Basics Of Welding; Stick Electrode Welding; Tig Welding - LORCH HandyTIG 180 DC ControlPro Manuel D'utilisation

20

Basics of welding

20.1

Stick electrode welding

Coated stick electrodes are used for the well-known
manual metal arc welding process (stick electrode weld-
ing). The coating of the electrode melts off during the
welding process together with the core wire. The coating
generates the gas shield. Additionally the coating may
alloy the weld pool with some elements, which are lost
during the arc process. On top of the melted bath a slag
layer is generated, which covers and protects the freez-
ing bead against the air.
The coatings of the electrodes differ from thickness and
type, i.e. chemical composition. This results in different
welding properties and consequently different applica-
tions for the electrodes. Types and nomenclature is de-
fined in DIN EN 499 (formerly DIN 1913).
Base metal
20.2

TIG welding

The TIG welding process is a universally applicable pro-
cedure which leads to high-quality joints.
The electrode of the TIG-process consists of non-melting
tungsten, the shielding gas is an inert gas.
Inert gas is chemically neutral and does not react with
the weld metal. Inert gases are e. g. Argon, Helium, and
their mixtures. Usually pure Argon (99.9 %) is used. The
shielding gas shall be dry. DIN 32 526 defines the differ-
ent types of shielding gas.
Basics on TIG welding
A non-melting tungsten electrode is positioned through
a clamping sleeve into a gas- or water cooled torch. The
arc burns between electrode tip and workpiece in an
inert shielding gas atmosphere. So the tungsten elec-
trode acts as an arc carrier. The arc melts the workpiece
point by point and forms the weld pool. The shielding
gas escapes through the gas nozzle. The gas protects
the tungsten electrode, the arc, the weld pool against
the environmental air. So an unfavourable oxidation is
avoided. Consequently poor welding results may occur
from trouble of shielding gas supply.
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Stick electrode
coating
Core rod
Gas/slag
Arc
Molten zone
In case additional filler material is required, filler wire is
supplied either manually, like gas flame welding, or au-
tomatically by means of a cold wire feeder. The filler wire
shall be equal to or higher alloyed than the base mate-
rial. Without filler wire, flange and corner welds may be
easily manufactured.
Shielding gas
Tungsten-
electrode
Gas nozzle
Shielding gas
Welding seam
Arc
Basically AC and DC may be used for TIG welding. The
type of current and polarity depend on the material to be
welded.
Non- or low-alloyed steel, high-alloyed steel, and copper,
as well as titanic an tantalum are welded with DC. The
electrode is connected at the minus pole because of the
stronger current loading.
When welding of aluminium and magnesium, as well as
their alloys, ACwill be used in order to tear up the high-
melting and tough oxide skin covering the melting bath
or being on the working piece. Is the oxide skin missing,
e.g. is has been welded on the same part for a longer
time, consequently, the arc can be instable or breaks up
from time to time.
Shape of the electrode tip
Tungsten electrodes has to be ground always length-
wise, because the grinding marks crosswise cause a
nervous/flattering arc.The shape of the electrode for DC-
welding has to be sharp as a pencil. The angle of the
point depends on the welding current.
Basics of welding
Filler wire
Power source
Workpiece
10.15