Sandvik Coromant Heat resistant super alloys - Manual (Page 64)

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Typical components – aerospace
Combustion casings Discs Rings Blades/blisks Mounting brackets
Machining strategy
Features
Most HRSA components are critical parts of
the aircraft engine with complex features to
be machined. For example when machining
an engine casing the most time consuming
operation is machining the band between
the bosses. Careful planning and applica-
tion of modern cutting tool materials can
dramatically reduce cycle time. Planning the
order of operations in order to reduce part
distortion is also an important factor when
planning the machining strategy.
Machine requirement
Horizontal/Vertical
For larger components such as engine cas-
ings where there are many different fea-
tures and where access is an issue it is
best to use a horizontal machine. This also
makes it easier to evacuate the chips, pre-
venting re-cutting of the chips, giving a more
secure tool life. For some ring components
and mounting brackets vertical machine
tools can create improved stability.
Configuration – 3/4/5-axis
It is common to have a fourth/fifth axis on
horizontal machines to give good accessi-
bility e.g. for casings and closed faces.
For complex parts (3D profiles, blisks)
5-axis rigid machines are used, with fully
simultaneous five access control.
Spindle speed
Three cutting strategies dictate the spindle
speed requirements:
a) Solid carbide tools – (low torque) – the
cutting speed (v
c
) is between 30 to 100
m/min. For cutter diameters 8 to 16 mm
this will give an rpm requirement between
4000 to 600 rpm
b) Carbide inserts – (high torque) - the
cutting speed (v
c
) is normally limited to a
maximum of 40 m/min, for cutter diame-
ters 25 mm to 80 mm this will give an rpm
requirement of 500 rpm to 159 rpm.
c) Ceramic inserts – (high power and
torque) – typically cutting speeds (v
c
) can
be as high as 1000 m/min, for cutter diam-
eters 50 mm this will give an rpm of 6365.
Table feed
For roughing, using carbide inserts, the
table feed is naturally relatively low, putting
demands on stability rather than speed.
For roughing, with ceramics, the table feed
can be up to around 2.5 m/min. Whilst this
is not an extreme table feed, care must be
taken that the control system can cope with
direction change at this feed to avoid under-
cutting/shortcuts etc.