Characterization of the CBN wheel wear and modelling or its effects on NGV grinding.
Vidal Irusta, Gorka
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This thesis is focused on improving a paramount grinding process used in the aeronauticindustry. The process is one of the last manufacturing steps of the nozzle guide vanes, whichform the stator of the exhaust of aeroengines. The enhanced physical properties of the materialswhich these components are made of, result in adverse conditions during the grinding processin terms of thermal and mechanical loads. Besides, the short cycle time needed foraccomplishing the high productivity of this sector promotes the appearance of issues relatedwith these loads, such as thermal damage and vibration marks.That being said, the scrapping of the nozzle guide vanes at this late state of their manufacturingprocess involves significant economical loses because of the accumulated work carried out withexpensive advanced technologies. The methodology of this thesis has been established in orderto understand the influence of the affecting parameters and thus, improve the productivitywhile the good quality of the parts is ensured.The wear suffered by the wheels is considered as one of the most influential aspects on thegrinding performance. Therefore, at first, a topographic analysis of the grinding wheel surfacewas conducted on different moments of the grinding wheel life. In this way, the wear types andtheir evolution could be detected and measured from a brand-new wheel to a totally wornwheel.Secondly, the process was studied in detail through experiments. Due to the complexity of theindustrial process, a test bench was specially designed for reproducing the grinding conditionsin a controlled manner. In order to enhance the consistency with the industrial process, thesame superabrasive material and workpiece alloy were used. In addition, the value of the inputparameter was calculated taking the industrial process as a reference. In this way, not only theinput, but also the outputs could be controlled and measured. Thus, the forces and the surfacequality were measured in order to understand the influence of the input parameters such as thegrinding speed and contact depth.Finally, the information gathered in the previous two steps was used for developing a numericalmodel based on the finite element method. The model reproduced the contact between amultigrain surface and the workpiece material. Both of them were defined with the physicalproperties of the materials used in the industrial process. In addition, the model addressedaccurately the geometry of the grinding wheel since the real topography was imported into themodel through a procedure specially developed for this study.The results obtained from this study revealed that there was a coherency between theexperiments and the model that can be explained through mechanical and thermal principlesmentioned previously by other authors. Thus, the results obtained from this study allows tounderstand the influence of the input parameters on the process. On this basis, themethodology developed in this thesis present a useful scenario for the study of grindingprocesses by means of experiments and numerical models that comprises some aspects thathave not being comprised previously in bibliography.