Pieces of Plastic

Blow Molding for Air Handling

The 2.0-liter four-cylinder turbocharged engines found in several BMW models—including the 4, 5 and 7 Series, and the X3, X4, X5—are being fitted with a blow-molded charge air duct (it goes between the turbocharger and the charge air cooler) that is being produced by MANN + HUMMEL (mann-hummel.com) with a high-temperature polyamide, Ultramid Endure D5G3 BM, from BASF (basf.com). It is a polyamide 66 material that has 15 percent glass fibers.

In this application, the component is subjected to both heat—it is temperature resistant up to 220°C in continuous use and up to 240°C peak loads—and pressure: as the duct channel compressed hot air from the turbocharger to the integrated charge air cooler, pressures higher than 2.5 bar can be achieved.

While charge air ducts are sometimes made with hydroformed rolled aluminum sheet, the blow molding process lends itself to providing the varying shapes that are required to fit within the compact space required on the engine. And compared with other plastic materials, the interior surface of this polyamide 66 is said to be smoother, which facilitates air flow.

And speaking of other plastic materials, polyphenylene sulfide, which is used to produce ducts, doesn’t have the same acoustical properties that the BASF material does: according to the company, depending on the temperature and humidity levels, it offers damping values up to 10X better than polyphenylene sulfide.

In terms of attaching the duct to other parts, this can be performed with processes like infrared welding. Although with the low glass fiber content it might seem that the weld line would be a weak spot, there is a stabilization mechanism in the Ultramid Endure BM that helps strengthen the area: it has been determined that after 1,000 hours at 220°C, there is no cracking at the joint.

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Stiffer than Metal

According to Borealis (borealisgroup.com), its carbon fiber reinforced polypropylene (PP) grades, Fibremod, offer stiffness as high as 20,000 MPa and an extremely low density. In this regard, it can outperform aluminum and magnesium and provides a light-weighting potential, compared with steel, of more than 60 percent. Included in its portfolio are a number of Fibremod grades that have varying levels of carbon fiber reinforcements in its PP. Applications for these materials range from headlamp housings to oil pans to seat frames to gear-shift gates.

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Making Connections

BASF (basf.com) has developed a new polybutylene terephthalate (PBT) grade specifically for applications such as wire harness connectors. The material, Ultradur grade B4340ZG2 High Speed (HSP), has high flowability for molding and good impact strength for application. It also features good electrical properties which allow minimum distances between the conductor tracks in plug-in connectors.

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Formed with Color

The high-gloss, piano-black A-pillar trim pieces for the Peugeot 3008 SUV are being produced within one minute in a molding operation being performed by a Swiss supplier, Weidplas GmbH, via the ColorForm process developed by KraussMaffei (kraussmaffei.com).

In the operation a thermoplastic base body is formed in a mold; it is flow-coated directly in a second cavity with a two-component polyuria or polyurethane paint.

The operation is being performed at Weidplas with a KraussMaffei SpinForm GXW 650-1400/2000 injection molding machine that has a clamping force of 6,500 kN.

The parts are long and narrow: one meter long and 35-mm wide.

After being molded, they are handled by a Kuka IR 1500 robot. Ultrasonic welding is used to attach the cover to seal carriers.

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Thermoplastic for Transfer Molding

Glass fibers. Carbon fibers. Aluminum. Steel. Thermoplastic (Polyamide 6). All of these materials are combined in the frame for the roof shell used for the Roding Roadster R1 sports car in a process developed by KraussMaffei (kraussmaffeigroup.us). The metal components are setup and assembled, then placed in a mold along with the fabric where T-RTM—that’s thermoplastic resin transfer molding, as distinct from the more familiar RTM, which uses an epoxy resin or polyurethane—is performed.

There are two caprolactam components injected into the mold—one is a base material and the other the catalyst. Because the matrix material has a low viscosity—five millipascal-seconds—it readily wets the fiber layers even though there are comparatively low clamping forces (e.g., 3,500 kN) applied. The T-RTM process lends itself to producing near-net-shaped parts, which minimizes material waste.

What’s more, parts can be made with very thin walls.

Another benefit for applications like the roof frame is that the PA6 material that is used has both higher impact strength and ductile fracture behavior than thermoset plastics, which means that it can absorb more impact before fracturing occurs.

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How is the Batmobile Like A Saturn SL1?

One of the more-interesting plastics-based automotive developments of late is, well, a Batmobile, specifically a LEGO Batmobile from Chevrolet, inspired by the Batman Speedwagon in The LEGO Batman Movie.

The vehicle is produced with 344,187 LEGO bricks. LEGO bricks are, of course, made with plastic, acrylonitrile butadiene styrene (ABS) plastic, for the most part.

Like the Saturn S-models (1991-2002, which means the period of Michael Keaton, Val Kilmer and George Clooney as Batman), the LEGO Batmobile is constructed on a frame. In this case, it is a frame produced with approximately 86 feet of square tube aluminum that weighs 282.5 pounds. The total weight of the vehicle is 1,695.5 pounds.

Know that it is 83 inches high, 204 inches long and 111 inches wide. The Batmobile was designed and built in the LEGO Model Shop in Enfield, Connecticut, by LEGO Master Builders—who spent 222 hours designing it and 1,833 hours assembling it.

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Extreme Polyamide

Plastic oil pans aren’t new. But given their locations—right above the road surface—they are certainly vulnerable to impacts from stones and other debris, which can cause all manner of problems for motorists should there be a crack in the pan.

LANXESS (lanxess.com) has developed a new material specifically for application in oil pans: Durethan BKV 235 H2.0 XCP. The last three letters stand for “Extreme Crash Performance.” It is a polyamide that’s rubber modified and reinforced with 35 percent special short glass fibers.

According to the company, at -30°C, the Charpy notch impact resistance of the new material is 18 kJ/m² (ISO 179-1eA). By way of comparison, the company’s standard polyamide 6 with 35 percent glass fibers, Durethan BKV 35 H2.0, impact resistance is 10 kJ/m² at -30°C.

What’s more, the XCP grade is exceedingly close to the standard polyamide 6 as regards e-modulus and tensile strength at break, meaning that the molded component can be stiff, strong and exhibit high impact resistance.

And it is good in the heat, too. The heat distortion temperature to ISO 75-1,-2 (HDT A, 1.8 MPa) of 203°C is nearly as high as that of Durethan BKV 35 H2.0.
 

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Process for Affordable Composite Parts

 

Can composite materials move from high-end autos to more mass-produced vehicles? According to Evonik (corporate.evonik.de), its newly developed process, PulPress, may make this happen.

PulPress combines compression molding and pultrusion.The process begins with a structural foam core, made with the company’s ROHACELL material, that’s wrapped with woven fibers before impregnation with resin. This is then compressed, under high temperatures and pressures, to the required shapes, which can be complex geometries and even include recesses.

The parts are said to provide good crash characteristics. They are also about 75 percent lighter than comparable steel parts.

And what probably goes to the point of being used for an array of vehicles, not just luxury: the cost of producing a part with PulPress compared with typical resin-injection processes is up to 60 percent less expensive.

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Fiber (Carbon) is Good for Autos
A variety of composite materials focused on automotive has been developed by Hexcel (hexcel.com), such as HiMax carbon fiber multiaxial fabrics that are specifically optimized for high-volume part production, as in being a non-crimp, high-drape fabric that can conform to complex mold geometries while offering the permeability required for fast resin injection and cure times.

There are prepregs, such as the HexPly M77, which cures in 1.5 minutes at 160°C. This material is being used by BMW for the 7 Series.

The HexPly M77 material is also being used by British supplier St. Jean Industries to produce a suspension knuckle that is an aluminum structure that is stiffened with the carbon fiber reinforced plastic material, thereby increasing stiffness (compared to aluminum-only) by 26 percent. The prepreg stacks are bonded to the aluminum with a fast-curing film adhesive, Redux 677, which fully cures in four minutes at 150°C (at 3.5 bar). The film adhesive can also be used to bond HexPly M77 to other metals, thermosets and thermoplastics.

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World’s Largest PC Rear Windows
According to SABIC (sabic.com), the rear quarter windows that are being deployed on the new China-market Buick GL8 and GL8 Avenir crossovers built by SAIC-General Motors feature the world’s largest polycarbonate (PC) rear quarter windows.

The window measures 1,200 mm x 450 mm. Molded from LEXAN resin, the rear quarter window is 40 percent—or 3 kg—lighter than a comparable glass window. And more impact-resistant.

The windows are being molded by Ningbo Shentong Auto Decorations (shentong.en.chinaningbo.com), which installed a new production facility for PC glazing, in a two-shot injection compression molding process: in addition to the PC for the transparent area, there is CYCOLOY resin, a PC/acrylonitrile-butadiene-styrene (ABS) material used for the blackout area.

Jun Luo, Shetong’s deputy general manager, said, “In addition to significant weight reduction, PC glazing allows for greater innovation than is now possible in glass, like design and styling freedom, thermal efficiency and parts integration.
 

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Plastics Under the Hood

The Polimotor 2 is the brainchild of Matti Holtzberg, president of Composite Castings, who wants to create a 2.0-liter, 350-hp turbocharged four-cylinder racing engine that is significantly lighter than standard engines—on the order of 140 pounds, or about 90 pounds less than conventional—thanks to the extensive utilization of polymer materials in place of metal. (Yes, even the engine block is a composite, not a metal.)

Solvay (solvay.com) is one of the key suppliers to the project, with its materials being used for:
  • Cam sprockets: TorlonPAI 7130 30 percent carbon fiber
  • Oil line scavenger: KetaSpire PEEK KT-820 CF30 30 percent carbon fiber
  • Water outlet: Amodel® PPA A-8930 HS 30 percent glass fiber
  • Water outlet seal: Tecnoflon FKM PL 855
  • Fuel rail: Ryton PPS XK-2340 40 percent glass fiber
  • Oil pump: AvaSpire PAEK AV-651 CF30 30 percent carbon fiber,
  • E-water pump: Ryton PPS R-4-220 40 percent glass fiber
  • Cam cover Radel PPS R-5500

One of the interesting technical developments is the plenum chamber. This is being made with Sinterline Technyl, a polyamide 6 powder with 40 percent glass beads. It isn’t being molded, but it is being 3D printed with selective laser sintering.

However, before printing the part, they applied a predictive simulation program to the part. Called MMI Technyl Design, a service powered by Digimat from e-Xstream, an MSC Software company (mscsoftware.com), the simulation showed that the original plenum design could be 30 percent lighter without sacrificing performance parameters. As Holtzberg, who is also the lead designer of Polimotor 2, puts it, “Integrating the 3D printed part with predictive simulation demonstrated all the additional benefits we could obtain to further reduce weight.”