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Precision is one of the most important aspects of manufacturing. High precision creates high quality, high performance, exchangeability, reliability, and added value for industrial products. Over the past decades, remarkable advances have been achieved in the area of high-precision manufacturing technologies, where the form accuracy approaches the nanometer level and surface roughness the atomic level. These extremely high precision manufacturing technologies enable the development of high-performance optical elements, semiconductor substrates, biomedical parts, and so on, thereby enhancing the ability of human beings to explore the macro- and microscopic mysteries and potentialities of the natural world. In this paper, state-of-the-art high-precision material removal manufacturing technologies, especially ultraprecision cutting, grinding, deterministic form correction polishing, and supersmooth polishing, are reviewed and compared with insights into their principles, methodologies, and applications. The key issues in extreme precision manufacturing that should be considered for future R&D are discussed.

High-efficiency precision grinding can shorten the machining cycle of aspheric optical elements by a factor of 2–10. To achieve this objective, ultrasonic vibration (UV)–assisted grinding (UVG) has been increasingly applied to manufacture aspheric optics. However, the mechanisms of material removal and surface formation in UV-assisted aspheric grinding of glass ceramics have rarely been studied. Herein, rotary UV-assisted vertical grinding (RUVG) was used to explore the machining mechanism of coaxial curved surfaces. First, RUV-assisted scratch experiments were conducted on aspheric surface of glass ceramics, which exhibited multiple benefits over conventional scratching. These include a reduction in the scratch force by 37.83–44.55% for tangential component and 3.87–28.15% for normal component, an increase in plastic removal length by 43.75%, and an increase in material removal rate by almost a factor of 2. Moreover, grinding marks on the aspheric surface in RUVG were accurately simulated and optimized by adjusting grinding parameters. RUVG experiments were performed to verify the accuracy of grinding texture simulations and investigate the UV effect. The results demonstrate that UV can improve the surface quality of aspheric grinding when compared with conventional vertical grinding. In particular, the total height of the profile of form accuracy and its root mean square were significantly improved by a factor of 3.38–4.54 and 7.15–10.82, respectively, and the surface roughness reduced by 10.03–12.10%. This study provides deeper insight into material removal and surface generation mechanisms for RUVG of aspheric surfaces, and it is thus envisaged that these results will be useful in engineering applications.

Micro-lens array (MLA) has been widely used for 3D imaging, etc., due to its excellent functional performances. Ultra-precision diamond turning (UPDT) offers a satisfying solution to the high-quality fabrication of MLA with sub-micrometric form accuracy and nanometric surface roughness. However, in UPDT tool setting, errors would deteriorate form accuracy as a crucial factor. This study focuses on discussing the tool setting effect on form error of MLA and proposes a new two-step tool setting method for UPDT. Firstly, a theoretical model was established for form error of MLA under tool setting errors. Moreover, a new two-step tool setting method was developed with high accuracy to control the tool setting errors. Finally, a series of experiments were carried out with different tool setting errors for the MLA fabrication, and its form error would be measured. The theoretical and experimental results are found that the proposed tool setting method is effective with a high-precision accuracy and the tool setting errors would crucially induce periodical form error at the MLA of UPDT. Significantly, the study draws up a comprehensive understanding of the tool setting effect on form accuracy of MLA in UPDT with the further improvement.

Honing is a finishing process used for the inner cylindrical surfaces of engine blocks or liners. The process involves abrasive particles bonded to the surface of a honing head, which come into contact with the inner bore surface, performing an oscillating and rotational motion. These motions follow a specific pattern, allowing for the creation of crosshatch patterns on the inner bore surface, thereby improving dimensional accuracy, form accuracy and reducing surface roughness. Common honing processes are divided into four distinct phases: material removal, crosshatching, finish honing, and plateau honing. Each phase corresponds to specific tasks such as material removal from the bore, creating crosshatch patterns, honing the peaks in the crosshatch, and final surface finishing. In computer numerical control (CNC)-based honing machine, individual control commands are typically used to manage each of these phases separately. The commands are combined according to process requirements to achieve the desired honing results. To enhance the efficiency of the honing process, this study focuses on the hydraulic feed of the abrasive strips on the honing head, specifically examining the automatic continuous switching between finish honing and plateau honing. The research analyzes the honing principles, develops a control algorithm for dual-process automatic switching, and validates the process through machining tests. Compared to single-process control, the proposed algorithm significantly improves processing efficiency. Additionally, this algorithm can be applied to other dual-process automatic switching controls, providing valuable insights for the design of CNC honing systems.

Accurate and fast three-dimensional (3D) measurement for industrial products/components designed to possess 3D structured shapes is a key driver for improved productivity. However, challenges for current techniques are considerable to measure structured specular surfaces. A technique named segmentation phase measuring deflectometry (SPMD) is proposed in this paper, which enables structured specular surfaces to be measured with high accuracy in one setup. Concept of segmentation in topology is introduced into phase measuring deflectometry, which separates a surface with complex structures into continuous segments. Each segment can be reconstructed based on gradient information to achieve good form accuracy, and all reconstructed segments can be fused into a whole 3D strucutred form result based on their absolute spatial positioning data. Here, we propose and discuss the principle of SPMD, a segmentation technique to separate a strucured surface into segments, a spatial positioning technique to obtain absolute position of the segments, and a data fusion strategy to fuse all reconstructed segments. Experimental results show SPMD can achieve nanometer level accuracy for form measurement of continuous segments by comparing with stylus profilometer, which is significantly higher than the accuracy of direct phase measuring deflectometry. Meanwhile, SPMD has micron level spatial positioning accuracy for structures by measuring two specular steps and comparing with coordinate measuring machine, which differentiates this technique from gradient-based phase measuring deflectometry that extends measurement capability from continuous specular surfaces to complex structured specular surfaces. Compared with the existing measurement techniques, SPMD significantly improved the convenience and ability to measure freeform and structured specular surfaces with the advantages of high measurement accuracy, fast measurement, and potential application for embedded measurement.

Fast tool servo (FTS) in ultra-precision machining (UPM) is an enabling and efficient technology for fabricating optical freeform surfaces or microstructures with submicrometric form accuracy and nanometric surface finish. There are many kinds of FTS in the different driving principle to present their various performances currently. Their kernel technologies influence the machining ability and accuracy of freeform surfaces, consequently receiving much research attention and interest. These technologies are generally summarized as the development of FTS structure, the advanced control algorithms, tool path planning, machining condition monitoring, and surface measurement and error compensation. This paper aims to survey the current state of the art in machining freeform optics by FTS. An analysis of the principle, performance, and application of FTS machining with regard to freeform optics is presented. And the key machining technologies for optical freeform surfaces by FTS are then introduced in detail. The challenges and opportunities for further studies are concluded according to the FTS machining difficult of optical freeform surfaces finally.

Ultra-Precision Machining (UPM) is a kind of highly accurate processing technology developed to satisfy the manufacturing requirements of high-end cutting-edge products including nuclear energy producers, very large-scale integrated circuits, lasers, and aircraft. The information asymmetry phenomenon widely exists in the design and control of ultra-precision machining. It may lead to inconsistency between the designed performance and operational performance of the UPM equipment on stiffness, thermal stability, and motion accuracy, which result from its design, manufacturing, and control, and determine the form accuracy and surface roughness of machined parts. The performance of the UPM equipment should be improved continuously. It is still challenging to realize the real-time and self-adaptive control, in which building a high-fidelity and computationally efficient digital twin is a valuable solution. Nevertheless, the incorporation of the digital twin technology into the UPM design and control remains vague and sometimes contradictory. Based on a literature search in the Google Scholar database, the critical issues in the UPM design and control, and how to use the digital twin technologies to promote it, are reviewed. Firstly, the digital twins-based UPM design, including bearings module design, spindle-drive module design, stage system module design, servo module design, and clamping module design, are reviewed. Secondly, the digital twins-based UPM control studies, including voxel modeling, process planning, process monitoring, vibration control, and quality prediction, are reviewed. The key enabling technologies and research directions of digital twins-based design and control are discussed to deal with the information asymmetry phenomenon in UPM.

In this paper, an automatic and quick evaluating method for the micro-hole size and form accuracy with a computer-aided technique was proposed. A special ultrasonic microforming method, that is, micro-ultrasonic thin-sheet-metal forming using molten plastic as flexible punch (short as Micro-USF), was used to punch out micro-holes with diameters of 500, 600, and 700 μm on a copper sheet with a thickness of 30 μm. Using the evaluation method proposed in this paper, the forming accuracy of micro-holes was discussed. The experimental results showed that the ratios of the maximum size error and the maximum roundness error of micro-holes to the corresponding punching die diameter were 1.40 and 1.47%, respectively. The ratios of the maximum size error range and the maximum roundness error range of micro-holes to the corresponding punching die diameter were 0.70 and 0.72%, respectively. This indicated that the accuracy and precision in the Micro-USF method were high for punching micro-holes. Moreover, it was found that there is no significant direct correlation between micro-holes sample errors and these forming parameters when the forming parameters such as ultrasonic power, ultrasonic time, and cylinder pressure were varied, which indicated that the sample errors were random to some extent.

In this paper, a novel mask electrochemical additive and subtractive combined manufacturing technique was proposed. This is a machining method at the atomic level, and it can be used to produce metal microstructures with high-profile accuracy and low surface roughness. Due to the accumulation of electric field lines during mask electrochemical deposition, the height of the edges of the microcolumns is usually twice or more than the height of the central position in the deposition plane. A combined machining method based on the electric-field constraint of the mask is thus proposed to improve the accuracy of the profile and its surface roughness. The feasibility of the proposed method was verified by both simulations and experiments. The height difference between the column center and the surrounding layer on the surface of nickel microcolumns was reduced from 13 to 2 µm, and the roughness of the tops of the microcolumns was also improved. Experiments to examine electrolysis leveling were carried out to verify the correctness of the results of the simulations and theoretical calculations. Finally, the parameters were optimized using orthogonal experiments, and an array of nickel microcolumns with a diameter of 200 µm and a height of nearly 50 µm was obtained using these optimal parameters. The profile accuracy and surface roughness of the high-precision microcolumn array were improved by using the mask electrochemical additive and subtractive combined machining technique, and a high-precision microcolumn array structure was manufactured.

Micro-structured surfaces possess excellent properties of friction, lubrication, drag reduction, antibacterial, and self-cleaning, which have been widely applied in optical, medical, national defense, aerospace fields, etc. Therefore, it is requisite to study the fabrication methods of micro-structures to improve the accuracy and enhance the performance of micro-structures. At present, there are plenty of studies focusing on the preparation of micro-structures; therefore, systematic review of the technologies and developing trend on the fabrication of micro-structures are needed. In present review, the fabrication methods of various micro-structures are compared and summarized. Specially, the characteristics and applications of ultra-precision machining (UPM) technology in the fabrication of micro-structures are mainly discussed. Additionally, the assistive technologies applied into UPM, such as fast tool servo (FTS) technology and slow tool servo (STS) technology to fabricate micro-structures with different characteristics are summarized. Finally, the principal characteristics and applications of fly cutting technology in manufacturing special micro-structures are presented. From the review, it is found that by combining different machining methods to prepare the base layer surface first and then fabricate the sublayer surface, the advantages of different machining technologies can be greatly exerted, which is of great significance for the preparation of multi-layer and multi-scale micro-structures. Furthermore, the combination of ultra-precision fly cutting and FTS/STS possess advantages in realizing complex micro-structures with high aspect ratio and high resolution. However, residual tool marks and material recovery are still the key factors affecting the form accuracy of machined micro-structures. This review provides advances in fabrication methods and assistive technologies of micro-structured surfaces, which serves as the guidance for both fabrication and application of multi-layer and multi-scale micro-structures.