Multi-Material Vehicles - Manufacturing the Car of the Future
Fuel price; it’s one of the biggest bug bears for vehicle owners the world over. Even though the current price at the petrol station is one of the lowest consumers have seen in a while, the issue still arises – what makes a car more efficient?
Well, as a motorist, you will know that driving carefully - in terms of calculated braking and acceleration - plays its part, and electric drivers will know that miles per gallon (MPG) ratings of up to 97 MPG can be achieved.
However, it’s what happens at the manufacturing plant that can make the most difference, and with ever tightening regulations around emissions and fuel economy – car producers will be looking at even the smallest parts in order to shed unnecessary weight on their final design.
The recently developed Multi-Material Lightweight Vehicle (MMLV) – a concept vehicle brought to life by Ford and Magna under a project funded by the US Department of Energy’s Vehicle Technologies Office – for example, allowed for almost 25% weight savings, while increasing its fuel efficiency by 15% to 20% . These outstanding results were achieved by combining the aluminium-intensive structure with carbon fibre, magnesium and titanium.
Automotive IQ sat down with Chris Needes, Global Market Manager, Automotive Chassis and Powertrain, and Hans-Jürgen Jäger, Global Market Manager, Automotive Exterior, NORGLIDE® Bearings and RENCOL® Tolerance Rings – experts at Saint-Gobain to gain an insight into the challenges faced by car manufacturers aiming to integrate MMLV principles into their production.
“While we believe that multi-material cars are an important part of the automotive industry, there are a number of challenges that we have had to overcome to help to make it a reality,” explains Needes. “Multiple materials used within a small confine of space within systems such as a steering column, door hinge or motor stator, for example, can lead to an accelerated rate of corrosion and therefore risk damaging more expensive parts of the car over a shorter period of time – eliminating the benefits of weight saving in the short term.”
“If we take a hinge for example,” says Jäger, “there is the possibility that steel and aluminium will be interacting in a tight space. This could be due to the hinge straps (aluminium) playing the role of a cathode, the bearing and pin (often steel or steel elements) the anode, and together with an electrolyte - you’ve created a battery; a perfect environment for accelerating corrosion.”
The challenge, therefore, is to create a bind between two different metals without encouraging corrosion to occur and rust to take over.
“We’ve invested many years of research and development into the use of multi-materials in car components and how they react with one another,” says Needes.
“In certain critical areas, such as: steering columns, door hinges and electric motor stator mounts, the use of innovative small, but important, parts can make a big difference to the overall mechanism performance.”
“In order to remove weight from the car, save on emissions and unnecessary fuel expenditure, we firstly had to identify these potential ‘sacrificial elements’ where dissimilar materials could be used in place of heavier metals.”
“The collapsible steering column, for instance, poses an ideal candidate for light weighting as it consists of interlocking shafts where steel can be replaced with aluminium. Specifically for this application, Saint-Gobain designed its high-quality carbon steel and alloy based tolerance rings, which are radially sprung component fasteners that enable optimal joining between mating steering column shafts – to enable the use of dissimilar materials. The use of different materials enables significant weight savings.”
Their design also dismisses a further manufacture and customer concern during the light weighting of vehicles – noise. “By using specially developed tolerance rings we can ensure a perfect fit between steering shafts, which leads to reduced vibration, ensuring a noise-free environment inside the car.”
Tolerance rings are often used to replace heat-to-press methods and adhesives, for example, in electric motor stator mounts as a way to save weight; again via the use of multi-materials: stator casing can now be made from lighter aluminium. Tolerance rings streamline assembly by simply being inserted around the stator and press fitted into housings.
“Did you know that there can be up to 25 electric motors in a modern day car? If we can make weight savings on each of those individual motors, those savings are multiplied by 25 – making for a significantly lighter vehicle.”
The tolerance rings also compensate for differential expansion, greatly reducing the chance of assembly failure when dissimilar materials like steel and aluminium are used.
It’s therefore apparent that where manufacturers can save on weight, they will. Another key area where this weight saving can be achieved is in the door of the car, and in particular the hinge. There are many hinges throughout the car; in the doors, boot, bonnet, overhead canopy opening and more – as a result, the weight saving can be substantial.
“In the car hinge application, automotive manufacturers and suppliers can now achieve up to a 40% weight saving of the total component compared to using purely steel parts, for example,” comments Jäger.
“The bearings in these components sit between the hinge pin and housing to ensure smooth movement when the door is opened and closed. As opposed to the conventional bearing, composite bearings’ Polytetrafluoroethylene (PTFE) liner – as used in NORGLIDE® Bearings - also compensates for any misalignment between the straps and the pin within the car hinge, ensuring smooth movement.”
Composite bearings in this application extend the lifetime of the hinge, preventing paint from chipping and eliminating red rust. In addition, when the vehicle is in use, the PTFE liner within the composite bearing compensates for tolerance variations, such as thermal expansion, ensuring the perfect fit between the hinge pin and the housing. The PTFE properties in the layer greatly reduce the risk of the door squeaking when opened or closed throughout the car’s life cycle.
The multi-material car is a step in the right direction. Lighter cars means less emissions and increased fuel efficiency for consumers. However, if manufacturers focus purely on the weight issue they run the risk of facing problems further down the line, such as the aforementioned corrosion and rust. With a partner that understands the bigger picture, right down to the smallest intricate details, manufacturers can not only provide users with the car of tomorrow, today – they can do so well on into the future.