Driven by fuel economy and emissions regulations, the automotive industry continues to develop composite materials for light vehicles:
· Current US company average fuel economy (CAFE) standards require an average vehicle fuel consumption of 54.5 mpg (23.2 km / l) by 2025. (Note: President Trump has proposed to reduce these standards, but as of early November 2019, this reduction has not yet been implemented.)
· The average fuel consumption (CAFC) of Chinese companies has set a vehicle target of 20 km / l by 2020;
· The EU emission regulations stipulate that by 2021, carbon dioxide emissions must be only 95 g / km, a further 15% reduction by 2025, and by 2030, carbon dioxide emissions will be reduced by another 30% compared to 2021.
Chris Reed of Composites Forecasting and Consulting Co., Ltd. (Mesa, Arizona, USA) estimated at the CW Carbon Fiber 2017 Conference that the carbon fiber market in automotive applications exceeds 7,000 metric tons per year and there are currently more than 100 models designated OEMs Components use carbon fiber reinforced plastic (CFRP). He predicts that by 2025, this market will grow to nearly 11,000 metric tons.
China is the world's largest auto market, with 27.8 million cars produced in 2018, including all passenger cars, light commercial vehicles, trucks, buses and coaches. In contrast:
· The United States produced 11.3 million cars
· Japan produced 9.7 million vehicles
· India produced 5.2 million cars
· Germany produced 5.1 million cars
· Mexico produced 4.1 million cars
· South Korea produced 4 million cars.
Therefore, it is not surprising that the composite structures (not only high-end options or concept / prototype models) used in actual mass production vehicles are led by Asia and Europe. The recently released composite parts product projects of the Chinese automotive industry include :
· HBSS Automotive Lightweight Technology Company announced that JMC will use advanced composite materials in the pickup boxes of its new Yuhu 3 and Yuhu 5 pickups. material.
· GZJF Composites Technology Co., Ltd. and system supplier Brose Fahrzeugteile (Coburg, Germany) collaborated to develop a door module that uses three types of KingPly organic sheet and KingStrong unidirectional belt and is reinforced with pultrusion PP-LGF injection molding With ribs and complex surfaces, Ford Focus is 35% lighter (1 kg) compared to the PP-LGF 30 door module bracket.
· Magna Automotive Exterior Systems and Guangzhou Automobile Components Co., Ltd. (Guangzhou, China) formed a joint venture to start the production of thermoplastic composite materials (TPC) for cross-border vehicles of global automakers from the end of 2018.
BJKD Composites Technology Group (Hong Kong) and Beiqi Automobile signed an agreement to establish an Industry 4.0 smart factory in Changzhou, starting production of CFRP body and other parts in 2019, and will expand to an annual output of 6 million parts-an annual output of 66,000 tons The carbon fiber plant will start production in Rongcheng in 2023;
· JSHR commissioned Carbures (El Puerto de Santa María, Spain) to produce the first rapid porous injection compression molding mass production technology (RMCP) automatic composite material production line.
Polestar, Volvo's new brand electric high-performance car company, started production of the first model Polestar 1 at its new Polestar production center in Chengdu in 2019.
General Motors (GM, Detroit, Michigan, USA) launched the industry's first carbon fiber composite pickup box in 2018. GM actually built the first composite box for full-size trucks in 2001, but the use of Silverado and Sierra Pro-Tec box options is only 10% of what GM expects. Therefore, it waited more than 15 years before being tried again. The CarbonPro pickup box is also an option, and in 2019 GMCSierra was jointly developed with Teijin Automotive (Tokyo, Japan), which acquired Continental Structural Plastics (CSP, Auburn Hills, Michigan, USA) in 2017. Has experience in manufacturing composite material boxes for Honda Ridgeline and Toyota Tacoma trucks, both of which are made of chopped glass fiber sheet molding compound (SMC). When the first-generation Honda car box debuted in 2005, it was 30% lighter than steel, but its 2017 update did not use SMC on both parts, but instead chose direct long fibers for the side walls and headboard Thermoplastics (D-LFT) and short fiber blends for spare tire trays are injection molded using fiberglass and polypropylene (PP). The 2019 GMC CarbonPro box also uses Teijin's Sereebo thermoplastic composite manufacturing process. This process combines 20 mm long carbon fiber felt with nylon 6 and performs compression molding. The part cycle time is 60-80 seconds.
This growing trend in the use of thermoplastics in automotive composites has benefited from processes such as secondary molding. In this process, blanks (called organic sheets) made of woven or unidirectional fibers in a thermoplastic matrix It is compressed into a three-dimensional shape, while reinforced plastics are injection molded on and around the top to form complex geometric structural ribs, bosses, inserts, and connection points. Components under development or production include seat backs, seat back plates, airbag shells, A and B pillars, door beams, bumper beams and large floor components. Although overmolding is usually thermoplastic, the Opto-Light project managed by the Aachen Integrated Light Structure Center (AZL) at the University of Aachen, Germany, demonstrates thermoplastic overmolding on thermoset carbon fiber / epoxy resin housings, with 2 The cycle time of minutes generates the three-dimensional structural part of the BMW i3 floor in the fully automatic unit. The project also demonstrated the ability to monitor the state of cure through Netzsch Gerätebau (Sebour, Germany) in-mold sensors to achieve thermoplastic to thermoset connections without the need for laser ablation as an intermediate step. The second step is to stop the compression molding of the high-performance, low-creep thermosetting shell at the optimized time to leave enough reactivity in the epoxy resin to achieve covalent bonding, hydrogen bonding and / or secondary molding. PA6 thermoplastic semi-interpenetrating network.
It is worth noting that the demo part of Opto-Light starts with a unidirectional (UD) band. Compared with woven or non-crimped fabric (NCF) reinforced materials, the trend to use UD tape to reduce waste continues to grow. Because the fiber tape can be accurately cut and placed, almost no waste is generated, and the fibers can be aligned more accurately to match the load. A classic example is the CFRP rear wall of the Audi A8 luxury sedan, which was produced by Voith Composites (Gaxing, Germany) on a fully automated Industry 4.0 production line. Compared with three to five welded aluminum parts, it can reduce the weight by 50% and reduce the torsional rigidity of the drive unit by 33%. The rear wall starts with 35K carbon fiber from Zoltek (St. Louis, Missouri, USA), spreads the carbon fiber into a 50 mm wide adhesive UD tape, cuts it and places it at a specified angle to form a customized blank machine in a single—the Voith Roving Applicator. The blank is formed into a 3D preform in a hot press provided by FILL (Gurten, Austria). When the press mold forms various areas of the preform that are clamped by the forming tool of ALPEX Technologies (Mils bei Hall, Austria), the The blank material can adapt to the applied pressure. Then, the finished preforms are injected into resin and compression molded using the Ultra RTM process developed by Audi. The process uses a pressure of less than 15 bar, while the high-pressure RTM (HP-RTM) is usually 140 bar. Therefore, compared with HP-RTM's 2500 kilonewtons, only 350 kilonewtons of pressure is required. Although VORAFORCE 5300 epoxy resin needs to be cured at 120 ° C for 90-120 seconds, the total partial cycle time is 5 minutes.
Another alternative to HP-RTM is wet compression molding (also known as liquid compression molding), which does use fast curing resin and NCF, but the pressure is also lower. The automated equipment does not need to inject the resin into the preform, but distributes the resin on the fabric and then transfers it to the thermoforming press. BMW predicts that without pre-forming steps, it can provide a production cycle of less than 90 seconds, and the cost of equipment is lower. Therefore, the use of wet compression molded parts is expected to increase significantly. Huntsman Advanced Materials (Basel, Switzerland) has developed a next-generation process called Dynamic Fluid Compression Molding (DFCM), which claims to have a fiber volume of up to 65% and can form more complex geometries.
In terms of exterior parts, ultra-lightweight SMC continues to develop in the direction below 1.0g / cc, carbon fiber is also gradually popularized, Polynt Composites (Italy Scanzorosciate), Aliancy (Schaffhausen, Switzerland) and CSP have added new SMC in the past few years Production lines, these production lines are capable of producing carbon fiber SMC. Polynt has also introduced Polynt-RE recycled carbon fiber SMC into its products, as well as UDCarbon and TXTCarbon composites with unidirectional and fabric reinforcement, respectively. The potential of these products is seen in the development of the former subframes completed by Magna International (Aurora, Ontario, Canada) and Ford Motor Company (Dearborn, Michigan, USA). The former uses local enhancements And the co-molded chopped carbon fiber SMC, the patch is made of carbon fiber 0 degree / 90 degree NCF. The SMC structural sub-frame must withstand huge loads, supporting the engine and chassis components, including the steering gear and the lower control arm that secures the wheels. Although only a development part, it achieved a 82% reduction in parts, replacing 54 stamped steel parts with two compression molded composite components and six secondary molded stainless steel inserts, while reducing weight by 34%.
Ford's Global Research and Advanced Engineering team worked with its British chassis engineering team to mix SMC and prepregs to redesign the production of steel suspension knuckles for C-class vehicles. By co-molding the carbon fiber fabric prepreg layer with the chopped carbon fiber SMC, a high-performance suspension knuckle with a complex shape can be produced with a cycle time of less than 5 minutes and a weight reduction of 50%. Other developments include hybrid carbon fiber / aluminum alloy versions of high-performance car suspension knuckles developed by Saint Jean Industries (Saint Jean D'Ardières, France) and Hexcel (Stanford, Connecticut, USA). Compared with the section, its stiffness increased by 26%. At the same time, Williams Advanced Engineering Company (Grove City, Oxfordshire, UK) developed a CFRP cross arm, which uses unidirectional carbon fiber and recycled carbon fiber nonwoven felt (weight accounts for 80% of composite parts) and Compared with the traditional aluminum version, it can reduce the weight by 40%, but its cost is comparable to that of aluminum forgings. Using the HP-RTM process called RACETRAK, part forming can be completed in 90 seconds, and the total cycle time including lamination is 5 minutes.
Pultrusion is another development trend. In 2018, L & L Products launched its Continuous Composite System (CCS) pultrusion product, which is made of polyurethane resin and glass, carbon or hybrid fiber reinforced materials for automotive applications such as side sills and crash structures. The CCS pultrusion process is designed to replace the traditional metal structure that requires the necessary rigidity of the separator. The process is lightweight, 75% lighter than steel, 30% lighter than aluminum, and economical. In 2019, the 2020 Chevrolet Corvette Stingray released the automotive industry's first curved, multi-hollow pultruded carbon fiber bumper beam. This part has been under development since 2016. This part is used by Shape Corp. (Grand Haven, Michigan, USA) using Scott Bader (Northamptonshire, UK), Crestapol urethane acrylate resin and Thomas Technik & Innovation (TTI, Bremervoerde, Germany) Radius-Pultrusion system production. Pultrusion once again became the top priority of the MAI Skelett project. This project thermoformed and overmolded UD carbon fiber thermoplastic pultrusion in a two-step, 75-second process to produce a BMW i3 structural roof component. Presenter. The part exceeded all previous version requirements, integrated clips for fixtures, and changed the crash behavior from brittle to ductile failure mode to increase the residual strength of the body-in-white (BIW).
The last trend is toward mixed metal composite structures. The system integrates the multi-material lightweight design of the "Multi-material, integrated, lightweight design for electric vehicles" (SMiLE) project, combining composite materials and non-ferrous metals to reduce the overall body-in-white structure of battery electric vehicles Quality and cost. The rear loading floor module uses eight layers of 60% by weight UD glass fiber reinforced PA6 Ultratape and 40% by weight glass fiber / PA6 Ultramid direct long fiber thermoplastic (D-LFT), both from BASF (Ludwig, Germany) Greek port). SMiLE has developed a new process that uses pre-cured fiber tape laminates and selective reinforcement with D-LFT where reinforcement ribs and complex geometries are needed. Then, it was placed in a die press with two aluminum profiles and several metal inserts, and quickly circulated to form a 1.3 x 1.3 meter part. The rear module is bonded and mechanically connected to the second hybrid / thermoset composite forward-loaded floor, made of RTM and carbon fiber-reinforced epoxy resin, with integrated metal inserts and a partial sandwich structure containing a polyurethane foam core.
In the FlexHyJoin project managed by the Verbundwerkstoffe Institute (Kaiserslautern, IVW, Germany), an automated process was implemented by laser pretreatment of the metal bracket and connecting it to the composite roof arch. The process allows the thermoplastic composite roof structure to be assembled into a metal BIW. Connected by induction and laser. This is achieved in a single automated production cell with integrated process control and online non-destructive testing (NDT) with a cycle time of 140 seconds.