Ultra-precision Machining Method Research Articles

Adaptive processing strategy of pulse ion beam for sub-nanometer precision optical components

Ion-beam figuring (IBF) imposes strict requirements for machine tool accuracy when achieving nano-precision material removal. This study proposes a novel method for pulsed ion beam (PIB) processing. The continuous IBF ion beam is discretized and the fixed-point quantitative removal of the ion beam was accurately achieved by controlling the frequency and duty cycle of the pulsed beam flow. The impact of the dynamic performance of the machine tool on machining as well as the additional removal layer caused by continuous beam flow was examined. First, the principle of the PIB realization was explained, and its good processing performance and excellent material-removal resolution were verified. Second, the advantageous range of PIB machining was simulated and analyzed, leading to the development of a processing strategy based on the error distribution gradient. Furthermore, the ant colony algorithm was used for processing trajectory optimization, reducing 57.7 % of the invalid paths. Finally, using PIB and the novel processing strategy, an optical surface with an RMS of 0.552 nm was achieved within an effective aperture of 90 mm, thereby confirming the feasibility of the novel processing system and strategy.This study expands the application scenarios of ion beams as an ultraprecision machining method that can be positioned as a preferred approach in areas where large-area trace-material removal is required.

Enhancement mechanism of Y-doped Ce1−xYxO2 for photocatalytic-assisted chemical-mechanical polishing

Photocatalytic-assisted chemical-mechanical polishing (PCMP) is an ultra-precision machining method which combines photocatalytic technology with chemical-mechanical polishing (CMP) technology. CeO2 has unique physicochemical properties (tribological properties and photochemical oxidation activity) and is applied to industrial fields extensively. In this paper, a series of Ce1−xYxO2 nanoparticles with controlled size and shape were produced by the molten salt method. SEM images show that Ce1−xYxO2 nanoparticles are nearly spherical with a size of about 113–148 nm. Ion doping can adjust the defect concentration and further enhance the chemical activity of samples. XPS spectra show that doping is beneficial to improve the concentration of Ce3+ and oxygen vacancy. In this way, the photocatalytic activity of CeO2 nanoparticles can be improved. Quartz glasses were polished by synthetic Ce1−xYxO2 nanoparticle polishing solution, where x is the doping amount. The results show that the material removal rate (MRR) of Ce0.95Y0.05O2 abrasives in PCMP was increased by 34.5%. The PCMP mechanism of CeO2 nanoparticles is further discussed. Ultraviolet irradiation increased the reactive sites on the surface of Ce1−xYxO2 nanoparticles, making them have better chemical activity. The hydration layer and Ce-O-Si bond on the surface of quartz glass are formed more easily, thus improving the material removal rate.

Effects of Cutting Force on Formation of Subsurface Damage During Nano-Cutting of Single-Crystal Tungsten

Abstract Single-crystal tungsten is widely utilized in various fields, benefiting from its outstanding properties. Nano-cutting, as an ultra-precision machining method, can realize high efficiency and low damage. However, from the atomic perspective, the formation mechanism of subsurface damage during the nano-cutting of tungsten is still unclear. Herein, the molecular dynamics (MD) simulation of nano-cutting single-crystal tungsten was established to elucidate the evolution of subsurface damage and the effects of cutting force on subsurface damage. The corresponding results showed the existence of damage including atomic cluster, vacancy defect, “V-shaped” dislocation, stair-rod dislocation, and dislocation ring on the subsurface during the cutting. There were dislocation lines in 1/2<111>, <100>, <110>, and other directions due to plastic deformation dominated by dislocation slip, and the 1/2<111> dislocation lines could be merged into stable <100> dislocation lines under certain circumstances during the cutting. The variation of cutting force and cutting force fluctuation induced by changing cutting parameters had a great influence on the subsurface damage of tungsten, including the number of surface defect atoms, dislocation density, and thickness of the subsurface damage layer. In nano-cutting of single-crystal tungsten, a smaller cutting depth and appropriate cutting speed should be selected to reduce subsurface damage. This study provides an insight into the evolution mechanism of subsurface damage of tungsten and is high of significance for achieving low-damage machining of tungsten components.

Effects of pH Values and H2O2 Concentrations on the Chemical Enhanced Shear Dilatancy Polishing of Tungsten.

In order to obtain tungsten with great surface qualities and high polishing efficiency, a novel method of chemical enhanced shear dilatancy polishing (C-SDP) was proposed. The effects of pH values and H2O2 concentrations on the polishing performance of tungsten C-SDP were studied. In addition, the corrosion behaviors of tungsten in solutions with different pH values and H2O2 concentrations were analyzed by electrochemical experiments, and the valence states of elements on the tungsten surface were analyzed by XPS. The results showed that both pH values and H2O2 concentrations had significant effects on tungsten C-SDP. With the pH values increasing from 7 to 12, the MRR increased from 6.69 µm/h to 13.67 µm/h. The optimal surface quality was obtained at pH = 9, the surface roughness (Ra) reached 2.35 nm, and the corresponding MRR was 9.71 µm/h. The MRR increased from 9.71 µm/h to 34.95 µm/h with the H2O2 concentrations increasing from 0 to 2 vol.%. When the concentration of H2O2 was 1 vol.%, the Ra of tungsten reached the lowest value, which was 1.87 nm, and the MRR was 26.46 µm/h. This reveals that C-SDP technology is a novel ultra-precision machining method that can achieve great surface qualities and polishing efficiency of tungsten.

High-efficiency nano polishing of steel materials

Abstract The application of a specific rheological polishing slurry is proposed first for high-efficiency machining of steel materials to achieve high-quality ultraprecision finished surfaces. The rheology of the polishing slurry was explored to show that the non-Newtonian medium with certain parameters of content components exhibits shear-thickening behavior. Then the new high-efficiency nano polishing approach is applied to process spherical surfaces of bearing steel. Several controllable parameters such as shear rheology, abrasive data, rotational speed, and processing time are experimentally investigated in this polishing process. A special finding is that the surface roughness and material removal rate can increase simultaneously when a small abrasive size is applied due to the thickening mechanism during the shearing flow of slurries. Excessive abrasives can decrease surface quality due to the uneven agglomeration of particles scratching the surface. Under optimized conditions, a high-accuracy spherical bearing steel surface with a roughness of 12.6 nm and roundness of 5.3 μm was achieved after a processing time of 2.5 h. Thus, a potential ultraprecision machining method for target materials is obtained in this study.

Anhydrous based shear-thickening polishing of KDP crystal

Based on the special physical–chemical characteristics of optical crystal in the field of aeronautics, a new anhydrous based shear-thickening polishing (ASTP) method has been proposed to restrain deliquescence and to improve physical properties for KDP machining. The ultra-precision polishing of KDP crystal is completed by ASTP. A kind of anhydrous based thickening polishing slurry (ATPS) was proposed in our work, and high-performance rheological properties were determined to achieve the ASTP of KDP crystal. A material removal model of ASTP in KDP machining is established, followed by the verification experiment of the prediction model. The maximum error of the predictive model is only 9.8%, which proves the validity of the material removal model for KDP polishing. The polishing experiments were carried out on the polishing platform developed by ourselves. The results show that the new polishing method can polish 20 mm × 20 mm × 5 mm KDP crystal and obtain a super-smooth surface with a surface roughness of 1.37 nm and high shape accuracy. The surface accuracy of polished KDP crystal reaches up to 0.68λ (RMS). The experimental results show that the ASTP is a potential ultra-precision machining method for KDP crystal.

X-ray Optics and Ultraprecision Machining in <i>Heisei</i> : A Review —Development of Diffraction-Limited X-ray Condenser Mirror as a Cutting-Edge Application of Ultraprecision Machining Methods—

X-ray Optics and Ultraprecision Machining in <i>Heisei</i> : A Review —Development of Diffraction-Limited X-ray Condenser Mirror as a Cutting-Edge Application of Ultraprecision Machining Methods—

Progress in femtosecond laser fabrication of artificial compound eye

Compound eyes of arthropods are widespread and fascinating visual systems created by natural evolution. Compound eyes consist of many identical small eye units called ommatidia, each of which is an individual imaging system composed of cornea lens, crystalline cone and rhabdome. Compared with single eyes, compound eyes have distinct advantages in small volumes, large field of view, large depth of field, and high temporal resolution. Therefore, it has sparked considerable research interests in developing various manufacturing technologies towards the fabrication of artificial compound eyes that can be applied in robot vision, three-dimension imaging, motion detection and medical examination. To date, various methods have been proposed for fabricating artificial compound eyes, such as hot embossing method, thermal reflow method, microdroplet jetting method, and ultraprecision machining method. However, these methods inherently suffer from low accuracy and multi-step processing. In particular, it is extremely difficult for these methods to acquire curved artificial compound eye lens, which is quite important for promoting the optical performance and practical applications of artificial compound eyes. In recent years, femtosecond laser direct-writing (FsLDW) has emerged as a practical and promising technique for fabricating artificial compound eyes owing to its capability of three-dimensional (3D) processing and high fabrication precision. First of all, FsLDW is performed by point by point scanning process layer by layer, making it capable of realizing various 3D structures as designed. Second, the extremely high transient intensity of femtosecond laser pulses leads to a non-linear absorption effect (two-photon absorption or multi-photon absorption) with materials in a much smaller volume than the cubic size of wavelength, which endows it with a high resolution (tens of nanometers) beyond the optical diffraction limit. Moreover, the high power of femtosecond laser pulses also provides the ability to process various materials, from soft photopolymer materials to rigid substrates as hard as diamonds. For soft materials, the fabrication mechanism is two- or multi-photon polymerization of photosensitive polymers triggered by the high energy at the localized laser focus region. Through point by point process, two-photon polymerization technology by FsLDW becomes a powerful tool for fabricating complex 3D structures. In spite of this, its shortcoming is obvious as well. The single point scanning procedure causes a relatively low efficiency, which needs further improvement. For hard materials, femtosecond laser serves as an ablation source to form micro-hole, where the local material is removed or chemically modified. Femtosecond laser ablation can be combined with a subsequent etching treatment for improving efficiency, including wet etching and dry etching. The drawback of etching assisted femtosecond laser ablation technology lies in that usually only concave structures can be obtained, further soft embossing treatment is needed in order to acquire convex compound eye lens. In this review, the latest progress in femtosecond laser fabrication of artificial compound eyes is summarized. Manufacturing of artificial compound eyes by FsLDW is introduced according to the two methods mentioned above: femtosecond laser two-photon polymerization that belongs to additive manufacturing and femtosecond laser ablation that is regarded as a subtractive manufacturing method. Then, the diverse applications of artificial compound eyes produced by FsLDW are described. At last, current challenges and future perspectives in this field are discussed.

Theoretical and experimental investigation of the effect of the machining process chain on surface generation in ultra-precision fly cutting

Ultra-precision fly cutting (UPFC) is an enabling ultra-precision machining method since it has many advantages such as providing uniform high surface quality, high flexibility necessary for machining freeform or micro-structural surface, etc. However, low machining efficiency is still a problem for UPFC. This paper attempts to increase its machining efficiency by shortening its process chain based on theoretical analysis. A dynamic model considering the whole process chain in UPFC is developed in this study. The dynamic process chain model (DPCM) is basically divided into two parts. The first part is a single UPFC model consisting of geometry parameters and spindle vibration which are primary factors of surface generation. The second part is the preceding surface topography model of the workpiece. An additional coordinate transfer model is developed to combine the above two parts together. Simulation and actual experiments have been conducted to verify the DPCM. The predicted results from the DPCM match the results from the actual machining experiments well. It is found that the parameters are optimized to shorten the process chain in UPFC. In some conditions, the required surface quality is achieved by a single machining step of UPFC directly from traditional turning. On the whole, the process chain model of UPFC provides a feasible way to simulate the dynamic process and observes the change of the surface generation of workpieces when machining parameters change so as to optimize the process chain in UPFC.

The coupling effect of slow-rate mechanical motion on the confined etching process in electrochemical mechanical micromachining

By introducing the mechanical motion into the confined etchant layer technique (CELT), we have developed a promising ultra-precision machining method, termed as electrochemical mechanical micromachining (ECMM), for producing both regular and irregular three dimensional (3D) microstructures. It was found that there was a dramatic coupling effect between the confined etching process and the slow-rate mechanical motion because of the concentration distribution of electrogenerated etchant caused by the latter. In this article, the coupling effect was investigated systemically by comparing the etchant diffusion, etching depths and profiles in the non-confined and confined machining modes. A two-dimensional (2D) numerical simulation model was proposed to analyze the diffusion variations during the ECMM process, which is well verified by the machining experiments. The results showed that, in the confined machining mode, both the machining resolution and the perpendicularity tolerance of side faces were improved effectively. Furthermore, the theoretical modeling and numerical simulations were proved valuable to optimize the technical parameters of the ECMM process.

Fluid hydrodynamic fixed abrasive grinding based on a small tool

A new grinding technology called fluid hydrodynamic fixed abrasive grinding (abbreviated as FHFAG process) is being proposed in this research. It combines the fixed abrasive grinding process and the fluid hydrodynamic theory. This research will examine the feasibility of applying the innovative process as an ultra-precision machining method for hard and brittle materials such as fused silica glass and silicon. It aimed to turn fixed abrasive grinding processing into a kind of deterministic surfacing processing method. Besides, the method could improve the machining efficiency and machining accuracy at the same time. Specifically, a thin liquid film between the grinding pad and the workpiece is introduced. The cutting depth based on one single grinding pad with a settled particle size can be controlled by controlling the thickness of the liquid film. From the machining mechanism, the grinding tool’s rotary speed and the original input pressure dominate the deterministic properties of the process. A special self-balancing device and a special fluid supply method which supply the grinding liquid from the center of the motorized spindle are proposed to realize the new processing technology. The grinding pad can float on the workpiece steadily from a preliminary experiment result. It is clearly demonstrated that the FHFAG process can be used as a deterministic processing method if the identified working parameters are well controlled.

Progress in Ultra-precision Machining Methods of Complex Curved Parts

Progress in Ultra-precision Machining Methods of Complex Curved Parts

100 µm-size stationary spot machining in elastic emission machining

Recently, by using various ultraprecision machining methods, optical devices having both nanometer-level figure accuracy and nanometer-level smoothness have become obtainable. However, improvement of the spatial resolution in figuring is still strongly required, particularly when the shape of optical devices is complicated. We have been developing a figure correction system using elastic emission machining (EEM). In this study, an EEM nozzle head having a minute aperture with a diameter of less than 60 µm was developed. The minute hole was prepared by micro-electrical discharge machining (EDM). A stationary spot profile with a diameter of 100 µm was experimentally obtained. Using the developed nozzle, spatial resolution better than 100 µm is expected to be realised in the EEM figuring system.

Effect of crystal orientations on nanocutting based on quasicontinuum multiscale method

Nanocutting is one of the most important ultra-precision machining methods to obtain complex optical elements with high quality finish. Molecular dynamics is widely used to investigate the nanocutting mechanism due to the nano-scale cutting depth. For high efficiency and large scale simulation, multiscale method is significantly necessary. Quasicontinuum (QC) multiscale method, using the embedded atom method (EAM), is applied to study the effect of crystal orientation on nanometric cutting of single crystal copper. The results show that the generation and emission of dislocation and the distribution of residual stress in workpiece strongly depend on the crystal orientation and cutting direction. It is recommended to fabricate a higher quality surface when the cutting direction is along on crystal orientation (111). Finally, it is proved that QC method is an efficient approach to study the nanocutting mechanism.

Experimental Study on Micro-Deliquescence Ultra-Precision Polishing with Fine Water Mist for KDP Crystal

KDP crystal (Potassium dihydrogen phosphate single crystal) is extremely difficult to obtain flawless surface because of its soft, brittle, and hygroscopic. And a large amount of time has been spend on obtaining flawless surface with ultra-precision machining methods. In order to quickly reduce surface roughness on KDP crystal, a new micro-deliquescence polishing method with fine water mist was proposed, the polishing tool with fine water mist was designed, and the polishing experiment was carried out. The micro-deliquescence polishing with fine water mist can improve the surface quality of KDP crystal quickly, so it is an effective preprocessing before ultra-precision machining.

Study of Cluster Magnetorheological-Chemical Mechanical Polishing Technology for the Atomic Scale Ultra-Smooth Surface Planarization of SiC

The growth of epitaxial layer of SiC wafer requires the surface of SiC substrate to reach an atomic scale accuracy. To solve the problems of low machining efficiency and low surface accuracy in the polishing process of SiC wafer, a novel ultra-precision machining method based on the synergistic effect of chemical reaction and flexible mechanical removal of the magnetorheological (MR) effect, the MR-chemical mechanical polishing (MRCMP) is proposed. In this technique, magnetic particles, abrasives and chemical additives are used as MR-chemical polishing fluid to form a cluster MR-effect flexible polishing platen under an applied magnetic field, and it is expected to realize an atomic scale ultra-smooth surface planarization with good controllability and high material removal rate by using the flexible polishing platen. Polishing experimental results of C surface of 6H-SiC crystal substrate indicate that an atomic scale zero-defect surface can be obtained. The surface roughness of C surface of SiC wafer decreased from 50.86nm to 0.42nm and the material removal rate was 98nm/min when SiC wafer was polished for 60 minutes.

Effect of focusing flow on stationary spot machining properties in elastic emission machining

Ultraprecise optical elements are applied in advanced optical apparatus. Elastic emission machining (EEM) is one of the ultraprecision machining methods used to fabricate shapes with 0.1-nm accuracy. In this study, we proposed and experimentally tested the control of the shape of a stationary spot profile by introducing a focusing-flow state between the nozzle outlet and the workpiece surface in EEM. The simulation results indicate that the focusing-flow nozzle sharpens the distribution of the velocity on the workpiece surface. The results of machining experiments verified those of the simulation. The obtained stationary spot conditions will be useful for surface processing with a high spatial resolution.

Ultraprecision micromachining of hard material with tool wear suppression by using diamond tool with special chamfer

This study aims to develop an ultraprecision machining method which enables to suppress tool wear in the machining of hard material by using the tool with special chamfer. As a result, the cutting point swivel machining is proposed, and its effect is experimented in the machining of SiC. Then, the relationship between the speed ratio and tool wear is investigated. By applying the proposed machining method to curved microgrooving and curved surface machining on Tungsten Carbide, it is confirmed that cutting point swivel machining enables to realize ultraprecision machining of complex shape.

Design, fabrication and characterization of three-dimensional patterned microstructured surfaces with self-cleaning properties from hydrophilic materials

The generation of self-cleaning surfaces requires strong water repellence, which is usually realized by either fabricating a rough surface from low-surface-energy material, or modifying a rough surface with microstructures. The advancement of the ultra-precision machining technology enables the later approach to be a more prospective and flexible method to produce microstructured self-cleaning surfaces. This article presents a study for the design, fabrication and characterization of three-dimensional patterned microstructured surfaces with self-cleaning properties by using ultra-precision machining technology. The study starts with the design of three-dimensional microstructured surfaces based on the derivation and simplification of some microstructures possessing self-cleaning properties in nature, and theoretical analysis for water contact angle of the designed structures. According to the scales and patterns of the three-dimensional microstructures, an appropriate ultra-precision machining method is selected to fabricate the microstructures. The machined surface is then examined and characterized. A series of experiments have been undertaken to produce patterned microstructures by an ultra-precision raster milling process, and the micro-structured surfaces were measured and characterized in terms of their geometrical form accuracy and water repellence performance. The experimental results indicate that such kind of three-dimensional patterned microstructures can achieve a large static water contact angle, which is near 150°, by modifying the structural scales and patterns of hydrophilic materials. This provides an important means to generate surfaces with self-cleaning properties in mass production by precision injection moulding.

The Improvement of Removal Function in Local Wet Etching by Using Eccentric Rotation System

Numerical controlled local wet etching is a novel non-contact deterministic figuring method in ultra precision optics fabricating and functional material manufacturing fields, and the cross-sectional shape of the traditional removal spot is a simple cylinder, so the removal function has no adjustability. In order to create more practical and regular removal function, an eccentric rotation system is introduced to improve the LWE system. By controlling the eccentricity, it can achieve varied shapes removal function. When the rotary axis is controlled to a proper eccentricity, the removal function can be close to the Gaussian function. Moreover, the theoretical calculation and experimental validation are coincident and can give the research a steady foundation. The improvement not only can increase the adjustability of the removal function in LWE, but also can expand its applied field and provide reference for other ultra precision machining methods whose removal function does not have circular symmetry.