More components in the cars we drive now are made of plastic as material developments bring structural advantages and better crash behaviour
The automotive industry’s acceptance of plastic can be traced back to the early part of the century, but its story really starts with the development of advanced, high-performance polymers.
Their use has risen from an average of about 27kg per vehicle in 1970 to more than 165kg today. Forecasts indicate that in five years the average plastics content per vehicle will approach 180kg (some vehicles already surpass that figure). And, as plastics continue to break new ground in applications such as exterior body panels and secondary structural parts, they can be expected to have an even larger presence in the future.
The use of plastics in an ever-wider range of automotive applications can be attributed to one overriding factor: they have demonstrated compelling advantages over existing materials. Often the use of plastic was the result of thinking outside the box in order to meet the high demands of the marketplace.
As plastic technology continues to evolve, more and more components that have traditionally been made of steel are moving over to plastics. Automakers are discovering that for both exterior and interior components, as well as those under the hood, there are manufacturing, aesthetic and commercial advantages to adopting an increasing plastic content in car design.
Some parts such as bumper brackets and tailgates have been standard plastic applications for many years, primarily because of the structural benefits and behaviour in crash conditions. Long-fibre reinforced and continuous filament reinforced thermoplastic materials provide excellent toughness that ensures a ductile behaviour with no tendency to splinter in a crash. That ductile behaviour is maintained even at low temperatures and does not demonstrate the low temperature brittleness typical of non-reinforced and short fibre-reinforced polymers.
The trends in exterior applications extend through to a modular design in the roof area, thus overcoming the separation between exterior and interior applications. Development is also leading towards components that don’t necessarily require painting on all exterior surfaces.
With regard to interior vehicle applications an essential distinction must be made between semi-structural and structural parts on the one hand, and trim parts on the other. Components such as dashboards and seat structures have already been used for many years, while door modules have been added more recently. Here, as well as in other sectors, development is moving towards a modular design, such as the instrument panel from Ford that serves 12 models throughout its range of vehicles. Trim components such as the roofliner, door trim, pillar cover and trunk liner are well known visible parts in the vehicle, but the more stressed components such as parcel shelves and load floors now also fall under this category. Natural fibre reinforcements are also used in this field besides glass fibres. The option of laminating these materials in one step, with a textile decoration layer, offers interesting technical and economic advantages over conventional technologies.
Like exterior applications, those beneath the bonnet are focused on structural characteristics and behaviour in crash situations. Spare-wheel pans, underbody panelling/shielding and parts of the chassis are the components used in series production.
Underbody shielding is designed to meet the various vehicle segment requirements, from pure aerodynamic panelling and trim, to hard off-road operations. Weight reduction with enhanced acoustics will be the development trend in the years to come. The spare-wheel pans made in Glass Mat Thermoplastics (GMT) have now become a standard component for various car manufacturers. Besides the weight saving, they also offer cost advantages and feature a very high level of functional integration.
Initial applications in the chassis sector bear witness to the excellent suitability of the continuous filament-reinforced grades/materials in comparison with aluminium. Besides weight advantages, these materials primarily offer clear benefits in the sector of fatigue strength. Here as well, the trend is towards modularisation through to complete floor modules from bumper to bumper.
“The longstanding trend towards paint elimination in automotive components is driven by both cost and environmental considerations,” Tom Wehner of plastics manufacturer Solvay Engineered Polymers explains. “In the auto interior, low-gloss materials are being moulded in colour as replacements for painted parts.
“Pre-coloured thermoplastic polyolefins (TPOs) have been commercialised in grained, injection-moulded applications such as instrument-panel sections, glove box doors, air bag covers, and roof pillar covers. These combine aesthetics with impact resistance, which is important in the event of air-bag deployment. Vulcanised thermoplastic elastomers (TPVs) are being proposed as the surface layers in laminates with TPO structural substrates to provide colour, low gloss, and soft feel for interior parts. These components can be thermoformed into their final shapes.
Wehner continues: “On the exterior, painted parts, and the associated emissions of volatile organic compounds (VOCs), are being targeted by high gloss, pre-coloured materials that have been compounded for surface durability. Paint film technology is also effective in eliminating VOC emissions. This dry coating technique is in development in conjunction with the thermoforming process for the production of bumper fascias.”
Another advancement is the use of both hard and soft thermoplastics in automotive weatherseals. Techniques of multi-material extrusion are being developed that employ TPOs as the structural backbone and soft TPVs (or TPEs) as the flexible, sealing surface in an all-polyolefin weatherseal profile. This promises to replace traditional configurations of metal and thermoset rubber. The environmental benefits of recyclability and elimination of solid waste (process or endof- life) are important in such an application.
Solvay Engineered Polymers has devoted a productionscale, multi-material extrusion line at its Automotive Applications Development Centre in Auburn Hills, Michigan for the advancement of this technology.
As in all facets of automotive manufacturing, reducing complexity, or increased modularity, is a key concern. Ford, along with its Tier One plastic sub-assembly supplier, Faurecia, have developed a modular plastic cockpit model.
The same IP carrier is now used with 6 IP designs, on 12 vehicles sold around the world. It was designed by Faurecia as part of a new cockpit strategy called Syntes to commonise components and systems across multiple platforms. It meets or exceeds all global safety standards and cost targets, while still retaining each vehicle's signature look and feel. The Syntes cockpit system integrates over a dozen features, including the vehicle's cross-car beam, and is lighter than traditional steel-intensive cockpits. The new concept was launched last year across an entire Ford platform – for the Ford Focus and C-Max, the Volvo S40 and V50, and the Mazda3 passenger vehicles.
The IP, and particularly its carrier, has a very important structural and safety role in a passenger vehicle, essentially functioning as the skeleton of the cockpit. In fact, it functions as the base architecture to which IP components are attached and off which they function. Most importantly, during offset crashes, the IP beam must transfer loads for opposing sides of the vehicle to help prevent crushing inwards. It holds the front-end of the passenger compartment (the command centre), ties the left and right side of the vehicle together, stiffens the front-end for crash, supports the steering column, holds the airbag deployment canisters and HVAC system, and is the structural component from which hangs the IP topper, instrument cluster, centre console, knee bolsters, and glovebox door. The IP carrier must pass rigorous testing since it has to withstand high loading during impact and the required safety standards and tests which vary by geography.
Moving from a multi-component, steel design to the hybrid composite/steel carrier was a key element to meeting Faurecia's programme goals for its integrated cockpit design. A common IP design reduces design time and validation testing vs. multiple designs. The challenge was to create sufficient flexibility in the design so the finished IP had a unique appearance to each model. In contrast to a conventional carrier, the new compression-moulded GMT composite/steel design features a highly complex, singlepiece moulding that incorporates the cross-car beam, and integrates the functions and fixations for the air ducting, airbag support, steering-column support and knee bolster.
The hybrid carrier greatly simplifies assembly, improves NVH performance, reduces weight by 2-3kg and, for the first time ever with a single carrier design, meets or exceeds all US, European, and world safety standards (for full frontal and offset crashes with belted and unbelted occupants).
In fact it actually improves crash performance in some tests over the baseline steel design. It does all this while reducing overall manufacturing costs by 12 per cent, and offering high productivity (>6,000 parts/day), as well as high repeatability and reproducibility (R&R) on low-cost tooling. In fact, because the same common carrier can now be used for so many different styles and platforms, tooling costs were significantly reduced, as was the cost of analysis and crash testing. Additional programme savings were achieved through clever tooling design, where an insert is used so the same tooling can mould IPs for both left- and right-side drive vehicles. At the end of the vehicle’s life, the IP carrier can be disassembled and recycled, since it is made of a polypropylene/chopped glass fibre composite and the steel beam.
Two technology breakthroughs were featured in this design. First, a new material – Quadrant GMT E100F40 composite – and an optimised blank placement were required to provide improved impact performance, flowability and knitline integrity to ensure the cross-car beam was fully encapsulated at junction points during moulding. The part must absorb the energy during crash without brittle failure. The new grade also provided higher impact strength while allowing performance targets to be met at 2kg lower weight. Since blanks of the material are cut thicker (5.8mm) by Quadrant, less handling is needed during carrier manufacture. Secondly, a very significant breakthrough was required to prevent the steel tube from being crushed during compression moulding in the 2,000 T, high-speed presses. In fact, FPK was awarded a process patent for this development. Because of both technologies, the steel tube is fully encapsulated at junction points by the GMT composite during moulding, with the resin matrix flowing completely around the beam at these locations. This eliminates knitline issues seen in injection-moulded parts and helps prevent the steel bar from tearing away from the carrier during a crash.
Ford considered metal for the Mustang grille opening reinforcement (GOR) but research showed that stamping would require multiple pieces and still wouldn't be able to form the necessary complex shapes. Ford also considered die-cast aluminium and magnesium, which would have cost twice as much in piece price and tooling.
Computer analysis also predicted how the material would flow and mould, enabling tooling adjustments to produce a very precise component. The GOR is shipped to the assembly plant in finished form, requiring fewer man-hours per vehicle during assembly.
“The grille opening reinforcement is a rather large plastic part that extends from fender to fender - the whole width of the vehicle," says Robert Vasbinder, Product Design Engineer at Ford. "I've worked on a number of them over the last eight years. In the case of the Mustang GOR, we've used a variety of materials in the past. In considering a GOR for the new Mustang, we wanted to reduce secondary operations, tooling and cycle time.
“Our supplier was able to blend a particular resin that met all our requirements. What's more, this resin is 65 per cent post-consumer recycled material; in other words, about two-thirds of its parts' weight is recycled pop bottles!
I find that particularly self-satisfying from an environmental standpoint. The part also exceeds Ford's mandate of at least 25 per cent post-consumer content. Then, we also save two pounds on weight and 50 per cent on tooling costs compared to other materials, even the plastic we were previously using. We couldn't have done this part in a traditional steel stamping. Plastic also lets us put together an entire integrated front-end system; that's a most remarkable thing. And, for niche vehicles, or even mainline vehicles, one of the tremendous advantages of using plastics is the ability to make changes very quickly at low cost.
“We can move a hole and have it done within a week, whereas with metal it's not even feasible to put a hole in, no matter how much we want to spend.”
With designers seeking ever more innovative uses of plastics, and the moulding technology continuing to evolve, plastics will surely form a greater part of the cars of the future. In the powertrain, integrated plastic air intake and fuel systems will feature a fuel rail that is moulded into the air intake manifold, plus injectors and injector pods with an integrated throttle body and air ducts and air cleaners.
Another major development will be all plastic radiators, shaped any way automotive designers want for front ends that are lower and flatter.
Several Tier Ones are working on entire front-end modules that incorporate safety and energy absorption and support headlamps and the radiator all in one. They'll also provide added design flexibility and enhance appearance.
It's likely that the first third of the vehicle up to the wheel well will be all one plastic module.
Inside cars, instrument panels will include moulded-in electronics, including pre-assembled radio and control centres, to be shipped as a one-piece module. It will not only be easy to assemble but pleasing shapes and ergonomic designs will complement the driving experience.
Bold new plastics applications are continuing to emerge to meet rigorous challenges and create exciting opportunities. Plastics have not only made possible the innovations detailed here, they also open the door for exciting new concepts that are likely to occur in the next few years.