MICHAEL SOMMER, DIPL.-CHEM. DIRECTOR, SALES AND MARKETING MENZOLIT COMPOUNDS INTERNATIONAL GMBH, GERMANY
(Published on July-August 2007 - JEC Magazine #34)
Composites have been used in automotive and truck applications since the early 1950’s. Major reasons for using them in automotive were weight reduction and design freedom at lower cost, with yearly demand ranging between 30,000 and 80,000 vehicles. In truck applications, the cabin (or at least parts of it) is usually designed in SMC to take advantage of the excellent corrosion resistance of those materials. In the USA, all truck cabins are made from composites, mostly SMC, and many car models have parts made from SMC, or even the whole exterior (Thunderbird, Corvette). In Europe, many luxury vehicles have SMC parts due to the volumes that make SMC much more competitive than sheet metal.
More than half a century of SMC
Original equipment manufacturers (OEM) in the automotive industry started using SMC in 1950 with the first Corvette and, in Europe, with Renault 5 bumpers and functional parts. Slowly, more and more parts were developed using the performance of SMC and BMC to fulfil the needs of those days.
In the 1980’s, demands increased for appearance on cars, and “Class A” was implemented as a surface quality equivalent to good steel parts. On modern trucks as well, superior surface quality is a demand that has changed the appeal of trucks, even though the surface quality is not exactly the same as for passenger cars.
Over the past eight years, however, new requirements have changed SMC and BMC utilisation and manufacturing. Among these are reproducibility demands, specially for larger series and with the use of SMC and BMC parts on high-end models such as the Mercedes-Benz CL (SMC decklid), and requirements coming from legal or environmental standards. The fact that functions can be integrated into the part also leads to more exciting developments. Finally, the on-line paintability of SMC is used more and more to get a perfect colour match in hybrid solutions with steel or aluminium.
Modern processing requirements
OEM’s also have increased their quality and cost requirements, and a modern part-manufacturing process has to fulfil those criteria. As a result, several part manufacturers have invested in fully automated production lines that handle the SMC or BMC from the start of the process up to the final primed part that goes into E-coat and ESTA (electrostatic) painting afterwards. In terms of research & development and production, this means more accurate processing control so that the robots can use the material. This applies to both SMC compression moulding and BMC injection moulding.
This also requires increasing the packaging weight of materials, especially that of SMC rolls. From a standard packaging used in the industry, Menzolit was the first to implement the Jumbo roll, carrying up to six times more material than the commonly used rolls.
Modern chains processing SMC parts for exterior applications are based either on a complete product flow after moulding through a primer station, to ensure better paint adhesion afterwards and create surface conductivity for the electrostatic painting process, or on total off-line painting together with other plastic fascia parts such as bumpers.
For many OEM’s, however, on-line painting is an easy way to optimise the colour and surface structure match between the SMC parts and the other steel or aluminium parts on the bodyin- white during ESTA online painting. The extremely high drying/curing temperatures of the E-coat require the SMC part to withstand a temperature of 200°C for at least 45 minutes without deformation, bonding structure or surface appeal. Menzolit developed special materials for this application, the SMC 0400 compounds, which have been homologated and are in use at several OEM’s.
The integration of functions is achieved not only by integrating parts and functions into the mould (which requires excellent flow properties of the material), but also after moulding. SMC parts are transparent to antenna waves. New vehicles like DaimlerChrysler’s CL or the new Volkswagen EOS have antennas integrated into the inner decklid side so they are not visible, but are fully functional. Antennas for radio, mobile phone, door opening system, GPS and others are integrated here.
Many improvements have also been implemented in the injection moulding process. Fully automated lines mould the parts, demould them, clean them and then send them to priming and metallizing for extremely nice-looking headlamp reflectors. Clear polycarbonate windows have replaced glass on headlamps, so that the scattering area is now in the reflector instead of the glass, and the parts have to be very accurate in dimensions and have a very low elongation at high temperature. As they are visible from the outside through the transparent polycarbonate, perfect surface quality is required too. Menzolit offers a compound meeting all those demands for modern reflectors: BMC 3100. To reduce the production cost of headlamps, recent development has involved attempts to avoid the primer step. A special BMC compound has been developed to ensure good anchorage of the metallization directly on the unprimed finished part.
|Menzolit, a split of the former Menzolit-Fibron group, specialises in the development, marketing and sales of compounds such as SMC (sheet moulding compound), BMC (bulk moulding compounds) and CIC (continuous impregnated compound). |
These materials are fibre-reinforced thermosets that are compression, injection or injectioncompression moulded. Menzolit has a central R&D laboratory in Vineuil, France, with facilities to develop, mould and test the compounds. SMC is produced in Menzolit’s four plants in France, Italy, Spain and the UK. BMC is produced in France, Italy and the UK; and CIC, only in France. The company serves major tier-one suppliers and OEM’s in Europe.
Legal and environmental requirements
To meet the legal and environmental requirements for parts, Menzolit had to take into account several aspects: emission, fogging and smell for meeting CARB 2000, further weight reduction for better fuel consumption, and the EU regulation on end-of-life vehicles (ELV), achieving eco-balance, and recycling.
The implementation of the VDA and CARB (California Air Resources Board) emission standards required drastic changes to the formulations to meet the low emission demands of the individual part and of the whole vehicle according to the CARB regulation. In co-operation with the raw-material supplier, an acceptable level was achieved. Fogging was also reduced by eliminating certain raw materials, and smell was drastically reduced by changing the organic materials used in the formulation.
To save even more weight versus steel, low-density materials were homologated at the OEM’s and are now used in the new Mercedes-Benz CL decklid. Under the bonnet, SMC 1400, BMC 1400 and CIC 1400 are used more and more for valve covers, oil sumps and carburettor housings, because of their improved strength and temperature performance compared to thermoplastic materials, and their excellent resistance to automotive fluids. The weight reduction potential is significant, as fibre-reinforced materials do not require high part thickness. For truck engines, one of the demands is that the engine be able to stand on the oil sump if the engine is dismantled for repair purposes.
To meet the EU regulation on end-of-life vehicles, a recycling concept was developed and a company called European Composite Recycling Concept (ECRC) was established in Brussels to develop recycling solutions for composite parts. An ecological impact study carried out by BASF proves that the ecobalance of SMC parts (here a decklid) is very positive, especially when compared to steel and aluminium.
Considering the yearly number of vehicles for which SMC and BMC parts are feasible, it is clear that there is no limitation for smaller injection-moulded parts. The short cycle time of stateof- the-art Menzolit compounds and the ability to have multiple cavities allow an extremely high output per hour.
For larger compression-moulded SMC parts, there are limitations for steel and SMC in mass production (see graph below).
Assuming that a vehicle has a lifecycle of nine years and “facelifts” after three and six years, the graph indicates that, for an annual volume of 60,000 vehicles, SMC is definitely the best choice in terms of cost. One tool only is required for the inner shell and one for the outer shell, and the total costs are much lower than for a sheet-metal solution. As steel parts need five tools to form the inner shell and at least five tools for the outer shell, tooling costs are tremendously high for volumes under 100,000 p.a.
But even at a volume of 150,000 p.a. with three tools each for inner and outer shell, SMC becomes worthwhile if facelifts are implemented as described above.
In the automotive industry, SMC, BMC and CIC materials are widely used for structural, exterior, functional and engine applications. With the recent developments and adaptations of Menzolit, there is a great potential for the materials to fulfil the changing requirements, especially for fuel consumption and CO2 emission.
The latest developments are CarbonSMC® and AdvancedSMC®, a carbon-fibre-reinforced material used for the Mercedes- McLaren SLR’s scuttle panel, which forms a part of the body-inwhite structure of the vehicle. Carbon-fibre compounds can further reduce the part weight.