October 2008

These papers were presented at scientific Conference MATAR 2008, Prague and Brno

Mechatronic Approach in Modelling, Identification and Control of Thermal Deformation of Quill

MM (Modern Machinery) Science Journal, October 2008
Martin Mares, Pavel Barta
Research Center for Manufacturing Technology, CTU in Prague, Czech Republic
Abstract

The demands on machining accuracy have been increasing lately and therefore research of thermal behaviour of machine tool structures is crucial for successful manufacturing.
Generated heat diffuses into the structure of the machine tool components. This process is affected by heat sinks such as heat transfer on the surfaces and cooling systems. Meanwhile the heat warms up the structure of the machine tool and thermal dilatation deforms it. This deformation subsequently affects machining accuracy in a negative way. Different systems are used to eliminate the thermal error, but their efficiency depends on the quality of the thermal machine tool model. This article brings up new approach in the thermal modelling, which combines thermal transfer function modelling and Matlab® tools such as Matlab system identification toolbox® and Matlab® Simulink®.

Keywords: machine tool, quill, thermal error, thermal transfer function, identification, control, Matlab
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Machine Tool Lightweight Design and Advanced Control Techniques

MM (Modern Machinery) Science Journal, October 2008
M. Sulitka1, L. Novotny1, J. Svéda1, P. Strakos1, J. Hudec1, J. Smolik1, P. Vlach2
1Research Center for Manufacturing Technology CTU in Prague, Czech Republic
2Kovosvit MAS, a. s., Sezimovo Ústí, Czech Republic
Abstract

Mass reduction of the machine tool movable parts is a tool for achieving lower energy demands of the machine tool operation. Lower weight can bring elevation of the machine tool dynamic properties with the application of new materials, which assure the equivalent static and dynamic compliancy compared to the usage of common materials. However, if the machine frame compliancy is increased, it is possible to compensate the missing stiffness by means of advanced control methods. The paper introduces the results of the RCMT involvement in the EU project EcoFIT, which is aimed at the development of machine tools with significantly reduced mass of movable structures.

Keywords: machine tool lightweight design, machine tool energy consumption, non-conventional materials in the machine tool design, control of flexible structures, feed drive complex model
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Economy of Titanium Milling

MM (Modern Machinery) Science Journal, October 2008
G. J. Trmal1, P. Bach2
1RAMP, UWE, Bristol, United Kingdom
2Research Center for Manufacturing Technology, CTU in Prague
Czech Republic
Abstract

This paper describes benefits of close collaboration between technologists and analysts of machine tools. After all, any innovation in machine design can only be proven by producing components of required quality more economically.
The combined expertise can be utilized especially in machining new materials, such as titanium, which are more difficult to machine. The decisive factor in optimization of the production process is the cost: cost of labour, machine and tools. The cost of tools is important and the paper proposes a new model of tool life, which is experimentally verified. The model allows determination of a combination of machining parameters for minimum cost. Increase in axial depth of cut could improve the removal rate but is limited by stability of the cutting process.
That is why the paper proposes machining at very low speeds, where the stability limit is higher and the lowest cost can be achieved. At these low speeds it is beneficial to use not carbide but HSS tools.

Keywords: titanium, cost of machining, tool wear
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Operational behaviour of high speed spindle unit

MM (Modern Machinery) Science Journal, October 2008
J. Jedrzejewski, W. Kwasny, Z. Kowal, W.Modrzycki
Wrocław University of Technology in Wroclaw, Poland
Abstract

The paper presents the behaviour of a high speed spindle unit during operation, with changes of: speed, centrifugal forces, bearing working clearance/tension, thermal deformations and temperature distribution. Moreover, spindle and rolling elements of bearing material’s influence on heating up and spindle displacements will be shown for different spindle working conditions.

Keywords: machine tool, spindle unit, high speed
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Variation of Eigenvalues of a HPC Motor Spindle due to Changing Axial Depth of Cut

MM (Modern Machinery) Science Journal, October 2008
B. Späh, S. Kern, R. Nordmann
Mechatronics in Mechanical Engineering
Technische Universität Darmstadt, Germany
Abstract

The influence of the milling-process on the system-dynamics of a hybrid bearing HPC (high performance cutting) motor spindle is investigated. An additional electromagnetic actuator allows for identification and active vibration control. Semi-discretization is used to calculate the eigenvalues of the motor spindle depending on increasing axial depth of cut.
This result is used to design a controller for chatter suppression that accounts for the influence of the process on the system dynamics. The controller increases the critical depth of cut considerably. The results of the semi-discretization as well as the effect of the active damping are validated by experimental identification during slot-milling of aluminum.

Keywords: milling, chatter-suppression, active vibration control, semi-discretization
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Modelling the orthogonal machining process using cutting tools with different geometry

MM (Modern Machinery) Science Journal, October 2008
J. Zouhar, M. Piska
Brno UT, Faculty of Mechanical Engineering Brno
Czech Republic
Abstract

This paper deals with modelling of the orthogonal machining process using tools with different geometries. The finite element method (FEM) is used for a simulation based on the Lagrangian formulation including ANSYS/LS-DYNA software.
The constitutive Johnson – Cook material model regarding strain, strain rate and temperature to predict material plasticity and chip separation is used. Chip morphology, stress, strain, strain rate, residual stress and temperature have been obtained for a range of tool rake angles, cutting edge radii and friction coefficient values. Results are compared with experimental results and other references.

Keywords: FEM, orthogonal cutting, LS-DYNA, Johnson – Cook
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