Bugatti’s supercar gets a transparent PC roof

Bugatti’s record-breaking supercar with polycarbonate roof

Produced by KRD Sicherheitstecnik, based at Geeshacht in Germany, the grey-tinted targa top on Volkswagen Goup’s new Bugatti is the first commercial application for the BMS IR-absorbing colours, which are claimed to give polycarbonate glazing elements the same levels of IR protection as glass equivalents.

Weight and a proven record in glazing applications were key criteria in the selection of BMS’s Makrolon polycarbonate for the transparent and removable roof, according to Daniel Starmann, glazing project manager in Bugatti’s exterior engineering department.

"To make the roof easy to handle and also reduce its weight significantly, we opted to use Makrolon in our design. This polycarbonate from Bayer MaterialScience is an established material for series production of lightweight automotive glazing,” he said.

Despite measuring 1.23m long and 1.05m wide, the finished panel weighs just 5.6kg including the polyurethane sealing bead. The weight of the complete targa top assembly comes in below 14kg.

Bugatti’s production volumes rule out the use of injection moulding the roof panel. So KRD, which has a long track record in manufacture of lightweight polycarbonate safety glazing for special vehicle applications, developed a special thermoforming production process for the project.

Each roof panel is made from a 5mm thick sheet of Makrolon AG2677, a specially developed automotive glazing grade developed by BMS. The sheets are produced by Bayer Sheet Europe, which has developed an optimised extrusion technology to produce sheets with no streaks or surface defects that could compromise optical quality.

The grey IR absorbing colorant is incorporated into the AG2677 resin prior to extrusion and provides a direct solar transmittance value in this application of 5%. The same system can also be used in injection moulded glazing applications, according to BMS.

KRD prints each sheet to create a black border before thermoforming to the required shape. The formed parts are then coated using the AS4000 polysiloxane wet-coat system from Leverkusen-based company Momentive Performance Materials, which provides scratch resistance and UV protection to the polycarbonate.

The final step is to mill the edges ready for fitting of a polyurethane sealant bead, which is applied by BBG, of Mindelheim in Germany, in preparation for mounting in the carbon-fibre composite roof frame.

"The challenge for us, given the small quantities involved, was to quickly produce a component that satisfies the automaker’s strict test regulations and narrow tolerance requirements despite the numerous steps involved in the manufacturing process," says Korinna Brammer, managing director of KRD.

The BMS BayVision automotive glazing development team worked closely with KRD, BBG and Bugatti to ensure the complete roof system met all performance requirements. It carried out extensive CAE analysis to determine the precise location of the adhesive bead to prevent unacceptable distortion of the panel thermal expansion or wind loading.

Car enthusiasts wanting to put the new polycarbonate roof to the test should be warned, however. Prices for the Veyron 16.4 Grand Sport start from €1.4m.

Bayer MaterialScience will be presenting its latest developments in polycarbonate glazing materials and processing at the fifth Plastics in Automotive Glazing conference in Frankfurt, Germany, in November. Click here for more information about this event.