Single Crystal Diamond Tool Research Articles

Ultrasonically Assisted Single Point Diamond Turning of Optical Mold of Tungsten Carbide.

To realize high efficiency, low/no damage and high precision machining of tungsten carbide used for lens mold, a high frequency ultrasonic vibration cutting system was developed at first. Then, tungsten carbide was precisely machined with a polycrystalline diamond (PCD) tool assisted by the self-developed high frequency ultrasonic vibration cutting system. Tool wear mechanism was investigated in ductile regime machining of tungsten carbide. The cutter back-off phenomenon in the process was analyzed. The subsequent experimental results of ultra-precision machining with a single crystal diamond tool showed that: under the condition of high frequency ultrasonic vibration cutting, nano-scale surface roughness can be obtained by the diamond tool with smaller tip radius and no defects like those of ground surface were found on the machined surface. Tool wear mechanisms of the single crystal diamond tool are mainly abrasive wear and micro-chipping. To solve the problem, a method of inclined ultrasonic vibration cutting with negative rake angle was put forward according to force analysis, which can further reduce tool wear and roughness of the machined surface. The investigation was important to high efficiency and quality ultra-precision machining of tungsten carbide.

Material removal mechanism and surface integrity in ultraprecision cutting of porous titanium

Porous titanium presents unique material properties with a wide variety of mechanical and biomedical applications. Porous titanium components fabricated by near net-shape technologies require further machining processes to improve the surface quality and form accuracy, and in turn, the added value of the products. In this work, major factors dominating the surface integrity in ultraprecision cutting of porous titanium using single-crystal diamond tools were investigated. The results demonstrated that the presence of pores significantly changed mechanism of cutting. The chip morphology and surface topography depended on pore size and undeformed chip thickness. At an extremely small undeformed chip thickness, a majority pores were closed due to the welding phenomenon, leading to a sharp drop of surface porosity. In contrast, large pores cause craters on the machined surface and segmentation of chips and protruding lamella, especially at a large undeformed chip thickness. A coolant could lubricate the tool-workpiece interface and the shear deformation, which decreased cutting forces. On the other hand, the rapid cooling effect enhanced the work hardening effect and increase the hardness of the machined surface. Tool wear in cutting porous titanium is suppressed compared with that of pure titanium, especially in wet cutting.

Ultra-precision diamond turning of optical silicon—a review

In traditional approach of silicon optical lens production, grinding, lapping, and polishing are employed. Success of these steps depends on the quality of the preceding ones; therefore, use of precision grinding is becoming an unwise decision during manufacturing of optical lenses with complicated surfaces. Owing to this, an alternate manufacturing approach for producing silicon optical component was sought. Ultra-precision diamond turning using a single-crystal diamond tool with a high negative rake angle while maintaining a cutting regime in the ductile mode is now widely used as the alternate approach. However, depending on view point, machinability in ultra-precision machining may be in terms of tool wear rate, hardness, chip shape, surface roughness, and other benchmarks. Therefore, determining proper machining conditions, such as tool geometry and processing parameters, is crucial in achieving the required surface finish and optical form accuracy. In determining the optimal process parameter settings in silicon diamond turning, numerous process trials are generally required to evaluate the most favorable machining variables and their interactions. To improve the machinability of silicon, this review article presents an overview of the previous research on the effects of both machining parameters and tool geometry to optical silicon machinability. This is aimed at facilitating adequate understanding of the deformation, fracture, surface quality, and microstructural changes of both silicon and diamond to ease attainable product quality, utility, and quality cost.

Study of materials effects on the single cutting in ultra-precision raster milling

Ultra-precision raster milling (UPRM) rotates a single crystal diamond tool to discontinuously remove materials from the workpiece and can directly produce freeform surfaces with sub-micrometric form accuracy and nanometric surface finishing. This paper presents theoretical and experimental investigations on the workpiece material effect on single cutting profile in UPRM. Experiments are conducted to study the material effect on cutting profile by single cutting four materials including copper, aluminium alloy 6061, brass and aluminium bronze under the same cutting conditions in UPRM. A characterisation method is presented in the paper to study the effect of different workpiece material on the cutting profiles in UPRM. The experimental results show that copper alloy makes the smallest effect on the single cutting profile because of the lowest elastic recovery ratio while the material effect of aluminium bronze is the highest due to the highest elastic recovery ratio and the highest hardness.

Suppression of diamond tool wear in machining of tungsten carbide by combining ultrasonic vibration and electrochemical processing

As an important ceramic material, tungsten carbide (WC) is utilized as the typical mold in precision glass molding, which has replaced conventional grinding and polishing to provide a highly replicative process for mass manufacturing of optical glass components. Ultra-precision grinding, which is time consuming and has low reproducibility, is the only method to machine such WC molds to high profile accuracy. Although diamond turning is the most widely used machining method for fabrication of optical molds made of metals, diamond turning of WC is still considered challenging due to fast abrasive wear of the diamond tool caused by high brittleness and hardness of WC. Ultrasonic vibration cutting has been proven to be helpful in realizing ductile-mode machining of brittle materials, but its tool life is still not long enough to be utilized in practical diamond turning of optical WC molds. In the current study, a hybrid method is proposed to combine electrochemical processing of WC workpiece surface into the diamond turning process. Cutting tests on WC using poly-crystalline diamond tools were conducted to evaluate its effect on improvement of tool wear and surface quality. Validation cutting tests using single crystal diamond tools has proven that the proposed hybrid method is able to significantly reduce the diamond tool wear and improve the surface quality of machined ultra-fine grain WC workpiece compared to ultrasonic vibration cutting without electrochemical processing.

Fabrication of an Anisotropic Superhydrophobic Polymer Surface Using Compression Molding and Dip Coating

Many studies of anisotropic wetting surfaces with directional structures inspired from rice leaves, bamboo leaves, and butterfly wings have been carried out because of their unique liquid shape control and transportation. In this study, a precision mechanical cutting process, ultra-precision machining using a single crystal diamond tool, was used to fabricate a mold with microscale directional patterns of triangular cross-sectional shape for good moldability, and the patterns were duplicated on a flat thermoplastic polymer plate by compression molding for the mass production of an anisotropic wetting polymer surface. Anisotropic wetting was observed only with microscale patterns, but the sliding of water could not be achieved because of the pinning effect of the micro-structure. Therefore, an additional dip coating process with 1H, 1H, 2H, 2H-perfluorodecythricholosilanes, and TiO2 nanoparticles was applied for a small sliding angle with nanoscale patterns and a low surface energy. The anisotropic superhydrophobic surface was fabricated and the surface morphology and anisotropic wetting behaviors were investigated. The suggested fabrication method can be used to mass produce an anisotropic superhydrophobic polymer surface, demonstrating the feasibility of liquid shape control and transportation.

Nanometer-scale chip formation and surface integrity of pure titanium in diamond turning

Titanium is attracting great attentions in aerospace and medical applications where high surface quality plays an important role in improving the product performance. For developing nano-precision machining technology for titanium, clarification of the nanometer-scale chip formation mechanism is essential. In this study, the surface formation mechanism of pure titanium in ultraprecision cutting tests using single-crystal diamond tools was investigated. The results demonstrated that decreasing undeformed chip thickness from the micrometer scale down to the nanometer scale had profound impacts on the shear angle, specific cutting force, and chip morphology. Chip tearing phenomenon occurred when undeformed chip thickness is smaller than a critical value (~ 100 nm), which significantly affected the chip morphology and machined surface integrity. In nanometer-scale cutting, tool feed mark is no longer a major reason of surface roughness; instead, material plucking, debris, scratches, and chip adhesion influenced the surface integrity. The high pressure generated in the nanometer-scale cutting caused a hardness increase in workpiece material and promoted workpiece material adhesion to the tool surface, as well as tool wear.

Investigation on diamond tool wear in ultrasonic vibration-assisted turning die steels

ABSTRACTThis paper presents comprehensive theoretical analyses and experimental investigations for evaluating the ultrasonic vibration-assisted turning (UVAT) of die steels with single-crystal diamond tools. The diamond tool wear was found to rely heavily on the feed rate and the cutting speed while being insensitive to the depth of cut and the tool relief angle under the cutting conditions used in the tests. The tool wear characteristics were further studied based on the observation of wear zone using Raman spectral analysis and energy-dispersive X-ray (EDX) analysis. The detection results of the tool worn topography, the phase transformation and the carbon diffusion of diamond crystals revealed that tool wear mainly occurred on the tool flank face due to the graphitization and the diffusion of the diamond tool. Analytical results of the function mechanisms of the ultrasonic turning indicated that the friction force between the tool flank face and the machined surface, which depended mainly on the ratio of the cutting speed and the vibration speed, could be effectively reduced in ultrasonic turning process. The analytical and experimental results indicated that compared with conventional turning (CT), the cutting performance, in terms of the tool life, was markedly improved by applying ultrasonic vibration to the cutting tool.

Precision cutting of single crystal silicon using CBN tool with large top corner radius

A lot of studies on the ultra-precision cutting of single crystal silicon have been reported and they used the diamond cutting tools. However, the diamond cutting tools are very expensive. Therefore, if the single crystal diamond tools were replaced with sintered CBN tools, the cost of machining could be fairly reduced. However, it is easily expected that the CBN tools wear out faster than the diamond tools. Therefore, it is very important to find out the optimum cutting conditions in order to reduce tool wear. In this study, precision cutting of single crystal silicon was machined with using CBN cutting tools having chamfer at cutting edge and large nose radius, and the effect of feed rate, cutting speed, depth of cut and nose radius on the tool wear were studied. As a result, the local minimum of width of flank wear land appeared at the feed rate of 30~50 µm/rev.

Precision cutting of single crystal silicon using CBN tool with large top corner radius

A lot of studies on the ultra-precision cutting of single crystal silicon have been reported and they used the diamond cutting tools. However, the diamond cutting tools are very expensive. Therefore, if the single crystal diamond tools were replaced with sintered CBN tools, the cost of machining could be fairly reduced. However, it is easily expected that the CBN tools wear out faster than the diamond tools. Therefore, it is very important to find out the optimum cutting conditions in order to reduce tool wear. In this study, precision cutting of single crystal silicon was machined with using CBN cutting tools having chamfer at cutting edge and large nose radius, and the effect of feed rate, cutting speed, depth of cut and nose radius on the tool wear were studied. As a result, the local minimum of width of flank wear land appeared at the feed rate of 30~50 µm/rev.

Cutting Performance of PCD Tools Improved by Ultraviolet-Ray Irradiation Polishing

The polycrystalline diamond (PCD) is made of sintered diamond fine powder with binder material, and shows clear isotropic characteristics and high toughness without frequent cleavage. As the PCD cutting tools require relatively low tool cost compared with single crystal diamond tools, they have wide applications as the precision cutting tools with the high abrasion resistance. The more sharp or complex shapes of PCD cutting tool are deeply expected even though they have the machining difficulties. In this study, the ultraviolet-irradiation polishing of single crystal diamond substrates developed in our laboratory (abbreviated as UV-polishing in this paper) was applied to realize advanced PCD tools with ultra-sharp or chamfered cutting edges. Firstly, the UV-polishing properties of PCD substrate were investigated, and high-quality polished surface with 2.6 nmRa was obtained. Secondly, the UV-polishing was applied to the precision polishing of the flank face of PCD cutting tool, and an ultra-sharp cutting edge was finally achieved. The chamfered cutting edge with desired angle and width was additionally formed by the UV-polishing to suppress the chipping left on the sharpened cutting edge. The tool wear of chamfered PCD cutting tools could be reduced almost by half to the sharpened tool under high-speed cutting of high silicon-aluminum alloy.

Diamond micro-milling of lithium niobate for sensing applications

Lithium niobate (LiNbO3) is a crystalline material which is widely applied in surface acoustic wave, microelectromechanical systems (MEMS), and optical devices, owing to its superior physical, optical, and electronic properties. Due to its low toughness and chemical inactivity, LiNbO3 is considered to be a hard-to-machine material and has been traditionally left as as an inert substrate upon which other micro structures are deposited. However, in order to make use of its superior material properties and increase efficiency, the fabrication of microstructures directly on LiNbO3 is in high demand. This paper presents an experimental investigation on the micro machinability of LiNbO3 via micro milling with the aim of obtaining optimal process parameters. Machining of micro slots was performed on Z-cut LiNbO3 wafers using single crystal diamond tools. Surface and edge quality, cutting forces, and the crystallographic effect were examined and characterized. Ductile mode machining of LiNbO3 was found to be feasible at a low feed rate and small depth of cut. A strong crystallographic effect on the machined surface quality was also observed. Finally, some LiNbO3 micro components applicable to sensing applications were fabricated.

Cutting Characteristics of Binderless Diamond Tools in High-Speed Turning of Ti-6Al-4V – Availability of Single-Crystal and Nano-Polycrystalline Diamond –

In this study, the tool performance of two types of binderless diamond tools – single-crystal diamond (SCD) and nano-polycrystalline diamond (NPD) – is investigated in the high-speed cutting of titanium alloy (Ti-6Al-4V) with a water-soluble coolant. The NPD tool allows for a larger cutting force than the SCD tool by dulling of the cutting edge, despite NPD being harder than SCD. This large cutting force and the very low thermal conductivity of NPD yield a high cutting temperature above 500°C, which promotes the adhesion of the workpiece to the tool face, thereby increasing tool wear. Based on the morphology of the tool edge without scratch marks and the elemental analysis by energy-dispersive X-ray spectroscopy (EDX) of both the flank face and the cutting chips, diffusion-dissolution wear is determined to be the dominant mechanism in the diamond tool. A thin TiC layer seems to be formed in the boundary between the diamond tool and the titanium alloy at high temperatures; this is removed by the cutting chips.

Influence of microstructure on the cutting behaviour of silicon

We use molecular dynamics simulation to study the mechanisms of plasticity during cutting of monocrystalline and polycrystalline silicon. Three scenarios are considered: (i) cutting a single crystal silicon workpiece with a single crystal diamond tool, (ii) cutting a polysilicon workpiece with a single crystal diamond tool, and (iii) cutting a single crystal silicon workpiece with a polycrystalline diamond tool. A long-range analytical bond order potential is used in the simulations, providing a more accurate picture of the atomic-scale mechanisms of brittle fracture, ductile plasticity, and structural changes in silicon. The MD simulation results show a unique phenomenon of brittle cracking typically inclined at an angle of 45°–55° to the cut surface, leading to the formation of periodic arrays of nanogrooves in monocrystalline silicon, which is a new insight into previously published results. Furthermore, during cutting, silicon is found to undergo solid-state directional amorphisation without prior Si–I to Si-II (beta tin) transformation, which is in direct contrast to many previously published MD studies on this topic. Our simulations also predict that the propensity for amorphisation is significantly higher in single crystal silicon than in polysilicon, signifying that grain boundaries eases the material removal process.

Tool wear of a single-crystal diamond tool in nano-groove machining of a quartz glass plate

Tool wear characteristics of a diamond tool in ductile mode machining are presented in this paper. Nano-groove machining of a quartz glass plate was conducted to examine the tool wear rate of a single-crystal diamond tool. Effects of lubrication on the tool wear rate were also evaluated. A numerical simulation technique was developed to evaluate the tool temperature and normal stress acting on the wear surface. From the simulation results it was found that the tool temperature does not increase during the machining experiment. It is also demonstrated that tool wear is attributed to the abrasive wear mechanism, but the effect of the adhesion wear mechanism is minor in nano-groove machining. It is found that the tool wear rate is reduced by using water or kerosene as a lubricant.

Development of a non-rigid micro-scale cutting mechanism applying a normal cutting force control system

A micro/nano-scale cutting mechanism using a non-rigid tool holder has been developed. This mechanism, which relies on a control principle that is based on a technique for nano-cutting using an atomic force microscope (AFM), can be used to fabricate grooves with a constant cutting depth on the order of a few micrometers. A linear displacement sensor is used to measure the deformation of a flexible cantilever beam to which a single-crystal diamond tool is attached. This sensor, operated in conjunction with a feedback control system and piezoelectric actuator, can maintain a constant normal cutting force during the machining process. Unlike other nano-cutting systems, this system is attached to a common machine tool that increases its machining area to a couple of square centimeters, which is required for practical applications. Several experiments were performed using this cutting mechanism to assess its performance during the cutting process, especially when the grooves are fabricated on inclined or curved surfaces without a prior knowledge of the surface geometry.

Investigation of focused ion beam induced damage in single crystal diamond tools

In this work, transmission electron microscope (TEM) measurements and molecular dynamics (MD) simulations were carried out to characterise the focused ion beam (FIB) induced damage layer in a single crystal diamond tool under different FIB processing voltages. The results obtained from the experiments and the simulations are in good agreement. The results indicate that during FIB processing cutting tools made of natural single crystal diamond, the energetic Ga+ collision will create an impulse-dependent damage layer at the irradiated surface. For the tested beam voltages in a typical FIB system (from 8kV to 30kV), the thicknesses of the damaged layers formed on a diamond tool surface increased from 11.5nm to 27.6nm. The dynamic damage process of FIB irradiation and ion–solid interactions physics leading to processing defects in FIB milling were emulated by MD simulations. The research findings from this study provide the in-depth understanding of the wear of nanoscale multi-tip diamond tools considering the FIB irradiation induced doping and defects during the tool fabrication process.

Experimental Investigation on Cutting Characteristics in Nanometric Plunge-Cutting of BK7 and Fused Silica Glasses.

Ductile cutting are most widely used in fabricating high-quality optical glass components to achieve crack-free surfaces. For ultra-precision machining of brittle glass materials, critical undeformed chip thickness (CUCT) commonly plays a pivotal role in determining the transition point from ductile cutting to brittle cutting. In this research, cutting characteristics in nanometric cutting of BK7 and fused silica glasses, including machined surface morphology, surface roughness, cutting force and specific cutting energy, were investigated with nanometric plunge-cutting experiments. The same cutting speed of 300 mm/min was used in the experiments with single-crystal diamond tool. CUCT was determined according to the mentioned cutting characteristics. The results revealed that 320 nm was found as the CUCT in BK7 cutting and 50 nm was determined as the size effect of undeformed chip thickness. A high-quality machined surface could be obtained with the undeformed chip thickness between 50 and 320 nm at ductile cutting stage. Moreover, no CUCT was identified in fused silica cutting with the current cutting conditions, and brittle-fracture mechanism was confirmed as the predominant chip-separation mode throughout the nanometric cutting operation.

Development of an innovative device for ultrasonic elliptical vibration cutting

An innovative ultrasonic elliptical vibration cutting (UEVC) device with 1st resonant mode of longitudinal vibration and 3rd resonant mode of bending vibration was proposed in this paper, which can deliver higher output power compared to previous UEVC devices. Using finite element method (FEM), resonance frequencies of the longitudinal and bending vibrations were tuned to be as close as possible in order to excite these two vibrations using two-phase driving voltages at a single frequency, while wave nodes of the longitudinal and bending vibrations were also adjusted to be as coincident as possible for mounting the device at a single fixed point. Based on the simulation analysis results a prototype device was fabricated, then its vibration characteristics were evaluated by an impedance analyzer and a laser displacement sensor. With two-phase sinusoidal driving voltages both of 480Vp–p at an ultrasonic frequency of 20.1kHz, the developed prototype device achieved an elliptical vibration with a longitudinal amplitude of 8.9μm and a bending amplitude of 11.3μm. The performance of the developed UEVC device is assessed by the cutting tests of hardened steel using single crystal diamond tools. Experimental results indicate that compared to ordinary cutting process, the tool wear is reduced significantly by using the proposed device.

Tool Temperatures and Wear in Micro-machining Cu-Ni Alloys with Diamond Tools: Models, Simulations and Experiments

Estimating cutting edge temperatures in micro-machining Cu-Ni alloys with single crystal diamond tools is the purpose of this paper, in order to assess how temperature affects tool wear, perhaps through a thermally activated mechanism. Classical heat conduction models, numerical temperature calculation models and finite element chip formation models are developed and applied to determine relations between temperature and cutting conditions in non-dimensional form that thus have a wide transferability.Experimentscalibrate and in part validate the results. Tool wear nose turning Monel 400 alloy is reported.It shows thermally activated dependence on temperature, with activation energy 53 ± 6kJ/mol.