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New Paradigm in Control of Machining Systems Dynamics

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

Journal of Machine Engineering

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2015

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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.

2

Improving machining performance against regenerative tool chatter through adaptive normal pressure at the tool clamping interface

Fu Q., Rashid A., Nicolescu C. M.

Journal of Machine Engineering

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2013

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Vol. 13, No. 1

93--105

EN

Chatter in machining process is one of the common failures of a production line. For a cantilever tool, such as a boring bar, the rule of thumb requires the overhang length of the tool to be less than 4 times the diameter. The reason is because longer overhang will induce severe tool vibration in the form of chatter during machining. When a longer overhang than 4 times diameter is necessary for performing special machining operations, damping methods are needed to suppress tool chatter. One of the methods is the constrained layer damping method. Materials, such viscoelastic material, are applied in the vibration node regions of the structure to absorb the concentrated vibration strain energy and transform the mechanical energy to heat. With a cantilever tool clamped in a tool holder, the clamping interface is usually the vibration node region. The friction in the joint interface with low normal pressure became another source of damping and can be used for tool chatter suppression in mechanical structures. Joint interfaces are well known to possess normal pressure dependent stiffness and damping. The normal pressure's effect on the structures frequency response function had been observed by H. Akesson [1] et al, and L.Mi [2] et al. However, the direct effect of the joint interface normal pressure on machining process stability hasn't been investigated. In this paper, a cantilever tool with 6,5 overhang length to diameter ratio is investigated. The direct effect of the tool clamping interface's normal pressure on the machining process stability is studied. Three different levels of clamping normal pressure are tested with an internal turning process. The machining results indicate another adaptable solution on shop floor for suppressing tool chatter.

3

Experimental analysis of a machining system with adaptive dynamic stiffness

Frangoudis C., Nicolescu C. M., Rashid A.

Journal of Machine Engineering

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2013

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Vol. 13, No. 1

49--63

EN

A main consideration in the operation of machine tools is vibrations occurring during the cutting process. Whether they are forced vibrations or self-excited ones, they have pronounced effects on surface quality, tool life and material removal rate. This work is an experimental study of interactions between natural characteristics, control parameters and process parameters of a machining system designed with adaptive dynamic stiffness. In order to comprehend these interactions, the effect of changes in dynamic stiffness on the system's response is examined. The system under study consists of an end-milling tool, a steel workpiece and a work holding device with controllable stiffness. Natural dynamic characteristics of the system components are determined through modal impact testing. Then the behaviour of the whole machining system is examined under both high and low cutting speed conditions by analysing vibration levels using acceleration signals acquired through a tri-axial sensor mounted on the workpiece. Cutting is performed in both directions of the horizontal plane of a CNC milling machine. In both cases the results are presented for two extremes of stiffness and damping in the work holding device. The effect of control parameters on the system's natural characteristics could be identified together with a relation between these parameters and the system's response in high and low cutting speed conditions. The high-damping configuration reduces the vibration amplitudes significantly, while the increase of pre-stress has a different effect depending on the cutting conditions.

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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.

5

Influence of organisational culture on company performance

Yusuff R. M., Busu A., Rashid A., Zulkifli N.

Journal of Achievements in Materials and Manufacturing Engineering

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2008

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Vol. 31, nr 2

837-845

EN

Purpose: The lack of organizational effort to assess cultural compatibility or fit prior to the engagement of firms has contributed to the failure of several mergers and acquisition. A Korean public listed company with manufacturing plants in Malaysia and New Zealand found that the performances of the newly acquired plants were significantly lower than the manufacturing plants in Korea. Design/methodology/approach: In this study, the influence of national culture on organizational culture and the effect on the organizational performance was conducted on 6 manufacturing plants in Korea (2), Malaysia (3) and New Zealand (1). Hofstede's culture dimensions were used to determine culture diversity between the manufacturing plants. Findings: The values survey module was used to calculate the index scores on five dimensions of national value system as components of national cultures: power distance, Individualism, Masculinity, Uncertainty avoidance and Long term orientation. Practical implications: The model of culture fit assesses the dimensions of socio-cultural environment, internal work culture and HRM practices. The resulting multiple regression analysis showed that there are cultural diversities between the manufacturing plants and national culture does influence organizational performance. Originality/value: The results also showed that a dimension of internal work culture does influence organizational performance.