Ultra-precision Manufacturing Research Articles

Frequency-dependent nonlinear dynamic stiffness of aerostatic bearings subjected to external perturbations

The dynamic characteristics of aerostatic bearings are critical to the performances of ultra-precision manufacturing equipment. Dynamic characteristics have recently been recognized to be significant to the dynamic stiffness of aerostatic bearings, and related research has seldom been reported up till now. In this paper, numerical simulations and experiments are carried out to investigate the influence of perturbations on the dynamic stiffness of aerostatic bearings. The thrust bearings of an aerostatic bearing spindle are selected for simulations and experiments, while the journal bearing is used as frictionless guide way. Dynamic mesh method is adopted to simulate the variation of gas film, and numerical simulations are performed by using ANSYS-Fluent-software based on the perturbation theory. Perturbations are generated via voice coil motor under different conditions in experiments. Simulations and experimental results reveal that the dynamic stiffness is much more sensitive to the perturbation frequency rather than the nanoscale perturbation amplitude. For the same amplitude of displacement perturbations, the axial stiffness coefficient increases whereas the axial damping coefficient decreases with the increase of perturbation frequency. It indicates that the dynamic stiffness of aerostatic bearings can be significantly improved by using active control of the gas film to generate perturbations with high frequency.

Quantification of Ultraprecision Surface Morphology using an Algebraic Graph Theoretic Approach

Assessment of progressive, nano-scale variation of surface morphology during ultraprecision manufacturing processes, such as fine-abrasive polishing of semiconductor wafers, is a challenging proposition owing to limitations with traditional surface quantifiers. We present an algebraic graph theoretic approach that uses graph topological invariants for quantification of ultraprecision surface morphology. The graph theoretic approach captures heterogeneous multi-scaled aspects of surface morphology from optical micrographs, and is therefore valuable for in situ real-time assessment of surface quality. Extensive experimental investigations with specular finished (Sa ∼ 5nm) blanket copper wafers from a chemical mechanical planarization (CMP) process suggest that the proposed method was able to quantify and track variations in surface morphology more effectively than statistical quantifiers reported in literature.

An Improved Method for Generating Cutter Points Based on Required Form Accuracy of the Machining Surface

Recently, freeform surfaces are widely used in optical field. Fabrication of freeform surface optics needs high machining accuracy and high efficiency simultaneously. Using the present ultraprecision manufacturing technologies, the form accuracy of freeform surfaces can reach submicrometric or even nanometer range but at the cost of low efficiency; moreover, the form accuracy cannot be predicted; the number and the position of cutter points cannot be accurately controlled before practical machining. A novel strategy of cutter points distribution is proposed in the paper, which is based on the required accuracy of the freeform surface and the machining efficiency can be improved by eliminating redundant cutter points on the processing trajectory. The new idea is detailed, simulations are conducted, and experiments are done to verify the feasibility of the proposed method in fabricating two sinusoidal ring surfaces.

Research Precision CNC Machine Error Analysis Hot Weights

The level of industrial strength is a measure of an important indicator of a country's pillar industry level is machinery manufacturing, in modern times, the rapid development of manufacturing technology, precision and ultra-precision manufacturing technology has become an important part of modern machinery processing and manufacturing,which CNC machine tools due to its own characteristics and soon became an important part of industrial manufacture. CNC machine tool manufacturing and processing machinery as an important tool, it is an important factor affecting the accuracy of indicators work-piece machining accuracy. Therefore, improving the accuracy of CNC machine tool research has been of great concern. This paper studies CNC machine thermal geometrical analysis accuracy error rights.

An Optimal Method of Tool Path Generation for Radial Sinusoidal Surface

Tool path generation is an important part of ultra-precision manufacturing, and spiral tool path is one typical driving path. For single point diamond turning (SPDT), two methods are commonly used to generate the driving points on the spiral tool path, which are equally spaced angles and equally spaced arcs for two adjacent cutting points. But these two methods both have the defects for machining radial sinusoidal surface with SPDT. In this paper, the theoretical analyses of the two different methods are conducted and compared respectively. Then, an optimal method of generating the spiral cutting tool path is proposed on the base of theoretical analyses, which can avoid disadvantages of two original methods. The proposed method can enhance the machining accuracy and fabricating efficiency for ultra-precision machining of the radial sinusoidal surface with SPDT.

The Error Analysis of Ultra-Precision Diamond Turning Machine Based on Tool Swing Feeding

In the respect of ultra-precision manufacturing of axisymmetric surface, the machine tool with tool swing feeding has less interpolation error sources compared to the conventional ultra-precision diamond turning machine tool. The installation errors of machine tool greatly affect the manufacturing accuracy of parts. Therefore, based on the multi-body dynamics theory , the structure characteristics of this machine tool, and the parts' relative positions of machine tool, in this paper we established the space geometric model and the integrated error model of machine tool integrated with the actual installation error of machine. The analysis results of the error model show that the relationship between the depth of axis (tool shaft and main shaft of machine) parallelism and the profile error is linear function; when the installation error of swing arm was lower than 150′′,the profile error of parts was less than λ/10.

A novel micro- and nano-scale positioning sensor based on radio frequency resonant cavities.

In many micro- and nano-scale technological applications high sensitivity displacement sensors are needed, especially in ultraprecision metrology and manufacturing. In this work a new way of sensing displacement based on radio frequency resonant cavities is presented and experimentally demonstrated using a first laboratory prototype. The principle of operation of the new transducer is summarized and tested. Furthermore, an electronic interface that can be used together with the displacement transducer is designed and proved. It has been experimentally demonstrated that very high and linear sensitivity characteristic curves, in the range of some kHz/nm; are easily obtainable using this kind of transducer when it is combined with a laboratory network analyzer. In order to replace a network analyzer and provide a more affordable, self-contained, compact solution, an electronic interface has been designed, preserving as much as possible the excellent performance of the transducer, and turning it into a true standalone positioning sensor. The results obtained using the transducer together with a first prototype of the electronic interface built with cheap discrete elements show that positioning accuracies in the micrometer range are obtainable using this cost-effective solution. Better accuracies would also be attainable but using more involved and costly electronics interfaces.

Two tool path generation methods for ultra-precision machining of off-axis convex ellipsoidal surface

Generally, two spiral tool path generation methods are applied to ultra-precision three-axis turning of off-axis convex ellipsoidal surface, which are tool path generating by revolving around the axis of convex ellipsoidal surface and revolving around the axis of cylindrical surface. In this article, two different computed results of spiral tool path generation for off-axis convex ellipsoidal surface are analyzed, and several key technologies during tool path generation are analyzed in theory. The general procedure of generating the precision tool trajectory is also presented. The characteristics of two different turning trajectories for the surface manufacturing are compared and studied in some typical aspects in the end. The studies show that each of the two different tool path generation methods has its own suitable work environment, and a reasonable method should be chosen according to the processing requirement and work environment during the process of single-point diamond turning. The analysis and argument presented provide an effective choice of the accurate spiral tool path generation method in ultra-precision manufacturing of the off-axis convex ellipsoidal surface, and the method can be used in the accurate spiral tool path choice of any kind of off-axis surface.

Ultra-Precision Machining of Off-Axis Convex Ellipsoidal Surface Using Two Different Accurate Spiral Tool Paths

The off-axis parabolic mirror plays more and more important role in high-tech areas since the advantages of reducing space and improving the quality of imaging. Two ultra-precision manufacturing methods are often applied to machining the off-axis ellipsoidal mirror, which one is revolving the cylindrical blank around the axis of ellipsoidal surface and another one is revolving around the axis of cylindrical surface. But which machining method can produce a better result has no rounded comparisons and analysis according to previous research. In this paper, the tool path generation method is presented and the corresponding tool paths of each manufacturing method for the off-axis ellipsoidal mirror are calculated respectively. The motion characteristics are also analyzed and compared correspondingly. Finally, the effects of diamond tool parameters are further analyzed in theory to avoid the tool interference. The studies processed in this paper provide a theoretical basis of choosing the ultra-precision manufacturing method for the off-axis ellipsoidal mirror and can improve the efficiency and precision of processing.

Current Research and Development Trends of Micro Machine Tool for Micro-cutting

Micro-cutting technology which has a unique advantage in 3D complex parts processing is a hot spot to precision and ultra-precision manufacturing technology research. Micro-cutting machine tool as an important part in micro-cutting technology has presented a miniaturized trend and became an emphasis in current research of micro manufacturing equipment. The research status of micro machine tool for micro-cutting are systematically summarized from the aspects of machine tool bed, micro spindle unit, feed table, micro cutting tools, NC system and monitoring system. Some key technology problems are analyzed such as miniaturized machine tool bed, high speed and high rotation accuracy of micro spindle, high precision and fast response of micro table, structure and performance of micro cutting tool, openness and high precision interpolation of NC system, visual monitoring of machining process, performance of machine tool and so on. Meanwhile, feasible countermeasures toward mentioned problems are presented. The development trend of micro machine tool for micro-cutting is forecasted.

Change detection in precision manufacturing processes under transient conditions

Early detection of changes in transient process behaviors from sensor signals is becoming essential for quality assurance in microelectronics and ultraprecision manufacturing processes. We present a Dirichlet process Gaussian State Machine (DPGSM) representation to capture complex dynamics as a random concatenation of nonlinear stationary segments, and develop a method to detect early-stage fault-inducing changes. Extensive experiments suggest that the present approach, compared to other methods tested, was able to detect slight changes that cause severe surface damage 48ms earlier in an ultraprecision machining (UPM) process, and at least 2000ms earlier in a chemical mechanical planarization (CMP) process.

A high-efficiency multi-beam splitter for optical pickups using ultra-precision manufacturing

In this paper, we propose a compact seven-port beam splitter grating (BSG), based on a novel double-groove structure. The parameters of the grating are investigated by Fourier expansion and gradient algorithm. For an incident beam with TE mode normally passing through this BSG, high efficiency of 91.81% energy is theoretically split into the −3T∼+3T orders. The proposed double-groove blazed grating is fabricated using ultra-precision manufacturing. Therefore, the double-groove structure holds a high potential for mass production. The deviation of measured results from the simulated values is less than 3%, which proves that the experimental results are in good agreement with the theoretical values.

Design and analysis of a novel large-aperture grating device and its experimental validation

Large-aperture diffraction gratings are the key elements for high-power petawatt-class laser facility. At present, it is difficult to directly manufacture high-accuracy large-aperture gratings by using ultraprecision manufacturing techniques. Mechanical tiling technique with segmented gratings can be employed to cope with the challenge in large-aperture grating manufacturing. In this article, a novel tiling and adjusting device for obtaining large-aperture gratings was proposed and built to overcome the challenges in developing a Big Science Facility. The idea of integrated design and precision analysis has been introduced into the design process of the device. The theoretical analysis on static and dynamic characteristics has been conducted on the key components of the device by using finite element method. Under a series of mechanical tests, the performance of the large-aperture grating tiling and adjusting device developed was evaluated against the industrial requirements. The testing results show that the device has the positioning precision and stability in light of the design specifications. The results also indicate an optimal linear accuracy of 20 nm and a rotational accuracy of 0.4 µrad being achieved at the device.

先进光学制造技术进展

The paper summarizes the recent progress of advanced manufacturing technology for the high power laser system in China. The ultra-precision manufacturing technologies, such as ultra-precision grinding, single point diamond fly-cutting and rapid polishing, have been developed for aspheric lens and KDP crystal flats. The preliminary results show the advantages in achieving high accuracy and the ability of yield. Several deterministic finishing technologies have been studied to meet the critical wavefront specifications. A novel removing-mitigating process has been applied to polishing fused silica components to reduce the subsurface defects.

Effect of residual chips on the material removal process of the bulk metallic glass studied by in situ scratch testing inside the scanning electron microscope

Research on material removal mechanism is meaningful for precision and ultra-precision manufacturing. In this paper, a novel scratch device was proposed by integrating the parasitic motion principle linear actuator. The device has a compact structure and it can be installed on the stage of the scanning electron microscope (SEM) to carry out in situ scratch testing. Effect of residual chips on the material removal process of the bulk metallic glass (BMG) was studied by in situ scratch testing inside the SEM. The whole removal process of the BMG during the scratch was captured in real time. Formation and growth of lamellar chips on the rake face of the Cube-Corner indenter were observed dynamically. Experimental results indicate that when lots of chips are accumulated on the rake face of the indenter and obstruct forward flow of materials, materials will flow laterally and downward to find new location and direction for formation of new chips. Due to similar material removal processes, in situ scratch testing is potential to be a powerful research tool for studying material removal mechanism of single point diamond turning, single grit grinding, mechanical polishing and grating fabrication.

Minimization of the residual vibrations of ultra-precision manufacturing machines via optimal placement of vibration isolators

Abstract Ultra-precision manufacturing (UPM) machines are used to fabricate and measure complex parts having micrometer-level features and nanometer-level tolerances/surface finishes. Consequently, low-frequency residual vibrations that occur during the motion of the machines’ axes must be mitigated. A long-standing rule of thumb in vibration isolation system design is to locate the isolators in such a way that all vibration modes are decoupled. This paper uses the 2D dynamics of a passively isolated system to show that coupling the vibration modes of the isolated system by altering the location of the isolators provides conditions which allow for the drastic reduction of residual vibrations. An objective function which minimizes residual vibration energy is defined. Perturbation analyses of the objective function reveal that the recommended practice of decoupling the vibration modes more often than not leads to sub-optimal results in terms of residual vibration reduction. The analyses also provide guidelines for correctly locating the isolators so as to reduce residual vibrations. Simulations and experiments conducted on a passively isolated ultra-precision machine tool are used to validate the findings of the paper; a 5-fold reduction of the dominant residual vibrations of the machine tool is achieved without sacrificing vibration isolation quality (i.e., transmissibility).

Nano-Micro Geometric Modeling Using Microscopic Image

In recent years, there are a lot of active researches on nano-micro manufacturing and metrology, since not only industrial fields but also medical fields require higher accuracy with respect to miniaturizing size of the target. However, we cannot make an effective use of three dimensional measurement data for the nano-micro design and manufacturing due to a wide variety of instruments, resolutions, and noises. In fact, the nano-micro geometric modeling is at an early stage of development in spite of its importance for the next generation. In order to find a solution to this problem, we propose to combine the multi-resolution processing with the microscopic images for high speed and non-destructive geometric modeling as well as for the homogeneous modeling from micro features to macro ones. This research includes measurement data tiling between different instruments, high resolution optical microscopic imaging, focus judgment of three dimensional microscopic data, and large scale point crowd processing. These built models are potentially applied to in-line inspections and numerical simulations. Therefore, the nano-micro geometric modeling contribute to further developments of ultra precise manufacturing and the biotechnology.

Influence of Different Steel Alloys on the Machining Results in Ultrasonic Assisted Diamond Turning

This publication focuses on the ultra precision manufacturing of hardened steel parts with single crystal diamond tools for optical applications such as injection moulding. Nowadays optical steel moulds are nickel plated, in order to be able to machine the surface with single crystalline diamond tools. One technology that has proven its potential for replacing this procedure is the ultrasonic assisted diamond turning technique. This process allows direct machining of hardened steel with single crystal diamond tools, which is conventionally not possible due to the high tool wear. The ultrasonic assisted diamond turning process is applied in order to machine different steel alloys that are conventionally used for mould manufacturing in injection moulding. The goal is to analyze the influence of the steel alloy and the material microstructure on the machining results. The presented analysis show the capabilities of this new technology and opens the door for it to compete with established manufacturing processes, such as the manufacturing of nickel plated mold inserts.

Fabrication of flexible metallic wire grid polarizer using thermal NIL and lift-off processes

► Double layer metallic/dielectric gratings were fabricated for WGP components. ► Thermal NIL, aluminum lift-off, and dielectric etching were adopted in experiments. ► 192:1 Extinction ratio and 1.2× brightness gain were obtained with 240 nm pitch WGP. ► Designed optical performance and better process tolerance could be achieved. ► Low retardation COP films provide adequate optical performance. This work is dedicated to the fabrication of metallic/dielectric double layer gratings on polymeric films for wire grid polarizer (WGP) to obtain designed optical performance as well as better process tolerance. The fabrication process was based on thermal nanoimprint and aluminum lift-off techniques. Polymeric substrates PET (Polyethylene terephthalate) and COP (Cyclo-olefin polymer) were brought into comparison for the birefringence property. At the same time, by applying RCWA (Rigorous coupled-wave analysis) simulated optical designs, it would be also capable of minimizing difficulties of ultra-precision manufacturing. Experimental results revealed that using the 240 nm pitch stacked metallic/dielectric gratings performed 192:1 extinction ratio and 1.2× brightness enhancement, which allowed larger pitch replacing the smaller pitch of WGP gratings, but still possessed similar optical performance. Hence, these designs and process configuration not only make the continuous roll-to-roll process more feasible, but also relieve the difficulties of fabricating the imprint roller stamp.

Influence of temperature and crystal orientation on tool wear during single point diamond turning of silicon

Owing to the capricious wear of cutting tools, ultra precision manufacturing of silicon through single point diamond turning (SPDT) operation becomes a challenging task. It thus becomes non-trivial to understand the contribution of temperature and crystal orientation during the SPDT process in order to suppress tool wear. Molecular dynamics (MD) simulation is an appropriate tool to study nanoscale processes occurring at the femtosecond/picosecond timescale which cannot otherwise be studied experimentally or by the finite element method (FEM). Accordingly, MD simulation has been deployed with a realistic analytical bond order potential (ABOP) formalism based potential energy function to simulate the single point diamond turning operation of single crystal silicon in order to understand the influence of temperature and crystal orientation on the tool wear mechanism. Results showed the strong influence of crystal orientation on the wear resistance of a diamond tool; cubic orientation performed better than dodecahedral orientation. It was also observed that high pressure phase transformation (HPPT) in the cutting zone was accompanied by the formation of dangling bonds of silicon. Under the influence of cutting temperature, the newly formed dangling bonds of silicon chemically combine with the pre-existing dangling bonds on the surface of the diamond tool resulting in the formation of silicon carbide (SiC), the main appearance of which was evident at the tool flank face. Continuous abrasion of the diamond cutting tool with SiC causes sp3–sp2 disorder of the diamond tool. Hence, both these processes proceed in tandem with each other. The mechanism proposed here is in good agreement with a recent experimental study, where silicon carbide and carbon like particles were observed using X-ray photoelectron spectroscope (XPS) technology after machining a silicon wafer with a diamond tool.