1. Gas Metal Arc Welding (GMAW) Flux Cored Arc Welding (FCAW)
(MIG) metal inert gas - incorrect because not always inert gases used
(MAG) - metal active gas

2. An electric arc between a continuously fed metal electrode and the base metal produces heat. The arc is shielded by a gas.

3. Used in production and repair shops auto body, agriculture

4. Popularity:
low cost used on all commercially important metals such as al, magnesium, stainless, carbon, alloys steels, copper etc.

5. FCAW main difference from GMAW -
electrode is hollow
shielding gas is created from the flux inside the tubular electrode as it melts
also used to add alloying elements
some FCAW still requires additional shielding gas to be supplied
those that don't - called shelf shielding electrodes

6. Equipment:
a constant voltage DC welder is used with this process shielding gases (carbon dioxide, argon, helium) metal electrode wire electrode feed device cable to carry: wire, current and shielding gas to the arc torch

7. SAFETY - same as for SMAW with addition of gas cylinder safety:
cap should be on cylinder when being moved or stored cylinders should be chained or secured to rigid object - wall etc. don't strike arc on cylinder store and use in upright position

8. Advantages of GMAW and FCAW:
1. continuous electrode - no stopping to change electrodes 2. no electrode stub loss 3. each pound of wire used, 92-98% becomes deposited weld metal (SMAW 60-70%) 4. no slag, just a very thin glass like coating over the weld bead 5. deeper penetration possible than with SMAW 6. less training and skill required

9. Disadvantages:
1. equipment costs more than SMAW 2. some joints hard to reach with welding gun 3. rapid air movement (strong wind) can blow shielding gas away from weld

10. Two adjustments are made on the welding machine by the operator
1. voltage 2. wire feed speed
arc length,current, transfer method, and shielding gas are determined by the setting of these two parameters

11. Metal transfer occurs in two ways
1.short circuiting method (short arc) 2 metal transfer across the arc which includes:
a. globular b. spray

12. 1. Short circuit transfer:
electrode touches molten pool, arc is no longer present, surface tension of pool pulls molten metal on the end of the electrode into the pool. repeats itself 100’s of times per second

13. Characteristics of Short Circuit
sounds like bacon frying
done with 100% CO2 or 75% CO2 and 25% argon
CO2 is a cold gas so get low heat input
minimizes distortion
for thin materials in all positions

14. 2. Spray transfer
increase the current setting above the current required for short circuit Very fine droplets of metal form and travel at high speed directly through the arc stream to the weld pool.(100's of droplets per second)

15. Characteristics of spray
hotter - higher voltage arc
makes a hissing sound
it’s fast, pours the metal down - used in production
it is wet and hot - not good for out of position welds
for 1/8” and thicker material
must be 80% Argon or more for spray to occur -

16. There is an additional type of transfer called globular transfer
occurs at a point between short circuit and spray
metal transfers across the arc as large irregularly shaped drops

17. Continued:
does not occur in U.S. because we can get Argon gas relatively expensive
about 6X more expensive than CO2
but in other countries, Argon is too expensive to use so they use CO2 and increase the weld current above that for short circuit

18. New technique called pulse
used to reduce fumes in production areas
sounds like a buzzing or humming when used properly

19. GMAW power sources: AC generator or alternator with a DC rectifier
AC transformer with a DC rectifier

20. DCEP most common
DCEN seldom used - is used with only one electrode called an emissive electrode
welding machine tries to maintain a CONSTANT VOLTAGE during welding while current varies widely
AC is never used

21. Selecting electrode wire determined by:
1. base metal 2. shielding gas 3. metal transfer method 4. welding position
electrodes designed for all positions are designated as (E71T-X)
#1 indicates all positions

22. wire diameters: .030" to .0625" (1/16")
large dia. wire - not used for out of position welds
soft electrodes like al. and magnesium with small dia cannot be pushed through cable easily, must use push pull wire feeder - also use a Teflon liner.

23. Wire (electrode) Drive Unit
Wire drive unit: pulls electrode from spool and pushes it to welding gun
two mated rollers are located in the wire drive unit.
one roller is driven by a electric motor

24. Drive unit continued:
Amount of pressure - only enough to advance the wire without the rollers slipping.
Too much force could flatten soft wire or crush flux cored wire.
alignment of the wire guides alignment of the drive rolls

25. Birds nest

26. Cleaning electrode cable
can use graphite powder in cable as lubrication

27. Shielding gasses:
inert: Argon (Ar)(most common), Helium (He) reactive: Nitrogen (N2), Oxygen (O2), carbon dioxide (CO2) they will mix with other chemicals such as the metal in the weld joint
reactive gasses gases are not used alone as shielding gases with exception of CO2

28. Gas selection consider:
1. type and thickness of base metal welded
2. amount of penetration 2. metal transfer method to be used
3. welding speed

29. Shielding gas flow rates:
see table for suggested flow rates
too little gas flow = weld is not protected - will have a popping sound, spatter will occur, weld will have porosity

30. Shielding Gasses Cont.
heavier shielding gases like CO2 and Argon will tend to drop away from the weld area when welding out of position so the rate must be increased
may use a gas mixer or gasses can come premixed
each shielding gas has a different effect on shape of the bead and penetration

31. Gas nozzles and contact tubes:
gas nozzle - usually made of copper - come in various shapes and sizes
electrode contact tube (inside gas nozzle) - made in many diameters for wire
must fit tight enough to make a good sliding contact with electrode

32. Gas Nozzles Cont.
gas nozzle and contact tube should be about EVEN end of torch
gas nozzle becomes spattered, the flow of shielding gas will becomes turbulent
causes contamination
use a cleaning reamer or anti-stick compounds

33. Welding procedures

34. Preparing metal surface: mechanically or chemically
groove angle for GMAW (30-45 deg) can be smaller than for SMAW (60-75 deg) (for of two reasons): 1. wire dia are smaller 2. GMAW penetrates better than SMAW

35. Electrode Extension:
amount the end of the electrode wire sticks out beyond the end of the contact tube.
maintain 1/4” to 1/2” extension for short circuit transfer method
too much extension = increase in resistance and cause current to heat along the extended wire - causes spatter, shallow penetration and low weld bead shape

36. Tack weld or place in fixtures prior to welding

37. Welding speed
determined by bead width and penetration

38. Torch angle
1. Use forehand torch position about 15 deg away from direction of travel

39. To start the arc, wire and gas, squeeze the trigger - no striking is necessary as in SMAW
as the arc pool reaches the proper width, welder moves electrode forward

40. Torch Motion
For MIG, don’t use whipping motion - moves out of weld pool

41. If welding without a runoff tab, the welder can move the electrode to the end of the weld then back over the completed bead about 1/2" to fill the crater

42. Glass like slag is produced from MIG
can be cleaned with a wire brush

43. WHISKERS:
lengths of electrode wire stick through the root side of a groove weld
electrode wire is advancing ahead of the weld pool
to fix reduce the wire feed or slow the welding speed

44. Automatic and semiautomatic GMAW and FCAW:
semi - when operator holds and moves the gun and the electrode wire fed automatically full automatic: when the gun is moved by a machine or robot

45. GMAW SPOT welding:
done on metals under 1/16" machine must be equipped with special controls