26 November/December 2023 | E-Mobility Engineering of changes in outside pressure, for instance if the packs are driven up mountains or flown in aircraft. The company will also integrate and use separate burst discs for thermal runaway scenarios. Module manufacturing Production of Hibernium modules begins with manufacturing and assembling the structural components and the Xerotherm system, after which comes the installation of the cells, foam, wire bonds and covers, followed by pack assembly. Xerotech’s manufacturing facilities contain injection-moulding systems, including a 100 t all-electric moulding machine, along with five-axis milling machines for CNC-cutting mould tools from metal billets; a spark erosion machine is also used for high-precision machining. Some jig fixtures also use these machines. One of the most critical injectionmoulded plastic components is a ‘separator plate’, which is an ABS frame composed of circular slots, six slots long and 16 wide, for holding 96 cylindrical cells in place. That enables installations of cells in groups of 96 at a time in modules and packs. Also injection-moulded are the module housing walls, coolant nozzles and MSD housings. There is also an eight-cavity metal mould tool used for forming the nozzles from ABS. As each module is 16 cells wide, eight ducts per module is standard, making for 16 nozzles (or two batches off of that mould) for each duct to have an inlet and an outlet. Before injection moulding, solid plastic parts and some manufacturing jigs are prototyped in Xerotech’s additive manufacturing (AM) facility, where 20 Prusa i3 Mk3 fused deposition modelling (FDM) printers extrude plastic components for validation. “It takes 6-12 weeks to make a mould tool, depending on its complexity, so AM is really useful for rapid prototyping,” Dr Flannery comments. “Some FDM printers we’ve used would skip layers or just break, but we’ve found the Prusa Mk3s have very good repeatability, and we’ll soon be buying a fleet of Bambu printers for prototyping parts in a V-0 ASA, which we’ll validate for potential safety gains. “In future, we’ll also investigate how multi-jet fusion and selective laser sintering printers could make plastic parts that we might only need for a few bits per pack but are too geometrically complex for injection-moulding.” Most of Xerotech’s proprietary machinery has been developed for manufacturing the coolant ducts, along with other plastic-related processes including joining plastic parts and assembling modules, along with processes requiring robotic or pneumatic machines. By analysing its production flows, the company periodically identifies bottlenecks and develops custom machines (or iterates existing ones) to reduce them. “Something like finding the speed at which we weld two pieces of plastic together to be too slow will drive a requirement to eliminate the process or make a more robust machine,” Dr Flannery says. “Less prioritised but still important is looking into potential cost savings from designing and building machines more tailored to our processes and components. We never outsource the building of one of our own machine designs, as we’ve found that’s far too expensive and requires transferring a substantial body of knowledge for the manufacturer to get it right.” The coolant ducts begin life as plastic pellets that are shipped into Xerotech’s facility and blended with proprietary materials to achieve the correct plastic formulation. That compound is then extruded through a tube-shaped die, before being blown with air to produce the thin-film walls and long form of the duct. After quality checks, the ducts are joined to the injection-moulded plastic nozzle subassemblies using proprietary heat welding processes optimised inhouse over several iterations. “Our current plastic-welding system is a fifth-generation machine, and is controlled precisely for timing, temperatures, pressure and geometries of the parts and the welding surfaces,” Dr Flannery says. “We’ve also come up with our own quality checks to determine whether a weld is good or bad, because no-one else is working with something like our ducts and sub-assemblies. If you’re making a One of Xerotech’s injection moulding machines; a metal mould tool is visible inside, beyond the cables on the left
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