High-aspect-ratio microdrilling of cobalt-based superalloy - High-aspect-ratio microdrilling of nozzle of marine diesel engine

It is necessary to develop a high-aspect-ratio microdrill method with a diameter of 0.2mm and a depth of 4mm (aspect ratio 20) that can be applied to the fuel injection nozzle of a marine diesel engine. However, the injection nozzle is made of cobalt-based superalloy, which is a difficult-to-cut material. In this study, the drilling conditions from viewpoints of thrust force and torque for the cobalt-based superalloy are determined. In addition, a thinning machine is developed for the convenient precise thinning of the microdrill. The effects of the thinning of the microdrill are verified to measure thrust force and torque during drilling. The following results are obtained. The thinning of the microdrill with a diameter of 0.2mm results in a reduction in thrust force by 20% and that in chip adherence to the drill by 25% during drilling.