Improving the reliability of ultrasonic welding: a hybrid FTA-DEMATEL-EC framework for cost and risk prioritization in mass production

Our research addresses the limited applicability of traditional reliability assessment methods by implementing a hybrid framework for the Branson 2000X AED ultrasonic welding system in mass production. We aimed to align the quantitative technical framework with the causality and financial impacts of identified failures. This approach created a tool that directly links failure frequency to its systemic causes and economic consequences. To do so, we developed a multi-dimensional hybrid model combining three analytical pillars: quantitative Fault Tree Analysis (FTA) to estimate failure probabilities, the DEMATEL method to uncover hidden causal links, and an Expected Cost (EC) model to prioritize risks based on financial impact rather than failure frequency alone. We found a significant gap between the failure frequencies manufacturers typically report and the actual causes of these failures. While our FTA identified component defects (25.9%) and process instability (24.0%) as the most common issues, our DEMATEL analysis pointed to inefficient maintenance budgeting as the primary root cause. Additionally, our economic model showed that the highest financial risks come not from routine scrap but from human errors during equipment setup and handling, which can lead to catastrophic, costly machine damage. Our results highlight that reliability management with hybrid models requires a dual strategy: rigorous process standardization to reduce scrap and technical measures to prevent low-probability failures that have a large impact on overall reliability. Ultimately, this hybrid framework offers production managers an analytical tool for better resource allocation, an outcome impossible to achieve with traditional standalone tools.