A strategy for improving reliability in assembly processes

Sammanfattning: This report presents an explorative examination of the scientific literature regarding current methods utilized in mixed-model assembly lines and the challenges that are faced. Empirical data from a real mixed-model assembly line was collected and analyzed to explore the application of the identified methods and the problems that are faced in a realistic situation.  The report consists of a theoretic framework on the topics of assembly systems and topics relevant to managing the challenges. In addition a case study is conducted where an assembly system is observed and real production data is collected. Product assembly lines make up one of the final steps in the manufacturing process of a product. By implementing proven methods for process improvements highly effective assembly lines are realized. If an assembly line is experiencing reliability issues the probability of the company’s end-customers being directly affected is considerably increased.  Ensuring reliability in a mixed-model assembly line (MMAL) is an important task with an increasing level of difficulty given the current evolution of advanced technology. The resulting increase in product variety and complexity made possible increases the demands on the entire manufacturing process and the assembly line in particular. Added product variety and complexity poses an increased challenge from an automation perspective as well due to the limitations in flexibility inherited by industrial robots in comparison to a human operator. Many challenges in manufacturing and assembly processes stem from product development, increased variation between product models, and changes in production systems, due to the resulting increase in the complexity of the production processes (ElMaraghy ​​& ElMaraghy, 2016). Historically, a vast number of manufacturing companies have seen significant improvements in their product quality and productivity, leading to improved financial results as well as customer satisfaction by implementing process development methods such as Lean production, Six Sigma, or Lean Six Sigma.  Therefore, the purpose of this report is to explore assembly system reliability and complexity management. The scope of this report is restricted to focus on reliability in assembly systems from a quality perspective. Suggestions for improvements are biased towards Lean Six Sigma methods and complexity management as described in current literature with the consequence of potentially valid methods and solutions being excluded. The theoretical framework of this report is based on selected books and scientific articles on the topics of complexity, assembly systems, process development, and human performance in the context of assembly systems.  The case study project is executed following the DMAIC-process as per the L6S methodology. Lean six sigma methodologies are applied in accordance with the selected literature with the objective of identifying a potential strategy for mitigating the quality deficiencies observed in the company´s assembly processes. The research presented in this report follows the abductive reasoning concept (Säfsten & Gustavsson 2020). Abductive reasoning is initialized by a conclusion, which is followed up by constructing a theory based on literature, and finally analyzing empirical data to validate the constructed theory in the context given by the initial conclusion.  Additionally, a root cause analysis is conducted. The root cause analysis is initiated by constructing an Ishikawa diagram to categorize and identify possible causes of the identified errors. By systematically working through each of the categories the examined problem is look upon from different points of view, making for a comprehensive analysis. In this step the 5-why’s method is utilized to support the deductive reasoning process. The potential root causes are then utilized to construct a list of possible solutions and suggestions for improvement for the examined problem. The improvement suggestions are based on deductive reasoning as well as documented improvements from the literature.