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Welding Process for Aluminum Bus‑Bars and Copper Rings in New‑Energy‑Vehicle On‑Board Power Distribution Systems

Aug 18,2026

On‑board power distribution systems of new‑energy vehicles widely adopt connection assemblies combining aluminum bus‑bars and copper conductive rings. Aluminum bus‑bars cut overall vehicle weight; copper rings feature outstanding conductivity, wear resistance and durability, suitable for repeated bolt‑tightening assembly.

Copper and aluminum are dissimilar metals with large material differences. Aluminum readily forms tenacious surface oxide layers. Conventional welding often causes cold joints, cracking, overheating under current, and delamination or detachment in service. Ultrasonic torsional welding delivers stable bonding for automotive aluminum‑to‑copper bus‑bar connections.

I Working Principle of Ultrasonic Torsional Welding

Under constant pressure, high‑frequency torsional vibration breaks oxide layers on aluminum bus‑bars and copper‑ring surfaces. Metal surfaces achieve intimate contact and inter‑diffusion. It is low‑temperature solid‑state welding, no filler metal, base metals remain unmelted and no brittle intermetallic impurities are generated. Weld spots feature high strength, stable conductivity and low tendency to overheat or deform.

II Key Advantages of Torsional Welding

1.Good weld ductility, resistant to vehicle vibration and temperature fluctuation, hard to crack or detach.

2.Low heat input; heat concentrates only at bonding interfaces. Insulating layers and adjacent components stay undamaged; no workpiece deformation.

3.Uniform circumferential stress on copper rings yields compact bonding; no offset welding or partial cold joints.

4.Thorough oxide‑layer removal creates tight interface contact, stable resistance and low temperature rise under high‑current operation.

5.Welding induces no squeeze‑caused deformation; copper‑ring position stays accurate to guarantee subsequent bolt‑assembly precision.

III Core Difficulties in Aluminum‑to‑Copper Welding

1.Aluminum oxidizes easily. Conventional welding cannot fully remove oxide films, creating barrier interlayers, cold joints and overheating.

2.Large difference in thermal expansion coefficients between copper and aluminum generates internal residual stress after cooling from high‑temperature welding, triggering weld cracking and ring detachment under vibration.

3.Conventional welding produces brittle intermetallic compounds. Brittle welds tend to fail and detach under road vibration.

4.Uneven force distribution in traditional welding causes copper‑ring offset and partial incomplete fusion, assembly accuracy cannot be ensured.

IV Welding Procedure

1.Pre‑weld Cleaning: Remove oil, dust, oxide scales and burrs from aluminum bus‑bars and copper‑ring surfaces to obtain clean interfaces and avoid hidden cold joints caused by uneven friction.

2.Precise Alignment: Nest copper rings centrally onto holes of aluminum bus‑bars without skew or one‑sided gaps; clamp with tooling to guarantee even stress distribution.

3.Low‑Pressure Pre‑Compression & Planishing: Apply soft steady pressure to eliminate micro‑gaps at interfaces and expel interlayer air for full aluminum‑to‑copper contact.

4.High‑Frequency Torsional Welding: Gentle vibration breaks oxide films and enables sufficient metal inter‑diffusion. Low‑temperature forming without damaging base materials.

5.Pressure‑Held Slow Cooling & Setting: Maintain pressure during cooling after welding to counteract material shrinkage stress and eliminate risks of micro‑cracks and delamination.

6.Final Inspection: Check workpieces for skew, crushing or thermal blackening. Sample‑test weld strength and electrical conductivity before releasing batches.

V Parameter Tuning Guidelines

1.Welding Pressure: Soft constant pressure for tight non‑slip contact. Too low pressure brings cold joints and overheating; excessive pressure dents aluminum bus‑bars.

2.Torsional Amplitude: Moderate amplitude. Insufficient amplitude leaves residual oxide and weak bonding; excessive amplitude scratches metal surfaces and induces micro‑cracks & brittleness.

3.Welding Duration: Short‑cycle rapid forming. Too short yields incomplete bonding; overly long time causes heat accumulation, oxidation and material embrittlement.

4.Holding‑Pressure Duration: Appropriately extend holding time to counteract spring‑back stress, prevent delamination and improve vibration‑ & temperature‑resistance of welds.

VI Common Defects

1.Skewed copper‑ring, partial cold joints: Poor fixture positioning, alignment offset, insufficient pre‑compression.

2.High resistance & severe heating under current: Incomplete oxide removal, interfacial impurities or micro‑gaps.

3.Dents & crushing on aluminum bus‑bar: Excessive welding pressure or vibration intensity.

4.Delamination after thermal‑cycling & vibration: Insufficient holding‑pressure time, residual cooling‑induced stress and hidden gaps.

5.Local blackening & oxidation of weld spots: Overlong welding time, local heat accumulation and poor heat dissipation.