Session 2: Design of thermal robust machine tools

Development of a dynamic model for simulation of a thermoelectric self-cooling system for linear direct drives in machine tools
E. Uhlmann (a), L. Prasol (a), S.Thom (a), S. Salein (a), R. Wiese (b)
(a)    Institute for Machine Tool and Factory Management, TU Berlin
(b)    Beuth University of Applied Science, Berlin

The growing awareness for sustainable production and increasing energy costs as well as the commitment to legal restrictions lead to a rising demand for energy efficient solutions for long-life production facilities. The applicability of energy harvesting concepts, in order to increase the energy efficiency of highly dynamic machine tools with linear direct drives, is one research objective at the Institute for Machine Tools and Factory Management (IWF). Therefore, thermoelectric generators are placed in the heat flow between the primary part of a linear direct drive and the cooling system to convert parts of the thermal losses into electric energy. It was investigated, if a so called thermoelectric self-cooling-system is applicable to operate a pump of a water cooling circuit, only supplied by thermoelectric generators. To determine the harvested energy and to simulate the steady and the transient state of the system a thermoelectric model was developed. The comparison of simulative and experimental determined data indicates high model prediction accuracy. Hence, the model turns out to be a powerful tool for the development and analysis of water flow thermoelectric self-cooling-systems. The results show that the thermoelectric generators can provide sufficient energy to operate a water pump in a decentralized cooling system with reasonable coolant flow rates.

System modelling and control concepts of different cooling system structures for machine tools
J. Popken, L. Shabi, J. Weber, J. Weber
Institute of Fluid Power, TU Dresden

The current problem with the existing cooling structure of machine tools is that a central fixed pump supplies a constant cooling volume flow to cool all the components of the machine tools, which does not match the individual temperature development of the components: Due to the different amounts of heat introduced (power losses) by the machine components, an inhomogeneous temperature field is generated within machine tools, which leads to a thermo-elastic deformation of their structure. This deformation is responsible for the displacement of the Tool Center Point (TCP) of the machine tools. Consequently, the machine’s accuracy during the production process is reduced.
The main target of this paper is to study the thermal behavior of the existing cooling system structure of a demonstration machine with the aid of an experimental investigation in order to develop a network-based simulation model and to introduce new control concepts for different cooling system structures.
Firstly, the paper presents the cooling system design of the demonstration machine and the experimental investigation, which are carried out. Furthermore, a network-based model of the existing cooling system is developed and validated against the measured data. Finally, the validated system model is used to study new control concepts of different cooling system structures in order to ensure a uniform temperature distribution to the machine tool at minimal energy consumption.

The electric drive as a thermo-energetic black box
S. Winkler, R. Werner
Chair of Electrical Power Conversion Systems and Drives, Chemnitz University of Technology

Electric drives in machine tools can generate several kW of power losses. Hence the modelling of drive losses and the resulting heating is essential for determining the thermally induced displacement of a machine tool. The present study examines the specifications necessary for the modeling and the requirements of the motor model to the input parameters, for example their temporal resolution. Not all parameters of the motor, in particular the slot geometry, are sufficiently known. Therefore it is shown which assumptions to the parameter estimation can be made and how these affect the accuracy of the model.

Thermal error compensation on linear direct drive based on latent heat storage
I. Voigt (b), S. Winkler (a), R. Werner (a), A.Bucht (b), W.-G.Drossel (b)
(a)    Chair of Electrical Power Conversion Systems and Drives, Chemnitz University of Technology
(b)    Fraunhofer Institute for Machine Tools and Forming  Technology IWU, Dresden

Linear motor feed drives induce time variable heat losses that cause thermoelastic deformations in the surrounding machine structure. Consequently, unsteady displacement fields arise leading to decreased position accuracy. In order to compensate for thermal errors of the tool center point position, latent heat storage can be used to provide a smoother temperature response of the machine tool. The proposed approach considers paraffin-based phase change materials infiltrated in aluminum foam structures. Performance and efficacy of the realized compensation component are numerically and experimentally validated.

Industrial relevance and causes of thermal issues in machine tools
M. Putz (a,b), C. Richter (b) J. Regel (a), M. Bräunig (a)
(a)    Institute for Machine Tools and Production Processes, Chemnitz University of Technology
(b)    Fraunhofer Institute for Machine Tools and Forming Technology IWU, Chemnitz

Regarding extensive research activities on the thermal behavior of machine tools, the question arises as to what relevance is given to thermal issues in industry. The answer comes from 75 small to very large machine tool manufacturers and mainly larger production companies from Europe and Asia. In contrast to machine users, machine manufacturers rate thermal failure higher than geometrical, static and dynamic manufacturing defects, even though production companies attribute a share of up to 50% to the thermally caused portion of scrap production. Users rate the relevance of thermal defects of workpiece, tool and machine tool for manufacturing accuracy to be almost identical. The assessments are based on their own experiences from the daily operation as well as on experimental investigations. The paper describes comprehensively the relevance of thermal errors. In addition, the occurring areas and methods for localization are explained. Finally, the causes and the conflict to energy-saving measures are clarified.