Aerospace & Defense Technology - October 2022 - 18

Aerospace Manufacturing
plasticized or sintered state, and inserts
can literally melt or plasticize. If special
considerations are not taken, this can
be catastrophic by damaging a tool or
even worse, the engine component.
To protect tools and workpieces, it's
important that the process produces as
little heat as possible when machining
HRSAs. One way to do this is to use
tools that cut and shear HRSAs rather
than push or plow material off. Another
is to not take too much material off too
quickly, like burying the insert too deep
into the material and plowing through.
Instead, a series of lighter and
faster cuts is more effective
and produces less heat. Most
computer-aided manufacturing
(CAM) packages offer this trochoidal,
or dynamic, technique
that makes it easier for shops to
apply.
Blisks, comprising both a rotor disk and blades, present unique
machining challenges. Blisks located on the cold compressor
side of the engine are made of titanium, while the hot turbine
side requires blisks made of heat-resistant super alloys.
One component that is used
in aerospace is the blisk, which
comprises both a rotor disk
and blades. Blisks are located
on the cold and hot sides of
aircraft engines and are generally
made of titanium alloys on
the compressor or cold side of
the engine, then migrating to
HRSA materials when they are
closer to the combustor or turbine
part of the engine, or hot
side. Blisk components present
unique machining challenges
because they are often made
from HRSAs. The components
demand tight dimensional and geometrical
tolerances, while maintaining
high standards of surface integrity
and surface finish. Machining these
components effectively, and to the
highest standards, requires optimized
tools and process knowledge relevant
to these advanced materials.
More Secure Machining
In response to these machining challenges,
some cutting tool companies
offer a number of tooling solutions
to support cost-effective, high-quality
machining of aero engine components.
One such method is high-feed side
milling. The technique involves a small
radial engagement with the workpiece,
which allows increased cutting speeds
and feed rates and axial cutting depths
with decreased heat, chip thickness
and radial forces.
To utilize this method, aerospace
machining operations need to consider
specialized milling tools. Sandvik
Coromant for example has developed
the CoroMill® Plura HFS high-feed side
milling range. The range features a
series of end mills with unique geometries
and grades and is made up of two
end mill families. One family is optimized
for titanium alloys, the other for
nickel alloys. Chip evacuation and heat
are specific challenges when machining
titanium, so the first family presents
a solid version of the tool for normal
chip evacuation conditions. The second
family features internal coolant and a
cooling booster for optimum swarf and
temperature control.
Sandvik Coromant's CoroMill® Plura yielded a 198% productivity increase for one customer and has been
applied to blisks and other components.
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Increasing Metal
Removal Rates
To illustrate as an example of where
optimized tooling led to improved
machining, a customer trial was performed
to test a 12 mm diameter CoroMill®
Plura HFS end mill against a
same-sized competing tool. This trial
involved machining a low-pressure
turbine (LPT) made from aged Waspaloy
nickel-based alloy, using a horizontal
machining center with an increased
axial depth-of-cut and reduced radial
depth-of-cut. The outcome was that
metal removal rates were increased
substantially with CoroMill® Plura,
Aerospace & Defense Technology, October 2022

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Aerospace & Defense Technology - October 2022

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