Technical Article
September 2011
Composite machining – improved performance and results
Product solutions from Sandvik Coromant and Precorp offer greater competitive gain
With the latest aircraft programmes dictating around 50 per cent composite material by weight,
achieving competitive advantage in machining operations is becoming increasingly important.
The key to success in this area is the application of proven solutions to a wide range of challenges,
which include the machining of both composite and composite/metallic stack materials using handheld, power feed and fixed bed CNC machines. Innovative tool development, customized designs
and assured applications support, also have a vital role to play.
This is where the combination of Precorp’s specialist technology and Sandvik Coromant’s tooling
and Application Center expertise provide aerospace manufacturers with industry leading support
for composite machining applications. Successfully applied recent solutions include cemented
carbide, diamond coated and PCD vein tools adapted for hole, edge and surface machining
applications.
A helping hand
Producing holes in CFRP using hand-held machines is common practice in the aerospace sector.
Aircraft structures such as the fuselage and wing spars are extremely large and it’s often simply
impractical to use a fixed bed machine tool.
Tools for hand-held machines need special qualities to resist deflection and the presence of nonaxial forces. Here the CoroDrill 452 range based on H10F uncoated carbide substrate offers great
potential when drilling, reaming and countersinking CFRP, both unidirectional and woven types
such as M21E and BMS8-276.
The drills (CoroDrill 452.1-C), which are stocked as standard from 2.5 to 12.7 mm (other sizes
made to order), offer low thrust force due to an innovative split point geometry design and smooth
drill exit thanks to a left-hand helix on a right-hand drill. Sharp cutting edges produce high quality
holes offering tolerances of ±0.025mm using drill bushing. This can be improved further, to
±0.01mm, using the range of reamers (CoroDrill 452.R-C). The countersink tools (CoroDrill 452.CC) offer a choice of 100° and 130° chamfer angles.
When drilling composite/metallic stack materials a greater number of variables are introduced to
the process due to presence of aluminium or titanium layers. But yet again, CoroDrill 452 can meet
the challenge when using hand-held drilling machines. CoroDrill 452.1-CM utilizes a double margin
flute design and self-centring drill point to enable optimized accuracy. Both pilot and non-pilot
versions are available depending on application and again, a low thrust force design reduces burr
upon exit. Reamers (CoroDrill 452.R-CM) are also available for these operations.
When drilling and reaming CFRP/aluminium stacks, cutting speed is typically around 60 m/min,
although this should be reduced to around 15 m/min when producing holes in composite/titanium
stack materials. A feed rate of 0.05 mm/rev can be maintained for both materials types.
www.sandvik.coromant.com
Staying power
Where possible, power feed drilling is preferred to hand drilling as the drill is locked into a drill
template that establishes both hole location and maintains the drill perpendicular to the workpiece.
In addition, these units can be programmed to drill at a given speed and feed, and some offer peck
cycles.
Using power feed machines on CFRP materials, solutions such as the 85PT series PCD vein drill
offers a shielded diamond design that is optimized for stable drilling processes. Available as madeto-order in diameters from 3-16 mm, through-coolant is also offered. Alternatively, 8F85 series
drills (based on H10F or N20C, CVD diamond coated) feature a carbide drill point that generates
good hole exit quality in demanding unidirectional and woven CFRP. The eight-facet point
geometry reduces common problems associated with these materials, such as splintering and
delamination. Users can expect to achieve cutting speeds in the order of 60 m/min at feed rates of
0.06-0.15 mm/rev, depending on application.
When drilling composite/metallic stacks using power feed machines, 86PTA is recommended for
CFRP/aluminium materials, while 86PTB is offered for CFRP/titanium stacks. Alternatively, the
40DH series (H10F or N20C) is a carbide tool with innovative flute design for optimized chip
evacuation, while for improved roundness accuracy and stability in larger holes up to 25.4 mm
diameter, PD – D2WM series (H10F or N20C) is recommended. Both PCD and carbide reamers
can be made to order with flute design dependent upon material and application.
Drilling and reaming CFRP aluminium stacks using power feed machines can typically be
performed at 60 m/min with a feed rate of 0.13 mm/rev, however this should be reduced to around
18 m/min and 0.03 mm/rev when hole making in CFRP/titanium stacks.
In control
Where drilling using CNC machine tools is possible, greater accuracy, security and productivity can
generally be achieved due to enhanced machine dynamics and rigidity.
The CoroDrill 859V vein PCD drill is designed purposely for the automated drilling of unidirectional
CFRP materials such as M21E as well as epoxy and BMI resins. It has also demonstrated good
performance on CFRPs with coatings such as fibre glass and copper. The Unique double angle,
sharp vein drill geometry helps improve quality and reduce delamination. Alternatively, the 85
series (N20C, H10F or CD10 PCD vein) are all-round drills with four-facet point geometry suitable
for various CFRP materials such as BMS8-276. It is available as carbide with diamond coating or
vein PCD, in diameters from 3-16 mm. For unidirectional CFRP and composites with high epoxy
resin content (including BMI resins), CoroDrill 856 (N20C) is recommended.
When CNC hole making in composite/metallic stacks using CNC machine tools, 86A and 86B
series (CD10) are the tools of choice for reduced burr and fibre breakout. Another option is the
carbide 40DH series drills (N20C or H10F) – these offer stable tool life in high speed/feed
applications and offer excellent chip evacuation due to 40° helix.
Edging closer to perfection
Cutting tools are put to the test when edge milling CFRP materials. The heterogeneous
combination of fibre and matrix resin means that a cutter encounters varying resistance due to the
inter-layered hard abrasive fibres and softer resin, which puts stress on the tool drive mechanism.
Furthermore, because the fibres are abrasive this can lead to rapid tool wear.
The secret is having a range of tools offering different geometries and different grades to create
application-specific solutions for edge milling. The CoroMill® Plura S215 is one such range.
CoroMill Plura S215 offers different geometries, such as a compression helix design for thicker
CFRP or when equal geometry is needed for both sides of the composite sheet. There is also a
low helix design of +5° when the bottom surface is the most important and -5° when the top side is
most important and down-forces are critical.
The tools come in different grades, such as 1610 and 1630 to maintain sharp edges, or N20C
diamond coated for longer tool life but where ultra-sharp edges are not top priority. There is also a
PCD brazed version for long tool life and optimum surface finish. CoroMill Plura S215 cutters are
made to order in diameters from 8-16 mm and with 2-8 flutes.
For edge milling of CFRP when the machine spindle is not in line with the component (for larger
cut-off operations) then CoroMill 329 is preferred. This standard product comes in diameters of
100-160 mm and widths of 2-5 mm.
Surface advantages
Surface machining of composites brings a new set of criteria. Here, finish, accuracy and high
integrity of primary surface structures are highly important to aerospace manufacturers. Cutting
tool solutions for flat and curved surface machining of CFRP is served by the CoroMill 590 light
cutting indexable insert face mill. Available in diameters above 40 mm, CoroMill 590 inserts come
in PCD and uncoated H10 grades with high precision tip seats for enhanced accuracy.
Machine shops should also look at CoroMill 390 for sculptured surfaces using sturtz milling
techniques. Sturtz milling can replace machining with ball end mills in many areas. This innovative
machining method involves tilting the tool relative to the component surface to create an elliptical
cutter path. The resulting shallow ellipse allows greater step-over to be used without exceeding the
maximum permissible cusp height.
Images: http://www.pinnaclecrc.com/PR_PICTURES/Sandvik/SAN398/
CoroMill 390 is ideal for sculptured
surfaces using sturtz milling
techniques
CoroMill 329
CoroMill 329
CoroMill 390
CoroDrill 452 range based on
H10F uncoated carbide substrate
offers great potential when drilling,
reaming and countersinking CFRP
Composite Machining Solutions
Introduction Video
Link:
http://www.youtube.com/watch?v=Pi3MjF860fM
– End –
Sandvik Coromant
Sandvik Coromant, a product area within Sandvik Tooling, is a global leading name in cutting tools
for turning, milling and drilling as well as modular tooling systems for lathes and machining centres.
With some 8,000 employees, Sandvik Coromant is represented by its own sales personnel and
specialists in more than 60 countries. In addition there is an established distributor network. 20
state-of-the-art Productivity Centres located around the world provide customers and Coromant
personnel with training in tooling solutions for increased productivity.
Contact details for sales enquiries:
Please go to: www.sandvik.coromant.com/
Contact details for public relations enquiries:
Nikki Stokes
Marketing Communications Specialist
Marketing & Sales Support
Tel: +44 (0) 121 504 5422
Email: nikki.stokes@sandvik.com
Website: www.sandvik.coromant.com
Jonathan Roberts
Account Director
Pinnacle Marketing Communications, Ltd
Tel: +44 (0) 208 429 6540
Email: j.roberts@pinnaclemarcom.com
Web: www.pinnaclemarcom.com
Birgit Schöniger
Account Manager
Pinnacle Marketing Communications, Ltd
Tel: +44 (0) 208 429 6554
Email: b.schoeniger@pinnaclemarcom.com
Web: www.pinnaclemarcom.com
Benoit Simoneau
Account Manager
Pinnacle Marketing Communications, Ltd
Tel: +44 (0) 208 429 6542
Email: b.simoneau@pinnaclemarcom.com
Web: www.pinnaclemarcom.com
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Ref: SAN398A