Smart Lightweighting at ACCE

I’m in Detroit, at the 2015 Society of Plastics Engineers’ (SPE) Automotive Composites Conference and Exhibition (ACCE), co-chaired by our contributor Dale Brosius and organized by our contributor Peggy Malnati. And I’m seeing real composite cars, and real, in-production composite parts. I’m also thinking about the recent article published in the September issue of CW on fast (snap) cure resins aimed at automotive applications. Before I get into what I’ve seen here at the show, I want to talk about an important resin product that I left out of that article in print: Daron resin transfer molding (RTM) resins from DSM Composite Resins AG (Schaffhausen, Switzerland and Zwolle, The Netherlands). DSM has updated the company’s RTM resin, trademarked Daron, to target fast processing of automotive structural parts. The new resin series actually consists of three resins, each with specific characteristics and T_g, but all tunable in regards to cycle time and specific designs.

Offering performance equivalent to epoxy, low-viscosity Daron was originally developed as a hybrid of unsaturated polyester and polyurethane. The hybrid system has been reported to consist of an unsaturated polyester polyol (A) component and an isocyanate (B) component of the MDI type. DSM says the resin chemistry provides high fracture toughness and good impact resistance, together with fast wetout, and is compatible with all fiber types. The company says Daron is relatively insensitive to process and fiber variation, and wets out carbon fiber very well. Sub-one-minute cure is possible, and cure can be tailored to part complexity and molding process by varying the mold temperature and accelerator type. Also, little or no post-cure is needed, and an efficient internal mold release system ensures hassle-free demolding in a serial production scenario.

In terms of Daron’s use by OEMs, DSM says the resins are currently being evaluated but no details can be discussed. That said, ESE Carbon Company (Miami, FL, US) is using Daron 200 to make an all-carbon aftermarket car wheel, reportedly the lightest carbon fiber wheels currently available at 5.2 kg, and rated for a maximum axle load of 1746 kg. The wheels are produced in ESE Carbon’s proprietary Next Generation Autoclave Process (NGAP), which combines a high-speed autoclave cure with liquid infusion. ESE Carbon chose Daron for its low viscosity, adjustable cure chemistry, good wetout of the carbon reinforcement and high mechanical properties at elevated temperatures, says company president Eric Escribano.

So, back to Detroit, and the 15^th year of the ACCE event. It’s now so large that the exhibits are in the exhibit hall of the Suburban Collection Showplace, while the presentations fill three big ballrooms. Papers of note: I was not familiar with cellulose nanocomposites, so I was glad to hear the great presentation by Kim Nelson, vice president of nanocellulose technology at American Process Inc. (Atlanta, GA, US). She noted that cellulose nanofibers aren’t new, but that her company has found a way to produce cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC) in a less-costly way while making the products more stable. Her group has also developed treatments for ensuring compatibility with polymer resins as well as much higher temperature resistance. She noted that her company is working with Futuris Group (Port Melbourne, Australia) on a sprayable binder resin containing CNFs for composite seating for Tesla cars. Another project involves collaborating with ORNL on using CNCs to reinforce and strengthen additive manufacturing /3D printing resins. Bottom line: even at very low concentrations, CNCs and CNFs can improve the properties of polymer resins, and in turn, composite parts, cost-effectively.

Parts of note: in the parts display, the chassis tub of the Zenos sports car is on display. Designed by Antony Dodworth, a fixture at ACCE events and the chief technical and manufacturing officer at his company Bright Lite Structures, with a wealth of Formula One design experience, the chassis is a complex honeycomb-cored structure with carbon face sheets that come from recycled carbon fabric off-cuts and trim waste. Each of the five elements of the tub incorporates intricate deep draws and shapes, made with Huntsman’s VITROX polyurethane resin and a plastic honeycomb. The tub elements reportedly are quickly layed in the mold, then sprayed with the resin, then thermoformed in a one-shot sub-15 minute cycle. The five pieces are adhesively bonded together, and to a central “spine” of aluminum extrusion that helps anchor the mid-positioned engine. David Bareis of Huntsman says the VITROX resin provides good toughness. Dodworth has designed the part with varying thicknesses of core to match loads, and with part consolidation in mind. No secondary operations are needed. This car is popular in the UK, particularly with racing enthusiasts, and about 10 cars are made per month. Here’s a link to a British car mag that test-drove the car, with pictures that include the carbon fiber tub: https://www.carthrottle.com/post/6-reasons-why-the-zenos-e10-s-is-the-best-sports-car-youve-never-heard-of/.

As Dale Brosius notes, we’ve entered a new era of “smart lightweighting,” where engineers are not just substituting composites for metals, but beginning to put materials where they’ll have the greatest impact on mass reduction, with the least cost penalty, in a more holistic approach to vehicle design. Perhaps it’s not what we expected 15 years ago, but it makes sense.