Single Crystal Diamond Tool Research Articles

Materials removal mechanism for ultra-precise cutting of single-crystal silicon with natural single-crystal diamond tools by experiment and atomic simulation

The influence of tool rake angle and cutting speed on the ultra-precision cutting of single crystal silicon with natural single crystal diamond tools is studied by experiment and molecular dynamics (MD) simulations. The findings demonstrate that the 0° rake angle tool attains superior surface quality, reduced cutting force and friction coefficient in comparison to the −10° and − 20° rake angle tools. Moreover, the MD results reveal that a smaller negative rake angle tool can decrease the formation of high pressure phase atoms and other defects. In addition, the PV, RMS and Ra surface roughness parameters decrease as the machine spindle speed increases. Additionally, higher cutting speeds improve the surface morphology of the machined workpiece and produce fewer defective atoms.

Online Orientation Recognition of Single-Crystal Diamond Tools in the Process of Indexing Grinding Based on HMM and Multi-Information Fusion

Single-crystal diamond tools occupy an important position in the field of optical processing as the basis and key to advanced optical manufacturing technology, such as grating manufacturing and optical mirror-turning processing. Single-crystal diamond tools have become the cornerstone of the development of related industries. This paper takes a single-crystal diamond arc tool as the research object. Sound signal analysis technology and vibration signal analysis technology are comprehensively applied to the online orientation identification of a single-crystal diamond tool in the indexing grinding process. The online orientation method of the tool is explored, the sound signal and the vibration signal are taken as the characteristic signals, and a wavelet algorithm (WT) is used to reduce the noise of the vibration signal and sound signal. The kurtosis of the sound signal and the kurtosis and skewness of the vibration signal in the high-order statistics strongly related to the grinding direction of a single-crystal diamond are used as the characteristic parameters, and the online direction recognition model of the tool is established using the Hidden Markov Method (HMM). The above characteristic parameters are used as model input for multi-information fusion. The mapping relationship between the characteristic parameters of the characteristic signal and the crystal orientation of the single-crystal diamond crystal face is obtained, and then the online orientation method of the single-crystal diamond arc tool in the process of indexing grinding is formed. The effectiveness of the method is verified by experiments, and effective orientation information is provided for research on the positioning control strategy of the tool grinding process to ensure the efficiency of grinding and improve the manufacturing level of the tool.

Special Issue on Advanced Metal Cutting Technologies

Cutting technologies are utilized in many industrial sectors, such as automobile, aircraft, and medical-device manufacturing as well as dies and molds. Thus, the requirements for higher geometric accuracy, better surface integrity, and longer component service lifetimes have substantially increased. In addition, maintaining high machining efficiency while simultaneously reducing power consumption and CO2 emissions during machining is important for sustainable development. This special issue features 11 papers on the most recent advances in cutting technologies for metals and composite materials. - Reverse finishing characteristics of drilling surfaces - Machining error simulation for end milling - Visualization of cutting phenomena using a single-crystal diamond tool - Milling of TiB2 particle-reinforced high-modulus steel - Electrodischarge-assisted turning of carbon fiber-reinforced polymers - Suppression of chatter vibration during double-insert turning - Prediction of surface roughness components during turning - Microtome blades for high-precision tissue sectioning - Boiling of coolant near the cutting edge in high-speed machining - Residual stress during drilling of aluminum alloy - Effect of strain hardening on burr control during drilling This issue provides an understanding of recent developments in cutting technologies, aiming to inspire further research in this field. We deeply appreciate the careful work of all the authors and thank the reviewers for their diligent efforts.

Wear mechanism of diamond-cutting tool in nano-cutting polycrystalline γ-TiAl alloy based on molecular dynamics simulation

The machining of γ-TiAl is susceptible to tool wear, and investigations into tool-wear mechanisms can contribute to enhancing machining efficiency and optimizing the surface integrity of workpieces. In this study, a molecular-dynamics method is employed to simulate the cutting process of polycrystalline titanium–aluminum alloys using a single-crystal diamond tool. The findings suggest that tool wear is induced by cutting forces and plastic deformation, with amorphization and diffusive wear as the primary mechanisms. Plastic deformation within the matrix facilitates interactions between internal dislocations in the grains, thus resulting in work hardening at the surface layer, increased cutting forces, and heightened susceptibility of the cutting edge to wear due to plastic deformation. Moreover, elevated temperatures and pressures in the cutting contact area induce atomic amorphization, which reduces both the strength and hardness of the tool while triggering structural phase transitions for certain atoms. Consequently, lattice distortion occurs within this region, thus causing matrix atoms to diffuse into the tool. The combined effect of amorphization and diffusion significantly exacerbates tool wear. This investigation provides valuable insights into wear mechanisms and guidance for enhancing the quality of γ-TiAl alloy.

Influence of Abrasive Grain Protrusion on High-Quality Machining of Cemented Carbide Using PCD Ball End Mills

In this study, cemented carbide was machined to a high quality using polycrystalline diamond (PCD) ball end mills characterized by various surface textures. The effect of the surface texture of the tools on the machining characteristics was studied using two types of PCD tools featuring abrasive diamond grains at various protrusion heights. In addition, a single crystal diamond tool with the same shape as that of the PCD tool was fabricated, and the experiment was repeated to study the differences in machining characteristics. The polished PCD tool yielded a high-quality machined surface with an average surface roughness of 1 nm. The polished PCD tool yielded superior sample surface roughness compared to the PCD tool for feed rates of 10–500 mm/min. The use of a polished PCD tool enables the efficient elimination of material through plastic flow, leading to the attainment of a high-quality machined surface while preventing the adhesion of materials on the tool surface. A single crystal diamond tool can also be used for machining cemented carbide within a feed rate range of 10–200 mm/min; however, its performance is inferior to that of a polished PCD tool. Experiments confirmed that the polished PCD tool was the most effective among the tested tools for the precision machining of cemented carbide.

Effect of cutting speed on the surface integrity of single point diamond turned (100)Ge

The surface integrity of single crystal (100)Ge machined by on-axis single point diamond turning was investigated. The specimen was machined with a -25◦ rake angle single crystal diamond tool, with a depth of cut of 10 μm and a feedrate of 4 μm/rev. Six circular bands were machined on the specimen at different cutting speeds, ranging from 0.2 m/s to 10 m/s, while keeping all other machining and geometrical parameters constant. The surface topography was measured by atomic force microscopy and the near surface lattice disorder was investigated by Raman spectroscopy. The cutting and thrust forces were measured during machining, and their frequency domain was analyzed. Machining resulted in four lobes with four-fold symmetry, with differing amounts of surface fracture at each cutting speed. It was found that increasing the cutting speed generates surfaces with less or no brittle fracture for all cutting directions, causing some lobes to be undistinguishable. As the speed increased, the cutting and thrust force decreased monotonically. The frequency content of the force changed accordingly with the appearance of the surface, with a shift from 8 oscillations per revolution to 4 oscillations per revolution.

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.

Cutting performance assessment on the modified single crystal diamond tool by focused ion beam

In this work, the ion implantation effect of focused ion beam (FIB) is employed to modify the single crystal diamond tools, and the cutting performances of the irradiated and unirradiated tools are further evaluated. Firstly, the characteristics of the irradiated rake face are measured to determine the impact of the implanted ions. The results show that the surface energy of the rake face irradiated by FIB decreases significantly. Secondly, cutting experiments are carried out on the Al6061 alloy substrates. The results demonstrate that the ion implantation improves the self-cleaning of rake face and the wear resistance of cutting edge, which is conducive to reduce the cutting force and cutting temperature, resulting in an improvement of the manchined surface quality. All the experimental observations confirm that the FIB implantation process is an effective method to improve the cutting performance of single crystal diamond tool.

Unusual material removal characteristics of the novel graphite/diamond composite in mechanical polishing

Novel graphite/diamond composite (Gradia) is ultrahard, tough and semiconductive. Surface finishing of Gradia is difficult because of the disparity in mechanical properties between diamond and graphite components. In this work, material removal characteristics of Gradia in mechanical polishing were studied with experiments and molecular dynamic simulations. First, the Gradia surface was well-finished. Then, microstructural investigation showed the main mechanism of phase transformation was amorphization during polishing. The graphite and diamond phases of Gradia underwent interconversion under the mechanical action. In addition, initial and diamond-transformed graphitic phases experienced distortion, twist and reconstruction, producing graphite film. Finally, a Gradia tool was created and demonstrated a lower wear rate than single-crystal diamond tool, suggesting an unusual self-lubricating characteristic with abrasion-induced generation of graphite.

Micro milling of fused silica using picosecond laser shaped single crystal diamond tools

Fused silica is widely used as a material for optical lenses owing to its excellent optical properties and low thermal expansion coefficient. However, as a hard and brittle material, there is very limited option of processing technologies to machining fused silica with surface structures. In this paper, a picosecond laser based single crystal diamond tool fabrication technology is proposed to generate micro milling tools with different geometrical designs, and the tool cutting performance is experimentally tested through micro-milling of fused silica under different cutting conditions. An optimal picosecond laser processing path is proposed to inhibit the graphitization of diamond tool and improve the concentricity of tool blades, and a multi-edge milling tool with a minimum rotary diameter of 0.4 mm can be obtained. The effects of rake angle on cutting force and the degree of brittle damage on the subsurface of fused silica are studied by micro milling tests of fused silica using the laser-shaped tools. The results show that the fused silica machined by diamond milling tool with a rake angle of −30° has the best surface finish (Ra = 41.2 nm). Using this laser-machined milling tool, a plurality of micro Fresnel lenses with aperture of 1.6 mm were successfully machined on a fused silica sheet.

Precision machining of single crystal diamond cutting tool via picosecond laser irradiation

Due to its high hardness and excellent wear resistance, single crystal diamond has been widely applied in mechanical processing. However, the outstanding hardness leads to great difficulties in the machining of diamond by traditional strategies. In this study, a synchronous feed laser method is developed to realize low damage, high efficiency, and high precision machining of single crystal diamond cutting tools. The disadvantages of traditional direct laser machining, including fullerene residue, bending behavior, and the plasma-shield effect, are well avoided by the good control of the scanning path during the laser fabrication, which enlarges the entrance of the kerf and reduces the air pressure inside the kerf. The synchronous feed laser machining can realize the remarkable increase of kerf depth at high speed, as well as a minimum roughness of ∼147 nm on the cutting surface. It provides a novel, high efficiency, and high precision strategy for the preparation of high quality single crystal diamond tools.

A study on the development of sub-micron single-crystal diamond tools for machining diffractive optical elements

A study on the development of sub-micron single-crystal diamond tools for machining diffractive optical elements

Study on tool wear mechanism of single-crystal diamond in ultrasonic vibration elliptical cutting of tungsten heavy alloy

Tungsten heavy alloy has been widely used in the nuclear industry, military, and other fields due to its excellent material properties. In this paper, the wear of single crystal diamond tool and its influence on surface roughness were studied by ultrasonic elliptical vibration cutting experiment of tungsten heavy alloy and compared with conventional cutting. The experimental results show that under ultrasonic elliptical vibration cutting, the flank wear of a single crystal diamond cutter is reduced by 74.5%, and the retreat of the cutting edge is reduced by 70.6%. After the cutting experiment, the elements on the cutting surface, chip surface, and diamond tool adhesion were detected and analyzed by Raman spectroscopy and X-ray photoelectron spectroscopy. The results show that compared with conventional cutting, ultrasonic elliptical vibration cutting can effectively inhibit the graphitization of single-crystal diamond tools and avoid chemical wear. This is an essential reason why single-crystal diamond tools can be used for tungsten heavy alloy processing under ultrasonic elliptical vibration cutting.

Enhanced machinability of Ni-based single crystal superalloy by vibration-assisted diamond cutting

The machined surface integrity of Ni-based single crystal superalloy is one major factor that affects the performance of its component. It is extremely difficult to achieve a nanometric surface quality by only using ordinary cutting (OC) technology due to the rapid tool wear. Hence, in this work ultrasonic vibration cutting (UVC) with single crystal diamond tool is applied to investigate the machinability of Ni-based single crystal superalloy, including a series of comprehensive investigations on the surface integrity machined in OC and UVC, such as surface roughness, surface morphology, chip formation, tool wear, sub-surface damage, and so on. The experimental results indicated that as compared to OC where finished surface deteriorates seriously due to rapid tool wear, the surface roughness by applying UVC is decreased from Sa 60 nm in OC to Sa 4.815 nm in UVC due to the efficient suppression of tool wear. And the maximum profile error of 1.314 μm achieved in OC is significantly reduced to 0.038 μm with eliminated anisotropic machining effect in UVC. It is also clarified that there are obvious grain refinements and severe plastic deformation near the sub-surface in OC, which is mainly caused by the huge thermo-mechanical loading driven by the tool wear. Moreover, due to the grains are significantly refined in OC, the workpiece material is seriously work hardened. In contrast, the thickness of sub-surface damage is decreased from 2.27 μm in OC to 0.1902 μm in UVC due to the small loading forces, accompanied with more uniform evolution of microstructures.

Microstructural effects on the single crystal diamond tool wear in ultraprecision turning of Ti6Al4V alloys

Single crystal diamond tools are common cutters in the ultraprecision machining, but the tool wear is a great concern in machining of difficult-to-cut materials. In this paper, material microstructural effect on the diamond tool wear is firstly investigated in ultraprecision turning of difficult-to-cut Ti6Al4V alloys. Equiaxial, bimodal and lamellar microstructures are used in the machining. Results show that more adhesion of Ti6Al4V workpiece is observed at the flank face instead of the rake face in turning of all types of microstructures. The tool wear in turning of the lamellar alloy is less than that of the equiaxial and bimodal alloys, giving rise to low cutting forces and high surface quality. Furthermore, discontinuous serrated chips are observed for the equiaxial and bimodal alloys at the cutting distance of 3000 m, while the chips remain continuous in machining of the lamellar martensitic alloys. Besides, the diamond tool wear mechanism is discussed from perspectives of tool wear modes and chemical reactions by characterizations of the scanning electron microscope, atomic force microscope atom, X-ray photoelectron spectra and high-resolution transmission electron microscope. This study aims to clearly understand the diamond tool wear mechanism in ultraprecision machining of the Ti6Al4V alloys.

Kinematic analysis of the dynamic contact in ultrasonic-assisted cutting based on the moving frame method

The dynamic contact characteristics between tool and workpiece (DCCTW) significantly affect the lubrication and cooling in ultrasonic-assisted cutting, closely related to tool wear and machining quality. Due to the complexity of the contact, it is hard to describe them effectively, which limits the understanding of the ultrasonic-assisted cutting mechanism. In this paper, a novel kinematic analysis method based on the moving frame method is presented to describe the DCCTW in ultrasonic-assisted cutting. In the kinematic modeling, the tool nose radius and tool vibration characteristics are both taken into account. The method can display visually the dynamic contact characteristics of each position on the cutting edge in one vibration cycle using velocity mapping diagrams (VMD). Using the method, DCCTW in three types of typical ultrasonic-assisted turning are compared theoretically, which provides a novel perspective to understanding their cutting mechanism. Additionally, experiments about ultra-precision turning optical steel mold using single-crystal diamond tools to manufacture micro-grooves are carried out using our developed elliptical ultrasonic vibration system. The proposed method gives an intuitive picture of the DCCTW in the ultrasonic elliptical vibration turning and is successfully applied to analyze the tool wear and surface quality under different machining conditions.

Accurate measurement of cutting-edge radius on a single-crystal diamond tool

Single-crystal diamond (SCD) tools are hard and can maintain a uniform sharp cutting edge and hence used in ultraprecision machining of optics. The tools typically have edge radii in the range of 10-100 nm. Direct measurement of the cutting-edge radius on the SCD tool accurately in the order of tens of nanometers using a scanning electron microscope (SEM) is not possible and arduous using an atomic force microscope (AFM). In this study, we have demonstrated a more accurate edge reversal technique to measure the SCD tool’s cutting-edge radius. A nano indent is made using the SCD tool on two polished pure copper blocks held together in a precise vise. After the nanoindentation, the copper blocks are separated, and the cross-section profile of the indentation mark, a replica of cutting-edge geometry, is observed in an SEM. A fitted circle on the indentation profile is used to obtain the edge radius. Due to the elastic recovery in the material, the indentation profile geometry changes slightly, and the radius measured from the SEM image is not the same as the actual tool radius of the SCD tool. We performed finite element method (FEM) simulations to quantify the amount of elastic recovery and calculate the elastic recovery factor for a given SCD tool geometry as a function of indentation depth and edge radius. From the simulation results, we found the error due to elastic recovery effect in edge radius measurement is only 10%. Due to the stick-slip condition and high stress concentration factor at the cutting edge of the tool, material pull-out is observed at the middle of the cutting mark on the substrate but at the ends of cutting mark on the substrate material was negligible. In this method, compared to the previous literature work the three primary sources of errors, elastic recovery effect, convolution effect of AFM tip, and material pull-out are eliminated. Hence, this method provides a more accurate measurement of the edge radius and can be adopted by research labs, universities, and industries having ultra-precision machining facilities without needing a special purpose SCD tool edge radius characterization facility.

Building a model of dressing the working surfaces of wheels during the two-side grinding of round end faces at CNC machines

This paper reports the spatial mathematical modeling of the process of dressing the working surface of grinding wheels for implementing the double-sided grinding of the ends of cylindrical components. Parts with high-precision end surfaces that are commonly used include bearing rollers, piston fingers, crosspieces of cardan shafts, and others. The geometric accuracy of surfaces is ensured by simultaneously grinding the ends at two-sided end-grinding machines with crossed axes of the part and wheels that operate under a self-blunting mode. Before starting the machining, the wheels are dressed in a working position. Moreover, the total orientation angle of the tools is selected subject to the condition of uniform distribution of allowance along the rough sections of wheels. Dressing involves a single-crystal diamond tool with a variable feed. That ensures different development of the surface of abrasive tools, which prolongs their operating time between dressings and improves overall stability. The constant size of micro irregularities at the calibration site enhances the quality of machining. The calibration site is made in the form of a straight line belonging to the plane that passes through the axis of rotation of the wheel and is perpendicular to the plane of the machined part. Based on the spatial mathematical models of the processes of removal of allowance and shape formation when dressing the wheel, the surface of the grinding wheel was investigated. Mathematical models for shaping the ends of parts when grinding with wheels with conical calibration sites have been proposed; it is shown that when applying the proposed machining scheme, there is no geometric error in the size of the part. In addition, due to the uniform distribution of the allowance along the rough area of the wheel, the quality of the surface layer of the ends of parts increases. The devised method for dressing the working surface of wheels could be used to grind the ends of non-circular components.

Suppression of diamond tool wear with sub-millisecond oxidation in ultrasonic vibration cutting of steel

• Compressed air suppresses diamond wear in ultra-sonic cutting of stainless steel. • Thicker Fe oxide layer on steel surface helps further suppression of tool wear. • High air pressure increases O 2 partial pressure at interface and oxide thickness. • Sufficient oxide layer on fresh-cut steel forms within ultra-sonic cutting interval. • Proposed hypothesis of oxidation replenishes the existing wear suppression theories. Ultrasonic vibration has been applied to suppress the chemical tool wear in ultra-precision diamond cutting of steel and other alloys. The tool wear is found significantly reduced with enriched ambient oxygen concentration. In this study, instead of supplying costly and potentially hazardous high concentration oxygen to the machining zone, a greener alternative, high-pressure air coolant has been applied to enhance the oxygen content at the cutting area. The effect of air-blowing pressure on ultrasonic vibration cutting of stainless steel was investigated, using both polycrystalline and single-crystal diamond tools. It has been found that an increased air blowing pressure and a more closely positioned nozzle not only improve the cutting performance but also reduce tool wear, reflecting consequences from both chemical and fluidic dynamics aspects. A higher air blowing pressure will increase the instantaneous air pressure as well as the density of oxygen molecules around the cutting zone. This increases the passivation speed for the freshly cut steel surface caused by the formation of thin oxide layers. Experimental results have formalized the findings that sub-millisecond oxide formation is the key factor to suppress diamond tool wear.

A Study on Focused Ion Beam (FIB) Milling Machining and Fabrication Technology of Nano-Scale Diamond Tool for Machining Fine-Patterns in a Free-Form Surfaces.

Recently, the technology of the industry has been increasing for diffractive optical elements, holograms, optical components, and next-generation display components. The advanced high value-added industry is designing fine patterns on ultra-precision optical components and applying them to various industries. In the case of the ultra-fine pattern, a contact-type machining technique is required because it requires a precise pattern in nano-scale units. In this paper, the fabrication technology of ultra-precision diamond which is essential in the ultra-precision processing technology was suggested. The material used in the experiment was a single-crystal diamond tool (SCD), and the equipment for machining the SCD used a focused ion beam (FEI COMPANY, system Nova 600) equipment. The back fire method was applied without metal coating in order to carry out the process study and the focused beam of 30 keV Ga+ ions were carried out processing for various fabrication of diamond cutting tools. As a result of applying the backfire method through the process experiment, the cutting edge width of the ultra-precision diamond tool was verified 275 nm.