Investigation of near dry EDM compared with wet and dry EDM processes

Journal of Mechanical Science and Technology - Material removal rate (MRR), tool wear ratio (TWR) and surface roughness (SR) obtained by near-dry EDM process were compared with wet and dry EDM at...     

A comparative study on citrate sol-gel and combustion synthesis methods of CoAl2O4 spinel

CoAl₂O₄ spinel was successfully synthesized by combustion synthesis method using glycine and urea by 1:1 molar ratio as fuels and sol-gel process using citric acid as a chelating agent. The as-synthesized powders were calcined at desired temperatures to obtain CoAl₂O₄ spinel as a single phase. X-ray diffraction, thermogravimetric, and differential thermal analysis results revealed that the formation of CoAl₂O₄ spinel in combustion method needs 300°C higher temperatures than those of sol-gel. Scanning electron microscopy and transmission electron microscopy analysis results revealed that “sol-gel spinel” had nanometric particle size which was smaller than those of “combustion spinel.” Temperature programed reduction with hydrogen and Fourier transform infrared spectroscopy results declared that there was a little residual cobalt oxide in combustion spinel while there is no oxide resided in “sol-gel spinel.” Consequently, the sol-gel method has more benefit in synthesizing spinel with sulfate precursors than combustion.     

Designing a double-negative metamaterial photonic crystal using the Thue–Morse sequence

Journal of Computational Electronics - This study investigates the propagation of electromagnetic waves through a one-dimensional quasi-photonic crystal with the transfer matrix method. Our...     

MODELING OF DRESSING FORCES DURING ROTARY DIAMOND CUP DRESSING OF VITRIFIED CBN GRINDING WHEELS

This paper presents a mathematical model of dressing of vitrified CBN grinding wheels by a diamond cup dresser. It predicts the dressing forces during rotary diamond cup dressing of vitrified CBN grinding wheels. This model is based on the fracture of abrasive grits, the fracture of the bond and the contact forces between dresser and grinding wheel. It considers the kinematical influences and in particular speed ratio and overlap factor during the dressing process. A Weibull distribution is used to predict the probability of bond fracture and also the collision number between the diamond grits of a rotating dresser and the CBN grits. This model is validated by experimental results. The theoretical modeling values agree reasonably well with the experimental results. On the basis of this model the effect of different cup dressing parameters on dressing forces is theoretically discussed with the aim of establishing appropriate dressing process configurations. Furthermore the presented model provides a basis for further prediction of wheel topography and the grinding process.     

Experimental study of rotary magnetic field-assisted dry EDM with ultrasonic vibration of workpiece

Dry electrical discharge machining (EDM) is a green machining method which replaces the gas instead of liquid as dielectric medium. Due to the environmentally friendly nature of this method, recently, researchers focused on characterization of this process. In this work, effects of rotary magnetic field and also ultrasonic vibration of workpiece were studied on dry EDM process performance. Conducted experiments were divided in two main stages. At first stage, preliminary experiments were carried out to determine the best tool design in material and geometry points of view by considering the material removal rate (MRR). Also, effect of magnetic field was studied in the first stage. Results of the first stage of experiments indicated that the brass tool with two eccentric holes has the highest MRR rather than the other existing tool. In the second stage of experiments, parametric study on dry EDM process were implemented by using a brass tool with two eccentric holes and by applying rotary magnetic field for all experiments of the second stage. Influences of parameters such as pulse current, pulse on-time, pulse off-time, tool rotational speed, air injection inlet pressure, and especially power of ultrasonic table were studied on MRR, surface roughness (SR), electrode wear rate (EWR), and overcut (OC). Results showed that magnetic field has positive effects on MRR and SR. Also, by application of ultrasonic vibration achieving to superior MRR is feasible. At the end of the work, mathematical models were developed to correlate a relationship between process inputs and main outputs.     

Regeneration of Activated Carbon Loaded with Cyclohexane Using Supercritical Carbon Dioxide: Experimental Results and Modeling

Regeneration of granular activated carbon loaded with cyclohexane by supercritical carbon dioxide was investigated at varying temperatures and pressures. Cyclohexane concentration‐time profiles were measured by means of a supercritical extraction apparatus coupled with an online GC analyzer. The maximum yield of regeneration was 68 % at 55 °C and 140 bar. A mathematical model was proposed which agreed well with the experimental data. Both the Toth and the Langmuir‐Freundlich isotherms were used as adsorption isotherms under equilibrium condition. The mathematical model for activated carbon regeneration was able to adjust the experimental data with relative absolute average deviations of about 4 % and 3.25 %, respectively, for the Toth and the Langmuir‐Freundlich isotherms.     

PREDICTIVE MODELS OF THE SPRING-BACK IN THE BENDING PROCESS

Spring-back is one of the most sensitive features of sheet metal forming processes because the elastic recovery during unloading leads to some geometric changes in the product. Three parameters that are most influential on spring-back in the V-die bending process are sheet thickness, sheet orientation, and punch tip radius. In this research, radial basis function (RBF) neural network and back propagation (BP) neural network approaches are used to predict the spring-back using the data generated from experimental observations. The performances of the models in training and testing sets are compared with those observations. Furthermore, output obtained through regression analysis is used to compare with the two developed model outputs. The results indicate that both networks can be applied successfully for prediction of spring-back against the input parameters of the V-die bending process. Also, the BP model shows better performance for prediction of spring-back with respect to the RBF model.