ZF Composites Tech Center The Art of Lightweight Design
The only way for vehicles to meet CO₂ emissions targets is to lose weight. ZF is developing revolutionary weight-saving components for series production.
The press slowly opens to reveal a wheel mount made out of carbon fiber-reinforced plastic. The exceptionally durable component feels very light in the hand. Even so, it’s hard to believe what it’s made of: the material – rolled-up mats of carbon fiber – looks more like fabric intended for the clothing industry.
Since July 2013, the ZF Composites Tech Center in Schweinfurt has been developing lightweight products made out of fiber-reinforced plastics (FRP) for a variety of structural components. Two types of composite materials are used: carbon fiber-reinforced plastics (CFRP) and glass fiber-reinforced plastics (GRP). ZF has already produced a lightweight wheel mount made out of both types of plastic. Combined with a lightweight damper, the new wheel mount takes care of damping and wheel guidance in cars – at the same time, it weighs 40 percent less than more conventional designs. To make sure such weight-saving solutions are put into series production as quickly and cost-efficiently as possible, ZF has invested 3.1 million euros (about 4.2 million dollars) in the Composites Tech Center, which has a total area of 400 square meters (4,300 square feet). The buildings, machinery and equipment all exude the spotlessly clean atmosphere normally associated with clean-room laboratories.
“We provide the production technology expertise required to design and build functioning, pre-production prototypes – but we’re not a production facility,” is how Dr. Ignacio Lobo-Casanova, head of the Center, describes its remit. “Because there’s a very close relationship between the manufacturing processes and product characteristics of fiber-reinforced plastics, we help the ZF divisions with their development work from a very early stage.” Dr. Michael Heselhaus, the man responsible for developing the Composites Tech Center, goes on to explain. “Compared to steel or aluminum, there are so many more variables to consider when you’re working with FRP. In other words, each component makes different demands on the material and how you work with it.”
Developing prototypes in-house
Other specifications include target production costs, planned quantities and required cycle times for series production. “We work with the product development teams to draw up detailed specifications covering all requirements, so we can make sure that when the FRP products go into series production, the whole process is as efficient and cost-effective as possible. This means, for example, adjusting product designs to achieve optimized cycle times while calculating the costs involved,” adds Heselhaus. Another advantage of the Composites Tech Center for ZF’s development network: the technology company is now able to produce FRP prototypes in-house, without resorting to external partners. The development departments in the various ZF divisions very much appreciate this facility.
The ZF Composites Tech Center exudes the spotlessly clean atmosphere usually associated with clean-room laboratories
Prototype of a combined suspension strut-wheel mount for cars, made out of carbon fiber-reinforced plastic (CFRP).
Early sample of a suspension strut-wheel mount module made out of CFRP – still a long way to go before it will be ready for series production.
Making the most of every fiber
In practical terms, collaboration between the ZF divisions and the Composites Tech Center – which is managed by the Corporate Production unit in Friedrichshafen – happens like this: once the general parameters and concept for an FRP component have been specified, the product engineers turn to the Composites Tech Center for advice and support. The first step is to produce material samples, which at this stage bear no resemblance to the finished product. They are tested for conformability, toughness and temperature resistance, along with a host of other properties.
The next step is for the math wizards to process the test data using simulation tools. A high-performance workstation is used to model every detail of the prototype – the part that will eventually end up as a CFRP wheel mount, for example. The software analyzes how the component will behave under different load spectra, and how its geometry could be optimized where necessary. The tools are even capable of testing how well the component will function in a vehicle – but only virtually, of course. Only then does the Schweinfurt team start working on the actual product prototypes. In the case of the wheel mount, a number of shaped layers are cut out of the fiber mats, and a robot then drapes them – paying meticulous attention to the orientation of the fibers – on a foam preform that is geometrically identical to the actual component. Lobo-Casanova and his team also develop a suitable mold for the press. Once the prototype has been produced using the RTM process (Resin Transfer Moulding), it must prove itself in real-world vehicle tests. For testing the suspension strut-wheel mount module, ZF uses a very exclusive car: the company’s all-electric innovation prototype.
Adding value instead of cost
“Emissions legislation is the main factor driving lightweight design in the automotive industry,” explains Lobo-Casanova, “because it will be very difficult for carmakers to meet future emissions targets simply by improving their engines.” The ZF Composites Tech Center only handles some of the company’s lightweight design initiatives, concentrating mainly on thermoset FRP materials ZF is also testing thermoplastic FRP composites (such as organic sheet), as well as lighter metals. Before ZF will even consider building structural components out of FRP, or approve the production of prototypes by the Schweinfurt Composites Tech Center, they must meet two important criteria. First, GRP and CFRP will only be used if they are the materials that best match the properties required of the component. And second, the new component must be capable of integrating multiple functions – ideally by replacing several hitherto separate components. “This allows us to offset a large proportion of the additional cost that’s still associated with using FRP as a source material and with the complex processing involved,” explains Lobo-Casanova.
Pictures: Peter Neusser