Hennecke said that to receive 4-star or 5-star ratings for their vehicles, manufacturers must make greater efforts to ensure pedestrian protection. The engine bonnet is critical. It should be designed to absorb as much energy as possible in a collision with the body. This requires free space underneath the bonnet. In current motor vehicles, all of the space in the engine compartment is filled.
Hennecke added that as a result, manufacturers have developed quick-acting systems that raise the bonnet in a collision while some are fitted with additional airbags. These are expensive, technically complex and need maintenance. They also take up more space and need design compromises to work.
Magna Steyr, part of Magna International, used its expertise in sandwich technology to develop and produce exterior parts in series, said Hennecke.
The resulting fibre composite bonnet has been produced with support from Ruhl Puromer and Hennecke. It is based on using fibre-reinforced polyurethane in an interlaced paper honeycomb structure.
The bonnet needed to meet Class A surface standard.
Ruhl Puromer from Friedrichsdorf, Germany, developed the PU system and Puropreg system to make honeycomb sandwich support structures. Ruhl also developed Purorim, which uses a Reaction Injection Moulding (RIM) process to ensure the required surface quality.
Hennecke’s PURSeite PU mixing and metering system was chosen to process the materials.
After the development period, series production of the bonnet is now imminent.
Hennecke said that, in principle, the sandwich structure of the bonnet resembles the design of a load-floor for luggage compartment system. A honeycomb core is used for the production of the bonnet, with glass fibre reinforcement applied from above and below. To achieve the different compression hardnesses and stability required in the bonnet, as might be needed for hinges, the honeycomb core is designed as a reinforced structure at the relevant points, Hennecke said.
Afterwards, the PU matrix is applied using the PUR-CSM spraying process. In this patented spray-up approach, the semi-finished fibre products are wetted on both sides with a thermally activated PU system. This makes it possible to apply a thicker layer of material in specific, targeted areas of the component. The part is then compressed and cured inside a mould. In the next stage, the RIM process is used on the outside and around the outer edge of the bonnet to produce the paintable class-A surface.
The polyurethane spray coat creates a durable connection between the glass fibre and the honeycomb core, which ensures extremely high stability and torsional rigidity. The thickness and structure of the honeycomb core allows the crash performance of the bonnet to be adjusted as needed. If the bonnet is designed to extend down to the radiator grille at the front, this area then also corresponds to the regulations for pedestrian protection and allows the designers almost total freedom to design the front section of a vehicle.
The structural design includes other positive effects. In addition to the substantially lower weight, the bonnet has excellent insulating properties thanks to its honeycomb core. A noise-absorbent mat, which is almost inevitable in conventional bonnets, is not needed.
It also thermally insulates the engine and means that cold starts can be reduced, meaning lower CO2 emissions.
The bonnet has passed all of the comprehensive approval tests for use in the automotive industry – and naturally also the new requirements for pedestrian protection.
KraussMaffei was demonstrating a glass-reinforced polyurea process that allowed the roof part to be painted directly after moulding. This makes automotive part production “considerably easier because there is no need for intermediate processes such as priming and pre-painting,” said Nicolas Beyl, head of the Reaction Process Machinery division at KraussMaffei.
He added that “there is no need for manual work such as polishing and smoothing. It also significantly reduces costs.”
A roof panel for the Roding Roadster R1 lightweight sports car was being produced live at the show. The roof panel is made from a CFRP endless fibre in a quasi-isotropic configuration and has a surface area of about 0.6 m2. The part is 2 mm thick and its surface material is 0.2 mm thick. It has a fibre content of around 50%. A Henkel PU system is used as matrix material. A Ruhl Puromer aliphatic polyurethane system forms the special surface coating, which is also UV stable.
KraussMaffei added that cycle times are fast because the resin reacts quickly and speedy clamping movements give short process times and consistently high component quality.
Two RimStar Nano 4/4 metering machines equipped for high-temperature processes – in which material temperatures can reach up to 80 °C – were used to prepare the polyurethane resin matrix. The wear-optimised design of the pumps in the RimStar pumps are designed to be wear-resistant and to give long-lasting process reliability with current polyurethane matrix systems. The machines have de-gassing storage tanks and a precise, energy-efficient temperature control system right up to the mixing head.
Polyurethane is poured into a slightly open mould which then closes ensuring good fibre wet-out and helps to keep the fibres in place. The high-pressure mixing head is self-cleaning, says KraussMaffei, and this helps to improve product consistency. The variable nozzles allow pour rates to be altered mid-shot without changing pressure or quality, says KraussMaffei.
Additionally, the heated RIM mould has vacuum assistance and a seal to help improve the part quality, says KraussMaffei.
KraussMaffei used K to show how its Spinform technology could use polyurea to save customers money and produce good quality, polyurea-coated automotive components. The firm was showing an example automotive part produced on the GXW 550-2000/380 multi-component SpinForm