六面顶压机油缸加工机的研制

我们研制了一种新型超精加工设备,用来修磨加工六面顶压机油缸的内孔.通过采用有效可行的工艺,特殊的超精磨具,保证了不易加工的大直径设备内孔的尺寸精度与表面粗糙度的要求.用该设备加工近百台压机油缸,经检验全部合格.该设备结构简单、维护方便、使用寿命长、有效地解决了六面顶压机油缸泄露问题,值得推广使用.     

Fabrication of free-form surfaces using a long-stroke fast tool servo and corrective figuring with on-machine measurement

Fabrication of free-form surfaces that are frequently demanded for the construction of optical imaging systems is described. To obtain a tool motion with large amplitude and high bandwidth, a novel long-stroke fast tool servo is proposed and installed on the Z-axis of a diamond turning machine as an additional synchronized axis. In addition, a special on-machine measurement device is used to measure the optical parameters of the machined surface and to compensate for the residual form of errors that are commonly produced in the diamond turning process. Actual machining test results show that the proposed procedures are capable of generating the copper free-form mirrors of 50 mm diameter to a form accuracy of 0.15 μm in peak-to-valley value error.     

Creation of Ultra-precision Microstructures with High Aspect Ratios

In recent years, ultra-precision micromachining technology has been used in a variety of fields such as optical instruments, electronic devices, medical equipments, etc. At present, it is essential to meet the requirement of producing various shapes, one of which is a structure with a high aspect ratio. Such structures are applied, for example, to a shaft of micro robot, a long part of microactuator and micromachine, a microneedle for syringe, etc. However, due to its fragile nature, it is extremely difficult to fabricate the structure with a high aspect ratio since it is easily damaged during cutting. It is intended to produce micro towers with high aspect ratios by applying the ultra-precision milling technology using a single crystal diamond cutting tool. The method enables accurate creation of a variety of microstructures with high aspect ratios. In addition, the study also proposes a new machining method to create microneedle arrays, avoiding the contact of cutting edge with already machined parts again. As a result, it is concluded that the proposed method has the potential of producing a variety of microstructures with high aspect ratios.     

A study of the diamond tool wear suppression mechanism in vibration-assisted machining of steel

Inability of machining steel strongly inhibits the application of diamond machining in manufacturing industry, especially in the fields of ultra-precision and micro machining. In recent years, vibration-assisted machining (VAM) has been proved to be capable of efficiently suppressing the diamond tool wear in cutting steel. Currently, the prevailing speculation claimed by most researchers for such suppression is that the tool–workpiece flash temperature was reduced in VAM, which would slow the chemical reaction between iron on steel and carbon on diamond. However, the correctness of this speculation has not been proved by any experimental or theoretical research. In this paper, in order to understand the true wear suppression mechanism of diamond tools in VAM of steel, a study is conducted by measuring the workpiece temperatures and modeling the cutting energy consumption in both VAM and conventional cutting (CC). Based on the comparison results, it is concluded that the cutting temperature and energy consumption in VAM are not smaller than in CC, and hence the reduced diamond tool wear in VAM should not be caused by the claimed reduced temperature, especially when the material removal rate is very small. Finally, based on the EDS analysis and the comparison of experimental results under different air pressure, two probable reasons are proposed for the significantly reduced diamond tool wear in VAM of steel: (i) increase of gas pressure at the tool–workpiece interface and (ii) generation of an oxide layer on the freshly machined surface.     

Fundamental investigation of ultra-precision ductile machining of tungsten carbide by applying elliptical vibration cutting with single crystal diamond

This paper presents essential investigations on the feasibility of ductile mode machining of sintered tungsten carbide assisted by ultrasonic elliptical vibration cutting technology. It lays out the foundations toward efficient application of elliptical vibration cutting technology on tungsten carbide. Tungsten carbide is a crucial material for glass molding in the optics manufacturing industry. Its grain size and binder material have significant influence not only on the mechanical and chemical properties but also on the machining performance of tungsten carbide. In order to investigate the influence of material composition on tungsten carbide machining, a series of grooving and planing experiments were conducted utilizing single crystal diamond tools. The experimental results indicated that as compared to ordinary cutting where finished surface deteriorates seriously, ductile mode machining can be attained successfully by applying the elliptical vibration cutting technique. It was also clarified that the binder material, the grain size, cutting/vibration conditions as well as crystal orientation of the diamond tool have significant influence on the tool life and the machined surface quality. Based on these fundamental results, feasibility of micro/nano-scale fabrication on tungsten carbide is investigated. By applying amplitude control sculpturing method, where depth of cut is arbitrary changed by controlling the vibration amplitude while machining, ultra-precision textured grooves and a dimple pattern were successfully sculptured on tungsten carbide in ductile mode.     

Ultra-precision machining of Fresnel microstructure on die steel using single crystal diamond tool

With the increasing demand for the replication of structured optical elements such as Fresnel lenses and prism arrays, more attention is being paid to the development of ultra-precision diamond machining technology for the fabrication of die steel molds. However, the machining process would be a catastrophic failure because of rapid and excessive tool wear if a diamond tool is used to machine die steel. In the present paper, a micromachining method for fabricating microstructures on die steel using single crystal diamond tool is presented. The presented technology is based on a thermochemical technique that uses plasma nitriding treatment to suppress the rapid and excessive tool wear in the diamond machining of steel. Experimental findings revealed that severe chemical tool wear, which is the main wear mechanism in the diamond machining of steel, was reduced significantly after plasma nitriding treatment, and a mirror-quality surface with an average surface roughness of 20 nm root-mean-square (RMS) was achieved over a cutting distance of approximately 5.4 km. Furthermore, a Fresnel microstructure with surface roughness RMS better than 40 nm was precisely fabricated on AISI 4140 die steel using single crystal diamond tool.     

An investigation into surface generation in ultra-precision raster milling

This paper presents a study of the factors that affect surface generation in ultra-precision raster milling. A series of experiments was conducted to study the effect of different factors on surface generation in ultra-precision raster milling. The results indicate that machining parameters, tool geometry, cutting strategy, and tool wear are the critical factors for achieving super mirror finish surfaces, while cutting strategies, tool path generation, and kinematic errors of the slides are vital to the form accuracy of freeform surfaces. The experimental results are useful for the diagnosis of systematic errors in machine tools, and the control of machining errors. Compensation strategies can be devised, and improvement can be made in the optimization of surface generation and hence the surface quality when using ultra-precision raster milling can be improved.     

Fixed abrasive diamond wire machining—part II: experiment design and results

Experimental results from fixed abrasive diamond wire machining of wood and foam ceramics are presented. Three types of wood—pine, oak, and fir, and three types of foam ceramic—silicon carbide, zirconia, and zirconia toughened alumina, are tested. The research investigates the life of diamond wire and effects of process parameters on the cutting forces, force ratio, and surface roughness. A scanning electron microscope is used to study the worn diamond wire, machined surfaces, and debris. The diamond wire saw is demonstrated to be very effective in machining foam ceramics. The wire life for cutting wood at slow feed rates is low. The short tool life for dry cutting of wood indicates that more research in new fixed abrasive diamond wire and wire saw machining technologies is necessary.     

Tool path generation for ultra-precision machining of free-form surfaces

The generation of tool paths for ultra-precision machining is still a limiting factor in the manufacturing of parts with complex optical surfaces. In conventional machining as well as in complex five axes machining the application of CAD- and CAM-software for the generation of tool paths is state of the art. But these software solutions are not able to generate tool paths according to the high requirements of ultra-precision machining. This paper describes possible ways to generate tool paths for ultra-precision machining when the optical surface can be analytically described or when the surface data is derived from optical design software. Ultra-precision milling experiments with different tool paths have been carried out and the quality of the machined geometry has been evaluated concerning the achievable form accuracy.     

Study on the adaptability of thick film diamond tool to cutting composites

In order to explore the adaptability of a thick film diamond tool to the finish machining of composites, tool wear and its effect factors as well the machined surface roughness are investigated in this paper. The experimental results show that the thick film diamond tool has a low wear rate and the machined surface cut with the tool has a fine finish for the cutting of composites. The negative rake is beneficial for the tool standing wear and collision.     

端面超精密车削中的面型误差辨识技术研究

为分析超精密车削过程中典型干扰因素对面型精度的影响机制以及这些干扰因素所造成面型误差的特性，基于国产超精密机床Nanosys600对Al6061进行单点金刚石车削实验。通过切削-面型轮廓测量-面型轮廓滤波-分析的迭代过程，辨识和排查了加工过程中的误差来源。在进行环境温度调控和更换导轨工作区域后，滤波后的面型轮廓波峰波谷差值由1 510 nm降低到203 nm。     

光学微结构超精密多轴铣削加工技术

采用单点金刚石飞刀加工可以直接加工出具有纳米级的表面粗糙度和亚微米级形状精度的光学微结构元件而不需要后续处理。通过超精密飞刀加工微V沟槽的实验,分析了主轴转速、进给速度、切削深度和切削行间距对微V沟槽加工精度的影响,并对切削参数进行优化。最后,利用优化后的切削参数加工出微V沟槽结构。实验结果显示,超精密飞刀加工微V沟槽可达到满足光学微结构加工精度的要求。     

Brittle–ductile transition during diamond turning of single crystal silicon carbide

In this experimental study, diamond turning of single crystal 6H-SiC was performed at a cutting speed of 1 m/s on an ultra-precision diamond turning machine (Moore Nanotech 350 UPL) to elucidate the microscopic origin of ductile-regime machining. Distilled water (pH value 7) was used as a preferred coolant during the course of machining in order to improve the tribological performance. A high magnification scanning electron microscope (SEM FIB- FEI Quanta 3D FEG) was used to examine the cutting tool before and after the machining. A surface finish of Ra=9.2 nm, better than any previously reported value on SiC was obtained. Also, tremendously high cutting resistance was offered by SiC resulting in the observation of significant wear marks on the cutting tool just after 1 km of cutting length. It was found out through a DXR Raman microscope that similar to other classical brittle materials (silicon, germanium, etc.) an occurrence of brittle-ductile transition is responsible for the ductile-regime machining of 6H-SiC. It has also been demonstrated that the structural phase transformations associated with the diamond turning of brittle materials which are normally considered as a prerequisite to ductile-regime machining, may not be observed during ductile-regime machining of polycrystalline materials.     

金刚石框架锯锯切研究（2）一锯切破碎机理

在对金刚石框架锯锯切加工动力学研究的基础上，通过单颗粒划痕和单个金刚石结块切削大理石试验，模拟金刚石框架锯锯切过程中，金刚石颗粒和结块在不同加工条件下的切削过程；测量分析了切削力、表面沟槽轮廊和有效切削磨粒数；观察并分析了加工表面形貌；运用岩石脆性断裂力学理论，分析了单颗粒金刚石切削机理。通过金刚石框架锯发加工大理石的切屑粒度分布分析，指出了实际加工切削条件对锯切破碎机理的影响。研究结果证实了金刚石框架锯锯工加工动力学研究的一些基本结论，最后提出了金刚石框架锯锯切大理石破碎机理模型。     

工艺参数对单晶硅超精密加工切削力的影响

为了了解单晶硅超精密车削过程中不同切削参数及刀具前角对切削力的影响,利用单晶金刚石车刀对单晶硅进行单因素变量超精密车削试验。试验结果表明:进给量f和切削深度a_p对X、Y、Z方向的切削力F均有增大的趋势;而在切削速度v_c增加时,各方向的F逐渐减小;切削前角减小时,切削力反而增大。通过各因素对切削力F的变化幅值可以得到,对F影响较大的参数为a_p及f。选取最佳组合参数对单晶硅进行超精密切削试验,得到极为光滑的表面。     

Analysis of 3D microtopography in machined KDP crystal surfaces based on fractal and wavelet methods

Potassium dihydrogen phosphate (KDP) crystal surfaces machined by precise milling and single point diamond turning (SPDT) methods are analyzed in this paper. The frequency information of 3D-machined KDP crystal surfaces are decomposed and analyzed by wavelet transform method, and 3D fractal properties of different KDP crystal surfaces are calculated and analyzed by fractal method. Through the integration of fractal and wavelet analysis, it can be found that the high-frequency information of machined surfaces is incorrelate with the machining process and it can reflect the anisotropic features of material structure. The anisotropy of the machined KDP surfaces is determined by the machining process. From analysis, the strong anisotropic surfaces are easier to form microscale waveness so as to impact the optical performance of KDP crystal components severely. The result of analysis reveals that the different machining method may produce unique feature in the machined surfaces and choosing reasonable machining method may improve the microtopographic structure of machined KDP crystal surface.     

Monitoring of distance between diamond tool edge and workpiece surface in ultraprecision cutting using evanescent light

The interaction between a tool and a workpiece during machining determines the quality of a machined workpiece. This study presents a novel direct monitoring method using evanescent light, which detects the distance between a diamond tool edge and the workpiece surface. In the proposed method, evanescent light is generated around the diamond tool edge, and the intensity of the reflected laser beam corresponds to the distance between the tool edge and the workpiece surface. Experimental results confirmed that the proposed method is capable of monitoring the distance change of a sub-micrometer scale.     

Research Progress of Diamond Tool Machining Technology for Ferrous MetalsEI北大核心CSCD

金刚石刀具是超精密加工最理想的刀具之一,但在黑色金属超精密加工领域“石墨化”导致刀具快速磨损,其应用极大地受到了限制。首先,针对金刚石刀具的磨损机理进行介绍。然后,综述金刚石刀具切削黑色金属的几种常见方法,如刀具表面改性、工件表面改性、低温辅助切削、超声振动辅助切削等,通过研究实例来分析各方法的应用效果和存在问题,并从技术层面分析影响金刚石刀具在黑色金属加工领域发展的关键因素。最后,对金刚石刀具切削黑色金属未来的发展趋势进行探讨。总结金刚石刀具在黑色金属领域的加工方法,分析加工黑色金属时抑制金刚石刀具磨损的核心技术,对黑色金属的精密超精密加工具有重要的引领和推动作用。     

Modeling of dynamic characteristic of the aerostatic bearing spindle in an ultra-precision fly cutting machine

Axis orientation stability of aerostatic bearing spindles has great influence on machining precision of ultra-precision fly cutting machines used for processing ultra-precision optical components of large diameter. Mid-spatial frequency errors (amplitude<0.1 μm, wavelength about 100 nm) always existed on the machined surfaces along feeding direction. Generally, the waviness errors on processed surfaces will impact the performance of workpiece used as optical components greatly, and the tilting motions of spindles were believed to be the main source which produced the waviness errors. In this paper, to study the tilting motions of spindles, the Euler dynamic equations of angular displacements of spindles were proposed, and analytic solutions of the equations were also presented. At the same time, the 3D surface profile simulations of workpieces based on analytic solutions of Euler equations were achieved. The simulation results have been verified by lots of experiments on an ultra-precision fly cutting machine. At last, the inertia tensor criterion which can decrease the waviness errors of machining surface was represented, and it can be applied to instruct the structure design of aerostatic bearing spindles.     

A theoretical and experimental investigation into multimode tool vibration with surface generation in ultra-precision diamond turning

In ultra-precision diamond turning (UPDT), tool's high frequency vibration is natural mechanism influencing nanometric surface roughness of machined components. Its first mode high frequency vibration has been overemphasized. However, its multimode high frequency vibration (MHFTV) has not been reported. In the paper, the MHFTV and its effects on surface generation in UPDT are firstly studied. The experimental and theoretical results verify that (i) diamond tool naturally possesses multimode high frequencies, i.e. one sub-high frequency (SHF) for the tool shank tip, one high frequency (HF) for the tool tip, and one ultrahigh frequency (UHF) for the diamond tip; (ii) dampers cause the variation of tool's multimode high frequencies, under which the MHFTV together produces non-uniform zebra-stripe-like patterns at a machined surface; and (iii) cutting force has a linear relationship with and tool's stiffness has a reverse proportion to the amplitude of the MHFTV to influence surface generation, which can be used to improve surface quality.