Reinventing the cog

German researchers turn to old Dutch windmills for inspiration in the development of composite cogwheels.


Engineers from Germany’s Fraunhofer Institute have looked to the past to develop cogs that are lighter, quieter and cheaper to manufacture than the conventional alternative.


Inspired by the cogwheels in 150-year old Dutch windmills, where metal teeth were individually mounted on wooden hubs, the team from the institute’s Technology Development Group (TEG) in Stuttgart has developed composite cogwheels with metal teeth and separate plastic or metal foam bodies.


These composite wheels are manufactured by attaching individual metal teeth to a flexible steel rolled strip, which is bent and joined at the ends and then filled with plastic or foamed metal.


The project’s deputy manager Dr Christian Feddern explained that the chief advantage of the new cogs is their relatively low weight, making them particularly suitable for use in the aerospace industry. ‘If you replace metal with plastic or metal foam, you can get a very high weight reduction,’ he said.


The cogwheels also have highly desirable sound damping properties. While current metal ones are loud and noisy, Feddern said that the plastic or metal foam material in a composite cogwheel will absorb vibrations, recommending it for applications within gears and engines in the automotive industry.


Feddern added that the composite cogs also have considerable maintenance advantages. While damage to just one tooth has previously meant the replacement of an entire wheel, the new concept would enable engineers to repair broken cogs onsite rather than wait for the delivery of a new wheel.


Following promising testing and simulation using Finite Element Analysis software, the team is currently running long-term stress tests on a number of cogwheels to gather further performance data. With a view to commercialising the technology, the team is also in the process of setting up a consortium of industrial partners who can evaluate the cogs in many different applications.


The plan is to invite up to 10 interested companies to join the consortium and invest and work on the development of the technology at the TEG laboratory in Stuttgart. Feddern said that depending on the level of investment, interested companies might then be granted exclusive rights to the technology.


He confirmed that he has already had a high level of interest from both Volkswagen and DaimlerChrysler.