Development of a model to predict the machining forces in the rolling process of powder metallurgical parts using the example of gears

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Powder metallurgical gears are porous and, therefore, achieve lower load-carrying capacities than full-dense, wrought steel gears. External transverse rolling increases the density of both the flank and the tooth root to increase their strength. The goal of this project is the development of a model which predicts the machining forces in the rolling process. Existing model, e.g. for sheet rolling, can not calculate the rolling forces due to the high complexity of the gear rolling process. This complexity originates out of the two-flanked tooth contact, the contact ratio and the continuously changing contact geometries. Additionally, the material properties are continuously changing because of the densification and work hardening. The knowing of the machining forces is crucial for the dimensioning of the tool machines and the process design in a very early state of the development. Known machining forces lead to shortened development time for both process and the tool machine itself. This is crucial since the process chain pressing - sintering - rolling is significantly shorter than the convectional, gear cutting process chain. Therefore, a fundamental development of a prediction model of the machining forces is necessary to facilitate this process chain for the industry on the long term. For the development of the model for the prediction of the machining forces in the rolling process of PM-parts the following sub goals need to be achieved: 1. Development of a constitutive material model which considers the changes in density in the rolling process. 2. A mathematical description of the penetration of tool-workpiece depending on the tool- and workpiece geometry and the process kinematics. 3. Conception and execution of analogy-tests to generate a database considering different contact conditions and recording the occurring forces 4. Development of a rolling force model bases upon the database of the analogy-tests. 5. Transferring the contact conditions of gear rolling onto the rolling force model and verification of the results. The development of a rolling force model leads to an improved understanding of the rolling process of gears and enables for a process design which meets the requirements of the machine, the process and the tools.