Drilling of Inconel 718 with Geometry-modified Twist Drills

This paper presents a method to adapt twist drills considering the mentioned demands by using geometry-modified tools. The aim is to increase the resistance against abrasive wear and to reduce the thermal loads; so that, tool life and bore quality can be improved. The analysis of the new tool geometry was realized by advanced Computational-Fluid-Dynamics (CFD) simulations. The simulations provide detailed information about the coolant flow and consequently the improved cooling of tool regions which are, on the suggested geometry, exposed to very high thermal loads. Experiments showed that the tool life can be in- creased by up to 50% in contradiction to a standard twist drill. The improvement on the bore quality was shown by determining the roundness deviation and the average surface roughness. In addition, micro hardness tests and metallurgy preparations were conducted to investigate the surface integrity of the bore surface layer. Although the presented geometry only represents a proto- type status, the results are impressive. The tool life and the bore quality have been improved, and the simulations showed clearly that there is a significantly better coolant flow, when using the new geometry.