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September, 2018
Leak Testing Hermetically Sealed Components
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pressure decay leak testing. This type of testing uses compressed air or vacuum to pressurize a cavity in a component and sensors measure how much the pressure in the part drops and compares that with the designat- ed acceptable leak rate. The pressure decay leak testing
method is capable of testing a large percentage of manufactured parts, but there are also many components that are hermetically sealed, mean- ing there is no opening in the part to pressurize for testing. Often, parts are leak tested mid-production, when there is still an opening to be tested. If the part passes the leak test, the opening is capped or a final weld occurs, sealing it. Well-tested hermetic seals
throughout a vehicle are essential for maintaining reliable, consistent vehicle performance in a variety of environments with fluctuating pres- sure and temperature. In order to perform a leak test on an assembly that no longer has an opening to test directly, a leak-tight chamber is required to test if air could penetrate into a component. This sealed inflow testing, also
known as enclosure integrity testing or ingress leak testing, is a less com- mon and more difficult type of test that puts a spin on traditional pres- sure decay testing. It can be chal- lenging to determine a leak-rate reject limit for ingress leak tests. In typical direct-outflow leak
testing, there is a correlation between a drop in pressure and a leak coming out of the component. Ingress leaks are more strict, because they are often testing for tiny molecules, such as water vapor, entering an assembly. The nature of ingress leak test-
ing makes coming up with a leak rate specification difficult. “It’s difficult, because the leak rate will change with time on a sealed component,” says Anne Marie Dewailly, technical direc- tor of ATEQ Corp. “There’s a finite amount of space inside the compo- nent, so the longer you test it, the less the leak rate will be. Pressure will build up inside the part.” Typically, a pressure decay test
is used to test hermetically sealed components. The test component is placed into a custom-made leak-tight chamber. The chamber is then pres- surized to a predetermined pressure with compressed air. When the chamber is cut off from the pressure source, air will flow into the test part if there is a leak, causing the cham- ber’s pressure to drop. This pressure change over time
is then used to calculate a leak rate. Occasionally, assemblies tested with the sealed component chamber test have a leak rate reject limit that is so large that parts that pass the test would not actually be considered her- metically sealed, because some air would be able to leak into the part, but not enough to have consequences for the consumer.
Testing Vehicle Cameras ATEQ was tasked by an OEM
automotive electrical device supplier to provide a stable and repeatable leak testing solution for its vehicle camera with a connected cable. In order to provide a testing solution
See at SMTAI, Booth 423
Fixtures are used to secure parts during testing.
compared for consistency. Instead of just using one fixed-volume tank, ATEQ’s adjustable volume “transfer tank” corrects for more subtle volume differences. A custom fixture with sil- icone tubing was also strategically built to hold the rubber cable steady for more accurate testing. As shown by the vehicle camera
with cable case study, having a good leak testing instrument is only half the battle. Figuring out how to incor- porate the tester into a custom fix- ture to test the component is a whole other challenge. For bench testing, a simple tester connected to a test part is often sufficient for a standard out- flow leak test, but when a customer wants an automatic leak test incor- porated into a production line, a leak testing engineer needs to work close- ly with a machine builder to meet the customer’s testing specifications.
Well-Designed Fixtures When leak testing an applica-
tion, the test fixture must be well- designed to produce the most accu- rate, efficient and repeatable results. Test fixtures use air or hydraulic cylinders to seal the test part in the fixture. It is important to take into account the design of the entire machine, the fixture and the seal. The design of a good seal is essential in ensuring a shorter test stabiliza- tion time and decreasing the chance for test-altering volumetric changes. For accurate test and better
repeatability, the fixture, test part and test lines should be made from rigid materials to avoid minute vol- ume changes caused by flexible materials. Protect test fixture areas from vibrations, air drafts, water, oil, and debris accumulations by placing fixture seals and test inlets on the upper part of the machine. Vibration- proof fittings should be glued and any tubing tied to the frame of the machine. Once a fixture is ready to be
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superior to a standard ingress leak test, ATEQ had to take its testing fix- ture to the next level using differen- tial sensor and pressurized valve technology. As opposed to using one testing
chamber for the test part, ATEQ used two testing chambers. One reference chamber contained a copied 3D print of the product and one test chamber contained the test product so that the reference and test volumes could be
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