7/28/2019 Welding Gases for Keyhole Laser Welding V2
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TECHNICAL SHEETS
Welding Gases for Keyhole Laser Welding
In laser welding to help stabilize the key-hole and protect the
molten weld pool against ambient air
are used some shielding gases. Other factors that the shielding
gas has an impact on include the speed of
welding, corrosion resistance, mechanical properties and the
working environment. Each of the various
components of shielding gases has its own effect. The components
are combined with precision foroptimal effect.
Properties of different gases for Welding
Gas Description/Benefits
Helium
Helium is an inert gas who has a very high thermal conductivity
then producing welds with an excellent aspect
ratio and the High ionization potential, producing excellent
plasma suppression and high weld speeds
Results in broader and deeper fusion and a better flow in the
weld pool.
Carbon
Dioxide
Carbon dioxide (CO2) is an oxidising gas. As an additive it
ensures arc stability and accurate welding profiles, he
is the gas which is active in generating the laser light itself,
i.e. infrared radiation. In this way it would be possible to
run a CO2 laser using only carbon dioxide as the laser gas.
However, in order to reach the very high laser powers
which are necessary for laser welding it is necessary to add
nitrogen and helium to the laser gas. As Carbon
dioxide is reactive gases which can form oxides, carbides or
nitrides with the weld metal. The mechanical
properties of the welds may therefore be impaired and for some
applications this disqualifies the use of carbon
dioxide and nitrogen as welding gases. However, in some cases,
reactive welding gases can be tolerated or even
be advantageous.
Nitrogen
The Nitrogen used as an additive when welding steels alloyed
with nitrogen increases corrosion resistance.
By using an electric discharge it is very easy to excite a
nitrogen molecule to its first vibrational energy level, which
has almost the same energy as the upper laser level of CO2.The
vibrational energy is easily transferred from N2 to
CO2 by collisions between the two molecules. Altogether it is
far easier to excite the upper laser level of CO2 by
using nitrogen as an intermediate than to use only CO2. Nitrogen
is added in order to reach very high laser
powers.
Argon
Argon is an inert gas who is the base of most shielding gases
(Does not react chemically).
Argon is part of a range of pure elemental gases and gas
mixtures can be used for laser welding. The plasmasuppression
properties of argon can be improved by admixing helium, oxygen or
carbon dioxide. The most
commonly used gases are argon and helium.
Hydrogen Hydrogen used as an additive because reduces oxidation
and results in broader and deeper fusion when welding.
Shielding Gas Ionization Potential Source: AWS C5.10-C5.10M:
2003, Recommended Practices for Shielding Gases for Welding
and Cutting (Miami: American Welding Society)
Shielding Gas Thermal Conductivity Source: Isidoro
Martinez, Professor of Thermodynamics, Department of
Thermodynamics, Ciudad Universitaria, Madrid
