JEC COMPOSITES MAGAZINE - Issue #77 - December 2012 - 56

tools
Tool manufacturers constantly develop new tooling to improve machining efficiency in (new) CFRP materials. Seco offers a full range of products to machine CFRP materials, available as standard tools. Custom tools can be designed and manufactured to suit special requirements. For these tools to contribute to effective and efficient manufacturing of CFRP parts, insight and knowledge are key success factors.
Fig. 5: Typical wear pattern on conventional routers (left) and on the Jabro JC870 line point geometry (right)

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The JC870 is different from a standard solid carbide routing cutter. The cross-cut serrations have a line point geometry which improves the coating adhesion and stability when cutting. This geometrical feature allows the tool to make light cuts and to operate at higher speeds and with faster feeds without reaching the matrix glass transition temperature level.

design of the point angle. The C1 geometry has a primary point angle of 130° and a secondary point angle of 60°. The point design reduces the generated axial forces and consequently minimises splintering or pushout of the workpiece material.

Application example: CFRP drilling
What kind of improvements can be achieved in a realistic production environment? This is an example of a CFRP drilling application in a 50% carbon fibre content medical part. The machine is equipped with a highpressure internal coolant system (80 bar). A shrink fit tool holder maintains minimum run-out and allows for high cutting speeds. Tool: Seco C1 ø7 mm drill Depth of cut (doc): 21 mm Cutting speed (vc): 600 m/min Rotations per minute (n): 27,300 rpm Feed per rotation (fn): 0.059mm/rev Table feed (vf): 1600 mm/min A superior surface finish is achieved, with hole size and geometry (shape) within specifications. A tool life of 2,800 holes is achieved, compared to 800 holes with the previous solution. Cutting data is significantly increased.
Fig.7: SECO JPD890 standard PCD 2 flute milling tool in action

Drilling CFRP with coated solid carbide drills
All the above-mentioned CFRP material aspects that influence the machining process are to be taken into account when drilling. Sharp angles generally prevent heat dissipation in drilling. Drilling tools for composites normally feature high positive rake angles for a clean cut that keeps heat generation to a minimum. They often incorporate clearance angles that are sufficient to prevent the edge of the tool from rubbing as it passes the CFRP material. Seco tools offer two different geometries (C1 and C2) specifically designed for the main application areas present in today’s marketplace in order to produce high-quality holes in a high productivity environment. By applying optimised point geometries, hole quality can be improved. The diamond PVD DURA coating results in up to 10 times more tool life compared to conventional TiCN/TiAlN coated tools.

Milling CFRP with PCD plated end mills
The matrix material’s high tensile strength combined with a high content of highstrength carbon fibres make high-performance CFRPs very suitable to be machined with poly-crystalline diamond (PCD) tooling, the SECO Jabro JPD890 series is a full range of CFRP focussed milling cutters available from stock.. Customised PCD tools, dedicated to CFRP machining, are also available. The very sharp cutting edge allows the PCD tool to operate consistently and securely. This means that the workpiece will have a good surface finish with no or minimum delamination or splintering.

C2 geometry – for stacked materials
The new C2 geometry was designed to provide optimum results when drilling stacked materials. “Stacks” are a combination of composite filler material between a “sandwich” of outer layers (normally aluminium or titanium). The 180° point angle guarantees small chip forming and excellent dust evacuation from the cutting zone. This enables the drill to produce superior hole quality without damaging the surface finish of the composite stacked material.

Drilling CFRP with PCD plated end mills
PCD drills have a special PCD drill point design that can be used in various applications. One of the strongest benefits of PCD drills is their ability to machine for long periods of time without the need for replacement. With a typical 30° helix angle securing dust evacuation, the sharpness and precise dimensional tolerance of a PCD tool ensure improved workpiece quality in terms of surface finish and tolerances. n
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C1 geometry – exiting in composite material
The C1 geometry is designed for a variety of composite materials. Its main feature is the

Fig. 6: Seco C1 geometry designed for drilling in CFRP materials

56 jec composites magazine / No77 December 2012

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JEC COMPOSITES MAGAZINE - Issue #77 - December 2012

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #77 - December 2012