4.4 Tungsten Preparation
Always use
DIAMOND
wheels when grinding
and cutting. While tungsten is a very hard
material, the surface of a diamond wheel is
harder, and this makes for smooth grinding.
Grinding without diamond wheels, such as
aluminium oxide wheels, can lead to jagged
edges, imperfections, or poor surface finishes
not visible to the eye that will contribute to weld
inconsistency and weld defects. Always ensure
to grind the tungsten in a longitudinal direction
on the grinding wheel. Tungsten electrodes are
manufactured with the molecular structure of
the grain running lengthwise and thus grinding
crosswise is “grinding against the grain.”
If electrodes are ground crosswise, the electrons
have to jump across the grinding marks and the
arc can start before the tip and wander. Grinding
longitudinally with the grain, the electrons flow
steadily and easily to the end of the tungsten tip.
The arc starts straight and remains narrow,
concentrated, and stable.
Electrode Tip/Flat
The shape of the tungsten electrode tip is an
important process variable in precision arc
welding. A good selection of tip/flat size will
balance the need for several advantages. The
bigger the flat, the more likely arc wander will
occur and the more difficult it will be to arc start.
However, increasing the flat to the maximum
level that still allows arc start and eliminates arc
wonder will improve the weld penetration and
increase the electrode life. Some welders still
grind electrodes to a sharp point, which makes
arc starting easier. However, they risk decreased
welding performance from melting at the tip and
the possibility of the point falling off into the
weld pool.
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