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.     

Modeling of grinding wheel topography based on a joint method of 3D microscopic observation and embedded grindable thermocouple technique

The grinding wheel generally has a complicated topography for the irregularity of abrasive grits, which always has an important influence on the final quality of the grinding workpiece. In this paper, a joint method of microscopic observation and grindable thermocouple technique was adopted to model the wheel topography. The grinding wheel topography was first modeled through microscopic observation by an in-position 3D microscope KH-7700 installed on the grinding machine. Based on the measurement of grit sizes, shapes, and distributions through the 3D microscope, a wheel surface model was established and a static grit number model based on Rayleigh distribution was proposed. Moreover, a numerical model was given to validate the proposed Rayleigh distribution model of an active grit number. In order to investigate the real abrasive grit number in a grinding process, an embedded grindable thermocouple was used to detect the dynamic variation of temperature signals, which will reflect the variation of in-process wheel topography under different process parameters, machine status, and even the grit-workpiece interaction status. Through the experimental analysis, it can be concluded that the increase of depth of cut a_p could help to greatly increase the active grit number to the grinding process, while the increase of workpiece speed V_w and decrease of wheel speed V_s could lead to a subtle increase of the grit number. Moreover, the active grit number is about one fourth to one third of the static grits. The contact arc length between the wheel (CBN) and the workpiece (Ti-6Al-4V) was calculated by the contact time from the workpiece surface temperature data, and it was found that the actual contact arc length was about 1.5~2 times of the geometric size.     

Study on micro-interacting mechanism modeling in grinding process and ground surface roughness prediction

In the research on grinding process modeling, the stochastic nature of grain sizes and locations need to be considered. A new numerical model was developed which will describe the micro-interacting situations between grains and workpiece material in grinding contact zone. The model was established based on a series of reasonable assumptions, the critical conditions of starting points of plowing and cutting stages, and the redefined grinding contact zone. It indicated that there are four types of grain existing in grinding contact zone: uncontact, sliding, plowing, and cutting grains. The number of grains per unit wheel volume (N _v ) and the undeformed chip thickness (h _cu,max), which are key parameters in grinding process modeling, were firstly obtained. The numbers and distributions of different grain types along grinding contact zone were then obtained and analyzed. Calculation results showed that only a small fraction of grains participate in cutting interactions and the changing laws of each grain types along grinding contact length are very different from each other, which gives a deeper insight into grinding process and can be a good foundation for more precise grinding force prediction and thermal analysis. Another important application of this model is for ground surface roughness prediction and a new method on this purpose was developed. At last, two comparisons were made between calculation results and existing experimental data for validating the work on paper. Comparison results showed that the roughness of ground surface can be well predicted and gave the method theoretically to reduce ground surface roughness.     

Analytical modeling of grinding wheel loading phenomena

Wheel surface condition plays an important role in the grinding operation. Grinding wheel loading, meaning chip accumulation in the space between grains, leads to deteriorating wheel cutting ability and causes excessive force and temperature. This paper presents an analytical model of wheel loading phenomena as a function of cutting parameters, wheel structure, and material properties. The model is based on the adhesion of workpiece material to abrasive grain surface. It is validated by experimental results from grinding nickel-based superalloy with cubic boron nitride vitrified wheel. This model considers wheel specifications including abrasive grains size and the number of cutting edges. Cutting parameters and process temperature are the other determinant factors. On the basis of this model and empirical results, the effects of the various process parameters are presented.     

Grinding force and power modeling based on chip thickness analysis

The ability to predict grinding force and power is important to many aspects of grinding process optimization, monitoring, and control. This paper presents the predictive modeling of grinding force and power based on the probabilistic distribution of undeformed chip thickness as a function of the kinematic conditions, material properties, wheel microstructure, and dynamic effects. The chip thickness is the main random variable and it is expected to assume a Rayleigh probability density function. The model takes into account the microstructure of the grinding wheel given by the grain geometry and the static grain density in terms of the radial depth into the wheel. The dynamic cutting edge density was calculated incorporating the effects of kinematic and dynamic phenomena such as the kinematic hidden grains and the local grain deflection. The elastic deformation of the grinding contact length was also considered. The model was used to predict the total tangential and normal forces in surface grinding and the total grinding power in cylindrical grinding. In both cases experimental measurement data in the context of chip thickness probability density, tangential force, normal force, and power have been presented and compared to model calculations.     

NUMERICAL SIMULATION AND EXPERIMENTAL VALIDATION OF THE TEMPERATURE FIELD IN SURFACE GRINDING

Three-dimensional numerical simulations are carried out to investigate the temperature field in the contact zone due to the thermal loading of the workpiece in surface grinding. This technique considers that the thermophysical properties of the workpiece material are non-linear according to temperature, the contact zone between the wheel and the workpiece is assumed as an arc surface, and the heat flux entering the workpiece is assumed as proportional to the local undeformed chip thickness. A good agreement is found between the simulated results and the experimental observations. The high grinding temperature leads to the thermal expansion of the workpiece material, which causes the thickness of the actual material removal layer to be larger than the cutting depth. The grinding temperature at the central portion is higher than that on the side of the workpiece during the wet grinding, thus the material removal layer in the central zone is thicker than that on the side zone, and the workpiece surface is concave across the grinding width.     

基于响应曲面法的轴承钢GCr15高速外圆磨削参数优化

为充分发挥轴承钢GCr15优越的材料性能,保证GCr15轴承等产品的加工质量和加工效率,开展了高速外圆磨削参数优化研究。选用立方氮化硼（CBN）砂轮进行GCr15的高速外圆磨削响应曲面试验,根据试验结果建立磨削力、磨削温度、变质层深度等磨削结果的回归模型。结合回归模型与磨粒的最大未变形切屑厚度模型,综合分析砂轮线速度、工件速度、磨削深度等磨削参数对磨削结果的影响规律。以磨削结果综合最小为目标,进行磨削参数的多目标优化,通过试验验证优化模型和优化结果的正确性。     

双端面磨削砂轮直线修整中最佳修整参数的研究

根据双端面磨削原理,分析并确定砂轮直线修整相关的设计参数。以磨削区域内上下砂轮端面形状为研究对象,建立磨削区域的几何方程并进行分析计算,得到上下砂轮端面高度在工件几何中心运动轨迹上的变化曲线。分别确定固定式修整及插补式修整的最佳修整参数,获得磨削区域中理想的砂轮端面几何形状,提高工件的加工精度和精度稳定性,降低工件表面粗糙度。     

Numerical modelling of surface topography in superabrasive grinding

A numerical simulation technique has been developed to generate the grinding wheel topography using square pyramidal grits. The ground workpiece surface has also been generated simulating the trajectory of all the abrasive grits and removing the interfering material. The average workpiece surface roughness is calculated and the effects of different grinding parameters on the average surface roughness of the generated workpiece have been studied. Finally, the variation of surface roughness with the maximum uncut chip thickness has been studied.     

On the attritious wear of abrasive grains

The overcut fly milling operation that closely simulates fine grinding has been used extensively to study the performance of several grain types at moderate and low wheel speeds. Results indicate that the wear of abrasive grains for a particular grain-work-piece combination is a function of chip thickness, chip length and wheel speed. For a constant chip length, the wear rate increases exponentially with increasing chip thickness. There is, however, an optimum value of chip length which gives minimum wear at any particular chip thickness.     

考虑耕犁的超声磨削表面微观形貌建模与预测

超声磨削加工在难加工材料领域得到广泛应用,超声辅助磨削过程中,超声振动参数对磨削后的表面微观形貌具有重要影响,因此,为了在加工前对超声加工后的表面微观形貌进行预测,以优化加工参数。提出一种考虑耕犁的超声磨削表面微观形貌建模与预测方法。假设磨粒为球形,磨粒直径与间距服从高斯分布,给出砂轮形貌的数值生成方法;根据超声磨削运动学,建立考虑磨粒实时切削深度与耕犁影响的三维运动轨迹方程;在此基础上,提出超声磨削表面微观形貌生成的区域逼近求解算法,进而给出超声磨削表面微观形貌生成模型,模拟出超声磨削的三维表面微观形貌。通过试验分别从表面微观形貌的轨迹纹理、表面粗糙度数值两个方面对超声磨削表面微观形貌的模型的正确性进行了验证。     

Characterization of abrasive grain’s behavior and wear mechanisms

Grinding is a finishing process largely used in motor industry, aeronautics, space industry and precision cutting tool manufacturers. The grinding process can be summarized by the action of a grinding wheel on a workpiece. The wheel is constituted by abrasive grains. Thus grinding is in fact the action of grains on the workpiece. The grain behavior changes according to numerous parameters (geometry, mechanical characteristics, wear mechanisms). In some cases abrasive wear is observed while micro-cutting is obtained in some other cases.In this paper two useful and complementary experimental approaches for the interface physics understanding is presented. The study of the cutting power is carried out using a high-speed scratch test device in order to understand the grain behavior and the wear mechanisms for several wheel surface speeds. In this paper an approach for the specific abrasion energy computation is also presented.     

面齿轮磨削力建模与工艺影响分析

建立了碟形砂轮磨削面齿轮的理论模型.应用切斜面磨削理论,将不规则的曲面齿面等效转化为平面,结合Gleason点接触椭圆等特征,方便对磨削力进行分析求解.将砂轮上的工作磨粒数均匀划分成单颗磨粒成屑力与滑擦力个体,精确阐述砂轮在磨削面齿轮时的磨削力.经过实验结果与仿真数值的比照分析得到磨削力对磨削用量的影响参数,实验结果表明,砂轮转速与面齿轮磨削力成反比例关系,工件进给速度与磨削速度与面齿轮磨削力成正比例关系.通过磨削力的实验结果与仿真数值对比分析,可得出最大相对误差为１７.９％,此数据证明了建立的模型与实验结果较为契合,能够很好地反映磨削力与磨削用量之间的关系变化,在提高面齿轮磨削精度与工艺上提供了基础的理论依据.     

磨削过程模拟及磨削机理研究（上）

在前人磨削理论基础上对砂轮结构做了更接实际的随机性假设,应用计算机数字模拟技术对磨削全过程进行了模拟,获得了磨削过程和磨削表面的许多重要数据和结果,给出了砂轮表层的磨料中中切削的磨粒数目和切屑的长度、厚度和体积。在研究砂轮结构的基础上得出砂轮磨粒分布的随机性是磨削加工能产生表面低粗糙度的重要因素。对砂轮磨料粒度及砂轮修整的定量研究表面,要获得超低粗糙度值磨削表面不仅需要选择较细磨粒,而且需要对砂轮     

点磨削工件微观形貌仿真与试验研究

点磨削属于外圆磨削技术的一种,其砂轮与工件轴线之间存在变量夹角α,加工过程中磨粒的运动轨迹发生改变。为探索α对工件表面粗糙度的影响,利用砂轮与工件之间的运动关系及坐标转化,将磨粒运动函数等效为抛物线,得出点磨削的切削路径。基于砂轮表面磨粒分布状态,沿砂轮轴向扩展有效干涉痕迹,得到工件的三维几何仿真形貌。将45钢淬火后作为工件材料,选择典型磨削参数,利用试验对模型进行验证。结果表明:仿真与实际工件微观形貌呈现相似特征,两形貌表面高度概率密度分布十分吻合,在不同磨削速度下,两结果之间平均相差7.8%。当α在0°～4°变化时,Ra的浮动范围小于0.1μm,工件表面粗糙度不会发生明显改变,几何仿真模型为实际磨削工件形貌分析提供了一种辅助和验证方法。     

螺杆转子砂带磨削装置开发及材料去除率预测

为实现螺杆转子表面磨削材料的均匀去除,开发了一种新型砂带磨削装置,该装置由接触轮式及自由式砂带磨削工具组成。针对磨削工具与工件的接触特点分别采用半解析法及几何近似法建立接触模型,获得接触区域内接触应力分布规律。提出了基于ThunderGBM算法的材料去除率预测模型,以接触应力及磨削工艺参数作为输入,对螺杆转子砂带磨削材料去除率进行了预测,然后针对五头螺杆转子设计并实施了磨削实验。实验数据与数值计算结果的对比表明提出的去除率预测模型具有较高的准确性与有效性。     

快速点磨削周边磨削层模型及参数

为深入研究快速点磨削机理及工艺,根据快速点磨削的技术与几何学特征,建立点磨削周边接触层及参数的数学模型,对砂轮和工件的等效速度和直径、磨削参数进行理论分析。在已建立快速点磨削接触层及参数的理论模型基础上,推证计及点磨削变量角度和磨削深度的砂轮周边理论接触宽度的计算公式,并对超薄快速点磨 削砂轮周边理论接触宽度和表面粗糙度进行数值仿真。结果表明：与普通外圆磨削不同,砂轮周边与工件实际接触宽度并不恒等于砂轮宽度,点磨削变量角度和磨削深度显著影响砂轮周边的实际接触宽度与工件表面粗糙度 数值。     

陶瓷CBN砂轮地貌建模与磨削仿真

针对砂轮表面上磨粒形状的不规则性、尺寸的不确定性以及分布的随机性特点,采用随机空间平面切分实体的方法生成了具有实际磨粒几何特征的不规则多面体磨粒;提出了虚拟格子法,实现了磨粒空间位置的随机分布,构建了陶瓷CBN砂轮地貌仿真模型;采用有限元法和光滑粒子流体动力学法的耦合方法进行了砂轮地貌模型磨削仿真,通过切削层SPH粒子的运动情况,分析了磨粒的切削机理及工件表面的创成机理。     

Mist-jetting electrical discharge dressing (MEDD) of nonmetal bond diamond grinding wheels using conductive coating

Diamond wheels are widely used in high-precision grinding of hard and brittle materials; unfortunately, they are difficult to true and dress. This paper addresses that problem in that it proposes an effective dressing technique—mist-jetting electrical discharge dressing (MEDD) of nonmetal bond diamond grinding wheels using conductive coating. A conductive phase is coated on the wheel surface to increase the conductivity of the nonmetal bond. Electrical discharge model was built to analyze feasibility and select optimized parameters of MEDD. Experiments were conducted to evaluate the dressing performance of MEDD in terms of surface morphology of the wheel surface, grinding force, and surface roughness of the workpiece. Experimental results show that abrasive grains on the wheel protrude are satisfied. The discharge parameters have an important influence on the dressing result. The grinding force and the surface roughness of the workpiece significantly reduced after dressing.     

快速点磨削侧边接触层模型及CBN砂轮磨损特性

根据点磨削原理和技术特征,讨论薄层CBN砂轮侧边实际接触区在材料去除过程中的作用,建立快速点磨削侧边接触区几何模型,对侧边接触区工件等效直径、几何与动态接触弧长、单颗磨粒切削深度、平均切屑断面积等接触层参数进行数学建模与解析。结合快速点磨削加工试验研究结果,分析侧边接触层参数对快速点磨削过程的影响机理及薄层CBN点磨削砂轮的磨损特征及规律。结果表明,点磨削过程中材料的去除主要是在侧边接触区内完成,薄层CBN点磨削砂轮的最大磨损速率发生在砂轮侧边最大直径处。