This research explores the optimization of ultrasonic welding parameters for aluminum-copper joints, specifically addressing the durability and performance of sonotrode geometries in automotive wire harness applications. The standard polygonal sonotrode geometry, while functionally accepted, exhibited premature wear and material failure after approximately 5,000 welding cycles. Mechanical degradation was attributed to stress concentration effects inherent in the geometric profile. To overcome this limitation, a redesigned sonotrode with a circular arc geometry was developed and implemented under identical welding conditions. The new configuration demonstrated superior process stability, reduced energy consumption, and extended tool life beyond 10,000 welding cycles without visible structural failure. Welded joints consistently exceeded mechanical strength thresholds (>600 N) and met stringent electrical resistance requirements in accordance with USCAR-38 standards. Furthermore, the circular geometry improved the consistency of voltage drop measurements and minimized material fatigue. The findings emphasize the critical influence of sonotrode geometry on tool longevity, joint integrity, and overall process efficiency. By enhancing weld reliability and reducing operational costs, the proposed design supports more sustainable and scalable ultrasonic welding practices in the automotive sector. This work also sets the foundation for future validation in series production and encourages the integration of geometry-specific optimization strategies in industrial welding systems.