Research On Measuring And Improving Flexibility For Manufacturing Systems With Environmental Requirements

The drastic competition of market, customization and variety of products have forced more and more companies to shift from mass production of highly standardized products to the batch production of customized products. In this situation, rigid facility is unable to retain high efficiency in production. The required high return of investment forces the capacity to be quickly shifted from producing one product to another without much setup cost. To respond to the fierce competition and drastically changed demands, companies need eagerly to find an effective way to improve their flexibility.However, the flexibility of a manufacturing system depends not only on its own capability structure, but also on the environment that it is in. The existing methods for improving flexibility often drop into two groups. Methods in the first group view flexibility as an intrinsic attribute of the system and irrelevant to the environment. So these methods for improving flexibility have the risk of omitting relevance because they omit external demand. Methods in the second group usually present empirical recommendations on flexibility improvement for specific industrial situations. Without considering system structure, however, these methods are case-sensitive in addition to the disadvantages of intensive computation. This thesis synthesizes the capability structure of a manufacturing system and some environmental characteristics, and investigates the flexibility improvement methods for manufacturing systems and supply chains. The main environmental characteristics that are captured in this thesis include two types: bill of material (BOM) constraints and demand characteristics. The research which synthesizes the capability structure and environmental characteristics overcomes the above drawbacks.The main topics of the thesis are analyzing the impacts of environmental characteristics (including BOM constraints and demand characteristics) on process flexibility measurement and improvement for manufacturing systems and supply chains, and developing methods for measuring and improving process flexibility considering environmental characteristics.The organization of the thesis is as follows:In the first chapter, the literature about the measurement and improvement of flexibility in manufacturing systems and supply chains are reviewed. The content and significance of this thesis are addressed. Chapters 2 and 3 deal with the impact of BOM constraints on process flexibility in manufacturing systems, and propose methods for measuring and improving process flexibility under BOM constraints. In Chapter 2, an effective measurement method is proposed for process flexibility of manufacturing systems. For the manufacturing system that consists of multiple assembly lines, process flexibility under BOM constraints is differentiated into two hierarchical and highly interrelated levels: the assembly line level and the system level. By interpreting process flexibility as the ability to shift capacity among different parts or product types in face of external and/or internal changes, approaches for measuring process flexibility on the two levels are proposed. In Chapter 3, structural properties and the guidelines for improving process flexibility on the two levels are investigated based on the measurement method developed in Chapter 2. The proposed guidelines can help the manager of a manufacturing system to make effective decisions on flexibility improvement without much computation effort. Chapters 4 and 5 consider the impacts of demand characteristics on process flexibility of manufacturing systems and supply chains, respectively. In Chapter 4, the impacts of demand characteristics on process flexibility of manufacturing systems are analyzed, and a flexibility measurement method considering demand variations and demand correlations is developed. Based on the measurement, guidelines for improving flexibility by adding a single link are proposed. In Chapter 5, the measurement method for process flexibility of supply chains in certain demand distributions is investigated. Drawbacks of an existing flexibility measure without considering demand characteristics and system structures are revealed. A new flexibility measure for supply chains is developed which is relevant to the demand distribution that it is in. Chapter 6 concludes the thesis, and gives some directions for further research.Innovations and contributions of this thesis are briefly summarized as follows:(1) Under environmental requirements, guidelines for improving process flexibility of manufacturing systems are proposed, which help the managers to make effective decisions on flexibility improvement without much computation.(2) By synthesizing the intrinsic attributes of the manufacturing system and the BOM structure of products, a new method for measuring process flexibility is proposed, which reflects both the intrinsic characteristics of the system and the impact of products structures. The method, for the first time, differentiates process flexibility with BOM constraints into two hierarchical and highly interrelated levels: the assembly line level and the system level.(3) By analyzing the impacts of demand characteristics on process flexibility of manufacturing systems, a synthesizing method which considers simultaneously the ability of capacity shifting and the probability of requiring capacity shifting among products is developed. Both the variations of and correlations between products demands are incorporated into the measurement method. Based on the proposed measurement, guidelines for improving flexibility are developed, which improve flexibility most by adding a single link to the original system.