ISSUE 011 Autumn 2021 Candela C-7 hydrofoil speedboat dossier l In conversation: Robert Hoevers l Battery recycling focus l Vehicle dynamics insight l ZeroAvia hydrogen-electric aircraft digest l Motor materials

and dimensions of mating surfaces, so many different die-cut gaskets have to be produced, meaning that the number of parts in inventories is large. Robotic dispensing cells can produce a broad range of sealing patterns with low defect rates though, thanks to automatic and precise positioning of the gaskets. The two most widely used dispensing processes result in the cured-in-place gasket (CIPG) and the formed-in-place gasket (FIPG). In the CIPG process, liquid gaskets are applied to and cured on the housing before its lid is fitted, allowing the lid to be removed in service for repair or to replace components. FIPG results in a connection that is not intended to be detached, as the sealant adheres to both the housing and the lid. In liquid dispensing, the sealant has to be applied very precisely, with the flow rate perfectly matched to the robotic motion in order to avoid any inconsistencies that could lead to leaks or failures. Particular care must be taken over the knit, which is the point at which the stop point of the bead meets the start point. This level of accuracy relies on full process control and extensive monitoring. The dispensing equipment used includes eccentric screw pumps driven by computer-controlled servo motors. Depending on the sealant material and application, either static or dynamic mixing of two-part sealants can be used. With static mixing, the base and the catalytic curing agent are mixed before dispensing, while in dynamic mixing the nozzles are designed to bring the two together as they are dispensed. Dynamic mixing is preferred for applications in which mixing quality is crucial and material characteristics are challenging, such as when the ratio of base to catalyst is particularly large, when the pot life – the time for which the sealant is malleable after mixing – is short or there are significant differences in viscosity between the base and the catalyst. When these strictures don’t apply, simpler static mixing is sufficient. One issue with current constant-speed dispensing machines is that their speed must be held to that at which rounded corners can be dispensed. Such corners are the bottleneck in current processes. To address this, the latest technology intelligently varies the dispensing speed to achieve the shortest possible cycle time compatible with the best resulting seal. In an early adoption of more advanced dispensing, a German Tier 1 company has teamed up with one of the sealant suppliers who helped with the research for this article to bond connectors for an engine control housing. The application of the sealant follows a contour of long, straight lines and tight curves. Using the company’s adaptive dispensing technology reportedly cut the cycle time from 44 seconds to 29. The system achieved that by optimally matching the speed at which the nozzle moved and the sealant output rate to the specified contour, applying a large quantity of single-component silicone in the shortest possible time on the straight lines, then slowing for the curves to dispense the material as precisely as possible. Where needed, large dots of silicone were applied at the highest possible dispensing speed. Solid alternatives However, there is also a trend towards solid seals to eliminate curing time after assembly to speed up future high- volume EV production. For example, a 7 m battery housing gasket applied as a liquid has to be done in a four-step process that involves cleaning the mating surfaces, applying a primer and then the liquid sealant and, finally, curing. By contrast, large-format solid gaskets can be fitted in one step by robots. Any system that might have to be opened up during its service life for maintenance or repair clearly needs a seal that can be re-used, particularly if the system is large. For example, a large battery housing should not have a seal that has to be applied as a liquid, some argue. Advanced solid seal designs are now available that include elastomers to provide the flexibility for tolerance compensation and rapid response for dynamic sealing. They can also be formed with complex cross-sections incorporating features such as double lips for redundant sealing and hard inserts to act as force shunts to protect them from destructive mechanical overload. When the space available for radial installation is limited, pre-formed ‘press- in-place’ seals are a good option, with the seal pressed into a defined groove in the battery housing. Carefully matching the gasket cross-section and groove allows for very space-efficient seals, including ones with double-lip designs achieved by giving the seal an X-shaped cross-section. Simulation of seal designs and application is increasingly important for mass-produced EV systems, enabling designers to run through multiple virtual iterations (Courtesy of Henkel) Autumn 2021 | E-Mobility Engineering 71 Focus | Sealing