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CALCULATION OF SPINDLE COMPLIANCE CONSIDERINGS IT ́S INTERACTION WITH MACHINE FRAME

The calculation of spindle dynamic compliance is usually performed taking into account only the mechanical system of the spindle and tool, while the influence of the machine tool frame is neglected. However, when performing machining operations characterized by high cutting forces – which typically arise e.g. during roughing – machine frame vibration may be induced. Under such conditions, a model of the spindle alone is not sufficient to predict the dynamic behaviour of the spindle; therefore, coupled models of the spindle and machine frame system need to be created. The paper presents two possible approaches that can be used for such tasks. The first approach consists in modelling the whole mechanical system in the Finite Element (FE) environment; the second one employs the technique of coupling modally reduced separate models of flexible bodies. The application of both approaches and their comparison is illustrated by an example of a real machine tool model. The influence of the machine tool frame on the spindle dynamic compliance is demonstrated using the machine tool coupled models.

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IDENTIFICATION OF MATERIAL PARAMETRES BY FEM

The article describes an identification of material parameters from set of experiments. The experiments were made with hollow cylindrical specimens. The specimens were fabricated from the steel (11375). In this study are used the data obtained from 5 experiments (axis force, torque and their combination). Software ANSYS v.11.0 based on Finite Element Method (FEM) was used as a tool for the identification of the material parameters (inverse algorithm). There were implemented many material models in the software. The article uses Multilinear material model, rate independent and Ramberg-Osgood approximation of constitutive equations (3. material parameters) for the problem solution. The data correlations and data dispersions were used for estimating new values of material parameters. The solutions were found by FEM (for selected material model, 3. material parameters) and were compared with the experimental data.

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SOFTWARE ARCHITECTURE FOR PARALLEL SIMULATION OPTIMIZATION

Manufacturing simulation issues can be solved in a variety of different COTS (Commercial off The Shelf) simulation software – for example ARENA, QUEST, SIMUL8, Siemens PlantSimulation, etc. The input and output values can be stored in databases, but the interface has to be implemented by a developer. The output values (such as manufacturing time, average time of product waiting, etc.) from one simulation run (simulator) are not the optimized values, but only the result from a particular run. The optimized values can be found after performing more simulation experiments. The number of experiments required increases with the complexity of the model and the independent input values. There is also the need to set up new input parameters correctly with consideration of optimization gradient prediction. If the model is very simple and accuracy is not important, the input settings can be made manually. For common cases this process must be automated. A software solution for the automation of the simulation optimization process in parallel logic SIMD (Single Instruction – Multiple Data Stream) was developed using Rockwell ARENA simulation software. The simulation can be speeded up rapidly with the aid of a parallel approach. This software also supports networking and also acts as the reference for further work on methodology for the optimization method and its choice of presets.

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ANALYSIS OF DELAMINATION IN DRILLING OF COMPOSITE MATERIALS

The aim of this work is to clarify the interaction mechanisms between the drilling tool and material. Among the defects caused by drilling, delamination appears as to be of the most critical and may occurs at both the entrance and exit plane. This paper presents a prediction Hocheng-Dharan model of thrust force for drilling without delamination. HSS twist drills with different geometry were used for drilling of carbon/epoxy composites. Experiments were performed to validate physical model of delamination and investigate the effect of tool geometry and drilling paramenters on delamination. The results showed that proposed delamination model is adequate and that damage around drilling hole can be reduced significantly by proper selection of drilling conditions.

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COMPENSATION OF MACHINE TOOL THERMAL ERRORS BASED ON TRANSFER FUNCTIONS

This paper reports on a new method for compensation of machine tool thermal errors that is based on system of thermal transfer functions. Due to their relative simplicity they enable real-time calculations which make them suitable for compensation algorithms of thermal displacements at tool centre point. The applicability and robustness of the thermal transfer function compensation model have been experimentally verified on a real machine tool. Tested compensation algorithms proved its ability to significantly reduce thermal errors. The thermal error minimization of more than 85 % of the standard compensation technique based on linear regression model was achieved in particular machine tool coordinate direction.

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PREDICTION OF MACHINE TOOL SPINDLE’S DYNAMICS BASED ON A THERMO-MECHANICAL MODEL

This paper presents a thermo-mechanical model of spindles with rolling bearings. The heat generated in the bearings and the motor is transferred to the ambient air, the motor coolant and the spindle head structure. It warms the spindle up and causes thermal deformations of spindle parts. Thermal deformation affects significantly properties (internal loads, stiffness) of rolling bearings and need to be considered in predictive models of spindles’ dynamics. The structure of the transient model contains thermo-mechanical loops which update the model with respect to the instantaneous condition of the spindle. The changes of the bearings’ internal condition and stiffness are calculated using the Jones’ nonlinear theory. The thermo-mechanical spindle model predicts temperature distribution, thermal growth of spindle parts, and transient changes in bearing stiffness and contact loads under specified operating conditions. The predicted bearing properties are then used to estimate the variation of natural frequencies and dynamic stiffness of the spindle.

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OPTIMIZATION OF ENERGY BY ROBOT MOVEMENT

This paper is describing the influences of movement parameters on energy consumption during robot operation. The experimental verification of mathematical models was performed in the laboratory of the Institute of Production Machines, Systems and Robotics at Brno University of Technology. The measure results are arranged in tables and diagrams from which final evaluation for praxis follow. One of them is the outline of movement parameters setting from the side of robot users before the program is put in manufacture. Another one is recommendation for robot producers to append new items to driving system menu referring to energy consumption calculator for off-hand programming as well as energy consumption meter.

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COMBINED LOADING OF THE SPECIMENS AND REALIZED EXPERIMENT

The article describes experimental results under combined loading of specimens manufactured from common construction steel 11523. Specimens were gradually loaded by amplitude of the torque and then by combination tension prestress. For evaluation of the results the Fuxa’s criterion was applied. The performed experiments and their results embody a good agreement with bellow mentioned conjugated strength criterion. The experiments were performed on reconstructed testing machine Shenck. The reconstruction and experiment will be described in the following article.

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POSSIBILITIES OF FEM APPLIED IN THE VERIFICATION OF X-RAY MEASUREMENT

Residual stress diffraction measurements in a thin surface layer are completely nondestructive. For subsurface stress profiling, the destructive X-ray analysis can be performed by sequentially removing surface layers by using electrolytic or chemical polishing. When stressed layers are removed, the measured stress values in depths beneath the surface are in general affected by the relaxation created due to the layer removal. Therefore a correction should be involved in the depth profiling procedure. Accepted procedures used till now presume the removal of the whole surface of the investigated laboratory samples. The aim of the contribution is to present the possibilities of FEM for evaluation of the credibility of X-ray stress-strain states measurements. An estimation of changes of depth distribution due to the stress relaxation created by the removed layers was simulated by FEM in the case of a small electrolytically polished area 12 mm in diameter in the middle of cylindrical samples of the height of 7 mm.

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Machine Tool Virtual Model

Machine tool development for high speed and highly precise cutting demands employment of advanced simulation techniques, which can enable already in the machine tool design phase to model the feed drive dynamic properties and feed drive control. The paper describes the current state of feed drive complex models development in the RCMT. Influence of an appropriate approach to machine frame structure modelling on the feed drive dynamic properties prediction is discussed together with the influence of the ball screw feed drive mechanical structure parameters. Shown are examples of complex models application in the tasks of machine tool development and optimization. Vision of the machine tool virtual models development aims at the possibility to simulate the cutting process with the employment of the Hardware in the Loop systems and cutting process model.

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NUMERICAL AND EXPERIMENTAL ANALYSIS OF RESIDUAL STRESSES INDUCED BY CONTACT LOADING

The paper deals with numerical and experimental solution of residual stresses, which occurs due to a contact loading. The first solved case corresponds to frictionless contact in an indent test accepted from literature. In the finite element analysis, three material options with isotropic, kinematic and combined hardening were tested. The model of Calloch and Marquis, which was implemented into the Ansys FE program by user subroutine, shows the best correlation with experiments. The experimental results were obtained by two experimental methods, namely by the Neutron diffraction method and by the Contour method, which is not well known in the Czech Republic. Hence, this paper includes also a brief description of the new destructive method. Both methods can lead to prediction of full field residual stresses distribution. Some difficulties from application of the contour method to own experiment in rolling contact fatigue domain are also discussed.

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MACROSCOPIC RESIDUAL STRESSES IN STEELS GROUND UNDER VARIOUS CONDITIONS OF HEAT REMOVAL

Macroscopic residual stresses on the surface and their depth distributions in steels ground in various cooling environments represent the central issue of this contribution. The specimens were manufactured from three ferrous materials – carbon steel C45, low carbon Mn-Cr steel 16MnCr5 and corrosion-resistant chromium steel M300, and consequently ground with face grinding machine and corundum wheel in three regimes of heat removal: ambient air, emulsion of water and synthetic fluid for grinding operations and cooling air from Ranque –Hilsch vortex tube. Methods of X-ray diffraction (XRD) analysis were applied for evaluation of anisotropic state of triaxial residual stress. Since the XRD is sensitive to surface layers of only a few micrometers in thickness, electro-chemical etching had to be employed in order to obtain gradients of chosen components of macroscopic residual stress tensor.

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INVESTIGATION OF MACROSCOPIC RESIDUAL STRESSES DISTRIBUTION AFTER PROGRESSIVE MACHINING OF TOOL STEELS

HSC (High Speed Cutting) and EDM (Electro Discharge Machining) belong to the progressive and harsh machining operations. They differ markedly in the manner of material removal and, consequently, in the process of a final surface formation. While HSC represents the so called chip machining, EDM embodies a utilization of controlled thermal material reduction. With respect to the usage of these technologies, tool steels K110 and W300 were chosen for the experiments. Samples made from both the materials were primarily subjected to either HSC or EDM and residual stresses were investigated by means of X-ray diffraction, Barkhausen noise, hole-drilling, and layer removal methods.

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Drive Based Vibration Reduction for Production Machines

Machine vibrations constitute a persistent challenge for high performance and high precision production machines that show resonant behaviour at some frequencies. Most remedies require additional actuators or precise knowledge of the dynamic behaviour of the machines under consideration. To overcome this limitation, we present several techniques that use the feed drives to dampen vibrations or avoid excitation and are applicable with minimal pre-knowledge. Moreover, we introduce an approach to treat machines with resonant frequencies that change with the tool centre point position.

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Automatized system of measuring and regulation in turning operations

A novel approach to the simulation of the dimensional wear of cutting tools with a subsequent element of correction in limit boundaries of parametrically determined optimal shifts is presented and discussed. Described in details is, however, only one aspect belonging to the polynomial transform of experimentally found discrete values of the cutting point positions to a continuous functional form, compatible with used SW. Special attention is paid to the proposal of the simulation scheme working with the mathematical model in the simulation environment with particular values of the given simulation parameters.

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Virtual animation for checking interference of globoidal cam

This article proposes some important tasks which are necessary in the modeling procedure of globoidal cams. These tasks are modeling and virtual animation of the globoidal cam mechanism for checking interference between components of the system. The acceptable cam is the one that has no interference between the cam and its rollers assuming that the clearance between cam surfaces and roller is zero or very small. Techniques of animation and checking interference of globoidal cam mechanism are performed in Pro/ENGINEER Wildfire 2.0.

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Comparison of Performance of Austrian made Si₃N₄ – Nitride Ceramic Tools Used to Machine Grey Cast Iron Work-piece Materials

This article presents comparisons of cutting performance of Austrian made – Si3N4 nitride ceramic – inserts used in machining a Type 422425 grey cast iron work-piece materials. Three commercial ceramic inserts Type FMG121C, FMG122C, and FMG134C were tested. Experiments were focused on tool life tests. A comparison approach involved exponents of Taylor’s type equations over an optimized cutting tool interval i.e. one constant depth of cut of 1mm, one constant feed rate of 0.2 mm/rev and the three cutting speeds 250, 320 and 380 m/min. Results were obtained from linear regression. Also conducted was an evaluation of intervals of reliability as well as corresponding standard deviations for each regression coefficient in experimental Taylor’s equations. The experiments allowed to compare, from statistical perspectives, at a 95 and greater confidence level, the trends and quantities of experimental cutting inserts. The results showed that a Type FMG122C ceramic insert had the most superior performance compared to other two types of experimental ceramic inserts investigated in this study.

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Potential of state-feedback control for machine tools drives

This paper describes basic principle of the state feedback control technique and its potential for the feed drive control in the machine tool domain. It evaluates the quality of the state control and compares it with the traditional cascade control. The emphasis is put on an estimation of the state variables using an FEM model of the feed drive mechanical structure and machine frame.

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Computer modelling of suction cups used for window cleaning robot and automatic handling of glass sheets

Optimizing vacuum grippers of robots for glass sheets handling and developing robots for glass cleaning, it is necessary to solve a number of problems calling for a similar approach to a solution. This paper analyzes deformation behaviour of vacuum gripping elements of vacuum grippers. The extent of deformation safety of an individual suction cup is monitored depending on the vacuum level and loading character. A computer model was suggested and filtered out allowing contact area changes to be observed depending on a friction model and vacuum level.

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Contribution to the production flexibility solution

Production (manufacturing) flexibility is one of the dominant requirements of the present engineering industry. Automated assembly systems have a special position because of their technical and technological complexity. At the present the problem of determination of existing or planned assembly systems flexibility is elaborating at the many research workplaces. The attention is focused on to elaborating of the base methodical steps for determination of a relative similarity of objects group (assembly parts and assembly grippers) with suitable statistical methods utilisation. The dichotomous parameters were defined for the objects similarity valuation.

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Effects of microstructure and chemical composition on strength and impact toughness of tin bronzes

The present study is concerned with examining metallurgical features and their significance on strength and impact toughness of tin bronzes, with particular reference to bells. It has embraced a number of interrelated aspects – alloy types – composition, constitution and properties, fabrication technology, service life and effects of environmental/working conditions on strength and impact toughness of bell materials from Gothic, Modern and Recent Eras. The results are discussed in terms of qualitative assessment of microstructural features of these different cast tin bronzes examined in destructive tests.

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Energy Consumption Forecasting and Optimisation for Tool Machines

Soaring energy prices, signs of a human-made climate change and legislative pressure have brought the energy consumption of machines to the attention of machine tool builders and their customers. To enable manufacturers and operators of machines to include energy consumption into their considerations in an objective way, we introduce an efficient method to model the energy consumption behaviour of machines. Based on that, we present methods to forecast the actual power drain profile and to optimise machines for minimal energy consumption under any given application scenario.

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Machine tool with undisturbed frame

One of the main disturbances of the machine tool frame is caused by operation of motion axis. Movement of high dynamic motion axis is connected with powerful force strokes that excite machine tool frame vibration and deteriorate machining surface quality and productivity. There are several possibilities how to suppress this vibration. One possibility is to use suspended motor, where the motor is connected with the machine body by spring and damper. This paper deals with new more advanced conception where the main motor is connected with the frame by an active element, that is controlled by intelligent control technique. The active element represents another linear motor, therefore the conception is shortly called “motor on motor”.

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Automatic On-Machine Measurement of Complex Parts

Milling spindles with inserted 3D tensometric touch probes were applied for on-machine measurement of highly precise parts produced on three - and five-axis milling machines equipped with linear motors and direct rotary drives. New methods of CNC control of angular NC axes during measurement were developed for parts containing hardly accessible surfaces. In-process calibration of multi-directional accuracy of probes has resulted in submicron sensitivity and highest absolute accuracy of on-machine measurements.

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Thermomechanical transfer functions and control of a machine tool cooling system

Nowadays the cooling systems are more than ever applied into the structure of a machine tool, but unfortunately there are no efforts being made in the control of the cooling systems, which doesn’t allow complete utilisation of their possibilities. This paper presents active cooling control (ACC) system, based on thermal transfer functions, which was experimentally tested on an inbuilt cooling jacket of a machine tool electrospindle.

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Criterion C –Based evaluation of the topography of abrasive waterjet – produced surfaces

In the contribution we present the utilization of criterion C for the evaluation of topography of metallic materials surfaces generated by the abrasive waterjet. The criterion C provides a realistic picture of the proportion of waviness (low-frequency irregularities) to the total number of surface irregularities. The critical value of parameter Cc = 0.66 was determined experimentally for metallic materials. This value differentiates the surface into two morphologically different zones. The first zone, which is there in the upper part of the cut, is characterised by the absence of conspicuous striations, and thus is considered to be of good quality. The other zone is characterised by conspicuous striations and thus is taken as a zone of poor-quality. The parameter C can also be used in the classification of materials by machinability.

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Qualitative consequences in finishing process of holes grinding into ceramics with the high power ultrasound application

The paper deals with qualitative changes of machining of holes in ceramic materials applying by finishing conventional grinding and high power grinding. Measured and determined values of surface roughness of machining material definitely indicated the advantages of high power ultrasound application. Ultrasound grinding is the technological method of grinding useful for hard machinable materials.

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Technical products and their attributes – theory and practical applications
This paper has been presented at workshop applied engineering design science AEDS 2008 held in Pilsen

Any technical product – technical system (TS) and its life cycle processes need to meet many requirements. These are not only requirements concerning the TS operation functions, their parameters and connection interfaces, but also high product safety and health protection, good appearance, easy manufacture, transport, maintenance and liquidation, low price, short delivery time, and many others. The paper introduces a system approach based on the “Map” of Engineering Design Science knowledge [Hubka&Eder 1988, Hubka&Eder 1996, Andreasen 2000, Eder&Hosnedl 2008, and many others] the aim of which is to achieve a higher transparency and user friendliness of the outlined and bounded engineering design areas, and shows practical applications, which have quite successfully validated the proposed improvements.

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

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®.

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Machine Tool Lightweight Design and Advanced Control Techniques

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.

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Economy of Titanium Milling

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.

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Operational behaviour of high speed spindle unit

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.

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Variation of Eigenvalues of a HPC Motor Spindle due to Changing Axial Depth of Cut

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.

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Modelling the orthogonal machining process using cutting tools with different geometry

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.

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Cognitive and systematic design

Following a lively discussion at the AEDS-SIG Workshop 2005, I had the pleasure of reading the doctoral thesis by Kalevi Nevala [2005a]. The following is a summary and interpretation of comments I made to Dr. Nevala. In discussions or considerations of design engineering problems and engineering designers, different words are often used. Designing is a process of transforming information about a future technical process and/or technical system, performed by iterative interacting between external representations and mental models. My comments are based on the pioneering work of Vladimir Hubka [1974, 1976, 1978, 1982, 1984, 1988a, 1988b, 1992 and 1996] with additions [Eder 1992, 1996 and 2008].

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Numerical and analytical modelling of a pallet used at a machining centre at high speed

A workpiece manipulation assembly includes two main parts. 1. A base permanently connected to a spindle. 2. A pallet manipulated by a rotary manipulation table from working place to setting place & vice versa. This assembly is rotating around the spindle axis. The FEM analysis and analytical analysis of the workpiece exchange manipulation system of vertical turning centre, deals with stress and deformation of an assembly that is composed by the base, the palette and the other parts, at high revolution load. As requirements of customers increase – revolutions of the workpieces increase. This leads to increase the load of parts.

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Problem of metamorphic structures in service robotics

Recent trends in the development of robots confirm that the concept of metamorphic – self-regulating structures has found its recent form in theoretical as well as practical robotics. This development direction is topical also for service robotics where the effects of this concept can be used more intensively in the benefit of utility features of service robots. The paper shows theoretical and design approaches to the solution of metamorphic service robots. It gives selected specific questions and problems connected with its design and construction. It submits the studies and designs of service robots solved on the principle of metamorphic – self-regulating structures.

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Exploring Efficiency of Tool Coating via Deep Drawing of Cylindrical Cups

The present investigation was set up to examine both predicted and experimental values of forces, power, press work and friction in drawing cups from low carbon steel blanks using the same die set but in different uncoated and TiN coated conditions. The results showed a good agreement between predicted and experimental values. In addition, the findings demonstrated that the TiN coated tools reduced the friction at a tool – blank – die – interface (by about 5%), which in turn reduced the forces, power and work (by about 7%) and improved the final product quality, when compared to the performance of uncoated tools.

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System methodology of risk assessment in machine tools

The contribution deals with the problem of safety assurance in machinery in accordance with the requirements of the Directive 2006/42/EC of the European parliament and of the Council of 17 May 2006 on machinery, and amending Directive 95/16/EC (recast), replacing the Directive 98/37/ES. The existing methods suitable for identification of hazards associated with machinery are reviewed. A new method of risk assessment in machine tools is presented, applying the system approach to hazard identification and to analysis and evaluation of risks associated with machinery, in accordance with the relevant Czech and EU legislation. Further, the contribution discusses a suitable way of documenting the risk assessment process.

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A study of computer assisted analysis of effects of drill point geomerical features on forces and power in dribling with general purpose twisk drills

This paper presents results of a systematic – computer assisted – study focused on determining, and describing, from a mathematical point of view, the relationship between the drill point geometrical features and predicted performance measures as assessed by the cutting forces (thrust and torque) and cutting power when drilling a Type Bisalloy 360 steel work-piece material with general purpose twist (GPT) drills. The current study presents an innovative predictive strategy for eliminating the need of experimental testing when comparing drilling performance of GPT drills. It employs an advanced computer assisted model to analyse the rake angle distributions along the drill lips and the chisel edge regions when changing the six main individual drill point geometrical features (D, 2W, δO, ψ, ClO, and 2P) in the software input and looking at their effects on the generation of thrust, torque and power in drilling. It is expected that this sort of information may be used to assist in optimisation of the cutting performance of drills via advances through the modification of drill point geometrical features.

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