aluminium in commercial vehicles - European Aluminium Association

104 EUROPEAN ALUMINIUM ASSOCIATION ALUMINIUM IN COMMERCIAL VEHICLES CHAPTER VII
5.2. Upsetting
The thread is achieved by plastic
deformation of the metal using a
tap with- a rounded polygon sec-
tion that has no cutting wedge.
The diameter of the pilot hole
will depend on the desired
thread depth, and must be
drilled accurately. Upsetting
speeds can attain 50 m/min,
cooling is done with cutting oil.
Tapping by upsetting offers a
number of advantages with aluminium
alloys:
• the tap has a long life,
• it increases the hardness of the
thread, its tearing resistance and
fatigue strength,
• no chips.
5.3. Threaded inserts
It is usual to use threaded inserts
– available in diameters M2 to
M68 (Figure VII.9) – when
screwed aluminium alloy assemblies
are required to be frequently
dismantled. The inserts are in
the form of a spring made from
rolled wire or are a diamond section
made of stainless steel.
Captive threads can also be used.
These have one or two flights
that grip the flanks of the screw
thread and counteract the loosening
effects of dynamic stresses,
vibrations or thermal shock.
Boring is done using a standard
twist drill, but tapping must be
done with a special tap. All chips
and cutting fluid must be
removed from the bore before
the insert is fitted.
Threaded inserts are fitted with
pneumatic hand tools which
hold them by a driver at the top
end of the thread. This can then
be broken off after fitting.
Threaded inserts can also be
used to repair a tap in aluminium
that is worn or has been rejected
during manufacture.
6. Deep drawing
Deep drawing is mainly used in
the automotive sector.
For more information on that
technique, please refer to the
Aluminium Automotive Manual:
http://www.eaa.net/aam/
FIGURE VII.9
HELI-COIL INSERTED THREAD
‰
‰
Notch
Driver