The future of mobility is based on complex designs: with several thousand cells, mechanical and electronic components, battery packs for electric cars can contain up to 10,000 individual parts, depending on their capacity. The already complex construction process requires both precision and cleanliness: metallic and non-metallic shiny particles in critical areas such as seals or electrical contacts can compromise the functionality of the batteries.
Foreign particles can impair seals, among other things, and lead to leaks. This is particularly critical in battery housings, as they must be hermetically sealed against water to prevent system failures. If particles come into contact with contact points, they can cause short circuits in the control electronics and thus promote malfunctions.
High cleanliness requirements
To prevent this from happening, manufacturers of electric vehicles and suppliers must work with as few particles as possible. Organizations such as the TecSa (Technical Cleanliness) industry association and the German Electrical and Electronic Manufacturers' Association (ZVEI) have defined what is known as technical cleanliness in corresponding guidelines. A component is considered technically clean if it does not contain any particles that impair its function or process. To achieve this, manufacturers must resort to clean production in special rooms and, if necessary, to specific testing methods, as specified by the Association of the Automotive Industry (VDA) in corresponding regulations, including VDA 19.1 and VDA 19.2.
This sets uniform standards for extraction, analysis, and documentation to ensure a harmonized approach to cleanliness testing. Manufacturers must always carry out the latter when critical assemblies or parts require it. In particular, sensors, oil lines, conductor tracks, and connecting elements in contact with them may require such an analysis to ensure the integrity of battery packs.
Focus on fasteners
Since complex fasteners play a literally crucial role in the battery packs of electric cars, these components are a particular focus: press-in screws, inserts, and brackets contribute significantly to stable and safe battery packs, securing covers and the battery pack inside the vehicle.
To ensure that the fastening solutions themselves do not pose a safety risk, manufacturers such as ARNOLD UMFORMTECHNIK subject them to analysis and subsequent meticulous fine cleaning to remove particles – especially when cleanliness requirements demand it. Particularly critical parts cannot do without such specifications. However, these vary from manufacturer to manufacturer and include different limit values with regard to the number and size of particles.
During forming, for example, connecting elements are created when external forces change the shape of a blank. Abrasion of the raw material used cannot be avoided, nor can it be avoided during subsequent inspection. The finished formed parts pass through camera systems at high speed and come into contact with each other, but also with the surrounding technology. In addition to these process-related particles, foreign bodies can enter the products from outside, for example through contact with work personnel.
Particles on the test bench
For critical components with corresponding cleanliness requirements, manufacturers carry out particle analysis, for which the VDA has established uniform standards. The test involves sampling followed by laboratory testing to determine whether products comply with certain particle limits. The particles to be analyzed can be obtained by wet or dry extraction.
In wet extraction, which is also used by ARNOLD UMFORMTECHNIK, particles are washed off the component using a spraying process described in VDA 19.1 and then collected with a filter. Particles larger than five micrometers remain in the filter. Dry extraction uses technologies to blow off or suck off the particles and also retains the particles by filtration for subsequent laboratory analysis.
The extracted particles are usually evaluated microscopically: measurement and classification are performed automatically, but the test personnel check the results, for example, in terms of metallic shine, non-metallic shine, fibers, or fusel. This provides information about the origin of the particles. In addition, an analysis clarifies whether the foreign particles detected are within the limit values. In most cases, cleaning is planned in advance and does not only take place when limit values are exceeded.
A wide range of cleaning options
Various processes can drastically reduce particles in the micrometer range. These include cleaning processes using solvents, water, or modified alcohol, which are used, for example, on joined parts made of galvanized steel, copper, and aluminum. In the clean room, special cleaning systems remove particles from the connecting elements. Appropriate cleaning media and swivel movements ensure removal.
Protection against recontamination
Tested and cleaned products are ready for packaging. Clean packaging in accordance with VDA 19.2 serves to ensure the technical cleanliness of components during transport, storage, and preparation for further manufacturing or assembly processes. Established processes for the production of multi-layer transport packaging for products with technical cleanliness requirements provide a remedy: they fix the parts in place inside the packaging and enable layer-by-layer unpacking.
The patented Cleanpac® concept involves products that are covered with a lid. In many places, robots take over the processes to avoid contamination risks caused by humans. A film layer then covers the lidded tray before it is welded in place. The individually positioned products do not rub against each other during transport, which prevents abrasion. Clean packaging should also be easily recyclable and not become a source of particles itself.
It goes without saying that cleanliness and testing requirements vary depending on the component being joined: different parts serve different purposes and therefore require a tailored approach. With individual analysis and cleaning, manufacturers of connecting parts can set the course for the technical cleanliness and safety of battery cells – but also for the development of new solutions. Sharp burrs or deep undercuts can be reduced through careful design, with positive effects on the production of connection solutions. Leading manufacturers therefore test their solutions early on for possible particle sources in their own screw connection laboratories – paving the way for safe e-mobility.
Leading in testing and cleaningARNOLD UMFORMTECHNIK has set standards in the definition and implementation of technical cleanliness: The Forchtenberg-based company has been working closely with the VDA for many years and has produced the two volumes of “Quality Management in the Automotive Industry” in cooperation with the Fraunhofer Institute in Stuttgart. With Cleancon®, the manufacturer of innovative fastening technology also offers a service package that includes cleaning, batch-accompanying analysis, coating, and clean packaging of fasteners. The company laid the foundation for this back in 2008 with a corresponding cleaning system and the multi-layer packaging concept CLEANPAC®. In its “Fastener Testing” center, ARNOLD UMFORMTECHNIK subjects fasteners to comprehensive testing before and during production. |
About the ARNOLD GROUP
The ARNOLD GROUP, internationally renowned for innovative fastening technology, has become a leading supplier and development partner for complex fastening systems thanks to its extensive expertise in the production of intelligent fasteners. Under the umbrella of “BlueFastening Systems,” the company positions itself as a comprehensive provider of engineering, fasteners, functional parts, feeding systems, and processing technology. This holistic combination of experience and expertise offers efficient, sustainable solutions on an international level. ARNOLD has been part of the Würth Group since 1994.
