| In recent years,hard and brittle materials,such as optical glass,silicon carbide and tungsten carbide,are widely used in optics,electronics,communications and aerospace industries,and the higher requirements for machining precision and efficiency have been put forward.The metal bonded super abrasive grinding wheels are usually applied in precision and ultra-precision grinding of difficult-to-cut materials.But the wheel surface will be blunt during grinding process,which can affect the wheel service life and the grinding performance,therefore it is necessary to dress the metal bonded wheels.Up to now,it is difficult to obtain the high accuracy wheel by traditional dressing methods.Aimed at the above-mentioned problems,the mechanism and the process of electrical discharge dressing on bronze-bonded fine grain diamond grinding wheel are studied to obtain high profile accuracy of wheel after truing and dressing.This research will offer a good academic and practical support for application of metal bonded super abrasive grinding wheels.The main research contents are as follows:(1)The micro process of electrical discharging dressing on bronze-bonded fine grain diamond grinding wheel under the condition of the continuous pulsed discharge was described.The single pulse erosion experiment was conducted and the crater topography was investigated.At the same time,a mathematical model for thermal transfer in electrical discharging dressing was built.The temperature distribution was simulated to discuss the influence of wheel speed and peak current on the temperature field of wheel surface.(2)The eletctrode wear rate of the copper electrode and other three copper tungsten electrodes was analyzed.Then the optimum electrical parameters were studied by orthogonal design to ensure low-wear rate of the self-developed copper tungsten electrode;the gap voltage and current during discharge process were measured.Then the variety of electrode wear phenomenon on the increase of the number of machined holes were observed and studied.Finally,the causes of carbon layer generation and the effect of electrode wear on carbon layer were analyze.(3)The experimental platform for electrical discharging dressing on bronze-bonded fine grain diamond grinding wheel was designed and set up.The influences of peak voltage,peak current,duty ratio,and wheel speed on radial circle run-out and axial surface roughness were investigated.Three kinds of inner-flushing copper tungsten electrodes with different arcs were designed in order to improve the dressing efficiency;the influence of long-arc area on dressing efficiency and accuracy was discussed based on the results of dressed wheel surface topography,grain protrusion height,radial circle run-out,and axial surface roughness.At last,tungsten carbide workpiece was machined to evaluate the dressing effect of fine grain grinding wheel according to grinding performance.(4)The dielectric flushing between the electrode and the grinding wheel was analysed by using computational fluid dynamics theory,and the movement of dielectric was explained by simulation.A high speed camera was adopted to observe the dielectric flushing during dressing process and the eroded materials were observed.It verified that the secondary discharge rate between gaps was increasing.This discussion could supply theoretical and experimental supports for further improvement of the dressing accuracy.(5)In the case of dressing bronze-bonded fine grain diamond grinding wheel,power index and transformational multiply linear prediction models and nonlinear GA-SVM prediction models on both of radial circle run-out and axial surface roughness on peak voltage,peak current,duty ratio and wheel speed were established.By testing,the values predicted from the transformational multiply linear prediction models were better than those from the power index prediction models,and relative errors between the predicted results and the experimental results in nonlinear GA-SVM prediction models were controlled less than 5%. |
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