At the FSK’s recent meeting ways in which PU helps car makers in the move to e-mobility were laid out.
By Liz White
Europe’s automotive manufacturers are under tough pressure: they need to keep cutting CO2 emissions, and at a faster rate than at present. They need to develop more viable electrically powered vehicles. And they are facing a market with slow growth and potential competition from models made in India and China in the not too distant future.
Experts from the automotive sector posed these challenges to an audience of polyurethane experts at the 6-7 Oct 2011 meeting of the FSK, the German association for makers of foamed plastic and polyurethane.
FSK’s meeting was held at the AutoUniv site in Wolfsburg, Germany, of Volkswagen AG, a recent addition to the group’s membership.
Electric vehicles are being forced on the world by the demands of climate change and the corresponding need to cut emissions, said Dr Lars Hoffman, head of technology for VW’s E-Traction business.
To meet the EU’s aim of CO2 emission levels of 20g/km per car by 2050 is a huge leap from the current average of 188 g/km.
Conventional drive technologies cannot achieve “the drastic goal of limiting global warming to 2°C by the year 2050 — the gap will only be closed with e-mobility,” Hoffman said.
Another important factor is that non-renewable energy resources are not available forever, Hoffmann stressed, noting that forecasts say “we are past the peak now.”
Urbanisation is also growing: by 2020 there will be 25 megacities with more than 19 million inhabitants. All this means more pressure on the environment, and hence an urgent need to develop workable e-mobility solutions, the VW expert said.
Currently e-mobility covers a wide range, with micro hybrids, full hybrid drives, plug in e-cars, and fuelcell technology. “We still have to work on making these economical,” Hoffmann commented, adding that VW will launch a VW-E-motion battery model in 2013.
Lightweighting of car components for current models is a crucial feature to reduce fuel consumption and cut CO2 emissions in conventional models. But Hoffman pointed out that also, with e-mobility, battery weights are about 300 kg, which will further dictate the move to lightweight components, even for structural parts.
This offers an opportunity to polyurethane part makers, with carbon-fibre-reinforced structural parts also gaining a lot of attention, he added.
Another limiting factor is that the range of battery cars is limited: driving at high speeds will cut the range further, from about 150 km to only 80 km. And heating or cooling such a car would cut the range even further, said Hoffman.
E-cars will need insulation
This adds another opportunity for the PU sector, because in future, “vehicle insulation will play a far bigger role,” Hoffman noted.
Insulating cars is a topic BASF has given some attention to recently, according to Dr Karl Rudolf Kurtz, senior vice-president of R&D for BASF Polyurethanes.
BASF is testing vacuum panels based on PU foam, in work that is at the laboratory stage, in the Smart Forvision concept car it is working on with Daimler.
Here, Kurtz mentioned paper honeycomb structures, which give high strength as the mid-section of sandwich panels, and make them 50 percent lighter, These panels have a lot of uses, in vehicle load floors, for example, he said.
Short and long glass-fibre injection to reinforce polyurethane parts gives lightweight products with “excellent mechanical qualities,” Kurtz said. Glass fibre content can be up to 35 percent in foamed PU, giving good stability at high temperatures and superior impact resistance.
Acoustic engine noise absorbers
In “this important rush to lightweight vehicles,” polyurethane acoustic absorbers have an important role to play, according to Dr Oliver Kuisle of Huntsman Polyurethanes.
Tyre noise is a major component in vehicle and road noise, but the engine compartment acoustic is also important, Kuisle said. In passenger cars, engine noise is only about 15 percent of the total car drive-by sound, while tyre noise is 45 percent, Kuisle said. For diesel-engine cars, the corresponding figures are 28 percent and 32 percent, while for trucks the engine noise is a much higher proportion – well over 40 percent, he said.
Kuisle also pointed out that, today, not one OEM in the EU has a vehicle which fulfils the CO2 emission limits. OEM fleets will pay a penalty for vehicles which break the EU’s CO2 emissions limits, increasing every year, hence lightweight car construction is increasingly in demand, to save energy, and cut emissions.
Acoustic damping and insulation are uses which favour hybrid solutions, because combining functions such as damping and insulation makes it easier to save weight, the Huntsman expert commented.
Kuisle said that currently acoustic absorbers for engine compartments are mostly fibre solutions (6 million vehicles) while PU foam is used in about 3 million, melamine foam in 1 million and thermoplastic types in perhaps half-a-million vehicles.
For engine compartment absorbers, Huntsman has developed a solution together with automotive acoustic part maker Borgers AG of Bocholt, Germany. This uses discontinuous box block foam, cut into sheets. These are thermoformed into complex geometries giving extremely light parts at 15 - 17 kg/m³ density, and very good acoustic absorption, he said.
Kuisle listed the main advantages of these light PU foam acoustic absorbers as:
- Simple decentralised process;
- Good acoustic absorption properties;
- Ease of thermoforming; and
- Significant potential for weight savings
Huntsman’s Acoustiflex S system has good physical and acoustic properties, giving an extremely lightweight semi-rigid foam.
For Huntsman, as a foam system supplier, it is “our job via chemistry and/cell morphology to give customers what they need,” which in the present case is an open-cell foam for good acoustic function, he said.
For Borgers, Klaus Menke commented that, in contrast to the non-PU alternatives, a critical advantage of the box foam approach is that it allows production in relatively small units at or near the Tier 1 customer. This avoids the high costs of transporting light semi-finished parts.
The foam is made in a batch process using a so-called “Golden Bucket” system, in which the isocyanate and polyol are mixed in a 20-30 kg capacity ‘bucket’ before being poured into the box mould for foaming.
To create components for the engine area, Borgers cuts the light foam into sheets, which it bonds mechanically or adhesively to a fleece covering.
Borgers then hot-forms the parts at 180°C, and mechanically pre-treats the foam to crush the cell structure and make it more flexible.
Borgers specialises in acoustic components for all parts of the vehicle – the passenger, engine and luggage compartment. One speciality is a proprietary damping PU foam for engine compartment use, called IBO Pur.
Menke noted that for these parts, dimensional stability is important, as is the material’s media resistance
An advantage of the PU systems is their good dimensional stability at different temperatures, over long-term use.
Menke gave an example of a component Borgers makes for Volvo, where using PU gives a part weight of 535g versus 1859g or 880g for fibre parts. “You do distinctly reduce weight here,” he emphasised.
On-line acoustic foaming at Audi
Machinery supplier Polyplan GmbH has worked with car maker Audi AG on in-line acoustic foaming since an initial project in 2004.
Together they developed high-pressure injection of liquid foam into cavities in the already coated car body, directly on the line.
Audi now has a fully automated line for application of acoustic foam at its plant in Neckarsulm, used for a range of models.
All car manufacturers, especially those in the premium sector, attempt to design cars whose interiors are quiet and comfortable. Different kinds of noises are audible in a car interior, including engine noise, rolling noise, and aerodynamic noise, said David Schwab of Audi.
Sound propagation can be partially absorbed by sprayable insulation or noise absorption mats, but car body cavities also need to be filled, he said.
One route is to use pre-formed acoustic foam in the form of baffles, to dampen noise. But these are “high-cost systems for small-volume production,” Schwab commented, hence Audi’s preference for on-line foaming.
Schwab said the Audi A8 model currently has 20 foaming positions to fill body cavities, with four robots applying foam simultaneously. The cycle time is 218 sec, and the process uses up to 2 kg foam per car (initially, foaming took 13 min).
Schwab said there are economic advantages in filling the A pillar of an Audi A8 with acoustic foam, as it is a low-cost solution and can be integrated into a production line on a small scale.
Audi has been using open-cell two-component acoustic foam from Dow, with “excellent reaction time and volume expansion.”
Schwab said Audi is now looking at the possibility of installing a fully automatic foaming line for the A8 model at its plant at Ingolstadt, in Germany.
As the dose of foam is totally controllable, cavities of any size may be filled. Other advantages are full automation, high reliability and reduction of weight compared to baffles, Schwab said.
Flexible polyurethane foam with low fogging rates is used. As some of the cavities are partially open, fast-reacting foam systems have become accepted. At a process temperature of 40°C, users can get a rise-time of about 4 seconds, with a foam density of about 32g/litre.
The number of foamed car types is constantly growing, as does the number of foaming points per car, Schwab noted.
For Polyplan, Dipl Ing Roland Schumacher noted that a camera on the robot is used to find the required hole before injection of the foam.
For acoustic uses, Schumacher said, the liquid foam outperforms other materials. The process is highly flexible, and easily automated.
Liquid foam also has strong potential in design, Schumacher explained. For example, pillars can be made thinner and more rigid, improving the rigidity of the car body. The foam helps with lightweight construction, and also helps optimise crash performance, making vehicle design easier, he concluded.
Sandwich technology for light parts
As well as making acoustic parts, 125-year-old Borgers also produces lightweight parts using sandwich technology, including load floors, said the company’s Sascha Fuckert.
In 1995, Borgers built a plant in the Czech Republic for PU sandwich production, and made the first baggage compartment system for Mercedes, with acoustic insulation.
In 2000 Hennecke developed its Fipurtec plus technology together with Borgers and in 2003 a series order resulted in Borgers setting up two production lines at its Czech plant.
“Sandwich construction was then basically exploding,” which is why two more lines were needed, said Hennecke’s Jens Winiarz.
In 2007, two further lines were installed, producing more and more complex components, followed by a further line in 2008. Winiarz said cost pressure meant two spray robots were also added.
Fuckert noted that fibre composites using textile fleeces or mats in the resin matrix allow processors to make parts of different rigidity or strength.
Hennecke’s CSM (composite spray moulding) expertise is now used to make sandwich panels, where two outer layers with a honeycomb core are fixed with sprayed foam. Such panels can take heavy loads and have very high bending resistance.
Load floors in car boots are now made of such sandwiches, with paper honeycomb cores. This gives very lightweight, recyclable parts, and use of glassfibre fleece gives elasticity and also low price. The parts are strengthened and bonded with PU, and can be covered and laminated for an attractive finish.
The construction is lightweight, flexible, elastic, strong, and its costs are good. Fuckert said every load area is a different shape — but they can all be produced on one line.
Winiarz said a curing time of 45-50 secs is used. Glass fibre is not easy to work with, so Hennecke has devised a feed system to prevent any contact with personnel. At the end of this year Hennecke will add a new fibre chopper, to allow a few tonnes of fibre to be chopped before the knife needs changing, Winiarz said.
Load floors have complex geometries, and vents and cable channels can easily be incorporated with this technology, he added.
Composites are now starting to be for exterior parts: Fuckert noted that under-chassis uses are “rather new for us.” He said Borgers has a focus on exterior parts such as boot lids, where fibreglass may be replaced by carbon fibre, for example.