1. GMAW FCAW and MCAW Gas Metal Arc Welding Flux Core Arc Welding
Metal Core Arc Welding
Unit 6

2. What is GMAW? Gas Metal Arc Welding
GMAW is produced by an electric arc between the base metal and a solid wire continuously fed electrode using a shielding gas.
Also called MIG welding (Metal Inert Gas)

3. What is FCAW? Flux Core Arc Welding
Very similar to GMAW, except it uses a tubular continuous electrode with a flux core.
Generally, does not require the use a separate shielding gas.

4. What is MCAW? Metal Core Arc Welding
Also, very similar to GMAW and FCAW, except it uses a tubular continuous electrode with a metal powder flux core.
Generally does require the use a separate shielding gas.

5. What are the benefits/disadvantages of GMAW?
High productivity, little waste
Most efficient, fast
Relatively easy to use.
Clean welds, little or no slag.
Equipment is specialized.
Equipment needs to be setup for specific applications.
Actually less types of metals can be welded when compared to SMAW and GTAW.

6. What are the benefits/disadvantages of FCAW?
Not designed for high productivity.
Somewhat fast and efficient.
Relatively easy to use.
Some slag, not as clean as GMAW.
FCAW welding wire is very expensive
Equipment is specialized.
Equipment needs to be setup for specific applications.
Only a few metals can be FCAW.

7. What are the benefits/disadvantages of MCAW?
Fast metal deposit.
Fast and efficient.
Relatively easy to use.
Some slag, not as clean as GMAW.
MCAW welding wire is expensive
Equipment is specialized.
Equipment needs to be setup for specific applications.
Only a few metals can be MCAW, generally steels and stainless steels.

8. What are some specific safety precautions for GMAW, FCAW and MCAW?
Similar to SMAW.
Produces intense ultra-violet rays.
Need to use number 10 shade lens.
U-V rays burn the outer layers of the skin/eyes.
Electrical shock.
Harmful Fumes/smoke

9. How do the GMAW, FCAW and MCAW processes produce heat?
Basically the same as SMAW
Resistance – produces heat.
Welder works at a lower voltage, pushes large amounts of electricity, across a gap.
Voltage is a constant, amperage varies as the feed rate of the electrode changes and arc length varies.

10. What are the key variables when GMAW, FCAW and MCAW?
Size and type of electrode wire
Type of shielding gas
Set shielding gas flow rate.
Set voltage.
Set wire feed speed, inches per minutes (ipm).
Welder characteristics, speed, skill, electrode angles.
FCAW the same except no shielding gas.

11. What are welders are used for GMAW, FCAW and MCAW?
Only one type:
Constant potential (voltage), set the voltage, amperage varies.
Uses either an inverter or a rectifier type

12. What types of electrical current used for GMAW, FCAW and MCAW?
DC – direct current, only
GMAW generally uses DCEP – reverse polarity, electrode positive, heat is greater at the metal, deeper penetration.
FCAW applications generally use DCEN – straight polarity.
MCAW applications generally use DCEP – reverse polarity.
As a general rule, use DCEP when using a supplied shielding gas and DCEN when not using a supplied shielding gas.

13. What are the characteristics of the shielding gases used for GMAW?
Argon – inert, all metals except steels.
Helium – Inert, Al, Mg, and Cu alloys.
Ar + He, Inert, better than He, same metals.
Ar + 1-2% O2, oxidizing, stainless steel, some alloy steels.
Ar + 3-5% O2, oxidizing, carbon and some low alloy steels.
CO2, oxidizing, carbon and some low alloy steels
Ar + 20 –50 % CO2, oxidizing, various steels, short circuiting arc.
90%He +7.5%Ar + 2.5% CO2, oxidizing, short circuiting.

14. What are the different types of metal transfer for GMAW?
Two basic types:
Short circuiting,
used with Argon +Co2 mixture gases, low amperage, wires less than 0.045”, low heat input to the base metal
Metal Transfer, 3 types
Globular metal transfer, higher welding current, high % of inert gas, larger diameter electrode wire.
Spray Arc, high current, voltage, usually 100% Argon, current is above the transition current, creating a fine spray of molten metal.
Pulsed spray, same as spray arc, except the welder pulses the current, good for thinner metal, sheet metal, auto body work

15. How do we identify the different types of GMAW electrodes?
Solid Wire Electrodes:
Example: ER70S-6
E – Electrode
R – Rod, carries the current
70 – tensile strength in 1,000#
S – solid wire
(last digit) – special characteristics, shielding gas, composition. 6 is general purpose wire.
Common sizes: 0.030”, 0.035”, 0.045” diameters

16. How do we identify the different types of FCAW and MCAW electrodes?
Tubular Wire Electrodes:
Example: ER71T-6
E – Electrode
R – Rod, carries the current
7 – tensile strength in 10,000#
1 = all positions, 0 = flat and horizontal only.
T - Tubular wire
(last digit) – special characteristics, indicates if FCAW or MCAW electrode.

17. References: Metals and Welding: pages 188 – 197.
Modern Welding: chapter 15.