Fundamentals of MAG Welding (CO2 Arc Welding)

4. Comparison of usability between solid wire and flux−cored wire

Comparison of usability between solid wire and flux-cored wire
Item Type of wire
Solid wire Flux−cored wire
For high current For low current Slag type Metal type
Less−slag type Much−slag type
Penetration Deep Shallow Slightly shallow Deep Slightly shallow
Welding position Flat,
Horizontal fillet
All positions All positions Flat,
Horizontal fillet
Flat,
Horizontal fillet
Bead appearance Slightly bad Fair Good Fair Good
Amount of slag Less Less Much Less Much
Spatter Much Less Very low Less Very low
Arcing
characteristics
With sharp
sound
Good Very good Good Very good
Amount of fumes Fair Less Less Less Less
CO<small>2</small> arc welding

5. Molten droplet transfer

The welding wire can be melted and transferred to the base metal as droplets in three different modes : short−circuiting transfer, globule transfer and spray transfer. Depending upon the mode, the appearance and shape of weld bead, quantity of spatter, and penetration can vary.

In CO2 arc welding, the short−circuiting transfer and the globule transfer can be observed.

(1) Short−circuiting transfer

The welding method that uses the short−circuiting transfer is called the short arc welding or the dip transfer welding. When a comparatively low welding current (200A or lower) is used in either CO2 arc welding or MIG welding, the droplet transfers to the base metal after short circuiting with it as shown in Fig. 2. It is suited for welding of thin plates and in all−position welding as vertical or overhead welding.

Fig. 2 Short−circuiting transfer vs. welding current

Fig. 2 Short−circuiting transfer vs. welding current

Fig. 3 Globule transfer (Globular droplet transfer)

Fig. 3 Globule transfer
(Globular droplet transfer)

(2) Globule transfer

This transfer mode is also known as the globular droplet transfer, which is observed in welding with a comparatively high welding current and the droplet as big as the wire diameter or bigger transfers to the base metal. Because of this, a slightly higher amount of spatter is emitted than in other modes of transfer. But it is used oftenest for it is highly efficient. In high current CO2 arc welding, the mode of droplet transfer becomes this mode.


Fig. 4 Spray transfer

Fig. 4 Spray transfer

(3) Spray transfer

In high current MIG welding with DC electrode positive polarity and inert shielding gas, the droplet becomes smaller than the wire diameter due to the effect of plasma flow on the arc column. This is why, the emission of spatter is little and the weld bead with good appearance can be obtained.


Short-circuiting transfer Globule transfer Spray transfer

6. Welding conditions and their effects

In CO2 arc welding, the weld bead appearance and penetration change markedly by welding conditions. It is, therefore, necessary to select proper welding conditions that suit the purpose of use. The effects of the welding conditions are shown in the figure below.

Changes in welding parameters vs. bead shape
When an arc voltage is changed
(with current and speed kept constant)
Arc voltage : Low → High
Arc voltage : Low → High
When a welding current is changed
(with voltage and speed kept constant)
Welding current : High → Low
Welding current : High → Low
When a welding speed is changed
(with current and voltage kept constant)
Welding speed : High → Low
Welding speed : High → Low

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