Mixed-Product Assembly Lines : Characteristics and Design Challenges

Flexible assembly systems have emerged in response to changing markets and increased variety in form of demands of new products and manufacturer’s need for differentiation. Assembly systems play a critical role in handling great variety and adapting to dynamic changes at the same time as securing product quality and productivity. Therefore, assembly systems should be designed to be able to handle changes. However, the design of flexible assembly systems is a challenge because it involves several subjects such as the configuration of the flow, the material handling and the flexibility to handle future changes and adjustment. In addition, time-to-market and time-to-volume are important which means that faster assembly systems designs are required.The design process of assembly systems concerns the procedures that guide the design work to achieve an assembly system proposal. The design process is divided into a number of stages/phases describing the activities that should be done and when they should be performed as well as the expected result after each phase supporting the decision-making process. Research argues that working in a systematic and structured way is important in order to achieve better assembly systems in shorter time.However, even though there is extensive research work in regard to flexibility, knowledge is limited concerning the design process of assembly systems. Therefore, the objective of this thesis has been to increase the knowledge about the design of flexible assembly systems by investigating the relation between the assembly system design process and flexibility. The characteristics of flexible assembly systems and how flexibility is considered during the design process have also been studied in this thesis.Literature reviews were conducted as well as three case studies and one exploratory survey in the manufacturing industry of heavy vehicles. Study I concerns the results of having studied an industrial international project of the design process of a flexible assembly system during two years. In study II, flexibility needs, enablers and challenges in assembly systems were identified. In study III, the mechanism used to achieve flexibility in the assembly systems of two companies were investigated. The exploratory survey study IV, was a pilot study to investigate the relationship between the design process of assembly systems and flexibility based on the association of different variables involved in the design process of flexible assembly systems.From the holistic perspective adopted in this thesis, the results showed that flexibility should be considered in a comprehensive way during all the design process. The design process of flexible assembly systems is iterative, circumscribed by different conditions, and requires support as well as the participation of different roles and functions to achieve a solution. The increased knowledge generated in the research is expected to lead to future development of working procedures that better can support the design process of flexible assembly systems.