3.2 x 10-4 mbar x 1/s: Von der Heyde (VDH) ensures safe aluminium cast wheels.

3.2 x 10-4 mbar x 1/s – get it? For those of use without an engineering degree – this is the value, which a VDH leak detection machine for aluminium wheels understands. Generally speaking: When exceeding this limit value of a leak rate, the wheel is considered leaky and is not allowed to be mounted on a car. 3.2 x 10-4 mbar x 1/s is the equivalent to an air loss of 0.2 bar within 6 months at a tyre pressure of 2 bar. This leak rate is the tolerance threshold, which is measured with a helium leak detection method. This is the latest technology.

In order to be able to build a machine for such a testing procedure, the manufacturer would need special expertise. A buyer could expect that a firm that holds market share of more than 90 per cent worldwide for leak detection systems with the companies that make OEM aluminium wheels would have the know-how. The specialty machine manufacturer’s name is Von der Heyde and is located in Lower Saxony’s city of Stade, along the Elbe River. 

Significant competition is only experienced when the company identifies copycats of its own test equipment, explains Wolfgang Fuhrmann, manager of development and sales at VDH. However, the technology of a helium leak detection machine is so complex that it is virtually impossible to create an exact copy. Imperfections in such manufactured duplicates are to be expected. Additionally, a constant continuum of development for the testing systems takes place so that remarkable progress has been possible, since the very first tester, which was built in the early 1990’s. In the early models, the testers used three to five litres of helium per wheel, now the testers use less than one litre per test. A litre price of about 1.5 to 2 euro cents for the “consumable helium” is an influential calculating factor, when a new investment in such a tester is being considered, either in addition to existing testing methods or as a substitute. 

Alternative technologies for leak detection with helium were explored, e.g., with ultrasound under water, but so far have not proved to be competitive. This is mainly, because the mass spectrometry method used by VDH in Stade is independent of temperature variations and performs in extreme low arctic temperatures as well as in tropical climates. The climate, in which a VDH-tester is set up, has no influence on the performance of the equipment. This is why you can find VDH-nameplates in aluminium casting plants around the world, whether in China, Brazil, South Africa or Germany, – “except in Japan,” Wolfgang divulges. However, the formula 3.2 x 10-4 mbar x 1/s is valid there too, because it is standard for all suppliers of aluminium cast wheel rims who deliver to the renowned automotive manufacturers in the world. 

One hundred per cent of the OEM wheels run through these leak testers, on average about 200 wheels per hour; VDH has three different types to offer: The standard design covers wheel sizes ranging from 13” to 20”; due to the manufacturing of larger wheel diameters in the past few years, VDH offers a tester for wheel sizes 16” to 22” and an evolutionary design for 17/18” to 24” wheels. The larger the wheels get, the more likely it is that the average cycle time will be exceeded and the smaller the wheel diameter is, the likelihood of falling below the average cycle time is great. Up to 13 or 14 year old helium leak testers are still used in production today and are a testimony to the equipment’s longevity rather than for investments, which, after a short period of time, usually become obsolete due to technical improvements. Nevertheless, the costs for maintenance increase over time and constantly modernized controls and components positively influence the cycle times, etc.

Cast aluminium wheels are tested this way (no matter what the composition) however, forged ones aren’t. No arguments for the submersion tests in water, which was the leading testing method until the early 1990s, can be compared to the helium mass spectrometry testing; not in regard to measurement precision, reproducibility, objectiveness and process safety. In regard to the cycle times, the submersion tests in water are hopelessly inferior to the helium mass spectrometry method. However, water testing is not obsolete: Because the helium leak detection machine totals all leaks, it can be useful to test a wheel in a submersion tank, which was clearly sorted out as a leaker in the helium tester, to determine where exactly the wheel is defect and shows a leak. By localizing the exact place of the leak in the submersion tank, potential problems in the production process of the aluminium wheel can be identified and possibly resolved so that the number of rejects can be kept under control.

In times of growing automation in production processes and the increasing demands of the automobile manufacturers, which regularly want to see the plants of their suppliers to be audited and certified, testing methods like water submersion are hopelessly old and obsolete. The high-tech testing procedures as carried out with the helium leak detection machines ensure that the product is technically flawless. This makes all the difference, because wheel rims are safety-relevant parts on an automobile.