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Experimental Research on Circular Milling of Bi-Layer Composite Materials Consisting of CFRP Laminates and Titanium Alloys

Recently, to construct an airframe 2-layer composite materials consisting of carbon fiber reinforced plastic (CFRP) laminates and TiAl6V4 still need to be machined, whereby drill holes are frequently machined. Special attention has to be paid to the machining quality, which implies hole dimensional accuracy, defect free peripheral zone, edge quality at inlet and outlet of hole and so on. Machining defects often occur as a consequence of excessive mechanical and thermal loads, which are often caused by wrong process conditions or by the wrong choice of machining process itself. With respect to widely used state-of-the-art machine tools providing high performance and equipped with potent control unit, for the comparatively large drill hole, circular milling gains interest as an alternative to the drilling operation [1, 2]. In this research, in order to select suitable machining conditions for 2-layer composite materials consisting of CFRP laminates and TiAl6V4 a large number of circular milling tests of 6 mm diameter are executed by using a high performance vertical milling machine. Hole diameter deviation from 6 mm and inner surface roughness in relation to number of hole machined are measured and evaluated for CFRP laminates and TiAl6V4. Moreover, from observations of cutting edges in relation to number of hole machined it is confirmed that under wrong machining conditions the difference of heat conductivity between CFRP laminates and TiAl6V4 induces for chips of TiAl6V4 to be deposited on the end cutting edges of endmill used. In this case tool life shortens extremely.