Sub-surface crack formation in ultrasonic vibration-assisted grinding of BK7 optical glass
21 Jun 2017-The International Journal of Advanced Manufacturing Technology (Springer London)-Vol. 93, Iss: 5, pp 1685-1697
TL;DR: In this paper, the ultrasonic vibration assisted grinding experiments of BK7 optical glass were carried out, and quite a few sub-surface cracks with different shapes were observed beneath the machined surfaces.
Abstract: Due to the inherent properties of high brittleness and low fracture toughness of optical glass materials, sub-surface cracks would be inevitably induced into the ultrasonic vibration assisted grinding process. Knowledge of the formation mechanisms of sub-surface cracks plays a key role in implementing high efficiency and precision machining of this kind of materials. In this work, the ultrasonic vibration assisted grinding experiments of BK7 optical glass were carried out. Processed by cross-sectional polishing and assisted by HF acid etching, quite a few sub-surface cracks with different shapes were observed beneath the machined surfaces. Categorized by the shapes and formation mechanisms, four kinds of sub-surface cracks (i.e., straight median sub-surface crack, arc median sub-surface crack, lateral sub-surface crack, and bifurcated sub-surface crack) and their corresponding formation mechanisms were both clarified. Experimental and analytical results suggest that the arc sub-surface cracks were formed by the relative shear stresses parallel to the plane of median crack frontiers, which are generated by nonsymmetric contacting between abrasive grains and glass specimen in ultrasonic vibration grinding. The bifurcation cracks were formed by the distortion in frontier fields caused by the impact effect provided by ultrasonic vibration as the abrasive grains vibrate down to the glass material. Effects of grinding and ultrasonic vibration parameters on the maximum depth of sub-surface cracks were also investigated in this work. The value of the maximum depth of sub-surface cracks showed a great dependence on the processing parameters.
Citations
More filters
TL;DR: In this paper, the ultrasonic vibration is applied to the axial direction of the main shaft, which can make abundant grains to impact the workpiece with the high-frequency reciprocating style.
17 citations
TL;DR: In this paper , the cutting force in ultrasonic vibration side grinding (UVSG) of brittle materials is modeled and a theoretical cutting force model was developed based on the analysis of force generated at three interaction stages, i.e., rubbing, plowing and cutting stages.
14 citations
TL;DR: In this article, the cutting force in ultrasonic vibration side grinding (UVSG) of brittle materials is modeled and a theoretical cutting force model was developed based on the analysis of force generated at three interaction stages, i.e., rubbing, plowing and cutting stages.
14 citations
TL;DR: In this article, a novel model is proposed to calculate the material removal distribution and the resultant surface figure and the final surface figures under several polishing conditions were simulated and were found to be in close agreement with the experimental results.
Abstract: Full-aperture polishing is a key process in the fabrication of large flat optical elements with a high-precision surface figure. Controlling of the surface figure, which is primarily dependent on the material removal distribution, during the polishing process is challenging. In this study, a novel model is proposed to calculate the material removal distribution and the resultant surface figure. The model determines the material removal amount of points on the workpiece by considering the kinematic parameters and pressure distribution along the sliding trajectory relative to the pad. Moreover, the pressure distribution during the polishing process is acquired from the mechanical and morphological characteristic of polishing pad. With this model, the final surface figures under several polishing conditions were simulated and were found to be in close agreement with the experimental results.
13 citations
TL;DR: In this article, a novel method is proposed to determine the lap shape error by rotating the lap while the measurement point is moved radially using a precision slide mechanism, and a small heating tool is proposed for correcting the local surface shape error of the pitch lap.
12 citations
References
More filters
TL;DR: In this article, a straight crack moving through an elastic medium is calculated and the stresses depend on the velocity and reduce to Inglis' solution when the velocity is zero, and the results may be applied to the spicular fracture of glass.
Abstract: Summary The stress field is calculated about a straight crack moving through an elastic medium. The stresses depend on the velocity and reduce to Inglis' solution when the velocity is zero. The results may be applied to the spicular fracture of glass.
663 citations
TL;DR: In this paper, the authors investigated the microfracture patterns observed around point indentations in brittle solids and derived the means for predetermining, in principle, the depth of fracture damage under given point loading conditions.
Abstract: The microfracture patterns observed around point indentations in brittle solids are investigated. A description is first given of the stress field in an elastic half-space loaded normally at a point in its surface. This field is then used as a basis for analysing the crack geometry. A localized zone of irreversible deformation forms about the contact point, thereby removing a singularity in the elasticity solutions and providing nucleation centres for the ensuing microcracks. Generally, two main types of ‘vent’ cracks are observed to propagate from the deformation zone: median vents, formed during indenter loading, spread downward below the point of contact on planes of symmetry, and lateral vents, formed during unloading, spread sideways toward the specimen surface. Of these, the median vent is relatively well-behaved, and is amenable to standard fracture-mechanics analysis. From such an analysis we derive the means for predetermining, in principle, the depth of fracture damage under given point loading conditions. The significance of the results in relation to important practical applications, such as glass cutting and surface fragmentation processes, is discussed.
629 citations
TL;DR: The keynote paper reviews the state-of-the-art regarding applied grinding tools, ultra-precision machine tools and grinding processes for electronic and optical industries as well as for astronomical applications.
Abstract: Ultra-precision grinding is primarily used to generate high quality and functional parts usually made from hard and difficult to machine materials. The objective of ultra-precision grinding is to generate parts with high surface finish, high form accuracy and surface integrity for the electronic and optical industries as well as for astronomical applications. This keynote paper introduces general aspects of ultra-precision grinding techniques and point out the essential features of ultra-precision grinding. In particular, the keynote paper reviews the state-of-the-art regarding applied grinding tools, ultra-precision machine tools and grinding processes. Finally, selected examples of advanced ultra-precision grinding processes are presented.
416 citations
TL;DR: In this paper, the surface and subsurface damages have been studied with scanning electron microscope (SEM) and the effects of grinding conditions on surface/subsurface damage have been discussed.
Abstract: The difficulty and cost involved in the abrasive machining of hard and brittle ceramics are among the major impediments to the widespread use of advanced ceramics in industries these days. It is often desired to increase the machining rate while maintaining the desired surface integrity. The success of this approach, however, relies in the understanding of mechanism of material removal on the microstructural scale and the relationship between the grinding characteristics and formation of surface/subsurface machining-induced damage. In this paper, grinding characteristics, surface integrity and material removal mechanisms of SiC ground with diamond wheel on surface grinding machine have been investigated. The surface and subsurface damages have been studied with scanning electron microscope (SEM). The effects of grinding conditions on surface/subsurface damage have been discussed. This research links the surface roughness, surface and subsurface damages to grinding parameters and provides valuable insights into the material removal mechanism and the dependence of grinding-induced damage on grinding conditions.
261 citations