Preliminary analysis on micro-EDM milling of features with sloped surfaces machined on Si3N4-TiN

In this paper, the study of the micro-EDM milling of 3D sloped pockets realized in Si3N4-TiN ceramic composite is reported. The goal of the analysis is the investigation of geometrical errors affecting the surface accuracy of inclined walls, characterized by different draft angles. Preliminary experiments have been performed using two different levels of energy and varying the layer thickness used to implement the layer-by-layer strategy. Also the number of electrical touches done to monitor tool wear rate and depth error during each erosion process has been changed. The experimental results obtained by the measurements performed directly on the micro-EDM milling machine show that most of the errors on the manufacturing of inclined surfaces are found in the first part of the erosion process. These errors are mainly due to: the number of touches (control number) and the proper initial setting of the parameter assigned to compensate tool wear, the adjustment factor. Morphological measurements performed using a 3D high precision conoscopic holography scanner have confirmed that the surfaces of the inclined walls suffer of some defects on the top of the pockets. However the surface profiles of the inclined walls are quite good and no step-like trends have been detected, suggesting that the layer thicknesses for all trials have been properly set. Moreover, the draft angles values are very close to the ideal ones