Single Point Diamond Research Articles

Modelling and Optimization of Electrostatic Discharge Machining Parameters Using Genetic Algorithm

Electrostatic Discharge is a phenomenon that results from separating two dissimilar solid surfaces that were in contact. It results from the transfer of electrons from one surface to the other. Hence, one of the surfaces is positively charged, while the other surface becomes negatively charged. This phenomenon takes place during single point diamond turning of contact lenses polymers such as ONSI-56. Since higher electrostatic discharge adversely affects surface roughness, there is need to optimize electrostatic discharge machining parameters. The aim of this study is to develop an electrostatic discharge model and optimize the electrostatic discharge machining parameters during single point diamond turning of ONSI-56. Multiple regression has been utilized for model development and Genetic Algorithm (GA) has been used to optimize the model parameters. The GA toolbox in MATLAB is used for optimization in this study. In this study, cutting speed, depth of cut and feed rate are the model variables, while electrostatic discharge is the response variable. The regression model’s effectiveness has been evaluated by the R2 value method. The model has an R2 value of 88.29%, indicating that there is a strong collective significant effect among the control and response variables. Additionally, the results indicated that cutting speed and feed rate are the most significant predictors, while depth of cut is a slightly less significant predictor. The optimization process yields the following optimal values for cutting speed, feed rate, depth of cut and ESD, respectively: 200 rpm, 12 mm/min, 10 µm and 1,28 kV. An assessment of population size against objective function execution time has revealed that a population size of 500 has the shortest execution time of 14.23 seconds. The results have revealed that the optimization technique (GA) is efficient in ESD process optimization during single point diamond turning of ONSI-56.

Design and Analysis of Ultra-Precision Smart Cutting Tool for In-Process Force Measurement and Tool Nanopositioning in Ultra-High-Precision Single-Point Diamond Turning.

Ultra-high-precision single-point diamond turning (SPDT) is the state-of-the-art machining technology for the advanced manufacturing of critical components with an optical surface finish and surface roughness down to one nanometer. One of the critical factors that directly affects the quality of the diamond-cutting process is the cutting force. Increasing the cutting force can induce tool wear, increase the cutting temperature, and amplify the positioning errors of the diamond tool caused by the applied cutting force. It is important to measure the cutting force during the SPDT process to monitor the tool wear and surface defects in real time. By measuring the cutting force in different cutting conditions, the optimum cutting parameters can be determined and the best surface accuracies with minimum surface roughness can be achieved. In this study a smart cutting tool for in-process force measurement and nanopositioning of the cutting tool for compensating the displacements of the diamond tool during the cutting process is designed and analyzed. The proposed smart cutting tool can measure applied forces to the diamond tool and correct the nanometric positioning displacements of the diamond tool in three dimensions. The proposed cutting tool is wireless and can be used in hybrid and intelligent SPDT platforms to achieve the best results in terms of optical surface finish. The simulation results are shown to be almost consistent with the results of the derived analytical model. The preliminary results pave the way for promising applications of the proposed smart cutting tool in SPDT applications in the future.

Introducing and Evaluating the Operational Performance of a New Interchange Design: The Continuous Green-T Median U-Turn Interchange

This study proposes a new design called the continuous green-T median U-turn (CGT-MUT) interchange and evaluates its operational performance compared to three interchanges. The selected interchanges for comparison are the Superstreet, Single Point Diamond Interchange (SPDI), and the Synchronized interchange. The evaluation is based on a microsimulation environment created in VISSIM combined with ASC/3 Software-in-the-Loop signal controllers. The findings show that the CGT-MUT enhanced the network-wide and intersection-level operations regarding various measures of effectiveness. Additionally, while the CGT-MUT did not always outperform all the other designs in terms of the on-ramp turning traffic travel times, it outperformed the Superstreet and Synchronized in terms of the off-ramp turning traffic travel times and resulted in the least through traffic travel times for all the tested scenarios. Particularly, the CGT-MUT’s through travel times were 9% – 30%, 26% – 42%, and 13% – 38% less than those for the Superstreet, SPDI, and Synchronized interchanges, respectively.

Gallium arsenide whispering gallery mode resonators for terahertz photonics.

As the field of terahertz (THz) photonics advances, we present a monolithic gallium arsenide (GaAs) disk-shaped whispering gallery mode resonator that has potential as a component in THz nonlinear optics. GaAs is a material with significant optical nonlinearity which can be enhanced when the crystal is shaped into a microdisk resonator. A 4-mm-disk-resonator was fabricated using single-point diamond turning and was characterized to obtain a quality (Q) factor of 2.21k at ∼150 GHz and 1.41k at ∼300 GHz. We also demonstrated the blue-shifting of up to ∼0.3 GHz of the THz modes using a block of metal. This post-fabrication degree of freedom could be useful for phase-matching requirements for nonlinear optical processes, such as detection based on optical up-conversion of THz radiation. This proof-of-concept demonstration can pave the way for the implementation of a compact, tunable and efficient device which could be integrated into nonlinear photonic platforms for THz generation, manipulation and detection.

Reducing the cutting tool wear in diamond turning of Zerodur glass-ceramic by the mechanical cleaning effect of ultrasonic vibration assistance

The effects and mechanisms of using ultrasonic vibration assistance (U.V.-assisted machining) combined with straight-nosed cutting tools on reducing the cutting tool wear in single-point diamond turning (SPDT) of Zerodur glass-ceramic are analysed and experimentally investigated. Aiming at the predominant abrasive wear in machining hard and brittle materials, analyses have shown that applying appropriate ultrasonic vibration to the cutting tool can induce considerable inertial acceleration to the wear particles residing on the tool-work interface for promoting their ejection from the contact area to reduce the abrasion. Meanwhile, the high thermal conductivity of diamond can prevent the possible excessive temperature elevation of the cutting tool surface that may result from the in-plane vibration components. To verify these, a longitudinal ultrasonic vibrator that works together with the Poisson's effect was designed for the SPDT processes with straight-nosed cutting tools. Machining tests on Zerodur optics have shown that the assistant ultrasonic vibration is able to decrease the tool flank wearland width by about 30 %, and the groove-like scratches on the tool flank wearland surface were reduced, which is consistent with the analytical deductions. Besides, no significant traces of structural change, element diffusion, and oxidation were found on the worn cutting tool surfaces under either the assisted or unassisted cutting conditions. The experiments have also shown that the enhanced durability of cutting tools has extended the cutting tool life for maintaining good machined surface quality, which is particularly beneficial to the ultra-precision machining of large-size optical parts.

Investigation on the ultra-precision diamond turning of ZnSe aspheric surfaces using straight-nosed cutting tools

Theoretical and experimental investigations on the machining performance and mechanisms in single-point diamond turning (SPDT) of ZnSe aspheric surfaces using straight-nosed cutting tools have been carried out. Analyses of the chip formation process have shown that using straight-nosed cutting tools can significantly reduce the cut thickness by about 60 % compared with using round-nosed cutting tools for facilitating the ductile-mode material removal and reducing surface damages. The analyses have also shown that the height of residual feed marks can be reduced by using the straight-nosed cutting tools by about 80 %, which can further improve the machined surface integrity. Experiments on the machining performance of using straight-nosed and round-nosed cutting tools were conducted to verify the analytical deductions. It has been shown that nano-scale surface finish with surface roughness Ra ∼ 1.5 nm can be achieved by using straight-nosed cutting tools, which is significantly improved comparing with that by the round-nosed cutting tools (Ra ∼ 7.8 nm) and is consistent with the analytical results. Needle-like chip with periodical layered structure was collected from the SPDT processes using straight-nosed cutting tools, indicating a relatively continuous chip formation process under the ductile-mode material removal. Raman spectroscopy has shown increased metallization of ZnSe occurred during the machining with straight-nosed cutting tools, which is considered to reduce the brittle fractures along with the chip formation process. It has been further found that the straight-nosed cutting tool can reduce work adhesion and micro-edge chipping of cutting tools for extending the cutting tool life.

Effect of cutting speed in single point diamond turning of (100)Ge

In this study the mechanical response of single crystal Ge machined over a range of cutting speeds of two orders of magnitude was investigated. Single crystal (100)Ge was machined by on-axis turning with a single crystal diamond tool. Surface topography was characterized by atomic force microscopy, and cutting and thrust forces were measured. It was found that increasing the cutting speed decreases the amount of brittle fracture left on the surface by the tool. It was also found that both the cutting and thrust forces decreased in magnitude as the cutting speed increased.

A single point diamond turning and integrated sensory system in nano machining: A survey, research issues and challenges

The modernization in the Nano machining field is increasing rapidly because of the monetary benefits and applications of Nano size product features. Scientists have made fewer attempts to do research in the field of Nano-turning, such as material removal at the Nano-scale. The principles of Nano-scale turning were discussed, as well as contemporary breakthroughs in sensory systems. Surface finishing of Nano-turned components is required due to material anisotropy, tool geometry, and machining settings, as surface finishing is a critical performance aspect.This article discusses Nano-turning advancements, with a focus on Single Point Diamond Turning (SPDT). This article focuses on Integrated Sensory Systems for SPDT as well as nanoscale computer modelling of cutting mechanics. Future research areas in Nano scale turning and machining include active control and in-process adjustments of sensors and automated systems for Nano-turning.

High-precision turning and ultra-smooth direct polishing of aluminum alloy mirrors.

Due to the high surface roughness requirements of aluminum alloy mirrors used in the visible light band, there are still great challenges in single point diamond turning of high-surface quality aluminum alloy mirrors. In this paper, a processing method for aluminum alloy mirrors is proposed. Based on single point diamond turning technology, the prediction model of aluminum alloy surface roughness was established. The mapping relationship between the surface roughness of the aluminum alloy mirror and each turning parameter was obtained, and the maximum possible surface quality was achieved. On the basis of the turning results, the method of small tool polishing was used to remove the turning texture generated by the copy effect of the tool arc radius, suppress errors of the medium and high-frequency, and reduce the surface roughness. The single abrasive removal efficiency model was established and mechanical removal in the polishing process was analyzed. Combined with the chemical action in the polishing process, two types of polishing liquid-acidic and neutral, were prepared and analyzed. The optimal polishing parameters were obtained through multiple single-factor experiments. On the basis of this, the surface roughness of the aluminum alloy after turning was optimized. The results show that the value was reduced from 4.811 to 1.482 nm, an increase of 69.2%. This method can effectively improve the machining accuracy of aluminum alloy mirrors and provide an important process guarantee for the application of aluminum alloy materials in visible-light systems.

Analysis and Prediction of Image Quality Degradation Caused by Diffraction of Infrared Optical System Turning Marks

This paper addresses the issue of reduced image quality due to annular turning marks formed by single-point diamond turning (SPDT) during the processing of metal-based mirrors and infrared lenses. An ideal single-point diamond turning marks diffraction action model to quantitatively analyze the impact of turning marks diffraction on imaging quality degradation is proposed. Based on this model, a fast estimation algorithm for the optical modulation transfer function of the system under turning marks diffraction (TMTF) is proposed. The results show that the TMTF algorithm achieves high computational accuracy, with a relative error of only 3% in diffraction efficiency, while being hundreds of times faster than rigorous coupled wave analysis (RCWA). This method is significant for reducing manufacturing costs and improving production efficiency, as it avoids the problem of being unable to compute large-size optical systems due to computational resource and time constraints.

Optical freeform reflective imaging system design method with manufacturing constraints.

With the development of space optics, optical freeform surfaces have gradually been utilized in reflective optical imaging systems in recent years. Freeform surfaces not only bring many benefits to the optical imaging system, but also present many challenges to their manufacture. Regardless of the machining method used, machining errors during the fabrication of freeform surfaces will exist, which limits the accuracy of freeform surface machining. In this paper, the deviation root mean square (RMS) of a freeform surface from the reference aspheric surface is proposed to evaluate the manufacturability of the freeform surface by using single-point diamond turning. Then the deviation RMS of freeform surfaces is added to the design process of the optical system as a manufacturing constraint. Subsequently, an off-axis three-mirror system and an off-axis two-mirror system with and without manufacturing constraints are designed, respectively. Then the imaging quality of these optical systems and the linear interpolation error RMS of freeform mirror are analyzed. It can be concluded that, on the basis of reaching the imaging quality requirements, the machining difficulty of a freeform mirror can be reduced when adding manufacturing constraints to the design process.

Sub-nanometer finishing of polycrystalline tin by inductively coupled plasma-assisted cutting

Polycrystalline tin is an ideal excitation material for extreme ultraviolet light sources. However, the existence of grain boundary (GB) limits the surface roughness of polycrystalline tin after single-point diamond turning (SPDT). In this work, a novel method termed inductively coupled plasma (ICP)-assisted cutting was developed for the sub-nanometer finishing of polycrystalline tin. The relationship between ICP power, processing time, and modification depth was established by thermodynamic simulation, and the fitted heat transfer coefficient of polycrystalline tin was 540 W/(m2·K). The effects of large-thermal-gradient ICP treatment on the microstructure of polycrystalline tin were studied. After 0.9 kW ICP processing for 3.0 s, corresponding to the temperature gradient of 0.30 K/µm, the grain size of polycrystalline tin was expanded from a size of approximately 20–80 µm to a millimeter scale. The Taguchi method was used to investigate the effects of rotational speed, depth of cut, and feed rate on SPDT. Experiments conducted based on the ICP system indicated that the plasma-assisted cutting method promoted the reduction of the influence of GB steps on the finishing of polycrystalline tin, thereby achieving a surface finish from 8.53 to 0.80 nm in Sa. The results of residual stress release demonstrated that the residual stress of plasma-assisted turning processing after 504 h stress release was 10.7 MPa, while that of the turning process without the ICP treatment was 41.6 MPa.

Nano-Precision Processing of NiP Coating by Magnetorheological Finishing.

NiP coating has excellent physicochemical properties and is one of the best materials for coating optical components. When processing NiP coatings on optical components, single-point diamond turning (SPDT) is generally adopted as the first process. However, SPDT turning produces periodic turning patterns on the workpiece, which impacts the optical performance of the component. Magnetorheological finishing (MRF) is a deterministic sub-aperture polishing process based on computer-controlled optical surface forming that can correct surface shape errors and improve the surface quality of workpieces. This paper analyzes the characteristics of NiP coating and develops a magnetorheological fluid specifically for the processing of NiP coating. Based on the basic Preston principle, a material removal model for the MRF polishing of NiP coating was established, and the MRF manufacturing process was optimized by orthogonal tests. The optimized MRF polishing process quickly removes the SPDT turning tool pattern from the NiP coating surface and corrects surface profile errors. At the same time, the surface quality of the NiP coating has also been improved, with the surface roughness increasing from Ra 2.054 nm for SPDT turning to Ra 0.705 nm.

Modification of diamond tool by focused ion beam in dry single-point diamond turning

The modified diamond tools (MDT) by focused ion beam (FIB) can reduce tool wear to a certain extent while avoiding the pollution of traditional cutting fluid. This paper investigates the dry single-point diamond turning (DSPDT) process for Al6061 alloy with MDT. DSPDT tests showed that MDT produced lower cutting forces and generated smoother machined surfaces. Furthermore, MDT has a lighter wear compared with the unmodified diamond tools. The reasons why the cutting performance of MDT is better than the unmodified diamond tools are the reduced surface energy of modified diamonds proved by the first principle calculations and contact angle tests, and the change of the C–C bond energy and bond length according to the first principle calculations. Therefore, it is feasible and promising to apply the MDT in the DSPDT of Al6061 alloy, which will contribute to carbon neutralization manufacturing.

Status of research on non-conventional technology assisted single-point diamond turning

With the increasing use of difficult-to-machine materials in aerospace applications, machining requirements are becoming ever more rigorous. However, traditional single-point diamond turning (SPDT) can cause surface damage and tool wear. Thus, it is difficult for SPDT to meet the processing requirements, and it has significant limitations. Research indicates that supplementing SPDT with unconventional techniques can, importantly, solve problems due to the high cutting forces and poor surface quality for difficult-to-machine materials. This paper first introduces SPDT and reviews research into unconventional techniques for use with SPDT. The machining mechanism is discussed, and the main advantages and disadvantages of various methods are investigated. Second, hybrid SPDT is briefly described, which encompasses ultrasonic-vibration magnetic-field SPDT, ultrasonic-vibration laser SPDT, and ultrasonic-vibration cold-plasma SPDT. Compared with the traditional SPDT method, hybrid SPDT produces a better optical surface quality. The current status of research into unconventional techniques to supplement SPDT is then summarized. Finally, future development trends and the application prospects of unconventional assisted SPDT are discussed.

저마늄 소재의 초정밀가공공정을 통한 표면특성분석 및 스포크형상 결함제거

Germanium, an optical material, has high transmittance and refractive index and low light scattering in the infrared region, and research is being conducted to utilize it in various industrial fields. Various forms of optical lenses can be subjected to ultra-precision machining with high quality surface roughness, and they form accuracy through single point diamond turning (SPDT). In particular, the diamond tool with a negative rake angle and the u-LAM process that applies a 1,064 nm laser to the material have been studied to fabricate brittle materials into optical lenses. In this study, the effects of process parameters, such as laser power (W), spindle speed (RPM), feed rate (mm/min), and depth of cut (μm), on the surface roughness of a sub-nanometer scale and the occurrence of defects during the machining process were analyzed for Germanium materials. The process of removing these defects was also analyzed.

Development of a fabrication process for production of diffractive optics.

In this study, a novel fabrication process, to the best of our knowledge, was developed to fabricate a glass harmonic diffractive lens. In this process, a polymethylmethacrylate master of the diffractive lens was machined using single-point diamond turning. Then an electrolytic plating process was conducted to grow a reverse nickel (Ni) mold. Precision compression molding was performed using the Ni mold to replicate the diffractive lens structures onto a glass surface. Surface measurements and optical testing show that the replicated diffractive lenses by the proposed method have high tolerances and require optical performance, demonstrating a high-volume, high-precision, and cost-effective process. The proposed method will be critical for consumer products where glass optics are increasingly used in lens assemblies.

Study on nanometer cutting mechanism of single crystal silicon at different temperatures

Thermal-assisted single point diamond turning technology is currently one of the most important methods for realizing nano-scale machining. However, the nano-chip formation mechanism as the core of the nano-cutting mechanism is still unclear, which limits the development of this advanced technology. In this study, based on the molecular dynamics simulations, the nano cutting behaviour of single crystal silicon at different temperatures were studied. The cutting force, crystal structure, particle motion characteristics, stress-strain distribution and temperature distribution during chip formation process were systematically analyzed. The underlying mechanism of nano-chip formation in single crystal silicon was summarized. The results showed that the chip formation mechanism can be divided into two types: crack and shear. At low temperatures, chips are formed by crack propagation. The concentrated distribution of high stress triaxiality and local high temperatures at the crack tip are the main causes of crack propagation. With an increase in temperature, the chip formation mode gradually changed from crack to shear. The highly resolved shear stress distributed along the slip plane is the main reason for the expansion of the amorphous bands. In addition, it's found that higher quality machined surfaces can be obtained through chip formation process by shear than by crack.

Fabrication of curved aspheric compound eye microlens array with high surface quality by precision glass molding

The curved compound eye microlens array (CEMLA) glass optical element is widely used in optoelectronic detectors because it affords a high image quality and a large field of view. However, fabrication of high-precision glass optical elements with a small cell size and many arrays on hard and brittle glass materials is challenging. Here, we report a fabrication method to address molding challenges for high quality CEMLA glass optical elements at molding temperatures up to 500 °C. First, an Ni-P with good turning performance and low adhesion to glass is chosen as the plating material, the CuNi is selected as the mold substrate for their close CTEs. To prevent the diffusion of P to the surface of optical elements and to improve the hardness and wear resistance of mold, a Ti-Ta-C coating is deposited on the Ni-P mold. By single-point diamond turning on the Ni-P surface using a fast tool servo, an aspherical CEMLA mold with a form accuracy PV less than 0.4 μm and surface roughness Sa less than 4 nm was machined. Finally, based on the creep testing of microdeformation compression, an accurate viscoelastic constitutive model of glass was established. Optimization of the molding process and accurate prediction of molding profile deviation were simulated. The aspheric CEMLA glass optical element with a form accuracy PV less than 0.5 μm and surface roughness Sa less than 4.5 nm was obtained by precision glass molding (PGM).

Feasibility study on the use of single crystal silicon carbide as a tool material

Monocrystal SiC has attracted considerable attention as a third-generation semiconductor material. However, the application potential of monocrystal SiC as a structural material has not sufficiently explored. Monocrystal SiC has excellent mechanical properties and chemical stability. In this paper, the practicability of using monocrystal SiC as a cutting tool material is investigated. SiC tool design scheme is studied and crystal plane parameters corresponding to rake/flank faces are proposed. Via large-scale molecular dynamics (MD) simulations, single point diamond turning (SPDT) machining on common metallic material monocrystal Cu and hard brittle material monocrystal Si have been carried out. An in-depth analysis of suitability of monocrystal SiC tools in SPDT machining is conducted. The results show that monocrystal SiC has excellent potential for use as a tool material. However, material deformation and removal process during processing with monocrystal SiC is distinct from those observed when using monocrystal diamond tools.