1. GAS METAL ARC WELDING (GMAW)

2. What is GMAW
An arc welding process that uses an arc between a continuous filler metal electrode and the weld pool to produce a fusion (melting) together of the base metal
The process is used with a shielding gas supplied from an external source without pressure.

3. Also Known AS Wire Feed MIG = Metal Inert Gas MAG= Metal Active Gas
Inert Gas= Inactive gas that does not combine chemically with base or filler metal
MAG= Metal Active Gas
Active Gas= Gas will combine chemically with base or filler metal

4. Advantages Disadvantages
Variety of Metals
All Position Welding
Quality Welds
Little to No Slag
Low Spatter
Disadvantages
Cost
Portability
Outdoor Welding
Clean Base Material

5. GMAW Safety Cover all skin to prevent Radiation burns
Cover hair to prevent sparks setting hair on fire
Wear ear plugs to protect from noise and burning ear drums with sparks
Use a 14 shade welding helmet to protect eyes
Wear safety glasses at all times
Make sure pants pockets are empty

6. GMAW Equipment Power Supply Wire Feeder
Direct Current Electrode Positive (DCEP)
(Electrons flow from – to +)
Wire Feeder
Electrical mechanical device that feed required amount of filler material at a constant rate of speed

7. GMAW Equipment (Cont) Welding filler electrode Shielding Gas
Small diameter consumable electrode that is supplied to the welding gun by the roller drive system
Shielding Gas
Gas used to protect the molten metal from atmospheric contamination
75%Argon (inert gas) & 25% Carbon Dioxide most common gas used for GMAW

8. Principles of the GMAW Process

9. GMAW Set UP Plug ground wire into (Neg) Terminal
Plug Wire Feeder into (Pos) Terminal
Select CV-Wire mode
Hot start is not used
Set Arc Control to “-5”
-10= soft arc (for use with inert gases)
+10= crisp arc (for use with CO2)
(See Next Slide)

10. Min. Arc Control Max Arc Control Soft Arc Thicker Materials
Deeper Penetration
More Fluid Weld Pool
Flatter / Smoother Weld
Reduce Spatter
Stainless Steels
Max Arc Control
Crisp Arc
Thin Materials
Arc Stability On Open Gaps
Convex Weld Bead
Increased Spatter
Colder Arc
Improved Weld Pool Control 12

11. GMAW Set Up (Cont) Set Volts Set Wire Speed Set gas flow
See Chart for proper setting
Set Wire Speed
Increase wire speed = Increase amps
Decrease wire speed = Decrease amps
Set gas flow
Pull trigger to get gas flowing then adjust regulator

12. Running a Bead Hold tip 1/16” to 1/8” from work piece
Angle of tip should be 10-15°
Can push or pull bead
Pull (preferred)
More stable arc
Less Spatter
Deeper penetration
Push
More spatter
Less penetration
Good cleaning action

13. Bead Formation

14. Wire Burnback Possible Causes Corrective Actions
* Drive Rolls in Poor Condition *Tighten, Clean, or Replace Drive Rolls
* Excessive Welding Voltage * Reduce Voltage
* Insufficient Electrical Stickout * Increase Contact Tip to Work Piece Distance
* Contact Tip in Poor Condition * Clean or Replace Contact tip
* Spatter on Contact Tip * Remove Spatter

15. Burnthrough Possible Causes Corrective Actions
* Excessive Amperage *Reduce Amperage
* Improper Travel Angle * Use a Push Angle
*Travel Speed Too Low * Increase Travel Speed
* Insufficient Electrical Stickout * Increase Contact Tip to Work Distance

16. Incomplete Penetration
Possible Causes Corrective Actions
* Insufficient Amperage *Increase Amperage
* Improper Travel Angle * Use Less of a Drag angle
* Excessive Electrical Stickout * Decrease Contact Tip to Work Piece Distance
* Weld Joint Too Narrow * Increase the Opening of the Weld Joint

17. GMAW Process Parameters
Steel Material ” wire Short-Arc Mode
Thickness
Gas 75%AR-25%CO2
Amps
Wire
Speed
Volts
1/8”
18-19
23-24
3/16”
24-25
1/4”
21-22
5/16”
25-26
3/8”
26-27