal settings can be found in the wire manufactures data book for both IPM and Current

11. 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).

12. 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

13. 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 .

14. Check the Manufactures data for settings

15. BASIC METALLURGY OF WELD METAL
Factor which influence HAZ size :
Heat input ;
H=(E.I/v) x 60
H:Joule (J),E : Volt,V, I : Ampere,A, v : travel speed,mm/min
State the factors which affected this heat input??

16. BASIC METALLURGY OF WELD METAL
Factor which influence HAZ size :
Cooling rate,cooling time ;
Weld zone = Weld metal + HAZ
Factor that influenced the weld zone cooling rate :
Heat input, (d) Inter pass temp,
Plate thickness, (e) Joint type
Pre-heat temp