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Optimisation of the tooth root geometry of plastic gears

At a glance


The use of plastic gears in drives is growing rapidly, especially in the module size range 0.5 to 1.5 mm and at maximum load cycles during the product life of 105 to 106. A key factor for reliability is the tooth root strength of the gears. Although injection moulding, which is the common production method for plastic gears, allows a high degree of freedom in designing the tooth root geometry, plastic gears are usually fully rounded with a constant radius, similar to the production of conventional steel gears. The calculation method according to VDI 2736 also assumes such a tooth root shape. However, the special properties of the material plastic (non-linear modulus of elasticity, transient behaviour) with its high strain rates are not taken into account.

To obtain meaningful results for an optimal tooth root rounding, the exact understanding of the damage criterion of plastics or plastic groups has to be researched. The focus here is on POM and PA66. With this knowledge, it is possible to design plastic gears in an optimum way concerning their load and the speed of the force impact. In the further course of the project, various tooth root geometries on plastic gears will be tested theoretically and experimentally and potentials for increasing the load-bearing capacity will be derived. Essentially, the material/failure behaviour of plastic gears is to be investigated in this research project, the tooth root geometry is optimised from this and thus impulses for the further development of VDI 2736 in the standards committee has to be made.