A SKILL-FORMATION MODEL FOR GRINDING OPERATIONS

A good part of grinding operations is still dependent on skilled operators. Against such a background, this study takes up cylindrical plunge grinding, and presents a skill-formation model based on the learning process similar to that in which a grinding operator acquires skills through trial and error. The model repeats learning by giving only the total grinding stock and initial infeed rate, changing infeed rate, and evaluating the size and the removal rate in the process end. The simulation result has proved that the model shows a skill-formation process similar to that of an operator and generates desirable infeed processes.     

A SKILL-FORMATION MODEL FOR GRINDING OPERATIONS

A good part of grinding operations is still dependent on skilled operators. Against such a background, this study takes up cylindrical plunge grinding, and presents a skill-formation model based on the learning process similar to that in which a grinding operator acquires skills through trial and error. The model repeats learning by giving only the total grinding stock and initial infeed rate, changing infeed rate, and evaluating the size and the removal rate in the process end. The simulation result has proved that the model shows a skill-formation process similar to that of an operator and generates desirable infeed processes.     

基于OpenGL无心外圆磨削仿真系统的研究

无心磨削是一种精密、高效的加工方法,在机械制造领域占有重要地位,以切入式外圆无心磨削为研究对象,介绍了仿真系统中各功能模块,对系统开发过程中所使用到的技术要点进行探讨,并对3DS模型在仿真系统中的读取与重现进行了分析,采用OpenGL技术实现了无心外圆磨削加工过程的仿真系统,提出了根据工件中心高的理论优化值计算托板高度的方法,在时域中对工件真圆度和磨削力进行了仿真,为进一步研究无心磨削的动态特性和提高磨削加工精度提供了依据。     

In-process force measurement for diameter control in precision cylindrical grinding

This article shows the theory and implementation of a force measurement-based approach to controlling workpiece diameter in cylindrical grinding. A simple model proposed is used to relate infeed velocity to grinding force. The model is extended to accurately control the amount of material removed in outer diameter plunge grinding given the normal force, which may be monitored in real-time. The model incorporates the key parameters, including the structural loop stiffness, the plunge infeed velocity, and the wheel and workpiece properties. However, only the infeed velocity must be explicitly known. The contribution of this work is experimental validation that the lag between infeed and stock removal can be predicted using force feedback without a priori knowledge of the grinding system. This allows very accurate diameter control (0.25 μm of nominal), even in the presence of thermal drift, wheel wear, and machine error.     

Modeling of the centerless infeed (plunge) grinding process

A computer simulation method for investigating the form generation mechanism in the centerless infeed (plunge) grinding process is described. For a 3-D simulation model of form generation, contact points are assumed to be on least squares contact lines at the grinding wheel, regulating wheel, and work-rest blade. Using force and deflection analyses, the validity of this assumption is shown. Based on the 2-D simulation model developed in the previous work and the least squares contact line assumption, a 3-D model is presented. To validate this model, simulation results were compared with the experimental works. The experiments and computer simulations were carried out using three types of cylindrical workpiece shapes with varying flat length. The experimental results agree well with the simulation. It can be seen that the effect of flat end propagated to the opposite end through workpiece reorientation.     

外圆切入磨削加工精度的研究

在考虑砂轮磨损和磨削能力变化的情况下,建立了磨削过程中工艺系统弹性变形微分方程式。分析了磨削过程中基本尺寸参数及工件原始形状误差的变化规律。并对磨削过程基本尺寸参数的变化及工件原始形状误差的纠正进行了试验研究。同时,带考察了切入进给速度对工件残余形状误差的影响。     

运用LS-DYNA的轴向缓进给磨削工程陶瓷的有限元仿真

介绍了轴向缓进给磨削加工原理,建立了单颗金刚石磨粒磨削工程陶瓷的仿真模型,并就磨削力在X、Y、Z向上的分力对仿真结果的影响进行分析。最后通过对不同磨削条件下的单颗金刚石磨粒的磨削过程进行仿真,研究了砂轮转速、砂轮轴向进给速度、工件转速,以及磨粒锥角对磨削力的影响。     

Modeling and simulation of cutting forces generated during vertical micro-grinding

Micro-grinding using micro-tools has become very prevalent due to the miniaturization of products with increased process requirements. Moreover, this process provides an edge over other competitive processes, especially as a final process step. The quality of the part produced by the micro-scale grinding process can be influenced by various factors, particularly by the induced mechanical forces. Therefore, predictive model of cutting force can provide guidance for further development and optimization of the process. Although there has been a lot of a research conducted on conventional grinding, little knowledge has been accumulated on micro-scale grinding due to the fact that it is an emerging field of research. The early grinding models developed are mostly based on parameters such as wheel and workpiece velocity, depth of cut and grit size of the grinding wheel. Those early models narrated that the grits penetrate and cut the material from the workpiece surface with the generated grinding forces proportional to the removed material. However, those models may not be appropriate for micro-scale grinding due to the mode of material removal and the method of contact between surfaces which is different from the macro-scale method. In addition to that, due to the small feed rate used in brittle material machining, ploughing force needs to be considered intensively in addition to the chip formation force. Therefore, a new analytical model has been proposed to evaluate cutting forces of micro-grinding process based on the process configuration, workpiece material properties and micro-grinding tool topography. The size effect of micro-machining has been carefully considered in this proposed model. Therefore, this approach allows the derivation of cutting force comprising of both the chip formation force and ploughing force. Experimental investigation in a micro-grinding configuration has been pursued to validate the proposed predictive model. The estimated cutting force showed a good correlation with the experimental values except for higher depth of cut and lower feed rate. Additionally, paired T test has been performed to quantify the difference between the predicted and experimental results.     

硬质合金磨削温度场的仿真与试验研究

在硬质合金磨削中,磨削能大部分转化为热量,导致磨削区温度升高,出现磨削烧伤和磨削裂纹等磨削缺陷问题。利用ANSYS中的载荷加载法以及单元生死技术对磨削过程进行温度仿真分析,得到硬质合金磨削温度场的整体分布规律,研究了不同工况条件下磨削区和已加工表面的温度变化。将仿真结果与试验测得结果进行对比,两者结果具有很好的一致性,说明采用仿真对磨削温度进行预测是可行的,随着工件进给速度的增大,仿真温度与试验温度越相近。根据仿真温度,可以更好地减少磨削缺陷,提高工件加工质量。     

高速精密磨削9CrWMn冷作模具钢的磨削力和比磨削能

分析了高速精密磨削9CrWMn冷作模具钢的机理,采用DEFORM软件对高速磨削模具钢9CrWMn过程进行了磨削力仿真。使用高精密高速平面磨床对模具钢9CrWMn进行了高速精密磨削试验,并在线测量了多种工况下的磨削力。结果表明:在其他两组工艺参数不变时,随着工件进给速度增加,磨削力特别是法向磨削力会增大近45%;法向磨削力和切向磨削力随着砂轮的线速度上升而下降,法向磨削力下降近33%;磨削深度对磨削力影响较大,大的磨削深度对法向磨削力的影响尤其显著,可使法向磨削力增大近100%。分析了磨削工艺参数对比磨削能的影响规律,结果显示:随着磨削深度和工件进给速度的增大,比磨削能呈比较明显的下降趋势,符合磨削加工中的尺寸效应;随着砂轮线速度的增大,比磨削能呈上升趋势。最后,对高速磨削前后工件表面的微观形貌进行了对比分析,磨削力试验结果和仿真理论分析相一致。     

智能控制型径向切入磨削加工系统

针对径向切入式磨削加工过程 (尤其是薄壁工件 ) ,提出了一套新的磨削工艺程式及与之相适应的递阶式智能控制模式。其上层是一个基于知识并具有学习能力的智能决策系统 ,它根据加工要求 ,按照当前加工条件 ,自动规划加工参数 ;下层的自适应环节能实现对磨削过程的在线监测和实时控制。仿真与试验结果表明 ,该方法能较好地应用于实际磨削过程 ,可在更短的时间内获得更理想的加工效果。这一系统具备了相当的柔性 ,可以适应小批量多品种的加工要求。     

Some observations on profile wear in creep-feed grinding

Tests were performed to investigate the effect of various parameters on the wear of a profiled grinding wheel when creep-feed grinding a nickel-base alloy. The wear of a number of different radii, angles and profile heights was monitored. It was found that this wear was strongly influenced by the total distance travelled by an individual grit while in contact with the workpiece and by the workpiece feed rate. In addition, using a neat oil grinding fluid resulted in less wear than a water-based fluid and a 120 grit wheel wore less than a 60–80 grit wheel. A simple theoretical model was developed for predicting the effect of stock removal rate on profile wear in the creep-feed grinding of a “difficult-to-grind” material and this gave good correlation with the experimental trends.     

加压内冷却砂轮的研制及磨削性能研究

针对高温合金材料在磨削加工过程中存在磨削烧伤问题,为避免气障效应并强化冷却液在磨削弧区的换热效果,提出采用加压式内冷却断续磨削方法。利用数值模拟方法和3D打印技术对砂轮基体、加压内冷却系统和密封结构等进行设计和验证,制备了用于平面磨削的加压内冷却开槽CBN砂轮。在相同的磨削加工参数条件下,使用加压内冷却方法与外部喷射冷却方法进行镍基高温合金磨削对比试验,分析了砂轮速度、磨削深度和工件进给速度等加工参数对磨削温度、加工表面粗糙度和表面形貌的影响规律,验证了加压内冷却断续磨削方法对磨削弧区的强化换热效果。结果表明：在相同试验参数条件下磨削镍基高温合金,加压内冷却法比外部喷射冷却法的换热效率更高,得到的磨削温度更低,表面粗糙度更小,加工表面更为光滑细腻。     

超声振动辅助磨削加工智能控制技术研究

根据超声振动辅助磨削加工的特点,结合检测难易程度和实际需要,选择磨削力比作为输入。利用磨削力检测系统获得磨削力比实时数据,对采样结果进行分析处理。采用分级控制,分别控制超声功率和工件进给速度。将磨削力比的变化和变化率作为模糊控制器的输入,工件进给速度作为控制器的输出。根据模糊控制规则,利用Matlab提供的Simulink仿真模块,对超声振动辅助磨削加工模糊控制系统进行了动态仿真,仿真结果符合模糊策略,进给速度能够随着磨削力比的变化实现调整,从而避免产生磨削烧伤和颤振。     

缓进给强力磨削工艺及磨削机理的试验与研究

本文阐述了缓进给磨削的特点。这是一种新型的平面磨削加工工艺,缓进给磨削时,砂轮的切削深度大,金属切除率高,比普通磨削高100～1000倍。它可有效地用于型面或平面磨削,并能在一次或几次行程内磨完全深,无须进行诸如铣、刨等粗加工工序。本文还论述了缓进给磨削23000千瓦燃气轮机叶片根槽的机床、砂轮、金刚石滚轮、冷却液的应用以及工艺和磨削机理等。缓进给磨削中关键的问题之一是大面积烧伤和裂纹的产生。因而,本文还叙述了缓进给磨削的切屑形成机理。试验结果表明,当出现烧伤时,工件上的温度由通常的100～130℃会突然上升到1000℃以上。正确选择砂轮、进给速度及冷却液的供应,可以控制工件表面光洁度、形状和公差。     

Frictional behaviour and its influence on quality in centreless grinding

In centreless through feed grinding the quality of the ground parts is influenced by several process variables. Some of these process parameters alter the frictional conditions at the control wheel-workpiece and the grinding wheel-workpiece interfaces which, in turn, influence the axial feed rate and rate of rotation of the workpiece. In addition, the type of cutting fluid plays an important role in determining the friction at the control wheelworkpiece interface. In this paper, an attempt is made to describe the influence of some of the process parameters on the slip in the axial movement and the change in the rate of rotation of the workpiece. Also the influence of different cutting fluids, which alters the nature of the frictional contact at the control wheel-workpiece interface, on the workpiece movements and quality of the ground parts is described. The experimental work carried out, in connection with this, is included. Further, from the analysis of the experimental results some useful conclusions have been derived which would be helpful in improving the performance of the process.     

基于ANSYS的平面磨削温度场的有限元仿真

通过确定移动热源的加载方式,运用ANSYS软件的热分析模块对磨削温度场进行仿真分析,得到了不同载荷步的温度场分布以及不同深度的节点的温度变化曲线,验证了越靠近热源磨削温度越高以及工件下层材料温升显著低于工件表面。通过改变砂轮线速度、工件进给速度和磨削深度,得到了主要的磨削参数对磨削区温度场的影响状况,证明了钛合金磨削存在临界磨削速度。在临界磨削速度附近某一区间磨削温度出现回落,因此适当的磨削速度、高的工件进给速度和小的磨削深度可以有效的减小磨削温度。     

TC4钛合金纵扭超声磨削力热耦合模型及其试验研究

为探究TC4钛合金纵扭超声磨削过程中的力热耦合机理,基于TC4钛合金纵扭超声磨削的磨削力模型、工件表面平均温度模型、质量热容计算表达式建立了其力热耦合模型,并对力热耦合作用下TC4钛合金纵扭超声单颗磨粒去除过程进行有限元仿真,分析磨削力、磨削温度的相互影响特性。理论与仿真研究发现,磨削区剧烈的温升会降低钛合金抵抗塑性变形的能力,抑制磨削力的增长速率。最后通过TC4钛合金纵扭超声磨削试验进行验证,结果表明,纵扭超声的引入能明显降低磨削力和磨削温度,磨削力和磨削温度的降低幅度分别达到19.39%和12.41%;磨削温度随着磨削深度、砂轮转速和工件进给速度的增大而升高,且随着磨削温度的升高磨削力增长趋势变缓;磨削力和磨削热的减小使工件表面塑性变形和犁沟两侧的塑性隆起高度减小;与普通CBN磨削相比,纵扭超声的引入对表面粗糙度的降低幅度可达到31.21%,在一定范围内增大超声振幅能显著提高加工表面的质量。     

Reduced models of grinding wheel topography and material removal to simulate dynamical aspects in grinding

Increasing competition and short product life cycles make it necessary to optimize and evaluate the outcome of manufacturing processes. In tool grinding, models for the final workpiece geometry and cutting forces are of particular interest. To establish a valid general grinding model, we investigated the cutting process and the influence of local grinding wheel engagements on the material removal. We consequently developed models of material removal and grinding wheel topography, which capture the main correlations in grinding. In combination, temporal cutting forces and final workpiece geometry are predictable and are in excellent agreement with experimental data. The introduced models are valid for grinding in general, since they are solely based on the geometry and process parameters, and hence are applicable for manufacturing process optimization.     

Kinematic simulation of the uncut chip thickness and surface finish using a reduced set of 3D grinding wheel measurements

This paper combined experimentally-measured grinding wheel topography data taken around the entire circumference of the grinding wheel with a kinematic simulation of the grinding process. Several new methods were developed in order to create the resulting high-fidelity and computationally-efficient simulation. First a novel peak-removal technique was developed and applied to effectively remove erroneous peaks in the raw wheel topography data. Next a method was found to determine only the active cutting points on the wheel model by considering the kinematics of the grinding process. This new approach was able to reduce the simulation time from over twelve hours to about four seconds without losing any information about the cutting edge–workpiece interaction. The resulting predicted workpiece surface was then experimentally validated by carrying out a grinding experiment using the same grinding wheel used to develop the grinding wheel computer model and then measuring the resulting workpiece surface profile. Good agreement between simulated and experimental workpiece profiles was observed. Finally, the validated simulator was used to develop a kinematically-exact method to calculate the maximum uncut chip thickness and the simulation results were investigated for different depths of cut, wheel speeds and workpiece feeds.