Plastic Cogwheels With Metal Teeth

Metal teeth and a body made of plastic or foamed aluminum – these could be the cogwheels of the future in a lot of applications. They are lighter, quieter and cheaper to produce than conventional models made entirely of steel.

The production of cogwheels often involves “broaching”: A file mills the teeth one by one round the edge of a steel cylinder. This takes time, and is correspondingly expensive. Engineers from the Fraunhofer Technology Development Group TEG and their project partners have developed a new generation of cogwheels – with metal teeth and a body made of plastic or of foamed metal. They are quiet, lightweight and cheap to produce.

The engineers used cogwheels about a hundred years old as their model. At that time, the hub was often made of wood, with the individual metal teeth mounted on it. To create modern variants of these composite wheels, the researchers attach metal cogs to a circular template. They fill the inside of the ring with plastic or with foamed aluminum. This fixes the roots of the cogs. Another alternative is to make cogwheels from steel rolled strips. In this case, individual metal teeth are glued or welded at defined intervals to a flexible steel rolled strip. Finally, the strip is bent and joined at the ends. As before, the hollow interior of the rolled strip is filled with plastic or foamed metal. “The great advantage of this type is its tremendous flexibility,” explains Matthias Böning, head of the production process department. “The steel strips can be processed while they are straight, and are easy to shape into a ring. This enables us to produce all kinds of cogwheel systems, and even corrugated roller coasters.”

The new cogwheels contain less metal, and are thus lighter than their predecessors and ideal for the aerospace industry. They also produce less noise, as the material of the wheel hub absorbs vibrations and therefore sound waves. Composite cogwheels offer a whole range of other advantages too: They are easier to manufacture than conventional models, and they require a smaller amount of expensive steel. The cost of warehousing is lower for manufacturers, too, as they only need to store separate parts such as metal cogs, steel rolled strips and filling material instead of pre-fabricated cogwheels. The parts are then assembled according to the customer’s specifications: Cogwheel size, number of teeth, shape, delivery date – all these things are determined by the user. Representatives of the manufacturing industry are already showing an interest in this technology. “We keep getting inquiries from industry as to when they can start producing these cogwheels,” says Böning. “In four or five months’ time we plan to produce a manual – a kind of recipe collection for composite cogwheels.”

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