As EVs move to 800V high-voltage platforms, harness cross-sections keep growing and conventional crimping faces reliability challenges under high current — ultrasonic welding is being adopted ever more widely for harness terminal connections.
Why ultrasonic welding for harnesses
Between multi-strand copper wire and the terminal, ultrasonic welding metallurgically bonds every strand to the terminal, achieving lower and more stable contact resistance than crimping. Less heat is generated under high current, giving better long-term reliability. The process is spark-free, so strands stay undamaged and joints look clean.
Power selection
Harness cross-section is the key factor: small harnesses (under 10mm²) are generally fine with around 2000W; high-voltage harnesses above 30mm² need 3000W–6000W high-power machines. Insufficient power leaves inner strands unwelded — a hidden defect.
Quality checks
Visual: the joint should be flat, with no loose strands and no burn discoloration.
Pull testing: test to the standard for the given cross-section — the most direct quality verdict.
Resistance measurement: compare DC resistance before and after welding; a good joint adds negligible resistance.
Cross-sectioning: for critical products, metallographic sections confirm all strands fused with no voids.
Production advice
Harness welding is fast-paced, suiting semi- or fully automatic cells with auto wire feed and unloading. Choose machines with energy monitoring and data logging for real-time quality verdicts and traceability that meet automotive quality system requirements.