Weldtronic TM250C Operating Manual page 27

Penetration Profiles
Different shielding gas formulations produce quite different and significant changes to the
penetrationprofile of the weld.
Selecting the Correct Shielding Gas
Base Material considerations

Base material type or classification

Base material thickness

Joint design

Welding position
Metal transfer mode

Spray transfer

Globular transfer

Dip transfer

Pulsed current transfer
Carbon Steel - Low content CO2 Mixtures

Most shielding gases are based on the argon/carbon dioxide/oxygen system for welding carbon steels.

Low content CO2 mixture (1-7% CO2) produce welds with a "Wine Glass" penetration profile similar to
that produced by pure argon, along with a very stable arc and low spatter levels.

Due to these mixtures having a relatively low heat input, fusion defects and porosity can occur when
welding heavy sections due to the penetration profile, low fluidity and the rapid freezing of the weld
pool.
Carbon Steel – Intermediate content CO2 mixtures

Intermediate content CO2 mixtures (8-15% CO2) produce a higher heat input giving improved
characteristics and broader penetration profile.

These mixtures are more versatile than the low content CO2 mixtures and sound welds can be
produced over a wide range of material thickness.

These mixtures usually produce the most stable welding arc characteristics and are normally the best
general purpose shielding gases for Mild, Carbon and Low Alloy Steels.
High content CO2 mixtures

High content CO2 mixtures (16-23% CO2) allow for further improvements in the fusion characteristics
and the penetration profiles of the weld.

These mixtures are ideally suited for welding heavy sections especially in multi pass situations.

The stiff weld pools cool relatively slowly which aids welding and complete fusion to the weld side
walls.

Any entrapped gas has time to disperse before freezing of the weld pool occurs.

The arc is less stable than with the low content CO2 mixtures which may result in increased spatter
levels.
TitanMig AU 250C Manual_ Issue A 0415
Quality aspect of the finished weld

Mechanical and chemical requirement

Surface finish

Penetration
Economics of the weld

Clean up costs (acceptable level of spatter)

Welding travel speed

Flow rate of shielding gas

Cost of shielding gas
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