Project area B

B01: Modelling of the thermal interaction between the environment and the machine tool and the effected deflection of the machine tool in order to deduce methods of design and compensation for a better thermal behaviour

It is interesting to know the influence of different thermal boundary conditions of the working accuracy during the development of machine tools. Mainly the finite element method is used for this. But there are only inadequate data for many necessary physical input and parameters for a thermal structure mechanical computation (static and transient) and also for the numerical fluid mechanics , especially for heat flow for the determination of the interaction between the machine tool and the environment. Target is to develop models with boundary conditions for this heat transfer; to determine and to optimize the parameters. This is planed preferably for air streams based of free and enforced convection  as well as the thermal radiation. Furthermore is planed to investigate the interaction  between the machine tool and the foundation. A further target is to deduce design and compensatory measures for a better thermal behaviour.
Task description

  • Modelling  of the thermal influence of the interaction between the machine structur and the environment based on transient thermo-elastic FE-Models
  • Modelling  of the interaction between the machine structur and the environment based on CFD-Models
  • Analysis of sensitivity with thermo-elastic FE-Models and  CFD-Models for the convective heat transfer and the thermal radiation
  • Experimental investigations of the temperatures at a machine tool and determining and verification of the parameters for the thermo-elastic FE-models for free and enforced convection as well as the thermal radiation
  • Check of the results of the thermo elastic FE-models against the CFD-Simulations und the measured temperature variations

B02: Calculation and modelling of heat transfer mechanisms between machine components

An accurate description of thermal resistances within contact regions of component assemblies is of paramount importance for the characterization of the thermal behavior of machine tools. The subproject aims to identify and quantify interdependencies between thermal contact resistance and its governing parameters, namely contact pressure and surface conditions. For the next funding period, developed models will be expanded in order to account for relative movements, as well as for intermediate fluids within the contact region.

B03: Investigation of Components and Assembly Groups

The first project phase focused on the development of test rigs for individual components (ballscrew system, linear guide, spindle bearing, bearing arrangement) of a machine tool and the measurement of the temperature distribution for different operating conditions. Based on the measurement data, FE models of the individual components were created and aligned.
The test rigs will be extended to analyze additional parameters (e.g. lubrication, size, preload) in the second project phase. The existing FE models will be optimized to consider the new influences. In a subsequent step, the individual models are transferred to subassemblies (spindle system, linear axis). Experimental and simulative investigation of these subassemblies will serve as a verification for the individual models.

B04: Identification of exemplary scattering and time-varying thermal model parameters

Thermal models of machine tools contain uncertain and time variant parameters that cannot be estimated with sufficient accuracy. Hence, a measurement-based parameter adjustment procedure is needed in the operational state of the machine tool. Up to now this involves a high effort. The project aims to the reduction of this effort. Therefore the systematization and generalization of this parameter adjustment procedure is a subject matter of the project. Based on this methods and software tools for an efficient support are developed and examined, which achieve the reduction of time as well as manual effort.

B05: Correction by Characteristic Diagrams

To continue phase 1, correction methods will be enhanced in the 2nd phase of B05 using higher dimensional maps for the current position of the Tool Center Point. Furthermore, the modelling of environmental effects will be extended from component level to the complete machine. In addition, the so far equidistant grid of the map will be minimized by adaptive FEM through local refinement and constant respectively better accuracy for an optimal use of the inhomogeneous smoothness of the model.
Finally, the flow model for translational components and the whole machine model shall evolve on basis of the results of the 1st phase of B01. Especially interdependencies through forced convection during the production process in the processing area will be analysed. The analyses of the thermo elastic behaviour by FE simulation will be transferred from steady-state to unsteady temperature fields. Experimental sensitivity analyses on variable environmental conditions are scheduled in the thermal cell of the IWU to determine the relevant load cases, which are mapped on a set of alpha values. These will be transferred to the whole surface of the machine tool subsequently.

B06: Correction of Load Dependent Machine Tool Deformations Based on Property Models

The first project phase focused on the development of a volumetric correction methodology for axes-related thermally induced displacements. In the second phase this method is applied to further components and influences, particularly the axes of rotation, the environment and the spindle. Additionally, a direct correction methodology based on of a few measurement points to adjust the indirect volumetric methodology for long time stability will be developed. Furthermore, the model has to be simplified to be used in an industrial environment. In this regard a cost-efficient, universally applicable load unit will be designed. Moreover, the modeling effort is reduced by integrating the correction model into the measurement methodology. By this means it is possible to predict the thermal behavior based on experiments with shorter time intervals.

B07: Structure based models for the correction of thermal deformations of machine tools

Project B07 works on the control integrated structure based correction of thermoelastic errors at machine tools. In the first stage the modules of the structure based correction are developed, implemented and tested using the examples of two demonstrator machines, booth with CNC-controllers in research-specific open architecture. Building on these results the modularised correction solution has to be generalized and improved on the example of another control system and for additional degrees of freedom of the demonstrator MAX. The aim is to transfer the correction solutions from the demonstrators to a production machine.

B08: Model Predictive Parameter and State Estimation and Optimal Sensor Placement

In this subproject we consider the online and self-calibrating identification of relevant parameters in transient thermo-elastic FE models. These parameters can include, for instance, heat transfer coefficients as well as heat inputs due to the machining process and electrical drives. Their knowledge is of paramount importance in particular for the subprojects developing online correction strategies. We will develop model-predictive parameter and state estimation schemes, which are using a moving time horizon to adapt the estimated parameters and state to measured temperature (or, when available, displacement) data. These techniques will be developed under the specific operating conditions of machine tools, i.e., having available only a limited number of measurements, high dimensional thermo-elastic FE models, and they will take into account the pose dependence. Parameter models developed in  subprojects B02-B05 will serve as so-called background information and stabilize the estimation process. Initial experiments are showing this procedure to be very robust and capable of reconstructing time-dependent changes in heat transfer coefficients by means of only a few temperature measurements. In actual machine geometries, it will be important to place the temperature sensors intelligently, and we will further develop our optimal sensor placement techniques in order to make best use of the available sensors also in these nonlinear identification settings.

B09: Identification of environment parameters of thermo-elastic models and correction algorithms based on high-dimensional characteristic diagrams

Project B09 will optimize the structure of the characteristic diagrams (CD) which uses to map temperature fields within a machine tool onto its TCP displacement via the use of adaptive FEM. The heat transfer between a machine tool and its surroundings will be investigated in more detail by assessing moving components and finally the complete machine tool for both stationary and transient temperature fields using CFD-simulations and experiments in a thermal chamber for validation. On the basis of heat transfer parameters ascertained for selected machine tool environment scenarios CDs will be used to decouple CFD- from structure-mechanical simulations to reduce the overall simulation time.