High speed analysis of the chip formation in small diameter deep hole drilling of high-strength and difficult-to-machine materials

• Applicant: Professor Dr.-Ing. Dirk Biermann
• Subject Area: Metal-Cutting and Abrasive Manufacturing Engineering
• Term: from 2015 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 277611053

The aim of this research project is to analyze the chip formation in small diameter deep hole drilling in-depth to set the stage for a productive and reliable machining of high-strength and difficult-to-machine materials. Focusing on industrial applications the machining of a nickel based alloy, a titanium alloy and a bainitic steel are investigated accurately. In small diameter deep hole drilling the chip formation is crucial for process stability. The formation of disadvantageous chip shapes respectively long chips leads to a chip flute plugging and finally results in tool breakage. Furthermore the development of disadvantageous chip shapes facilitates a contact between produced chips and the bore hole wall and thus causes a reduction of the surface quality. In this research project a specific experimental set-up will offer a substantiated chip formation analysis. The counterboring of bars made of difficult-to-machine materials, inserted in transparent and optically flawless glas, will be captured by a high-speed-camera and hence provide valuable insights into the chip formation along the cutting part and the removal of chips along the chip flute. Within the investigations conducted in single lip deep hole drilling the innovative experimental setup using a high-speed-camera will be advanced and subsequently used to analyze the influence of the process data and the cutting edge design on the chip formation. Moreover a simulation of chip formation will be used to gain further knowledge of the predominant mechanisms of chip formation. In this context the influence of the macroscopic cutting edge design on the chip formation will be analyzed in detail by means of the simulations. Thus, adequate process and tool parameters leading to an efficient deep hole drilling in the challenging materials will be identified. In addition, the high speed analysis will be applied to check the coolant wettability on the circumferential contact elements of the gun drills. The wettability of the guide pad and of the circular grinding chamfer correlates directly with the occurring wear and the produced surface quality. In this connection, tools with varying drill head tapering, circumferential shapes and cross-sections for oil supply will be compared regarding the qualitative and quantitative wettability. Subsequent to the high speed analysis for the identification of advantageous process and tool parameters, experimental tests with solid material will be conducted. The tests on small diameter single lip deep hole drilling will focuse on the manufacturing of bore holes with high length-to-diameter-ratios. The evaluation of the experimental work conducted considers tool loads, chip formation, tool wear as well as quality with respect to dimensional and form tolerances, surface quality, and alteration of recast layer.

• DFG Programme: Research Grants