自由曲面注塑凸模芯的数控精密磨削方法

针对自由曲面注塑模芯的精密加工困难的问题，提出在数控磨床上采用圆弧形金刚石砂轮进行等包络迹高度的数控成形磨削新方法。首先，建立等包络迹高度的行走路径计算方法，然后，分析等包络迹高度与曲面光滑平整成形的关系，最后，对分布在成形磨削表面的面形误差和表面粗糙度进行检测和评价。试验结果表明，减小等包络迹高度可以实现自由曲面的连续光顺性加工。在自由曲面上的非接触激光扫描检测结果显示，面形误差小于200μm。此外，在加工高速钢模芯时，表面粗糙度Rα可以达到50nm以下。     

金属基圆弧形金刚石砂轮在位精密修整实验研究

金属基圆弧形金刚石砂轮具有耐磨性好、结合强度高、寿命长等优点,广泛的应用于非回转、非对称大尺寸光学自由曲面的精密磨削中,但是,金属基体砂轮在位精密修整困难。基于此,采用旋转GC磨棒在位精密修整法,提出了金属基圆弧形金刚石砂轮的进给补偿在位精密修整策略,并在超精密机床上搭建在位修整系统,对D46金属基圆弧形金刚石砂轮进行了修整实验,同时对修整前后的砂轮轮廓误差进行了在位测量,最后采用超景深显微镜和Zygo白光干涉仪对修整后砂轮表面的金刚石磨粒和轮廓形貌进行了观察。结果表明,D46金属基圆弧形砂轮的修整效果明显,验证了本文提出的金属基圆弧形砂轮进给补偿修整策略的正确性和可操作性,实现了金属基圆弧形金刚石砂轮的在位精密修整。     

F-Theta自由曲面透镜的精密与镜面磨削

针对光学玻璃的F-Theta自由曲面透镜加工困难等问题,提出将金刚石砂轮的椭圆环面代替圆环面,进行F-Theta自由曲面磨削加工,研究形状误差的补偿磨削方法和光学玻璃的镜面磨削工艺。根据F-Theta透镜的自由曲面建立砂轮与工件相切的刀具轨迹法向算法。采用#46粗金刚石砂轮修整成椭圆环面,提出自由曲面磨削的法向误差补偿加工模式。最后,采用#3000超细金刚石砂轮的椭圆环面进行轴向磨削试验。试验结果表明:传统的垂直误差补偿磨削可减小面形误差45.9%及其PV值11.6%;而新提出的法向误差补偿磨削可减小面形误差47.9%及其PV值41.5%。此外,超细砂轮磨削可使得自由曲面的粗糙度达到28 nm,其镜面磨削工艺有别于较粗砂轮磨削工艺。因此,椭圆环面砂轮的法向补偿磨削是提高自由曲面加工精度的有效方法,而且,无需研磨抛光就可以实现光学玻璃的自由曲面镜面磨削。     

电镀金刚石砂轮高效精密修整及熔融石英磨削试验研究

大尺寸光学玻璃元件主要采用细磨粒金刚石砂轮进行精密/超精密磨削加工,但存在砂轮修整频繁、工件表面面形精度难以保证、加工效率低等缺点。采用大磨粒金刚石砂轮进行加工则具有磨削比大、工件面形精度高等优点,然而高效精密的修整是其实现精密磨削的关键技术。采用Cr12钢对电镀金刚石砂轮(磨粒粒径151 μm)进行粗修整,借助修整区域聚集的热量加快金刚石的磨损,可使砂轮的回转误差快速降至10 μm以内。结合在线电解修锐技术,采用杯形金刚石修整滚轮对粗修整后的电镀砂轮进行精修整,砂轮的回转误差可达6 μm以内,轴向梯度误差由6 μm降至2.5 μm。通过对修整前后的金刚石砂轮表面磨损形貌成像及其拉曼光谱曲线分析了修整的机理。对应于不同的砂轮修整阶段进行熔融石英光学玻璃磨削试验,结果表明,砂轮回转误差较大时,工件材料表面以脆性断裂去除为主;随着砂轮回转误差和轴向梯度误差的减小,工件表面材料以塑性去除为主,磨削表面粗糙度为Ra19.6 nm,亚表层损伤深度低至2 μm。可见,经过精密修整的大磨粒电镀金刚石砂轮可以实现对光学玻璃的精密磨削。     

圆弧形砂轮精密修整及其声发射在线监测技术

针对球面、非球面及自由曲面超精密磨削加工用圆弧形金刚石砂轮难以精密修整的问题,提出基于旋转绿碳化硅（GC）磨棒的端部在位精密修整方法及修整过程的声发射在线监测技术。基于圆弧形金刚石砂轮的结构特性,制订圆弧形金刚石砂轮的在位精密修整与修整过程的声发射在线监测技术方案。依据修整与在线监测方案,对D64圆弧形金刚石砂轮进行修整实验及其声发射信号采集,修整后跳动误差小于10μm,比修整前减小30μm左右,砂轮精度显著提高。利用声发射信号均方根值获取砂轮修整结束的特征预警阈值,实现了旋转GC磨棒端部在位精密修整过程的在线监测以及修整结束时间的准确判断,可以有效提高球面非球面磨削加工过程的效率。     

陶瓷飞行体的微沟槽结构曲面精密磨削与减阻性能

为减小飞行阻力和增强雷达散射,提出采用精密磨削和微细磨削组合加工工艺在陶瓷飞行体表面加工出曲面微沟槽结构。首先,利用精密修整后的金刚石砂轮圆环形端线沿数控曲线插补轨迹将陶瓷加工成光滑曲面,然后利用微细修整成角度为60°的金刚石砂轮V形尖端在曲面上沿飞行体轴向方向加工出微沟槽结构,最后通过风动试验分析不同曲面结构对空气阻力的影响。磨削试验结果显示,精密磨削和微细磨削组合加工可在高度32 mm、直径30 mm和表面粗糙度0.262?m的陶瓷曲面上加工出深度为578~581?m、角度为61.56°和尖端半径为48?m的微沟槽结构,其深度误差仅为3?m,曲面加工的平均形状误差为142?m,加工精度可控制在0.5%以内。此外,加工后的陶瓷表面粗糙度主要受砂轮粒度和磨削工艺的影响。风动试验结果表明:微沟槽结构曲面分别比光滑和粗糙曲面减小轴向阻力约36%和42%,也比光滑曲面减小侧面阻力约39%。因此,陶瓷飞行体的光滑曲面被加工出规则可控的微沟槽结构可以减小飞行阻力。     

小直径青铜结合剂微粉砂轮的电火花精密修整实验研究

青铜结合剂微粉金刚石砂轮常用于脆硬材料的超精密磨削加工,但其修整十分困难;采用内冲式弧面铜钨电极对W10青铜结合剂微粉金刚石砂轮进行了电火花修整试验研究;搭建试验平台并设计三种不同弧度的内冲式电极,采用超景深三维显微镜、精密粗糙度仪、CCD激光位移传感器以及扫描电子显微镜,对修整后的砂轮进行了表面形貌检测、轮廓检测和磨削性能测试;检测结果表明60?弧面电极的内冲效果最好,修整砂轮表面磨粒突出明显,数量较多且密集度高,金刚石磨粒保存完好;砂轮圆跳动误差值最小,可达1.7?m、1.8?m、1.8?m;试验验证了采用60?弧面电极修整砂轮的磨削性能最好,加工的试件表面粗糙度可达Ra2.273 nm,已基本达到超精密镜面磨削的质量。     

ELID精密镜面外圆磨削技术的应用

在线电解修整(ELID)精密镜面磨削有效地实现了许多难加工材料的平面精密加工和高效加工.本文介绍了ELID磨削技术在精密镜面外圆磨削上的应用.通过采用金属基超硬磨料砂轮在线电解修整对硬质合金、碳化硅陶瓷进行精密镜面外圆磨削,得到了表面粗糙度Ra=0.025～0.028μm的加工表面.     

基于放电修锐的粗金刚石砂轮干式镜面磨削技术

为解决超硬金刚石砂轮修锐效率较低以及环境友好性等问题，采用干式接触放电修锐(ECD)技术对粗金刚石砂轮进行修锐，获得较高的磨粒出刃，可以实现硬质合金和模具钢等高强高硬材料的高效精密镜面磨削加工。对46#金属结合剂粗金刚石砂轮进行机械修锐和干式ECD修锐，再利用修锐后的粗金刚石砂轮对硬质合金和模具钢进行干式轴向磨削加工，对比分析两种修锐条件下磨削工艺参数对硬质合金干磨削力、磨削表面粗糙度和磨削力比的影响。实验结果表明：硬质合金的干式轴向磨削力及其表面粗糙度随砂轮速度的增大而减小，随进给速度和切削深度的增大而增大；与机械修锐相比，干式ECD修锐能够获得更高的磨粒出刃和更好的表面质量，以及更小的磨削力和磨削力比；硬质合金和模具钢的干磨削表面粗糙度Ra分别可达0.058μm和0.022μm。     

圆弧形金刚石砂轮的数控对磨成形修整试验

针对圆弧形金刚石砂轮精密修整的操作困难和装置复杂的问题,提出一种新的数控对磨成形修整方法.在该成形修整中,金刚石砂轮被驱动沿着圆弧插补运动轨迹与GC磨石对磨,逐渐形成砂轮的圆弧形轮廓,用于超硬材料的曲面磨削.在建立砂轮圆弧形轮廓的数控修整模式的基础上,分析定位误差与修整形状偏差的关系.此外,建立修整精度和修整率的评价指标,进行正交试验,研究修整工艺参数,即砂轮转速、行走速率和进给深度,对修整精度和修整率的影响.对该数控修整模式分析表明,在该数控对磨成形修整中不同半径的砂轮圆弧形轮廓能够被修整成形,可用于不同曲率的曲面磨削.同时,当定位误差在0.1 mm以内时,最大的修整形状偏差不超过5μm/10 mm.成形修整试验结果显示,影响修整精度和修整率的主要修整工艺参数分别为砂轮转速和行走速率.增加砂轮转速可以同时改善修整精度和修整率;增加行走速率会提高修整率,但会降低修整精度.此外,采用适宜的修整工艺,目标形状误差和目标修整率可以分别达到25.1μm/8mm和7.31x10-3mm3/mm3,分别提高修整精度2～3倍和修整率约7倍.     

垂直式超硬砂轮圆弧修整器设计与砂轮修整

针对圆弧形超硬砂轮修整难度大、修整精度低的问题,对树脂结合剂圆弧形金刚石砂轮进行了精密修整研究。设计制造了一种垂直式超硬砂轮圆弧修整器,通过修整试验研究了不同粒度的圆弧形砂轮在修整前后表面粗糙度、弧形精度、圆度、表面形貌的变化情况。砂轮修整前后对氮化硅陶瓷轴承套圈沟道进行了磨削,并测量了磨削后的轴承套圈沟形精度。研究结果表明：相比修整前,修整后砂轮表面粗糙度平均值由1.731 8 μm减小至0.772 4 μm,减小了55.4%;弧形精度平均值由33.604 7 μm减小至8.527 6 μm,减小了74.6%,修整后4个砂轮的弧形精度更加稳定,且随着砂轮粒度的减小,弧形精度略有减小趋势;砂轮圆度平均值由43.721 μm减小至18.002 μm,减小了58.8%,修整使大量新的磨粒露出。所设计的垂直式超硬砂轮圆弧形修整器可对圆弧砂轮进行精密修整,可改善圆弧形砂轮的弧形精度及圆度,修整后砂轮磨削的轴承套圈沟形精度得到了大幅提高。     

Form-truing error compensation of diamond grinding wheel in CNC envelope grinding of free-form surface

In computer numerical control (CNC) grinding of free-form surface, an ideal arc profile of trued diamond grinding wheel is generally employed to plan 3D tool paths, whereas its form-truing errors greatly influence the ground form accuracy. A form-truing error compensation approach is proposed by using an approached wheel arc profile to replace the previously designed ideal one. The objective is to directly compensate the trued wheel arc-profile errors. It may avoid the time consumption of traditional approach that compensates the measured coordinate point errors of workpiece to an iterative grinding operation. First, the 3D tool path surface was constructed to plan the 3D tool paths. Second, the CNC arc truing of grinding wheel was conducted to analyze the form-truing error distribution relative to the applied wheel arc profile. Then, the form-truing error compensation was carried out in CNC envelope grinding. Finally, the iterative closest point (ICP) algorithm was used to match the measured coordinate points of workpiece to ideal free-form surface. It is shown that the 3D tool path surface constructed is practicable to plan arbitrary 3D tool paths for the form-truing error compensation. The ICP matching may be used to investigate 3D ground form error distribution. It is confirmed that the form-truing error compensation can directly improve the 3D ground form accuracy. It may decrease the 3D ground form error by about 20% when the 2D form-truing error is reduced by about 58% using the same truing conditions for CNC grinding.     

Experimental study on fabrication and evaluation of micro pyramid-structured silicon surface using a V-tip of diamond grinding wheel

A mechanical fabrication of micro pyramid-structured silicon surface is proposed using crossed grooving with a 60° V-tip of diamond grinding wheel. It can obtain high form-accuracy, good surface quality and efficient productivity in contrast to laser machining and etching, and also assure a high aspect ratio in contrast to other mechanical processes. In order to describe its micro-structured topography, a white-light interferometer was employed, and its measured point cloud was matched using an Iterative Closest Point (ICP) algorithm. In micro grinding, a novel CNC mutual-wear truing was first developed to sharpen the wheel V-tip; then, the effects of microscopic wheel topography, silicon crystal-orientation and grinding parameter were investigated on ground micro-topography, truing ratio and material removal ratio; finally, its form-accuracy, pyramid top radius, groove tip radius, surface roughness and aspect ratio were evaluated. It is shown that better microscopic grain protrusion topography on wheel V-tip produces much larger material removal ratio and much better micro-structured topography in micro grinding, but it leads to much less truing ratio in finer GC truing. In micro grinding, silicon crystal-orientation has little effect on micro-structured topography due to diamond crystal-orientations that are randomly distributed on wheel V-tip. Although the micro pyramid-structured form error is only about 3.4 μm, its V-groove bottom and pyramidal top have very large form errors (23.1-47.9 μm) due to the sharpness of wheel V-tip and the frangibility of micro pyramid top. On increasing feed speed, its pyramid top radius decreases and its groove tip radius slightly increases, ultimately leading to an increase in aspect ratio, whereas its surface quality descends. It is concluded that the micro-pyramid arrays may be precisely patterned on silicon surface using a SD600 wheel with crossed tool paths, on-machine V-tip truing and the depth of cut in 1 μm.     

树脂基圆弧金刚石砂轮的在位精密成形修整技术

针对球面、非球面及自由曲面超精密磨削加工用树脂基圆弧形金刚石砂轮难以精密修整的问题,提出基于旋转绿碳化硅(GC)磨棒的在位精密成形修整技术。在分析GC磨棒和圆弧砂轮几何关系的基础上,确定修整过程中圆弧插补轨迹的补偿方法及GC磨棒运动轨迹的设计方案。采用KEYENCE激光测微仪采集砂轮圆弧特征点,表征圆弧砂轮的修整状况。研究不同粒度的GC磨棒、进给深度和圆弧插补速度对圆弧金刚石砂轮修整率和修整精度的影响规律。研究结果表明,该修整方法可根据加工曲率半径要求实现不同圆弧半径砂轮的精密在位修整,修整后可自动消除砂轮垂直方向的位置偏差;采用400#和800#的GC磨棒对D3和D7砂轮均有较高的修整率(0.7~6.7);与400#和1500#的GC磨棒相比,800#GC磨棒更适合粒度为D3和D7圆弧金刚石砂轮的精密修整;相比圆弧插补速度,进给深度对砂轮的圆弧半径尺寸误差和形状误差影响更大,进给深度越小,圆弧半径尺寸误差和形状误差越小;修整后两种砂轮的圆弧半径误差均可控制在5%以内,D3砂轮的形状误差可控制在3μm/4 mm以内,D7金刚石砂轮可控制在6μm/4 mm以内,修整后比修整前形状误差提高14倍左右。     

Planar nanogrinding of a fine grained WC-Co composite for an optical surface finish

Nanogrinding of a fine-grained WC-Co composite was developed to achieve an optical quality surface without further polishing. Direct planar grinding was conducted with a CNC grinding machine using a metal-bond diamond wheel of grit size of 15 μm, under the nanogrinding conditions selected. The ground planar surfaces were examined using laser and optical interferometry, atomic force microscopy, and scanning electron microscopy to measure flatness, surface roughness, and surface integrity as a function of grinding conditions. Damage-free, planar mirror surfaces with a flatness (peak-to-valley, PV) at the submicron scale and surface roughness <5 nm R_a were obtained.     

微晶玻璃超精密磨削技术研究

分析实现微晶玻璃超精密磨削的技术条件和在线电解修整超精密磨削机理,并采用铸铁基金刚石砂轮结合在线电解的磨削方法对微晶玻璃进行了精密磨削,获得Ｒａ为２．３０８ｎｍ的超光滑表面。     

多线砂轮复合自动修磨装置的设计与精度检验

多线砂轮复合自动修磨装置采用CNC数控系统,利用两个独立金刚石滚轮休整器,实现单支和多支砂轮的高精度修磨,极大地降低了人工操作带来的加工误差,提高了产品加工精度和效率。通过表面粗糙度检测数据可知,具有多线砂轮复合自动修磨装置的数控丝锥螺纹磨床完全符合加工精度要求。同时,采用多元回归方程建立基于砂轮修整参数的表面粗糙度预测模型,并设计单因素试验,得到砂轮修整参数与表面粗糙度之间的关系。由显著性分析结果得出,径向修整进给量是影响表面粗糙度的主要因素。     

Grinding damage of BK7 using copper-resin bond coarse-grained diamond wheel

Coarse-grained wheels can realize high efficient grinding of optical glass. However, the serious surface and subsurface damage will be inevitably introduced by the coarse-grained wheels. In this paper, the grinding damage of a copper-resin bond coarse-grained diamond wheel with grain size of 150μm was investigated on optical glass BK7. The wheel was first properly trued with a metal bond diamond wheel, then pre-dressing for the wheel and grinding experiments are carried out on a precision grinder assisted with electrolytic in process dressing (ELID) method. The surface roughness (Ra) of ground surface was measured using an atomic force microscope (AFM) and the surface topography were imaged by a white light interferometer (WLI) and the AFM. The subsurface damage level of ground surface was evaluated by means of both MRF spot method and taper polishing-etching method, in term of the biggest depth of subsurface damage, distribution of micro defects beneath the ground surface, the cluster depth of subsurface damage, relationship between subsurface damage (SSD) and PV surface roughness (SR), propagating distance and pattern of cracks beneath the ground surface. Experimental results indicate that a well conditioned copper-resin bond coarse-grained diamond wheel on a precision grinder can generate good surface quality of Ra less than 50nm and good subsurface integrity with SSD depth less than 3.5ε for optical glass BK7.     

单层钎焊金刚石砂轮的修整实验研究

为满足单层钎焊金刚石砂轮高效精密加工的性能要求,对磨粒有序排布单层钎焊金刚石砂轮的修整进行了实验研究。采用磨粒有序排布的钎焊金刚石修整工具对钎焊砂轮进行了修整,该修整方法通过修整工具粒度的变化以及修整速比的调整来控制砂轮形貌,从而使氧化锆的磨削表面粗糙度达到了精密加工的水平。对砂轮形貌进行了观测统计,数据表明,砂轮磨粒的等高性得到明显改善且避免了磨粒端部的严重钝化。