先进光学磨削中杯形修整技术开发及应用

对于金刚石砂轮修整,尤其是有高精度要求的圆弧金刚石砂轮,杯形砂轮修整技术可以获得较好的砂轮磨削性能以及修整效率。本文开发了配套超精密平面磨床使用的杯形修整器,分析了其机械误差影响,并完成了修整实验及砂轮表面测量及半径拟合处理,从宏观上考察了该修整器对砂轮磨削性能的提高,结果证明该修整器可以进行有效修整,提高了加工工具精度,能满足金刚石砂轮修整使用要求。     

An experimental investigation of rotary diamond truing and dressing of vitreous bond wheels for ceramic grinding

Experiments of rotary diamond truing and dressing of vitreous bond grinding wheels were conducted to investigate the effects of feed, speed ratio, and overlap ratio on cylindrical grinding of zirconia. The applications of ceramic engine components with complex and precise form and the lack of technology for precision truing of diamond grinding wheels have driven the need to study the use of vitreous bond CBN and SiC wheels for form grinding of ceramics. Truing and grinding forces and the roundness and surface finish of ground zirconia parts were measured. By varying truing process parameters, a wide range of surface finish and roundness could be achieved. Experimental results showed that wheels trued at speed ratio below −1.0 could grind parts with fine surface finish and good roundness. The analysis of truing and grinding results showed the trend of increasing grinding force at higher specific truing energy and better surface finish at higher grinding force. The lack of speed control of the direct–drive, variable–speed truing spindle was observed and its effect on the reverse of direction of truing force at positive speed ratios was studied.     

Wire electrical discharge machining of metal bond diamond wheels for ceramic grinding

The application of cylindrical wire Electrical Discharge Machining (EDM) for profile truing of metal bond diamond wheels is presented. Instead of using the mechanical force to break the diamond and matrix in the grinding wheel, the wire EDM process uses the thermal energy or electrical sparks between the wire and rotating grinding wheel to remove the metal bond and form the wheel. The design and manufacture of a corrosion-resistant, precise spindle with the high-electrical current capability for wire EDM truing of grinding wheel is first introduced. Three truing configurations were designed to study effects of wire EDM process parameters and to investigate the level of form accuracy and corner radii achievable by the wire EDM truing of diamond wheels. Results show that the wire EDM process can efficiently generate the μm-scale precision form on the diamond wheels. The wheel, after truing, was used to grind the silicon nitride workpiece. Grinding forces and wheel wear rate were measured. In the beginning of the grinding, high wheel wear rate was identified. The subsequent wheel wear rate was considerably lower and stabilized.     

A novel laser-assisted truing and dressing technique for vitrified CBN wheels

The preparation of vitrified CBN or diamond wheels by truing and dressing has a large influence on the grinding performance. A worn diamond dresser cannot produce sufficient protrusion of cutting grain edges. To reduce the wear of diamond dressers and hence guarantee a desired wheel surface, a novel truing and dressing method, namely, laser-assisted truing and dressing, is proposed and tested to achieve good dressing quality and efficiency. A systematical experimental feasibility study on this newly proposed laser-assisted truing and dressing technique is conducted by investigating truing efficiency, truing accuracy, dresser wear, dressed wheel profiles, and specific forces in comparison with those of the conventional single diamond methods. Experimental results show that the new laser-assisted truing and dressing technique offers a number of advantages over the conventional single-tip diamond dressing and truing method. In addition, the underlying mechanism of the laser truing and dressing process is investigated through the careful analysis of the properties of chips and the microscopic structural characteristics of wheels.     

An experimental investigation of dry-electrical discharge assisted truing and dressing of metal bonded diamond wheel

Metal-bonded diamond wheels have superior qualities such as high bond strength, long wheel life, wear-resistant ability and high grinding efficiency. But it is very difficult to true and dress diamond wheel because of its highest hardness. Traditional mechanical truing does not guarantee truing accuracy of diamond wheel because of single diamond dresser wears out very quickly. To reduce wear of diamond dresser and hence guarantee a desired wheel surface, a novel truing and dressing method, namely, dry electrical discharge (dry-ECD) assisted truing and dressing, is proposed and tested to achieve good dressing quality and efficiency. Because the diamond wheel is mounted on the MK9025 optical profile grinder, dielectric liquid is forbidden. The new dry-ECD dressing/truing method basically eliminates the use of dielectric liquid. Therefore, it is free from the serious problem of electrolytic corrosion caused by electrolytic current flowing through water encountered in conventional ECD. The FE analysis of temperature distribution in dry-ECD assisted truing and dressing diamond wheel using ANSYS is performed in this study. Temperature field simulation helps to select optimized parameters under certain conditions. Energy dispersive X-ray (EDAX) analysis was used to measure the composition of diamond wheel before and after dry-ECD assisted truing and dressing. Further, hard alloy grinding experimental results proves that a little variation in material composition of diamond wheel after dry-ECD assisted truing and dressing does not influence grinding result. A series of experiments of dry-ECD assisted truing and dressing of metal bonded diamond wheel are conducted to investigate truing efficiency, truing accuracy, dresser wear, dressed wheel profiles and three-dimensional truing/dressing forces in comparison with those of the conventional single diamond methods. Experimental results show that the new dry-ECD assisted truing and dressing technique offers a number of advantages over the conventional single-tip diamond dressing and truing method. Furthermore, mechanism of the dry-ECD assisted truing and dressing is investigated through the careful analysis of the properties of chips.     

A study on ELID ultra precision grinding of optical glass with acoustic emission

ELID grinding of BK7 glass and Zerodur was investigated using acoustic emission. Experiments showed that the contacting area between the wheel and workpiece in a grinding process was critical to influence wheel loading for a fine grit size resin-bonded cup wheel. ELID can be used for efficient material removal when the wheel/workpiece contacting area is large. Correlations were observed between the dressing intensity on the ELID wheel and the detected AE signals. Aggressive ELID dressing parameters for grinding with finer grit size wheels corresponded to a lower AE level. With an increase in the processing time of an ELID wheel, low and stable AE amplitudes became large with fluctuations due to the deterioration of the grinding wheel. Results indicate that the AE sensing technique has the potential to be adopted as an effective method for monitoring an ultra precision grinding process, identifying the condition of the grinding wheel and investigating the mechanism of ELID grinding.     

Computer simulation of sub-micron-scale precision truing of a metal-bonded diamond grinding wheel

A new simulation mode of wheel profile generation was proposed in precision truing of a metal-bonded diamond grinding wheel by considering the mutual wear of grinding wheel and truer in sub-micron scale. The aim is to understand how truing parameters influence truing accuracy and truing efficiency, namely wheel profile flatness and truing number. In order to assure the sub-micron-scale accuracy of a trued wheel profile, dry electro-contact discharge was employed in arc envelope truing. First, an arc-shaped truing profile replicated on wheel profile was defined and analyzed theoretically and then identified by truing experiment; second, the micro-truing ratio describing the mutual wear of a grinding wheel and truer related to the depth of cut was investigated by micro-truing experiment; then the simulation mode of the truing grinding wheel was established by using dispersed profile coordinates of the grinding wheel and truer with reference to the micro-truing ratio; finally, simulation analysis was conducted to trace on-line formation of the trued wheel profile in truing process. It is confirmed that this simulation method is valid and applicable to visualize the sub-micron-scale truing process. It is also found that by decreasing the depth of cut or plunge truing number wheel profile flatness decreases but truing number increases. It is concluded that there exist minimum wheel profile flatness and minimum truing number in a truing process, which can be used to optimize truing parameters for efficient precision truing.     

Minimization of effect of CBN wheel wear on ground gear errors

Resistance to wear of CBN grinding wheels is much higher than that of conventional (Al₂O₃) wheels. However, CBN grinding wheels are seldom used in gear grinding, when production scale is small, due to the difficulty in truing. Moreover, wear of the grinding wheel greatly affects the accuracy of tooth trace, in most cases. Considering this problem, the authors proposed new processes in which the accuracy of the tooth trace and tooth profile was hardly affected by wear of the wheel. While grinding was performed using a conventional method, a concave tooth-trace error of about 2 μm occurred after grinding only 30 teeth. In one of the proposed methods, the concave tooth trace error never occurred even when 2000 teeth were ground by the same wheel. In the third method, the CBN layer is effectively used for gear grinding by giving an additional motion which is independent of the tooth profile generating motion.     

金刚石砂轮精密修整工艺研究

金刚石砂轮机械磨削是砂轮整形的传统方式。砂轮旋转速度以及工具砂轮的进给量是金刚石砂轮机械精密整形的主要工艺参数。通过在超硬材料砂轮整形机床上的大量实验和砂轮磨削力的分析,得到了金属结合剂和树脂结合剂金刚石砂轮精密整形的比较理想的工艺参数;确定了工具砂轮的线速度应在11 m/s左右,工具砂轮轴转速在1 050～1 800 r/min;金刚石砂轮轴转速设定在400～1 000r/min,金刚石砂轮的线速度为2.6～10.5 m/s。同时,分析比较了机械修锐和喷砂修锐的效果。     

熔石英磨削砂轮截面轮廓分析与优化

为提高熔石英光学元件磨削加工质量,降低亚表面缺陷层深度,通过实验和理论分析发现,具有平直截面轮廓的平行金刚石砂轮,在加工熔石英光学元件时砂轮边缘位置处会产生加工应力集中,该应力集中直接导致了元件表面产生"连续白线"状深缺陷,其深度达22 μm。为抑制砂轮边缘位置加工应力集中现象,设计了"中央平直线+两侧边缘圆弧过渡"的复合式截面轮廓,并提出了相应的修整方法。通过砂轮修整实验,验证了该方法的可行性,磨削元件"连续白线"状深缺陷得到明显改善,亚表面缺陷深度小于2.5 μm,实现熔石英元件的低缺陷磨削加工。      

陶瓷结合剂金刚石砂轮修整的研究(Ⅲ)——杯形砂轮修整器的修整机理

在前两篇文章中,笔者提出了一种以杯形砂轮为工具的金刚石砂轮修整方法。本文探讨了以该方法修整陶瓷结合剂金刚石砂轮的机理。主要结论如下:(1)杯形砂轮的修整作用主要取决于从GC砂轮上脱落下来的磨粒对金刚石磨粒和结合剂桥的冲击。(2)杯形砂轮越软,其上脱落下来的磨粒越大,修整效率越高,但金刚石砂轮表面越粗糙。(3)用烧结体多点金刚石笔修整时,从最外表面开始,金刚石砂轮表层磨粒依次被金刚石笔削去。(4)作为添加材料加入到陶瓷结合剂金刚石砂轮中的碳化硅磨粒,其顶端在磨削初期即被磨平。(5)磨削难磨材料时,最好使用无添加材料的陶瓷结合剂金刚石砂轮。     

Electrical discharge truing of metal-bonded CBN wheels using single-point electrode

Industrial application of superabrasive metallic-bond form-wheels is currently limited by problems arising when trying to recover geometrical accuracy after precision is lost due to wear. Literature shows this is a current field of research, and different configurations of the electrical discharge dressing process can be found. In this work an original method for form truing of metal bonded cubic boron nitride (CBN) form wheels is presented for the first time in literature. The method uses a single-point metallic electrode, thus eliminating the need for expensive form electrodes. A mathematical model was derived to predict electrode path and velocity. The model includes the effect of electrode wear. Experimental tests were carried out on a test bench, showing over 90% efficiency in the removal of material from the wheel surface. Wheel performance after truing was examined through grinding tests.     

金刚石砂轮V形尖端的数控对磨微细修整技术

针对金刚石砂轮V形尖端的微细修整困难的问题,开发出一种对磨成型的V形尖端修整技术。在数控修整中,砂轮作V形的直线插补运动与修整工具对磨,逐渐被修整成V形尖端。本实验中修整工具分别是#600和#180绿碳化硅(GC)油石,砂轮分别为SD 400和SD 600金刚石砂轮。实验结果表明,较细粒度的修整工具不仅可以将砂轮V形尖端修整出更小的圆弧半径,而且也能够将微小磨粒修锐得更锋利,从而使加工的单晶硅微沟槽形状更加整齐。此外,采用修整后的圆弧半径小于20μm的SD 600金刚石砂轮V形尖端可以实现光纤石英微阵列沟槽的微细加工,也可以在SiC陶瓷和WC合金基板上加工出微锥塔阵列空间的功能表面。因此,数控对磨在位修整的工艺可以用于金刚石砂轮V形尖端的微细修整,实现硬脆性基板的微细磨削加工。     

金刚石磨轮的接触放电修整方法

本文论述了该种修整方法的机理,对其工艺和评价指标进行了分析和总结。     

D杯形砂轮修整碟形金刚石砂轮试验研究

本文采用了D杯形砂轮与碟形砂轮对磨法来修整大直径树脂结合剂碟形金刚石砂轮。在分析研究杯形砂轮修整碟形砂轮的修整原理及修整方式的基础上，用自行研制的专用修整装置，从主轴转速、修整深度、修整工具结合剂类型等方面进行了对比工艺试验研究，总结了杯形砂轮修整碟形砂轮的不同工艺参数与修整效率、修整质量之间的工艺规律。试验结果表明，在本试验条件下主轴转速500r／min，修整深度0．02mm的修整效率较好；细粒度、中等浓度的青铜结合剂杯形金刚石砂轮与粗粒度、高浓度的杯形砂轮修整碟形砂轮相比，后者具有较好的修形效果和修整效率；D杯形砂轮与GC杯形砂轮交替配合使用可以大大提高碟形金刚石砂轮的修形效率和修锐效果。     

Wheel curve generation error of aspheric microgrinding in parallel grinding method

In aspheric grinding of hard brittle material, in-process wheel wear is a crucial factor affecting the profile error of the ground surface. To suppress wheel wear, parallel grinding is adopted. Since the wheel and workpiece contact point changes during parallel grinding, geometric wheel error influences machining accuracy significantly. In the wheel truing process with a cup truer, the wheel radius is determined by the angle and distance between the wheel and the truer. Through geometric analysis, this paper presents a new equation of wheel radius, which enables process parameters, such as setup error or thermal error, to be determined easily. Simulation results show that wheel radius error is predominantly affected by vertical deviation between the wheel rotation center and the truer center. Experimental results show that wheel radius errors match those from simulation well.     

杯形砂轮修整碟形金刚石砂轮磨削力研究

本文通过对杯形砂轮修整碟形金刚石砂轮的试验，对以研磨为主要因素的修整磨削力进行了研究，从磨削模型、砂轮参数、工艺参数等方面研究了修整时的磨削力规律，并用角正回归法推导了磨削力试验公式。实验结果表明：砂轮变速磨削，径向磨削力降低，切深量对磨削力的影响最大，而低速磨削时磨削力最大。磨削力信号是一种平稳的周期振动信号。角正回归法是一种高精度的回归法。变速磨削时修整效率最佳。     

A study on the mirror-like grinding of die steel with optimum in-process electrolytic dressing

In recent years, grinding techniques for the precision machining of brittle materials used in die, mold and optical parts have been improved by using super-abrasive wheels and precision grinding machines. The completion of the optimum dressing of a super-abrasive wheel makes possible the effective precision grinding of die steel STD-11. However, the present dressing system cannot have control of the optimum dressing of the super-abrasive wheel.In this study, a new system and the grinding mechanism of optimum in-process electrolytic dressing are proposed. This system can carry out the optimum in-process dressing of a super-abrasive wheel. Therefore, optimum in-process electrolytic dressing is a good method to for obtaining the efficient and mirror-like grinding of STD-11.     

金属结合剂金刚石砂轮的修整研究(Ⅱ)——修整金属结合剂金刚石砂轮的机理

在上一篇文章中。笔者提出了一种新的测量磨粒突出高度的方法,并就磨粒突出高度同砂轮磨削性能的关系进行了研究。本文探讨了结合剂密实型金刚石砂轮的修整机理,着重讨论修整时磨粒周围结合剂的会除过程。证明了去除结合剂的机制是杯形砂轮上脱落下来的GC磨粒的研磨作用。主要结论如下:(1)修整时,GC磨粒从杯形砂轮上脱落并研磨结合剂,从而产生修整效果。因此,杯形砂轮修整器在对金属结合剂金刚石砂轮进行整形的同时,也对其进行修锐。(2)控制冷却液流量使GC砂轮表面附有一层游离磨粒,可以使修整比最高。(3)只要修整次数足够多,平均磨粒突出高度只取决于修整条件。(4)游离GC磨粒的尺寸越大,研磨作用越强,因此修整比越高,平均磨粉突出高度越大。     

On-machine dry electric discharge truing of diamond wheels for micro-structured surfaces grinding

Precision grinding with diamond wheels gives a promising alternative to achieve high quality micro-structured surfaces on optical molds. However, it is difficult to true these diamond wheels efficiently, because of the remarkable resistance property and the geometrical limitation of small wheel profile. In this paper, an on-machine dry-EDT method to precision shape and prepare diamond wheels with various profiles was proposed for micro-structured surface grinding. Firstly, the fundamental truing errors were analyzed based on the dry-EDT kinematics. And then the capabilities of dry-EDT truing for high abrasive concentration metal bonded diamond wheels were presented. Next, the effects of kinematic parameters variables on trued wheel profile accuracy were investigated. Finally, the micro-structured surfaces on SiC ceramic and tungsten carbide WC were ground by these trued diamond wheels. The experiments results showed that the arc-shaped diamond wheel (diameter of 200 mm) with 4 μm profile error (PV) and 1.0023 mm profile radius, and the V-shaped diamond wheel with 22.5 μm V-tip radius and 120.03° profile angle could be obtained by on-machine dry EDT. The kinematic parameters of dry-EDT have an important influence on truing profile accuracy of diamond wheels, especially for the tip of V-shaped wheel. The subsequent grinding show that the edge radius of V groove array on SiC is less than 2 μm, while the radius of included corner is around 55 μm. The PV error of ground arc groove array on WC is less than 5 μm. The surface roughness of ground micro-structured surface R_a is 142 nm and 97 nm for SiC and WC, respectively.