To efficiently develop an automatic assembly system that can enhance the quality and assembly productivity of the shaft assembly in EV relays, a DMU model was utilized. After modeling each component of the assembly system using the CAD software CATIA, a DMU model of the assembly cells and the entire assembly system was created using the assembly model. Additionally, the DMU Kinematics Workbench was employed to verify and validate the design of the automatic assembly system for the shaft assembly, a key component of the EV relay, before actual construction. This approach helped reduce time and costs by minimizing trial and error.