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4.0 BASIC INFORMATION REGARDING MIG WELDING
MIG WELDING PRINCIPLES
MIG welding is autogenous, i.e. it permits welding of pieces made of the same
metal (mild steel, stainless steel, aluminium) by fusion, while granting both physi-
cal and mechanical continuity. The heat required for melting is generated by an
electric arc that strikes between the wire (electrode) and the piece to be welded. A
shield gas protects both the arc and the molten metal from the atmosphere.
4.1
CONNECTION AND PREPARATION OF EQUIPMENT FOR WELDING
Connect welding accessories carefully to avoid power loss or leakage of dan-
gerous gases.
Carefully follow the safety standards
Check that gas is delivered from the nozzle and adjust flow by means of the
pressure reducer valve.
CAUTION: Screen gas flow when operating in outdoor or ventilated sites; welding
operations may not be protected due to dispersion of inert shielding gases.
4.2
WELDING
1.
Open the gas cylinder and regulate gas outlet flow as required. Fit the earth
clamp on a part of the welding piece without any paint, plastic or rust.
b.
Select the welding current by means of switches (Sezione 3.2 a pagina 4);
bear in mind that the greater the welding thickness, the more power is
BASIC INFORMATION REGARDING MIG WELDING
Fe Ø 0.8
80Ar20CO2
Fe Ø 0.8
80Ar20CO2
Ss Ø 0.8
80Ar20CO2
Ss Ø 0.8
80Ar20CO2
Ss Ø 0.8
80Ar20CO2
Alu Ø 0.8
100 Ar
Alu Ø 0.8
100 Ar
Alu Ø 0.8
100 Ar
1.5 mm
3 mm
0.8 mm
2 mm
3 mm
1 mm
2 mm
3 mm
required.
4.3
CARBON STEEL WELDING
For MIG welding, proceed as follows:
1.
Use a binary shielding gas (commonly a AR/CO2 mixture with percentages
ranging from 75-80% of Argon and from 20-25% of CO2), or ternary mix-
tures such as AR/CO2/O2. These gases provide welding heat and a uniform
and compact bead, although penetration is low. Use of carbon dioxide
(MAG) as a shielding gas achieves a thin and well-penetrated bead but ioni-
sation of the gas may impair arc stability.
2.
Use a wire feed of the same quality of that of the steel for welding. Always
use good quality wire; welding with rusty wires can cause welding defects.
In general the applicable current range for wire use is:
- Ø wire mm x 100 = minimum Amps.
- Ø wire mm x 200 = minimum Amps.
Example: Ø filo 1.2 mm= minimum Amps 120 mm/maximum Amps 240.
The above range is used with binary AR/CO2 gas mixtures and with short-
circuiting transfer (SHORT).
3.
Do not weld parts where rust, oil or grease is present.
4.
Use a torch suited to welding current specifications
(GB) 7
For optimal welding, keep the torch in
the same direction as the wire feed, as
illustrated in figure.
GB
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