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- Al-Najjar, Basim
(author)
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Condition-Based Maintenance: Selection and Improvement of a Cost-Effective Vibration-Based Maintenance Policy for Rolling element Bearings
- 1997
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Doctoral thesis (other academic/artistic)abstract
- Modern machinery is expensive and therefore must run at high availability and effectiveness which cannot be achieved without an effective maintenance policy. Condition monitoring, (CM), techniques can be utilised to reduce or arrest the rate of deterioration of a component so increasing operating life. The main result reported in this thesis is that the rolling element bearing’s mean effective life could be extended appreciably if an existing vibration-based maintenance policy is used effectively. This result is achieved by a combination of data analysis and logical development. A new maintenance approach was developed to overcome some of the limitations of total productive maintenance, TPM, and reliability-centered maintenance, RCM, and is based upon the Deming managerial feedback cycle (Plan-Do-Check-Act). This method is called Total Quality Maintenance, (TQMain). It is a methodology to sustain and improve continuously the technical and economic effectiveness of the manufacturing process elements. It is shown logically that by using vibration-based monitoring, (VBM), program in the frame of a common database for a plant IT-system the causes behind quality deviations and failures can be identified and eliminated effectively at an early stage and the company’s economics would be improved. The condition-based maintenance effectiveness and accuracy are usually related to the ability of the CM system to detect failure causes and follow defect development. Criteria to select the most cost-effective VBM system and the most cost-effective vibration-based maintenance policy are developed. But, in most real cases, CM systems are not utilised effectively and companies are satisfied with the partial savings achieved in maintenance cost. It is shown, by two case studies, that improvements in vibration-based maintenance can be achieved by effective feedback of the results of failures, renewal condition and VBM history analysis. Unfortunately the data coverage and quality in these studies were not sufficient, among other reasons due to the low number of failures and long bearing lives, so the conclusions, although supported by the work results, remain strong qualitative indications, rather than statistical proof. Criteria to measure the effect of improvements to confirm whether it is economically beneficial and to identify the basic reasons why it is not, are developed. The contribution of this thesis is: The development of a sequential method for the selection and improvement of a cost-effective vibration-based maintenance policy. This methodology can be used to justify, on economic criteria, the use of VBM systems to indicate when rolling element bearings should be renewed. It is achieved through; Tools used in quality and maintenance technology and reliability analysis have either been modified or developed beyond their original concept such as; Maintenance cost equation, Total Time On Test-plots. Development of new tools to monitor maintenance effectiveness and accuracy, select the most informative CM parameter(s) and cost-effective vibration-based maintenance policy. A new maintenance approach, (TQMain), and a new envelope alarming method for VBM programs are also developed. Theoretical basis for improvements to the effectiveness of vibration-based maintenance of bearings in paper mill machines and two case studies which tend to confirm the theory.
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| 2. |
- Nilsson, Carl-Henric
(author)
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On Strategy and Manufacturing Flexibility
- 1995
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Doctoral thesis (other academic/artistic)abstract
- The era when customers bought what companies produced is long gone. The situation is now reversed and companies must produce what customers want; while the customers' preferences are, furthermore, becoming increasingly diverse. This has forced companies to adopt a new mode of thinking in order to survive. The strategy, by necessity, has become to manufacture flexibly. This thesis focuses on strategy and manufacturing flexibility. It includes a frame of reference and eight papers appended in full, reporting findings in four broad areas: • Manufacturing flexibility, • Manufacturing strategy, • Strategic flexibility, • Strategic manufacturing flexibility. The overall purpose of this study is to conceptualise the strategic role of manufacturing flexibility in the continuous realignment between the organisation and its environment. The guiding principle of the methodology applied in this thesis is to use the most appropriate paradigm and methodology given the individual problem at hand. The results of the studies in manufacturing flexibility are used firstly to provide elucidation of the understanding of managers' perceptions of manufacturing flexibility. Secondly, a framework for manufacturing flexibility is deduced which illustrates how to obtain consistency from manufacturing strategy to the resource characteristics in the production system. Thirdly, a method for the evaluation of flexibility in manufacturing, the capital-back method, is developed and analysed. The results of the study in manufacturing strategy are presented as a case, indicating how flexibility of the manufacturing function can be utilised in order to gain competitive advantage in an uncertain and dynamic market. A combination methodology, using both a top-down, grand strategy approach and a bottom-up, grounded methodology is developed and used in the study, and is shown to provide a sound basis for understanding external as well as internal factors impinging upon the company. Furthermore, Porter's (1980) taxonomy of generic strategies is scrutinised and the difficulties of classifying the strategy of a real company into one, and only one, of the deduced taxa are illustrated. Strategic flexibility is a broad area of research. Consequently, the study of this area embraces only a minor part of the field, namely a meta-analysis of the literature on strategic alliances. The analysis confirms, among other things, that the literature is overoptimistic towards strategic alliances. Finally, regarding strategic manufacturing flexibility, a suggestion for research is presented which involves the synchronisation of three continuous processes within the company, concerning manufacturing flexibility, manufacturing strategy and strategic flexibility. Three major suggestions concerning research in the field of strategic manufacturing flexibility are presented. Firstly, an integrative perspective on the competitive priorities - cost, quality, flexibility and dependability - is advocated due to synergistic effects. Secondly, since the concept appears to transcend disciplinary boundaries, a multi-disciplinary perspective is also advocated. Thirdly, due to the multi-dimensionality of the concept of strategy as well as flexibility, a multi-methodological approach appears to be advantageous in the pursuit of research within this field.
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