MODELLING ASPECTS OF REMOVAL MECHANISM AT ULTRASONIC AIDED ELECTRODISCHARGE MACHINING

The paper deals with researches concerning modelling of material removal mechanism at microgeometric level by computer aided finite element method (FEM) of ultrasonic aided electrodischarge machining (EDM+US). Simplifying hypotheses, boundary conditions and the method of meshing are presented. The approached microgeometries modelling can be assimilated as results of previous machinings: frontal milling, grinding, rough EDM etc. The microgeometries are parameterized to highlight the influence of various elementary surfaces and material characteristics on temperature distribution produced by discharges under conditions of ultrasonically aided EDM. At classic EDM finishing, FEM results emphasized the advantage of working with relaxation pulses, against commanded ones. When ultrasonic aiding of EDM finishing, commanded pulses become more effective compared to relaxation pulses. Moreover, commanded pulses can be produced within the ultrasonic semiperiod of liquid stretching, when working conditions facilitate the machining rate increase. In all cases, ultrasonic contribution within removal mechanism enlarges 4-5 times the volume removed by a single discharge. The comparison between FEM results and previous experimental data pointed out that the removal mechanism modelling, taking into account disposal and machined microgeometry dimensions, is essential in progress of understanding the complex process of EDM+US.