Magna produces compression moulded CFRP hoods for Cadillac CTS-V and ATS-V sedans

There was a strong focus on lightweight solutions at the annual VDI automotive plastics event. In this feature for Plastics News Europe David Vink reviews a selection of the papers and exhibits.

The 2016 VDI Plastics in Automotive Engineering Congress, in Mannheim, Germany in April, provided a showcase for the latest automotive innovations and technologies using plastics and composites.

“The first ever compression moulded CF prepreg hood in North America” was the application discussed by Dr Joseph J. Laux, EU composites business development and advanced engineering director at Magna Management in Cham, Switzerland. The hood application for the 2016 Cadillac ATS-V and CTS-V sedan cars uses heavy tow unidirectional CF (Zoltek, 50K) reinforced epoxide resin prepreg.

CFRP hood vent, front splitter, rear spoiler and rear diffuser options complete the standard CFRP hood, which consists of 1.2mm and 0.8mm outer (painted, 2.5 kg) and inner panels (exposed, 1.9 kg). UD-CF gave better (directly Class A paintable) quality than woven CF textiles. The hood, produced at Magna Polycon on a 2,500-tonne Siempelkamp press, weighs 20% less than the previous aluminium hoods. Laux said Magna wants to cut moulding cycle time to 2-3 minutes in future, and also will consider CF-SMC for the inner panel.

Composites materials producer Cytec (part of Solvay group) displayed a CFRP hood for the limited series BMW M4 GTS car. The hood was compression moulded by L?pple Automotive from preforms in conventional sheet steel press tooling, with less than 5 min cycle time.

It consists of inner and outer 1.2mm thick parts bonded together to form an 8 kg hood weighing 40% less than the aluminium predecessor. It was the first-ever CFRP small-series order for L?pple, which has recently set up a lightweight technology centre at its Heilbronn headquarters.

The prepreg is impregnated with MTR 760 epoxide resin during filament winding around a 1mm diameter mandrel. The wound material is slit to form tailored blanks, which are consolidated and cured between thermoplastics foil layers in the double diaphragm process.

Laux of Magna also presented a paper on the GOR grille opening reinforcement for the 2016 Ford Shelby GT350 Mustang. This is produced in the BASF A3WC4 grade of 20% short CF reinforced PA66, with the use of resistive implant welding (RIW), and was shown on the Magna IAA 2015 stand and on both Magna’s and BASF’s VDI congress stands (details in Plastics News Europe March 2016). The GOR saves 25-30% weight and 75% costs over the previous plastic/metal hybrid GOR. BASF stated on its stand that A3WC4 is lighter than 50% GF-PA, but it has 117% higher tensile modulus (13,000) and 75% higher tensile strength (184 MPa).

Alain Choquet, marketing and innovation planning manager at Reydel Automotive, described Decoprint, a 10?1,000 parts/day individualised automotive interior inkjet printing decoration system. An articulated arm robot presents trim for plasma treatment, then to several ink jet print heads and UV-cure equipment.

Repeat printing produces textures up to 0.2mm thick, “comparable with automotive deep graining”. Choquet said Decoprint covers 80% of automotive decorative needs. He called Decoprint “a cost effective solution positioned between in-mould and lamination processes”. Smaller print heads, new and less expensive inks and varnishes and improved processing capability would enable additional decoration effects.

In oil pans, Dr Jean-Michel Fiard, thermo-mechanical consultant at Renault in Guyancourt, talked about stone impact tests for the GF-PA6 oil pan of the Kwid car, introduced in September 2015. Mecaplast moulds the pan, which weighs 1 kg less than an aluminium pan.

Jorge Soares, head of engine compartment advanced development at Polytec Plastics, described the first plastic oil pan in the Porsche 911 Carrera, produced for the new 3.0 litre 6?cylinder Boxer motor. It consists of unusually ?at upper and lower mouldings in 30% glass fibre reinforced PA6 (Lanxess Durethan BKV 30 H2.0). The new 2.6 kg oil pan replaced a 4.51 kg cast aluminium pan.

Honeycomb and irregular (chaotic) rib pattern simulation showed advantages for the latter in burst pressure and stress, but Porsche stayed with honeycomb ribbing bearing in mind all types of mechanical load, despite slightly lower acoustic dampening. Polytec has already been moulding honeycomb-ribbed pans for Audi and VW models in GF35-PA6 from Lanxess. Porsche found no disadvantages in using PA6 instead of PA66, and the latter was said to be used “mainly for historical reasons”. Soares said there is further part integration potential and hydrolysis?stabilised PA6 could enable cooling water line integration in future.

Dr Ulrich Karsch, innovation director at Kautex Textron, said the company supplied the first all-plastic pressure tank for Volvo XC90 and VW Passat GTE PHEV hybrid electric drive cars, made from two half-shells in the New Generation Fuel System process. The tanks replace the previous sole PHEV solution: hybrid plastic/steel tanks with exterior steel strengthening. He explained that pressure builds up in hybrid vehicle tanks when they are closed during electrical drive.

Karsch said high-pressure tanks need to withstand 250 and 700-bar pressure respectively with compressed natural gas (CNG) and hydrogen. So these are made by overwinding thermoplastic tanks with carbon fibre – more recently with impregnated CF tape – which welds to the thermoplastic during resin cure.

He said he did not perceive all-electric drive cars as an immediate threat to plastic tanks, as low oil prices act as a brake on the development of new drive technology, aside from ongoing concerns about the driving range of all-electric cars.

Volkswagen’s Robert Mielke, instrument panel development engineer, and Petra Dierks, head of plastics division design and development, said the 2015 Tiguan instrument panel (IP) is physical foam moulded in glass fibre reinforced PP. Mielke said the process does not require holding pressure, so there is lower warp tendency and higher dimensional stability. The 2015 Tiguan IP weighs 650g less than the 2007 IP, due to foam moulding and high functional integration of, for example, the airbag channel. The 2015 IP replaced a screwed, riveted and welded metal IP.

Separate foamed PE air ducts substitute conventional injection moulded ducts, for better acoustic insulation, tighter sealing against air leaks and better space utilisation. The IP cladding has aliphatic PU sprayed on top and foamed aromatic PU underneath. This allows variable thickness, unlike PVC slush, which provides only one thickness.

In a paper on the Audi A4, Manuel José Rodriguez Tellez, interior development manager at Audi, described moulding of the car’s IP with the Trexel MuCell microcellular foam moulding process. In a review of advantages and limitations, Tellez also stressed how avoiding holding pressure helps part stability.

Engelbert Meurer of Covestro talked about the two honeycomb structure crash absorbers (each weighing 6 kg) within the BMW i3 electric car’s carbon fibre reinforced plastic (CFRP) side skirts (sill) area, protecting batteries during side?impact collision. Eckerle injection moulds the part in Covestro’s unreinforced Makroblend KU2-7912/4 PC/PBT blend (BASF Ultradur B4040 G6, a 30% glass fibre reinforced PBT/PET blend, was previously identified in this application in European Plastics News’s BMW i-series supplement, October 2014). Meurer said that compared with PC/PBT, expanded polypropylene (EPP), polyurethane and zinc foams and an aluminium honeycomb all underperformed in stiffness and energy absorption over a long path.

Horst Schmidhuber, Webasto executive VP for roofs and components, talked about greater opportunities for polycarbonate glazing following the introduction in Autumn 2015 of more favourable scratch tests (UN ECE R43) for windscreens and front side windows. This encouraged Webasto to introduce a Webasto 360 project, to get PC into all types of automotive glazing, all around the car.

Trinseo launched Pulse XT, a family of PC/ABS blends for exterior applications, classified by heat stability, emphasising 10-15% cost advantage over PC/PET. It stressed low thermal expansion in a new Opel Astra Sports Tourer station wagon roof rail application in 15% mineral filled Pulse XT9215, produced by SRG Global with 50% weight saved over painted aluminium.

Marketing manager Anis Tehib told Plastics News Europe: “The exterior area is where we want to go with XT, with potential XT applications also in mirror housings, front grilles and spoilers”. He said Pulse XT competes here with 20% mineral filled PC/PBT blends.

The small lower external side grille on the Audi A4 is still in the Pulse GX50 grade of PC/ABS, Tehib said: “But if we would start today, it would be in XT too”. He explained that XT has better flow and heat stability than low gloss GX grades, and that XT is available as both low and high gloss versions.

Tehib also presented a paper with Gérard Liraut, polymer expert leader at Renault in Guyancourt, on development in 2012 of the all-plastic 40% long glass fibre (LGF) reinforced PP semi?structural tailgate of the Renault Clio, which saves 15% weight over the previous steel design. The “mono-material” design involves three parts: the LGF40-PP structure, a 15% mineral filled unpainted PP interior panel and a 30% talc filled PP outer panel.

The Clio experience was extended in 2015 to the “mono-material liftgate” of the new Renault Espace. Among other features, using PP as a mono-material solution in tailgates enables thermal expansion matching and laser welding.

In his paper with Renault, Tehib said minimising glass fibre shortening during moulding is critical, and that key here is in the plastifying screw rather than in the mould.

The highlight of the Borealis stand was new Fibremod Carbon 20-40% short carbon fibre reinforced PP compounds, and a KTM Motorcyles frame trial part in CB401SY, a 40% short carbon fibre reinforced PP grade was on display as a potential steel replacement.

Borealis talked about particularly high mechanical properties achieved through chemical coupling of the CF to the PP matrix, resulting in flexural modulus up to 20,000 MPa: “the strongest PP ever produced”, automotive marketing manger Nick Kolesch told Plastics News Europe. Borealis also stated that Fibremod Carbon offers higher specific stiffness than GF30?PA6, without a cost premium, and it is in any event cheaper than CF-PA. Kolesch said Fibremod Carbon can be based on either virgin or non-virgin CF.

“Impact is a bit more on the challenging side with CF-PP against CF-PA”, Kolesch admitted, “but we are still in the explorative phase at the moment. It’s not just about the material, but also to engineer the different areas of the part, as unlike metal, certain parts can be much thinner and you can see that in the motorcycle frame, which is simply two parts bolted together.”

As before, substitution of GF-PA with high performance GF-PP grades was also a theme, with examples including: 40% glass fibre reinforced Fibremod GB477H in a seat carrier; a Brose rear arm rest; a Takata Petri airbag housing saving 45% weight over PA, with future potential to use foam moulding; as well as an Audi TT frontend.

Kolesch pointed to the example of the Brose armrest, where Borealis is working on a concept of overmoulding short fibre reinforced PP onto PP-based long fibre organic sheet, cutting weight from 7-8 kg in a steel armrest down to 3.4 kg.

Overmoulded organic sheet door carriers are also in evaluation at Brose. Kolesch said: “It’s incredibly light and incredibly strong. And there are in general opportunities to overmould with CF-PP too now.”

The Borealis 12% mineral filled elastomer-modified PP grade Daplen EE112AE for primer?free, 2-layer exterior painting has been adopted by BMW for 7-series bumper and tailgate panels, and some 3-series parts too, Kolesch added. The material won a “new surfaces for plastics parts award” in 2015 in the European Plastics Innovation award scheme, jointly organised by PlasticsEurope, EuPC and SPE.

Short carbon fibre featured in the display by compounder Akro Plastic of a Mini Clubman central console, moulded in the company’s 10% CF reinforced PA66 grade Akromid A3 ICF 10, a stiff material with flexural modulus of 33,000 MPa. Developed together with BMW and automotive parts supplier Grammer, the part won a JEC 2016 innovation award.

Dr Ralf Langendorf, engineering group manager at Opel in Rüsselsheim, and Dr Erik Licht, business development manager at Basell Deutschland (LyondellBasell) talked about PIT Plastic Interface Technology developed in PP compounds at LyondellBasell in Frankfurt/Main. The PIT in-mould process applies decorative materials to plastic mouldings. Alongside the display of an aluminium foil clad PIT engine cover, LyondellBasell showed how application of a 0.2mm thick aluminium foil in the PIT process not only provides decoration, but also increases stiffness of a Hostacom PPU 2090L moulding from 2,000 MPa to 8,500 MPa.