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.     

Modeling of metal removal during an internal grinding in view of kinematics cutting features

A new model of the metal removal in internal grinding permits calculation of the margin actually removed, the internal radius, the time for complete removal of the margin, and other parameters. In the model, the metal removal is determined with specified machining parameters; elastic deformation and the cutting kinematics are taken into account. The calculation is based on the model of the cutting force in internal grinding, which covers most of the factors affecting the cutting force (such as changes in the programmed and actual radial supply, the mechanical properties of the workpiece, the geometry of the wheel–workpiece contact zone, the wheel characteristics, and the blunting of the abrasive grains). Types of wheel–workpiece contact with inclination of the wheel axis on account of elastic deformation of the system are noted.     

Temperature fields in grinding by abrasive wheels

A method is proposed for calculating the temperatures at the surface of the workpiece and within its interior on grinding by abrasive wheels of different design (discontinuous, composite, or hybrid wheels). On that basis, the temperature fields in the cutting zone are calculated.

     

形貌重构砂轮磨削试验研究

设计了一种金刚石纤维切削装置,用其对白刚玉砂轮进行断续飞切来加工出断续微沟槽,从而实现砂轮的表面形貌重构。采用原始砂轮及形貌重构砂轮分别进行GCr15淬硬轴承钢的常温干式、浇注式磨削的对比试验研究,探讨了形貌重构砂轮的磨削性能。试验结果表明：相较于原始砂轮,在相同的试验条件下形貌重构砂轮在磨削时其磨削力和磨削温度均可以显著降低。通过常温干式、浇注式润滑条件下的磨削对比试验验证了形貌重构砂轮可以更有效地将磨削液带入磨削区进行润滑冷却。     

Force modeling and machining characteristics of the intermittent grinding wheels

In the surface grinding operations, the grinding fluid cannot be supplied sufficiently in the cutting zone. Temperature generated in the cutting zone increases rapidly and causes thermal damage such as burning on the surface of a workpiece. To reduce thermal damage, the intermittent grinding wheels, which have an excellent cooling effect, have been applied. This paper describes machining characteristics by using intermittent grinding wheels. The grinding force of the intermittent wheels has been simulated by the SIMULAB, which is a program for simulating dynamic systems. Using the intermittent grinding wheels, the characteristics of grinding force, temperature, surface roughness, and geometric error have been evaluated experimently.     

非一致曲率表面下的气压砂轮磨粒剪胀及加工试验研究#br#

针对软固结磨粒气压砂轮在加工异形曲面时,工件所受的切削力以及接触区内磨粒速度因工件曲率发生变化,导致工件不同曲率处材料去除量不均匀的问题, 基于修正的Rowe剪胀理论建立砂轮切削力模型,提出了非一致曲率表面下修正的气压砂轮材料去除模型。通过EDEM软件建立了软固结磨粒气压砂轮模型,分析了砂轮下压量为1.5 mm时工件曲率对接触力以及接触区内磨粒速度的影响。搭建气压砂轮加工试验平台,通过光整加工试验验证修正的材料去除模型。研究结果表明：修正的材料去除模型平均绝对值误差为0.095,而原始的材料去除模型平均绝对值误差为0.291,说明修正的材料去除模型可以用于气压砂轮抛光过程中的定量分析,且工件加工表面划痕明显减少。     

An investigation on surface grinding of hardened stainless steel S34700 and aluminum alloy AA6061 using minimum quantity of lubrication (MQL) technique

In grinding process, the abrasives plunge and slide against the workpiece during material removal with high specific energy consumption and high grinding zone temperature. To improve process efficiency, lubrication becomes an important requirement of the grinding fluids, along with chip removal and cooling the grinding zone. Grinding fluids have negative influences on the working environment and machining cost in terms of the health of the machine operator, pollution, the possibility of explosion (for oil), filtering, and waste disposal. The use of minimum quantity of lubrication (MQL) with an extremely low consumption of lubricant has been reported as a technologically and environmentally feasible alternative to flood cooling. This paper deals with an investigation of the grindability of hardened stainless steel (UNS S34700) and aluminum alloy AA6061 using dry, MQL, and conventional fluid techniques. One type of SiC and five types of Al₂O₃ wheels (corundum) as well as vegetable and synthetic ester MQL oils have been tested. The influences of wheel and coolant–lubricant types have been studied on the basis of the grinding forces, surface topography, and surface temperature. Synthetic ester MQL oil was found to give better grinding performance than the vegetable MQL oils. It was argued that the improved performance of the ester oil is caused by the formation of tribo-films on the abrasives and the workpiece, which enhances lubrication by inhibiting metal–abrasive interaction. Also, the grindability of the machined specimens was found to increase substantially by using the MQL grinding process with soft and coarse wheels. In MQL grinding of AA6061 alloy, the use of vegetable oil resulted in the lowest surface roughness, whereas using synthetic ester additives lead to highest surface roughness because of higher chip loading on the grinding wheel and consequently more redeposited material on the workpiece surface.     

Experimental study of time-dependent performance in superalloy high-speed grinding with cBN wheels

The time-dependent performance of grinding is expressed as the change of process output measures as a function of time during grinding. Although the wheel capability will be restored by dressing, the time-dependent performance of grinding during one dressing skip is the determinant on the grinding quality variation in terms of surface integrity and workpiece geometric accuracy. Therefore, understanding of grinding time-dependent performance in relation with the wheel–workpiece microscopic interaction is critical for wheel and process development to achieve stable grinding processes. In this article, the grinding of superalloy with cubic boron nitride (cBN) grinding wheels is performed. The time-dependent performance is recorded to represent the characteristic features, and the microscopic wheel topography is measured under scanning electron microscope (SEM) throughout the grinding process, so as to reveal the root cause for the time-dependent performance and its impact on the workpiece quality variation. The experiment results indicate that during the grinding process, there exist three characteristic stages, namely, initial wheel wear stage, severe wheel wear stage, and wheel resharpening stage. Moreover, the change trend of spindle power consumption, workpiece quality on surface hardness and roughness, wheel wear condition, and G ratio are consistent with the wheel topography evolution reflected by SEM photos, which can be used to present the three grinding stages. The wear and replacement of the efficient grain cutting edges result in the time-dependent performance during superalloy high-speed grinding with cBN wheels.     

Wear behavior and mechanism of single-layer brazed CBN abrasive wheels during creep-feed grinding cast nickel-based superalloy

Wear behavior and mechanism of single-layer brazed CBN abrasive wheels during creep-feed grinding nickel-based superalloy K424 was investigated. Grinding force and temperature acting on the abrasive wheels were measured. Optical microscopy and scanning electron microscopy were utilized to detect grain protrusion and wheel wear morphology. The normal distribution of the protrusion height of the brazed CBN grains on the wheel surface was determined. The results show that, though the grinding zone temperature is merely about 180°C during creep-feed grinding nickel-based superalloy, the grinding heat still has an important effect on the grain wear owing to the high temperature of the individual grain up to 500–600°C. Wear patterns of brazed wheels are composed of mild wear (attritious wear and grain micro-fracture) and severe wear (grain macro-fracture, erosion of the bonding layer). Strong joining of brazed CBN grains and Ag–Cu–Ti bonding layer improves significantly the resistance to grain pullout.     

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.     

氮化硅陶瓷镶块低粗糙度磨削的研究

提出氧化铝砂轮磨削陶瓷表面的加工过程是砂轮磨粒与工件表面凸峰的碰撞－碰撞与摩擦共同作用－摩擦抛光。对砂轮速度，工件转速、砂轮横向进给量、光磨次数，陶瓷材料硬度以及切削液等因素对表明粗糙度的影响进行了分析，表明氧化铝砂轮通过挤压和磨削抛光作用使陶瓷工件表面的粗糙度得到显著改善，实现了在普通磨床上对陶瓷材料的高质量加工。     

A new approach to calculating the workpiece temperature distributions in grinding

In a previous paper it was shown how the wear of the grinding wheel could be characterized by an increase in negative rake angle of the cutting edges in addition to a growth in area of the wear flats on the grits and how in this way the increase in grinding forces with wheel wear could be accounted for. The results for cutting and rubbing forces from the previous paper are used in this paper to determine the heat fluxes needed in calculating temperatures in the contact area between wheel and workpiece. The temperature distributions are obtained by superimposing the distributions in the vicinity of individual cutting edges and wear flats currently engaged with the workpiece upon the temperatures produced by grits which have left the contact area. A random approach, in the sense that the effect of many abrasive grits of varying sizes subjected to different forces and randomly distributed on the wheel is considered, is adopted. Results are presented showing the influence of wheel wear on temperatures.     

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.     

ENERGY PARTITION FOR GRINDING OF NODULAR CAST IRON WITH VITRIFIED CBN WHEELS

An investigation was undertaken to determine the energy partition to the workpiece for grinding of an automotive nodular cast iron with a vitrified CBN wheel. The energy partition is a critical parameter which is needed for calculating grinding temperatures and predicting the occurrence of thermal damage to the workpiece. Straight surface grinding experiments were conducted over a wide range of removal rates to measure the workpiece temperature response and spindle power. Temperature matching analyses were then applied in order to obtain the energy partition. Values for the energy partition were found to range from 3 to 6% when the temperature at the grinding zone was maintained below the fluid burnout limit. Such low energy partitions indicate cooling of the workpiece by the fluid at the grinding zone. Higher energy partitions up to 60% were obtained by reducing or eliminating the fluid, which also raised the temperature above the burnout limit.     

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。     

叶序排布磨粒对砂轮的磨削温度场效应

在砂轮磨削过程中,磨削热影响工件表面完整性,而磨粒排布是影响磨削温度场的重要因素之一。针对磨粒叶序排布的砂轮,采用有限元法对磨削温度场进行了计算模拟分析,获得了叶序系数对工件磨削温度场的影响规律。研究结果表明,随着叶序排布系数的增大,被磨工件的表面温度和温度梯度减低。     

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.     

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。     

研磨轮结构参数对工件加工精度的影响

通过建立研磨轮和工件的相对运动数学模型，得出研磨轮在工件上的切削运动轨迹方程，由此得到超精密平面研磨中，不同结构参数研磨轮的滑移轨迹长度，引入精度系数的概念，用于评价不同结构参数研磨轮对工件的加工效果，采用微粒金刚石研磨轮对单晶硅和压电陶瓷材料进行研磨实验的结果表明，使用设计合理的研磨轮可以提高研磨的加工精度。     

3D metal removal simulation to determine uncut chip thickness, contact length, and surface finish in grinding

The two most important geometric parameters that describe the mechanics of grinding are the uncut chip thickness and the contact length. Currently, analytical approaches are used to estimate these parameters. The accuracy of these approaches, however, is limited because they do not take into account the random shape, size, and protrusion height and placement of the abrasive grains around the circumference of the grinding wheel. In this paper, a simulation technique was used to gain new insight into the effect of the stochastic nature of grinding wheels on the geometric properties of the grinding process. The simulator was used to calculate the number of active grains, uncut chip thickness, and contact length for a stochastic wheel model of Radiac Abrasive’s WRA-60-J5-V1 grinding wheel. These values were then mapped to every grain on the grinding wheel and used to determine the instantaneous material removal rate of the wheel and workpiece surface finish. There was excellent agreement between the predicted and experimentally measured surface topology of the workpiece. The results suggest that only 10–25 % of the grains on the grinding wheel are active and that the average grinding chip may be as much as ten times thicker and ten times shorter than would be produced by a grinding wheel with a regular arrangement of cutting edges as assumed by existing analytical approaches.