Moreover, he says that the technology is not limited to battery structures, but is applicable to any component that demands cost-efficient, lightweight design.Įlsewhere in Germany, work over the last couple of years by a consortium of companies has developed a battery housing made from a glassfibre reinforced SMC (sheet moulding compound) mounted on an aluminium baseplate. Dr Weidmann adds there has already been encouraging feedback from the wider industry. The project involved the development of battery housings for a plug-in electric vehicle and a fully electric bus with OEM involvement, respectively, from Fiat and Iveco.
“It is a battery structure entirely made of polymers and composites that can contain any battery shape.” He adds that apart from light weight, cost-efficiency and electrical non-conductivity, the development facilitates a freedom of design encompassing both geometry and material choice to support “almost any application requirement including very strong flame resistance.” “It does not require any metal for structural reasons,” he states. He is confident that the resulting material and process combination offers an attractive mix of capabilities. Dr Weidmann notes that “no commercially available simulation solution exists.” The project did, however, successfully validate appropriate simulations for shrinkage and warpage and also for bonding behaviour in the latter case using a new methodology developed by Dr Weidmann himself. “But we are the only ones worldwide to have pushed it to such a large and technologically demanding 3D structure as a battery casing.”Ī particular issue that had to be tackled involved the prediction of shrinkage and warpage of the sandwich structures as well as the critical bonding development between foam core and composite facesheets. “This process of in-situ CFRTP sandwich moulding is very new within the field of thermoplastic composite hybrid injection moulding technologies,” he states. At present the required cooling time before the workpiece can be removed from mould is close to 120 seconds but Dr Weidmann is confident that much shorter times can be achieved.Īlthough sandwich-type material formulations are already a well-established means of achieving a combination of light weight and high strength, Dr Weidmann says that this project still boasts a number of innovative features. “The temperature of mould and material during processing is defined in a way that enables strong bonding between the foam core and composite face sheets.” He says that the required injection pressure is very low and that the injection of the foam core takes about five seconds. “This is basically a fusion bonding process of polymer interfaces,” notes Dr Weidmann. The outer layers are then mated with the foam layer in an injection moulding process that bonds them together to create the load-bearing capacity. “We introduce a thermal cycle locally just where we need to bend the contour to achieve the 3D preform,” he notes. Moreover, says Dr Weidmann, this ‘thermobending’ technique avoids a more generalised alteration of the crystalline properties of the material, which might otherwise cause problems during the actual battery housing manufacturing process. “The cut-outs and their specific contour enable a folding into the 3D preforms, similar to a packing case or carton,” explains Dr Weidmann. The necessary consolidation process is achieved using double belt presses, which Dr Weidmann describes as “the most cost-efficient way to manufacture thermoplastic composite laminates.” They are then ‘3D preformed’ in a procedure involving laser cutting and localised thermoforming that only introduces a heating and cooling cycle to those parts of the structure that need to bend to achieve the required shape. In the manufacturing process, the outer layers are first formed from a cross-ply unidirectional (UD) tape lay-up procedure. “Until now this has been very expensive, but our new material and process approach is much more competitive in cost-sensitive applications.” This is a classical way to follow a lightweight design approach in components and can be found in many applications,” he states. “The construction is based on sandwich architecture, which aims to achieve very high mechanical properties at low weight. Dr Felix Weidmann, who led the project, confirms the details.