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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.

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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.

The vibrations of a shaft in rotary mechanical systems supported by angular contact ball bearings are investigated theoretically and experimentally for various preloads in this paper. In the theoretical part of the study, a dynamic bearing model is presented, a rigid shaft supported by EHL angular contact bearing has been modelled as 5 DoF. Non-linear equations of motion are solved numerically by the Runge–Kutta method. In the second part of the study, an experimental setup that enables performing different operating cases has been designed to validate the theoretical results. Theoretical and experimental data are investigated and compared in both time and frequency domains and the results are compared. It is observed from both the theoretical and experimental studies that preload has a significant effect on the vibration behaviour. Results show that the increase in preload reduces the amplitude of the variable compliance frequencies of bearing, the natural frequency of system is shifted to a higher value, and using signal processing with an envelope spectrum gives better results in spectral analysis; small deviations occur between the theoretical and the experimental data due to modulation and noise from machine elements such as gear, motor, misalignment, waviness, etc. Therefore, the presented dynamic bearing model can be used with a reasonable accuracy to examine effect of preload on the vibration of shaft-bearing system.

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Aerostatic journal bearing applications mainly focus on high-speed precision machining, so predictable and smooth functioning of the system is crucial. Air is supplied to the bearing through a number of orifices and any unevenness in the size of these orifices will affect the performance of the system. The size difference could be due to manufacturing error and/or blockage of the orifice because of foreign materials in the air system. In this study, the performance of an aerostatic bearing with a partially blocked orifice is numerically investigated. Firstly, the airflow in the bearing clearance was modeled with Reynolds equation and this equation was numerically solved with the finite difference and differential transform hybrid method to obtain the pressure distribution. Then, the force and the stiffness are calculated from the pressure distribution for different blockage cases of the orifice and different blockage ratios. The results show that the partial blockage of the orifice significantly changes the performance of the system in a positive or a negative way according to the feeding hole position, and the blockage ratio also affects performance.

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