34 May/June 2024 | E-Mobility Engineering Nick Flaherty assesses the various materials and processes used to seal and protect a battery pack Sealing the deal Sealing a battery pack safely is a key requirement for e-mobility systems. While there may be concerns about the ingress of moisture or dirt, there are also issues over venting gasses and preventing electromagnetic interference. As a result, the choice of materials and the processes for sealing a battery pack, including cleaning the surfaces, are a series of engineering trade-offs. Hot riveting The applications of hot riveting are wide ranging. Sometimes it is used to pre-fix a component, such as a busbar or a lead frame, in the production flow before casting, soldering, welding or wire bonding. It can also be used to post-fix a cover to the housing after applying a sealing adhesive to enable the assemblies to be transported while the adhesive is curing. In most cases, however, it is used for connections that need to withstand defined forces with vibration and climatic loads over the service life of a vehicle. Likewise, the range of products for which hot riveting is used is extensive. Typical uses include permanently fixing circuit boards in and on a battery pack or fixing covers with housings, joining busbars, insulators, cooling plates or microelectronic components. Processing battery cells requires special process know-how and a lot of experience, and different hot-riveting applications are used for battery packs. Busbars are fixed with rivet points, while the insulators, cooling plates or frames, and side parts or stiffening plates and spacer plates are caulked. There are also various material pairings, including plastic-metal, plastic-plastic, plasticFR4 and plastic-isothermal, that have to be considered. Since a large number of closely positioned rivet points are provided due to the component size, and the necessary holding force and stability, custom machines are used for these battery applications. When joining the assemblies, the expansion of the battery cells must be taken into account, so they must have a high assembly tolerance and be put together securely without any critical temperature input to the cells. At the same time, the joining applications must maintain high levels of strength.
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