Introduction Several researchers have used fault tree analysis (FAT) method to analyze the vast majority of industrial system reliability problems. FAT is a deductive failure analysis which focuses on one particular undesired event and which provides a method for determining cause of this event . Factors that contribute to the events are traced to the smallest sub-divisions termed as basic events. The cascading effects of several sub-systems may be linked together and multiple effects may be captured through logical AND and OR relationships. Head event probability is determined from basic events in the fault tree.
Tanana and Fan  presented the approach based on a fuzzy fault tree model and determined the maximum possibility of system failure from the usability of failure of each component within the system according to the extension principle. Hessian et al.  discussed FAT for system design, development, modification, and verification. Geometry and Beckon  discussed the application of knowledgeableness and a methodology for the assessment and measurement of reliability, availability, maintainability, and safety of industrial systems using fault tree representation.
Schweitzer et al.  discussed reliability analysis of transmission protection using fault tree methods. Chaos and Sheen  discussed FAT of dust suppression mechanism in a spray system with wetting agent. King  investigated and compared a set of existing component importance measures and select the most informative and appropriate one for guiding the maintenance of the system. Change et al.  proposed a new approach by combining the FAT and FEMME and the reactor system’s reliability was analyzed quantitatively.
Hong et al.  studied the reliability assessment of protection system for switchboard using FAT. Choc and Choc  discussed a practical method for accurate quantification of large fault trees. Hoist and Lu [1 1] studied risk informed design refinement of a power system protection chem.. Volcanism et al.  discussed application of the fault tree analysis for assessment of Journal of Reliability and Statistical Studies, December 2011, Volvo. 4 (2) power system reliability. Zen]ii et al. 13] studied reliability evaluation of flood releasing structures power supply of hydroelectric power station by FAT. In this paper, fault tree method is used to analyze the reliability of piston manufacturing system. Also, risk reduction worth is adopted as a measure of importance for identifying the crucial element that has significant impact on the reliability. This paper is organized as follows: In section 2, some basic concepts are described. In section 3, piston manufacturing system is discussed. In section 4, fault trees for piston manufacturing system are constructed.
In section 5, quantitative analysis of piston manufacturing system is presented. The conclusion is discussed in section 6. 2. FAT Basic Concepts In this section, some basic concepts of FAT are presented [1 , 14]. 2. 1 Fault Tree Symbols . Top Event: An undesired state of a system caused by events occurring within the system or in the system environment. Top event is represented by cetacean. Intermediate Event: An intermediate event is a fault event which occurs from a combination of other events via logic gates.
Intermediate event is also represented by rectangle. Basic Event: The circle describes a basic initiating fault event that requires no further development. In other words, it signifies that the appropriate limit of resolution has been reached. Undeveloped Event: An event which is not further developed either because it is of insufficient consequence or because information is unavailable. OR Gate: Output fault occurs if at least one of the input faults occurs. AND Gate: Output fault occurs if all of the input faults occur. 2. Minimal Cut Set Minimal cut sets ( MASC. s ) constitute the simplified fault tree through the Boolean operation. To determine the MASC. s of a fault tree, the tree is first transformed to its equivalent Boolean equations and then either the “top-down” or “bottom-up” substitution method is used . Any fault tree consists of a finite number of MASC. s , which are unique for the top event. The minimal cut set expression for the top event can be written in the general form, k Top MASC.’ Reliability Analysis of Piston Manufacturing System 45 where of MACS
Top is the top event and M n minimal cut set and k is the number . Each minimal cut set consists of combination of specific basic events and hence in general n – component minimal cut set can be expressed as n where X I is the I the basic event and n is the number of basic events in a minimal cut set. 2. 3 Risk Reduction Worth (RAW) One significant quantity in the reliability assessment is the “measures of importance”. One may obtain the importance of elements influencing reliability by RAW as well as know where the weakness of the system is.