Modeling of Maintenance Operations

Introduction

Complex equipment and machinery systems used in the production of goods and delivery of services constitute the vast majority of capital invested in industry. These systems are subject to deterioration with usage and time. System deterioration is often reflected in higher production costs and lower product quality. To keep production costs down while maintaining good product quality, preventive maintenance is often performed on systems subject to deterioration. The cost of maintenance related activities in industrial facilities has been estimated by Mobley (1990) as 15-40% of total production costs and the trend toward increased automation has forced the managers to pay even more attention to maintain the complex equipment and keep them in available state. If the equipment is maintained only when it fails, it is called corrective maintenance (CM), while scheduled maintenance is called preventive maintenance (PM). It should be noted that preventive maintenance is different from pre-emptive maintenance. While pre-emptive maintenance plans are considered at the design stage to eliminate the maintenance requirement, preventive maintenance plans are applied during equipment operation in order to eliminate failures. In this chapter, we have considered preventive maintenance and related models to determine effective procedures and to minimize failures. Traditionally it is known that the probability of failure would increase as a machine is aged, and that it would sharply decrease after a planned PM is implemented. However, the amount of reduction in failure rate, due to introduction of a PM has not been fully studied. In particular, it would be desirable to know performance of a system before and after the introduction of a PM with specific type and rate.

Extensive studies have been carried out in the areas of reliability and maintenance management. The existing body of theory on system reliability and maintenance is scattered over a large number of scholarly journals belonging to a diverse variety of disciplines. In particular, mathematical sophistication of preventive maintenance models has increased in parallel to the growth in the complexity of modern manufacturing systems. Research work has been published in the areas of maintenance modeling, optimization, and management. Literature abounds with research papers in the areas of reliability and maintenance. While a survey of maintenance models for multi-unit systems has been presented by Cho and Parlar (1991), a review of maintenance optimization models is made by Dekker (1996). Sheu and Krajewski (1994) presented a decision model based on simulation and economic analysis for corrective maintenance policy evaluation. Some researchers, such as Waeyenbergh, et al. (2001), have discussed detailed procedures, knowledge based concepts, and frameworks in maintenance policy development and implementation in industry. Komonen (2002) presented a cost model of industrial maintenance for profitability analysis and maintenance models for production systems with intermediate buffers have been studied by Kyriakidis and Dimitrakos (2006). Leon Hijes and Cartagena (2006) presented a maintenance strategy based on equipment classification using a multi-criterion objective. Modeling of reliability and maintenance operations of flexible manufacturing systems (FMS) and flexible manufacturing cells (FMC) has been studied in detail by Savsar (2000, 2011a, 2012), Aldaihani and Savsar (2005, 2008), and Savsar and Aldaihani (2008). Savsar (2005, 2006a) analyzed the effects of maintenance policies on FMC performance. Also, Savsar (2006b, 2008, and 2011b) developed discrete mathematical and simulation models to analyze preventive and corrective maintenance operations of serial production lines. Al-Salamah et al. (2010) discussed conflicting issues between operations and maintenance. Most of the models presented in the literature consider theoretical aspects of system reliability and optimum maintenance. In this chapter, we have considered analysis and models for equipment maintenance, which can be applied in practical situation. First, formulations and procedures are presented to determine various maintenance parameters based on data obtained from equipment operation. Then, several models and tools are presented for determination of best maintenance practice.