The automotive industry continues to develop composites for lightweighting vehicles, driven by fuel economy and emissions regulations:
- Current U.S. corporate average fuel economy (CAFE) standards mandate a fleet average of 54.5 mpg (23.2 km/L) by 2025. (Note: President Trump has proposed scaling back these standards, but as of early November 2019, that scale-back had not been implemented.)
- China’s Corporate Average Fuel Consumption (CAFC) sets a fleet target of 20 km/L by 2020; and
- EU emissions regulations mandate a mere 95 g/km of CO2 by 2021, with another 15% reduction by 2025, and in 2030, a further 30% reduction from 2021.
The market for carbon fiber in automotive applications was estimated at more than 7,000 metric tons (MT) per year by Chris Red of Composites Forecasts and Consulting LLC (Mesa, Ariz., U.S.) at CW’s Carbon Fiber 2017 conference, with more than 100 models currently specifying carbon fiber-reinforced plastic (CFRP) for OEM components. He projects this market will grow to almost 11,000 metric tonnes by 2025.
China is the number one automotive market, producing 27.8 million vehicles in 2018, which includes all passenger cars, light commercial vehicles, trucks, buses and coaches. This is compared to:
- 11.3 million vehicles in the U.S.
- 9.7 million vehicles in Japan
- 5.2 million vehicles in India
- 5.1 million vehicles in Germany
- 4.1 million vehicles in Mexico
- 4.0 million vehicles in South Korea.
CarbonPro pickup box. Source | General Motors Co.
Thus, it isn’t surprising that development of composite structures used in actual series production vehicles — not just high-end options or concept/prototype models — is being led by Asia and Europe. Recent composites development announcements in China include:
- CSP VICTALL (Tanshan, China) has announced that Jiangling Motors Corp. (JMC) will use advanced composites for the pickup boxes of its new Yuhu 3 and Yuhu 5 pickup trucks, the first such use of composites in the Chinese automotive industry.
- Kingfa (Guangzhou, China), working with systems supplier Brose Fahrzeugteile (Coburg, Germany), has developed a door module, which uses three types of KingPly organosheets and KingStrong unidirectional tapes, augmented with pultruded PP-LGF injection molding material for ribs and complex surfaces, to cut weight 35% (1 kilogram) for the Ford Focus vs. a PP-LGF 30 door module carrier.
- Magna Exteriors formed a joint venture with GAC Component Co. Ltd. (GACC, Guangzhou, China) to begin production of thermoplastic composite (TPC) liftgates for a global automaker's crossover vehicle starting in late 2018.
- Kangde Group (Hong Kong) entered an agreement with BAIC Motor to build an Industry 4.0 smart factory in Changzhou to produce CFRP car body and other components beginning in 2019 and scaling to 6 million parts/yr — its 66,000 MT/yr carbon fiber facility in Rongcheng will begin production in 2023;
- HRC (Shanghai, China) commissioned the first Rapid Multi-injection Compression Process (RMCP) automated composites production line from Carbures (El Puerto de Santa María, Spain); and
- Volvo’s new, separately branded electric high-performance car company Polestar started production of its first model, Polestar 1, in 2019 in the new Polestar Production Centre in Chengdu.
The industry’s first carbon fiber composite pickup box was unveiled in 2018 by General Motors (GM, Detoit, Mich., U.S.). The first-ever composite bed for a full-size truck was actually built by GM in 2001, but the take-up rate on the Silverado and Sierra Pro-Tec box option was only 10% of what GM expected. Thus, it waited more than 15 years to try again. The CarbonPro pickup box, again an option, but for the 2019 GMC Sierra, was developed with Teijin Automotive (Tokyo, Japan), which acquired Continental Structural Plastics (CSP, Auburn Hills, Mich., U.S.) in 2017. CSP has years of experience manufacturing composite boxes for the Honda Ridgeline and Toyota Tacoma trucks, both made from chopped glass fiber sheet molding compound (SMC). The first-generation Honda bed was 30% lighter than steel when it debuted in 2005, but its 2017 update switched away from SMC in two of the components, opting for a direct long-fiber thermoplastic (D-LFT) for the sidewalls and headboard and for a short-fiber compound for the spare tire tray, both injection molded using glass fiber and polypropylene (PP). The 2019 GMC CarbonPro box also uses Teijin’s Sereebo thermoplastic composites manufacturing process, which combines a mat of 20-millimeter-long carbon fibers with nylon 6 that is compression molded for part cycle times of 60-80 seconds.
A section of the BMW i3 Life Module floor panel demonstrates a serial production hybrid composite molding cell which uses a central swivel platen to accommodate both thermoset prepreg compression molding and thermoplastic overmolding while photonics provides essential part referencing and more. Source | AZL at RWTH Aachen University
This growing trend toward use of thermoplastics in automotive composites is aided by processes such as overmolding, where blanks made of woven or unidirectional fibers in a thermoplastic matrix — known as organosheet — are compression molded into a 3D shape while reinforced plastic is injection molded on top and around to form complex-geometry ribs, bosses, inserts and attachment points. Parts in development or production include seat backs, seat rests, airbag housings, A and B pillars, door cross beams, bumper beams and large floor components. Although overmolding is typically all-thermoplastic, the Opto-Light project, managed by Aachen Center for Integrative Light Construction (AZL) at RWTH Aachen University (Aachen, Germany), demonstrated thermoplastic overmolding onto a thermoset carbon fiber/epoxy shell to produce a 3D structural portion of the BMW i3 floor panel in a fully automated cell with a 2-minute cycle time. The project also showed the ability to use cure-state monitoring via Netzsch Gerätebau (Selb, Germany) in-mold sensors to achieve thermoplastic-to-thermoset joining without laser ablation as an intermediate step. This second advance stops compression molding of the high-performance, low-creep thermoset shell at the optimized time to leave sufficient reactivity in the epoxy resin to achieve covalent bonding, hydrogen bonds and/or semi-interpenetrating networks with the overmolded PA 6 thermoplastic.
Notably, the Opto-Light demonstration part started with unidirectional (UD) tape. This trend to use UD tapes to reduce waste compared to woven or noncrimp fabric (NCF) reinforcements continues to grow. Because the tapes can be cut and placed precisely, very little scrap is produced and fibers can be aligned more precisely to match loads. One notable example is the CFRP rear wall for the Audi A8 luxury sedan made in a fully automated, Industry 4.0 production line by Voith Composites (Garching, Germany). It provides 50% weight reduction compared to three to five welded aluminum parts, and 33% of the drive cell’s torsional stiffness. The rear wall begins with Zoltek (St, Louis, Mo., U.S.) 35K carbon fiber which is spread into bindered, 50-millimeter-wide, UD tape, which is cut and laid at specified angles to form a tailored blank in a single machine — the Voith Roving Applicator. This blank is shaped into a 3D preform in a heated press supplied by FILL (Gurten, Austria) which adapts the pressure applied as it stamp-forms separate regions of the preform clamped in the forming tool made by ALPEX Technologies (Mils bei Hall, Austria). The completed preform is then injected with resin and press-molded using the Audi-developed Ultra-RTM process, which uses less than 15 bar of pressure compared to 140 bar common for high-pressure RTM (HP-RTM). Thus, only 350 kilonewtons of press force is needed compared to 2,500 for HP-RTM. Although the VORAFORCE 5300 epoxy resin cures in 90-120 seconds at 120°C, the total part cycle time is 5 minutes.
FlexHyJoin demonstrates a mass production process for producing a thermoplastic composite roof stiffener with welded metal brackets for assembly into a metal body-in-white, like that of the project’s use case, the Fiat Panda city car. Source | IVW
Another alternative to HP-RTM is wet compression molding (a.k.a., liquid compression molding), which does use snap-cure resins and NCF, but also lower pressure. Instead of injecting resin into the preform, automated equipment spreads resin over the fabric and then transfers this into a thermoforming press. Eliminating the preforming step and offering cycle times less than 90 seconds and less-expensive equipment, BMW has predicted a significant increase in wet-pressed parts. Huntsman Advanced Materials (Basel, Switzerland) has developed a next-generation process called dynamic fluid compression molding (DFCM) that claims fiber volumes up to 65% and the ability to mold more complex geometries.
For exteriors, ultra-lightweight SMC continues its push below 1.0 g/cc and carbon fiber is also gaining ground, with Polynt Composites (Scanzorosciate, Italy), Aliancys (Schaffhausen, Switzerland) and CSP all adding new SMC production lines over the past few years, all of which have the ability to make carbon fiber SMC. Polynt has also introduced Polynt-RECarbon recycled fiber SMC to its product offerings, as well as UDCarbon and TXTCarbon compounds featuring unidirectional and fabric reinforcements, respectively. The potential for these products can be seen in the front subframe development project completed by Magna International (Aurora, Ontario, Canada) and Ford Motor Co. (Dearborn, Mich., U.S.), which uses locally reinforced and co-molded chopped carbon fiber SMC with patches of SMC made with carbon fiber 0-degree/90-degree NCF. This SMC structural subframe must handle significant loads, supporting the engine and chassis components, including the steering gear and the lower control arms that hold the wheels. Though only a development part, it achieved an 82% parts reduction, replacing 54 stamped steel parts with two compression molded composite components and six overmolded stainless steel inserts, while cutting weight by 34%.
Hybridizing SMC with prepreg is an approach used by Ford’s global Research and Advanced Engineering group teamed with its Chassis Engineering group in the U.K. to redesign a production steel suspension knuckle for a C-class vehicle. By co-molding layers of woven carbon fabric prepreg with chopped carbon fiber SMC, a complex-shaped, high-performance suspension knuckle was produced with a cycle time of less than five minutes and a 50% weight reduction. Other developments include Saint Jean Industries (Saint Jean D’Ardières, France) and Hexcel (Stamford, Conn., U.S.) developing a hybrid carbon fiber/aluminum version of a performance car suspension knuckle, which increased stiffness by 26% compared to an all-aluminum knuckle. Meanwhile, Williams Advanced Engineering (Grove, Oxfordshire, U.K.) has developed a CFRP wishbone that uses unidirectional carbon fiber and recycled carbon fiber nonwoven mat — up to 80% of the composite part, by weight — to cut weight 40% compared to conventional aluminum versions, yet its cost is comparable to aluminum forgings. The part molded is in 90 seconds using an HP-RTM process called RACETRAK for a 5-minute total cycle time, including layup.
Scott Bader’s Crestapol resins were used to produce a curved, multi-hollow pultruded carbon fiber bumper beam for the 2020 Chevrolet Corvette Stingray. Source | Scott Bader
Pultrusion is another growing trend. In 2018, L&L Products launched its Continuous Composite Systems (CCS) pultrusions using polyurethane resin and glass, carbon or hybrid fiber reinforcement for automotive applications such as side sills and crash structures. Designed to replace traditional metal structures that require bulkheads for necessary stiffness, CCS pultrusions offer light weight — 75% less mass than steel and 30% less than aluminum — at an economic price. In 2019, the automotive industry’s first curved, multi-hollow pultruded carbon fiber bumper beam was unveiled in the 2020 Chevrolet Corvette Stingray. In development since 2016, the part is produced by Shape Corp. (Grand Haven, Mich., U.S.) using Scott Bader (Northamptonshire, U.K.) Crestapol urethane acrylate resin and Thomas Technik & Innovation’s (TTI, Bremervoerde, Germany) Radius-Pultrusion system. Pultrusion is again front and center in the MAI Skelett project, which thermoformed and overmolded UD carbon fiber thermoplastic pultrusions in a two-step, 75-second process to produce a demonstrator BMW i3 structural roof member. The part exceeds all previous version requirements, integrates clips for attachments and changes crash behavior from brittle to ductile failure mode for increased body-in-white (BIW) residual strength.
The SMile Source | Fraunhofer Institute for Chemical Technology
One final trend is the move toward hybrid metal-composite structures. The System integrated Multi-Material Lightweight Design for E-mobility (SMiLE) consortium combined composites and non-ferrous metals to reduce mass and costs for the entire BIW structure of a battery-electric vehicle. The rear load floor module uses eight layers of 60-wt% UD glass fiber-reinforced PA6 Ultratape and 40-wt% glass fiber/PA6 Ultramid direct-long-fiber thermoplastic (D-LFT), both from BASF SE (Ludwigshafen, Germany). SMiLE developed a new process, taking a preconsolidated tape laminate and selectively reinforcing that with D-LFT where ribs and complex geometries are needed. This is then placed, along with two aluminum profiles and several metallic inserts, into a compression molding press and quickly cycled to form a 1.3-by-1.3-meter part. This rear module is adhesively and mechanically joined to a second, hybrid/thermoset composite forward load floor, made using RTM and carbon fiber-reinforced epoxy with integrated metallic inserts and local sandwich structures containing polyurethane-foam cores.
In the FlexHyJoin project, managed by the Institut für Verbundwerkstoffe (IVW, Kaiserslautern, Germany), an automated process enabling a thermoplastic composite roof structure to be assembled into a metal BIW was achieved by laser pretreating metal brackets and attaching these to the composite roof bow via induction and laser joining. This was achieved in a single, automated production cell with integrated process control and inline nondestructive testing (NDT) with a cycle time of 140 seconds.
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