Note: This is the second article of a three-part series covering automotive lightweighting (1) trends, (2) material/process advances and (3) applications.
Innovative materials together with new production methods and reinforcing structures will play an important role in reducing automotive vehicle weight. Lower vehicle weight not only improves fuel efficiency but also reduces the load on the brakes and suspension systems.
Currently, 15 percent of the average car's total weight (roughly 360 pounds) is plastic material, with its use accelerating. Experts predict this use will more than double over the next five years as the auto industry gears up to meet new emissions regulations. The trend to replace metal with plastics is also allowing integration of functionality often not possible in metal versions.
A good example of automotive lightweighting with plastics is the first PMMA (polymethyl methacrylate or acrylic) molding compound for auto glazing. Plexiglas Resist AG 100 developed by Evonik Industries AG is the first PMMA molding compound for automotive glazing.
The specialty molding compound for injection molding and extrusion provides huge design freedom, low weight and the option of integrating a variety of functions. It offers the high resistance to ultraviolet (UV) light and outdoor weathering for which Plexiglas acrylic is known. It's also impact-modified and has up to 30 times the breaking strength of mineral glass. The new specialty compound can be processed by injection molding, compression molding or by extrusion with subsequent sheet thermoforming.
Unlike other thermoplastics — such as polycarbonate, which must undergo a two-step coating process to achieve UV and scratch resistance — the new Resist is inherently resistant to UV light and weathering and therefore requires a single coating only. One-step coatings that are suitable for Plexiglas have been successfully tested and also meet the requirements of ECE R 43, the United Nations safety standard for automotive glass.
Also, driving in the rain is far less noisy with PMMA glazing, compared to the use of polycarbonate.
Next, let's look at the CAMISMA (the Carbon-Amide-Metal-based Interior Structure using a Multi-material system Approach) Project used in the design optimization of lighter, safer car seating.
Johnson Controls is reducing use of metals in vehicle seat structures by replacing them with multimaterial systems in its CAMISMA research project. CAMISMA's goals include:
- Reuse of byproducts from carbon fiber production and/or recycled fibers to help limit incremental component cost and help reduce carbon dioxide emissions for CFRP (carbon fiber-reinforced plastic) structures.
- Enable low-cost, short-cycle manufacturing by combining thermoforming with injection overmolding and attachment of metal inserts in a one-shot process.
- Develop an automobile seat design that reduces weight versus conventional metallic constructions.
- Meet front and rear impact safety requirements.
For this cutting-edge work Johnson Controls received the 2014 CLEPA (European Association of Automotive Suppliers) Innovation Award in the "Green" category.
These seats are approximately 40 percent lighter than conventionally manufactured seat structures and equally as safe. The seat back design cut weight by 40 percent versus conventional metal construction by integrating parts and functions into a unitized, mass-producible multimaterial structure.
The team used the best features of two short-cycle molding processes, thermoforming and injection molding, and three distinct material forms to fabricate the complex, ribbed automotive seat back with metal inserts in an automated, one-shot, 90-second cycle.
CAMISMA takes advantage of three recently developed technologies.
The first is a new type of unidirectional (UD) polyamide (PA, or nylon) prepreg tape, developed by Evonik Industries AG and Toho Tenax Europe GmbH. The second technology helped CAMISMA meet its material cost-reduction goal. PA12-powder-impregnated nonwoven mats were made for this project from recycled carbon fiber by Materials Innovation Technologies Reengineered Carbon Fiber. The third technology, a hybrid injection molding/thermoforming process, enabled forming of the PA12 tapes and mats, overmolding of plastic features and incorporation of metal inserts in one step.
The project uses an innovative industrial manufacturing process for volume production with about 200,000 units per production line, allowing for the first time the highly concentrated, efficient use of carbon fiber, while at the same time meeting all safety requirements.
Finally, let's review an industry-first active glove box knee airbag.
Ford Motor Company has developed a new type of airbag technology that enables more compact packaging and reduced weight. The technology is essentially a passenger knee airbag that fits in the panel door of the car's glove box. It provides inflatable resistant protection, while reducing airbag weight and allowing designers to increase passenger cabin space.
The system, which appears in the 2015 Mustang, replaces a traditional textile airbag with an injection-molded plastic bladder, integrated into the glove box door. Upon impact, the bladder is inflated, extending the outer glove box door panel toward the front passenger's legs to provide cushioning. The bladder is attached via hot plate welding. Toolmaker Extol Inc. was responsible for the hot plate welding development. Ford also developed a hydrostatic burst tester to validate the strength of the seal.
MLive/Ford Motor
Ford active glove box airbag system (left); plastic airbag bladder in glove box (right).
The active glove box, a three-part design supplied by Faurecia, is comprised of the following:
- A rear reaction surface panel is injection molded in a 20 percent talc-filled polypropylene (PP) from Advanced Composites (a high stiffness ADX 5017 grade).
- A front panel in a thermoplastic olefin (TPO), a TT850N grade from Mitsubishi Corporation formulated to perform well at high strain rates over a wide temperature range.
- An injection-molded bladder produced in a high-rubber-content PP, an ADX 5028 grade also from Advanced Composites, sandwiched between the door front and rear reaction panel.
The new technology provides a weight savings of 65 percent over a traditional glove box and airbag pairing. It has a cost reduction of $5 to $10 per vehicle. The 75 percent smaller inflator allowed designers to move the Mustang's dashboard closer to the windshield, creating more space in the cabin.
Ford has been granted 15 patents for this technology, with more pending. The company was named the winner of the Society of Plastics Engineers' 2014 Automotive Innovation Awards for the injection-molded knee airbag/glove box system.
