Model-based control of surface integrity in hard turning

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The aim is the combined direct and indirect process monitoring and control of defined production-related surface integrity properties during the turning of quenched and tempered 42CrMo4 steels (48 HRC, Rm = 1557 MPa) with CBn or carbide tools. Thus a material will be investigated for components whose peripheral zone properties significantly influence functionality. Direct process monitoring refers to the detection of the surface integrity properties via micromagnetic eddy current methods in the process. Indirect process monitoring is carried out via sensors that can be used in industrial environments, which record temperatures and cutting force components online in the process and allow conclusions to be drawn on current surface integrity properties based on models. During the process, the boundary zone properties of the grain size distribution, residual stresses and phase fractions are to be monitored. First of all, a reliable monitoring system will be implemented in the first funding period, which will then be extended to include a regulation in the second funding period. Due to limited accessibility, it is not possible to monitor the thermal and mechanical state variables in the industrial turning process with high spatial and time resolution in the KHz and 10 µm range. However, it can be achieved in the form of integrated thermocouples, acoustic emission sensors, dynamometers and pyrometers for selective or integral monitoring of state variables. However, it is not known how these selective or integral measurements of the state variables with low temporal and spatial resolution correlate with high-resolution state variables in the entire cutting zone. This correlation is investigated in an analogy process, which approximates the conditions of the turning process and at the same time permits accessibility for the application-oriented sensor technology for the turning process as well as high spatial and time resolution sensors (high-speed cameras). In order to predict the correlation between process state variables that can be measured in the machining zone and spatially and time-resolved state variables that cause a modification of the metal edge zone, physical or empirical models are then developed. For the high spatial and time resolution, both the DIC method for measuring strain and strain rate fields and thermography are used for determining temperature fields. The developed models can be used in conjunction with application-oriented sensors for the turning process to indirectly control the surface properties, as far as the relationship between process state variables and edge zone modification is known. This also requires the analysis of this correlation in the analogy process or by means of validated numerical simulations. Parallel to this, micromagnetic eddy current measurement methods are used in the analogy process, which permit direct control.