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On use of acoustic emission in monitoring of under and over abrasion during a water jet milling process

Mikler J.

Journal of Machine Engineering

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2014

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Vol. 14, No. 2

104--115

EN

Water jet milling process is a new emerging technology with many interesting applications. Low cutting forces, no thermal distortion, process flexibility and ability to machine difficult to cut materials make it very attractive for many technological operations. However, its wider application is hindered by lack of proper solutions of process monitoring that would allow accurate control of the material removal process. The research contributions so far focused on use of acoustic emission, thus the purpose of this paper is an evaluation of the proposed strategies and analysis of applicability of acoustic emission for this purpose. An extensive amount of AE data was collected during waterjet machining with various feed rates, abrasive flows, and pump pressures, and analyzed with the aim to determine whether there exists any feature of the AE signal correlated with under- and over abrasion. Monitoring and control of removal rate is possible only if it is possible to discriminate between AE signal samples originating from different states of the abrasive process. In this paper I present results based on extensive one-way ANOVA study of the AE samples, showing, that the standard AE signal features proposed in the literature the energy and statistics of the AE signal do not allow such discrimination, and are not suitable to monitor abnormalities of the abrasive process. The research covers also principle component analysis of the AE signal energy performed in the aim to study if there exists any subset of the energy allowing better discrimination between the investigated process states.

2

On a systematic approach to development of maintenance plans for production equipment

Mikler J., Frangoudis C., Lindberg B.

Journal of Machine Engineering

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2011

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Vol. 11, No. 1-2

87--101

EN

Reliability is a collective term covering several abilities of the technical system: to deliver required functions, to uphold quality of products and services, to assure that the safety requirements associated with the system are properly fulfilled with regards both to the users and the environment and finally to uphold the durability of the technical system during its whole life cycle. All this has to be performed at acceptable risks, optimal cost, and correspond to operational needs of the business. Even though there is an advanced, well thought-out concept for this purpose - reliability centred maintenance (RCM) - that correctly applied might result in very good quality maintenance programs, it is not broadly used in the industry due to the vast efforts required for its implementation. An appropriate methodology supporting systematic functional break down of a studied systems, and guidelines how to couple functional failures to failure modes, integrated with RCM, would greatly speed up generating of effective maintenance programs. In this paper we present our research towards development of such a methodology, and show a pilot implementation to analysis of machine tool spindle. The methodology is based on Hubka's theory of design and AFD/TRIZ.

3

Life cycle costing used for justifying transition to predictive maintenance strategies

Mikler J.

Journal of Machine Engineering

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2011

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Vol. 11, No. 4

49--58

EN

As the market imposes constantly increasing levels of reliability and availability of production equipment, it is necessary to shift the focus of maintenance toward predictive strategies. However, as any other investment, implementation of the required condition monitoring systems has to be cost justified. This paper presents a case study showing use of LCC calculations to assess changes of maintenance strategy for a CNC machining centre. It was proven that replacing reactive maintenance tasks with simple condition monitoring and preventive activities results in lower whole life cycle cost of the analysed machining centre.