Wyniki wyszukiwania - Biblioteka Nauki

1

Dynamic parameter identification in nonlinear machining systems

100%

Nicolescu M. , Archenti A.

Journal of Machine Engineering

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2013

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tom Vol. 13, No. 3

91--116

EN

The demand for enhanced performance of production systems in terms of quality, cost and reliability is ever increasing while, at the same time, there is a demand for shorter design cycles, longer operating life, minimisation of inspection and maintenance needs. Experimental testing and system identification in operational conditions still represent an important technique for monitoring, control and optimization. The term identification refers in the present paper to the extraction of information from experimental data and is used to estimate operational dynamic parameters for machining systems. Such an approach opens up the possibility of monitoring the dynamics of machining systems during operational conditions, and can also be used for control and/or predictive purposes The machining system is considered nonlinear and excited by random loads. Parametric and nonparametric techniques are developed for the identification of the nonlinear machining system and their application is demonstrated both by numerical simulations and in actual machining operations. Discrimination between forced and self-excited vibrations is also presented. The ability of the developed methods to estimate operational dynamic parameters ODPs is presented in practical machining operations.

2

Identification and Analysis of Linked SystemsDynamic Accuracy Proposal of a Measurement Approach and Instrumentation

100%

Dapero A. , Archenti A.

Journal of Machine Engineering

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2015

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tom Vol. 15, No. 3

90--105

EN

In this paper a measurement approach and instrumentation for capturing the dynamic stiffness of a linked system is proposed. The approach is based on the loaded double ball bar (LDBB) in combination with an integral dynamic shaker. The innovation is the introduction of a dynamic load besides the static one given by the LDBB and consequently able to extract the frequency response functions, taking advantage of the possibility of orienting the LDBB in different directions of the machine tool. The dynamic behaviour is studied through experimental modal analysis. The test conditions are therefore more similar to a cutting situation in which both a static and a dynamic component of force characterise the system. However, it must be underlined that the introduced dynamic force does not replicate the one arising in a cutting operation, but it is chosen instead for its spectrum characteristics, i.e. the energy introduced must equally cover a given range of frequencies. The test method is able to reveal machine tool characteristics not obtainable with existing methods, for instance the variation of dynamic stiffness in the working space. The paper will include some theoretical aspects on the approach as well as some experimental investigation.

3

Hybrid machining: abrasive waterjet technologies used in combination with conventional metal cutting

80%

Wanner B. , Archenti A. , Nicolescu C. M.

Journal of Machine Engineering

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2017

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tom Vol. 17, No. 3

85--96

EN

Abrasive Waterjet technology is one of the fastest growing metal cutting technologies. Even so, very little published material is available on hybrid processing where abrasive waterjet cutting is one of two or more metal cutting methods. There is also limited published material on thin-walled components cut with abrasive waterjet technology. This paper makes a comparison of conventional metal cutting methods to the more unconventional abrasive waterjet technique. It will serve as a stepping stone in building knowledge aiding in hybrid machining development. It will show the possibilities and limitations during milling of thin-walled Aluminum components and then compare this to the capabilities of abrasive waterjet cutting the same components. Differences in material removal and revert control as well as in vibrations and force requirements will be reviewed. In addition, the environmental issues will be discussed and it will be determined which of the methods is more sustainable. The paper also includes a large section on process methodology.

4

Evaluation and representation of machine tool deformations

80%

Archenti A. , Osterlind T. , Nicolescu C. M.

Journal of Machine Engineering

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2011

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tom Vol. 11, No. 4

105--117

EN

This paper presents a novel test concept for the evaluation of the accuracy of NC machine tools. The evaluation of machine tools deformations is performed by help of a device similar to the double ball bar (DBB) with the difference that an adjustable load generated by the devic can be applied between spindle nose and machine tool table. This load eliminates the play existing in machine tool joints, thus reproducing the testing conditions that exist during machining. Collected data are used to plot diagrams displaying characteristic aspects of machine tool performance and a number of key figures such as static stiffness may be determined. The data can also be used for trend analysis; to predict any accuracy deviations, and further to conduct preventive maintenance instead of emergency calls. The determined static behaviour could also be used to improve digital models for process simulations and compensation of errors that are caused by deflection.

5

Operational modal analysis during milling of workpiece, fixed on a stiffness controllable joint

80%

Osterlind T. , Frangoudis C. , Archenti A.

Journal of Machine Engineering

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2013

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tom Vol. 13, No. 2

69--78

EN

Vibration in metal cutting processes has been studied to a great extent resulting in for instance stability lobe diagrams under which stable machining parameters can be selected. One limitation of accurately estimated stability diagrams is the change in process and dynamic characteristics of the machine tool under operation. The machine tool dynamic response is often analysed with experimental modal analysis under off operational conditions. One drawback with this approach is the large number of measurements required to fully describe a machine tool and workpiece in different positions and time of machining. Another drawback is that the change of dynamiccharacteristics under operation is excluded. Operational modal analysis has been applied in machining under different conditions resulting in successfully improved stability lobe prediction. This research includes operational modal analysis of the workpiece, fixed on a stiffness controllable joint and stability prediction to stress the importance of various machining conditions.

6

Machine tool ability representation: a review

80%

Sadasivam L. , Archenti A. , Sandberg U.

Journal of Machine Engineering

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2018

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tom Vol. 18, No. 2

5--16

EN

Smart manufacturing and predictive maintenance are current trends in the manufacturing industry. However, the holistic understanding of the machine tool health condition in terms of accuracy, functions, process and availability is still unclear. This uncertainty renders the development of models and the data acquisition related to machine tool health condition ineffective. This paper proposes the term machine tool ability as an interconnection between the accuracy, functions, the process and the availability to overcome the lack of the holistic understanding of the machine tool. This will facilitate the further development of qualitative or quantitative methods as well as models. The research highlights the challenges and gaps to understand the machine tool ability.

7

Extending stability limits by designed-in damping

80%

Daghini L. , Archenti A. , Osterlind T.

Journal of Machine Engineering

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2013

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tom Vol. 13, No. 1

37--48

EN

With advances in material technology come challenges to productivity. New materials are, in fact, more difficult to machine with regards to tool wear and especially machine tool stability. This paper proposes to extend the stability limits of the machining system by enhancing the structures damping capability. The aim of the research work presented here is to introduce a unified concept based on the distribution of damping within the machining system components exploiting the dynamic properties of the existing joints. To maintain a high level of static stiffness, it was chosen to adapt hydrostatic clamping systems to the tools. Damping is designed in the structure via high damping interfaces (HDI), intentionally introduced interfaces where the damping ratio is enhanced by introduction of viscoelastic polymer metal composites between the two metallic surfaces composing the interface. In this paper HDI are introduced at two joints, between tool and turret and between turret and lathe. The tests show that the designed-in damping is effective and allows extending the stability limits of the machining system. The implementation of designed-in damping allows the end user to select the most suitable parameters in terms of productivity avoiding the hassle of tuning the devices, having to acquire a deep knowledge in structural dynamics or having to use additional control systems. In addition to this, the enhanced machine tool system becomes less sensitive to stability issues provoked by difficult-to-machine materials or even fluctuations of the work material properties that might occur in everyday production processes.

8

Performance Evaluation of Machining Strategy for Engine-Block Manufacturing

80%

Tigist A. F. , Bianchi M. F. , Archenti A. , Nicolescu M.

Journal of Machine Engineering

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2015

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tom Vol. 15, No. 4

81--102

EN

This paper will introduce a novel methodology for the performance evaluation of machining strategies of engine-block manufacturing. The manufacturing of engine components is vital to the automotive and vehicle manufacturing industries. Machining are a critical processes in the production of these parts. To survive and excel in the competitive manufacturing environment, companies need to improve as well as update their machining processes and evaluate the performance of their machining lines. Moreover, the lines and processes have to be robust in handling different sources of variation over time that include such examples as demand fluctuations, work-piece materials or even any changes in design specifications. A system dynamics modelling and simulation approach has been deployed to develop a methodology that captures how machining system parameters from the machining process are interacted with each other, how these connections drive performance and how new targets affect process and machine tool parameters through time. The developed model could provide an insight of how to select the crucial machining system parameters and to identify the effect of those parameters on the output of the system. In response to such an analysis, this paper provides (offers) a framework to examine machining strategies and has presented model that is useful as a decision support system for the evaluation and selection of machining strategies. Here a system dynamics methodology for modelling is applied to the milling operation and the model is based on an actual case study from the engine-block manufacturing industry.

9

Active alignment chuck for ultra-precision machining

80%

Daghini L. , Archenti A. , Rashid A. , Nicolescu C. M.

Journal of Machine Engineering

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2011

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tom Vol. 11, No. 4

39--48

EN

Ultraprecision (UP) components have become common in everyday life products such as mobile phones or compact high resolution digital cameras. Thus the need of producing such components with high accuracy and low production cost. UP machine tools are capable of extremely high accuracy in tool positioning but still today the workpiece is positioned by hand, hence the high production cost of UP components. A fully automated chain of production has been developed within the EU-IP project "Production 4 micro". This paper describes the active alignment chuck for workholding in UP machining. The chuck has been provided with a high damping interface (HDI) and to evaluate its efficiency the chuck has undergone an experimenta modal analysis (EMA) as well as machining tests. The chosen operation was grooving by fly cutting using a diamond tool. The EMA showed that the HDI was effective for those modes where there was relative displacement between one side and the other of the HDI. This result was confirmed by the machining tests as well. The HDI resulted being effective in damping high frequency modes (around 4 - 5 kHz), hence one expected benefit would be a longer tool life.

10

Design and dynamic characterization of composite material dampers for parting-off tools

80%

Daghini L. , Archenti A. , Nicolescu C. M.

Journal of Machine Engineering

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2010

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tom Vol. 10, No. 2

57--70

EN

This paper introduces a novel design for parting-off tools and the method to characterize their performance. The principle followed in the design phase was to enhance the damping capability minimizing the loss in static stiffness through implementation of composite material interfaces. The tool has been characterized by the dynamic characteristics criterion, i.e. frequency and damping ratio, of the machining system, as well as the roughness of the machined surface criterion. This paper demonstrates a new model-based method for characterizing the machining system dynamic properties, applied, in this sThe presented mathematical model of the machining system is based on the data recorded by a microphone during operational conditions. In this way, a step beyond the classical method of analyzing the dynamics of a machining system, which separately identifies the structural and process parameters is taken. The analyses together with the experimental results proved that the parting-off tool was able to machine over a wide range of cutting parameters. It was found that the limiting factor for increasing cutting parameters is not the damping capability of the tool but the tool clamping system stiffness and the workholding system dynamic properties. This implies that, in order to further optimize the machining performance, it is vital to take consideration not only the tool-clamp-turret system but the whole machining system.

11

New Paradigm in Control of Machining Systems Dynamics

70%

Nicolescu M. , Frangoudis C. , Semere D. , Archenti A. , Rashid A.

Journal of Machine Engineering

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2015

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tom Vol. 15, No. 3

117--137

EN

The increasing demands for precision and efficiency in machining call for effective control strategies based on the identification of static and dynamic characteristics under operational conditions. The capability of a machining system is significantly determined by its static and dynamic stiffness. The aim of this paper is to introduce novel concepts and methods regarding identification and control of a machining system’s dynamics. After discussing the limitations in current methods and technologies of machining systems’ identification and control, the paper introduces a new paradigm for controlling the machining system dynamics based on design of controllable structural Joint Interface Modules, JIMs, whose interface characteristics can be tuned using embedded actuators. Results from the laboratory and industrial implementation demonstrate the effectiveness of the control strategy with a high degree of repeatability.