Model-based control of rim zone properties during hard turning

 

In today's manufacturing technology, the efficient design of processes and process chains with consistently high workpiece quality is of utmost importance. Hard turning of hardened steels can replace the grinding process step by increased metal removal rates and largely eliminate the use of cooling lubricants. However, high thermo-mechanical loads lead to damage of the workpiece rim zone, e.g. due to negative residual stress changes.

The aim of the project, which is funded within the framework of the priority program SPP 2086 of the German Research Foundation DFG, is the combined direct and indirect process monitoring and control of defined rim zone properties during the turning of quenched and tempered steel. In the process, modifications of the boundary zone properties, grain size distribution, residual stresses and phase fractions are to be monitored. In the first funding period a reliable monitoring will be realized, which will be extended by a process control in the second funding period.

Due to limited accessibility, it is not possible to monitor the thermal and mechanical state variables with high spatial and temporal resolution during turning. However, industrial sensors, e.g. dynamometers and pyrometers, permit selective or integral monitoring of these state variables. Within the framework of this project, a model-based correlation between low time- and location-resolved state variables and high-resolution state variables in the entire machining zone is now being developed. This relationship is investigated during orthogonal cutting, which approximates the conditions of the turning process and at the same time allows access for integral as well as high spatial and time resolution sensors. With the help of numerical or analytical models, it is now possible to determine and predict a modification of the boundary zone properties using precise knowledge of the thermomechanical load spectrum.