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MANUAL METAL ARC PROCESS (MMA WELDING)
When an arc is struck between the metal rod (electrode) and the workpiece, both the rod and workpiece
surface melt to form a weld pool. Simultaneous melting of the flux coating on the rod will form gas and slag
which protects the weld pool from the surrounding atmosphere. The slag will solidify and cool and must be
chipped off the weld bead once the weld run is complete (or before the next weld pass is deposited).
The process allows only short lengths of weld to be produced before a new electrode needs to be inserted in
the holder. Weld penetration is low and the quality of the weld deposit is highly dependent on the
skill of the welder.
TYPES OF ELECTRODES
Arc stability, depth of penetration, metal deposition rate and positional capability are greatly influenced by the
chemical composition of the flux coating on the electrode. There are many types of Electrodes, and these
are generally matched to the base metal. For example if welding Mild Steel then select a Mild Steel (General
Purpose Electrode). Electrodes are identified by a universal numbering system (AWS Type code).
Electrodes are often packed in sealed packaging to keep moisture out. However, if a pack has been opened
or damaged, it is essential that the electrodes are redried according to the manufacturer’s instructions.
ARC FORCE
Also called Dig and Arc Control. Gives a power source variable additional amperage during low voltage
(short arc length) conditions while welding. Helps avoid “sticking” stick electrodes when a short arc
length is used.
POWER SOURCE
Electrodes can be operated with AC and DC power supplies. Not all DC electrodes can be operated on AC
power sources; however AC electrodes may be used on either AC or DC
Base Metal
Electrode Type
Type
Mild Steel
Mild Steel General Purpose
6013
Stainless Steel
Stainless Steel 316L
316L
Dissimilar Metals
Dissimilar 680
312
Cast Iron
Nickel Arc 98
Ni99
High Strength Steel
Low Hydrogen
TC16
TRIGGER
WELDING WIRE
FLUX COATING
ROD
ARC
CONTACT TIP
DROPLETS
SHIELDING GAS
ARC
MOLTEN WELD METAL
SHROUD
WORK PIECE
WORK PIECE
WORK PIECE
WORK PIECE
WORK PIECE
WORK PIECE
WORK PIECE
WORK PIECE
STRAIGHT GROUND
CORRECT PREPERATION
- STABLE ARC
INCORRECT PREPERATION
- STABLE ARC
RADIAL GROUND
ARC WANDER
TUNGSTEN ELECTRODE
GAS LENS
STABLE ARC
FLAT TIP
POINTED TIP
GRINDING WHEEL
GRINDING WHEEL
FILLER WIRE
Note: Do not use wheel for other jobs or tugsten can become contaminated and cause lower weld quality