TIG welding
T
ungsten inert gas (TIG)
welding is a high quality
low deposition rate
welding process. It uses an arc
struck between a nonconsumable tungsten electrode
and the work to fuse the base
material and thereby form a
welded joint.
The TIG welding process may
be used on thin sheet material
without the addition of a filler
metal (autogenous TIG welding).
Alternatively, when working on
thicker sheet or when joining
dissimilar materials, a separate
wire filler metal is added into the
arc region where it is melted and
directed by the welder into the
molten weld pool.
The weld pool, the hot
tungsten electrode and the
melting filler wire are protected
from atmosphere by a shield of
inert or slightly reducing gas.
Argon is often used although
productivity and quality benefits
can be gained by using mixtures
of argon and helium or argon and
hydrogen (see the table of
recommended GeminiTM gases
over the page).
Operation
TIG welding is suitable for
manual, mechanised and
automatic (orbital) operation.
In manual welding, the
operator points the tungsten
electrode in the direction of
welding and uses the arc to melt
the base material along the joint,
Double operator AC TIG welding of an aluminium vessel.
ahead of the molten weld pool.
The filler metal is generally
added at the leading edge of the
advancing weld pool.
Welding current
Both Direct Current (DC) and
Alternating Current (AC) may be
used when TIG welding, the
choice depending upon the type
of material to be welded.
DC (electrode negative) is
used for the following
materials:–
carbon steel
● copper
● stainless steels
● nickel alloys
● titanium
● zirconium.
AC is used for the following
materials:–
● aluminium and its alloys
● magnesium
● aluminium bronze.
●
Non-consumable
electrodes
Ozone reduction
Electrode diameter to current
dia. mm
maximum operating current (A)
thoriated DC
zirconiated AC
1.2
70
40
1.6
145
55
2.4
240
90
3.2
380
150
4.0
440
210
4.8
500
275
Research carried out by Air
Products’ European Technology
Group has shown that, when
welding stainless steels, the
AstecTM and HytecTM ranges
of GeminiTM gases produce
significantly lower levels of
harmful ozone than traditional
shielding gases.
GeminiTM gases for TIG
welding
Taken from British Standards BS3019: Part 1
Pure tungsten electrodes may be
used for TIG welding. Special
tungsten electrode materials with
controlled additions of metallic
oxides are, however, generally
preferred because they allow
easier arc starting and provide
enhanced arc stability.
Thoriated tungsten electrodes,
containing generally 2% thorium
oxide, are commonly used for DC
welding of steels. Zirconated
tungsten electrodes, containing
2% zirconium oxide, are recommended for the AC welding of
aluminium and its alloys.
The diameter of the non-consumable TIG electrode is chosen
to suit the welding current. Below
the minimum current, for a given
electrode, the arc becomes unstable and cannot be maintained.
Above the maximum current, the
electrode may become overheated, erode quickly and even melt.
Autogenous TIG welding of stainless
steel.
Reduced ozone
180 Mean ozone parts per billion
breathing zone
proximate zone
160
140
120
100
Occupational exposure standard
8 hour TWA reference period
80
60
40
20
0
argon
AstecTM30
HytecTM2
ozone measurements for TIG welding 304 stainless steel
Argon may be used for all of the
commonly welded materials.
However, the AstecTM range of
gases gives enhanced welding
speeds and deeper penetration in
a range of applications when
compared to argon. The HytecTM
gas mixtures provide improved
weld profile, welding speed,
penetration and surface finish
when compared to argon for
the welding of austenitic
stainless steels, cupro-nickel
and nickel alloys.
Recommended GeminiTM gases for TIG welding
carbon
austenitic
ferritic/
duplex/
aluminium
magnesium
copper
cupro
nickel
titainium
steels
stainless
steels
martensitic
stainless
steels
super duplex
stainless
steels
& alloys
& alloys
& alloys
nickel
& alloys
& alloys
Hytec TM2
AstecTM30
DuplexTM1
AstecTM75
argon
AstecTM75
HytecTM2
argon
HP argon
AstecTM30
argon
DuplexTM2
AstecTM30
AstecTM75
AstecTM30
AstecTM
AstecTM75
AstecTM75
argon
argon
argon
argon
AstecTM50
The selection of optimum GeminiTMgas for your application depends upon a number of features
including material thickness, welding position etc.
GasSelector✓
For advice about the right gas for the job and all GeminiTM Services call our
Customer Services Team on telephone 0345 020202
Air Products PLC
Chineham, Basingstoke
Hampshire RG24 8YP
Telephone: 0345-020202
Fax: 01256-707199
L5386 B/5.96.DG