Speciality chemicals company LANXESS and Kautex Textron, a Textron Inc. company, have been collaborating for several years to research whether battery housings for electric vehicles can be designed and manufactured from technical thermoplastics.
Together, they have developed a near-series technology demonstrator in a feasibility study. With a length and width of around 1,400mm each, the system is a technically sophisticated, large-format all-plastic housing part with a weight in the mid-double-digit kilogram range.
The goal of the project was to demonstrate the advantages of thermoplastics over metals in terms of weight and cost reduction, functional integration and electrical insulation behaviour.
“As a first step, we have completely dispensed with the use of metallic reinforcement structures while proving we can commercially produce these complex large components,” explained Felix Haas, Director Product Development at Kautex Textron.
Dr Christopher Hoefs, Project Manager e-Powertrain at LANXESS added: “Going forward, Kautex and LANXESS want to use the results of the cooperation to enter into development projects for series production with automotive manufacturers.”
Single-stage manufacturing process with short cycle times
The demonstrator was developed based on the battery housing of a C-segment electric vehicle. It consists of a housing tray with crash structure, a housing cover and an underrun (underbody) protection. The housing components can be produced in a single-stage Direct Long Fibre Thermoplastic (D-LFT) moulding process. LANXESS has optimised Durethan B24CMH2.0 as the material for the D-LFT moulding compound. Kautex Textron compounds the PA6 for the process with glass fibre rovings. The local reinforcement of the housing structure is carried out using continuous fibre-reinforced thermoplastic composites of the Tepex dynalite brand from LANXESS.
“The process enables shorter and thus more economical cycle times than the processes in which steel or aluminium are processed,” Haas explained.
No complex metal forming, fewer production steps
Today, housings for high-voltage batteries are primarily made of extruded steel or aluminium profiles. Depending on the vehicle class, the housing length and widths can be well over 2,000 or 1,500mm, respectively. The size, the number of components and the numerous manufacturing and assembly steps make metal housings very cost-intensive. For example, complex structures made from strand press profiles require many secondary work steps such as welding, punching and riveting. In addition, the metallic components must be protected against corrosion in an additional process step by cathodic dip coating.
“Plastics, on the other hand, can fully exploit their design freedom. By integrating functions such as fasteners and thermal management components, the number of individual components of a battery housing can be greatly reduced. This simplifies assembly and logistical effort, which reduces production costs,” said Hoefs.
Plastics are also corrosion-resistant and electrically insulating. The latter ensures, for example, that there is a reduced risk of the system short-circuiting. The low density of plastics and their potential for lightweight construction lead to significantly lighter housings, which benefits, among other things, the range of electric vehicles.
Complex mix of high requirements
High-voltage battery housings must meet a variety of highly demanding technical requirements. For example, they must be stiff and strong and yet be able to absorb a significant amount of energy in the event of a crash. This is tested via mechanical shock- and crush tests. The housings must also be flame-retardant in the event of a vehicle fire or thermal run-away of the electrical cells. Finally, the housings must be integrated into the vehicle structure.
“We continue to work together on optimising the production and structural design of the components. The aim is to carry out the majority of the development work virtually, in order to save costs in prototype design and to shorten the time to market of future series components,” concluded Hoefs.