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2.0 MIG Operating Manual

7BOC Smootharc Advance MIG 200C/275C/275R/350R Operating manual

2.1 Introduction to Metal Inert Gas (MIG)

MIG 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.

Operation

MIG welding is usually carried out with a handheld torch as a semi-

automatic process. The MIG 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 ﬁller 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 welding can be carried out using solid wire, ﬂux cored, or a copper-

coated solid wire electrode. The shielding gas or gas mixture may consist

of the following:

Argon

■

Carbon dioxide ■

Argon and carbon dioxide mixtures ■

Argon mixtures with oxygen or helium mixtures ■

Each gas or gas mixture has speciﬁc advantages and limitations. Other

forms of MIG welding include using a ﬂux-cored continuous electrode

and carbon dioxide shielding gas, or using self-shielding ﬂux-cored wire,

requiring no shielding.

2.2 Introduction to Flux Cored

Arc Welding (FCAW)

How it Works

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 ﬁller wire and the workpiece, melting both

the ﬁller 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 process and while there are many common

features between the two processes, there are also several fundamental

differences.

As with MIG, direct current power sources with constant voltage output

characteristics are normally employed to supply the welding current.

With ﬂux-cored wires the terminal that the ﬁller wire is connected

to depends on the speciﬁc 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 effect on the

quality of the welds produced.

The wire feed unit takes the ﬁller 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 ﬂux-

cored wires to assist feeding and to prevent crushing the consumable.

Typical MIG set up

Torch trigger

Welding wire

Weld

Weld pool

Torch

Shroud

Gas diffuser

Contact tip

Shielding

Droplets

1 2 3 4 5 6 7 8 9 10 11 12 ... 31 32

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