Advanced Welding Processes: Technologies and Process Control

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Advanced welding processes
For shielding, the gases used are similar to those employed for GTAW
and plasma welding, but, in the case of laser welding, ionization of the gas
or metal vapour to form a plasma is undesirable (see Chapter 8) and gases
with a high ionization potential, such as helium, are favoured. The common
gas mixtures used for shielding are:
∑ argon, helium and argon/helium mixtures, used for most materials including
steel and the reactive metals titanium and zirconium;
∑ nitrogen can be used for less demanding applications on austenitic stainless
steel.
If a plasma does form, a jet of gas may be used to displace or disrupt the
plasma; [78] the normal gas used for this purpose is helium.
5.4 Summary
The range of gases used for shielding in arc and laser welding processes is
limited but gas mixtures containing from two to four active components may
be used to obtain the optimum welding performance. The range of gases
commonly used for gas-shielded arc welding and their applications are
summarized in Table 5.3.
Table 5.3 Common shielding gases for arc welding processes
Gas
Argon
Helium
Argon + 25 to 80%
helium
Argon + 0.5 to 15%
hydrogen
Carbon dioxide
Applications
GTAW all metals, GMAW
spray/pulse Al, Ni, Cu
GTAW all metals;
especially Cu, Al. GMAW;
high current spray with Al
GTAW and GMAW Al and
Cu
GTAW austenitic stainless
steel and Cu/Ni alloys
GMAW plain carbon and
low alloy steels. Dip
transfer and FCAW
Features
Inert. GTAW; good arc
initiation, stable arc, efficient
shielding, low cost. Poor
bead profile in GMA welding
of steel
Inert. High heat input, higher
voltage than argon,
improved fusion, low arc
pressure. Require higher gas
flow for effective shielding
Inert. Improved fusion and
bead profile, good shielding
efficiency, stable arc
Active. Improved fusion,
edge wetting and reduced
oxides
Active. Low cost, good
fusion, effective shield. May
have poor process stability
and high spatter