Analysis of local cutting edge geometry on temperature distribution and surface integrity when dry drilling of aeronautical alloys

A suitable choice of tool geometry and tool material and the optimization of cutting conditions is the way towards dry machining, especially for difficult to machine materials. The current paper proposes an experimental work about dry drilling of AA 7075 aluminium and more particularly Ti-6Al-4V titanium alloys. Effects of complex drill geometry on thrust force and cutting temperature variations are explored. This study includes drill normal rake angle definition using a mathematical formulation based on tool CAD definition. Temperature distribution along the drill cutting edge is estimated with a specific device. Cutting forces are measured using a dynamometer table. Hole surface integrity is studied by observation of microstructures, on surface and sub-surface. Micro-hardness tests complete the measurements. Results show that temperature is much higher when drilling titanium Ti-6Al-4V than when drilling aluminium AA7075, with variations from 450 to 540 A degrees C along the main cutting edge. Temperature variation along the cutting edge depends on cutting speed, work material and local geometry. Microstructural observations reveal that surface and subsurface are affected with grains elongation in cutting direction. Temperature and microstructural deformation increase with drilling depth.