Composites make the move into structural applications
When it comes to reducing the weight of vehicles, every little bit helps to lower emissions. To replace metal, manufacturers need to look beyond monolithic materials to composites, in order to meet the multiple requirements of the application, including strength, operating temperatures, resistance to a variety of chemicals and environments, manufacturability, scrap reduction, recyclability, and re-tooling costs.
Continuous Fiber Reinforced Plastic (CFRP) composites have a long history of successful applications – primarily in the aerospace industry, and generally based on thermosetting polymers. The automotive industry, however, is relatively new to this class of materials, with industry leaders noting the lack of a transparent supply chain for composites as the main reason they are reluctant to invest in these materials. Additionally, material requirements for automotive applications vary widely, with the main focus on costs and cycle times. As the industry moves in the direction of the connected car via the introduction of various types of electrical vehicles, the material requirements are also changing, and quickly.
This means that it will be exceedingly difficult for a single material to meet all the specifications optimally. This is why DSM has been conducting a number of pilot-scale projects in automotive applications over the last five years to determine the nature of metal substitution and optimum cost-to-benefit ratios. These pilots have shown us that making vehicles lighter is not simply an issue of replacing metal with composites. Instead, our approach focuses on the skillful use of multiple materials to lower automobile curb weight without compromising comfort or safety.
The fundamental building blocks in this approach are CFRPs – commonly called Unidirectional Tape (UD tapes). Our proprietary manufacturing process uses polymer resin extrusion to make glass-fiber and carbon-fiber reinforced thermoplastic ribbons or tapes up to 1 meter wide, and in any desired length. Our unique production process enables the processing of a variety of polymer matrices from low-temperature, commodity polymers such as polypropylene (PP), all the way up to high-temperature engineering polymers such as polyphenylene sulphide (PPS) or polyetheretherketone (PEEK).
With our end goal focused on achieving weight savings throughout the vehicle, our approach includes creating technology partnerships in the supply chain so that we can present a global solution to OEM and Tier end-users. These technology partnerships ensure we can process UD tapes into intermediate goods such as laminates with cycle times of minutes instead of hours, and better aligned with the expectations of the industry. We have also ensured our processing methods use equipment that is widely available in the industry, such as 3-axis and 6-axis machines and hot presses, to keep re-tooling costs at a minimum. The intermediate goods are supplied in kit form to the final manufacturing stage, where laminates are thermoformed to final part shape, often with overmolded features, a common practice in the injection molding industry.
We have tested our multi-material approach, based on UD tapes, in three common manufacturing processes: tape winding, metal-composite hybrid fabrication, and automated tape layup (ATL). We have also tested the use of metal inserts, metal-UD tape hybrids, weaving UD tapes into non-crimp fabrics, and using cross-ply forms to cover large surfaces more favourably than other composite forms such as organo sheets. All materials and combinations are tested under various load conditions, including torque and fatigue resistance. Material cards are available to facilitate simulation studies.
In one application, we have developed a lighter and stronger steel wheel, where the wheel rim is made 50% thinner, and over wrapped in three critical locations with a 60% by weight glass fiber-reinforced UD tape. Radial fatigue testing shows a 30% increase in fatigue life over a standard steel wheel. The weight saving was 2kg per wheel for standard passenger vehicles, and about 6kg per wheel for commercial trucks.
Learn more about how UD tapes can help reduce weight in your application – contact us today.