November 2010

ANALYSIS AND SIMULATION OF NONLINEAR SELF-EXCITED VIBRATIONS IN MACHINE TOOLS

MM (Modern Machinery) Science Journal, November 2010
J. Zeleny, T. Repak, P. Fojtu
Research Center of Manufacturing Technology
Faculty of Mechanical Engineering, CTU in Prague, Czech Republic
Abstract

Commonly applied theories of self-excited vibrations in machine tools are prevailingly based on frequency domain analysis of linear models, and in most cases only focus on evaluation of stability limits of strictly linear systems. In this way the behaviour of more stable or more unstable systems cannot be studied and analyzed. Neither is it possible to study certain important nonlinear effects because of limitations connected with the classical representation of systems only in the frequency domain. Evaluation of stability by analysing nonlinear systems in the time domain has not been applied until recently. The paper shows a new approach based on an interpretation of self-excited vibration systems as nonlinear servo-systems. With this approach linear and nonlinear systems of any degree of stability can be studied using a combination of frequency and time-domain methods. This can considerably contribute to better understanding of complex phenomena in various regimes and specific situations.

Keywords: machining, machining process, machine tools, vibrations
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USING SIMULATION APPROACH FOR DESIGNING OF ACID PICKLING LINES

MM (Modern Machinery) Science Journal, November 2010
S. Simeonov
Institute of Production Machines, Faculty of Mechanical Engineering, Systems and Robotics Brno University of Technology
Abstract

Presented paper deals with problems of discrete simulation within acid pickling lines. These types of lines are complicated mechanical systems required special algorithm for controlling. The paper discussed using of simulation approach both for projecting and controlling of acid pickling lines. Several experiments with the simulation model were performed to verify the production system design. In the paper are only mentioned simulation experiments which balance two alternatives; alternative with one crane, and alternative with two cranes. The key factor to be followed was the throughput (number of produced coils per hour) of pickling line in a steady state.

Keywords: Discrete Simulation, Acid Pickling Lines, Transport System, Production Rate
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DESIGN AND MATERIAL OF LARGE COMPLICATED CASTINGS OF STAMPING DIES FOR AUTOMOTIVE INDUSTRY

MM (Modern Machinery) Science Journal, November 2010
A. Herman
Czech Technical University, Department of Manufacturing Technology
Prague, Czech Republic
Abstract

This research report deals with analysis of large shape-difficulty casting of stamping die for automotive industry – made from materials steel, grey iron and ductile iron. The main goal of this research is to choose a material for any type of stamping die. Second goal is to find problematic areas in the casting design and to change the stamping die design and to recommend optimal technology for casting. The results of this research confirm trend of using ductile iron as better and more suitable material than steel. There are comparing next material – grey iron, ductile iron and steel.

Keywords: ductile iron, stamping die casting, steel, grey iron, casting design
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QUALITATIVE ANALYSIS OF COMPOSITE ZN-PTFE COATINGS

MM (Modern Machinery) Science Journal, November 2010
M. Pazderova, M. Bradac, M. Vales
Aeronautical Research and Test Institute, Testing laboratories,
Prague, Czech Republic
Abstract

The aim of this work is to obtain completely new technology of surface treatment. Studies and research in the area of deposition showed that lubricant composite coatings based on zinc with PTFE (polytetrafluoroethylene) particles offer unexpected possibilities of electrodeposition and innovative approach to surface protection. Integral part of this research is a characterisation of applied coatings and it requires the development of reliable methods to determine the coatings ́ composition, PTFE content and distribution in the composite coatings. A number of analytical methods were used to characterise all required parameters. Optical microscopy, infrared spectroscopy, Raman spectroscopy, and optical emission spectroscopy were used for characterisation of prepared coatings. Each method proved better or lesser ability to describe tested coating. It is possible to say, that IR spectroscopy allows an easy qualitative analysis of the coatings.

Keywords: Composite coating, Zinc coating, PTFE, IR spectroscopy, Raman spectroscopy
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