Weldtronic TM250C Operating Manual page 26

Shielding gases have a strong influence over..

Stability of the arc

The shape of the weld bead/face

Mechanical properties of the weld

Cost efficiency of the welding process being used

Control of fume generation rates
Gases used in Shielding Gas Formulations
Argon

The tendency for argon to produce a "Wine Glass" penetration profile can make it difficult to ensure
complete fusion of the weld especially if "Arc Wander" is occurring.

For GMAW applications small additions of oxygen or carbon dioxide will assist in eliminating "Arc
Wander" by producing a uniformly oxidized surface for the arc root to "Anchor" to. The addition of
helium produces a broader and deeper fusion profile.
Carbon Dioxide CO2

The first shielding gas used for GMAW, MIG welding.

Spray transfer using GMAW cannot be achieved with carbon dioxide.

At low currents a good dip transfer mode can be obtained.

At high currents the transfer mode is globular and significant spatter is produced

Carbon Dioxide is less than ideal for use alone as a shielding gas but it is an essential ingredient of
most GMAW shielding mixtures.

High Carbon Dioxide (18 to 23%) mixtures are particularly suited to welding steels which are coated
with paint, primers and other surface contaminants, or where higher penetration is required.
Helium

Rarely used alone as a shielding gas.

Completely inert.

Lighter than air therefore less efficient as a shield.

High ionization potential which can cause arc initiation problems.

Essential ingredient for many shielding gas mixtures.

Helium rich shielding gas mixtures provide excellent weld fusion characteristics for GMA welding
applications. The high heat input obtained by using helium produces a hot arc and allows for high
deposition welding.
Oxygen

Oxygen is never used as a shielding gas on its own.

Oxygen is a vital component in many mixtures and performs two main functions...

It aids stability within the arc ionizing at a similar level to argon and influences the arc rooting
characteristics by producing a uniform oxide layer on the electrode and work piece.
It also reduces the surface tension of the metal droplets and the molten weld pool.

The benefits of these two functions are reduced wire losses as a result of spatter and the more
efficient use of deposited metal due to reduced reinforcement (weld metal build-up).
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