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Magnesium (Mg) based alloys are promising candidates for many applications, but their untreated surfaces usually have low strength and hardness. In this study, a single point diamond turning (SPDT) technique was applied to refine the grain size and improve the mechanical properties of the surface layers of Mg-Li alloys. By refining grains in the topmost layer to the nanometer scale (∼ 60 nm), the surface hardness was found to be enhanced by approximately 60%. The atomic plastic deformation process during the SPDT was then studied by the real-time atomistic molecular dynamics (MD) simulations. A series of MD simulations with different combinations of parameters, including rake angle, cutting speed and cutting depth, were conducted to understand their influences on the microstructural evolution and associated plastic deformation mechanisms on the surface layer of the workpieces. The MD simulation results suggest that using increased rake angle, cutting speed and cutting depth can help to achieve better grain refinement. These simulation results, which provide atomic-level details of the deformation mechanism, can assist the parameter design for the SPDT techniques to achieve the high-performance heterogeneous nanostructured materials.

The increasing demand for machining non-rotational optical surfaces requires capable and flexible cutting tool path generation methods for ultra-precision diamond turning. Furthermore, the recent interest in on-machine metrology and corrective machining requires efficient as well as accurate algorithms capable to handle point cloud based surface data. In the present work, a new computation method for the tool path generation is proposed that focuses on three-axes corrective machining. It is based on the principle of defining the surface to be machined by a point cloud of given density, since surface measurement data is usually available as point cloud. Numeric approximation techniques are used to compute the surface normal vectors and calculate the resulting positions of the cutting tool path preserving a uniform radial axis motion for face turning. Investigations are performed in order to quantify the error between the calculated tool path and the exact analytical solution. The error dependencies are analyzed regarding the local surface slope and numerical parameters. Error values below 1 nm are achieved. In addition, form deviation results prove the method's capability for corrective diamond turn machining., The International Journal of Advanced Manufacturing Technology, 120 (9-10), ISSN:0268-3768, ISSN:1433-3015

Fresnel micro-lens arrays with close-to-wavelength features have significant advantages in minimization of optical systems. However, in the fabrication of an array of Fresnel micro-lenses by conventional diamond turning, the discontinuous features of the surface profile cause interference between the tool flank face and the finished surface. In this manuscript, a novel off-spindle-axis diamond turning method is proposed to fabricate Fresnel micro-lens array mold insert and a toolpath generation algorithm is developed. The generation of each lenslet is treated as an independent turning operation, and the whole fabrication of a Fresnel micro-lens array is completed by a succession of repetitive turning operations. With this approach, the interference between the tool and the finished surface is avoided, and the form accuracy and surface integrity are improved for each lenslet. Then, the Fresnel micro-lens array mold insert is further utilized in precision glass molding to replicate the micro-lens structures onto transparent polymer substrates. The experimental results indicate that both the diamond-turned and molded Fresnel micro-lens arrays are achieved with homogeneous quality. As an application, a compact imaging system based on the molded Fresnel micro-lens array is demonstrated. The proposed machining method in this study can be employed in the fabrication of Fresnel micro-lens arrays and other micro-optics with discontinuous profiles with high accuracy and machining efficiency.

Although it has long been known that tools with more negative rake angles allow the ductile regime to be achieved when machining monocrystalline silicon; little has been discussed about the tool-material interaction in terms of the microgeometric contact of the tool tip at this interface. In this paper, the tool rake angle was varied in order to change the undeformed chip thickness value once the tool cutting radius, formed in front of the tool rake face, changes when the tool rake angle becomes more negative. Based on the statistical design of the experiment applied to cutting tests, a map relating values of transition pressure and different crystallographic directions is built to assist in determining machining conditions with a ductile response within a wider spectrum based on tool rake angle under different machining conditions. The results obtained allowed to answer questions under which machining conditions and tool geometry account for better surface finishes, lower machining forces, and lower residual stresses. The response surfaces generated provided answers capable of establishing under which cutting radii yielded more ductile mode material removal and avoided a brittle response, related to anisotropic response due to change in the crystallographic direction. Finally, we used the brittle-to-ductile transition map to determine a more suitable machining condition to diamond turn Fresnel lenses in single crystal silicon.

Random micro-structured surfaces (RSS) have great application potentials as various functional surface elements, such as optical diffusers, with homogeneous surface properties. Conventional fabrication methods for RSS, such as chemical etching, can no longer meet modern requirements of high precision and controllability. In this study, a novel method was proposed for fabricating micro dimple arrays with controllable randomness in dimple size and depth by using fast tool servo (FTS)-based single-point diamond turning. Firstly, for tool path generation, a computer program was developed to periodically arrange small patches of quadratic surfaces over a large surface area. Then the position, height, and size of each quadratic surface were adjusted by applying random values, whose dynamic range was preset, to control the spatial difference among the dimples. Finally, the designed RSS was machined by continuous and segment cutting methods, respectively, to evaluate their effects on dimple edge formation. Results showed that the segmented cutting method improved the edge accuracy, thus was effective for RSS machining. The machined surface matched precisely with the designed surface with a form error of 10 nm level. The machining method proposed in this study enables high-precision patterning of mold inserts for molding/imprinting RSS on polymer materials.

Diamond turning, fly-cutting, and milling are the primary manufacturing technologies for generating free-form surfaces; however, they are not sufficiently effective in machining free-form optics on hard and brittle materials. Ultra-precision grinding has been demonstrated to have an outstanding capability in machining difficult-to-cut materials. Therefore, we proposed a novel surface generation technique for free-form optics based on a slow tool servo with diamond grinding wheels (STS-DGW). First, the generation strategies of the wheel path for grinding biconical optics were explored. Subsequently, the generation process of surface topography was theoretically analysed, and the interference between the diamond wheel and biconical optics in the process of surface generation was checked. Eventually, typical biconical free-form optics were fabricated on single-crystal silicon. Submicron profile accuracy and nanometer surface roughness were achieved, and the influence of the processing parameters on the surface topography and material removal mechanism was investigated.

In the single-point diamond turning (SPDT) of optical spherical/aspheric surface, tool deviating from the spindle rotation center significantly deteriorates the form accuracy of the spherical/aspherical surface and its optical performance. In this study, the influence of tool deviation on the form accuracy of a convex spherical surface and the cutting force forms during the turning process were studied first, following which a force-based tool deviation model was derived to identify the tool deviation using cutting force. Finally, by analyzing the influence of tool deviation on the three-dimensional (3D) form of residual structures at the center of the convex spherical surface, the 3D form of the convex spherical surface was predicted online. Results indicate the existence of a mapping relation between the tool deviation and the cutting force form, which could be further used to online predict the 3D form of the machined convex spherical surface in SPDT through the established geometric model.

Laser-assisted diamond cutting is a promising method for the cost-effective machining of hard and brittle materials. A deep knowledge of the material removal mechanism and the attainable surface integrity is crucial to the development of this new technique. This paper focuses on the application of laser-assisted diamond cutting to single-crystal silicon to investigate key characteristics of the process. These characteristics are the critical depth of cut for ductile–brittle transition, machined surface roughness, resultant micro-cutting force, friction coefficient, temperature distribution, microstructure change, and the subsurface damage of the machined silicon. Laser-assisted diamond cutting method is compared with the conventional single-point diamond cutting method. The experimental results reveal that laser-assisted diamond cutting can enhance the silicon’s ductility and machinability by decreasing the softened material’s hardness and promoting the atomic activity in the subsurface layer. The critical depth of cut has been increased by up to 364% with laser assistance, and its degree generally increases with the increase of temperature. The friction coefficient has been decreased by up to 27.95%. The cross-sectional transmission electron microscope observation results indicate that laser-assisted diamond cutting is able to effectively inhibit the formation of the distorted layer and produce less subsurface damage of single-crystal silicon. In comparison to the conventional single-point diamond turning of single-crystal silicon, a significant improvement of surface quality has been obtained by laser-assisted diamond cutting: Sz has been reduced by 87%, and Sa has been reduced by 50%.

Surface roughness is one of the most significant factors to indicate the product quality. Diamond turning is an efficient and highly accurate material removal process to improve the surface quality of the workpiece. In the present study, the arithmetic mean absolute roughness (Ra) and total height of profile (Rt) of spherical surface during finish turning of a commercial brass alloy CuZn40Pb2 were modeled using Response Surface Methodology (RSM). The experimental investigations were carried out using the Central Composite Design (CCD) under dry conditions. The effect of cutting parameters such as spindle speed, feed rate and depth of cut) on spherical surface quality was analyzed using analysis of variance (ANOVA). A cuckoo search (CS) algorithm was used to determine the optimum machining parameters to minimize the surface roughness. Finally, confirmation experiments were carried out to verify the adequacy of the considered optimization algorithm.

Fast tool servo and slow slide servo-based diamond turning are very important and widely used machining methods for freeform surfaces. In diamond turning of freeform surfaces, the research on tool path generation and machined surface topography prediction is generally for diamond turning processes using zero rake angle tools. But diamond turning with non-zero rake angle tools is also of great importance, for which very little research has been done on tool path planning and surface topography modeling. Therefore, based on coordinate transformations, this paper develops a new tool path generation method and discusses the tool geometry parameter selection for diamond turning utilizing non-zero rake angle tools. In addition, a new surface topography prediction model based on the actual position and orientation of the tool cutting edge is constructed for the machined surface. The machining experiments of a typical freeform surface are conducted based on the calculated tool paths and necessary critical tool geometry parameters. The measured results validate the developed tool path generation and tool geometry selection methods, and the constructed surface topography model.

The surface roughness required for the optical application and lenses is in the range of nanometers possible to achieve in single-point diamond turning (SPDT). The machining parameters like feed, s...

Machining Rapidly Solidified aluminium (RSA) 6061, a widely used optical material by Ultra-high precision diamond turning, has enabled high accuracy and surface integrity. However, improved quality and productivity require precision surface and machining process monitoring because the duo has a great influence on machine part performance. The study presented in this paper investigates the effects of cutting parameters (i.e., depth of cut, feed rate and cutting speed) on machining output variables (surface roughness and acoustic emission potentials) during ultra-high precision diamond turning of RSA 6061. With the aid of Box-Behnken design (BBD), a response surface methodology, and the analysis of variance (ANOVA), the correlation between cutting parameters and machining output variables were analyzed and modeled. The results showed that both surface roughness and acoustic emission potentials are greatly influenced by feed rate and cutting speed. For a better-quality surface roughness and low acoustic emission during ultra-high precision diamond turning of RSA 6061, high cutting speed and low feed rates are the right combinations and vice versa.

Precision-engineered components which operate in demanding conditions often require the application of hard coatings such as tungsten carbide (WC) to improve their functional properties. Following the coating deposition process, a surface finishing or machining operation is often required to correct the sizing or achieve adherence to geometrical tolerancing and surface finish requirements. Single point diamond turning (SPDT) is a widely used ultraprecision machining technique for the fabrication of high-end engineering components made up of ductile materials, making it a desirable technique as a post-coating machining or finishing process. In this study the machinability of hard CVD W/WC coatings with a hardness of 1120 ± 15 HV and a thickness of 100 μm using SPDT was investigated. Here we report the results of axial and transverse turning using a cutting speed of 600 rpm and feed rates of 1 and 5 μm respectively. Experimental results show that an Ra of 0.2 μm is achieved with a diamond tool having a 0.5 mm nose radius. Significant tool wear was observed at the rake/flank edge of the diamond tool due to the coating's hardness. Surface and cross-sectional analysis of the samples' machined areas revealed presence of adhesive and abrasive wear. The occurrence of material pile-up due to tool loading on the surface of the coating was investigated through the indentation technique which demonstrated the occurrence of material deformation contributing to the overall surface roughness.

Diamond tools are known to wear rapidly during the machining of ferrous materials because of the catalytic effect of iron on diamond graphitization. This work aims to perform a relative comparison of the wear mitigation efficacy of candidate two-dimensional (2D) materials, viz., graphene oxide (GO), hexagonal boron nitride (hBN), molybdenum disulfide (MoS2) and tungsten disulfide (WS2), when used as cutting fluid additives during diamond turning of steel. The 2D material suspensions (0.15 wt.%) are first characterized for their hydrodynamic diameter distributions. Multi-pass turning studies are then conducted using monocrystalline diamond tools. Tool wear, cutting forces and surface roughness are used as the comparison metrics. Overall, graphene oxide has the highest reduction in tool wear (60 %) over the baseline case. It is followed by hexagonal boron nitride, tungsten disulfide and molybdenum disulfide that offered 52 %, 45 % and 38 % wear reduction, respectively, over the baseline case. Overall, hBN provides the best combination of low tool wear, low cutting forces and low surface roughness. The tool wear mitigation efficacy of the materials can be explained in terms of their specific chemical/physical interactions at the iron-diamond interface. X-ray Photo Spectroscopy (XPS) measurements reveal a clear correlation between the tool wear trends and strength of the graphitic carbon/carbide signals obtained on the machined surfaces. XPS measurements in the B1s and S2p regions shed light on the chemical reactions responsible for the performance of hBN, WS2 and MoS2. The unique surface chemistries of the resulting surfaces offer the potential of a rich exploration landscape for downstream applications.

The metallurgical modification in non-ferrous metal alloys is carried out to adapt not only physical or mechanical properties to their applications, but also to improve their machinability. In the case of aluminum alloys for optical applications, the reduction in grain size is an alteration aimed at adapting the dimensions of the microstructure to the dimensional scale used in the machining conditions. The dimensions of the cutting section are often much smaller than the average grain size, which causes anisotropic effects on both the material removal mechanism and surface integrity. The objective of this study is to compare the effect of the material's microstructure, in this case, grain size, on the removal mechanism, energy dissipation and surface generation involved in the ultraprecision diamond turning of aluminum alloy 6061-T6 using micrometric and submicrometric cutting conditions. Cutting forces results showed that below feedrate of 10 μm/rev there is a reversal effect on the cutting forces, thrust force becomes greater than the main cutting force. The specific cutting energy reaches values one order of magnitude higher than conventional values when machining with nanometer range undeformed chip thickness. The impurities, hard inclusions, void formation and the effect of anisotropy will be assessed and discussed by explicating the influence on surface finish at nanoscale level. Based on observations of optical profilometry and scanning electron micrographs, the machined surfaces and chips removed were assessed and the effects of the aforementioned factors on the cutting mechanism were identified. Under nominal undeformed chip thickness smaller than 286 nm the machined surface does not show parallel groove marks left by the diamond tool. As the undeformed chip thickness decreases, the friction coefficient becomes high, leading the energy dissipation due to rubbing action at the tool-chip interface to move downward to cutting edge portion. Below this value the surface generation mechanism is attributed to a burnishing of the round part of the tool cutting edge and the portion adjacent to tool flank face. It was observed that the microstructure and metallurgical process involved to obtain each type of aluminum alloy play an important role on the performance of the cutting process and on the surface formation. Under chip cross sectional area greater than 50 μm2 hard particles dragged by the cutting tool are observed on machined surface. This causes the surface roughness to increase.

Ultra-precision machining of single-crystal silicon can be realized by applying single-point diamond turning with micro-laser-assisted machining technology, through which the ductility of silicon can be enhanced. However, it is difficult to explain the role of temperature accurately in such technology in a traditional manner. In this study, numerical simulation technology was utilized to obtain the temperature distribution conquering the limitations of the traditional measurement method. Besides, a diamond grooving simulation model considering the temperature effect was developed using the smoothed particle hydrodynamics (SPH) algorithm. The shortcoming of the accuracy of calculation brought by applying the finite element method can be overcome effectively. By analyzing the evolutions of cutting force, the ductile-to-brittle transition behavior was distinguished. The comparison of the quantitative values of critical depths of cut between the simulations and grooving experiments corroborated the high accuracy of the as-established SPH model. In addition, the significance of temperature on ductile-to-brittle transition is successfully divulged. The simulation results demonstrate that the critical depth of cut of ductile-to-brittle transition increases in pace with an increase in temperature due to the thermal softening effect, indicating the enhancement of ductile response of the material. This study provides a novel method for the investigation of ductile-to-brittle transition mechanism and the optimization of processing parameters of single-crystal silicon.

Cellulose nanofiber (CeNF)-reinforced polymer composites have wide potential applications in the manufacturing of optical and mechanical parts owing to their light weight, high mechanical strength, and optical transparency. In this study, CeNF-reinforced homogeneous polypropylene (PP-CeNF) was machined under various conditions by ultraprecision diamond turning, and the results were compared with those of pure PP without CeNF addition. The influence of CeNFs on material removal was investigated by examining the surface topography, chip morphology, cutting forces, and cutting temperature. It was found that the surface defects in pure PP cutting were surface tearing, while the surface defects of PP-CeNF were surface tearing and micro-holes induced by the pulling-outs of CeNFs. Surface tearing increased with cutting speed; pulling-outs of CeNFs were slightly affected by cutting speed but strongly dependent on the tool feed rate. Under a small tool feed rate, the surface roughness could be reduced to ∼10 nm Ra for PP-CeNF. The thermal effect was insignificant in the experiments, whereas the effect of strain rate-induced material hardening was dominant for both workpiece materials at a high cutting speed. This study helps to understand the mechanisms for ultraprecision cutting of CeNF-reinforced polymer composites and provides guidelines for improving the machined surface quality.

In single-point diamond turning (SPDT), two-dimensional (2D) tool centre error is caused by the tool deviating from the workpiece rotation centre both in the horizontal direction (tool feed direction) and vertical direction (perpendicular to tool feed direction). This greatly affects the form accuracy of the machined surface and its optical function. Traditional tool centre error identification is usually performed off-machine manually with high-precision instruments, which is time-consuming and labour-dependent. In this paper, a novel force-based 2D tool centre error identification method in SPDT is introduced. First, according to the relative position between the tool and workpiece centre, the tool centre error is classified into nine cases. The relation between the cutting force profiles and the tool centre error is analysed for each case. Then, a numerical fitting model and a geometric model are established to identify tool-above-centre and tool-below-centre errors, respectively. Additionally, a geometric model is established to calculate the normal distance from the tool interference/exit cutting to the workpiece centre, which serves as a reference for the horizontal tool centre error identification. Finally, the on-machine identification results of the 2D tool centre error are verified by experiments. Theoretical and experimental results show that the proposed on-machine 2D tool centre error identification method is effective and accurate, which greatly improves the cutting efficiency in SPDT.

High-precision optical components with nanometric surface finish can be obtained directly through single point diamond turning. However, residual cutting marks on the machined surfaces are likely to cause serious diffraction and deteriorate the optical performance of a machined component. This paper proposes a novel method for diffractive optical characterization of diamond-turned surfaces based on the vector diffraction theory. The distribution characteristics of the diffraction spots are revealed by using the finite-difference time-domain method. Simulation results supported by experimental verification demonstrate that the height and spacing of nanometric surface topography exert different influences on the intensity and angle of the diffraction spots. The intensity of high-order diffraction spots would be more prominent if a laser beam with a smaller wavelength and incident angle is used to illuminate the machined surface. Even if the areal surface roughness Sa changes less than 2 nm, the gray values of high-order diffraction spots may increase by nearly 5 times under certain conditions.

Improving the technology of diamond turning of aluminum alloys is of great importance for expanding the application areas of metal-optical products based on aluminum in aerospace technology. The aim of this work was to study the effect of surface inhomogeneities of the initial aluminum alloy substrates on their optical and mechanical characteristics and to determine ways of improving the quality of aluminum reflector mirrors manufactured using nanoscale single point diamond turning. The investigated reflector mirrors were made from AMg2 aluminum alloy. The optical surface treatment was carried out on a precision turning lathe with an air bearing spindle using a special diamond cutter with a blade radius of ≤ 0.05 μm. The analysis of the surface structure of the AMg2 alloy substrates was carried out by scanning electron microscopy / electron microprobe. The quality control of the surface treatment of the manufactured reflector mirrors was carried out by atomic force microscopy. The reflectivity and radiation resistance of these samples were also investigated.It is shown that an important problem in the manufacture of optical elements from aluminum alloys is the inhomogeneity of the structure of the initial material, associated with the presence of intermetallic inclusions. Heat treatment of the AMg2 alloy substrates at T ≥ 380 °C makes it possible to improve the quality of surface and the radiation resistance of aluminum mirrors both by removing mechanical stresses and by partially homogenizing the starting material. The optimum is heat treatment at the maximum allowable temperature for the AMg2 alloy T = 540 ºС, as a result of which there is a complete disappearance of intermetallic inclusions with an increased magnesium content. The use of high-temperature heat treatment of AMg2 alloy substrates allows, in comparison with unannealed samples, to reduce the surface roughness from 1.5 to 0.55 nm, to increase the reflectivity of mirrors at a wavelength of 1064 nm from 0.89 to 0.92, and to increase the laser damage threshold from 3.5 to 5 J / cm2.

Multiscale optical surface (MOS) that contains non-rotational symmetry micro-features and large sag height macro-features is promising in optics, due to their special optical advantages. Diamond turning with the slow tool servo (STS) or fast tool servo (FTS) is widely used for fabricating optical surfaces. However, due to the limited dynamic performance of STS and the small stroke of FTS, applying STS or FTS alone cannot efficiently fabricate MOS. Therefore, in this paper, a hybrid tool servo (HTS) diamond turning technique was presented to efficiently produce MOS. By integrating characters of the high dynamic performance of FTS and long stroke of STS, the new technique fulfills the strict requirements of manufacturing MOS. Methods for generating tool path in CAD software and separating the tool path into STS path and FTS path based on its spectral features were proposed. Besides, tool path evaluations were conducted to predict the profile errors with considering the dynamic performance of STS and FTS, based on the suitable machining parameters selected. A machining experiment of a typical MOS was carried out using the proposed technique. Results showed that the MOS was efficiently fabricated with no tool interference mark on the fabricated surface and a maximum profile error of about 2.8 μm.

On the demand of low-cost, lightweight, miniaturized, and integrated optical systems, precision lenslet arrays are widely used. Diamond turning is often used to fabricate lenslet arrays directly or molds that are used to mold lenslet arrays. In this paper, mainly by real-time monitoring position following error for slow tool servo, different fabrication parameters are quantitatively studied and optimized for actual fabrication, then by actual fabrication validation, uniform and high-fidelity surface topography across the actual whole lenslet array is achieved. The evaluated fabrication parameters include sampling strategy, inverse time feed, arc-length, etc. The study provides a quick, effective, and detailed reference for both convex and concave lenslet array cutting parameter selection. At the end, a smooth zonal machining strategy toolpath is demonstrated for fabricating concave lenslet arrays.

Slow tool servo (STS) turning takes an important role in fabrication of freeform optical elements. However, in conventional STS turning, it is technologically difficult to obtain nanometer-level form accuracy due to multiple error factors such as tool trajectory errors, tool alignment errors and dynamic follow-up errors of machine tools used. In this study, a deterministic process flow was proposed where all the main error factors were comprehensively analyzed, simulated and then compensated before machining based on the feedforward method, and the workpiece form error after compensation was predicted accurately. The proposed process flow enabled achieving nanometer-level form accuracy by a single cut without the necessity of repetitive trial-and-error. To demonstrate the effectiveness of the proposed method, cutting tests of a two-dimensional sine wave grid were attempted on single-crystal silicon and the proposed error compensation was applied. As a result, the form error was reduced to 8 nm P–V (peak to valley) with a surface roughness of 1 nm Sa by a single cut.

A quantificational approach was proposed to analyze the discrepancy of monocrystalline silicon surface roughness along different crystal orientations in diamond turning on Statistical Product and Service Solutions software. This work aimed to understand how crystal orientation affects surface generation in the cutting behavior of monocrystalline silicon. In this study, the measured surface roughness data were first processed in advance to eliminate some adverse effects of outliers. The average values of surface roughness distributions were obtained. The surface roughness values of different measurement directions were compared, and the influences of crystal orientations on surface roughness were analyzed. Results indicate that the crystal orientation and the cutting parameters have much influence on machined surface roughness. Finding some special crystal orientations using Euclidean distance analysis with average analysis is effective. The vibration induced by crystallographic orientation is the main reason to make surface nonuniform roughness in single-point diamond turning. This finding is verified by analyzing the surface generation mechanism.

With the increase in dimensions of optical elements in addition to ever rising demand for aspherical optics, the millimeter-scale periodic waviness that is naturally produced by machining (such as diamond turning) process in precision optical engineering has been one of the most crucial issues in the development of high surface quality optical elements. Even an extremely small waviness can affect the laser beam profile significantly through interference caused by Bragg scattering. This paper presents a novel method for improving a laser beam profile by utilizing the characteristics of Bragg scattering without requiring established final surface finishing processes such as optical polishing. By engraving an artificial periodic structure with a period of a few hundred microns, the Bragg scattering angle that influences the formation of interference fringes in the laser beam profile was drastically enlarged. Consequently, the quality of the beam profile was improved at a propagation distance where the 0th and 1st (− 1st) order beam modes are spatially separated, only by diamond turning machining without the surface finishing process. In addition, this approach represents an important contribution to green technology, which seeks energy saving and waste reduction in the optical surface manufacturing process.

In diamond turning of polymer bonded explosives (PBXs), a transient temperature monitoring tool is crucial for the processing safety issues. Three design principles are proposed in this work to fulfill the accurate prediction of the temperature distribution on tool cutting edge by using gradient calibration method and heat transfer simulation. Subsequently, the detailed design, microfabrication, and self-calibration test are successfully performed to establish the temperature measuring tool based on a natural diamond cutting tool. A theoretical model is further established to predict the transient temperature of the tool tip in the limit turning experiment and explore the safe cutting factors of typical PBXs. The results show that (1) the unsteady heat transfer model can better describe the self-calibration process of the tool, and it can accurately predict the transient temperature on the tool tip using the error distribution law; (2) finite element method can not only obtain the global temperature distribution field but also analyze the influences of tool structure, material selection, and thermal boundary conditions on prediction errors; and (3) cutting speed, tool tip wear, dry cutting are the key factors that affect the cutting safety of PBXs, and the maximum safe cutting speed vmax ≈ 33.5 m/s.

In ultra-precision machining of ferrous materials, diamond tools are easy to graphitize due to chemical reactions with ferrous materials, which can cause severe tool wear. The sharpness of the original cutting edge therefore cannot be maintained to machine mirror-level surface roughness. It cannot through a high-efficiency and low-cost way to obtain the workpiece surface integrity with high quality. Studying the wear mechanism of diamond tools and wear suppression methods is very important to improve the cutting efficiency of ultra-precision machining. In the present research, wear mechanisms and suppression schemes in diamond tools turning ferrous materials are reviewed and focusing on three major wear mechanisms and four effective suppression methods. In the end, this paper discusses the magnetism property of diamond-turnable materials, and introduces the feasibility of the magnetic field-assisted scheme to suppress diamond tool wear (DTW).

Polycrystalline copper is widely applied to the manufacture of optical components. Our previous experiments found that some irregular microstructures appeared on the machined surface; however, it had lacked sufficient studies about generation mechanism. The present research conducted a theoretical and experimental study on the generation mechanism of irregular microstructures. Firstly, the appearance and distribution of irregular microstructures on the machined surface was studied. Secondly, the effects of crystal orientations on the generation of irregular microstructures were investigated. Finally, the cutting performances were investigated by both molecular dynamics simulations and experiments. Theoretical and experimental results show that (1) material properties under different grain orientations are the major cause of the appearance of irregular microstructures; (2) with the changes of crystal orientations, the force signal, chip morphology, shear slip of material, and subsurface defect are also different; and (3) higher cutting velocities have the suppression effect on the generation of irregular microstructures. The present research provides a deep insight into the generation mechanism and suppression method of irregular microstructures in single point diamond turning polycrystalline copper.

Surface topography is an important element that reflects the machining quality of workpieces and the functional performance of components. To avoid expensive cutting experiments, forecasting the surface topography before actual machining is necessary. Surface topography of diamond turned surfaces is directly affected by generated tool path in ultraprecision single point diamond turning (SPDT). In this study, a novel surface topography modeling method was presented. The planned tool path based on active machining precision control was considered in this method. Simulation and experiment of an umbrella surface diamond turning were conducted to testify the usability of the proposed model. Through comparing the simulation and experimental data of surface topography and machining error, the results showed that the proposed model can be applied to forecast the surface topography and machining error in SPDT using the generated tool path.

Freeform optics are defined as nonrotational symmetric optical surfaces in the manufacturing industry. Freeform optics are extensively applied to many areas in order to improve system performance. Fast tool servo (FTS) assisting single-point diamond turning technology has high application prospects in freeform optics machining. This paper discusses the interpolation algorithm for tool path generation of FTS through the application of a radial basis function (RBF) algorithm. For this purpose, a positive definite RBF with compact support was employed as the interpolant. The existence is mathematically proven. Numerical simulations were performed to compare the performances of the RBF algorithm and commonly used algorithms for satisfying the requirements of existence, smoothness, and accuracy. Machining experiments were also conducted to validate the applicability of the algorithm. The simulation results showed that the RBF interpolation algorithm outperformed other algorithms in terms of smoothness. The RBF algorithm also provided the highest interpolation accuracy. Furthermore, the RBF interpolation algorithm exhibited the highest accuracy for error distribution, with large errors distributed mainly in transition areas. The machining results were also in general agreement with the simulation results although obvious practical errors were observed. Overall, RBF interpolation can provide higher accuracy and better smoothness in the tool path generation of FTS.

Single-point diamond turning (SPDT) is a machining process with high levels of profile accuracy and nanometric surface characteristics. SPDT is a leading technology in advanced manufacturing of ultra-precision optical components for critical applications. Different efforts have been undertaken to improve the cutting condition and optimize the machining parameters during SPDT. The implementation of on-machine metrology system (OMMS) has helped to improve the outcomes of SPDT in terms of machined profile accuracy and understand the effects of various processing parameters on optical surface generation. OMMS could be implemented in the hybrid SPDT platforms to effectively improve machining conditions by measuring and diagnosing, and providing testing procedures. Different sensors and principles have been used in the design and development of OMMS including laser-based optical systems. However, measuring the micrometric and nanometric parameters during diamond cutting is difficult to achieve at relatively low resolutions. The purpose of this study is to design and simulate an electro-optical vibrometer (EOV) for measuring machine-tool and workpiece vibration during the SPDT process. The proposed EOV has the capability of measuring, monitoring, and analyzing the vibration characteristics in different machining conditions. In addition, the designed system can communicate with the main control units of the hybrid SPDT platforms. Design specifications and simulation results have shown that the implemented mechanism is functional and has met requirements for a successful profiling vibrometry system that can be employed on SPDT machines.

High-entropy alloy (HEA) is an emerging alloy which consists of five or more metallic elements with equimolar concentrations and exhibits excellent mechanical properties at cryogenic temperature. However, its machinability is almost unknown. In this study, high frequency one-dimensional ultrasonic vibration-assisted diamond turning (UVDT) experiments were conducted on an FeCrCoMnNi-based HEA to investigate the micro-nanoscale material removal mechanisms. Compared with conventional diamond turning, UVDT produced thinner chips, lower cutting forces, less tool wear and better surface integrity. Due to the ultrasonic vibration-assisted burnishing effect, surface scratches were significantly eliminated. A freeform surface was test-fabricated with optical-level finish.

Freeform surface optical components have gained increasing attention in recent years, and higher requirements have been put forward for economical and efficient fabrication techniques. Single point diamond turning with fast tool servo is the method to process nonrotational symmetric surface with high quality. However, the surface quality of different areas is not always the same in this way. In this paper, a microlens array is fabricated by fast tool servo cutting. The reason of surface difference is analyzed theoretically, and the Position-Velocity-Time interpolation method is used to improve the surface quality and reduce the difference between different regions. A microlens array consisting of 900 spherical lenslets was machined, the size of each spherical lenslet is 1.08 mm×0.5 mm. The form error of lenslet is about 1.5 um at the edge and 1 um at the center respectively, and the roughness value of Sa are 11 nm and 8.6 nm, the results show that the theory and simulation are correct, and the ability of fast tool servo technology to realize freeform processed with high precision is demonstrated.

Ion beam finishing techniques of aluminium mirrors have a high potential to meet the increasing demands on applications of high-performance mirror devices for visible and ultraviolet spectral range. Reactively driven ion beam machining using oxygen and nitrogen gases enables the direct figure error correction up to 1 μm machining depth while preserving the initial roughness. However, the periodic turning mark structures, which result from preliminary device shaping by single-point diamond turning, often limit the applicability of mirror surfaces in the short-periodic spectral range. Ion beam planarization with the aid of a sacrificial layer is a promising process route for surface smoothing, resulting in successfully reduction of the turning mark structures. A combination with direct surface smoothing to perform a subsequent improvement of the microroughness is presented with a special focus on roughness evolution, chemical composition, and optical surface properties. As a result, an ion beam based process route is suggested, which allows almost to recover the reflective properties and an increased long-term stability of smoothed aluminium surfaces.

Quartz is one of the difficult-to-machine materials due to its low fracture toughness and high hardness. In this study, the machinability of this material during single point diamond turning (SPDT) was numerically investigated using finite element method (FEM). First of all, the accuracy of the FE model was verified based on the experimental data available in literature. Then, the machinability of quartz was analysed in terms of cutting force, tool/workpiece temperature and tool wear rate. Also, the influence of tool vibration on cutting force and tool wear rate was investigated. Furthermore, an empirical/mathematical model was developed to express the machining outputs as a function of the micro-machining parameters. The obtained results indicate the good performance of FEM in analysing the machinability of quartz during SPDT process.

Spiral tool path generation methods for the ultra-precision diamond turning of freeform surfaces can significantly affect machining efficiency and surface quality. However, effective methods for freeform surfaces with a high slope, especially nonrotation symmetric surfaces and those determined by the recursive formula, are unavailable. Therefore, a new spiral tool path generation method based on a nonuniform rational B-spline (NURBS) parameter space is proposed for the ultra-precision diamond turning of freeform surfaces. The discrete points are used for NURBS global interpolation by discretizing the surface in a radial Cartesian coordinate system, thereby forming a NURBS surface. A more uniform spiral tool path of freeform surfaces with a higher calculation efficiency can be obtained by directly utilizing the parameters on the NURBS surface than by applying existing methods. In addition, a solution is provided for freeform surfaces determined by the recursive formula. Simulation and experiments are conducted to show the effectiveness and adaptability of our method.

Aluminum alloy 6061(Al6061) is one kind of precipitation hardening alloy, and its precipitate generation highly influences the mechanical properties and finished surface quality in diamond cutting. To accurately estimate the surface roughness in diamond turning of Al6061, an improved surface roughness prediction model is proposed in this study with the full consideration of the minimum undeformed chip thickness, the materials plastic side flow, elastic recovery and precipitation effect. Pre-heating treatments and diamond turning experiment are conducted on Al6061 samples to build the relationship between pre-heating conditions, precipitation generation and surface roughness in single point diamond turning (SPDT). The experimental results show that precipitation effects are found on both the deformed chips and the fresh generated surface. The effect of pre-heating conditions on precipitates generation agrees well with its effect on surface roughness of Al6061 in SPDT. Compared with the previously proposed models, the developed model considering the precipitation effect of Al6061 remarkably improves the prediction accuracy by 26 %.

In this paper, molecular dynamic (MD) simulation was adopted to study the ductile response of single-crystal GaAs during single-point diamond turning (SPDT). The variations of cutting temperature, coordination number, and cutting forces were revealed through MD simulations. SPDT experiment was also carried out to qualitatively validate MD simulation model from the aspects of normal cutting force. The simulation results show that the fundamental reason for ductile response of GaAs during SPDT is phase transition from a perfect zinc blende structure (GaAs-I) to a rock-salt structure (GaAs-II) under high pressure. Finally, a strong anisotropic machinability of GaAs was also found through MD simulations.

In multiple applications of advanced instrumentation, single-point diamond turning (SPDT) is a popular and effective process to generate novel surfaces with nanometric surface roughness and sub-micron surface irregularities, albeit at a high cost. In SPDT, precision diamond tooling contributes significantly to the process cost escalation. Hence, for SPDT, it is vital to have an optimal precision diamond tool deployment. In this article, details of comprehensive precision diamond tool selection and tool characterization are discussed. Three makes of selected ultra-precision diamond (UPD) tools and standard diamond tools (of a global make), designated as CFT, are considered for this study. In this tool bench-marking exercise, the fabrication of Cu–Be alloy predesigned precision components (PDPCs) of a critical geometry is selected. UPD and CFT tools are deployed to fabricate (under similar machining-metrology conditions) the PDPCs. These diamond tools are evaluated in terms of the quality parameters (variation in radius of curvature, form error, and surface roughness) of the workpieces. Further, to explore the progressive wear of these tools, multiple machining cycles are conducted on these workpieces, and their quality parameters are analyzed. Thus, the precision diamond tools of three makes are benchmarked against the CFT tool. Based on the final outcome of this analysis, suitable recommendations are provided to precision diamond tool manufacturers to improve their product in terms of performance and optimized costs to meet the ever-growing tooling demands of the SPDT community.

Ultra-precision single-point diamond turning (SPDT) is a recent realm in advanced manufacturing of optical components with nanometric features. SPDT has various applications in different industry sectors including space science, biomedical engineering, military, defense, and optics. However, different factors negatively impact the outcome of SPDT process and limit the success of optical surface generation. In addition, standard SPDT is based on the pure mechanical action of cutting and is limited when it comes to turning brittle and hard-to-machine materials. These materials have low machinability, and cutting them with diamond tool has been affected by high tool wear, short tool life, and consequently low quality of optical surface finish. Non-conventional machining techniques have been implemented to assist the purely mechanical SPDT process in order to eliminate the existing limitations, reduce effects of influencing factors, and enable an optimized machining environment. Different methods have been developed and used for assisting the SPDT process. In this review paper, recent trends and advances in technologies used for assisting SPDT are surveyed. Studying constructive and destructive effects of these SPDT-assisted technologies could provide necessary information for using the best possible solutions in diamond turning of different materials while improving targeted parameters. In addition, studying the effects of assisting technologies could provide a good perspective on hybrid SPDT process limitations and possible solutions. Although various techniques and solutions have been developed, there are still limitations for enabling an ultimate turning process. The paper highlights the possible trend of new technologies related to SPDT. More attention needs to be given, especially, to the development of novel techniques to completely solve existing limitations and enable best SPDT performance. Future studies need to be focused on the development of hybrid SPDT platforms, based on suitable combinations of non-conventional technologies, to achieve the best possible quality in terms of optical surface generation.

Bionic artificial compound eyes inspire a promising field of miniaturized imaging systems. In this research, a novel infrared (IR) three-dimensional (3D) compound eye imaging system, consisting of a double-side molded 3D microlens array and an aperture array, was designed and fabricated by combining modulated slow-tool-servo diamond turning and precision glass molding. To facilitate the complex profiles on the mold inserts, two novel slow-tool-servo strategies were adopted, namely virtual-axis based diamond broaching and adaptive diamond turning. This microlens array consists of 3 × 3 channels for a field of view of 48° × 48° with a thickness of 1.8 mm. The freeform microlens array on a flat surface was employed to steer and focus the incident light from all three dimensions to a two-dimension (2D) infrared imager. Using raytracing, the profiles of the freeform microlenses of each channel were optimized to obtain the best imaging performance. To avoid crosstalk among adjacent channels, a 3D printed three-dimensional micro aperture array was mounted between the microlens array and the IR imager. The imaging tests of the infrared compound-eye imaging system using the molded chalcogenide glass lenses showed that the asymmetrical freeform lenslets were capable of steering and forming images within the designed field of view. Compared to a conventional infrared camera, this novel microlens array can achieve a considerably larger field-of-view while maintaining low manufacturing cost without sacrificing image quality.

The interference microscope is a powerful tool for surface topography measurement, but its high sensitivity to vibration hinders its application to on-machine use. To measure surface roughness on a machine for the ultra-precision machining, a vibration-resistant interference microscope (VRIM) with an assistant focusing function is developed. The basic principle of VRIM is an error-compensated phase-shifting interferometry. An iterative algorithm is presented to calculate the surface phase with the phase shift amounts as unknown variables, where the phase shift amounts are calculated and compensated with least-squares method. A narrow bandwidth illumination is employed to alleviate coherence envelop influence, and a simplified intensity model is established to decouple the variables. Assisting the microscope to find fringe quickly, the focusing is realized by introducing an off-axis thin beam to generate two spots, of which their relative position relates to the defocus. The focusing method is directional and determinant, and has a large range up to 0.3 mm. In the vibration disturbances of 0.2 μm and 0.4 μm amplitudes over 0 Hz to 20 Hz frequency region, the roughness accuracy and repeatability of measuring an ultra-precision machined surface are both up to the sub-nanometer level. The developed instrument is applied to a single-point diamond turning machine and achieves a sub-nanometer accuracy and repeatability.

Single-point diamond turning (SPDT) is an emerging process for achieving nanometric surface finish, required in various optical devices made from metals like aluminum, copper, and nonmetals like polymers. The optical devices are manufactured in different shapes and profiles, preferably flat and curved surfaces. During the manufacturing of optical devices, controllable and noncontrollable parameters affect the desired surface finish. In this article, controllable machining parameters such as the incremental distance of X slide, feed rate, spindle speed, and depth of cut are selected to study their effect on surface finish and vibration generation of the curved surface. The chosen workpiece material is polymethylmethacrylate (PMMA). Design of experiment (DoE) is used to find out the optimum parameters of surface finish and infeed vibration responses. According to the Taguchi and analysis of Variance (ANOVA) analysis, the feed rate is the most influencing parameter for surface roughness, and incremental distance is for infeed vibration. A confirmation test is carried out to verify the experimental responses with a mathematical regression model, and it shows a close difference within 2.7 percent. Further, minimum surface roughness is perceived as 12.4 nm, corresponding to an infeed vibration amplitude of 4.9 µm/s2, which is signified at a lower frequency.

This research aims to establish a methodology for machining of toric lenses, using fast tool servo-assisted single point diamond turning and to assess the generated surface for its characteristics. Using the established mathematical model, toric surface is explained to understand the geometry and to generate the parameters required for fast tool servo machining. A toric surface with a major diameter of 18.93 mm and a minor diameter of 15.12 mm has been cut on the intelligent ultra-precision turning machine (iUPTM). The surface profile and surface roughness were measured. After analysing the measurement data of the machined surface, on two perpendicular axes of the toric lens, form accuracy of 0.49 µm peak-to-valley (PV), and surface roughness of 12 nm in Ra, 4–8 nm in Sa are obtained. From the experimental results obtained, it can be concluded that the proposed method is a reasonable alternative for manufacturing toric lens mould.

Hard and brittle materials (HBMs) are promising materials for aerospace and astronomy applications, due to their excellent mechanical, optical, and chemical properties. However, they are difficult and costly to machine using conventional machining methods such as single point diamond turning. Laser assisted machining uses a focused laser beam to heat local areas of the workpiece and remove softened material from the ductile region, leaving high quality and crack-free surfaces. Over the past decades, the study of laser assisted machining of HBMs has been attracting progressively more interest from researchers in academia and industry. This paper serves as a state-of-the-art review with a particular focus on typical HBMs and their machining challenges; the mechanism of laser heating and thermal analysis; pre-heat and in-process-heat laser assisted machining methods; and optimizing the machining quality of laser assisted machining. The review also presents a perspective on future development trends for laser assisted machining technology.

The low thermal conductivity of titanium alloys causes an accumulation of high cutting heat at the tool/workpiece interface and thus deteriorates surface integrity of the machined surface in ultra-precision machining (UPM). In response of this underlying source causing the poor machinability of the materials in UPM, in this study, a novel fixture composed of thermoelectric cooler (TEC) is firstly developed and applied into single point diamond turning (SPDT) of titanium alloys, aiming to dissipate the cutting heat in the machining process. The TEC contacted with workpiece during the whole turning process and caused a dissipation of cutting heat from the workpiece. By using the fixture with TEC device, the cutting force variation and surface roughness involved in SPDT were reduced. This study presents the preliminary results of application of TEC fixture on UPM of titanium alloys and shows the feasibility of the use of TEC device in UPM area, suggesting a new approach to resolve the problematic high cutting heat of titanium alloys in UPM.

Single-point diamond turning (SPDT) is a leading machining technology for advanced manufacturing of high-accuracy optical components characterized by their nanometric surface characteristics. By employing SPDT, optical surfaces with roughness down to 1 nm could be machined. However, in a purely mechanical ordinary SPDT procedure, different factors may influence the outcome of the process and significantly affect the quality of the diamond-turned optical surface. In the last few years, non-conventional machining technologies have been successfully implemented on the basis of traditional mechanical SPDT for optical surface generation. These non-conventional methods assist the purely mechanical SPDT process to improve the diamond machining performance and machinability of various optical materials. They attempt to eliminate the process disturbances that occur during mechanical interactions between the tool and workpiece in order to further reduce the surface roughness indicator. Recently, the application of hybrid SPDT methods in optical surface generation has emerged, in which more than one non-conventional machining technique impact the workpiece surface during the mechanical interaction with the diamond tool cutting edge. Compared with conventional SPDT solutions, in a hybrid SPDT method, superior results in terms of optical surface quality could be obtained. In addition, development of intelligent SPDT solutions for achieving the best possible results in optical surface generation is a novel approach. In an intelligent SPDT solution, in addition to the hybrid machining methods, automatic control systems and advanced on-machine metrology systems need to be implemented on the diamond turning machine platform. This may help further improve the quality of optical surface by continuously performing in-process error diagnosing and consequently conducting in-process tuning of the diamond cutting parameters and optimizing the machining conditions. In this review paper, recent advances in ultra-precision SPDT based on hybrid methods, associated metrology systems, and their process control systems are surveyed. In addition, the effect of developed various hybrid SPDT methods and influencing factors that may affect optical surface generation have been discussed. At the end, guidelines for further developments of intelligent SPDT platforms by using hybrid SPDT methods, automatic process control, and in-process metrology solutions are proposed.

Single-point diamond turning (SPDT), which cuts the workpiece with a single crystal diamond tool, is considered as a promising manufacturing technology in modern industry. In SPDT, it is found that the surface roughness near the center of the workpiece is poor when the cutting depth is small or the feed rate is large. In order to obtain better surface quality, the spindle speed must be increased, which thus reduces the productivity and causes the unnecessary abrasion of the cutting tool. Meanwhile, the influence of feature size effect to the fracture formation in SPDT has not yet been mentioned. In tandem with this, this paper has provided a hybrid damage model to predict appropriate feed rate, cutting depth, and cutting speed of SPDT. Based on the Johnson Cook model, a revised function to quantify the influence of size effect is introduced, and the pre-strained method using the split Hopkinson pressure bar (SHPB) is conducted to calculate the unknown coefficients of the model. The experimental result shows that feature size effect will cause surface rough patterns when feed rate and cutting speed are lower than the predicted critical speed. By implementing the critical energy, which is calculated by the hybrid damage model with different strain rates and heat treatment conditions, the multi–strain-rate fracture diagram (MFD) is carried out and the fracture caused by size effect in SPDT is revealed and predicted. This paper has thus provided an in-depth understanding of the influence of size effect in SPDT.