超声纵振珩磨表面微观特性的试验研究

在文献[1]中，作者对径向超声振动磨削和纵向（轴向）超声振动珩磨的磨削特点进行了对比研究，建立了磨粒径向超声振动珩磨的切削模型，推导了纵向超声振动珩磨临界速度的计算公式，为了验证所建模型的正确性及进一步研究超声纵振珩磨的磨削表面特征，本文对工程陶瓷ZrO2和高强度P钢进行了纵向超声振动珩磨试验，通过电镜SEM观察分析了表面磨削特征，研究表明：纵向超声振动珩磨具有比普通珩磨较大的材料去除率，并且磨削表面光滑，粗糙度低。     

小直径砂轮超声振动磨削SiC陶瓷的表面质量研究

用小直径砂轮超声振动磨削和普通磨削加工SiC陶瓷零件,对比研究砂轮线速度、工件进给速度、磨削深度和超声振幅对其磨削表面质量的影响。结果表明:与普通磨削相比,超声振动磨削的磨粒轨迹相互交叉叠加,工件表面形貌更均匀,表面质量更好。由于超声振动时的磨粒划痕交叉会使磨粒产生空切削,因而降低了其磨削力,使磨削过程更加稳定。超声振动磨削的表面粗糙度和磨削力随砂轮线速度和超声振幅的增加而降低,随工件进给速度和磨削深度的减小而降低。且砂轮线速度、工件进给速度较小时,超声振动磨削的效果更明显。      

切向超声振动辅助磨削几何参数分析

根据超声振动辅助磨削运动简图,分析了平面磨削时砂轮对工件的相对运动关系.建立了单颗磨粒的切削模型,给出了单颗磨粒相对工件的运动方程和切削速度方程,进而推导了单颗磨粒在磨削区内的振动次数及其在磨削区内的运动路径总长度、净磨削路径总长度的计算公式.分析表明:切向超声振动辅助磨削可以得到更短的切屑,更长的切削路径长度.     

Nd-Fe-B烧结永磁材料超声辅助磨削试验研究

对Nd-Fe-B烧结永磁材料普通磨削和径向超声振动辅助磨削的工艺进行了对比试验,系统分析了在两种工艺条件下磨削用量对法向磨削力的影响;深入研究了超声振动和磨粒切削的复合过程,指出超声振动形成的断续磨削机制是降低法向磨削力的主要原因.径向超声振动的辅加改善了磨削加工效果,在一定程度上避免了脆崩现象,保证了Nd-Fe-B烧结永磁材料加工表面的完整性.     

二维超声磨削复相陶瓷加工表面质量的试验研究

本文通过对二维超声磨削纳米复相陶瓷和普通磨削进行对比试验研究,分析了磨削深度、工件速度、砂轮粒度对工件表面质量的影响.研究结果表明,采用二维超声振动磨削能大大提高工件的表面质量;表面粗糙度随着切深的增大而增大,随着切削深度的进一步增加,超声振动在磨削加工中所起的作用减弱;二维超声振动磨削大大扩大了复相陶瓷磨削的塑性加工区域,二维超声振动磨削过程的塑性域是切削深度小于5μm,而普通磨削塑性域是磨削深度小于2μm;二维超声振动磨削时,表面粗糙度随着砂轮粒度的减小而明显减小,且比较稳定,故二维超声振动磨削有利于使用细粒度砂轮;工件速度对二维超声振动磨削表面粗糙度影响很大,其值随着工件速度的增加而增大.     

超声振动珩磨表面残余应力数值模拟研究

目的磨削产生的残余应力对工件表面特性有重要影响,超声振动珩磨使磨粒具有极大的加速度而改变了材料去除机理,研究超声振动对工件表面残余应力的影响及产生机理。方法分析残余应力形成有限元理论,建立基于热弹塑性有限元法的超声振动单颗CBN磨粒切削40Cr Ni Mo A热力耦合有限元模型,并设置两次切削、卸载、约束转换及冷却等分析步。通过数值模拟得到不同振动参数下表面残余应力的分布情况,并对模拟结果进行分析。结果有限元计算得到的各分析阶段应力分布存在差别,超声振动参数设置达到仿真要求;对磨粒施加超声振动后珩磨力下降约26%,珩磨热降低约17%,切向残余压应力有所减小,垂直珩磨速度方向拉应力减小并向压应力转变。结论超声振动使珩磨力和珩磨热有一定程度降低从而改变了残余应力的分布及数值;振动频率在20 k Hz波动时对残余应力的影响不大;磨削速度减小,切向残余压应力增大,垂直磨削方向残余拉应力减小;振幅增大时,切向残余压应力减小,垂直方向残余应力增大。     

超声振动辅助磨削弧区的单颗磨粒切厚特征

为准确描述超声振动下的单颗磨粒切厚特征,实测多层金属结合剂金刚石砂轮表面的相邻2颗磨粒的周向间距以及磨粒出刃高度;依据超声振动辅助磨削的磨粒运动轨迹方程及相邻磨粒运动轨迹干涉理论,采用等分线法,利用MATLAB软件求解磨粒在完整接触弧区的单颗磨粒切厚值,并分析各主要参数对单颗磨粒切厚特征的影响。结果表明:相邻磨粒间距、相邻磨粒高度差对单颗磨粒切厚的影响均呈线性变化;单颗磨粒切厚随超声振幅的增大而线性增大,且随超声振动频率的增大而阶段性变化;超声振动辅助磨削的单颗磨粒切厚特征受砂轮转速、磨削深度的影响较大,受工件进给速度的影响相对较小。      

基于切向超声的平面磨削参数有效性研究

根据切向超声振动辅助磨削运动简图,分析了砂轮与工件的相对运动关系,建立了单颗磨粒的切削模型,并给出了单颗磨粒切削轨迹方程和运动速度方程。通过分析切向超声振动磨削应用的局限性,建立了不同砂轮线速度下和不同超声振动振幅下的单颗磨粒切削轨迹模型,最终选定出合适的砂轮线速度和超声振动振幅。结果表明:在已知条件下,砂轮线速度在1.25~8m/s之间取值,超声振动振幅在相应范围内取值,切向超声振动对磨削加工作用影响显著。     

超声振动辅助缓进给磨削温度场仿真与试验分析

目的通过对比研究磨削过程中超声振动辅助缓进给磨削工件表面的温度变化,验证超声振动对磨削热的影响,为进一步研究磨削机理提供依据。方法基于磨削温度场解析模型,建立了磨削热源平均强度。运用ANSYS软件热分析模块分别对普通缓进给磨削和超声辅助缓进给磨削进行了工件表面温度场仿真,得到了不同载荷步的温度场分布以及工件表面的温度时间变化曲线,较准确地反映了磨削工件时工件表面的温度变化。结果试验和模拟表明,缓进给磨削工件时,工件表面温度较高,对工件施加超声振动后,能够有效降低磨削力,减少磨削过程中产生的热量,降低工件表面温度20%左右。结论超声振动辅助磨削工件时,由于工件高频振动导致磨粒与工件间断性接触,使磨削过程变为有规律的脉冲状断续磨削,有利于工件散热,降低了磨削温度,为避免缓进给磨削时容易出现的磨削烧伤现象提供了技术支持。     

轴承内圆轴向超声高速磨削理论建模与试验研究

目的 以GCr15材料的6309型轴承内圆为研究对象,探究高转速超声磨削过程中超声辅助振动对磨粒运动轨迹、磨削后表面粗糙度、圆度以及微观形貌的影响规律。方法 基于超声内圆磨削磨粒切削轨迹及超声振幅与砂轮转速对轨迹影响的理论仿真,构建磨削去除量与磨削表面粗糙度的理论模型,通过对轴承内圆进行超声磨削试验,研究高转速（16 000～22 000 r/min）下各工艺参数对内圆表面质量的影响并验证理论粗糙度评价模型。结果 超声振幅的增大使磨粒与内圆接触轨迹变长,但随砂轮转速的提高,磨粒切削轨迹的密集程度也有所下降。振幅和砂轮转速的增大可使切削去除量增大、粗糙度降低,铬刚玉粒度100#陶瓷结合剂砂轮磨削GCr15轴承内圆后,其表面质量更有优势,单因素下表面质量变化趋势与理论分析结果相一致。结论 在相同磨削参数下,1.5μm振幅超声磨削可使内圆圆度降至0.92μm,粗糙度降至130.5 nm,与传统磨削相比,粗糙度最高减小了41.5%,圆度最高减小了52.6%。在高转速下,各因素按砂轮对磨削后表面质量的影响由大到小的顺序依次为砂轮转速、超声振幅、进给速度,当磨粒线速度超过41.8 m/s、进给速度...     

On the mechanics of the grinding process, Part III—thermal analysis of the abrasive cut-off operation

This is Part III of a 3 part series on the Mechanics of the Grinding Process. Part I deals with the stochastic nature of the grinding process, Part II deals with the thermal analysis of the fine grinding process and this paper (Part III) deals with the thermal analysis of the cut-off operation. Heat generated in the abrasive cut-off operation can affect the life of resin bonded grinding wheels and cause thermal damage to the workpiece. Thermal analysis of the abrasive cut-off operation can, therefore, provide guidelines for proper selection of the grinding conditions and optimization of the process parameters for improved wheel life and minimal thermal damage to the workpiece. In this investigation, a new thermal model of the abrasive cut-off operation is presented based on statistical distribution of the abrasive grains on the surface of the wheel. Both cutting and ploughing/rubbing that take place between the abrasive grains and the work material are considered, depending on the depth of indentation of the abrasives into the work material. In contrast to the previous models, where the apparent contact area between the wheel and the workpiece was taken as the heat source, this model considers the real area of contact, namely, the cumulative area of actual contacting grains present at the interface as the heat source. It may be noted that this is only a small fraction of the total contact area as only a small percentage of the abrasive grains present on the surface of the cut-off wheel are in actual contact with the workpiece at any given time and even a smaller fraction of them are actual cutting grains taking part in the cut-off operation. Since, the Peclet number, N_Pe in the case of cut-off grinding is rather high (a few hundred), the heat flow between the work and the contacting abrasive grains can be considered to be nearly one-dimensional. In this paper, we consider the interaction between an abrasive grain and the workpiece at the contact interface. Consequently, the heat source relative to the grain is stationary and relative to the workpiece is fast moving. The interface heat source on the grain side as well as on the workpiece side is equivalent to an infinitely large plane heat source with the same heat liberation intensity as the circular disc heat source. However, it will be shown in the paper that the contacting times are different. For example, the abrasive grain contacts the heat source, as it moves over the wheel-work interface, for a longer period of time ( milliseconds) whereas the workpiece contacts the heat source for shorter period of time ( a few microseconds). The temperature in the grinding zone is taken as the sum of the background temperature due to the distributed action of the previous active grains operating in the grinding zone (global thermal analysis) and the localized temperature spikes experienced at the current abrasive grain tip-workpiece interfaces (local thermal analysis), similar to the work reported in the literature [Proc Roy Soc (London) A 453 (1997) 1083]. The equivalent thermal model developed in the present investigation is simple and represents the process more realistically, especially the heat partition. The model developed provides a better appreciation of the cut-off operation; a realistic estimation of the heat partition between the wheel, the workpiece, and the chip; thermal gradients in the workpiece due to abrasive cut-off operation, and an insight into the wear of the cut-off wheels.     

On the mechanics of the grinding process – Part I. Stochastic nature of the grinding process

Grinding of metals is a complex material removal operation involving cutting, ploughing, and rubbing depending on the extent of interaction between the abrasive grains and the workmaterial under the conditions of grinding. It is also a stochastic process in that a large number of abrasive grains of unknown geometry, whose geometry varies with time, participate in the process and remove material from the workpiece. Also, the number of grains passing through the grinding zone per unit time is extremely large. To address such a complex problem, it is necessary to analyze the mechanics of the grinding process using probability statistics, which is the subject of this investigation. Such an analysis is applicable to both form and finish grinding (FFG), such as surface grinding and stock removal grinding (SRG), such as cut-off operation. In this investigation, various parameters of the process including the number of abrasive grains in actual contact, the number of actual cutting grains per unit area for a given depth of wheel indentation, the minimum diameter of the contacting and cutting grains, and the volume of the chip removed per unit time were determined analytically and compared with the experimental results reported in the literature. Such an analysis enables the use of actual number of contacting and cutting grains in the grinding wheel for thermal and wheel wear analyses. It can also enable comparison of analytical work with the experimental results and contribute towards a better understanding of the grinding process. The analysis is applied to some typical cases of fine grinding and cut-off operations reported in the literature. It is found that out of a large number of grains on the surface of the wheel passing over the workpiece per second (˜million or more per second), only a very small fraction of the grains merely rub or plough into the workmaterial (3.8% for FFG and 18% for SRG) and even a smaller fraction (0.14% for FFG and 1.8% for SRG) of that participate in actual cutting, thus validating Hahn’s rubbing grain hypothesis.     

On the mechanics of the grinding process, Part II—thermal analysis of fine grinding

Thermal analysis of fine grinding is conducted taking into consideration the stochastic nature of the distribution of abrasive grains and its role under fine grinding (dry) conditions to determine the grinding temperatures and the heat partition at the contacting interface. The analysis considers the grain–workpiece interactions at the local level and the wheel–workpiece interactions at the global level. The workpiece temperature in the grinding zone is taken as the sum of the background temperature due to distributed action of all the previous active grains operating in the grinding zone (global thermal analysis) and the localized temperature spikes experienced at the current abrasive grain tip–workpiece interfaces (local thermal analysis), similar to the work reported in the literature. Since the Peclet number, N_Pe, in the case of fine grinding is very high (a few hundred), the heat flow between the work and the contacting abrasive grains can be considered to be nearly one-dimensional. In this paper, we consider the interaction between an abrasive grain and the workpiece at the contact interface. Consequently, the heat source relative to the grain is stationary and relative to the workpiece is fast moving. The interface heat source on the grain side as well as on the workpiece side is equivalent to an infinitely large plane heat source (with the same heat liberation intensity as the circular disc heat source). However, it will be shown in the paper that the contacting times are different. For example, the abrasive grain contacts the heat source, as it moves over the interface, for a longer period of time (˜milliseconds) whereas the workpiece contacts the heat source for a shorter period of time (˜a few microseconds). The equivalent thermal model developed in the present investigation is simple and represents the process more realistically, especially the heat partition. The analytical results reported here are found to be in good agreement with both the analytical and experimental results reported in the literature by other researchers.     

单颗CBN磨粒高速磨削过程的仿真研究

为研究单颗CBN磨粒高速/超高速磨削的微观机理,以随机形状CBN磨粒为模型,采用Lagrange/Euler流固耦合方法,仿真分析不同工艺参数下的CBN磨粒磨削SHK-9高速钢的过程。结果表明:CBN磨粒（124~150μm）在切削深度a_p 20 μm、30 μm,切削速度120m/s时,切向磨削力达到最大,但在a_p 40 μm切削深度下反而最小。随着CBN磨料粒度尺寸变小,磨削力下降明显,磨粒可以在工件表面形成更为窄密的耕犁沟痕,配合适当的磨削深度有助于提高表面磨削质量。      

GCr15轴套纵扭超声磨削表面形貌预测及试验研究

目的 构建纵扭超声磨削(LTUG)表面形貌预测模型,分析工艺条件和参数对表面粗糙度Ra值的影响,揭示GCr15轴套LTUG内圆表面形成机理。方法 基于弹性变形对LTUG单颗磨粒运动轨迹的影响,根据切削厚度概率密度函数和相邻磨粒轨迹重叠效应,建立了多磨粒超声振动作用下的最大未变形切削厚度模型,利用表面残余材料高度公式建立了GCr15轴套内圆磨削形貌预测模型,以LTUG和普通磨削(OG)方式对GCr15轴套内圆进行试验,采用正交试验验证表面形貌模型的准确性,观察并分析LTUG和OG作用后的GCr15轴套内圆表面形貌,最后利用所建立的表面形貌模型,研究磨削参数和超声振幅对表面Ra值的影响。结果 结果表明,基于所建立的表面形貌模型计算而得的表面Ra值与试验结果间的误差在13.2%以内,与OG相比,LTUG作用下的表面沟槽磨痕更均匀;LTUG作用下的表面轮廓呈现规律的周期性波动,且随振幅的增大,表面轮廓顶峰之间的间距逐渐增大;LTUG作用下的表面Ra值均低于OG,表面Ra值的降低幅度最大达到20%,随振动幅值的增大,表面Ra值逐渐减小,当振幅增大到一定程度时,表面Ra值呈现增大趋势。结论 建立的LTUG形貌预测模型具有良好的准确性,在合适的工艺参数下,LTUG可明显降低表面Ra值,与OG相比,在相同时间内,LTUG作用下的磨粒运动轨迹长度更长,且LTUG区域的弹性变形对磨粒运动轨迹和最大未变形切削厚度均有不同程度的影响。     

Simulation of surface grinding process, part 2: interaction of the abrasive grain with the workpiece

This paper is the second part of the two-part series, which describes the kinematic simulation of the grinding process. The complex wheel–workpiece interaction is taken into consideration in the generation of the workpiece surface. An algorithm is proposed to identify the active abrasive grains and their attack angles from the wheel topography. Based on the critical values of the attack angle, the abrasive grain is determined either to cut, plough or rub the workpiece. A numerical example is used to validate the approach.     

Simulation for optimizing grain pattern on Engineered Grinding Tools

Engineered Grinding Tools (EGT) are characterized by a predetermined and controlled arrangement of the abrasive grains. The distribution of the abrasive grains can be used to enhance the grinding process by improving space for coolant supply and for chip removal. This is especially interesting for grinding operations with high specific material removal rates. A numerical method was developed to optimize the grain pattern on EGT. This method consists of a stochastic tool model, a kinematic process model, a material removal model and a grain wear model. The tool model comprehends the relevant geometric properties of the abrasive layer. The material removal model is based on the assumption of a kinematic-geometrical cutting condition. The wear model is based on a grain load limit and the grains’ load is assumed to be proportional to its cutting area. Once the cutting area of one grain exceeds the limit value, wear takes place. The model validation is presented comparing the wear behavior of EGT and workpiece roughness achieved with numerical and experimental methods.