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COMPOSITES MACHINING


such as aircraft wing skins, fuselage sections, cabin walls and fl oors. However, machining a stack of materials of differ- ing strengths and physical properties presents several layers of challenges. The main goal is to avoid bending or fraying the core structure or delaminating the face sheets. Sand-


wiched composite material that is cut unevenly or deformed loses its strength, much as creasing corrugated cardboard destroys its rigidity. Like corrugated cardboard, a sandwiched composite is comprised of a lightweight core structure, usually resembling the hexagonal cells of a honeycomb, backed by rigid facing sheets. Depending on strength requirements, the honey- comb cells may be formed from high-tech paper, cardboard, carbon-fi ber-reinforced plastic or aluminum. The face sheets can be paper, plastic, aluminum or titanium and are bonded to the open ends of the honeycomb cells. A balance of bending, compression and shear forces among the elements of sandwiched composites, results in materials that are lightweight, rigid and remarkably strong. Sandwiched composite parts typi-


Iscar’s SUMOCHAM ICF drilling head geometry for drilling composite materials provides low axial forces for smooth penetration during the cutting process without the splintering phenomenon.


84 AdvancedManufacturing.org | September 2016


cally are fl at or mildly curved panels that range in thickness from 0.250 to 0.500" (6.35–12.7 mm). The panels are fabricat- ed to near-net-shape and fi nish-machined to trim outer edges, mill out widows and other various shaped openings and holes. For fi nish machining, shops must use high-speed end mills specifi cally designed for such sandwiched composites. Sharp end mill cutting edges and high cutting speeds are key factors in cleanly machining sandwiched com- posite materials. The situation is much like slicing bread—cut too slowly, and the bread compresses instead of shearing cleanly. While on the other hand, fast-moving, sharp cutting edges generate clean cuts. When machining sandwiched composites, slow cutting speeds can distort the face sheet and the honeycomb structure itself. High cutting speeds, however, gener- ate heat, and that poses problems be- cause many of the constituents of sand- wiched composites are heat-sensitive. Accordingly, light radial engagement—on the order of 5% of cutter diameter-mini-


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