Molecular dynamics modeling of a single diamond abrasive grain in grinding

In this paper the nano-metric simulation of grinding of copper with diamond abrasive grains, using the molecular dynamics (MD) method, is considered. An MD model of nano-scale grinding, where a single diamond abrasive grain performs cutting of a copper workpiece, is presented. The Morse potential function is used to simulate the interactions between the atoms involved in the procedure. In the proposed model, the abrasive grain follows a curved path with decreasing depth of cut within the workpiece to simulate the actual material removal process. Three different initial depths of cut, namely 4 ?, 8 ? and 12 ?, are tested, and the influence of the depth of cut on chip formation, cutting forces and workpiece temperatures are thoroughly investigated. The simulation results indicate that with the increase of the initial depth of cut, average cutting forces also increase and therefore the temperatures on the machined surface and within the workpiece increase as well. Furthermore, the effects of the different values of the simulation variables on the chip formation mechanism are studied and discussed. With the appropriate modifications, the proposed model can be used for the simulation of various nano-machining processes and operations, in which continuum mechanics cannot be applied or experimental techniques are subjected to limitations.     

Effects of honed cylinder surface topography on the wear of piston-piston ring-cylinder assemblies under artificially increased dustiness conditions

This paper presents results of the measurement of the surface roughness and other physical properties of the outer layer of honed cylinders. The cylinders tested had various surface topographies as a result of honing by abrasive tools of differing design. The results of wear measurements of the cylinders and piston rings mating with them during automotive gasoline Polonez 1500 engine operation under artificially increased dustiness conditions are presented and analysed.     

INFLUENCE OF WHEEL STRUCTURAL PARAMETERS ON MACHINING ACCURACY OF ULTRA-PRECISION PLANE HONING

A new idea for designing wheel patterns is presented so as to solve the problems about machining accuracy ofworkpiece and wear of honing wheel in ultra-precision plane honing. The influence factors on motion principle and pattern structures are analyzed and optimization machining parameters are obtained. By calculating effective cutting lengthon the surface of workpiece cut by wheel's abrasive and the orbit of one point on the surface of workpiece contactingwith wheel, the wear coefficient of different kinds of wheels and accuracy coefficient of workpiece machined by corresponding wheels are obtained. Furthermore, the simulation results show that the optimal pattern structure of wheel turnsout to have lower wheel wear and higher machining accuracy.     

Roughness variability in the honing process of steel cylinders with CBN metal bonded tools

Herein are presented roughness results of honing of steel cylinders with cubic boron nitride (CBN) abrasive tools. Different honing parameters such as honing stone pressure against the workpiece, tangential speed of the honing head as well as grain size of the abrasive stone were varied in order to determine their influence on the surface roughness of cylinders. Four different strategies were implemented to measure and characterise roughness of inner surfaces of honed steel cylinders. The variability in results obtained with each strategy is compared. The first three strategies consist in measuring roughness at one, three or nine points, respectively, which are uniformly distributed over a circumference located at one of the cylinder ends. The fourth strategy is based on the third one: it entails measuring roughness at nine points, and then subsequently filtering results to eliminate any extreme roughness value lying outside the boundaries set by Chauvenet's criterion. At each point of measurement, roughness is measured in the direction of the cylinder generatrix. It was verified that the larger the number of measurement points, the lower the variability in roughness values obtained. Therefore, it is recommended to make at least nine measurements per cylinder and to filter values to avoid any non-representative, outlier value. The variability in these values was quantified firstly according to relative differences. Secondly, variability was quantified by means of the coefficient of variation which provides smaller values than the relative difference, although less intuitive and less direct.     

Effects of particle size, polishing pad and contact pressure in free abrasive polishing

The objective of this research is to better understand the mechanisms of material removal in the free abrasive polishing process. Experiments were carried out to understand the effects of particle size, polishing pad and nominal contact pressure on the wear rate and surface roughness of the polished surface. A theoretical model was developed to predict the relationship between the polishing parameters and the wear rate for the case of hard abrasive particles sandwiched between a soft pad and a workpiece (softer than the abrasive particles). Experimental results and theoretical predictions indicate that the wear rate increases with an increase in particle size, hardness of polishing pad and nominal contact pressure, and with a decrease in elastic modulus of the polishing pad. Surface roughness increases with an increase in particle size and hardness of polishing pad, and nominal contact pressure has little effect on the roughness. A dimensionless parameter, wear index which combines all of the preceding parameters, was introduced to give a semi-quantitative prediction for the wear rate in free abrasive polishing. It is also suggested that when polishing hard material, in order to achieve a high materials removal rate and a smooth surface, it is preferable to use diamond as the polishing particles because of their high deformation resistance.     

Sensor elements made of conductive silicone rubber for passively compliant gripper

Grinding is regarded as a special multiple edge cutting process, in which the abrasive grains remove the workpiece material at the microlevel. The grain–workpiece interaction, which resembles the microcutting process, directly modifies the workpiece surface and dominates all the output measures of grinding process. Recently, a virtual single-layer cubic boron nitride (CBN) grinding wheel model is developed by simulating each wheel fabrication step, which makes the estimation of the single grain material removal mode possible in grinding. Therefore, the study of the grain–workpiece interaction through microcutting behavior on the abrasive grains becomes necessary for the quantitative investigation of grinding processes. In this paper, the influence of the grain orientation on the microcutting performance of CBN grains is studied through finite element method (FEM) simulation based on response surface methodology (RSM). The FEM simulation helps in both qualitative and quantitative understanding of microcutting process. And the RSM analysis is proved to be an effective tool for factorial analysis in this paper. The results indicate that the single grain microcutting force is sensitive to the grain wear condition and orientation status, and there exists preferable orientation condition for microcutting with abrasive grains to achieve minimum cutting force.     

Cu-3镍铜合金砂带磨削试验研究

分析了Cu-3镍铜合金砂带磨削加工过程中,砂带粒度和磨削用量的不同对磨削加工效率、工件表面质量和砂带磨损的影响。采用氧化铝磨料砂带在不同的砂带线速度或磨削压力下对镍铜合金进行了工艺试验,对材料去除量、工件表面粗糙度和砂带磨损量进行了测量。研究表明:增加砂带线速度和磨削压力可在一定程度上提高材料去除率和磨削比;随着磨削压力的增大,工件表面粗糙度呈增大趋势;随着砂带粒度的增大,工件表面粗糙度呈减小趋势;砂带线速度为25m/s,磨削压力为43N,砂带粒度为P240时,镍铜合金综合磨削效果最好。     

Modeling surface roughness for polishing process based on abrasive cutting and probability theory

The surface roughness is a variable used to describe the quality of polished surface. This article presents a surface roughness model based on abrasive cutting and probability theory, which considers the effects of abrasive grain shape, grit and distribution feature, pressure on surface roughness. The abrasive grain protrusion heights are thought to close to Gaussian distribution, and then the relationship between the indentation depth and the pressure based on Hertz contact theory is obtained. Surface roughness prediction model is established by calculating indentation depth of the abrasive grains on workpiece surface. The maximum surface profile height (R_y) is approximately equal to the maximum indentation depth of the abrasive grain. The arithmetic average surface roughness (R_a) is equal to the average indentation depth of the abrasive grain. The effects of process parameters such as pressure and grit on R_y and R_a were simulated and analyzed in detail.     

磨削加工中的尺寸效应机理研究

从比切削能和比摩擦能的大小变化与磨削参数的关系出发,研究了磨削加工中的尺寸效应问题,结果认为：比切削能的尺寸效应是金属剪切流动应力的尺寸效应和磨粒顶端钝圆影响的综合作用结果;当磨削深度或工件进给速度减小时,平均未变形切屑厚度减小,金属材料的剪应变效应和剪应变率效应增强,而热软化效应减弱,从而金属材料的剪切流动应力增大;当未变形切屑厚度减小时,磨粒顶端钝圆的影响增大;比摩擦能的尺寸效应是由于工件和砂轮的实际接触面积与磨削深度之间存在非线性关系及工件和砂轮间的摩擦因数的速度效应造成的;当工件进给速度减小时,工件与砂轮磨损平面间的摩擦因数增大。     

Tribological mechanism of carbon group nanofluids on grinding interface under minimum quantity lubrication based on molecular dynamic simulation

Carbon group nanofluids can further improve the friction-reducing and anti-wear properties of minimum quantity lubrication (MQL). However, the formation mechanism of lubrication films generated by carbon group nanofluids on MQL grinding interfaces is not fully revealed due to lack of sufficient evidence. Here, molecular dynamic simulations for the abrasive grain/workpiece interface were conducted under nanofluid MQL, MQL, and dry grinding conditions. Three kinds of carbon group nanoparticles, i.e., nanodiamond (ND), carbon nanotube (CNT), and graphene nanosheet (GN), were taken as representative specimens. The [BMIM]BF₄ ionic liquid was used as base fluid. The materials used as workpiece and abrasive grain were the single-crystal Ni–Fe–Cr series of Ni-based alloy and single-crystal cubic boron nitride (CBN), respectively. Tangential grinding force was used to evaluate the lubrication performance under the grinding conditions. The abrasive grain/workpiece contact states under the different grinding conditions were compared to reveal the formation mechanism of the lubrication film. Investigations showed the formation of a boundary lubrication film on the abrasive grain/workpiece interface under the MQL condition, with the ionic liquid molecules absorbing in the groove-like fractures on the grain wear’s flat face. The boundary lubrication film underwent a friction-reducing effect by reducing the abrasive grain/workpiece contact area. Under the nanofluid MQL condition, the carbon group nanoparticles further enhanced the tribological performance of the MQL technique that had benefited from their corresponding tribological behaviors on the abrasive grain/workpiece interface. The behaviors involved the rolling effect of ND, the rolling and sliding effects of CNT, and the interlayer shear effect of GN. Compared with the findings under the MQL condition, the tangential grinding forces could be further reduced by 8.5%, 12.0%, and 14.1% under the diamond, CNT, and graphene nanofluid MQL conditions, respectively.     

Physicochemical wear of abrasive grains during grinding processes

One of the modes of the wear of abrasive grains that occur during grinding is physicochemical wear, which is caused by the intensive interaction between an abrasive material and a material being ground. Despite the short duration of contact between a grain and a blank at high surface temperatures with the friction of the material being ground against the wear site of the abrasive grain, as well as juvenile and subsequently oxidized surfaces, predetermine the physicochemical interaction between the abrasive material and the material being ground. The problem of developing a quantitative characteristic of these processes has not yet been solved. A system of coefficients of the chemical affinity of the abrasive material and the material being ground that characterize the intensity of the physicochemical processes that occur in the zone of contact is proposed.     

Experimental and numerical research on magnetic pulse forming of DP600 high-strength steel with driver sheet

This study aims to investigate the effect of the three cutting parameters (rotation, feed rate, and number of tool strokes) on the values of roughness (Rk, Rpk, Rvk, Mr1, Mr2, Rp/Rt ratio, and Vo) in flexible honed crankcase cylinder of hermetic compressors. The study was based on a full factorial design 2 × 2 × 3, where the rotation and the feed rate were investigated in two levels and the number of tool strokes in three levels. The cylinders were initially honed using a multi-spindle honing machine, Gehring model. A set of three honing tools was used each with two strokes, the first for roughing (120 mesh), the second for semi-finishing (270 mesh), and the third for finishing (600 mesh). For conventional honing (CH), the depth of the cut and the feed rate were kept constant. The flexible honing process was carried out after conventional honing (C+FH) in a CNC milling machine using a Silicon Carbide flex hone tool 800 mesh and 24.2 mm nominal diameter considering 12 different cutting conditions. An electromechanical surface roughness tester was used to carry out roughness measurements. The measurement uncertainty was assessed following the recommendations of the GUM-JCGM 101. The analysis of variance (ANOVA) technique was applied, and it was observed that the number of the tool strokes was the factor that contributed the most to the improvement of the surface finish of the cylinders.     

Surface roughness modeling in chemically etched polishing of Si (100) using double disk magnetic abrasive finishing

Abstract

The present paper focuses on proposing a new method for determining the surface roughness of chemically etched polishing of Si (100) using double disk magnetic abrasive finishing (DDMAF). Based on chemical etching in KOH solution Vicker’s hardness of Si (100) at different concentration of KOH was determined in context to chemical etching phenomenon. A mathematical relationship was established to relate Vicker’s hardness of Si (100) as a function of the concentration of KOH. The penetration depth of abrasive particle into Si (100) workpiece was determined considering viz; the normal force acting on the abrasive particle under the influence of magnetic flux density and Vicker’s hardness of etched Si (100). The other modeling variables such as wear constant, penetration area of the abrasive particle into Si (100) workpiece which is dependent on the penetration depth of abrasive particle was modified in terms of magnetic flux density and concentration of KOH. The process parameters such as working gap, abrasive mesh number and the rotational speed of the primary magnet were also considered in modeling the surface roughness. The results of surface roughness obtained by the model were also experimentally validated. The theoretical and experimental findings agreed well with each other.     

A new approach to modeling the surface topography in grinding considering ploughing action

The ground workpiece surface is generated simulating the trajectory of all the abrasive grains and trimming these trajectories by the appropriate method. A realistic simulation requires the trajectory to be correctly modeled. In the stage of trajectory modeling, most of the current approaches only consider the kinematics interaction between the grains and the workpiece, neglecting ploughing and rubbing. To overcome these problems, a new approach to modeling the surface topography in grinding is proposed in this paper. First, the depth of grain participated in the grinding is defined as a real-time cutting depth due to its changes with time, and the relationship between cross-sectional area of an un-deformed chip and real-time cutting depth is established. Second, the three-dimensional cutting trajectory of a grain is defined considering ploughing action is given assuming that the area of the remaining material on each side of the grain path is proportional to the un-deformed cutting area of the grain. With the 3D cutting trajectory, the surface topography is generated by simulating the trajectory of all the grain and removing the interfering material. Finally, this model has been validated by the experimental results for different cutting depth and feed rate.     

An investigation of the abrasive wear of mineral-cutting tools

The paper describes an investigation of wear of tools in cutting abrasive rock and is relevant to the problems encountered in the coal mining industry. The emphasis of the paper is on tribological aspects rather than tool performance aspects and the treatment is at a macroscopic level. A range of tool geometries and materials were included in the investigation and the effects of length of cut and depth bf cut studied.It is concluded that the wear of a cutting tool differs from the wear observed in conventional sliding contact situations with respect to the relationship between wear and applied load. This is attributed to the displacement control, rather than load control, of the cutting process and the consequent degradation of the abrasive under high contact pressures. The rate of removal of material by wear at the cutting edge of the tool, within the range of variables examined, (a) is independent of the rake and clearance angles of the tool and the width of the wear flat, (b) is proportional to the distance cut (excluding an initial high rate) and the width of the tool, and (c) decreases with increasing depth of cut and tip hardness.     

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.     

射流束切削时在边壁约束下的直径增大变形及加工表面质量研究

利用氯化钠晶粒射流切削生物骨材料时,射流束变形可能会导致骨材料切削断面产生预期之外的损伤,不利于生物组织的后期恢复。为探索射流束切削加工时在边壁约束下产生的变形,以及相应加工表面的质量特点,设计了磨料水射流切削可视化实验。使用高速摄影机拍摄磨料水射流加工过程,利用可视化手段观测射流束变形情况,并使用表面粗糙度Ra表征加工表面质量。研究发现,射流束在前端边壁与两侧边壁共同约束下存在沿切削进给方向的直径增大变形,该变形使加工表面粗糙度沿切深的减小幅度增大及出现频率增多。最后对表面粗糙度Ra沿切割深度的变化数据进行二次处理,提出了一种新的建立磨料水射流切削材料表面粗糙度预测模型的思路。     

高压磨料水射流切割工程陶瓷研究

采用高压磨料水切割和工程陶瓷,研究高压磨料水工艺参数对其切割深度的影响.从陶瓷材料力学和高压磨料水流体力学基础出发,建立冲击力和加工参数关系.实验结果表明切割深度与水的压力成正比,与喷嘴移动速度成反比.采用硬质合金和陶瓷两种材料制备了磨料喷嘴,研究了喷嘴磨损量与加工参数的关系,采用SEM分析了喷嘴磨损原因.     

固着磨料加工碳化硅反射镜的材料去除率及表面粗糙度的理论研究

本文基于固着磨料加工碳化硅反射镜的微观作用原理，理论上定量分析探讨了金刚石磨料压入碳化硅工件的深度对材料去除率、光学元件表面粗糙度的影响，分别获得了材料去除率数学模型及粗糙度的仿真计算结果。通过去除率及粗糙度的实验与理论模型的对比结果来看，实验值虽与理论值有偏差，但基本稳定在同一数量级内，由此验证了理论分析的正确性。固着磨料工艺的这一易于理论预测的特性对实际的光学加工有着极为重要的意义，因此这种较为新颖的固着磨料工艺在碳化硅反射镜加工领域内有着广阔的应用前景。     

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.