时变去除函数在气压砂轮抛光中的应用研究

针对气压砂轮抛光中通过驻留时间控制材料去除量需在模具表面多去除一层材料及抛光效率低等问题,提出了一种基于时变去除函数的抛光材料去除量控制方法。该方法以抛光工具所能达到的最大进给速度在模具表面进行抛光加工,无需多去除材料,通过实时改变抛光工具的去除能力以适应面形误差的变化,极大地缩短了抛光时间;开展了抛光材料去除过程研究,建立了气压砂轮抛光工具进给速度与面形数据和抛光去除函数之间的关系,提出了抛光过程时间的计算方法;针对时变去除能力超出抛光工具最大去除能力的问题,提出了在气压砂轮抛光中对需去除的材料进行分层抛光的思想。最后,通过抛光过程时间对材料去除量控制的两种方法进行了对比分析。研究结果表明,在气压砂轮抛光中采用时变去除函数来控制材料去除量能极大地提高抛光效率。     

计算机控制光学表面成形技术的驻留时间算法

为了提高镜片的加工精度与效率,利用计算机控制光学表面成形技术(CCOS)的抛光方法对光学镜片进行抛光全过程动态仿真。根据Preston方程建立材料去除函数模型,对抛光过程中压力、转速以及工件与抛光磨头相对半径比对抛光去除速率的影响进行分析。为建立球面镜片的动态全过程仿真,结合卷积原理,推导加工残余误差与去除函数和驻留时间三者间的线性关系,根据镜片的对称性,将元素个数从2m+1点简化为m+1点,以提高运算效率。最后为获得仿真最小残余误差,采用非负最小二乘法求解驻留时间。结果表明,材料去除速率函数类似于高斯分布,抛光后能使镜片面形误差收敛,对模拟表面进行仿真,半径为100mm的镜片其初始表面形貌粗糙度的均方根值从0.467μm收敛到0.028μm,轮廓最大高度从6.12μm收敛到1.48μm。对实测表面进行加工仿真同样令其表面形貌粗糙度的均方根值从3.007μm收敛到0.107μm,轮廓最大高度从160.73μm收敛到13.76μm,因此提出的驻留时间求解方法对于球面镜片抛光全过程动态仿真有一定的可行性。     

非球面柔顺研抛的边缘效应机理研究

在整个非球面柔顺研抛的过程中,如果运动速度、进给速度和外加压力都不发生变化,非球面边缘区域的研抛进给路径是其他区域的一半,所以理论上边缘区域去除量应该更少,但实验结果正好相反。针对该边缘效益,从研抛过程的基础动力学状态转换过程入手,重新研究了柔顺研抛的工艺过程,发现在边缘区域虽然加工时间以线性方式减少一半,但接触压力以二阶幂指数方式由原值递增至无穷大,决定去除效率的因素中,接触压力比加工时间更占主导,所以边缘区域实际去除量会更多。     

蛇纹石抛光工艺的研究

以试验为基础研究了蛇纹石的抛光工艺，并对各种抛光条件对表面光泽度的影响进行了探讨。结果表明，选用合适的抛光剂、抛光时间、预加工光泽度、冷却方式及抛光工具材料，光泽度可达９０以上。此抛光工艺简单、经济、高效     

Experimental investigation and analytical modelling of the tool influence function of the ultra-precision numerical control polishing method based on the water dissolution principle for KDP crystals

A single crystal of potassium dihydrogen phosphate (KH₂PO₄, KDP), which possesses unique excellent non-linear electro-optical properties, is currently the only material suitable for electro-optic switches and high power laser-frequency conversion applications in laser-induced inertial confinement fusion. However, KDP crystals are difficult to produce because of their inherent softness, brittleness, and water-solubility, as well as their strong anisotropy and temperature sensitivity. Obtaining high-quality near-lossless KDP elements is an issue that should be solved urgently. In this study, an ultra-precision numerical control polishing method based on the water dissolution principle was introduced to achieve a controllable material removal. A small polishing tool was used to process a large KDP surface, and an accurate tool influence functions is required for deterministic fabrication of KDP surface. In order to quantify the influence of critical parameters (e.g., polishing speed, polishing pressure, water content, and directions of revolution and rotation) on material removal rate distribution, a tool influence function model was established based on the Preston equation. The model was then modified based on experiments, and its accuracy was verified. This modified model lays the foundation for ultra-precision water dissolution polishing of large KDP crystals. A very smoothed surface with high surface accuracy (peak-to-valley value below 0.4 λ) and low surface roughness (Ra 1.598 nm) could indeed be obtained by using the model. This research is also applicable to the polishing of other water-soluble materials.     

Research on unbounded abrasive polishing process with assisted ultrasonic vibration of workpiece

Ultrasonic-assisted machining was an effective method to improve the material removal quality especially to difficult-to-cut metal materials. The ultrasonic vibration was usually superimposed on the machining tool but seldom on the workpiece, although the ultrasonic vibration of workpiece could improve the processability of material more effectively. In this paper, a rectangle hexahedron ultrasonic sonotrode with optimized slots was developed as a platform to realize the assisted ultrasonic vibration of workpiece and the ultrasonic-assisted polishing process of austenitic stainless steel was also studied. The unbounded abrasive was selected as polishing medium, and the path compensation strategy of soft polishing tool was carried out for getting uniform polishing force. The orthogonal experiments were designed to study the optimization of ultrasonic polishing parameters and the relation between different types of ultrasonic polishing path and polishing quality. The results appear that the horizontal ultrasonic vibration of workpiece can reduce polishing force and improve polished surface roughness, which can also reinforce the proportion of plastic shear effect in the material removal process. The ultrasonic polishing path keeping consistent with workpiece vibration direction can get more uniform polishing force and better surface roughness. And the 45° oblique crossing ultrasonic path can get the maximum average polishing force reduction by 75.2 %.     

基于喷射抛光实验研究结果的异形抛光实验台设计

介绍了标准的液体喷射抛光实验,提出了近壁面附近固液两相流中的颗粒作用导致的流体摩擦剪切去除材料的机制假设,然后通过实验研究了抛光时间、样品表面初始粗糙度、喷头形状、喷射距离、喷射压力和pH值对抛光结果的影响。结果表明,抛光结果随时间趋于稳定并与初始粗糙度无关,圆形喷头比扇形喷头抛光效率高,喷射距离和压力影响一致,pH值越低影响越大。最后基于理论假设和实验结果设计了一个可以用于精密光学制造中异形表面抛光的实验装置。     

Material removal model considering influence of curvature radius in bonnet polishing convex surface

The bonnet tool polishing is a novel, advanced and ultra-precise polishing process, by which the freeform surface can be polished. However, during the past few years, not only the key technology of calculating the dwell time and controlling the surface form in the bonnet polishing has been little reported so far, but also little attention has been paid to research the material removal function of the convex surface based on the geometry model considering the influence of the curvature radius. Firstly in this paper, for realizing the control of the freeform surface automatically by the bonnet polishing, on the basis of the simplified geometric model of convex surface, the calculation expression of the polishing contact spot on the convex surface considering the influence of the curvature radius is deduced, and the calculation model of the pressure distribution considering the influence of the curvature radius on the convex surface is derived by the coordinate transformation. Then the velocity distribution model is built in the bonnet polishing the convex surface. On the basis of the above research and the semi-experimental modified Preston equation obtained from the combination method of experimental and theoretical derivation, the material removal model of the convex surface considering the influence of the curvature radius in the bonnet polishing is established. Finally, the validity of the model through the simulation method has been validated. This research presents an effective prediction model and the calculation method of material removal for convex surface in bonnet polishing and prepares for the bonnet polishing the free surface numerically and automatically.     

大口径非球面反射镜误差分离组合加工技术

为了解决大口径非球面反射镜材料去除效率与面形收敛效率之间的矛盾,提出了基于高低阶面形误差分离的组合加工技术。首先,分析了不同尺寸磨头对不同周期面形误差的控制能力。然后,比较了不同磨头的收敛效率与加工时间之间的关系。最后,根据大口径非球面反射镜加工过程中面形误差的特点,将大口径非球面反射镜的面形误差分离为低阶面形误差与高阶面形误差,使用不同加工方式分别对高、低阶面形误差驻留时间进行求解。通过多种加工方式组合加工的方法建立了具有针对性的加工策略,有效提高加工效率。结合工程实例,对一块口径为2.04m的非球面SiC反射镜进行了加工试验,单个组合加工周期内面形收敛效率达到61.2%。结果表明,高阶与低阶面形误差均得到较好的去除。材料去除效率与面形收敛效率均得到提高,达到了良好的效果,满足加工需求。     

Theoretical and experimental investigation of surface generation in swing precess bonnet polishing of complex three-dimensional structured surfaces

Three-dimensional structured surfaces (3D-structured surfaces) possessing specially designed functional textures are widely used in the development of advanced products. This paper presents a novel swing precess bonnet polishing (SPBP) method for generating complex 3D-structured surfaces which is accomplished by the combination of specific polishing tool orientation and tool path. The SPBP method is a sub-aperture finishing process in which the polishing spindle is swung around the normal direction of the target surface within the scope of swing angle while moving around the center of the bonnet. This is quite different from the ‘single precess’ and ‘continuous precessing’ polishing regime, in which the precess angle is constant. The technological merits of the SPBP were realized through a series of polishing experiments. The results show that the generation of complex 3D-structured surfaces is affected by many factors which include point spacing, track spacing, swing speed, swing angle, head speed, tool pressure, tool radius, feed rate, polishing depth, polishing cloth, polishing strategies, polishing slurry, etc. To better understand and determine the surface generation of complex 3D-structured surfaces by the SPBP method, a multi-scale material removal model and hence a surface generation model have been built for characterizing the tool influence function and predicting the 3D-structured surface generation in SPBP based on the study of contact mechanics, kinematics theory, abrasive wear mechanism, and the convolution of the tool influence function and dwell time map along the swing precess polishing tool path. The predicted results agree reasonably well with the experimental results.     

Investigation on the polishing of aspheric surfaces with a doughnut-shaped magnetic compound fluid (MCF) tool using an industrial robot

Aspheric elements have become essential optical surfaces for modifying optical systems due to their abilities to enhance the imaging quality. In this work, a novel method employing a doughnut-shaped magnetic compound fluid (MCF) polishing tool, and an industrial robot was proposed for polishing aspheric surfaces. Firstly, investigations on the MCF tool, including the formation process and geometry, were conducted to form an appropriate polishing tool. The distribution of abrasive particles was observed using SEM and EDX mapping. Thereafter, a conic workpiece constructed from 6061-aluminum alloy was selected as the workpiece, which was used to discover the effects of the parameters on the polishing ability of aspheric surfaces. Finally, a polishing experiment was conducted with an aspheric element under the optimized conditions. The obtained results are shown as follows. (1) A relatively regular MCF tool was obtained when the eccentricity (r), amount of MCF slurry supplied (V), revolution speed of the MCF carrier and magnet (n_c and n_m, respectively) were given at appropriate values. (2) Abrasive particles entrapped in or attached to the clusters were observed abundantly on the MCF tool sample. (3) The surface profile of the conic workpiece after 60 min of polishing indicated that material was removed evenly, and an annular polishing area was attained. Meanwhile, a higher material removal rate and better surface roughness were achieved with a smaller working gap (h) and larger volume of the MCF slurry supplied (V). (4) The roughness (Ra) of the aspheric surface decreased from 49.81 to 10.77 nm after 60 min of polishing. The shape retention obtained a Pearson correlation coefficient (Pcc) of 0.9981, which demonstrated that this novel method is appropriate for polishing aspheric elements.     

Effect of interfacial friction force on material removal in full aperture continuous polishing process

Full aperture continuous polishing using pitch lap is a key process of finishing large flat optical workpiece. The friction force of the workpiece and pitch lap interface significantly affects material removal. In this work, the friction force was determined by a measurement system that uses force transducers to support the workpiece. Experimental and theoretical analyses have been carried out to investigate the evolution of friction force with polishing time and its effect on material removal. Our results show that the friction coefficient of the workpiece/lap interface decreases during polishing, which is due to surface smoothing of the viscoelastic pitch lap by loading conditioner. In addition, the spatial average and uniformity of material removal rate (removal coefficient) increases with the increase of friction coefficient, which is due to rough lap surface, provides more sharp asperities to charge the polishing particles.     

ZF6重火石玻璃非球面数控加工技术的研究

由于重火石玻璃的密度很大,材料较软,在数控加工过程中难以控制材料的去除量。现主要针对Ф62mm ZF6非球面凸透镜,对铣磨成型工艺、抛光工艺、抛光设备及抛光液等相关工艺参数进行了研究,采用弹性模预抛光与小抛头修正抛光相结合的两步研抛法对零件表面快速抛光,给出了一套规范的ZF6玻璃非球面的数控加工工艺,同时保证了零件具有较高的面形精度,实现了该非球面元件的快速批量生产。Ф62mm口径非球面最终面形精度达到0．5μm以下,表面光洁度达到Ⅲ级,明显改善成像质量,减少系统中光学零件数目,满足了非球面的使用要求。     

铜电致化学抛光抛光液的成分及其作用

电致化学抛光是通过电化学反应生成刻蚀剂并利用扩散控制反应实现工件表面无应力抛光的新方法,抛光液的特性则是实现扩散控制反应和可控去除的关键因素。分析电致化学抛光的基本原理,并根据理论模型提出了抛光液所应具备的基本条件。针对铜的电致化学抛光,提出以FeSO_4为电活性中介体,H_2SO_4为p H调节剂,BTA为侧向电子传导抑制剂的抛光液。通过使用XRD以及XPS等表征手段对加工后的表面进行分析,研究了铜抛光液中的p H调节剂H_2SO_4以及侧向电子传导抑制剂BTA的作用机理。研究结果表明,pH调节剂H_2SO_4的主要功能为去除Cu表面的氧化层,从而促进刻蚀反应的进行,而BTA则通过吸附于铜工件表面,从而有效地抑制了加工过程中的侧向电子传导。     

Restraint of tool path ripple based on the optimization of tool step size for sub-aperture deterministic polishing

Tool path ripple error (TPR_error) is one of the main reasons due to the medium-high spatial frequency error on the surface of aspheric optics. The purpose of this paper is to analyze the effect of the tool step size to the TPR_error in sub-aperture deterministic polishing (SDP) and study a method which can optimize the tool step size to restrain this error. Three groups of simulation experiments were conducted using three different tool influence functions to simulate the uniform removal of the material. As the TPR_error is influenced by three factors, which are full width at half maximum (FWHM) of tool influence function (TIF), tool step size, and depth of material removed, each group of the experiments was conducted under the fixed TIF and depth of material removed. It turns out that both peak-to-valley (PV) and root-mean-square (RMS) values of the TPR_error become larger with the increase of the tool step size, and the variation tendency likes a reversed “L” shape curve. And, the method adopted in the simulation was further validated by the experiment. Therefore, the tool step size at the inflection point would be optimal to restrain the TPR_error together with saving the polishing time to a certain extent. This method could be used to determine the best-suited tool step size in SDP whose typical TIF is a Gaussian or Gaussian-like shape.     

磁流变变间隙动压平坦化加工力特性研究

磁流变变间隙动压平坦化加工利用工件的轴向低频振动使磁流变液产生挤压强化效应,可以有效提高加工效果并使光电晶片快速获得纳米级表面粗糙度。通过旋转式测力仪试验研究不同变间隙参数对磁流变变间隙动压平坦化加工过程中抛光正压力的影响规律,结果表明,在工件轴向低频振动作用下,抛光正压力形成脉冲正值和负值周期性的动态变化过程;将工件轴向低频振动过程分解为下压过程与拉升过程,下压速度和拉升速度对动态抛光力有不同的响应特性;随着最小加工间隙的减小抛光正压力会急剧增大;设置最小加工间隙停留时间观察抛光正压力变化,可以发现在工件最小加工间隙停留期间抛光力从峰值逐渐衰减并趋于平稳;挤压振动幅值对抛光正压力影响较小。建立了磁流变变间隙动压平坦化加工材料去除模型,弄清了在动态压力作用下,磨料更新及其附加运动机制,研究了磁流变变间隙动压平坦化加工过程中磨料颗粒对工件表面柔性划擦和微量去除的作用机理,为磁流变变间隙动压平坦化加工的工艺优化提供了理论依据。     

Prediction of surface quality considering the influence of the curvature radius for polishing of a free-form surface based on local shapes

When machining a free-form surface automatically and digitally, especially in the case of sophisticated surface shapes, it is very difficult to control the surface quality, and thus sophisticated surfaces are usually polished using manual labor. Over the past few years, there has been little attention to the calculation of material removal depth models and construction of theoretical roughness models considering the influence of the curvature radius. Bonnet polishing can be automatically adapted to polish complex free-form surfaces. This paper explores key problems related to forecasting surface quality with respect to bonnet polishing of free-form surfaces. First, for the convex and planar sub-regions, this paper deduces the relationship expressing the maximum pressure distribution and the curvature radius, and presents a computational expression for material removal depth, taking into consideration the influence of the curvature radius. An expression is also deduced for the dwell time relationship between the adjacent processing points according to the experimental results pertaining to the material removal depth. From this, a theoretical roughness model is constructed that relates the bonnet curvature radius and the workpiece curvature radius. The validity of the experiments is summarized in the conclusion. The research findings provide a basic theory for the prediction of surface quality that can be automatically adapted to a free-form surface shape in bonnet polishing.     

回转对称非球面气囊抛光控制算法研究

介绍一种新型的非球面光学零件抛光方法———气囊抛光,这种方法可以得到高质量的光学表面。针对气囊抛光加工回转对称非球面的特点,进行抛光路径规划,对去除函数进行降维处理,提出抛光驻留时间的计算方法。最后,给出抛光算法的实现框图,并按照实现框图指导实际的玻璃非球面加工,取得满意结果,验证了算法的有效性。     

集群磁流变变间隙动压平坦化加工试验研究

为了提高光电晶片集群磁流变平坦化加工效果,提出集群磁流变变间隙动压平坦化加工方法,探究各工艺参数对加工效果的影响规律。以蓝宝石晶片为研究对象开展了集群磁流变变间隙动压平坦化加工和集群磁流变抛光对比试验,通过检测加工表面粗糙度、材料去除率,观测加工表面形貌、集群磁流变抛光垫中磁链串受动态挤压前后形态变化,研究挤压幅值、工件盘转速、挤压频率以及最小加工间隙等工艺参数对加工效果的影响规律。试验结果表明：集群磁流变平坦化加工在施加工件轴向微幅低频振动后,集群磁流变抛光垫中形成的磁链串更粗壮,不但使其沿工件的径向流动实现磨粒动态更新、促使加工界面内有效磨粒数增多,而且在工件与抛光盘之间的加工间隙产生动态抛光压力、使磨粒与加工表面划擦过程柔和微量化,形成了提高材料去除效率、降低加工表面粗糙度的机制。对于2英寸蓝宝石晶电（1英寸=2.54 cm）集群磁流变变间隙动压平坦化加工与集群磁流变抛光加工效果相比,材料去除率提高19.5%,表面粗糙度降低了42.96%,在挤压振动频率1 Hz、最小加工间隙1 mm、挤压幅值0.5 mm、工件盘转速500 r/min的工艺参数下进行抛光可获得表面粗糙度为Ra0.45 nm的超光滑表面,材料去除率达到3.28 nm/min。证明了集群磁流变变间隙动压平坦化加工方法可行有效。     

数控抛光中不同运动方式下小抛光盘抛光特性之比较

阐述行星运动与平转动两种运动方式下数控抛光中小抛光盘的工作函数,论述了抛光盘本身在不同运动方式下的材料磨损情况。通过采用计算机对抛光盘工作函数及磨损曲线的模拟将抛光盘的两种运动方式进行了分析与比较。