What is Air Tightness Testing for EV Battery Cold Plates

Power batteries serve as the core energy component for electric vehicles and energy storage systems. Massive heat generates during charging and discharging cycles. Insufficient heat dissipation will trigger battery performance degradation, shortened service life, and even severe thermal runaway hazards. Liquid cooling stands out as a mainstream thermal management solution thanks to its efficient and uniform heat dissipation performance.

Aluminum cold plates, commonly fabricated from 3003, 5052 and other aluminum alloys via stamping, brazing and friction stir welding, are critical heat transfer components inside liquid cooling systems. Internal intricate flow channels allow circulating coolant to absorb heat from battery modules steadily. Therefore, cold plates must maintain complete airtightness and pressure resistance. Even tiny leaks will cause severe consequences:

• Coolant loss leads to sharply reduced heat dissipation and battery overheating
• Conductive ethylene glycol coolant may contact high-voltage terminals and cause short circuits
• Overall battery pack failure and failure to meet IP67 dustproof and waterproof standards

Air tightness testing acts as an indispensable final inspection procedure in cold plate manufacturing, safeguarding product quality and operational safety.

This is the most widely adopted and highly automated testing solution. Dry compressed air or nitrogen is injected into sealed cold plates until preset pressure such as 250kPa is reached. The system then enters pressure holding phase. High-precision sensors monitor real-time pressure fluctuations. Pressure drop within designated holding duration, typically 30 seconds, determines leakage status.

Advantages: Fast testing speed, quantitative results, non-destructive inspection, easy integration into automated production lines, objective judgment

Disadvantages: Unable to pinpoint leakage locations; testing accuracy affected by ambient temperature and workpiece deformation

• Direct Pressure Type: Measures internal pressure variation directly with low equipment cost
• Differential Pressure Type: Compares pressure difference between tested workpiece and standard reference part. It eliminates interference from ambient temperature and pressure fluctuation, delivering superior detection precision for high-standard requirements.
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A traditional intuitive testing approach. Pressurized cold plates are fully submerged in water. Operators observe bubble generation to identify exact leakage positions.

Advantages: Simple operation, low cost, accurate leak positioning

Disadvantages: Low testing efficiency, subjective judgment, mandatory post-test drying process, incapable of detecting micro leakage. Mainly applied for random inspection, laboratory verification and leak troubleshooting.

It features top-tier detection accuracy in the industry. Helium gas owns tiny molecular size, strong penetration and extremely low natural atmospheric concentration, serving as ideal tracer gas.

• Vacuum Chamber Method: Place cold plate into vacuum chamber. Inject helium internally after vacuum pumping. Escaped helium is captured and analyzed by spectrometer.
• Sniffer Probe Method: Fill cold plate with helium and scan welding seams and joints with sniffer probe to locate micro leakage points precisely.

Advantages: Ultra-high sensitivity up to 10⁻⁹ Pa·m³/s, accurate leak rate quantification, micro leak positioning

Disadvantages: High equipment and operational cost, complicated operation. Suitable for aerospace, high-end energy storage products and standard calibration verification.

This method verifies long-term sealing reliability rather than conventional leakage inspection. Cold plates are placed in temperature alternating chamber under extreme working conditions ranging from -40°C to 85°C. Repeated thermal expansion and contraction generates mechanical stress on welding seams and sealing joints. Secondary air tightness tests are conducted after cycling to check sealing durability.

It evaluates potential cracking risks caused by material fatigue under long-term temperature fluctuation.

• Standard testing pressure: 200kPa to 250kPa, 2 to 2.5 times actual working pressure for sufficient safety margin
• Qualification criteria: Pressure drop shall be less than 100 Pa within 30-second pressure holding period
• IP Rating Matching: Automotive battery packs are required to reach IP67 protection grade. Qualified cold plate airtightness lays solid foundation for overall waterproof and dustproof performance of battery packs. Unqualified leakage will directly result in IP67 certification failure.

1. Pre-treatment: Clean workpiece and seal all ports with customized fixtures
2. Gas charging and pressure stabilization: Inject testing gas and stabilize pressure to eliminate temperature impact
3. Pressure holding and real-time monitoring: Execute formal detection and record pressure variation data
4. Automatic qualification judgment and product sorting
5. Leak positioning: Apply water immersion or helium detection for defective products to optimize manufacturing process

Air tightness testing for power battery cold plates integrates precision machinery, sensor technology and strict quality control. Pressure decay method dominates online mass production for its high efficiency, stability and automation compatibility. Helium mass spectrometry provides ultra-precision inspection for high-end products and research validation. Water immersion test and thermal cycle test serve as auxiliary means for leak location and durability assessment.

As stricter safety and reliability requirements are raised in new energy industry, cold plate air tightness inspection will develop toward higher precision, efficiency and intelligent operation.