Lighter engines and transmissions

by Hans Diederichs

WGP develops lightweight design solutions for future modern mobility

That gear wheels, for example, can be manufactured up to 60 percent lighter was demonstrated by scientists from the WGP (Scientific Society for Production Technology) as part of the Massive Lightweight Construction Initiative of the Federal Ministry of Economics and Energy (BMWi). And the production time for individual parts could also be reduced by a third. "We were able to achieve those cross-application research results because we are broadly positioned within the WGP and do often work in a multidisciplinary manner," clarifies Professor Mathias Liewald, head of IFU Stuttgart and one of the project leaders. "For this project, among others, metal forming engineers, process developers and IT experts collaborated successfully within this project.“

Gear wheels re-designed

The WGP scientists not only developed so-called "built gears", but also created corresponding manufacturing chains for their production. "The gear wheels were broken up into two or three individual parts: the gear ring, the gear wheel body and the shaft-hub connection," explains Liewald. "With the help of further developed production processes, we produced so-called built gear wheels, in which different local strength requirements were taken into account. This in turn enabled us to drastically reduce the weight of the gears. A total of five WGP institutes were involved in the research work: IFU Stuttgart, IWT Bremen, ISF and IUL Dortmund and utg Munich together with The Gear Research Centre (FZG) Munich. "The innovative gear wheels could be used not only in automotive engineering, but above all in lighter transmissions such as those used in scooters or e-bikes," reports Liewald. "We were able to achieve such cross-application research results because we are broadly based within the WGP and we can work in a multidisciplinary manner. For this project, for example, metal forming engineers, manufacturing process developers, drive system engineers, IT and other experts joined in the mentioned project initiative.  

The weight reduction of 60 percent while maintaining the same functionality was made possible by combining different materials in the "built" gear compared to the "full-body" gear. Normally, gear wheels are manufactured monolithically, i.e. from one material as a single workpiece. "We developed a new way to separate them into two or three individual parts: the gear body, which transmits the torque, the connection of the wheel to the shaft and the gear ring, which must be particularly stiff and wear-resistant due to the high torques and contact pressure acting on it," says Robert Meissner, project member at IFU Stuttgart, describing the innovation. The researchers therefore chose a high-strength material for the gear ring, which in turn was not necessary for the gear body.

New manufacturing processes

In a first process, the scientists inserted circular discs of sheet metal stacked into packages into the gear ring, which was heated up to 200 degrees Celsius. In this case such kind of design of using packaged sheet metal layers as a gear body was investigated here the very first time. Alternatively, a steel or aluminium body was formed into the inner side gear ring without heating. This joining process by plastic deformation also was approved as an innovation for gear production. Although it requires higher forces than the conventional forging of one-piece gear wheels and the metal forming tools wear out more quickly, as expected. However, compared to packetizing, the energy for heating up to 200 °C can be saved in this process route. Cold extrusion - in this case the established lateral extrusion process was utilized - is nevertheless much more energy efficient than previously mentioned processes. "In the past of course we found numerous designs of built gear wheels in industry”, says Meissner. "But the new process is much more economical because we have combined multiple manufacturing steps into one.“

Piston Pins - Lighter and Cheaper

The new manufacturing process for manufacturing more lightweight piston pins was developed by means of numerical simulations that took into account the requirements for the strength of the component varying locally. First, the researchers simulated the metal forming process of a piston pin and in a second step they simulated the load applied to the component during use on the computer. In the virtual world, during joint project work it became apparent that indeed individual steps in established production processes of piston pins in future can be left out. As a result, the production time for the new piston pin design could be reduced by more than 30 percent.

Finally, the researchers calculated the maximum weight reduction of piston pin by use of topology analysis. In relation to conventional piston pin design, researchers achieved weight savings by 4%. "Considering the fact, that piston pins have been optimized again and again for more than a hundred years, this is, relatively speaking, an astonishing result," emphasizes Liewald. This further weight reduction was made possible by using a helix shaped design on instead of the previously cylindrical inner contour of pin, which was produced by ironing. With the help of this advanced cold forming process, the strength of the soft-annealed raw material for the piston pin was increased by 38 percent. These optimized pins can be used in any combustion engine, but also in completely diverse applications, such as in short shafts in electric motors or new axle elements in future chassis. "The limitation lies primarily in the length of the tube" Meissner clarifies. "More economical production should result from the reduced production time, which ultimately leads to lower production costs. But not only mentioned components improved in this public funded joint work by 5 WGP institutes in future are open to various applications: "The further developed manufacturing process based on an ironing process to produce such helical shape on the part inner surface is not only suitable for piston pin production, but also for the production of weight-reduced hollow components such as thin walled housings or threaded sleeves in general. This means that in future weight can be significantly saved in a wide range of different areas in most of the diverse vehicles," says Liewald.

Source: WGP                 Photo: IFU Stuttgart

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