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Extending stability limits by designed-in damping

Daghini L., Archenti A., Osterlind T.

Journal of Machine Engineering

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2013

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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.

2

Active alignment chuck for ultra-precision machining

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

Journal of Machine Engineering

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2011

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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.

3

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

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

Journal of Machine Engineering

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2010

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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.