Elastic Emission Machining Research Articles

Rolling model analysis of material removal in elastic emission machining

Elastic emission machining (EEM) is one of the most effective technologies for obtaining ultra-smooth surface. The polishing particle is supplied to a specific position on the workpiece surface by the polishing wheel and chemically reacts with the workpiece to realize non-destructive material removal. However, the interaction between polishing wheel and slurry, as well as the mechanism of atom removal remain unclear. In this study, the mutual dynamic interaction between the polishing wheel and slurry is considered in a three-dimensional state, and a rolling model is developed to analyse the energy transfer during atom removal process. The movement of the fluid and particles is calculated using computational fluid dynamics, and the energy required for atom removal is calculated based on molecular dynamics simulation. The effectiveness of the rolling model is verified by comparing with the material removal profile obtained from the experiments and the rolling model. The rolling model explains how the particle can break the back bond of atom on the workpiece surface to achieve material removal. The study findings suggest that the energy required for atom removal is primarily supplied by the fluid. This understanding of the energy source provides valuable insights for proposing methods to enhance the material removal rate. Finally, in the surface polishing experiment, the use of the EEM results in the achievement of an ultra-smooth surface with roughness of 0.1 nm root-mean-square, demonstrating the excellent ability of EEM to effectively reduce surface roughness.

Polishing Approaches at Atomic and Close-to-Atomic Scale

Roughness down to atomic and close-to-atomic scale is receiving an increasing attention in recent studies of manufacturing development, which can be realized by high-precision polishing processes. This review presents polishing approaches at atomic and close-to-atomic scale on planar and curved surfaces, including chemical mechanical polishing, plasma-assisted polishing, catalyst-referred etching, bonnet polishing, elastic emission machining, ion beam figuring, magnetorheological finishing, and fluid jet polishing. These polishing approaches are discussed in detail in terms of removal mechanisms, polishing systems, and industrial applications. The authors also offer perspectives for future studies to address existing and potential challenges and promote technological progress.

Research progress of elastic emission machining in optical manufacturing

The predecessor of China Optics was China Optics and Applied Optics Digest, which was founded in 1985. At that time, it was the only retrieval journal in the field of optics in China. At the end of 2008, China Optics and Applied Optics Digest was renamed

On the characterization of a 1 m long, ultra-precise KB-focusing mirror pair for European XFEL by means of slope measuring deflectometry.

Recently, the European X-Ray Free Electron Laser (XFEL) has successfully produced its first X-ray photon pulse trains. This unique photon source will provide up to 27 000 photon pulses per second for experiments in different fields of science. In order to accomplish this, ultra-precise mirrors of dedicated shape are used to guide and focus these photons along beamlines of up to 930 m in length from the source in the undulator section to the desired focal point at an experimental station. We will report on a Kirkpatrick-Baez-mirror pair designed to focus hard-X-rays in the energy range from 3 to 16 keV to a 100 nm scale at the SPB/SFX instrument of the European XFEL. Both mirrors are elliptical cylinder-like shaped. The figure error of these 1 m long mirrors was specified to be better than 2 nm pv in terms of the height domain; this corresponds to a slope error of about 50 nrad rms (at least a best effort finishing is requested). This is essential to provide optimal experimental conditions including preservation of brilliance and wavefront. Such large and precise optics represents a challenge for the required deterministic surface polishing technology, elastic emission machining in this case, as well as for the metrology mandatory to enable a precise characterization of the topography on the mirror aperture. Besides the slope errors, the ellipse parameters are also of particular interest. The mirrors were under inspection by means of slope measuring deflectometry at the BESSY-NOM slope measuring profiler at the Helmholtz Zentrum Berlin. The NOM measurements have shown a slope error of 100 nrad rms on a aperture length of 950 mm corresponding to a residual figure deviation ≤20 nm pv for both mirrors. Additionally we found a strong impact of the mirror support conditions on the mirror shape finally measured. We will report on the measurement concept to characterize such mirrors as well as to discuss the achieved results.

Effect of the surface roughness on X-ray absorption by mirrors operating at extremely small grazing angles.

This study theoretically analyzes an increase in X-ray absorption by a grazing incidence mirror due to its surface roughness. We demonstrate that the increase in absorption can be several hundred times larger than predicted by the Nevot-Croce formula. As a result, absorption enhances by several times compared to a perfectly smooth mirror despite the extremely small grazing angle of an incident X-ray beam (a fraction of the critical angle of the total external reflection) and the high quality of the reflecting surface (the roughness height was 0.5 nm in modeling). The main contribution to the absorption increase was dictated by the mid-scale roughness (waviness) of the virgin substrate surface, whose quality thus defines an absorption enhancement. The approach was applied to the analysis of two real mirrors used in a synchrotron (BESSY-I) and a European X-ray free-electron laser (XFEL) beamline. The modern surface finishing technology of elastic emission machining provides extremely low substrate waviness, guaranteeing the negligible effect of the surface roughness on the absorption increase.

Novel Disc Hydrodynamic Polishing Process and Tool for High-Efficiency Polishing of Ultra-Smooth Surfaces.

Nowadays, large aspheric surfaces, including non-rotationally symmetric surfaces, are increasingly used in ground- and space-based astronomical instruments. The fabrication of these surfaces with sub-micrometric form accuracy and nanometric surface finish, especially for hard and difficult-to-machine materials, has always been a challenge to the optics industry. To produce ultra-smooth surfaces efficiently without subsurface damage and surface scratches, a novel disc hydrodynamic polishing (DHDP) process is proposed through the combination of elastic emission machining and fluid jet polishing. Firstly, the polishing tool for DHDP was carefully designed and the feasibility of the proposed method was experimentally verified. The liquid film was found to act as a carrier of abrasive grains between the polishing tool and the polished surface. Next, computational fluid dynamics (CFD) was used to study the effects of process parameters on the slurry film flow in DHDP. Finally, preliminary experiments were conducted to verify the CFD simulations. The experimental data reasonably agree with the simulation results, which show that increasing rotational speed has no influence on the film thickness for the polishing tool without grooves, but leads to increased film thickness for the polishing tool with grooves. Moreover, DHDP can efficiently reduce the surface roughness and acquire ultra-smooth surfaces without subsurface damage and scratches.

Flow field analysis of the thin fluid film in disc hydrodynamic polishing

Nowadays, large aspheric surfaces, including non-rotationally-symmetric surfaces, are increasingly used in ground and space-based astronomical instruments. The fabrication of these surfaces with sub-micrometric form accuracy and nanometric surface finish, especially for hard and difficult-to-machine materials, has always been a challenge to the optics industry. To efficiently produce ultra-smooth surfaces without the subsurface damage and surface scratches, a novel Disc Hydrodynamic Polishing (DHDP) is proposed by the combination of Elastic Emission Machining (EEM) and Fluid Jet Polishing (FJP). Firstly, the polishing tool for DHDP was carefully designed and the feasibility of the proposed method was experimentally verified. It is interesting to find that the liquid film acts as a carrier of abrasive grains between the polishing tool and polished surface. Then, computational fluid dynamics (CFD) was used to study the effects of process parameters on the slurry film flow in disc hydrodynamic polishing. Finally, preliminary experiments are conducted to verify the CFD simulations. The experimental data reasonably agree with the simulation results. The results also show that increasing rotation speed has no influence on the film thickness for polishing tool without grooves, but leads to increased film thickness for polishing tool with grooves. The film thickness increases as the inlet pressure is increased for these two polishing tools.

Atmospheric, Non-Contact and High Speed Electro Chemical Machining Processes for X-ray Optics

This paper will discuss efforts to design an atmospheric, non-contact, low cost/high speed electrochemical machining process to produce next-generation ellipsoidal x-ray optics via a scalable pulse-reverse electrochemical manufacturing approach. Unlike conventional electrochemical surface finishing processes, the pulse-reverse process does not require low conductivity/high viscosity electrolytes or the addition of hazardous chemical species (like HF) to remove the oxide film associated with electropolishing of passive and strongly passive materials like Si. This paper will focus on the potential of pulse/pulse reverse electrochemical machining process to produce optics such as Kirkpatrick-Baez mirrors and compound refractive lenses for X-ray optic technologies being used at synchrotron facilities. Initial trials of this atmospheric, non-contact process demonstrated a material removal rate of 40 µm/h, 100 times faster than the currently used Elastic Emission Machining technique.

Atmospheric, Non-Contact and High Speed Electro Chemical Machining Processes for X-Ray Optics

High resolution X-ray focusing optics is critical component in many spatially resolved techniques at many synchrotron facilities, such as micro X-ray fluorescence, micro-diffraction, and micro-spectroscopy. In order for these optics to achieve modern capability goals, they must embody various key performance attributes such as a minimum in spatial resolution, a maximum in focusing efficiency, a practical working distance (no more than a few meters), and ideally robust achromaticity (negligible photon energy dependence). The state of the art in X-ray optics encompasses, among others, diffractive zone plate optics, Kirkpatrick-Baez (K-B) mirrors, and compound refractive lenses (CRLs). Among these, only K-B mirrors provide highly efficient collection of X-ray photons and essentially perfect achromaticity, but require elliptical mirrors of exceptionally precise figure and placement, as well as sub-nanometer smoothness1. In attempting to identify potential advances in X-ray optics beyond this state of the art, one promising solution is the design of single-bounce, axially symmetric mirror optics with parabolic inner profiles capable of focusing x-rays simultaneously in two orthogonal directions, which may overcome the long focal length limitation of KB mirrors. Manufacture of such precise optics as these novel one-bounce mirrors or the traditional K-B mirrors requires highly advanced surface finishing techniques. Silicon is mostly used in this application due to its low CTE, low thermal deformation, low z, high reflectivity, and low radiation adsorption. The conventional manufacturing approaches used to prepare aspherical, low roughness, and high-z coated silicon mirrors, included Ion Beam Figuring, Elastic Emission Machining (EEM), Plasma Machining, Lapping/Polishing2,3. Of these techniques the Plasma and Ion Beam approaches require vacuum atmosphere for processing limiting the size of the components that can be produced. Meanwhile, EEM can achieve better final finishes (up to 1 A) under atmospheric, non-contact conditions, however it is several orders of magnitude slower (0.1 to 0.001 µm/min) than these approaches. Furthermore, contact machining techniques like Lapping/Polishing tend to lead to surface defects that must be removed prior to mirror usage. Therefore, the design of low cost/high speed machining and polishing systems that can form high resolution x-ray focusing optics over large mirror areas is critical for the formation of next generation of x-ray optics. This paper will discuss ongoing efforts by Faraday to design an atmospheric, non-contact, low cost/high speed electrochemical machining process to produce next-generation ellipsoidal x-ray optics via a scalable pulse-reverse electrochemical manufacturing approach. Unlike conventional electrochemical surface finishing processes, the pulse-reverse process does not require low conductivity/high viscosity electrolytes or the addition of hazardous chemical species (like HF) to remove the oxide film associated with electropolishing of passive and strongly passive materials like Si. This paper will focus on the potential of pulse/pulse reverse electrofinishing process to produce optics such as Kirkpatrick-Baez mirrors and compound refractive lenses for X-ray optic technologies being used at synchrotron facilities. In particular, this talk will discuss fundamental processing techniques and the performance observed in ongoing studies. Initial trials of atmospheric, non-contact process demonstrated a material removal rate of 40 µm/h which is 100 times faster than currently used EEM technique. Acknowledgement This material is based upon ‎work supported by the Department of Energy under ‎Award No‎. ‎DE‎-‎ SC0015201. References S. Matsuyama., et.al., “Textbook for hard X-ray focusing with Kirkpatrick-Baez optics.” Online resource: http://cheiron2009.spring8.or.jp/images/PDF/Practicals?16_29XLU.pdf. Accessed 15 Oct 2015. H. Takino., et.al., “ Ultraprecision Machining of Optical Surfaces.” Nikon Corporation.Y. Mori., et.al., “Development of plasma chemical vaporization machining and elastic emission machining systems for coherent X-ray optics.” SPIE 4501, 2001.

50-nm-resolution full-field X-ray microscope without chromatic aberration using total-reflection imaging mirrors

X-ray spectromicroscopy with a full-field imaging technique is a powerful method for chemical analysis of heterogeneous complex materials with a nano-scale spatial resolution. For imaging optics, an X-ray reflective optical system has excellent capabilities with highly efficient, achromatic, and long-working-distance properties. An advanced Kirkpatrick–Baez geometry that combines four independent mirrors with elliptic and hyperbolic shapes in both horizontal and vertical directions was developed for this purpose, although the complexity of the system has a limited applicable range. Here, we present an optical system consisting of two monolithic imaging mirrors. Elliptic and hyperbolic shapes were formed on a single substrate to achieve both high resolution and sufficient stability. The mirrors were finished with a ~1-nm shape accuracy using elastic emission machining. The performance was tested at SPring-8 with a photon energy of approximately 10 keV. We could clearly resolve 50-nm features in a Siemens star without chromatic aberration and with high stability over 20 h. We applied this system to X-ray absorption fine structure spectromicroscopy and identified elements and chemical states in specimens of zinc and tungsten micron-size particles.

Preliminary study of disc hydrodynamic polishing.

In this paper, a developed polishing method based on elastic emission machining and Jules Verne-a variation on fluid jet polishing-is presented. This method is named disc hydrodynamic polishing (DHDP). A computational fluid dynamics (CFD)-based model that consists of a CFD model and an erosion model is introduced to predict the surface roughness obtained by DHDP. The performance of DHDP is studied by experiments. The slurry used in the experiments comprises 95% deionized water and 5% cerium oxide particles. Fused-silica glass is chosen as the workpiece. After the experiments, an ultrasmooth surface without cracks is obtained. The simulation results principally coincide with the experimental results. The experimental results show that the actual roughness is slightly less than the prediction and smaller particles are more favorable for obtaining a better surface roughness.

Present research status of piezoelectric bimorph mirrors in synchrotron radiation sources

The third-generation synchrotron radiation sources are widely used in physics, chemistry, material science, etc. due to their light beams with high brilliance and low emittance. In order to efficiently utilize such light beams for scientific research, reflective mirrors with excellent figure quality are required. The reflective mirrors on the beamlines of synchrotron radiation sources consist of fixed polished shape mirrors and bendable mirrors. Bendable mirrors have been attracting the attention of the synchrotron radiation community because their curvatures can be varied to realize different focusing properties. Classical bendable mirrors are realized by applying mechanical moment at the ends of the mirror substrates. In this paper, we introduce a new concept of bendable mirrors, X-ray adaptive mirrors which are based on the adaptive optics technology and the properties of piezoelectric bimorph systems. X-ray adaptive mirrors exhibit many advantages over the classical bendable mirrors, such as mechanics-free, figure local corrections, and good focusing properties. The piezoelectric bimorph mirrors have been used in astronomy to correct the wavefront distortions introduced by atmospheric turbulence in real time. The piezoelectric bimorph mirror was first introduced into the field of synchrotron radiation by European Synchrotron Radiation Facility (ESRF) in the 1990s for making an X-ray reflective mirror. Compared with astronomy community, synchrotron radiation community is not interested in high-speed wavefront correction, but looking for the ultimate precision of the surface shape of piezoelectric bimorph mirror. In the second part of this paper, the usual structure and working principle are briefly described. Piezoelectric bimorph mirrors are laminated structures consisting of two strips of an active material such as zirconate lead titanate (PZT) and two faceplates of a reflecting material such as silicon. A discrete or continuous control electrode is located between the interfaces of PZT-PZT, while two continuous ground electrodes are located between the interfaces of Si-PZT. The PZTs that are polarized normally to their surface, any voltage applied across the bimorph results in a different change of the lateral dimensions of two PZTs, thereby leading to a bending of the whole structure. The relationship between the curvature of the bending mirror and voltage is given. In the third part of this paper, the technical issues as well as the design concepts are discussed in detail. Several Si-PZT-PZT-Si bimorph mirrors are first fabricated and tested by ESRF. The dimensions of each of them are 150 mm in length, 4045 mm in width, and 1518 mm in thickness. PZT is selected as an active material because of its high coupling factor, high piezoelectric coefficient, and high Curie temperature. The faceplates need to be easy to polish such as silicon and silica. Owing to the symmetrical layered structure Si-PZT-PZT-Si, the mirror is less sensitive to temperature variations from the process of bonding and polishing. The bimorph mirrors are confirmed to be promising by experimental tests. As the state-of-art polishing technique, elastic emission machining (EEM) becomes available commercially, and diamond light source brings EEM into the bimorph mirror to achieve a novel adaptive X-ray mirror coupling adaptive zonal control with a super-smooth surface. This super-polished adaptive mirror becomes the first optics with a bendable ellipse with sub-nanometer figure error. Spring-8 fabricates an adaptive mirror with different structures, and two strips of PZTs are glued to the side faces of the mirror. This mirror shows a diffraction-limited performance. Finally, the wavefront measuring methods and control algorithm are introduced. Wavefront measuring devices used in the metrology cleanroom include long trace profiler, nanometer optics component measuring machine, and interferometer. At-wavelength measuring methods used on the beamline include pencil-beam method, phase retrieval method, X-ray speckle tracking technique, and Hartmann test. The wavefront control algorithm is aimed at obtaining the voltages applied according to the inverse of the interaction matrix.

Optics for coherent X-ray applications.

Developments of X-ray optics for full utilization of diffraction-limited storage rings (DLSRs) are presented. The expected performance of DLSRs is introduced using the design parameters of SPring-8 II. To develop optical elements applicable to manipulation of coherent X-rays, advanced technologies on precise processing and metrology were invented. With propagation-based coherent X-rays at the 1 km beamline of SPring-8, a beryllium window fabricated with the physical-vapour-deposition method was found to have ideal speckle-free properties. The elastic emission machining method was utilized for developing reflective mirrors without distortion of the wavefronts. The method was further applied to production of diffraction-limited focusing mirrors generating the smallest spot size in the sub-10 nm regime. To enable production of ultra-intense nanobeams at DLSRs, a low-vibration cooling system for a high-heat-load monochromator and advanced diagnostic systems to characterize X-ray beam properties precisely were developed. Finally, new experimental schemes for combinative nano-analysis and spectroscopy realised with novel X-ray optics are discussed.

Machining Property in Smoothing of Steeply Curved Surfaces by Elastic Emission Machining

In optics fields, an extremely smooth surface with a complex form is necessary for the lens and mirror used in advanced optical systems, although their surfaces are still difficult to polish. Here, we describe the machining of steeply curved surfaces by rotating-sphere EEM (elastic emission machining). Thus far, the use of rotating-sphere EEM has been limited to flat and gradually curved surfaces in spite of its high performance. We demonstrated the successful application of rotating-sphere EEM to a glass cylinder, resulting in a decrease in RMS (root mean square) surface roughness from 0.30 to 0.16nm.

100 µm-size stationary spot machining in elastic emission machining

Recently, by using various ultraprecision machining methods, optical devices having both nanometer-level figure accuracy and nanometer-level smoothness have become obtainable. However, improvement of the spatial resolution in figuring is still strongly required, particularly when the shape of optical devices is complicated. We have been developing a figure correction system using elastic emission machining (EEM). In this study, an EEM nozzle head having a minute aperture with a diameter of less than 60 µm was developed. The minute hole was prepared by micro-electrical discharge machining (EDM). A stationary spot profile with a diameter of 100 µm was experimentally obtained. Using the developed nozzle, spatial resolution better than 100 µm is expected to be realised in the EEM figuring system.

A Precision Grazing-incidence Angle Error Measurement of a Hard X-ray Condenser Mirror Using Single-grating Interferometry

Third-generation synchrotron radiation facilities enable us to use X-rays of extremely high brightness and low emittance, which are efficiently concentrated into a nanoscale area by a focusing device. Such progress has significantly enhanced the throughput of X-ray analyses based on scanning microscopy. On the other hand, the spatial resolution of scanning microscopy directly depends on the focal spot size. Many diffractive [1, 2], refractive [3, 4], and reflective [5, 6] focusing devices are currently available for producing small focal spots. Reflective optics realize the highest throughput with a sufficiently long working distance. Furthermore, among the above-listed focusing devices, reflective devices produce the smallest focal spot size in the hard X-ray region. A total reflection mirror may attain sub-30 nm focal spot size [7], while a multilayer mirror may attain sub-10 nm focal spot size [8]. The achievable focal spot size is significantly degraded by errors in the mirror shape and misalignment of grazing-incidence angle. In the hard X-ray region, the focusing mirror surface requires accuracies below 2 nm PV and 1 nm PV for sub-30 nm and sub-10 nm focusing, respectively. The error in the grazing-incidence angle must not exceed 0.5 × 10−6 rad and 0.1 × 10−6 rad for sub-30 nm and sub-10 nm focusing, respectively. Current advances in fabrication and mirror testing technologies have realized highly accurate deterministic figuring processes that can meet these requirements. Fabrication techniques include ion beam figuring [9, 10] and elastic emission machining (EEM) [11], while figure testing is achieved using optical interferometers [12, 13] or slope profilers [14, 15, 16]. In contrast, alignment accuracy is still evaluated by conventional beam profiling methods such as knife-edge scanning methods. The alignment is optimized by an iterative procedure of beam profiling and glazing-incidence angle adjustment. This procedure is very time-consuming and frequently introduces a significant profiling error from shape imperfections and/or vibration of the object to be scanned. Accordingly, the grazing-incidence alignment often determines the achievable focal spot size. The error in the grazing incidence angle generates a coma aberration, which is essentially a wavefront distortion with a cubic function. Hence, adjusting the grazing-incidence angle by monitoring the wavefront shape is possible. The wavefront shape can be characterized by several methods, such as phase retrieval [17] or ptychography [18, 19]. However, to obtain a wavefront shape of accuracy smaller than λ/4, the limit imposed by Rayleigh's criterion, large amounts of intensity information are required. In addition, these methods are unsuitable for the shot-by-shot measurements demanded in X-ray free-electron laser (XFEL) focusing.

Effect of focusing flow on stationary spot machining properties in elastic emission machining

Ultraprecise optical elements are applied in advanced optical apparatus. Elastic emission machining (EEM) is one of the ultraprecision machining methods used to fabricate shapes with 0.1-nm accuracy. In this study, we proposed and experimentally tested the control of the shape of a stationary spot profile by introducing a focusing-flow state between the nozzle outlet and the workpiece surface in EEM. The simulation results indicate that the focusing-flow nozzle sharpens the distribution of the velocity on the workpiece surface. The results of machining experiments verified those of the simulation. The obtained stationary spot conditions will be useful for surface processing with a high spatial resolution.

ノズル型EEM(Elastic Emission Machining)における100μｍ微小スポット加工の加工特性

ノズル型EEM(Elastic Emission Machining)における100μｍ微小スポット加工の加工特性

C08 Elastic emission machining の加工点における粉末粒子挙動(OS10 班磨技術(2))

C08 Elastic emission machining の加工点における粉末粒子挙動(OS10 班磨技術(2))

Recent development in Kirkpatrick–Baez focusing systems at the ESRF

European Synchrotron Radiation Facility (ESRF) in-house designed Kirkpatrick–Baez (KB) focusing systems have been extensively used for high efficiency beam focusing over the past years. More recently however, increasing interest in nanofocusing techniques has directed our development efforts towards more compact, higher stability designs for dynamic focusing systems in which the optimization of numerous parameters enables mirror bending approaching its mechanical limits. Simultaneously, progress in fixed focus mirror fabrication techniques – notably ion beam figuring, differential deposition and elastic emission machining – now make the fabrication of highly elliptical, fixed focus X-ray optics an interesting option. This has simplified conception (no bending mechanics) which in turn has led to the design of miniaturized KBs.A general overview of these recent developments in both dynamic bending and fixed focus KB systems is presented.