Surface integrity of Inconel 718 during drilling operation

Abstract

Superalloys such as Inconel 718 have high strength at elevated temperatures, which make them attractive towards various applications in aerospace industry. However, these materials are considered difficult to machine materials. The state of a workpiece surface after machining is definitely affected by cutting parameters, such as cutting speed, feed rates, drill types and drill geometries. Drilling tests, at different spindle-speed, feed rates, drills and point angles of drill, were conducted in order to investigate the effect of the above parameters on the quality of machined holes and surface integrity of Inconel 718. The quality of machined holes was evaluated in terms of the geometrical accuracy and burr formation. Surface integrity involved the aspect of surface roughness, metallurgical alterations and microhardness of the substrate of the hole surface. High hole quality was observed even at holes produced using worn tools, in relation to dimensions, surface roughness and burr height. However, microhardness measurements and microstructural analysis of work-piece showed significant microstructural changes related with a loss of mechanical properties. In general the cutting parameters have significant effects on the surface quality and surface integrity when drilling Inconel 718 using uncoated carbide drill.