Innovative Manufacturing Method for Gears for Heavy Vehicle Application
Abstract: The present thesis is a summary of research result on an innovative manufacturing method for production of PM gears for application in heavy vehicle. The method uses a powder metal densifications process route to ensure full density. The thesis addresses an innovative processing route where loosely packed powder goes through a double pressing followed by double sintering combined with hot isostatic pressing at the end of the chain in order to reach the full density for the PM gear. The thesis addresses three research questions. First the feasibility of reaching full density for a gear constructed of standard modules relevant for heavy vehicles is investigated. Then the effect of gear geometry on the PM processing is studied. It is revealed that gear geometry influences the density distributions hence the final result. Therefore, the part of the research focusing on the relationship between gear dimensions and the densification results is conducted. It is shown that specific gear geometrical parameters could be more suitable to reach full density. Finally, a prediction model is proposed which can be used in order to measure the density before HIP and exclude risky geometries. A combined numerical and experimental research methodology is implemented in order to address the research questions in the thesis. A verified hardening model for one sample powder mixture is developed in ABAQUS using experimental densification tests. The model helps us to simulate the first pressing and follow the density gradients generated during the first pressing step. The density gradient will be stored in the green component and modified after first sintering and then is used as the input for the second pressing simulation. The result of the second pressing simulation is then modified to include the second sintering effects and finally it is used as the input for HIP simulation. This chain of simulations helps us to understand the gear geometry influence on the density gradients and neutral zone formation during the pressing process. It also ensures that the transition of open pores to closed pores occurs before HIP as a requirement to reach fully density in the analysis. Physical experiments were performed in order to validate FE simulations predictions. Density measurement and dimensional measurement are used to compare the results of FE simulations and physical trial results in order to validate and support the final conclusions based on FE model. Using the validated FE model, a methodology to predict the density before HIP is designed where different gear geometries are modelled and then a regression model is extracted which can predict the minimum RD in neutral zone of the gear before performing costly experiments for a specific material and gear dimensions.
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