DETROIT — Auto makers and their suppliers continue to use obsolete quality-control tests to check critical components and operating systems on their assembly lines.
More than 80 percent of the leak-detection tests conducted on auto-industry production lines are outmoded and ineffective, according to Thomas Parker, North American automotive sales manager for INFICON, a leading global supplier of leak-detection equipment.
“Inexpensive but out-of-date leak-detection methods such as water-bath and pressure-decay tests are still the norm within the car industry,” Thomas notes. “Using these test methodologies today could have a serious and potentially dangerous impact on product quality.
“What is needed is reliable, repeatable, precise and economical test methodology that can be provided by tracer-gas leak-detection systems.”
Thomas points out that a variety of parts and assemblies still are being tested with water. Components are pressurized and then submerged. Operators then are required to detect leaks by observing the formation of bubbles. Entire transmissions, gearboxes, rear ends, differentials and gas tanks still are tested by the water-bath method, which relies completely on the ability and constant attention of an operator.
In addition, water-bath reliability is affected by bubbles inadvertently rising to the surface as a part submerges. Leaks that may affect quality and incur warranty costs also can escape detection because they may be too small to overcome water-surface tension in order to form bubbles. Test parts and assemblies must be thoroughly dried after testing to prevent corrosion and discoloration as well. Similar problems occur when a soap solution is applied to a part to detect bubbles.
Pressure-decay is another outmoded test method that relies on filling a part with clean, dry air at a specific pressure, then watching for pressure losses. Vacuum testing is an alternative. A pressurized component is placed in a vacuum chamber where pressure increases over time can be measured. Either method is simple and can be automated, but there are problems with both.
Temperature variations due to sunlight, nearby heat sources or drafts, can affect pressure as well as test results. If the temperature rises during a test, for example, leaks may not be discoverable, and if the temperature drops leak indications will be false. If a part such as a plastic container is expandable or unable to withstand high pressure, pressure-decay tests also are unreliable. A very-small leak, while significant to quality, might be undetectable in a large-volume component.
Quality-control engineers and production managers today are faced with unusual challenges when tasked with leak testing. Specifications for leak-tightness, for example, may be unavailable or lacking in specification clarity.
“Older test methods frequently deliver unacceptable levels of performance,” Thomas adds. “What is needed today is reliable, repeatable, precise and economical test methodology which is something that tracer-gas leak testing can deliver.”
Compared to water-bath and pressure-decay testing, tracer-gas testing is:
- Reliable and precise. It has more than 100 times the sensitivity of either water-bath or pressure-decay testing.
- Repeatable under unfavorable conditions like variable ambient temperatures, humidity or wetness.
- Highly economical. Tracer gas is directly recoverable.
- Simple to use for operators or in robotic applications.
- Inexpensive in many cases.
- Does not require a specific test-jig supplier. INFICON is a supplier to major test-jig assemblers.
- Measureable. Results are directly relatable to specific acceptable leak rates, from 10-2 to 10-10 mbar-l/s (0.5 sccm-0.0000000006 sccm).
- Capable of finding porosity leaks in “Light-weighting” castings, such as aluminum, soon after original casting.
- Safer. There are no wet or soapy floor areas.
- Compatible with flexible parts due to direct measurement at low pressures.
- Faster to rework. Localizing leaks facilitates rapid rework and adds to overall value.
Although seemingly fast and inexpensive, water-bath testing has a number of other drawbacks. Energy may be required to fully dry parts after testing. Water and chemicals in the test tank may require frequent change and environmentally sensitive disposal. Easily visible leaks up to 3 sccm also require lengthy immersion times with even longer times to detect smaller leaks. In every case, an inspector must have a clear view of the part and locations for bubble formation. If a part is sprayed with a soap solution, it then must be cleaned prior to further assembly operations.
Tracer-gas leak testing commonly takes one of three forms: accumulation, sniffer, or vacuum leak-detection.
- Accumulation testing requires a test chamber that can be tightly sealed. The part or assembly to be tested is filled with forming gas (commonly 5-percent hydrogen and 95-percent nitrogen or helium) through a test port, then sealed in a test chamber. Leaking test gas is equally distributed within the chamber by fans and an INFICON leak detector measures the total leakage rate, regardless of leak position.
- Sniffer testing is similar. The tested component, an engine for example, is filled with tracer-gas or other medium. A “sniffer” probe operated robotically or manually is passed along seams in the component to detect and localize leaks for repair. Sniffer tests can be performed after a pressure-decay test to confirm and pinpoint leaks.
- Vacuum testing is capable of finding the most minute leak. The test parts are filled with tracer-gas—often hydrogen— and placed into a vacuum chamber. Tracer-gas that escapes is measured by a leak detector. Vacuum systems with exceptional leak sensitivity and short measurement cycle times are used to test airbag inflators and medical pacemakers.
INFICON is one of the world’s leading developers, producers and suppliers of instruments and devices for leak detection in air conditioning, refrigeration and automotive manufacturing. The company has manufacturing facilities in Europe, China and the United States, as well as sales and service offices throughout the world.
More information about INFICON automotive technology is available online at www.inficonautomotive.com.