Adapting Tool Design for the Integration of Miniaturized Thin-film Sensors in Deep Hole Drilling

The production of high-quality bore holes with high drilling depth requires the use of specialized deep hole drilling tools in metal-cutting of complex and cost-intensive parts. Due to the asymmetrical cutting edge design, which results in radial forces and forming processes at the guide pads on the bore hole wall, high surface qualities are reached. The cutting and forming processes lead to high temperatures in the contact zone of the cutting inserts and the guide pads, subsequently followed by significantly cooler drilling oil. The thermomechanical load in combination with high temperature gradients induce residual stresses and, depending on the workpiece material, microstructural transformations (e.g. white etching layers) in the bore subsurface. The resulting surface integrity has an influence on the fatigue strength of the often highly stressed components. Depending on the subsurface requirements the deep hole drilling process is followed by secondary post-processing. With sufficient information about the produced surface integrity and the deep hole drilling process, the post-processes could be omitted. Due to the inaccessibility of the contact zone from the outside and the challenges of non-destructive measuring on the workpiece-side, process monitoring at the tool has great potential for the continuous analysis of the process. Miniaturized thin-film sensors are developed for in-process measurement of mechanical loads, wear, and temperatures in deep hole drilling directly in the contact area between tool and workpiece. The first-time integration of thin-film sensors in combination with a wireless telemetry system on the tool-side requires modifications of the guide pad and drill head design for electrical connection of the sensors without effecting the drilling process. Besides integrating the sensor system into the drill head, routing the sensor signal through the tool and a reliable signal transmission from the rotating deep hole drilling tool are in focus. Experiments with modified guide pads have been conducted and compared to validate the design modifications.