Die & Mould Making - CNC - Computer Numerical Control

50
METHODS FOR MACHINING OF A CAVITY
A. Pre-drilling of a
starting hole. Corners
can be pre-drilled as
well. Not recommendable
method as one
extra tool is needed.
Which also adds more
unproductive positioning
and tool changing
time. The extra tool also blocks one
position in the tool magazine. From a cutting
point of view the variations in cutting
forces and temperature when the cutter
breaks through the pre-drilled holes in the
corners is negative. The re-cutting of chips
also increases when using pre-drilled holes.
B. If using a ball nose end mill, inserted or
solid carbide, it is common to use a peckdrilling
cycle to reach a full axial depth of
cut and then mill the first layer of the cavity.
This is then repeated until the cavity is
finished. The drawback with this start is
chip evacuation problems in the centre of
the end mill. Better than using a peck-drilling
cycle is to reach the full axial depth of
cut via circular interpolation in helix. Important
also then to help evacuate the chips.
C. One of the best methods is to do linear
ramping in X/Y and Z to reach a full axial
depth of cut. Note that if choosing the
right starting point, there will be no need
of milling away stock from the ramping
part. The ramping can start from in to out
or from out to in depending on the geometry
of the die or mould. The main criteria
is how to get rid of the chips in the best
way. Down milling should be practised in
A
B
Peck-drilling cycle with
a short delay between
each down-feed to
evacuate chips.
1
2
3
4
5
Required
depth of cut
for machining
the first layer.