Objective: To investigate the application of statistical process control (SPC) in defining accurate acceptance limits for tightening angles in threaded connections. The aim is to enhance process reliability and product quality by addressing gaps in existing standards, such as ISO 22514 and VDI 2645, through the integration of torque and angle data into a unified control framework. This research seeks to optimize manufacturing efficiency, reduce rework and production downtime, and contribute to sustainable industrial practices by minimizing waste and ensuring safer, more reliable products. Theoretical Framework: This research is grounded in the principles of Statistical Process Control (SPC), which provides the foundational methodology for analyzing and improving process variability. SPC focuses on monitoring and controlling manufacturing processes to ensure they operate at optimal efficiency and within defined limits, aligning with the standards outlined in ISO 22514 for process capability and performance. The study also draws upon the concepts presented in VDI/VDE 2645, which emphasize the role of torque and angle as auxiliary quantities for ensuring proper preload in bolted joints. These standards highlight the complexities of managing tightening parameters, such as torque and angle, and the need for precise assessment of their interrelation to guarantee joint integrity. The application of Gaussian distribution models and quantile-based methods provides statistical tools to identify outliers and define normal process behavior, particularly in non-normal data distributions. By integrating these theoretical perspectives, this study establishes a robust framework for enhancing the reliability and sustainability of fastening processes in industrial applications. Method: This research comprises a quantitative approach, focusing on the statistical analysis of torque and angle data collected from an automotive assembly line based in international deployed standards, to define an application method for fastening control. The study design included monitoring fastening events under controlled conditions, with torque as the primary controlled variable and angle as the monitored metric. Data collection was conducted through real-time observations using fastening controllers equipped with integrated torque and angle measurement systems. The data were analyzed using statistical tools, including Gaussian distribution models and quantile-based methods, to define control limits and identify outliers. The methodology ensured a comprehensive understanding of process variability and facilitated the development of a robust framework for evaluating joint quality. Results and Discussion: The results obtained revealed a significant improvement in the quality and reliability of threaded connections, with reduction in rework and minimized production downtime. The statistical analysis demonstrated that integrating torque and angle metrics effectively identifies process anomalies, allowing for precise control limit definition. Quantile-based methods proved superior in handling non-normal data distributions, enhancing the robustness of the process evaluation. In the discussion, these findings are contextualized within the theoretical framework, reinforcing the importance of statistical process control in industrial applications. The relationship between torque and angle as indicators of joint behavior aligns with prior studies, emphasizing their predictive value in ensuring connection integrity. However, limitations such as data dependency on equipment precision and the need for large sample sizes were identified. These factors highlight areas for future refinement and broader application in diverse industrial settings. Research Implications: The practical and theoretical implications of this research provide valuable insights into the application of statistical process control in fastening processes. The findings can significantly influence practices in the fields of industrial manufacturing and quality management, particularly in sectors such as automotive, aerospace, and construction. Practical implications include the enhancement of production efficiency, reduction in rework and downtime, and improved product safety and reliability. Theoretically, the study reinforces the importance of integrating torque and angle metrics in quality control, offering a robust framework for future research on non-normal data distributions and their implications for process optimization. Originality/Value: This study contributes to the literature by introducing an innovative approach to statistical process control in fastening processes, emphasizing the integration of torque and angle metrics for defining precise control limits. By addressing gaps in the practical application of statistical methods for non-normal data distributions, the research offers new insights into optimizing manufacturing efficiency and quality. The relevance and value of this study are evidenced by its potential to reduce rework, minimize downtime, and enhance product reliability in critical sectors such as automotive and aerospace. These contributions provide a robust foundation for advancing both academic understanding and industrial practices in quality management.
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