In this study, the variations of machining performance outputs, namely workpiece surface roughness, surface profile power spectral density, workpiece removal rate, electrode wear rate, relative wear, workpiece surface hardness, and workpiece surface microstructure were experimentally investigated with the varying machining parameters for metal powder mixed dielectric liquid in electrical discharge machining (EDM). The machining tests were conducted by using a prismatic steel workpiece and copper electrodes with graphite and boric acid powders (H3BO3) mixed kerosene dielectric at different powder concentrations and pulse time settings. The experiments have shown that the type and concentration of the powders mixed into the dielectric and the pulse time were effective on machining performance outputs in EDM.
In the current paper, the radial, axial, rocking, and yawing vibrations of a rigid grinding spindle supported by a pair of angular contact ball bearings are studied. A computer program was developed to simulate the dynamic behaviour of the spindle and results are presented in the time, frequency, and waterfall diagrams. Results from the simulations for different spindle speeds show the characteristic ball passage frequency (BPF) (varying compliance) and its harmonics due to non-linear Hertzian contact between the balls and the races for even a defect free bearing. This behaviour is, of course, predicted theoretically, but most of the previous simulations only give the effect of BPF when it coincides with the natural frequencies of the system or under specific conditions. This paper will be a guide for researchers studying vibrations of a spindle supported by ball bearings as it describes the details of the theoretical background of the modelling and simulation.
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