SensDrill - Sensory BTA deep hole drilling tool to observe the center variation

Drilling deep holes is often required in many areas of the oil and printing machine industry and in aviation. BTA deep-hole drilling is a frequently used process for the production of deep-hole bores. BTA deep-hole drilling is characterized by an external oil supply between the bore wall and the drill head. The oil transports the produced chips through the drill head and the drill pipe to the outside. To increase process reliability, the Institut für Fertigungstechnik und Werkzeugmaschinen (IFW) Hannover is developing a sensory drill pipe together with BTA-Tiefbohrsysteme GmbH. The aim is to be able to determine and monitor the center deviation during machining. The center deviation to be determined is calculated from the radial deflection of the boring bar at the boring head or the bending line of the boring bar. For the calculation of the bending line, the strain distribution over the length of the boring bar and the relative alignment between machine and boring bar and workpiece are required. The measuring system developed for this purpose consists of several subsystems, which are shown schematically in the figure. Using signals from optical strain sensors (fiber Bragg sensors) distributed over the length of the boring bar, a continuous strain distribution is reconstructed. In contrast to strain gauges, where a change in electrical resistance is measured, fiber Bragg sensors can be used to determine the strain from wavelength changes of light. The fiber used for this has a diameter of only 0.1 mm. The calculation of the center deviation was evaluated for the first time in laboratory tests. For this purpose, the center deviation of the drill pipe was measured by laser sensors and compared with the calculated center deviation. A maximum deviation of 5 % was found at the tip of the bar. This means that the accuracy is sufficient for calculating the center deviation.