A single-shot production method
The Ex-Core process was discovered almost by accident, when Donkervoort’s development engineers noticed some of its foam sandwich materials expanding uncontrollably in the hot sun. It set off a light bulb and started the company on the long road to developing the correct type of foam insert and, with it, the Ex-Core process.
The foam had to be lightweight, with a specific rate of expansion at a specific temperature, with specific pressure on the carbon fibre and resins from the inside, and then stop.
This self-expanding foam then takes on some of the properties of the outer skin of the carbon-fibre itself, making a stronger product.
It took ten years to find the right recipe and to test and validate the foams to make the concept work properly.
Less complex, more versatile
Ex-Core is not just consisting in the recipe of the expanding syntactic foam. It’s the entire process, with uniquely designed “oven” tooling designed to function as directly as possible to precisely steer the process.
The tooling itself is made from carbon-fibre and it has integrated heating elements and pressure sensors, so it can precisely heat up the foam to push the carbon fibres out so they can be shaped by the tooling’s inner surface.
The tool itself is the Ex-Core mold, with the enormous benefit that internal pressure can deliver intricate, complex shapes that are unprecedented with carbon-fibre.
Yet another benefit is that Ex-Core produces fewer hidden defects inside its carbon-fibre shapes. Because it pushes out with internal pressure, it forces the fibres into every corner in a precise way, so there is no longer a requirement to design in extra material for assumed defects.
It can press the fibres against the tool at 2, 8 or 20 bar of pressure, depending on the recipe and the cure profile.
With no male and female tooling the Ex-Core system is also less complex for its specialists to operate and therefore there is less that can go wrong.
Conceived for automotive
Donkervoort developed Ex-Core for its own use, but quickly learned there was demand from other industries, like yacht makers, motorsport operations, bicycles, specialist sports and even drones.
The European Union’s SME2 grant program has challenged Donkervoort to develop a mass production method for Ex-Core within the next two years, and the company is well on its way to surge beyond its automotive base.
For all of the possibilities outside the automotive industry, one big opportunity is the car industry’s move towards electric cars. The batteries alone add hundreds of kilograms to electric cars, and any technologies that can reduce the mass of the rest of the car will be valuable.
In addition, Ex-Core reduces noise, vibration and harshness in the vehicle. NVH has proven very problematic in electric cars, especially those with CFRP structures, and Ex-Core products absorb them more effectively.
Additionally, Ex-Core increases energy absorption on impact, reduces risk of catastrophic structural failure after small impacts and is easier to repair than current CFRP monocoque structures due to the foam core.
Its automotive possibilities extend beyond EVs, though. This year’s European emissions regulations should be expensive for companies that don’t reach much lower targets, and those targets will be reduced again in 2025 and yet further in 2030.
Technologies: Other Processing Method