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When welding, the operator might accidentally bring the
electrode too close to the weld pool, thus causing a
short circuit and consequently the blowing out of the
arc. In this case, the power source momentarily
increases the welding current supplied until the short
circuit ends; this technique is called
‘Arc Force’
.
The techniques used to weld joints are several;
consequently, only a few indications on how to operate
can be given.
The figures above show two examples of a typical butt
(fig. A) and T weld (fig. B). The inclination of the
electrode varies according to the number of passes; its
movement is a traverse swinging with brief stops on the
bead sides in order to prevent weld material from
accumulating at the centre.
Welding with covered electrodes implies that the slag
shall be removed after each pass. This operation is
extremely important to achieve a uniform and smooth
weld. Slag is removed with a small hammer or with a
metal brush, if it is crumbly.
10 MIG/MAG welding: procedures and
technical data
MIG/MAG welding is a method used to weld carbon and
low-alloy steels in an inert environment (CO
2
or
Argon/CO
2
) with the help of a solid or cored steel wire.
To weld stainless steel, the wire should match the
characteristics of the material being welded, and the
gas should be a mixture of Argon/CO
2
/O
2
.
To weld aluminium, the wire should be a type
compatible with the material and the gas should be pure
Argon; moreover, the use of a Teflon torch liner is
suggested.
A MIG/MAG welding machine is essentially made up
by:
•
a dc power source (welding machine)
•
a wire feeder
•
a torch and a cable
•
a gas cylinder with a flow meter and regulator
When welding, the torch is manoeuvred by the operator
along the joint while the wire is fed into the weld pool by
the wire feeder and forms the weld bead.
It is suggested that instruction should be sought as to
how the machine operates in the case of first use. As a
matter of fact, a basic knowledge of the welding
procedure is necessary to be able to adjust welding
parameters and to avoid spattering.
The adjustment of welding parameters consists in
finding out the correct balance between voltage and
wire speed to achieve a good-looking weld bead.
H
SI
L
G
N
E
A
B
45°
45
°÷
70
°
WIRE SPOOL
PIECE
WIRE FEEDER
G
A
S
