UK-developed composite chassis technology could enable low-cost, high-volume production of lightweight cars.
Many different materials are currently used to manufacture automobile chassis. For mass-produced vehicles, steel and aluminium pressings are most commonly employed; while for limited-production vehicles, such as racing cars, sandwich panels using hexagonal-cell honeycomb materials are used as a core in light-weight, adhesively bonded sandwich structures.
But all of the major chassis-manufacturing materials presently used – be they carbon fibre, extrusions, tubular frames, aluminium pressings or steel pressings – have their own limitations. Typically, the high-volume manufacturing processes require a very high investment in capital equipment, while the low-volume processes cannot cost-effectively be scaled up for high production runs.
Now, however, Dorset-based Inrekor has developed a lightweight structural panel that it claims can be used cost-effectively to build a chassis at whatever volumes a car manufacturer might demand.
The composite Inrekor two-dimensional panels are constructed through a process of lamination. In the process, a core of ARPRO expanded polypropylene plastic foam manufactured by JSP is coated with adhesive then bonded between two thin sheets of aluminium, after which the adhesive between the two faces is cured.Once the two-dimensional panels have been manufactured, they are bonded together to form a three-dimensional chassis.
Inrekor identified the ARPRO material as suitable for use in its composite panel because of its cost and the ease by which it can be moulded, as well as its energy absorption and insulation properties – all characteristics that make the finished panels a suitable alternative to aluminium honeycomb panels while not incurring any of the expensive associated CNC machining costs.
Each of the two-dimensional composite panels sport tongue-and-groove joints that interlock with one another, a design feature that guarantees a large surface contact area between each panel, ensuring that the panels bond effectively with one another when assembled to form a three-dimensional chassis.
Aware of the fact that joints bonded with adhesives are usually stronger in compression, shear and tension than in peeling and tearing, Inrekor has also patented several methods of designing the structures of the tongue and grooves in the panels, including the use of bespoke apertures inside them that it claims create anchor points that prevents peeling and tearing from occurring.
While most high-volume chassis manufacturers use three-dimensional moulded parts from which to construct their chassis, many expensive high-end vehicle chassis are also built up using similar two-dimensional aluminium parts.
While acknowledging that fact, Inrekor’s technical director Stewart Morley claims that the cost of manufacturing present-day two-dimensional chassis restricts such approaches to low production runs. ’Once you go above 3-4,000 cars per annum, then the manufacturing processes become prohibitive. We wanted to allow the cost signature of the panels to remain consistent whatever volume of chassis was required,’ he said.
“We wanted the cost of the panels to stay consistent whatever the volume of chassis was required”
Stuart Morley, Inrekor
As such, the company claims it is able to manufacture three-dimensional as well as two-dimensional panels if a manufacturer called for higher volumes of chassis to be produced.
Like other panels on the market, the Inrekor panel can incorporate internal air ducting, cable drawing and loom sets. To affix these to the panel, the core material can be manufactured with any number of static or flexible fixing points, allowing the bill of materials of all fixtures and brackets on a chassis to be reduced by hundreds of parts.
The company launched the product at an event in London where it showed a prototype of a two-door, four-seat, front-engine car chassis it built using the material, claiming that it reduced the weight of a comparable mass-produced chassis by 140kg – down from 300 to 160kg. Because of the mass reduction made possible by associated weight savings in other components of a vehicle, Inrekor believes the total weight reduction in a typical family car could be as high as 300kg.
To ensure the roadworthiness of chassis built from Inrekor panels, independent structural tests have been conducted by the Warwick Manufacturing Group and crash testing has been performed at MIRA. The MIRA crash tests, which involved subjecting the front end of the chassis to 1.3 tons at 66km/per hour, confirmed that it would meet the stringent five-star safety regulations set by the NCAP (National Car Assessment Programme).
To highlight how uncomplicated it is to design and build a chassis from the composite material, Inrekor worked with engineers at the Dorset-based Chesil Motor Company to create a chassis for a replica of a 356 Speedster, reducing its weight by 15 per cent in the process. While Morley designed the chassis from the material, as well as incorporating the suspension, wishbone systems and brakes, engineers at Chesil supplied the fibre-glass body shell that was then attached to it. The entire design and construction of the vehicle took a period of just 13 weeks.
As well as seeing a future for the material in custom and kit cars, Morley believes that its properties make it suitable for use in hybrid or electric vehicles under development at start-ups. He feels that these companies will be in the best position to take advantage of the new material.
Along those lines, he claimed that several electric vehicle companies had already approached the company to build their chassis structures after realising they could take delivery on as few as one to five chassis at a reasonable price due to the low initial capital outlay required to manufacture them.
The company has also disclosed that it is involved in two projects to build chassis for two major automobile manufacturers. While Morley was reluctant to disclose who they might be, he did say they were new vehicles that would be rolling off the production line in two-to-three years’ time.
While the company’s current projects have involved manufacturing both the panels and the chassis, Morley sees a future in which the company could simply make the panels then ship them to an automobile manufacturer in a flat pack, from which point they would be assembled in a clean environment to form a complete chassis. Such a move would mean that, rather than shipping several completed chassis in one container, 300 or 400 could be delivered simultaneously.
As word about the material has spread, so have enquires from manufacturers who have seen potential for the material outside the automotive arena.
At present, the company is tooling up its facility in Poole to manufacture containers for sensitive marine equipment found on boats.