Single Point Diamond Machining Research Articles

Diamond machining of additively manufactured Ti6Al4V ELI: Newer mode of material removal challenging the current simulation tools

Single point diamond machining (SPDM) produces smooth machined surfaces that other production methods cannot match. While the mechanics of machining of cast alloys with SPDM is well-explored, the realm of SPDM for additively manufactured parts remains largely uncharted. This work reveals new insights into the surface generation process of an additively manufactured titanium alloy, specifically, a Ti6Al4V Extra Low Interstitials (ELI) alloy workpiece. Our examination of the chip morphology unveiled a distinct mode of chip removal, previously unrecorded in existing literature. During SPDM of additively made Ti6Al4V ELI workpiece, identification of numerous pores and discontinuities in the chips flowing on the tool rake face, indicating periodic intermittent cracking during the material's plastic flow was seen. To examine this phenomenon, a finite element analysis (FEA) model was developed. While the FEA model can well explain the machining mechanics and chip morphology of SPDM of cast Ti6Al4V ELI reported in the literature, it failed to describe the chip morphology that are obtained during machining of additively made workpiece in this work. This disparity underscores the need for innovative simulation approaches tailored for additively manufactured components. The experimental observations in this study highlight a unique form of chip formation in contrast to conventional Ti6Al4V alloy machining processes. At lower feeds, there was a presence of short, discontinuous chip formation with tearing at the outer periphery. Conversely, at higher feeds, a long, continuous ribbon-like chip formation was observed. In addition, some typical additive manufacturing defects appear on the machined surface and chips. Through optimisation of the SPDT parameters, a surface roughness (Ra) value of about 11.8 nm was achieved on additively manufactured Ti6Al4V ELI workpiece. This work provides a fresh perspective on the mechanics of SPDM for additively manufactured components, offering a stepping stone for subsequent studies.

Optimization of Surface Roughness of Aluminium RSA 443 in Diamond Tool Turning

Context—Rapidly solidified aluminium alloy (RSA 443) is increasingly used in the manufacturing of optical mold inserts because of its fine nanostructure, relatively low cost, excellent thermal properties, and high hardness. However, RSA 443 is challenging for single-point diamond machining because the high silicon content mitigates against good surface finishes. Objectives—The objectives were to investigate multiple different ways to optimize the process parameters for optimal surface roughness on diamond-turned aluminium alloy RSA 443. The response surface equation was used as input to three different artificial intelligence tools, namely genetic algorithm (GA), particle swarm optimization (PSO), and differential evolution (DE), which were then compared. Results—The surface roughness machinability of RSA443 in single-point diamond turning was primarily determined by cutting speed, and secondly, cutting feed rate, with cutting depth being less important. The optimal conditions for the best surface finish Ra = 14.02 nm were found to be at the maximum rotational speed of 3000 rpm, cutting feed rate of 4.84 mm/min, and depth of cut of 14.52 µm with optimizing error of 3.2%. Regarding optimization techniques, the genetic algorithm performed best, then differential evolution, and finally particle swarm optimization. Originality—The study determines optimal diamond machining parameters for RSA 443, and identifies the superiority of GA above PSO and DE as optimization methods. The principles have the potential to be applied to other materials (e.g., in the RSA family) and machining processes (e.g., turning, milling).

Research on Image Mapping Spectrometer Based on Ultra-Thin Glass Layered Mapping.

The imaging quality of the Mapping Imaging Spectrometer (IMS) is crucial for spectral identification and detection performance. In IMS, the image mapper significantly influences the imaging quality. Traditional image mappers utilize a single-point diamond machining process. This process leads to inevitable edge eating phenomena that further results in noticeable deficiencies in imaging, impacting spectral detection performance. Therefore, we propose a manufacturing process for the image mapper based on ultra-thin layered glass. This process involves precision polishing of ultra-thin glass with two-dimensional angles, systematically assembling it into an image mapper. The surface roughness after coating is generally superior to 10 nm, with a maximum angle deviation of less than 3'. This results in high mapping quality. Subsequently, a principle verification experimental system was established to conduct imaging tests on real targets. The reconstructed spectrum demonstrates excellent alignment with the results obtained from the Computed Tomography Imaging Spectrometer (CTIS). We thereby validate that this approach effectively resolves the issues associated with edge eating (caused by traditional single-point diamond machining), and leads to improved imaging quality. Also when compared to other techniques (like two-photon polymerization (2PP)), this process demonstrates notable advantages such as simplicity, efficiency, low processing costs, high fault tolerance, and stability, showcasing its potential for practical applications.

Topology Optimization of a Single-Point Diamond-Turning Fixture for a Deployable Primary Mirror Telescope

CubeSats, known for their compact size and cost effectiveness, have gained significant popularity. However, their limited size imposes restrictions on the optical aperture and, consequently, the Ground Resolution Distance in Earth Observation missions. To overcome this limitation, the concept of deployable optical payloads with segmented primary mirrors which can unfold like petals has emerged, enabling larger synthetic apertures and enhanced spatial resolution. This study explores the potential benefits of leveraging Additive Manufacturing (AM) and Topology Optimization (TO) in the realm of ultra-precision machining, specifically single-point diamond machining. The goal is to reduce fixture weight while improving stiffness to minimize deformations caused by rotational and cutting forces which compromise optical performance. Through Finite Element Analysis, this research compares conventionally machined fixtures with those produced using AM and TO techniques. The results reveal that concept designs created via TO can achieve a remarkable 68% reduction in weight. This reduction makes the assembly, including the machining fixture and 12 U deployable segments, manageable by a single operator without the need for specialized lifting equipment. Moreover, these innovative designs lead to substantial reductions of up to 86% and 51% in deformation induced by rotational and cutting forces, respectively.

Shoulder Damage Model and Its Application for Single Point Diamond Machining of ZnSe Crystal.

The damaging of ZnSe crystal has a significant impact on its service performance and life. Based on the specific cutting energies for brittle and ductile mode machining, a model is proposed to evaluate the damage depth in the shoulder region of ZnSe crystal during single point diamond machining. The model considers the brittle-ductile transition and spring back of ZnSe crystal. To verify the model, the elastic modulus, hardness, spring back, and friction coefficient of ZnSe crystal are measured by nanoindentation and nanoscratch tests, and its critical undeformed chip thickness is obtained by spiral scratching. Meanwhile, orthogonal cutting experiments are conducted to obtain the different shoulder regions and cutting surfaces. The shoulder damage depth is analyzed, indicating that the effect of the feed on the damage depth at a high cutting depth is stronger than that at a low one. The model is verified to be effective with an average relative error of less than 7%. Then, the model is used to calculate the critical processing parameters and achieve a smooth ZnSe surface with a roughness Sa = 1.0 nm. The model is also extended to efficiently predict the bound of the subsurface damage depth of a cutting surface. The research would be useful for the evaluation of surface and subsurface damages during the ultra-precision machining of ZnSe crystal.

Ultra-Precision Machining: Cutting With Diamond Tools

Abstract This article is written as a tribute to Professor Frederick Fongsun Ling 1927–2014. Single-point diamond machining, a subset of a broader class of processes characterized as ultraprecision machining, is used for the creation of surfaces and components with nanometer scale surface roughnesses, and submicrometer scale geometrical form accuracies. Its initial development centered mainly on the machining of optics for energy and defense related needs. Today, diamond machining has broad applications that include the manufacture of precision freeform optics for defense and commercial applications, the structuring of surfaces for functional performance, and the creation of molds used for the replication of a broad range of components in plastic or glass. The present work focuses on a brief review of the technology. First addressed is the state of current understanding of the mechanics that govern the process including the resulting forces, energies and the size effect, forces when cutting single crystals, and resulting cutting temperatures. Efforts to model the process are then described. The workpiece material response when cutting ductile and brittle materials is also included. Then the present state of the art in machine tools, diamond tools and tool development, various cutting configurations used, and some examples of diamond machined surfaces and components are presented. A discussion on the measurement of surface topography, geometrical form, and subsurface damage of diamond machined surfaces is also included.

Predictive model for surface accuracy in ultra-high precision single point diamond machining of monocrystalline silicon using RSM and MD

Silicon has enjoyed extensive usage in electronic devices, solar cells and infrared (IR) optics because of its high transmittance at 1.2 to 6.0 μm wavelength range. High quality optical silicon components (Ra less than 8 nm) requires appropriate choice of ductile regime machining cutting conditions that can improve surface roughness and facilitate accurate prediction. To achieve this, three factors, i.e., feed rate, rake angle and nose radius were varied while keeping cutting speed, depth of cut and clearance angle constant. An MD study of the experiment was also carried out for comparison. The result obtained showed that; BBD standard runs 5, 6, 8, 9, and 10 with Ra values between 1.8 and 7 nm are of high form accuracy and satisfied the basic requirement of Ra over the entire IR region for silicon. The MD study was also observed to conform with the Ra result as obtained in the experiment.

Predictive model for surface accuracy in ultra-high precision single point diamond machining of monocrystalline silicon using RSM and MD

Silicon has enjoyed extensive usage in electronic devices, solar cells and infrared (IR) optics because of its high transmittance at 1.2 to 6.0 μm wavelength range. High quality optical silicon components (Ra less than 8 nm) requires appropriate choice of ductile regime machining cutting conditions that can improve surface roughness and facilitate accurate prediction. To achieve this, three factors, i.e., feed rate, rake angle and nose radius were varied while keeping cutting speed, depth of cut and clearance angle constant. An MD study of the experiment was also carried out for comparison. The result obtained showed that; BBD standard runs 5, 6, 8, 9, and 10 with Ra values between 1.8 and 7 nm are of high form accuracy and satisfied the basic requirement of Ra over the entire IR region for silicon. The MD study was also observed to conform with the Ra result as obtained in the experiment.

Optimisation of Cutting Parameters for Minimal Surface Roughness in Single Point Diamond Turning of TI6AL4VELI

In this study the effect and optimisation of machining parameters on surface roughness in a facing operation of Ti6Al4VELI by single point diamond machining have been investigated. The experimental studies carried under varying cutting speeds, feed rates, different tool nose radius and depths of cut. The orthogonal array, signal-to-noise ratio (S / N) and variance analysis (ANOVA) were used to examine the performance characteristics of the Ti6Al4VELI alloy turning by using single-point diamond cutting tool. The influential factors on the surface roughness after machining are feed rate and cutting speed after the conclusions revealed. Whereas the feed rate had the most significant effect on tool life. Minimal surface roughness achieved after machining is in nano-level which is better than other conventional precision machining.

Characterization of the chips generated by the nanomachining of germanium for X-ray crystal optics

Micro-Raman spectroscopy, scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HR-TEM) were used to study the effect of cutting speed and cutting depth on the mode of the single-point diamond fly cutting of Ge(110) surface via crystallinity of the chips. Reducing the cutting depth from 15 to 2 μm and concurrently cutting speed from 10 to 2 mm/min at 2000 rpm, the content of amorphous phase in the chips increased at the expense of the crystalline one from 28 to 46%. Simultaneously, the chip morphology visible by SEM suggested transition from a brittle to a mixed brittle-ductile mode of nanomachining. The damage transition line indicates 1/3 portion of the ductile component at 2-μm cutting depth that produced twisted lamellae of a width of 18–20 μm without any signs of a fracture. As the feed rate here was 1 μm/rev, the tool made 18–20 revolutions while passing the same point of the nanomachined surface that was enough to gradually remove the surface region damaged by the brittle cutting component along with the entire amorphous region beneath, both being delaminated by the chips. This explains the dislocation-free single-crystal lattice beneath the Ge(110) surface machined under these conditions. A close relationship between the brittle mode of nanomachining and crystallinity of the chips observed by micro-Raman spectroscopy and SEM was confirmed by HR-TEM showing dense occurrence of nanocrystals in the chips coming from the nanomachinings with 5-μm and 15-μm cutting depths. These results demonstrate potential of the single-point diamond machining for the preparation of high-quality X-ray surfaces with undistorted single-crystal lattice beneath for next-generation X-ray crystal optics.

Micro-optical fabrication by ultraprecision diamond machining and precision molding

Ultraprecision diamond machining and high volume molding for affordable high precision high performance optical elements are becoming a viable process in optical industry for low cost high quality microoptical component manufacturing. In this process, first high precision microoptical molds are fabricated using ultraprecision single point diamond machining followed by high volume production methods such as compression or injection molding. In the last two decades, there have been steady improvements in ultraprecision machine design and performance, particularly with the introduction of both slow tool and fast tool servo. Today optical molds, including freeform surfaces and microlens arrays, are routinely diamond machined to final finish without post machining polishing. For consumers, compression molding or injection molding provide efficient and high quality optics at extremely low cost. In this paper, first ultraprecision machine design and machining processes such as slow tool and fast too servo are described then both compression molding and injection molding of polymer optics are discussed. To implement precision optical manufacturing by molding, numerical modeling can be included in the future as a critical part of the manufacturing process to ensure high product quality.

Surface damage mechanism of WC/Co and RB-SiC/Si composites under high spindle speed grinding (HSSG)

The surface damage mechanisms of WC/Co and Reaction-bonded SiC/Si (RB-SiC/Si) composites under high spindle speed grinding (HSSG) were investigated in the present work. Sharp edge loss and grit splintering were identified as two typical diamond wheel wear mechanisms. Plastic scratching grooves, Co extrusion and WC dislodgement were generated on the machined surface of WC/Co after grinding, while micro-pits of varied sizes at the phase boundaries and plastic scratching grooves were the main surface characteristics for RB-SiC/Si. Moreover, it was found that non-uniform surface finish at different radial positions resulted from the increase in material removal rate for both WC/Co and RB-SiC/Si, and the simulated results based on Soneys' model mostly corresponded with the measured outcomes. In addition, obvious relative wheel-workpiece vibration induced surface waviness was found, and its effect on the surface profile was analyzed for the wheel edge profile considered, which differed with that from single point diamond machining (SPDT).

Rapid fabrication of miniature lens arrays by four-axis single point diamond machining

A novel method for fabricating lens arrays and other non-rotationally symmetric free-form optics is presented. This is a diamond machining technique using 4 controlled axes of motion - X, Y, Z, and C. As in 3-axis diamond micro-milling, a diamond ball endmill is mounted to the work spindle of a 4-axis ultra-precision computer numerical control (CNC) machine. Unlike 3-axis micro-milling, the C-axis is used to hold the cutting edge of the tool in contact with the lens surface for the entire cut. This allows the feed rates to be doubled compared to the current state of the art of micro-milling while producing an optically smooth surface with very low surface form error and exceptionally low radius error.

Optical Effects of Surface Finish by Ultraprecision Single Point Diamond Machining

The single point diamond turning process has been used extensively for direct optical surface fabrication. However, the diamond machined surfaces have characteristic periodic tool marks, which contribute to reduced optical performance such as scattering and distortion. In this paper, studies of the characteristics of diamond machined surface and scattering from the diamond machined surfaces are presented. Four different parameters, the first order optical diffraction, the zero order reflection, the surface roughness, and the residual tool mark depth, are used as indicators for the machined surface quality. Four sets of tests are presented showing the relationship between machined surface quality and machining conditions such as spindle speed, feedrate, and machining process. Finally, an empirical model is given based on the measurements.

Effect of nanoscratch conditions on both deformation behavior and wet-etching characteristics of silicon (1 0 0) surface

This paper investigates the effect of single-point diamond machining conditions, such as the Berkovich tip orientation (0°, 45°, and 90°) and the normal load (0.1, 0.3, 0.5, 1, 2, 3, 4, 5 mN and 0.1 μN), on the both deformation behavior and the chemical properties of single-crystal silicon through nanoscratch with 20 wt.% KOH-etching tests. The tip orientation had a significant influence on the coefficient of friction, which varied from 0.16 to 0.38, the material removal mode, and the KOH-etching property of silicon. In normal load ranges from 0.1 to 1 mN, the friction coefficient remarkably increased with decreasing normal. KOH-etching results showed that, as a whole, the size of etch-hillock structures increased with an increasing normal load, indicating that that the higher the load that is applied to the material surface, the more the etch-mask effect of the mechanically affected layer increases. Contrarily, the groove surface machined under a very low load (0.1 μN) showed only the etch-promotion effect. The evolution of the morphology of a scratched Si(1 0 0) surface during the etching process was visualized by 20 wt.% KOH-etching tests under dipping times ranging from 0 to 30 min. The initial size of the etch-hillock structure was closely related to that of the contact zone between the diamond tip and materials.

220 高機能光学素子金型用アモルファス合金のコンビナトリアル探索(超精密・マイクロ加工)

This paper reports combinatorial search of novel amorphous alloy for advanced optical element (such as aspheric glass lens with diffraction grating etc.) forming die. Required properties of the amorphous alloy are as follows ; (a) the amorphous alloy film can be fabricated thickness more than 50μm on blank die. (b) Even if die of the amorphous alloy forms on a glass in air, the alloy do not crystallize and oxidize, and don't adhere to the glass. (c) Ultra-precision machining (surface roughness under 30nm Rmax) by single-point diamond machining (SPDM) is applicable to the alloy. (d) The fracture strength is more than 0.6GPa at least. To search the novel amorphous alloy, we employ combinatorial arc plasma deposition (CAPD). Pt-Hf-Zr-Ni amorphous alloy was picked out from over 25,000 samples using CAPD. The alloy filled the request and it succeeded in fabricating an advanced optical element forming die by SPDM.

Microwear of cutting tool in ultraprecision single-point diamond machining of polymers for optical and bioengineering application

This paper is a continuation of a long duration research and it reports new results in the investigation of wear of natural monocrystalline diamond cutting tool in single-point precision and ultraprecision machining processes of vitreous thermoplastic amorphous polymeric materials for various applications, for example, for photon-optical and bioengineering applications. In these investigations, we have been using up-to-date methods and devices, including Atomic Force Microscopy, interferometers and optical profilers, 3D Topographic Analysis Systems, optical-polarisable microscope, etc. Wear criteria were chosen as the technological criterion of the diamond tool cutting wedge clearance face wear, criterion of temperature rise and criterion of cut surface deterioration. The compulsory replacement of cutting tools on reaching of appointed value of wear allows to provide high quality level of the machined surfaces of the articles from polymers and their long durability.

Machining and metrology systems for free-form laser printer mirrors

A major challenge in optics is to make optical components like mirrors and lenses smaller and cheaper. This is achieved by designing optical components that have conformal or free-form shapes. A free-form optic is defined as one that is not symmetrical about any axis. These highly demanding requirements are met by single point diamond machining in rigid ultra precision machine tools.

Nanoscale ductile grinding of glass by diamond fibres

Chemical vapour-deposited diamond fibres have been used to grind soda glass. The surface topography was studied using scanning electron microscopy and atomic force microscopy techniques. The diamond surface facets and edges led to grinding without surface cracking and to surface roughness, Ra, values in the range 3–50 nm. The grinding mechanism involved the formation by ductile flow of glass ribbons adjacent to the grinding grooves. This grinding mechanism was similar to that reported for single-point diamond machining. The potential for ductile grinding with diamond fibres is discussed.

High resolution studies of crystalline damage induced by lapping and single-point diamond machining of Si(100)

Si(100) wafers were prepared by both diamond turning and standard lapping and polishing techniques. For single-point diamond machining, characterization of subsurface damage resulting from ductile-regime machining identified a plastic-yield zone consisting of slip planes and dislocation networks extending 1 to 3 μm deep despite surface root-mean-square roughness values as low as 5 nm. For conventional lapping and polishing using alumina grit, a transition from brittle to ductile yield was observed for grit sizes less than 300 nm. Subsurface damage depth correlated to surface roughness in a more straightforward manner than for the diamond point machining. Completely damage-free material removal was obtained only when a chemical component to the polishing was present.