Modeling of machining process of EB-PVD ceramic coatings using discrete element method

Abstract

In this work, a new discrete element model (DEM) for simulating the machining process of thermal barrier coatings is presented. The effects of cutting processing parameters, including cutting depth and cutting speed, on the cutting force and chip morphology are studied. In the model, a columnar grain microstructure mimicking the electron-beam physical vapor deposition (EB-PVD) coating is used. The results show that, as the cutting depth increases, the cutting chip morphology changes from fine powder form (ductile mode) to large chuck pieces (brittle mode). The transition depth or the critical cutting depth is determined based on the Griffith fracture criterion. The transition is also illustrated using the numbers of broken bonds and cutting energy changes in the DEM model. In the ductile mode, the number of broken bonds is increased gradually. In contrast, at larger cutting depths, the brittle mode causes a step-wise increase. Moreover, the maximum cutting force is found correlated to the cutting depth, which agrees well with an analytical solution based on fracture mechanics principles. The period in the cutting force is consistent with the diameter of the column grain. Finally, the cutting speed has little effect on the cutting force and chip morphology due to no strain rate sensitivity.