BOC Smootharc Multi 180 - MIG;MAG Welding Introduction; Flux Cored Arc Welding (FCAW)

Metal Inert Gas(MIG) and
MetalActiveGas(MAG)welding
33BOC Smootharc Multi 180/200 Operating manual
Introduction
MIG/MAG welding embraces a group of arc welding processes in which
a continuous electrode (the wire) is fed by powered feed rolls (wire
feeder) into the weld pool. An electric arc is created between the tip of
the wire and the weld pool. The wire is progressively melted at the same
speed at which it is being fed and forms part of the weld pool. Both the
arc and the weld pool are protected from atmospheric contamination by
a shield of inert (non-reactive) gas, which is delivered through a nozzle
that is concentric with the welding wire guide tube.
MIG/MAG welding is usually carried out with a handheld torch as a semi-
automatic process. The MIG/MAG process can be suited to a variety of
job requirements by choosing the correct shielding gas, electrode (wire)
size and welding parameters. Welding parameters include the voltage,
travel speed, arc (stick-out) length and wire feed rate. The arc voltage
and wire feed rate will determine the ller metal transfer method.
This application combines the advantages of continuity, speed,
comparative freedom from distortion and the reliability of automatic
welding with the versatility and control of manual welding. The process
is also suitable for mechanised set-ups, and its use in this respect
isincreasing.
MIG/MAG welding can be carried out using solid wire, ux cored, or a
copper-coated solid wire electrode. The shielding gas or gas mixture may
consist of the following:
→ Argon (MIG)
→ Carbon dioxide (MAG)
→ Argon and carbon dioxide mixtures (MAG)
→ Argon with oxygen mixtures (MAG)
→ Argon with helium mixtures (MIG)
Each gas or gas mixture has specic advantages and limitations. Other
forms of MIG/MAG welding include using a ux-cored continuous
electrode and carbon dioxide shielding gas, or using self-shielding ux-
cored wire, requiring no shielding.
Successful welding depends the correct selection of consumables, power
source, polarity, shielding gas, application techniques, electrode angle,
electrical stickout, travel speed and welding preparation.
Flux Cored Arc Welding (FCAW)
Flux-cored arc welding (FCAW) uses the heat generated by a DC electric
arc to fuse the metal in the joint area, the arc being struck between a
continuously fed consumable ller wire and the workpiece, melting both
the ller wire and the workpiece in the immediate vicinity. The entire arc
area is covered by a shielding gas, which protects the molten weld pool
from the atmosphere.
FCAW is a variant of the MIG/MAG process and while there are many
common features between the two processes, there are also several
fundamental di󹟽erences.
As with MIG/MAG, direct current power sources with constant voltage
output characteristics are normally employed to supply the welding
current. With ux-cored wires the terminal that the ller wire is
connected to depends on the specic product being used, some wires
running electrode positive, others running electrode negative. The work
return is then connected to the opposite terminal. It has also been found
that the output characteristics of the power source can have an e󹟽ect on
the quality of the welds produced.
The wire feed unit takes the ller wire from a spool, and feeds it
through the welding torch, to the arc at a predetermined and accurately
controlled speed. Normally, special knurled feed rolls are used with ux-
cored wires to assist feeding and to prevent crushing the consumable.
Unlike MIG/MAG, which uses a solid consumable ller wire, the
consumable used in FCAW is of tubular construction, an outer metal
sheath being lled with uxing agents plus metal powder. The ux ll is
also used to provide alloying, arc stability, slag cover, de-oxidation, and,
with some wires, gas shielding.
Typical MIG/MAG set up
Torch trigger
Welding wire
Weld
Weld pool
Torch
Shroud
Gas di󹠢user
Contact tip
Shielding
Droplets