Diamond Fly-cutting Research Articles

Material removal mechanisms affected by milling modes for defective KDP surfaces

Surface defects which are caused by diamond fly-cutting can degrade the optical characteristics of KDP crystals by inducing the laser damage and resultantly shortening the service life when working in the condition of extremely high-power laser irradiations. The ball-end milling repair can totally remove the defects and correspondingly enhance the ability of the KDP crystals to resist laser damage. However, because of the existence of pull-milling, push-milling, down-milling, and up-milling in the complex machining trajectory, it is of great challenge for soft-brittle KDP crystals to achieve full plastic domain milling of repair points for obtaining ultra-smooth repaired surface. In this study, theoretical models of the maximum uncut chip thickness (UCT) considering the defect are constructed in the various milling modes. The cutting force and surface morphology affected by milling modes on the defective surface are simulated using a three-dimensional (3D) finite element model. Combined with the simulations, micro-milling tests are employed to confirm the influence of milling modes on the material removal mechanisms for defective KDP crystals by cutting force, surface morphology, surface roughness and specific cutting energy (SCE). It is found that defects could reduce the maximum UCT to distinct degrees in the various milling modes. Defects have a greater influence on the maximum UCT in the push-milling mode than that in the pull-milling mode, while the influence is the same in the up-milling and down-milling modes. Interestingly, the ductile removal mode occurs on the both defect-free and defective surfaces in the pull-milling mode when the feed per tooth (fz) is 0.5 µm/z. In contrast, the brittle-ductile transition caused by surface defects occurs in the other three milling modes. Furthermore, defects would lead to severer size effect in the all milling modes. When the fz is 0.1 µm/z, for the defective surface, the SCE is larger and the ploughing effect is more significant in the push-milling mode compared to the pull-milling mode. More importantly, as a result of the difficulty of chip discharge, the SCE is greater in the up-milling mode than in the down-milling mode on the defective surface. This work reveals the influence mechanism of milling modes on the material removal process for defective KDP crystals and offers a theoretical foundation and technical value for improving the repaired surface quality of functional KDP crystals served as the optical devices.

Formation Mechanism of Dkdp Surface in Single Point Diamond Fly-Cutting Process and the Resulting Degradation of Laser-Induced Damage Performance

Formation Mechanism of Dkdp Surface in Single Point Diamond Fly-Cutting Process and the Resulting Degradation of Laser-Induced Damage Performance

CGHMM based fault identification for single point diamond flycutting machines

The ultra-precision single point diamond flycutting method is commonly used to produce fine optical surfaces. But the motion errors of machine tool are very weak, it is hard to achieve the error detection for single point diamond flycutting machines. To solve this problem, different measuring data such as vibrations and temperatures of different components were collected synchronously, and then we established the fault identification method based on hidden Markov model (HMM) to analyse the acquired measuring signals. The method includes signal analysis of raw data, fault recognition based on continuous Gaussian mixture density hidden Markov model (CGHMM) and information fusion. It combines the advantages of HMM and information fusion, to identify fault information accurately. Results show that the identification rates of the temperature signals to classification status by GRMS can reach 92% and vibration signals are little related to the surface quality of the workpieces classified by GRMS.

The micro-wear mechanism of diamond during diamond tool fly-cutting KDP (KH2PO4) from first principle calculations.

First principle calculations were used to study micro-wear mechanism of diamond when diamond fly-cutting was performed on KDP (KH2PO4). Since the (001) surface of KDP is the relatively stable surface by analyzing the chemical bonds and surface energies, we choose the (001) surface of KDP to build the KDP/C interfaced models and KDP/C co-crystal model. According to the populations of interaction models, we can find that the preferential reaction between C and O/P atoms lead to the wear of tool.

Investigate the initialization of materials removal and deformation in single point diamond fly cutting technique using multiscale method

Diamond fly cutting (DFC) is a technique which can accurately and efficiently generate shapes in the micro & nanometer scale. However, the miniaturization of parts and the small depth of cut make the materials removal or deformation in the DFC different from the common machining technology. It is difficult to investigate materials deformation or failure by means of pure macroscopic or microscopic scale method. Multiscale method can study material behavior across different length & temporal scale simultaneously which is helpful about uncover important properties and materials response in DFC and thus being employed in this work. The results show that several slipping-dislocation systems are generated with feeding of the cutting tool while most of them extend along the rake angle of cutting tool. The plastic deformation is a discrete process in the atomic scale while it is generally considered as continuum process in the macroscopic scale. The first slipping-band becomes the boundary of the following slipping process which leads to the different generation mechanism of the following dislocation. The dislocation density, cross-slip and junction increase with the increasing of strain rate. The dislocation density is gradually decreased far away from materials surface which justifies that most of the dislocation ought to be generated by the surface defects than by the internal defects. The dislocation can also be regenerated by the complicated dynamic behavior of the existing dislocations without external loading which lead to the complexity of the deformation process. The slipping-band can be considered as the green-channel of stress relaxation as the maximum stress is originated at the tool-workpiece contact area and gradually decreased in the further area.

Investigation on the influence of aerostatic pressure upon surface generation in flycutting

Single-point diamond flycutting is an important technology for cutting flat KH2PO4 (potassium dihydrogen phosphate) crystals of large size. However, there always exist some undesirable waviness errors on the machined surface, which can directly reduce the optical performance of the potassium dihydrogen phosphate crystals. This article presents a kind of low-frequency waviness errors with wavelength about 26 mm along the feeding direction in single-point diamond flycutting, which has not been described yet. In order to find the main source of the mentioned waviness errors, the relationship between the displacement of the cutting tool and the aerostatic pressure was quantitatively studied for the first time. And then, surface simulation considering the aerostatic pressure fluctuations was carried out based on the relationship. Besides, a novel method that can achieve online submicron feeding along axial direction in single-point diamond flycutting without complex structure was proposed considering the spindle motion errors, the spindle dynamic characteristics and the aerostatic pressure. The experimental results validate that the mentioned waviness errors are mainly generated by the bolt stretched phenomenon and deformation of the big disk flycutting head due to the aerostatic pressure fluctuations. And the proposed method can achieve a cutting depth of about 120 nm when the aerostatic pressure increases from 0.52 to 0.56 MPa, which can reduce the cutting force and is beneficial for the performance of single-point diamond flycutting.

Investigation on the generation of the waviness errors along feed-direction on flycutting surfaces

Ultra-precision single-point diamond flycutting (SPDF) is an irreplaceable technology for cutting KH2PO4 (KDP) crystals with large size. However, some undesirable waviness errors along feed-direction exist on the machined surface, which could greatly deteriorate the optical performance of KDP crystals. The spindle dynamic characteristic of SPDF plays an important role in the formation of such waviness errors. This paper presents an on-line measurement method with five-capacitance displacement sensors in nanometer range for monitoring the motion errors of the aerostatic spindle. An error transform theory which is based on kinematic error propagation was introduced to obtain the three-dimensional trajectory of the cutting tool. Then, the spindle motion errors and the cutting tool trajectory were analyzed in frequency domain to investigate the main source of the waviness errors. Simultaneously, the three-dimensional topography of work-piece was simulated by combining the motion trajectory and the geometrical morphology of the cutting tool. The results showed that the waviness errors along feed-direction were caused by the spindle rotation fluctuation with a frequency about 10.8 Hz, and the topography simulations showed good agreement with the machining results. Besides, the experimental results indicated that the error can be diminished by changing the spindle control system to the digital control method. This study established the contact between the measured spindle motion errors and the machined surfaces, which contributes to deeper understanding of the dynamic characteristics of the spindle in SPDF.

Wafer-level hermetic thermo-compression bonding using electroplated gold sealing frame planarized by fly-cutting

In this paper, a novel wafer-level hermetic packaging technology for heterogeneous device integration is presented. Hermetic sealing is achieved by low-temperature thermo-compression bonding using electroplated Au micro-sealing frame planarized by single-point diamond fly-cutting. The proposed technology has significant advantages compared to other established processes in terms of integration of micro-structured wafer, vacuum encapsulation and electrical interconnection, which can be achieved at the same time. Furthermore, the technology is also achievable for a bonding frame width as narrow as 30 μm, giving it an advantage from a geometry perspective, and bonding temperatures as low as 300 °C, making it advantageous for temperature-sensitive devices. Outgassing in vacuum sealed cavities is studied and a cavity pressure below 500 Pa is achieved by introducing annealing steps prior to bonding. The pressure of the sealed cavity is measured by zero-balance method utilizing diaphragm-structured bonding test devices. The leak rate into the packages is determined by long-term sealed cavity pressure measurement for 1500 h to be less than Pa m3s−1. In addition, the bonding shear strength is also evaluated to be higher than 100 MPa.

Investigation on the generation of the medium-frequency waviness error in flycutting based on 3D surface topography

Undesirable medium-frequency waviness error along the cutting direction was often left on the machined surface of KDP crystals adopting ultraprecision single-point diamond flycutting (SPDF), reducing the optical performance of KDP crystals and restricting their capability in the inertial confinement fusion (ICF). In order to reduce such medium-frequency waviness error, an indirect method for investigating the generation of the error was proposed in this paper. The tool-tip vibration was indirectly extracted by combining the intermittent cutting trajectory of the flycutting process and the medium-frequency waviness error, which was extracted from the 3D surface topography using 2D wavelet transform method. The main frequency of the extracted tool-tip vibration was calculated and compared with the modals of the machine tool spindle system, which was obtained by FEM analysis and modal test. Finally, an improved spindle system was proposed based on the FEM analysis, and contrast tests between origin and improved machine tool were carried out. Results show that the tool-tip vibration can be effectively extracted by the proposed method, which deduces that the vibration that produced the medium-frequency waviness error is mainly generated by the sixth-order modal of the spindle system. In addition, the quality of the machined surface has been greatly improved with the improved spindle system.

Research on the Shape Precison of the Micro-groove in the Silicon under Diamond Fly-cutting

Based on the mechanical physical characteristics of the silicon wafers and the superior processing character of the diamond fly-cutting, the diamond fly-cutting was applied to the machining of the microgroove in the silicon, and the effect of the processing parameters on the machining shape precision of the microgroove arrays in the silicon was mainly studied. Firstly, the cutting model of the microgroove in cross section under the diamond fly-cutting was established and the theoretical curvature radius of the microgroove was obtained. Secondly, the shape precision of the microgroove is deduced. Finally, the processing experiment of the microgroove in the silicon was carried out. The experimental results reveal that the higher spindle speed n and the smaller cutting feed f are beneficial to machine the better microgroove in the silicon, but it is important to choose the appropriate cutting depth to machine the better microgroove in the silicon.

Control of a Thermal Actuator for UP-milling with Multiple Cutting Edges

Ultra-precision (UP) milling processes can be dramatically sped up, and thus made more cost-efficient, by utilizing tools with multiple cutting edges. This, however, requires a dedicated actuating mechanism to interactively control the cutting radius of the individual cutting edges with nanometer precision. This paper presents recent advances in developing a tool holder for diamond fly-cutting that enables the alignment of two or more cutting edges via thermal elongation of the substrate material. After building a comprehensive model of the actuator and verifying it in a static test setup, a closed-loop control was developed that allows setting the elongation in a static setup with nanometer accuracy.

Study on Influence Laws of Surface Roughness of Micro-Groove in Single Crystal Silicon under Diamond Fly-Cutting

Single crystal silicon has both important application value in the fields of micro-optics and MEMS, and it has been considered as one of the most difficult-to-cut materials because of its hardness and brittleness. Removal mechanism of the silicon was discussed, and the model of undeformed chip thickness was established in this article. According to the data of micro-groove surface roughness from the diamond fly-cutting experiment, the nonlinear relationship curve, between the largest undeformed chip thicknesshmaxand microgroove surface roughnessRa,were obtained using Gaussian-fitting principle, and the regression equation of the fitting curve was also got. Thus the prediction mathematical model of microgroove surface roughness was derived. The influence laws of the main working parameters on theRawere obtained based on the result of this experiment and the response surface of the prediction model, and some conclusions were summarized: the surface roughnessRaof microgroove in the single crystal silicon decreases with the decrease of the cutting depthap, the feed f and the increase of the spindle speednunder the diamond fly-cutting; the experimental results also showed that feedfaffects the value ofRavery much, cutting depthapless, and spindle speednthe least.

High Speed Machining Method of Large-Size Precision Freeform Mirror

This study describes the non-rotationally symmetric diamond turning (XZC turning) for producing large-size precision freeform mirror. This is a high speed machining method as compared with the traditional XYZ diamond milling or fly-cutting. Moreover, the application of this method is a key factor in the development of the ultra-precision light-weight freeform mirror for outer space use. This report introduces these cutting-edge approaches.

Research on single-point diamond fly-grooving of brittle materials

The purpose of this paper is to investigate the machining mechanisms that accompany the single-point diamond fly-cutting operation in grooving of brittle materials. Single-point diamond fly-cutting is widely used in precision machining of free-form optics, semiconductor devices, and micro-electromechanical system (MEMS) components among many others. The undeformed chip zone was analyzed and its relation to the critical brittle/ductile transition depth of cut was discussed. Then, a mechanics-based model was proposed to describe the material stress condition under the diamond tool. The machining parameters were incorporated into the model to understand fly-cutting behavior. It was shown that the fly-cutting technique is highly suitable for the ductile removal of brittle materials by generating large compressive pressures in the chip formation zone. This condition can be further enhanced by a small feedrate and a large negative rake angle of the diamond tool used. The theoretical results were substantiated and verified by fly-grooving experiments performed on mono-crystalline silicon.

Research on compensation of suction deformation error of potassium dihydrogen phosphate crystal

Potassium dihydrogen phosphate (KDP) crystals used in high power laser systems require high figure accuracy. Deformation caused by vacuum suction is one of the most significant factors affecting the final surface figure accuracy. It is difficult to compensate the error caused by the suction deformation when using a single point diamond flycutting method. This paper presents a spiral turning method to machine KDP crystals on a common ultraprecision lathe, and the transfer rule and compensation theory of the suction deformation error are studied. The in situ measurement of deformation error is accomplished with a displacement test apparatus, which can acquire submicron precision, and then compensates for it by utilizing the three-axis servo control technology. Meanwhile, cutting parameters are strictly controlled to achieve full-aperture ductile material removal. The compensation experiments for both reflected and transmitted wavefront error are carried out on a Φ270 mm KDP crystal and the transmission wavefront error of 0.591λ (peak-to-valley, λ = 632.8 nm) and 25 nm/cm (gradient root-mean-square) are obtained after one compensation with full-aperture surface roughness of about 2 nm RMS.

Topography simulation and vibration analysis of ultra-precision diamond flycutting micro V-groove

Ultra-precision diamond flycutting is an important method to manufacture micro V-groove with sub-micrometer form accuracy. The relative vibration between the tool and the work piece is one of the most critical factors which determine the manufacturing precision during the flycutting process. In order to restrain the vibration influence, a vibration analysing method in flycutting process is presented. The dynamical model of micro V-groove is established according to the character of ultra-precision diamond flycutting. Three-dimensional topography is simulated with and without vibration. The V-groove surface roughness is analysed based on the spatial frequency spectrum. Ultra-precision flycutting experiments are carried out, and the V-groove surface roughness is measured by the stylus profilometer along the V-groove. The vibration is identified on the basis of spectrum analysis results. The vibration character of flycutting system is obtained, and the cutting parameters are optimised.

Effect of surface condition and bonding pressure on quality of diffusion bonded high purity copper for linear collider accelerator structures

Tests have been carried out to assess the feasibility of diffusion bonding as a fabrication technology for vacuum tight joints in linear accelerator cells for the Next Linear Collider. High purity copper specimens were diffusion bonded over a range of temperatures from 400 to 1000°C, under high (3.45 MPa) and low (3.45 kPa) bonding pressures, and at two different diamond machined surface finishes. Experiments showed that diffusion bonds with strengths equal to, or greater than, that of silver brazed joints could be made at temperatures ≥700°C at the 3.45 MPa bonding pressure, or ≥800°C at the 3.45 kPa bonding pressure. Partial strength diffusion bonds were made at temperatures as low as 400°C at the high bonding pressure, whereas no bonding (zero strength) was observed at temperatures below 700°C at the low bonding pressure. Observations of the fracture surfaces of the diffusion bonded specimens showed that bonding begins by point asperity contact. At low bonding pressures, surfaces created by diamond turning of annealed copper specimens produce higher strength bonds than those created by diamond flycutting of unannealed surfaces, whereas at higher bonding pressures the effect of surface finish was less important.

斜入射Ｘ線反射鏡用数値制御ダイヤモンド切削装置

斜入射Ｘ線反射鏡用数値制御ダイヤモンド切削装置

工具切込み量の回転角同期制御による非球面鏡の加工

A numerically controlled, precision diamond flycutting mechanism has been developed, where tool cutting depth is dynamically controlled in synchronizing to tool rotational angle. This technique permits fabrication of aspheric mirrors used in soft X-ray application equipments, with a contour accuracy of 0.1 μm peak to valley. A piezoelectric stack actuator is used for tool cutting depth control. To correct hystcresis and drift with a piezo-acytuator, a referential piezo-actuator with the same characterisitics as that of the tool is driven in a closed roop control. The signal supplied to the referential piezo-actuator simultaniously drives the tool actuator. Aspherical mirror and a toroidal mirror are cut to evaluate developed flycutting technology.