非球面超精密磨削误差建模与补偿研究

为提高课题组自研的超精密磨床加工精度,基于多体系统理论,运用齐次坐标变换原理,分析该超精密磨床37项几何误差来源,对非球面超精密磨削的综合误差建模。超精密磨床的多项几何误差元素已在制造阶段标定、补偿,取砂轮对刀误差和砂轮轮廓半径磨损误差作为主要面形误差来源,分别推导其对综合误差的传递函数,分析误差辨识方法,建立误差修正补偿模型,提出基于直接补偿的点补修正法。试验结果表明：建立的综合误差模型正确,根据误差辨识方法和修正补偿模型,修正误差后面形误差显著降低,有效提高面形精度。     

超精密车床加工端面实时误差补偿及平面度测量系统

本文提出了一种超精密车床加工端面实时误差补偿方法,并对工件加工表面进行在线测量,用最小二乘方法计算平面度误差,结果表明零件平面度改善了６２％,证明所提方法是可行的。     

超精密加工用金刚石工具的研发动态

使用高精度高刚性机床和锐利光滑切削刃的单晶金刚石切削工具的超精密切削加工作为被切削性良好的软质金属的稳定高效高精度加工技术已趋向成熟。特别是在非球面反射镜和发动机部件的精加工中正在全面地采用超精密切削加工。另外，Si和Ge等非金属材料的红外光学元件的加工和作为透镜，导光板等光学元件的模具Ni—P镀层的加工，虽存在工具磨耗大这一问题，但目前没有其它的有效加工技术，现仍采用这种加工技术。     

现代超精密加工机床的发展及对策

超精密加工机床是实现超精密加工的重要机械装备。介绍了当前国内外超精密机床的发展现状,从系统的角度分析了影响机床加工精度的因素,并对我国超精密加工机床的研发提出了一点建议。     

微小振动影响超精密非球面加工精度的研究

超精密磨削已广泛应用于轴对称非球面光学元件及硬脆材料的加工，加工过程中砂轮的不平衡量和机床主轴引起的振动直接影响工件表面精度及粗糙度。为了适应非球面工件超精密加工的要求，本文通过分析加工过程中产生的振动现象，建立磨削中振动引起工件表面轮廓误差的数学模型，研究主轴转速变化及磨削加工参数对工件表面精度的影响；通过建立工件与砂轮之间的运动关系，得出砂轮的振幅、频率及加工速度的变化对工件表面精度的影响条件。研究结果表明：选择合理的加工参数能降低工件表面波纹度，提高工件的表面精度。     

精密外圆磨削圆柱度在位测量与补偿工艺

圆柱度是评价轴类零件加工精度的重要指标,通过对精密轴类零件外圆磨削过程中圆柱度误差产生机制的研究,获得适用于精密外圆磨削的圆柱度误差在位测量工艺,并实现可视化定量在位补偿,大大提高了传统外圆磨削的精度和效率,减轻了对操作者经验的依赖程度。     

大口径方形非球面镜的高效磨削技术研究

本文基于X/Y/Z三直线轴平面磨床,研究了圆弧砂轮应用于大口径方形非球面镜的平行磨削新技术,介绍了圆弧砂轮平行磨削的机理、重点解决了砂轮形状误差在线检测、元件面形误差在线检测与误差补偿等关键技术问题.以430 mm×430 mm非球面镜为样件,进行了多轮高效精密磨削工艺实验,面形精度PV均值为4.2μm,表面粗糙度约0...     

Profile error compensation in ultra-precision grinding of aspheric surfaces with on-machine measurement

A compensation approach based on the on-machine measurement was developed for the grinding of tungsten carbide aspheric moulds. In this approach, the on-machine measurement was employed to eliminate the profile error caused by the re-installation of the workpiece. A new method was proposed to reconstruct the actual ground profile based on the measured profile data. The overall profile error after grinding was obtained by subtracting the target profile from the actual ground profile along normal direction and was then used to generate a new tool path for compensation grinding. The experimental results showed that after three compensation grinding cycles the aspheric surface had a profile accuracy of 177 nm (in PV) with a roughness of 1.7 nm (in R_a). The on-machine measurement was in excellent agreement with the off-machine measurement by commercially available profilometers.     

Development of an on-machine profile measurement system in ELID grinding for machining aspheric surface with software compensation

Efficient manufacture of dimensionally accurate optical surface on hard and brittle materials is a major concern for optoelectronic industry. Electrolytic in process dressing (ELID) grinding is proved as a reliable process to achieve this optical quality nano-surface finish on hard and brittle materials. Besides surface finish it is important to ensure dimensional accuracy by improving profile and form accuracy of the ground aspheric surface. Kinematic factors are commonly considered the reasons for the dimensional inaccuracy in a machined part. Software compensation is a direct and economical method to overcome several kinematic factors and improve the dimensional accuracy. Last, but most important, is the monitoring of achieved surface profile to ensure more accurate profile radius in the finished part. So an on-machine profile measurement system based on coordinate measuring machine (CMM) principle has been developed to check the profile radius of the ground surface. In this study software compensation was applied in ELID grinding of an aspheric surface in order to compensate the wheel wear until the measured surface profile machined on BK7 glass reaches within tolerable limit.     

A mesoplasticitiy analysis of cutting friction in ultra-precision machining

The control and minimization of cutting force variation is of prime importance in obtaining a consistent surface finish and form accuracy of a machined workpiece in ultra-precision machining. However, most continuum theories do not take into account the effect of crystallographic anisotropy that causes variation in the shear plane at the grain level and hence of the cutting force. The periodicity of the fluctuation of cutting forces is found to be dependent on the frictional condition during cutting. However, investigation of the in situ relationships among the cutting friction, the crystallographic orientation of workpiece and the periodic fluctuation of cutting forces has received relatively little attention. In this paper, a mesoplasticity approach is proposed to access the crystallographic and frictional effect on the fluctuation of micro-cutting forces in diamond turning of crystalline materials. The predictions were able to explain the experimental results based on the power spectrum analysis of the cutting force variation. The research findings throw light on the possibility of an indirect in situ assessment of the frictional condition in ultra-precision machining.     

Dynamic long axis for ultra-precision machining of optical linear structures

Currently, fly cutting is the most popular manufacturing technology for the machining of planar groove structures. The disadvantage of this technology is the long machining time. A promising alternative technology for the machining of planar grooves is planing. The main disadvantage of planing in comparison to fly cutting is the limitation of conventional precision axes concerning a high dynamic movement. Regarding to this aspect the Fraunhofer IPT has developed a precise linear axis. It allows high dynamic movements by using an impulse decoupling system (AiF-FV-Nr.: 13,270 N). The paper describes the mechanical setup and the development and optimization of the mechanical main component. The detailed simulation of the drive system (including motor control loop and impulse decoupling system), results of static and dynamic measurements and test machining results are presented.     

Rotary-axial spindles for ultra-precision machining

By combining pressurized fluid journal bearings with a novel magnetic thrust bearing, a rotary-axial spindle design is presented to achieve both rotary motion for cutting and mm-range linear motion along the axial direction for feeding. The advantages of such rotary-axial spindles include stiffer structure loops, fewer components, higher accuracy and resolution, and less heat generation. Our first prototype has demonstrated 9000 rpm, 600 N axial load capacity, 100 N/μm dynamic stiffness, 1 mm axial stroke, and 5 nm resolution. These are significant improvements over aerostatic spindles of comparable size.     

A review of surface roughness generation in ultra-precision machining

Ultra-precision machining (UPM) is capable of manufacturing a high quality surface at a nanometric surface roughness. For such high quality surface in a UPM process, due to the machining complexity any variable would be possible to deteriorate surface quality, consequently receiving much attention and interest. The general factors are summarized as machine tool, cutting conditions, tool geometry, environmental conditions, material property, chip formation, tool wear, vibration etc. This paper aims to review the current state of the art in studying the surface roughness formation and the factors influencing surface roughness in UPM. Firstly, the surface roughness characteristics in UPM is introduced. Then in UPM, a wide variety of factors for surface roughness are then reviewed in detail and the mechanism of surface roughness formation is concluded thoroughly. Finally, the challenges and opportunities faced by industry and academia are discussed and several principle conclusions are drawn.     

Fabrication of aspheric surface using ultraprecision cutting and BMG molding

A new process to replicate an aspheric lens is presented in this study. A mold of oxygen free copper (OFC) is fabricated using ultraprecision machining, which is a popular material for machining due to its good machinability. But OFC has a very low hardness of 1.606 GPa, it is not suitable for the subsequent molding process. Then, this OFC mold (known as the first mold) is used to hot emboss on Mg₅₈Cu₃₁Y₁₁ amorphous alloy to form a secondary mold which is one kind of metallic glass. The hardness of the secondary mold is as high as 3.445 GPa, whereas the glass transition temperature (T_g) of the Mg₅₈Cu₃₁Y₁₁ metallic glass is as low as 413 K (140 °C), at which the Mg₅₈Cu₃₁Y₁₁ metallic glass shows a good glass-forming ability (GFA). In order to perform superplastic microforming, the working temperature must be close to the glass temperature around 413 K. Therefore, in this study, the temperatures of the hot embossing experiments to fabricate the secondary mold are set at 423 K (150 °C). It shows experimentally that the working temperature is dependent on the applied stress level. Since the Mg₅₈Cu₃₁Y₁₁ metallic glass has superplastic property at the supercooled liquid region, it can be easily formed by the master die. This embossing process on the Mg₅₈Cu₃₁Y₁₁ metallic glass makes molding process faster and more diverse applications. Next, the secondary mold is used to emboss on polymethylmethacrylate (PMMA) sheets for replication process. The Mg₅₈Cu₃₁Y₁₁ metallic glass is not only a good material for hot embossing process to fabricate micro-structure directly, but also an excellent fast-molding material for hot embossing process. It is expected that the machining processes described in this paper could be applied to the related fields to fabricate precision components required of micro, sub-micro, or nano order of dimensional accuracy.     

半球谐振子曲面加工干涉分析及其超精密磨削工艺

半球谐振子作为半球谐振陀螺的核心部件,其加工精度和表面质量直接影响半球谐振陀螺的工作精度和使用寿命。为解决半球谐振子加工难题,提高半球谐振陀螺的性能,从半球谐振子的结构特征出发,对谐振子加工过程中的干涉进行理论分析;再根据球头砂轮磨削区域分布的特点进行磨削轨迹规划,确定谐振子不同磨削阶段球头砂轮的最佳转角;最后在自研的半球谐振子超精密磨削机床上进行加工实验。超精密磨削后的谐振子表面粗糙度（Ra值）由0.6158 μm提升至0.0402 μm,面形精度（PV值）由4.5904 μm提升至0.3390 μm;经磁流变抛光后谐振子表面粗糙度（Ra值）进一步提高至0.0032 μm。研究表明:采用轨迹规划后的磨削工艺可避免砂轮与工件间的干涉,并加工出高质量的半球谐振子零件。      

Waviness compensation of precision machining by piezo-electric micro cutting device

Recently, precision machining technology has been developed continuously in order to achieve high productivity and assured quality of precision parts in several industrial fields such as; lasers, optics, quartz vibrators, semiconductors, aircraft and artificial satellites etc. Waviness may occur on the surface of machined parts due to the table motion error and the dynamic cutting mechanism between the tool and the workpiece and may impair the form accuracy of the precision machined parts. In this research, a micro cutting device with piezo-electric actuator has been developed in order to control depth of cut precisely and compensate the waviness on the surface of the workpiece. Experiments have been carried out on a precision lathe. The characteristics of the surface profile and the cause of the waviness profile have been analyzed and waviness profiles of some cases have been compared with those of experiments.     

High-precision machining by measurement and compensation of motion error

This paper describes a systematic method to model and compensate geometric errors of machine tools. In order to separate geometric errors from other errors, measured errors are analyzed in the frequency domain by using the Fourier series. Then, the frequency components corresponding to geometric errors are selected based on the repeatability of their wavelength. Finally, the components are reconstructed and forwarded for the compensation by a fine motion drive. A CNC machine tool with a fine motion mechanism on the Z-axis was developed to compensate the error components in the Z direction on the XY plane. A flat surface machining with non-rotational cutting tools was tested to validate our approach. On the plane of 45 mm×70 mm, the fluctuation of the relative displacement was reduced from 1.3 to 0.5 μm P-V. Machining experiments with a single-crystal diamond tool were also carried out and the straightness of the profile curve was reduced from 1.0 to 0.4 μm. The result of the experiments showed that the geometric errors were compensated separately from the vibration due to the bending mode of the machine column.