The automotive sector is honing its sights on lightweight vehicles. The trend is conditioning producers of materials and technology in the field of plastics
The automobile industry has set itself the target of curbing fuel consumption and polluting emissions, and has identified weight reduction as the leading strategy to meet this goal. To this purpose, the use of thermoplastic composites with their good mechanical strength, thermal and chemical performance for an increasing number of structural or parts in the engine compartment appears to be an increasingly promising solution.
A good example is provided by PSA Peugeot Citroën, the second largest car maker in Europe. The ambitious but feasible project is to lighten the total mass of vehicles by an average of over 200 kilograms by 2020-2025. This would permit staying below the threshold of 95 grams of carbon dioxide (CO2) a kilometer in average emissions for car makers required by the EU regulation. «100 kilos less means a 10 gram reduction per kilometer of CO2 emissions: for example, in the engine compartment alone, replacing metal with reinforced plastic reduces the weight of each vehicle by about 11 kilos» Patrick Cazuc, European director of DuPont Performance Polymers notes.
In collaboration with Peugeot Citroën, DuPont has developed a side impact beam, which has led to a 40 percent weight reduction compared to the original beam, made from ultra-high hardness steel (UHHS): the composite material, furthermore, effectively absorbs kinetic energy and has passed crash tests performed by the French car maker. The part was produced incorporating new Vizilon technology, which uses an organic sheet (i.e. semi-finished thermoplastics reinforced with continuous fibre), combining the moulding technology with inserts and overmoulding. The process takes place in two stages to ensure optimal control of the orientation of pre-preg fibre, enabling the required stiffness and impact absorption capacity for the car’s structural or bearing elements: seat frame, crossbeams, bumpers and suspension systems.[box title=”Ultralight sumps” color=”#f8911b”]
«Since 2013-2014, the Euro 6 standards for emissions will spur a new generation of engines with the same limitations on emissions being imposed on diesel and petrol engines: producers therefore propose to reduce exhaust gas and fuel consumption equally. A trend under the bonnet, which meets these requirements, is to make oil sumps in 6.6 polyamide with a 35 percent glass fibre content» Klaus Bendl from ElringKlinger explains. The company has used Zytel by DuPont, a 6.6 polyamide reinforced with 35 percent glass fibre, for moulding two oil sumps mounted on diesel engines of Mercedes-Benz 4 and 6 cylinder lorries: they weigh 4.5 and 6.3 kilos, half the weight of the same pieces in aluminium, and are approximately 2 dB quieter. They integrate the oil sump unit and oil level sensors, they are resistant to impact. «The fluidity of Zytel has permitted rapid crystallization times and very fast moulding cycles – DuPont underlines –. The low viscosity of the melt ensures thin and intricate sections of the mould are filled to achieve accurate tolerance control, critical in such a large component».
The trend is confirmed by DSM Engineering Plastics, which provided Akulon Ultraflow K-FHG7 polyamide 6, filled with 35 percent glass fibre, stabilized to heat and highly fluid, for an application developed in collaboration with the French mould manufacturer Steep Plastique and Peugeot. The injection moulded oil sump weighs 60 percent less than the previous metal version.[/box]
A hybrid approach that combines engineering polymers and composites like the ones made by DuPont has also been adopted by BASF in its Ultracom package, devised as an integrated platform for the complete development of a product from concept to testing. A laminate composed of a continuous, uni-directional glassfibre-based fabric is impregnated with polyamide or PBT – the resins are selected according to application specifications –, preformed by heating in the mould, overmoulded with a thermoplastic compound, also PA or PBT based, and applied to a engineering polymer support with structural functions.
Developed with TenCate a manufacturer of composites and Owens Corning the supplier of glass fibre, the Ultracom technology comes to life in finished products in the pilot facility of Ludwigshafen (Germany), comprising a unit for automatically inserting laminate in the mould frame by means of a six-axis robot equipped with suction cups, an IR infrared heating station and a KraussMaffei KM 300 1400C2 injection moulding machine a with clamping force of 300 tons, interfaced with robot and temperature controller. Inside this cell, three semi-finished pieces are simultaneously produced automatically in the different process stages. Cycle times are approximately one minute, which is similar to standard overmoulding. At K 2013, BASF exhibited some pieces moulded using Ultracom technology: in particular an Ultralaminate impregnated resin based on PA6 in combination with Ultramid G12 COM with 60 percent glass fibre reinforcement as overmoulding compound. A second application example, designed for maximum impact strength, is a package of Ultralaminate and Ultramid ZG7 COM.
To ensure upstream and downstream compliance of the components with application requirements, BASF has developed the Ultrasim simulation software and the CIFO multifunctional test (Combination of In-mold Forming and Overmolding), which analyses more than twenty parameters to assess the characteristics and potential criticalities of the pieces.
Automation of hybrids
Composites make light and very sturdy plastic components, which can replace metal, enabling the auto sector to pursue its objective of reducing the weight of vehicles and CO2 emissions. Organomelt technology developed by Engel serves the purpose perfectly, because it allows the user to overmould a thermoplastic laminate (carbon or glass fibre sheet pre-impregnated with a thermoplastic resin) to make a light, rigid, very robust component of consistent quality and with acceptable production costs and times, even for lots that are relatively large for composites. The repeatability and productivity of the process are made possible by the help of robots for precise handling of laminates, crucial for determining the sturdiness of the item: the calibrated layout of pre-preg fibres, studied with the help of CAE simulations, determines the effectiveness of the component.
Hybrid Organomelt moulding consists of an avant-garde technology developed by Engel, which won it the Composite Innovations Award 2011 for the production process of a composite brake pedal, with optimized geometry to stand up to repeated stress and fully able to replace the metal component.
The final version of the process, which has been subject to continuous improvement to meet the needs of the automobile industry, has been presented at K 2013, where an automated cell will manufacture components ready for assembly without the need for post-process operations. Developed in collaboration with ZF-Friedrichshafen, the piece is made from an organic sheet, heated with an IR system, positioned by the Engel easix anthropomorphic robot, preformed in the mould and overmoulded with polyamide on the vertical injection Engel insert 1050H/200 machine. The component weighs 30 percent less than steel pedals, and offers comparable mechanical strength. The control unit of the anthropomorphic robot is incorporated into the injection machine, therefore the robots movements are coordinated and programming is easier: because the robot can access the injection machine’s, the grippers can enter the mould area while the mould is opening, slashing cycle times. Synchronization of movements is particularly important to prevent the pre-heated semi-finished parts from cooling before they are moulded. The multi-axis robot, with precise sheet positioning, guarantees consistent process quality.
Engel is rapidly establishing itself in the composites sector, for which it has already made complete systems for the production of lightweight parts made of carbon fibre impregnated with polyurethane or epoxy resin, thanks to the use of resin transfer moulding technology (RTM), of similar interest for its favourable cost/performance ratio. The system is fully automated, and its main feature is in the v-duo vertical press. This is a compact machine (the range is made up of models with clamping units of between 400 and 3,600 tons), of limited height to facilitate maintenance, and equipped with an energy-efficient ecodrive. At the K fair in Düsseldorf, an Engel v-duo 700 vertical press, incorporating a linear viper 20 robot, produced car body parts (doors) for the sporty X-Bow by KTM (cover photo), with a polyurethane resin by BASF reinforced with carbon fibre preforms supplied by Wethje.
Direct long fibre moulding
The mechanical performance of the reinforced composites is directly proportional to the length of the reinforcement fibres. In collaboration with Süddeutsche Kunststoff-Zentrum SKZ, the German injection machine manufacturer Arburg has developed a dedicated method for long fibre injection moulding (PIMC): it has produced a pair of airbag compartments using an Allrounder 820 S hydraulic press with a clamping force of 4,000 kN. The injection works in two stages: in the first, it combines the compound granules, in the second the 100 millimetre glass fibres are added in a feed pipe supplied by Coperion. The latter acts much like a twin-screw extruder: the fibres are cut into variable lengths in a rotary cutting system supplied by Wolfangel. The fibre feed device at the front end of the injection unit prevents the fibres from being damaged: mechanical shrinking during the metering step is reduced significantly.
The moulded parts are removed by a Multilift Select robotic system and arranged in a palletizing system: they weigh 330 grams and are produced in a cycle time of 75 seconds. Another significant competitive bonus of the system, according to Arburg, is the use of basic materials – polymer and fibre – that are less costly than reinforced engineering polymer pellets. The injection machinery manufacturer is planning additional developments of direct long fibre moulding. It is experimenting with natural carbon or glass fibre reinforcements, and working to integrate all the elements in the Selogica control system to deliver a complete production unit that is easy to manage.
Another interesting technology that the German machinery manufacturer is optimizing is the PCIM, a plastic injection process (ABS, PP or TPE) in a piece constituted of expanded polypropylene particles (EPP). During injection, the surface of the expanded polypropylene is cast in a predefined way: this creates a lasting seam between the two components. The advantages are clear. Light items are easy to manufacture (the density of the expanded polypropylene particles is between 20 and 60 grams per litre), that guarantees excellent performance in terms of durability, shape precision and functionality.
In a single cycle
The production processes that apply the concept of hybrid moulding share the common feature of a process in two stages – laying and preheating of the laminate, and overmoulding. Toshiba Machine (whose presses have been distributed in Italy by EPF Automation since this year) further rationalizes the two stages to reduce the cycle time by eliminating the pre-heating stage. The heart of the direct injection moulding system is the inline compounding of long fibre CFRP (carbon fibre reinforced polymers). The EC100SX-2AP injection unit is the centrepiece of a plant in which carbon fibre filament feeding takes place in the single-screw extruder at a strategic point, in order to prevent the filaments from being damaged during mixing. In addition, the design of the extrusion screws was devised to facilitate the uniform distribution of the fibre in the matrix.
The system permits the reinforced components to be produced with pre-pregs characterized by a tensile strength of 785 MPa and good mechanical performance, modeled into the desired form by pre-heating in the compression mould with an infrared system – specially optimized to control the orientation of the fibres – and injected with resin reinforced with carbon fibre. This all takes place in a single process stage.
An example of application was developed using the Tepex D Dynalite 201 laminate by Bond Laminates (a subsidiary of Lanxess), consisting of a 6.6 polyamide matrix with reinforcement carbon fibres by Toray. The system includes a single-screw in-line injection machine EC100SX-2AP interfaced with a Scara TH850A robot for a repeatable positioning of the pre-preg, an infrared heater reaching a temperature of 240 °C, in other words near the melting point of the polyamide. The pre-preg is reinforced with overmoulded ribbing. Components made using this process weigh one quarter compared to similar components in steel and their rigidity is approximately 1.7 times higher.
More resistant than steel, aluminium and magnesium, Tepex thermoplastic composite laminates by Bond Laminates (a registered brand of Lanxess) «Are ideal also for light car parts: rapid cycle times and superior process repeatability permit the manufacture of 3D objects at a relatively low cost, competitive compared to thermosetting composites – Christian Obermann, managing director of the company says –. Polyamide is the most commonly used matrix for structural applications, but polypropylene, TPU and PPS are also used, while aramid, glass and carbon are used as continuous fibres.
Generally, fibres are the same length as the finished component, a characteristic that makes them extremely rigid and robust. Impregnation of reinforced semi-finished parts, previously a challenging technology due to the high viscosity of the mixes, is facilitated by the adoption of a technological innovation in compression moulding, that allows the manufacture of large components with large-scale and tailor-made, uniform impregnation. Because of the adhesion between the two plastic materials, laminates back-injected with polyamide 6 have proven in torsion tests to be similarly rigid but stronger and with a greater impact energy strength than polyamide or metal hybrids – 50 percent and 65 percent respectively».[box title=”PUR-RIM bumpers and body parts in and PC headlights” color=”#f8911b”]
Polyurethane is now lighter, and Bayer is taking advantage with its Bayflex Lightweight polyurethanes, with reduced density compared to products in the Bayflex 180 series, and have a similar or lower weight compared to polypropylene matrix materials traditionally used for car body parts. Products such as Bayflex 180 are normally used for non-structural parts subject to impacts, such as bumpers, wheel boxes and parts for car bodies generally, thanks to the integration of reinforcement mineral fibres in the polyurethane matrix.
Bayflex RIM Lightweight has been conceived for reducing density by approximately 30 percent while maintaining superior mechanical strength. This goal has been achieved thanks to the integration of carbon fibre reinforcement as an alternative to traditional mineral fillers, making the product particularly suited for the production of bumpers and parts of car bodies for sports cars. In the case of Bayflex RIM Lightweight polyurethane, Bayer has also developed formulas that use carbon fibre recycled from waste from processing CRP components (Carbon Reinforced Plastic): fibres 500 micron in length deliver the desired mechanical characteristics.[/box]