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5 Tech., L. & Ins. 1 (2000)

handle is hein.journals/tnlylwad5 and id is 1 raw text is: FN' Spo Technology, Law and Insurance, 2000 5, 1-7 Ageing analysis of manufacturing equipment: a case study M. BRAGLIAl*, R. GABBRIELLI2 and D. MICONI2 'Dipartimento di Ingegneria Meccanica, Nucleare e della Produzione, FacoltA di Ingegneria, UniversitA degli Studi di Pisa, Via Bonanno Pisano 25/B, 56126 Pisa, Italy 2Dipartimento di Energetica, Facolt& di Ingegneria, University degli Studi di Pisa, Via Diotisalvi 2, 56126 Pisa, Italy Received 10 September 1999 Ageing analysis is applied in an important company which is an industry leader in the production of roller bearings. A modern CNC vertical lathe is analysed to confirm whether preventive maintenance is needed in order to improve the system availability. The rate of occurrence of failure (ROCOF) model is estimated, after a pre-analysis aimed at identifying an infant mortality period. A general approach to equipment ageing analysis is proposed. This methodology is based on several plotting analyses and statistical tests used to confirm whether a preventive maintenance programme should be implemented. Keywords: reliability, maintenance, ageing analysis, manufacturing system, ROCOF Introduction It is often the case that companies consider equipment breakdowns to be inevitable and tackle these situations with corrective maintenance op- erations. In the current global request for quality, cost reductions and safety, a decrease in main- tenance costs (costs of repair, equipment down- time, idle labour, loss of production, schedule delay, customer dissatisfaction, etc.) plays a critical role (O'Connor, 1991; Dillon, 1985). The primary operational choice is whether to repair equipment before its malfunction (preventive maintenance) or wait and then repair it after its failure (corrective maintenance). Preventive maintenance is per- formed prior to breakdown, and the extent of the intervention could range from a minor operation to a complete overhaul or replacement (Tersine, 1985). The decision as to whether to implement a preventive maintenance programme is faced by one of the world leaders in the production of roller bearings (20% world market share). In the Italian production plant under examination, a new ad- vanced CNC vertical lathe is considered a critical resource because every machine stoppage causes an overall decrease in productivity of 50%. The *Author for correspondence. management of this firm estimates that the failures result in a profit loss of L32 m (about US$17 700) per year. This value assumes that (i) the most important product is being processed, (ii) the production rate equals 80 items per hour, and (iii) the sale price for the item is L15 000 each (about US$8.3). Moreover, the CNC machine works 20 hours a day, 7 days a week and 50 weeks a year. It is integrated with the firm's CAD-CAM system, which was introduced to reduce time to market. For this reason a high reliability of the CNC work- centre is required: it should 'never stop'. To achieve this situation, the shop-floor equip- ment is supervised and monitored by a software system (the API PRO System produced by Frontec, Denmark) which makes possible integrated main- tenance management. In particular, with this soft- ware it has been possible to collect the failure data (time of failure, type of failure, time to repair, etc.) of the lathe. Using these data, a complete failure mode effect and criticality analysis (FMECA) of the CNC centre has been performed recently. Now, the management is interested in a statistical data analysis to evaluate the possible advantages deriv- ing from a preventive/renewal maintenance policy. In other words, the company would like to know if the facility availability can be improved by inte- grating a significant new preventive maintenance Technology, Law and Insurance ISSN 1359-9372 print ISSN 1468-4500 online © 2000 Taylor & Francis Ltd www.tandf.co.uk/journals

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