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DR-80 & DR-85 are
high CBN content materials, diffusion bonded at the manufacturing
stage to a tungsten
carbide substrate. This
substrate enables flexibility in tool fabrication, making
it possible to apply a high
PCBN content material where the solid indexable format of DR-100
is not suitable.
PCBN cutting tools machine
hardened steels with apparent ease because, using relatively
high surface
speeds,
heat is generated at the point of cutting so
that the PCBN tool cuts locally softened
material. The
heat is carried away from the workpiece by the chip,
which rapidly air-cools to provide a brittle
and
harmless swarf, and the CBN tool, which has a high thermal conductivity.
This leaves the component cool,
with its hardness unaffected.
Cutting
forces are generally of the order experienced by hard metal cutting
tools machining soft steel. High CBN is
employed as a semi-finishing or roughing tool using negative rake
geometry wherever possible.DR-80 &
DR-85 are
commonly used to produce grooving tools, threading tools
and form tools. DR-80 & DR-85
are not as effective as
DR-100, when operating under ideal conditions,
but can often provide a compromise solution.
Although
DR-80 & DR-85 are tough, vibration or deflection will result
in reduced tool life and poor quality components.
While they have been used on some very antiquated machines with
excellent results, rigidity is essential
for success.
Tool holders
should be as large as possible and in good condition. Coolant has
little effect on the cutting mechanism
since
the heat generated in the shear zone is sufficient to vaporise any
coolant provided.
Coolant does, however,
serve two major purposes:-
If a substantial
amount of material is to be removed, and a number of passes will
be required, or any heating of the component
will make measuring the part difficult, coolant can be used to stabilize
the temperature of the workpiece.
Coolant
can be used to drive the swarf away from the shear zone where it
might interfere with the cutting edge.
Coolant
should not be used for interrupted cutting any hardened materials.
DR-80 is
(80% CBN) has a greater particle size than DR-85, (85% CBN). DR-80
is better for hardened
steel, but DR-85
has better wear characteristics when machining cast iron, particularly
when the
structure contains some Ferrite.
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