In the automotive industry, the quality of components is becoming increasingly important. This is often accompanied by higher demands on tightness - requirements that can no longer be met using traditional methods such as water bath or pressure drop measurement. In more and more applications, only modern test gas methods offer the accuracy and reliability required in the manufacturing process - whether it is heat exchangers for exhaust gas recirculation systems for nitrogen oxide reduction or charge air coolers for modern turbo engines. Precise leak testing is also essential at the various stages of the production process for traction batteries for EV/HEV vehicles. This is the only way to guarantee the operational safety and service life of the expensive battery - from the tightness of the individual battery cell to the cooling circuit and the entire housing.

Pressure drop test

Some suppliers still rely on the supposedly cost-effective pressure drop test. This involves filling the test part with air up to a defined overpressure and measuring any changes in pressure over a defined time interval. If the pressure drops, there is a leak. The smallest leak rates that can ideally be determined in this way are in the order of ^10-3 mbar∙l/s. However, a major problem with the method is its susceptibility to temperature fluctuations. If the temperature only rises by fractions of a Kelvin during the test, leaks often go undetected. If, on the other hand, the temperature drops, the pressure drop test detects phantom leaks. Attempts to compensate for temperature changes reduce this effect, but do not eliminate it completely.

Helium testing in the vacuum chamber

Test gas methods are far more reliable here. A vacuum leak tester such as the LDS3000 from Inficon is highly sensitive, allows very short cycle times and is therefore recommended for automated testing systems in production lines. With the vacuum method, the test specimen is placed in a hermetically sealed chamber in which pumps create a vacuum. The test specimen is also evacuated and filled with the test gas helium so that it can escape through any leaks into the vacuum of the chamber, where it is detected by the leak tester.

This means that even larger components can be tested against the smallest limit leakage rates - down to ^10-12 mbar∙l/s under optimum conditions. Typical applications of vacuum testing are tests on air conditioning components - evaporators, condensers or filling valves (up to ^10-5 mbar∙l/s) -, on common rail injection systems (^10-6 mbar∙l/s) or on fuel systems and fuel tanks (^10-5 mbar∙l/s).

Vacuum testing is also the method of choice for battery cells. Whether they are prismatic, round or pouch cells: Once the manufacturer has filled them with the flammable electrolyte and sealed them, he must test the tightness of the battery cell housings against leakage rates of ^10-5 to ^10-6 mbar-l/s. For this reason, 3 to 5 percent helium is often added to the electrolyte filling of the cells as a test gas.

Testing in the simple accumulation chamber

For small and medium-sized parts in particular, which are only tested for possible oil (^10-3 mbar∙l/s) or water leaks (^10-2 mbar∙l/s), testing in the simple and cost-effective accumulation chamber is recommended. This involves measuring how much test gas escapes from an oil, water or charge air cooler, for example, and accumulates in the accumulation chamber within a certain time interval.

The robot sniffer leak detector can be used to locate leaks. © Inficon

In practice, a device such as the LDS3000 AQ from Inficon determines leak rates of up to ^1∙10-5 mbar∙l/s in the accumulation chamber. Instead of helium, the device can also use less expensive forming gas, a non-flammable, commercially available mixture of 95 percent nitrogen and 5 percent hydrogen. Using the accumulation method, this device detects liquid leaks just as reliably as only helium vacuum testing could in the past - and at the same cost as a simple air test.

Dynamic robot sniffer leak detection

Sniffer leak detection with test gas is not only intended to identify leaks, but also to locate them precisely. It is also often used to determine whether the joints between components that have already been assembled are tight, for example before the vehicle is installed on pre-assembled air conditioning modules or if the tightness of a traction battery housing to the outside must be guaranteed in accordance with IP67 or IP69K. A distinction is made between static and dynamic sniffer leak detection. In the latter, the sniffer probe moves over a larger area of the test part.

Dynamic robotic sniffer leak detection, in which the measuring head is attached to the tip of a robot arm and is automatically guided over the test part, is particularly technically demanding. Inficon devices such as the XL3000flex with the test gases helium or forming gas and the Protec P3000XL (with helium) are predestined for this scenario. They draw in the air to be tested at a very high gas flow of 3,000 sccm, whereas conventional multi-purpose leak detectors operate at just 60 sccm. Thanks to the high gas flow, the measuring head can maintain the required safety distance from the surface of the test part (often 5 or 6 mm) during dynamic and automatic sniffer leak detection and at the same time still identify leaks 100 percent even at higher feed rates of 10 cm/s or more. Typical limit leak rates that must be tested against in dynamic robot sniffer leak detection are ^10-2 mbar∙l/s for water tightness, ^10-3 mbar∙l/s for oil tightness and ^10-4 mbar∙l/s for tightness against liquid fuels.

Multigas sniffer leak detection after installation

Even after the actual installation of the air conditioning components, the OEM still has to test the tightness of the connection points or check the refrigerant circuit of the installed traction battery for leaks. In such cases, a multi-gas sniffer leak detector such as the Ecotec E3000 can use the respective refrigerant -_{CO2 or} R1234yf - itself as a test gas and detect any leaks directly. In fact, such a multi-gas sniffer leak detector is the only way to test the filling valve for leaks after it has been closed. It can also detect fuel leaks in the common rail connections. The smallest leak rate that can be detected with the device corresponds to 0.05 g/a of the refrigerant R134a or a helium leak rate of ^10-6 mbar∙l/s.

Sandra Seitz, Market Manager Automotive Leak Detection Tools, Inficon / am

More about leak testing
Inficon offers even more information on the physical principles and application scenarios of "Leak testing in the automotive industry" in a detailed manufacturer-neutral guide. You can download this e-book free of charge here: www.inficon.com/automobilindustrie-ebook