Deep hole drilling using senor integrated tools to adjust defined functional characteristics into the near-surface peripheral zone

• Applicants: Professor Dr.-Ing. Hans Christian Möhring; Professor Dr.-Ing. Stefan Weihe, since 4/2023
• Subject Area: Metal-Cutting and Abrasive Manufacturing Engineering ; Metallurgical, Thermal and Thermomechanical Treatment of Materials
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 401792429

Deep holes in components being exposed to highly alternating pressure loads (e.g. injection components in large diesel engines) are subject to high demands on the near-surface peripheral zone properties. Microcrack formation in the bore wall must be avoided during machining, as these can lead to component failure. This is caused by surface defects or unfavorable residual stress conditions. High surface quality can be achieved by using the single-lip deep drilling method, but residual compressive stresses must be induced by subsequent machining processes (e.g. autofrettage). This is associated with additional machining effort as well as low flexibility in responding to transient conditions of previous deep drilling processes.The projects main object is the metrological detection of process changes and their compensation by means of in-process-capable control approaches. In the first project phase a sensor-integrated single-lip drilling tool for in-process detection of the thermo-mechanical state, a combined numerical-analytical compensation model of the machining temperature, machining and material models were developed and validated. Also a process controller was conceptualized. Machining tests were performed on the heat-treated steel 42CrMo4 (ASTM A331).The follow-on project is based on the results of the first funding phase and aims to develop a robust controller based on a soft sensor, with which the near-surface zone properties of deep holes can be specifically adjusted. The following sub-goals are pursued here: A detailed understanding of the mechanisms in the near-surface microstructure (crystal plasticity), on dislocation dynamics and on separation processes at the atomistic level in the material. Merge of models created in the first funding phase on the correlation between near-surface zone properties and machining parameters. Control strategies for the targeted influencing of the near-surface zone in a controller environment in which material- and requirement-dependent (not time-critical) and process-dependent boundary conditions (time-critical) are combined and brought together within a controller architecture. Concepts of a soft- and hardware-based in-process control for deep hole drilling, where input variables of the controller are the tool acceleration and temperature at the effective point (by means of sensor-integrated tool and compensation model taken from the first project phase) as well as the mechanical load (forces, moment via dynamometer). The control variables are the rotational speed and the feed rate of the single-lip drill. Based on the input and output variables as well as the time relevance of the output variables, a suitable controller concept is available, which divides the tasks of the controller into time-critical and -uncritical fields. The controller is connected to the machine control system. Controller and control strategies are validated on the basis of application scenarios.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2086: Surface Conditioning in Machining Processes
• Co-Investigator: Dr.-Ing. Thomas Stehle
• Ehemaliger Antragsteller: Professor Dr. Siegfried Schmauder, until 3/2023