Abstract
Subsurface cracks in ultrasonic-vibration-assisted grinding (UVAG) of optical glasses often exhibit diverse forms and proportions. Due to the variety of loads involved in crack formation and propagation, the crack forms and propagation depths have different sensitivities to each process parameter. Predicting the maximum subsurface cracks depth (MSSCD) by considering the varying effects of process parameters plays a key role in implementing effective control of the UVAG process. In this work, the subsurface crack forms and their proportions are investigated by conducting 40 sets of UVAG experiments. The varying effects of the grinding and ultrasonic parameters on the crack form proportions are unveiled by using grey relational analysis. The weighted least square support vector machine (WLS-SVM) prediction model for the MSSCD was developed. Twelve sets of UVAG experiments were carried out to validate the proposed model. The results show that arc-shaped cracks and bifurcated cracks account for 72.5% of all cracks, while ultrasonic vibration amplitude influences most of the proportions of arc-shaped and bifurcated cracks. Compared to other widely used prediction methods, the maximum and average relative prediction errors of the proposed model are 10.54% and 5.59%, respectively, which proves the high prediction accuracy of the model.
Highlights
Optical glasses are widely used in optical and aerospace applications
From Equations (3) and (5), it can be seen that the impulse of an abrasive grain is mainly affected by the penetration depth (w) and ultrasonic vibration amplitude (A), which mainly affected by the penetration depth (w) and ultrasonic vibration amplitude (A), means that changing grinding parameters n, V, or ap will not have an obvious effect which means that changing grinding parameters n,f Vf, or ap will not have an obvious effect on the distribution of arc-shaped and bifurcated cracks
A focus is on the systematic understanding of the influence of multiple process parameters on the proportion of subsurface crack forms from carefully designed experiments
Summary
Optical glasses are widely used in optical and aerospace applications. they are very brittle and have low fracture toughness, being prone to micro-cracks developing in the subsurface layers during conventional grinding processes. Li [5] developed a regression model for subsurface crack depth (SSCD) estimation by combining theoretical mechanical analysis and experimental approach, but the scratching tests conducted in this work differed from the practical machining, as the abrasive grains used in the latter are often random in shape and quantity. Pansare pointed an visible technique for authentication of epoxy composites by using UV visible and IR light, which may provide new methods for investigating the subsurface cracks in grinding of optical glasses [15] It can be concluded from the above literature survey that few reports provide a deeper understanding of multiple subsurface crack forms in the actual UVAG process. The varying effects of each grinding process parameter and the ultrasonic vibration amplitude on the subsurface crack forms and distributions were innovatively investigated using the grey relational analysis, and the strengths of all influencing factors were determined. To validate the prediction accuracy of the proposed model, ultrasonic-vibration-assisted grinding experiments were conducted on BK7 optical glass samples
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