基于二维位移传感器的砂轮表面形貌测量

砂轮表面的三维形貌对保证其磨削质量有重要意义。采用高精度二维位移传感器在线测量砂轮的表面形貌,再通过建立的砂轮三维形貌基准平面和数字滤波方法,用测量数据计算得到砂轮表面的三维形貌评价参数。结果表明:该评价参数与Zeta自动三维测量系统的测量结果基本相同,验证了该评价方法的有效性和实用性,可为砂轮修整及其磨削加工提供参考指标。      

砂轮表面形貌仿真方法研究

砂轮表面形貌对磨削加工过程和已加工表面质量有着极大影响,但由于砂轮表面磨粒分布的随机性,描述砂轮表面形貌非常困难。通过对砂轮表面进行采样和数据处理,运用统计学理论和Johnson变换方法获得了非正态分布砂轮表面形貌的数学描述方程,在此基础上对砂轮表面形貌进行仿真。选用伯明翰14参数集的部分参数作为评价标准,对测量的砂轮表面形貌和仿真形貌进行比较,结果显示:二者具有很好的一致性,6个参数的平均相对误差仅为2.97%。结果充分证明了该仿真方法的正确性。      

Simulation of precision grinding process, part 1: generation of the grinding wheel surface

This paper is in two parts describing the kinematic simulation of the grinding process. The first part is concerned with the generation of the grinding wheel surface. A numerical procedure for effectively generating the grinding wheel topography is suggested. The procedure is based on the transformation of a random field. The sufficient condition for the transformation is discussed, and two transformations satisfying the condition are introduced. Numerical examples are used to illustrate the viability of the approach. It will be shown that the generated and measured grinding wheel topography share the same probabilistic characteristics.     

Influence of controlled tool orientation on pattern formation and waviness in surface grinding

The surface of ground components can exhibit quality impairments which are attributed to grinding wheel irregularities. A remaining grinding wheel imbalance or a non-uniform grinding wheel topography results in a radial run-out which strongly affects the generated surface. By measuring and adjusting the phase-shift of the grinding wheel orientation during consecutive grinding passes, the resulting workpiece surfaces can significantly be improved. Experimental investigations show a strong effect of the phase-shift on the waviness profile and the pattern formation, as the pattern wave length coincides with the tangential feed. Setting the phase-shift directly affects the engagement conditions like the contact stiffness, remarkably influencing the dynamic process behaviour. The amplitudes of the normal force at rotational frequency have a strong effect on the workpiece surface, which can be influenced by a variation of the phase-shift. Constancy of table oscillating period will further increase due to faster machine control hardware, making longer periods of constant phase-shifts more likely to occur. As this parameter is mostly uncontrolled, it can cause intermittent grinding errors.     

砂轮表面形貌检测方法的研究进展

砂轮表面形貌特征是砂轮磨削性能的主要决定因素。准确地检测砂轮表面形貌不仅有助于进一步认识磨削机理,更是砂轮表面形貌建模和磨削仿真不可或缺的先决条件。本文中总结了典型的砂轮表面形貌检测方法,概述了各检测方法的基本原理,并分析了它们的优势和不足。最后,分析了国内外砂轮表面形貌检测方法的发展现状,指出了现阶段存在的问题,展望了砂轮表面形貌检测方法的发展前景。      

基于有限差分模型的磨削弧区流场动压力数值分析

磨削弧区动压力对通过磨削区磨削液的有效流量、润滑和冷却作用有重要影响。本研究基于流体动压理论,建立了磨削弧区的动压力分布数学模型,将微分方程简化至近似泊松方程形式后,采用有限差分法将连续方程离散化,得出了磨削区动压力的数值解,并提出了迭代优化算法,提高了计算效率。将砂轮特性参数纳入数学模型之中,可根据砂轮材质、砂轮与工件间隙、砂轮转速等参数预报磨削弧区的磨削液动压力分布。在此理论模型基础上,进行了验证实验,证明模型的科学性。结果表明:通过输入砂轮各项参数,该模型可以快速、准确地预报动压力的分布,为磨削加工提供参考。      

Improving grinding performance by controlling air flow around a grinding wheel

In grinding, high specific heat is generated, and hence, appropriate control of temperature through effective flow of grinding fluid is necessary to obtain a quality ground surface. It is known that in conventional fluid delivery method, most of fluid is wasted due to presence of a stiff air layer around the grinding wheel. This air layer is generated around the wheel due to the rotation of the porous grinding wheel at a high speed. To improve grinding performance, hence, penetration into this air layer is required.In this work, a pneumatic barrier set-up has been developed for controlling the stiff air layer around the grinding wheel. The formation of stiff air layer has been studied experimentally by measuring the variation of air pressure around grinding wheel periphery at different parametric conditions of pneumatic barrier. This pneumatic barrier tends to break the stiff air layer before the fluid flow area or grinding zone. A remarkable amount of reduction in pressure of the air layer is observed at the fluid flow zone. To observe beneficial effects of suppressing the air layer, grinding experiments are performed under dry, flood cooling and flood cooling with pneumatic barrier setup. Reduction of grinding forces and surface roughness are clearly observed with the use of pneumatic barrier setup, and hence, its applicability.     

表面形貌对砂轮磨削流体压力与润滑的影响

目的从磨削液压力及润滑方面找到减少磨粒磨损、磨削热和降低工件表面粗糙度的方法。方法基于实际情况,将砂轮突出的磨粒分布函数和工件在磨削之前存在的粗糙度函数等效为余弦函数,对陶瓷结合剂CBN砂轮磨削45号钢而产生的流体压力和膜厚进行了分析。结果考虑砂轮和工件的表面粗糙度时,压力波动集中在中心区域,磨削区最大压力和最大膜厚明显增大。在考虑热效应的情况下,当两表面波长相等、幅值同时增大时,最大膜厚及平均膜厚增大,而幅值相等、波长增大时,润滑情况没有改善;当砂轮表面幅值波长相等且变大时,最大膜厚及平均膜厚增大,由此也可以得出当砂轮表面幅值波长不变,工件表面如此变化时结果相同;当两表面幅值和波长不相等且都成倍增大时,最大膜厚及平均膜厚增大。结论膜厚增大利于润滑时,能降低磨削温度,减少磨削烧伤和热变形,降低工件磨削后的表面粗糙度,减少非工作磨粒的磨损,减少砂轮修正次数,延长砂轮寿命。但是膜厚不会无限增大,因为磨削区域并不封闭,在实际工程中可依据此理论来确定最优解,优化磨削过程。     

Assessment of Grinding Fluid Effectiveness in Continuous-Dress Creep Feed Grinding

Creep feed grinding is a high-productivity abrasive removal process that is often limited by thermal damage and high wheel wear. A review of current industrial practices in the area of fluid supply optimisation in grinding shows that very little knowledge of the pressure, flowrate and method of application exists in industry. This paper presents an experimental procedure to evaluate fluid supply conditions in grinding on a continuous-dress creep feed grinder. Using tapered workpieces, the authors have evaluated the influence of wheel speed and material removal rate on grinding fluid effectiveness, based on the material removal rate at the position of the wheel along the ramp when burn starts to occur and the corresponding spindle power surge. Correlations are investigated between visible discoloration, metallurgical examinations and change in spindle power, in order to establish the onset of grinding burn. This procedure serves to determine the upper limit of material removal rate or - respectively - the lower limit of fluid flow rate for given grinding systems consisting of specified wheel type, material type, fluid type and fluid supply nozzle. The advantage of the presented method is its easy and time saving application in industry, but it is also of help to researchers who need to optimise fluid supply conditions prior to their grinding tests.     

Experimental simulation of the efficiency of high speed grinding wheel cleaning

The grinding of certain materials such as ductile material which are hard to grind implies particular conditions of work. Maintaining the cutting ability of the wheel is necessary and wheel cleaning is one of these conditions. In this paper, the parameters which are influential in maintaining a clean wheel are identified. A cleaning criterion is proposed to estimate the efficiency of the cleaning process. Using an experimental setup, the significant of the influence of the nozzle position, the flow rate and pressure, the boundary layer of air around the rotating wheel and the particle rate contained in the fluid are assessed. It is observed too that the fluid temperature has no significant effect. Lastly, the best method to clean a wheel when high speed grinding is discussed.     

Effects of minimizing hydrodynamic pressure in ultra-precision mirror grinding

This paper describes an investigation about the fluid delivery method that minimizes the generation of hydrodynamic pressure and that improves grinding accuracy. Traditionally, grinding fluid is delivered for the purpose of cooling, chip flushing and lubrication. Hence, numbers of conventional investigations are focused on the delivery method to maximize fluid flux into the contact arc between grinding wheel and workpiece. It is already known that hydrodynamic pressure generates due to this fluid flux, and that it affects overall grinding resistance and machining accuracy. Especially in the ultra-precision mirror grinding process that requires extremely small amount of cut per each pass, its influence on the machining accuracy becomes more significant. Therefore, in this paper, a new delivery method of grinding fluid is proposed on the point of minimizing hydrodynamic pressure effect. Experimental data indicate that the proposed method is effective not only to minimize the hydrodynamic pressure but also to improve machining accuracy.     

Analysis and simulation of the grinding process. Part I: Generation of the grinding wheel surface

This paper is in three parts describing the analysis and simulation of the grinding process. This first part is concerned with the generation of the wheel surface by single point diamond dressing. In grinding, the grinding wheel has to be dressed periodically to restore wheel form and cutting efficiency. Understanding the process of generating the grinding wheel surface is important for the control of the grinding process. Generation of the wheel surface is simulated as a single diamond dressing process on a computer generated wheel. The wheel is simulated by grains randomly spaced in the wheel volume. The topography of the wheel cutting surface is generated by simulating the action of an ideal dressing tool as it dresses the wheel. The simulation of the wheel topography takes account of the motion of the dressing tool, grain size, grain spacing, grain fracture and grain break-out. The simulated cutting surface is used for further simulations of grinding. The simulation of grinding using the simulated grinding wheel surface is described in Sections 2 and 3 where a comparison is made of results predicted from simulation with results obtained from experiments. By matching simulated and experimental results, it is possible to explain the relative importance of dressing and grinding parameters.     

Mechanisms in the generation of grinding wheel topography by dressing

For the process of dressing vitrified bonded grinding wheels with diamond tools it has been unknown how the wheel topography is generated. Moreover, the influence of the kinematical dressing parameters on the wheel wear behavior has not been quantified. In the course of this article the grinding wheel was dealt with as a porous ceramic composite. In FEM simulations common dressing forces and usual dressing tool geometries were applied. The results were verified by dressing tests and grinding wheel scratch tests which show the wheel wear mechanisms. The common practice of decreasing the grinding wheel surface roughness by a finishing dressing stroke has to be reconsidered, because previous dressing strokes with higher depths of cut can weaken the grinding wheel structure and lead to an unsteady phase with high grinding wheel wear after dressing.     

高速超高速磨削工艺及其实现技术

高速超高速磨削加工是先进制造方法的重要组成部分，集粗精加工与一身，达到可与车、铣和刨削等切削加工方法相媲美的金属磨除率，而且能实现对难磨材料的高性能加工。本文主要论述了高速超高速磨削工艺技术的特点；分析了电主轴是高速超高速磨削主轴系统的理想结构，介绍了陶瓷滚动轴承、磁浮轴承、空气静压轴承和液体动静压轴承在主轴单元中的应用；超高速砂轮主要用电镀或涂层超硬磨料(CBN、金刚石)制成，介绍了超硬磨粒的特点和砂轮的修整，分析了在高速及超高速磨床上得到广泛应用的德国Hofinann公司生产的砂轮液体式自动平衡装置；介绍了高压喷射法，空气挡板辅助截断气流法，气体内冷却法，径向射流冲击强化换热法磨削液供给系统的特点；最后介绍了直线电机进给系统和声发射智能监测系统等实现高速超高速磨削的关键技术。     

应用ELID技术进行微晶玻璃超精密磨削

由于微晶玻璃具有优良的物理、机械性能，在光学等领域得到了越来越多的应用。ELID磨削利用在线．电解的方法修整超细粒度的金刚石砂轮，可以有效地实现硬脆材料的超精密加工。本文将ELID磨削技术应用于微晶玻璃的超精密加工，通过改进ELID磨削的关键技术，包括砂轮电火花整形、电解修整电源和ELID磨削液的改进，实现了微晶玻璃的超精密磨削加工，同时通过采用原子力显微镜对不同磨削参数下的工件表面进行分析，以保证在塑性状态下对微晶玻璃进行磨削。因此提高了ELID磨削的质量。获得了Ra2．308nm的较好表面质量。     

纳米微囊砂轮磨削工件表面自润滑层的形成

在磨削时磨削液难以有效渗入磨削区域起冷却润滑作用。提出利用润滑剂油酸（OA）填充碳纳米管（CNTs）制备 CNTs@OA 纳米微囊,并以其为填充剂制备树脂砂轮,磨削时随着纳米微囊的破裂,油酸可释放到磨削区形成自润滑层起润滑作用,从而提高砂轮的磨削性能。首先,制备纳米微囊并对其进行表征,分析微囊在砂轮中的存在形式,考察微囊的填充对其力学性能的影响;其次,研究砂轮磨削 GCr15 钢时纳米微囊的含量和磨削速度对磨削力、磨削温度、磨削比和表面粗糙度的影响,分析磨削过程中纳米微囊释放润滑剂油酸并产生自润滑作用的机制。结果表明,纳米微囊具有较好的热稳定性, 能够抵抗树脂砂轮的固化温度并保护其中的油酸,当微囊的填充量小于 16%时,砂轮的力学性能可以满足使用需求。与普通砂轮比,纳米微囊砂轮磨削时的磨削力可减小 40%,磨削温度降低 45%,工件表面粗糙度减少 15%,磨削比可提高 30%。磨削过程中,砂轮中的纳米微囊可将其空腔中的润滑剂油酸不断被释放到磨削界面上形成自润滑层,使砂轮具有了较好的自润滑作用,从而提高了其磨削性能。研究成果可为解决磨削过程的润滑问题提供一种可行的技术路线。     

面向绿色制造的快速点磨削磨削液供给参数计算

高速／超高速磨削条件下,砂轮边缘的高速空气带会阻碍磨削液注入磨削区。空气带压力与砂轮速度的平方成正比。快速点磨削是一种新型高速／超高速磨削技术,接触区很小,实际磨削功率低,冷却及散热效果好。在分析了高速／超高速磨削砂轮周围旋转空气带动压力及速度分布特点的基础上,根据热力学原理及快速点磨削特点,分析并建立了磨削液的供给流量和供液速度的理论模型。在此基础上,建立了面向绿色制造的快速点磨削的磨削液喷嘴直径及供液压力的工程计算公式。     

Useful coolant flowrate in grinding

A model has been developed for flowrate between a rotating grinding wheel and a workpiece. It was found that the useful flow that passes through the contact zone is a function of the spindle power for fluid acceleration, wheel speed and delivery-nozzle jet velocity. Two loss coefficients having values less than 1 are required to be calibrated for the particular grinding wheel and fluid delivery type. The model is then valid for a range of nozzle flowrates for the particular wheel and nozzle conditions. The flowrate delivered is related to unit width of the delivery nozzle assumed to be unit width of grinding contact. The model makes it possible to determine a suitable value of nozzle outlet gap to achieve a required fluid film thickness in the grinding zone. A guide is given to optimisation of the jet velocity in relation to the power required to accelerate the fluid and the particular velocity of the wheel. The model has been validated experimentally. Its simplicity and accuracy allow application to a wide range of grinding situations.     

Numerical modelling of ground surface topography: effect of traverse and helical superabrasive grinding with touch dressing

Grinding processes are often used for final finishing of components because of their ability to satisfy stringent requirements of surface roughness and dimensional tolerance. Surface topography generated during grinding depends upon many parameters like wheel parameters, wheel velocity, downfeed, grit density etc. and it also depends upon the type of grinding procedures (viz. plunge grinding, traverse grinding, helical grinding, touch dressing etc.) employed. Therefore, a correct examination of the parameters and type of process employed to carry out grinding are necessary. This paper is an attempt to develop the relation between the different grinding parameters and the grinding procedures like plunge, traverse and helical superabrasive grinding with touch dressing and the average surface roughness. For this purpose, a numerical simulation technique has been implemented to generate the grinding wheel topography. The ground workpiece surface has also been generated by simulating removal of work material depending upon the trajectory of the abrasive grits on the grinding wheel without taking rubbing and ploughing into consideration.     

Improving grinding fluid delivery using pneumatic barrier and compound nozzle

Grinding fluid is commonly applied to control grinding defects caused by high grinding zone temperature. Delivery of fluid to the grinding zone is obstructed by the formation of a stiff air layer around the grinding wheel. This results in huge wastage of grinding fluid. In the present paper, results of using a pneumatic barrier and a compound nozzle are discussed with respect to delivering fluid deep into the grinding zone. Grinding fluid passing through the grinding wheel contact zone is measured under different modes of fluid delivery using a flood cooling, or a compound, nozzle, with or without the application of a pneumatic barrier. It is found that the system using a pneumatic barrier with flood cooling nozzle, and that employing a compound nozzle perform better than the flood cooling nozzle. A compound nozzle along with a pneumatic barrier renders substantially less wastage of grinding fluid even at a low flow rate of grinding fluid. Above a fluid discharge of 475 ml/min, the compound nozzle alone shows effective penetration of grinding fluid through the grinding zone. Reduction of grinding force, specific energy and roughness of ground surface are obtained after using compound nozzle fluid delivery system. Compound nozzle may be used instead of flood cooling nozzle as it improves grinding performance even using 52.5 % less discharge of grinding fluid.