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Frontiers of Mechanical Engineering

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Special issue: Ultra-precision machining
Zhuangde JIANG,Dongming GUO
Front. Mech. Eng.. 2017, 12 (1): 1-2.   DOI: 10.1007/s11465-017-0445-y
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Precision glass molding: Toward an optimal fabrication of optical lenses
Liangchi ZHANG,Weidong LIU
Front. Mech. Eng.. 2017, 12 (1): 3-17.   DOI: 10.1007/s11465-017-0408-3
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It is costly and time consuming to use machining processes, such as grinding, polishing and lapping, to produce optical glass lenses with complex features. Precision glass molding (PGM) has thus been developed to realize an efficient manufacture of such optical components in a single step. However, PGM faces various technical challenges. For example, a PGM process must be carried out within the super-cooled region of optical glass above its glass transition temperature, in which the material has an unstable non-equilibrium structure. Within a narrow window of allowable temperature variation, the glass viscosity can change from 105 to 1012 Pa·s due to the kinetic fragility of the super-cooled liquid. This makes a PGM process sensitive to its molding temperature. In addition, because of the structural relaxation in this temperature window, the atomic structure that governs the material properties is strongly dependent on time and thermal history. Such complexity often leads to residual stresses and shape distortion in a lens molded, causing unexpected changes in density and refractive index. This review will discuss some of the central issues in PGM processes and provide a method based on a manufacturing chain consideration from mold material selection, property and deformation characterization of optical glass to process optimization. The realization of such optimization is a necessary step for the Industry 4.0 of PGM.

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Recent advances in micro- and nano-machining technologies
Shang GAO, Han HUANG
Front. Mech. Eng.. 2017, 12 (1): 18-32.   DOI: 10.1007/s11465-017-0410-9
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Device miniaturization is an emerging advanced technology in the 21st century. The miniaturization of devices in different fields requires production of micro- and nano-scale components. The features of these components range from the sub-micron to a few hundred microns with high tolerance to many engineering materials. These fields mainly include optics, electronics, medicine, bio-technology, communications, and avionics. This paper reviewed the recent advances in micro- and nano-machining technologies, including micro-cutting, micro-electrical-discharge machining, laser micro-machining, and focused ion beam machining. The four machining technologies were also compared in terms of machining efficiency, workpiece materials being machined, minimum feature size, maximum aspect ratio, and surface finish.

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Recent advances in ultrasonic-assisted machining for the fabrication of micro/nano-textured surfaces
Shaolin XU,Tsunemoto KURIYAGAWA,Keita SHIMADA,Masayoshi MIZUTANI
Front. Mech. Eng.. 2017, 12 (1): 33-45.   DOI: 10.1007/s11465-017-0422-5
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In this paper, the state of art of ultrasonic-assisted machining technologies used for fabrication of micro/nano-textured surfaces is reviewed. Diamond machining is the most widely used method in industry for manufacturing precision parts. For fabrication of fine structures on surfaces, conventional diamond machining methods are competitive by considering the precision of structures, but have limitations at machinable structures and machining efficiency, which have been proved to be partly solved by the integration of ultrasonic vibration motion. In this paper, existing ultrasonic-assisted machining methods for fabricating fine surface structures are reviewed and classified, and a rotary ultrasonic texturing (RUT) technology is mainly introduced by presenting the construction of vibration spindles, the texturing principles, and the applications of textured surfaces. Some new ideas and experimental results are presented. Finally, the challenges in using the RUT method to fabricate micro/nano-textured surfaces are discussed with respect to texturing strategies, machinable structures, and tool wear.

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Recent advancements in optical microstructure fabrication through glass molding process
Tianfeng ZHOU,Xiaohua LIU,Zhiqiang LIANG,Yang LIU,Jiaqing XIE,Xibin WANG
Front. Mech. Eng.. 2017, 12 (1): 46-65.   DOI: 10.1007/s11465-017-0425-2
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Optical microstructures are increasingly applied in several fields, such as optical systems, precision measurement, and microfluid chips. Microstructures include microgrooves, microprisms, and microlenses. This paper presents an overview of optical microstructure fabrication through glass molding and highlights the applications of optical microstructures in mold fabrication and glass molding. The glass-mold interface friction and adhesion are also discussed. Moreover, the latest advancements in glass molding technologies are detailed, including new mold materials and their fabrication methods, viscoelastic constitutive modeling of glass, and microstructure molding process, as well as ultrasonic vibration-assisted molding technology.

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Review of small aspheric glass lens molding technologies
Shaohui YIN,Hongpeng JIA,Guanhua ZHANG,Fengjun CHEN,Kejun ZHU
Front. Mech. Eng.. 2017, 12 (1): 66-76.   DOI: 10.1007/s11465-017-0417-2
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Aspheric lens can eliminate spherical aberrations, coma, astigmatism, field distortions, and other adverse factors. This type of lens can also reduce the loss of light energy and obtain high-quality images and optical characteristics. The demand for aspheric lens has increased in recent years because of its advantageous use in the electronics industry, particularly for compact, portable devices and high-performance products. As an advanced manufacturing technology, the glass lens molding process has been recognized as a low-cost and high-efficiency manufacturing technology for machining small-diameter aspheric lens for industrial production. However, the residual stress and profile deviation of the glass lens are greatly affected by various key technologies for glass lens molding, including glass and mold-die material forming, mold-die machining, and lens molding. These key technical factors, which affect the quality of the glass lens molding process, are systematically discussed and reviewed to solve the existing technical bottlenecks and problems, as well as to predict the potential applicability of glass lens molding in the future.

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Research progress on ultra-precision machining technologies for soft-brittle crystal materials
Hang GAO,Xu WANG,Dongming GUO,Yuchuan CHEN
Front. Mech. Eng.. 2017, 12 (1): 77-88.   DOI: 10.1007/s11465-017-0411-8
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Soft-brittle crystal materials are widely used in many fields, especially optics and microelectronics. However, these materials are difficult to machine through traditional machining methods because of their brittle, soft, and anisotropic nature. In this article, the characteristics and machining difficulties of soft-brittle and crystals are presented. Moreover, the latest research progress of novel machining technologies and their applications for soft-brittle crystals are introduced by using some representative materials (e.g., potassium dihydrogen phosphate (KDP), cadmium zinc telluride (CZT)) as examples. This article reviews the research progress of soft-brittle crystals processing.

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Advances in molecular dynamics simulation of ultra-precision machining of hard and brittle materials
Xiaoguang GUO,Qiang LI,Tao LIU,Renke KANG,Zhuji JIN,Dongming GUO
Front. Mech. Eng.. 2017, 12 (1): 89-98.   DOI: 10.1007/s11465-017-0412-7
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Hard and brittle materials, such as silicon, SiC, and optical glasses, are widely used in aerospace, military, integrated circuit, and other fields because of their excellent physical and chemical properties. However, these materials display poor machinability because of their hard and brittle properties. Damages such as surface micro-crack and subsurface damage often occur during machining of hard and brittle materials. Ultra-precision machining is widely used in processing hard and brittle materials to obtain nanoscale machining quality. However, the theoretical mechanism underlying this method remains unclear. This paper provides a review of present research on the molecular dynamics simulation of ultra-precision machining of hard and brittle materials. The future trends in this field are also discussed.

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A review of the scalable nano-manufacturing technology for flexible devices
Wenbin HUANG,Xingtao YU,Yanhua LIU,Wen QIAO,Linsen CHEN
Front. Mech. Eng.. 2017, 12 (1): 99-109.   DOI: 10.1007/s11465-017-0416-3
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Recent advances in electronic and photonic devices, such as artificial skin, wearable systems, organic and inorganic light-emitting diodes, have gained considerable commercial and scientific interest in the academe and in industries. However, low-cost and high-throughput nano-manufacturing is difficult to realize with the use of traditional photolithographic processes. In this review, we summarize the status and the limitations of current nano-patterning techniques for scalable and flexible functional devices in terms of working principle, resolution, and processing speed. Finally, several remaining unsolved problems in nano-manufacturing are discussed, and future research directions are highlighted.

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Ion beam figuring of continuous phase plates based on the frequency filtering process
Mingjin XU,Yifan DAI,Xuhui XIE,Lin ZHOU,Shengyi LI,Wenqiang PENG
Front. Mech. Eng.. 2017, 12 (1): 110-115.   DOI: 10.1007/s11465-017-0430-5
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Ion beam figuring (IBF) technology is an effective technique for fabricating continuous phase plates (CPPs) with small feature structures. This study proposes a multi-pass IBF approach with different beam diameters based on the frequency filtering method to improve the machining accuracy and efficiency of CPPs during IBF. We present the selection principle of the frequency filtering method, which incorporates different removal functions that maximize material removal over the topographical frequencies being imprinted. Large removal functions are used early in the fabrication to figure the surface profile with low frequency. Small removal functions are used to perform final topographical correction with higher frequency and larger surface gradient. A high-precision surface can be obtained as long as the filtering frequency is suitably selected. This method maximizes the high removal efficiency of the large removal function and the high corrective capability of the small removal function. Consequently, the fast convergence of the machining accuracy and efficiency can be achieved.

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Mesoscale fabrication of a complex surface for integral impeller blades
Xibin WANG,Tianfeng ZHOU,Lijing XIE,Li JIAO,Zhibing LIU,Zhiqiang LIANG,Pei YAN
Front. Mech. Eng.. 2017, 12 (1): 116-131.   DOI: 10.1007/s11465-017-0426-1
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Integral impeller is the most important component of a mini-engine. However, the machining of a mesoscale impeller with a complex integral surface is difficult because of its compact size and high accuracy requirement. A mesoscale component is usually manufactured by milling. However, a conventional milling tool cannot meet the machining requirements because of its size and stiffness. For the fabrication of a complex integral impeller, a micro-ball-end mill is designed in accordance with the non-instantaneous-pole envelope principle and manufactured by grinding based on the profile model of the helical groove and the mathematical model of the cutting edge curve. Subsequently, fractal theory is applied to characterize the surface quality of the integral impeller. The fractal theory-based characterization shows that the completed mesoscale integral impeller exhibits a favorable performance in terms of mechanical properties and morphological accuracy.

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Processing of high-precision ceramic balls with a spiral V-groove plate
Ming FENG,Yongbo WU,Julong YUAN,Zhao PING
Front. Mech. Eng.. 2017, 12 (1): 132-142.   DOI: 10.1007/s11465-017-0436-z
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As the demand for high-performance bearings gradually increases, ceramic balls with excellent properties, such as high accuracy, high reliability, and high chemical durability used, are extensively used for high-performance bearings. In this study, a spiral V-groove plate method is employed in processing high-precision ceramic balls. After the kinematic analysis of the ball-spin angle and enveloped lapping trajectories, an experimental rig is constructed and experiments are conducted to confirm the feasibility of this method. Kinematic analysis results indicate that the method not only allows for the control of the ball-spin angle but also uniformly distributes the enveloped lapping trajectories over the entire ball surface. Experimental results demonstrate that the novel spiral V-groove plate method performs better than the conventional concentric V-groove plate method in terms of roundness, surface roughness, diameter difference, and diameter decrease rate. Ceramic balls with a G3-level accuracy are achieved, and their typical roundness, minimum surface roughness, and diameter difference are 0.05, 0.0045, and 0.105 mm, respectively. These findings confirm that the proposed method can be applied to high-accuracy and high-consistency ceramic ball processing.

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12 articles