Ziqiang Yin

The cup-shaped grinding wheels with arc-shaped edges provide a satisfactory precision grinding solution for high-accuracy optical surfaces on hard and brittle materials. However, the complex profile of the arc-shaped edges of cup-shaped grinding wheels makes them challenging to truing. This paper proposes an on-machine truing technique targeting cup-shaped grinding wheels with arc-shaped cutting edge. First, a mathematical model was established to simulate the three-axis of on-machine truing the arc-shaped cutting edge using a diamond roller. Based on this model, a theoretical analysis is conducted to investigate the impact of tool setting errors, measurement errors of the diamond roller, and the pose error on truing accuracy. A compensation method was proposed, and experimental results validated its effectiveness. To investigate the grinding performance of cup-shaped grinding wheels after truing, a complex component is ground using a truing diamond grinding wheel. The experimental results demonstrate that this method enables precise on-machine truing of the arc-shaped edges of cup-shaped grinding wheels and is efficient. The average dimensional accuracy of the grinding wheel’s arc-shaped edge is reduced to 1.5 μm, with the profile accuracy (PV) of 0.89 μm.

Elliptical vibration-assisted cutting (EVAC), one of the advanced micromachining methods, enables results not possible with traditional ultra-precision machining. It is considered to be one of the most viable options for manufacturing micro/nanostructured surfaces. However, it is difficult to control the elliptical locus with different tilt angles; therefore, previous studies have primarily focused on fixed locus and investigated the effects of the amplitude and frequency on machining performance. In addition, tilt angle is an important factor affecting the characteristics of EVAC. To maximize the cutting performance of EVAC, the cutting characteristics of EVAC with variations in tilt angle of elliptical locus are investigated. The mathematical model of elliptical trajectory based on different tilt angles is established via geometric analysis. The effects of the different tilt angle (0–180°) on cutting forces, chip formation, defect generation and surface roughness are observed and theoretically analyzed in microgroove experiments. The experimental results show that the tilt angle has a significant effect on the cutting force, chip formation, defects and surface roughness. The best cutting performance can be obtained at the tilt angle of 30°, while the worst is recorded at 90°. The results can provide a valuable reference for further comprehensive studies to maximize the cutting performance of EVAC.

Hexagonal cube corner retroreflectors (HCCRs) are the micro-optics arrays with the highest reflectivity. However, these are composed of prismatic micro-cavities with sharp edges, and conventional diamond cutting is considered unmachinable. Besides, 3-linear-axis ultraprecision lathes were considered unfeasible to fabricate HCCRs due to the lack of a rotation axis. Therefore, a new machining method is proposed as a viable option to manufacture HCCRs on the 3-linear-axis ultraprecision lathes in this paper. For the mass production of HCCRs, the dedicated diamond tool is designed and optimized. The toolpaths are proposed and optimized to further increase tool life and machining efficiency. The Diamond Shifting Cutting (DSC) method is analyzed in-depth both theoretically and experimentally. By using the optimized methods, the large-area HCCRs with a structure size of 300 µm covering an area of 10 × 12 mm² are successfully machined on 3-linear-axis ultraprecision lathes. The experimental results show that the whole array is highly uniform, and the surface roughness Sa of three cube corner facets is all less than 10 nm. More importantly, the machining time is reduced to 19 h, which is far less than the previous processing methods (95 h). This work will significantly reduce the production threshold and costs, which is important to promote the industrial application of HCCRs.

Cube concer retro-reflector is an optical element with high reflectivity, widely used to improve safety in low light level environments. High-precision and surface finish die cores are used to mass produce high-quality retro-reflectors. There are periodic micro-morphologies on the die core surface machined by diamond fly-cutting, which weaken the reflection characteristics of optical elements. The finite element method theoretically revealed the relationship between optical defects and surface topography, and the fly-cutting experiment was carried out to verify the analysis. At the same time, an efficient machining method to eliminate the diffraction phenomenon is proposed. According to the machining results, the error source of this method is analyzed and calibrated. This research provides a new idea for obtaining the optical plane of retro-reflector with high efficiency and accuracy.

Vibration in ultra-precision machining is an inherent physical phenomenon and a key factor affecting surface generation. However, the influence of the vibration characteristics of aerostatic guideways on the machining morphology has not been fully studied. In this article, a diamond micro-planing experiment was carried out on an oxygen-free copper workpiece using a homemade three-axis machine tool, and a white-light interferometer was used to measure the surface topography of the planing surface. The power spectral density of the surface topography was analyzed, and the spatial wavelength components of the surface topography were extracted. Then, the vibration characteristics of the aerostatic guideway were measured in both the space domain and the time domain. A comprehensive analysis of the main components of the workpiece surface error morphology and the vibration characteristics of the guideway shows that the time-domain vibration of the aerostatic guideway is the main factor causing the surface topography error of the workpiece.

Roll-to-roll (R2R) imprinting is a high-throughput and low-cost continuous manufacturing technique for the mass production of high-quality functional optical polymer films. In fabricating optical films, roll molds with high precision and surface finishs are key tooling components in the R2R imprinting process. However, the trimmed radial Fresnel array results in discontinuity of the machining trajectory. Therefore, direct diamond turning of trimmed radial Fresnel array on a roller mold was considered infeasible. We use the diamond microscraping method to manufacture the trimmed radial Fresnel array on the roller mold. The trimmed radial Fresnel array is divided into trimmed and the complete Fresnel structure to be machined separately. The trimmed part adopts the rounded corners method to avoid a damage machined surface. Due to the large size and heavy weight of the roller mold, conventional offline measurement methods cannot be used, so we measure and evaluate its cross-sectional profile by an on-machine measurement method to verify the feasibility of the proposed method. We provide a solution for surface machining of discontinuous and complex microstructures on the roller mold.

Automation and on-machine manufacturing process measurement is essential in increasing product productivity. However, a significant challenge is the radial Fresnel lens structure-array machining and on-machine measurement research for a large-scale roller mold. We present a rotating A -axis machining method for manufacturing an array of a radial Fresnel lens structure, based on an ultraprecision four-axis drum roll lathe system developed by the team. Therefore, based on the principle of a virtual multiprobe, the traditional two-point method is improved and applied to the on-machine measurement of the radial Fresnel lens structure of the roll mold. Through the machining and on-machine measurement experiments of the radial Fresnel lens structure of the roller mold, the feasibility of the machining method and measurement method is verified.

The conventional aerostatic guideway with two relatively large opposed aerostatic bearing pads (OABPs) has large thrust forces at the lateral carriages. The structure is deformed due to the thrust force, and the thickness of the gas film becomes large and inconsistent, resulting in insufficient gas film stiffness. In this study, a fluid–solid coupling model is established for the aerostatic guideway, and the vacuum preloaded (VPL) aerostatic bearing with an eccentric vacuum chamber was obtained through optimization design and computational fluid dynamics (CFD) simulation. The CFD results show that the eccentric VPL aerostatic bearing has a larger stiffness. Then an experiment on the static performance of a lateral carriage with the eccentric VPL aerostatic bearing was carried out. The experimental results show that the lateral stiffness of the aerostatic guideway using the optimized VPL design is about 65 times as large as the previous OABP and the validity of the design optimization is demonstrated.