Relationship between subsurface damage and surface roughness of optical materials in grinding and lapping processes

As a kind of widely used optical material, optical glass BK7 is machined by first grinding and then polishing in industrial production. However, the polishing process is timeconsuming and high-cost. Therefore, it is very meaningful to produce high-quality BK7 workpieces by grinding. To understand the grinding characteristics of BK7, many studies were conducted and reported. But most studies available so far had low industrial relevance and were difficult to be applied to guide real production of BK7 glass. To fill this gap, in this study, BK7 grinding characteristics are investigated and special emphasis is laid on the effects of machining parameters in terms of machined surface morphology, subsurface damage, and grinding force. Results show that wheel depth of cut plays the most important role in BK7 grinding, and a little difference of it leads to completely different material removal modes. Wheel speed is the second important parameter. It cannot change the dominant removal mode but can slightly adjust the characteristics of machined surface, subsurface damage, and grinding force. Workpiece feed rate has a small impact on BK7 grinding. From the viewpoint of industrial application, it suggests that the wheel depth of cut of 1.0 μm, high wheel speed, and high workpiece feed rate are more rational and practical because under this condition the grinding process can produce BK7 workpieces, which possess crack-free surface and sublet subsurface damage, with high removal rates and stable grinding forces. The findings of this paper are expected to be meaningful to provide the experimental references for the studies of the BK7 grinding process and guide industrial production of BK7 optical components.

“…The observation of subsurface damage in this study is different from traditional techniques mentioned in [13,16]. As shown in Fig.…”

Section: Observation Of Subsurface Damagementioning

confidence: 71%

“…The predicted values by this relationship presented an acceptable match with experimental results. This relationship was further improved by Li et al [16] and Lv et al [17].…”

Section: Introductionmentioning

confidence: 89%

Experimental investigation on grinding characteristics of optical glass BK7: with special emphasis on the effects of machining parameters

Wang

2015

“…In this study, subsurface damages of ground SiC samples were investigated by magnetorheological finishing (MRF) spot technique [25], which is less destructive and more efficient in measurement of subsurface damages compared with ball dimpling [26] and tapering methods [27]. Typical subsurface damages involved in the MRF spot are observed using the SEM.…”

Section: Subsurface Damagesmentioning

confidence: 99%

High-performance grinding of a 2-m scale silicon carbide mirror blank for the space-based telescope

Zhang

Yang

Zheng

et al. 2016

Silicon carbide (SiC) is a competitive candidate material for building the space-based reflecting mirrors. However, SiC is also a typical difficult-to-machine material due to its extreme hardness. When SiC workpiece is machined by grinding, the wheel wears rapidly which leads to a deterioration of surface form accuracy. Grinding efficiency also becomes extremely low due to the frequent truing and dressing of grinding wheels. To achieve high-performance grinding process capable of producing accurate surface at high grinding efficiency, an ultrasonic vibration-assisted fix-point grinding technology was developed in this study. Wheel wear observation indicated that the wheel needs not to be dressed during the whole grinding cycle. Moreover, a laser tracker was used to achieve an on-machine measurement of the surface form error. A CNC tool microset was adopted to evaluate the wheel wear amount. On the basis of the above two results, surface form error could be predicted before grinding, and thus, an inprocess compensation of surface form error was carried out. Using the above-mentioned grinding strategies, a SiC mirror blank with an aperture diameter of 2 m was successfully ground to a form accuracy of 18 μm in peak-to-valley (PV). Therefore, this work provides an efficient and economical solution for grinding the large-scale SiC aspherical surfaces.

“…Within the following items, brittle-to-ductile transition, subsurface damage mechanism, surface roughness, subsurface crack width, and more exact SSD/SR relationship as mentioned in refs. [33,34,39] should also be discussed for estimating the surface integrity more accurately. In order to simplify the analysis, these are not considered temporarily in the present study.…”

Section: Introductionmentioning

confidence: 99%

Subsurface damage in high-speed grinding of brittle materials considering kinematic characteristics of the grinding process

Wang

Fang

Chen

et al. 2015

Subsurface damage (SSD) induced during abrasive grain machining process strongly influences the mechanical strength and subsurface quality of the brittle components. Therefore, it is meaningful to study the relationship between SSD and grinding parameters. The methods of theoretical analysis, numerical simulation and experimental testing are used to analyze the SSD of brittle materials in high-speed grinding. The results of numerical simulation are consistent with those of theoretical analysis and experimental testing, which indicates that the present numerical method is reasonable. The investigation focuses on the effects of wheel speed, grinding depth, and apex angle of the abrasive grain on the SSD of brittle materials. It shows that when maximum undeformed chip thickness (M-UCT) is greater than the critical thickness of brittle fracture, the material removal is mainly in the brittle mode. A high wheel speed is beneficial to achieving a good subsurface quality. However, under certain conditions, an ultra-high wheel speed with quite small grinding depth is not helpful in SSD control. Due to the kinematic characteristics of the grinding process, the effect of grinding depth on SSD is weaker than that of wheel speed and a smaller abrasive grain is of advantage to subsurface quality. In addition, the grinding force is one of the major factors influencing the subsurface quality.