JEC COMPOSITES MAGAZINE - Issue #45 - November/December 2008 - 55

Lighting 170-200°C, a 20-minute primer step at 160°C and a 20-minute painting step at 140°C, added to the environmentally costly pollution caused by volatile varnishes and residues, difficult to control and eliminate. To help synthetic materials hold their own against steel, we need to get away from the Class A concept, which practically doubles the cost of the drawn or moulded part. There are several solutions for dramatically reducing these costs. One is opting for matte rather than brilliant Class A-type finishes, which really have no functional raison d’être, but create distracting reflections and, barring continuous maintenance, lose their shine after a few months of use. We could easily save three to five hundred euros per vehicle by using matte paint finishes, like the ones on military vehicles or electrical appliances. Cost assessments in the automotive industry calculate down to eurocents, but the whim of a designer can raise that same cost by as much as a hundred euros − the justification being “the customer won’t like it if ” (see R-5 bumper above). By definition, styles change. Another, even better solution is to adopt an all-plastic/composite body with in-colour surface that is not subject to deterioration. a precursor for this). Other examples are the Aixam and Ligier mini-cars, which are made of thermoformed elements; - in the future, it should be possible to mould an entire shell directly in minutes on a dedicated moulding machine, eliminating the multiple parts (about 20,000 on a single vehicle), welded joints (about 3,000 points per vehicle), and dramatically reducing the required investment. Injection moulding would be the most cost-effective solution, but we don’t yet have the capability to make a TP composite incorporating long fibres using that closed-mould process. Thermoplastic composites Today there is another potential solution for creating a shell using a thermoformed or pressed long-fibre-reinforced thermoplastic composite, such as Twintex (long-glass-fibrereinforced PP), as shown in the estimated cost comparison below. The example is based on 2-m² body panels of roughly equivalent stiffness. Table 2: Comparative costs for a 2-m² body panel made of steel or of long-fibre-reinforced TP composite. 20-30 kg of paint Besides saving cost on investment (no more painting line), labour (no more varnishing step) and materials (no more primer, paint and varnish) and eliminating the need to recycle effluents, the use of polymers reduces the weight of the vehicle, both through the use of the more lightweight polymer and through the elimination of 20-30 kg of paint per vehicle! All the shell parts for Mercedes’ little Smart car are made of injected thermoplastic (a blend of PC and PBT), illustrating that it is possible to obtain attractive colours with moulded-in colour (a protective coat of varnish is applied, as well). For very large structural parts, the best solution is the use of compression-moulded, long-fibre-reinforced thermoset composites (SMC). SMC material is very suitable for auto bodies, but its natural colour is matte. Above all, a major recycling handicap is curbing its use: like all thermoset plastics, SMC is not reprocessable. It must be recycled in the form of fillers, for which there is limited use. Recycling SMC also turns out to be a losing proposition, cost wise. Sooner or later (and the sooner, the better) it will become absolutely necessary to switch to thermoplastics, which have a much shorter production cycle (only half as long) and can be reprocessed. For now, steel has the advantage because it is easily recycled. There are two options open to achieve the required mechanical properties, especially stiffness, using synthetic materials: - assembling elements made of injected engineering plastics such as the blends used for the Smart, or made of TP composites, using welding, adhesive-bonding or screw-assembly techniques on a bearing metal structure (the Citroen Mehari was Material Thickness (mm) Weight (kg) Price (€/kg) Material cost (€) Steel 0.6 9.4 0.7 6.6 Glass/PP composite 0.8 2.4 3 7.2 Drawing Process Investment (€) Cost allocation base (€/h) Cycle (parts/h) Processing costs (€) Mould (€) Mould incidence (200,000 parts) Finishing steps Cost per part (€) (2 drawing presses + cutting) 20,000 250 60 4.2 30,000 (2 moulds) 0.6 4 (painting) 15.4 Thermoforming Compression (1 thermoforming press + 1 NC) 5,000 60 10 6 15,000 (1 mould) 0.3 0 (no deterioration) 13.5 (press) 10,000 120 35 3.4 0.3 0 10.9 The costs are roughly equivalent, with a slight advantage for the TP composite that should enhance the economies of scale on materials consumption, and increasing productivity with acquired experience. Neophytes will object that a metal shell makes us feel safer, forgetting that Formula One race drivers are protected by composites. Whether or not the body is in steel or plastic has no effect on safety. At speeds upwards of 100 km/h – with or without seat belt or airbag – a frontal impact with a fixed obstacle like a wall or a tree will leave the car’s occupants either No45 November-December 2008 / jec composites magazine

JEC COMPOSITES MAGAZINE - Issue #45 - November/December 2008

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #45 - November/December 2008