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.     

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。     

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.     

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.     

A new model of grit cutting depth in wafer rotational grinding considering the effect of the grinding wheel,workpiece characteristics,and grinding parameters

Wafer rotational grinding is widely employed for back-thinning and flattening of semiconducting wafers during the manufacturing process of integrated circuits. Grit cutting depth is a comprehensive indicator that characterizes overall grinding conditions, such as the wheel structure, geometry, abrasive grit size, and grinding parameters. Furthermore, grit cutting depth directly affects wafer surface/subsurface quality, grinding force, and wheel performance. The existing grit cutting depth models for wafer rotational grinding cannot provide reasonable results due to the complex grinding process under extremely small grit cutting depth. In this paper, a new grit cutting depth model for wafer rotational grinding is proposed which considers machining parameters, wheel grit shape, wheel surface topography, effective grit number, and elastic deformation of the wheel grit and the workpiece during the grinding process. In addition, based on grit cutting depth and ground surface roughness relationship, a series of grinding experiments under various grit cutting depths are conducted to produce silicon wafers with various surface roughness values and compare the predictive accuracy of the proposed model and the existing models. The results indicate that predictions obtained by the proposed model are in better agreement with the experimental results, while accuracy is improved by 40%–60% compared to the previous models.     

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。     

超声振动螺线磨削表面微观形貌建模与仿真研究

为了实现高效率、高质量、低损伤的硬脆材料加工,对工件或砂轮同时施加砂轮轴向和径向的超声振动,该方法的显著特点是磨粒切削轨迹呈三维空间螺旋线型,将其定义为超声振动螺线磨削方法。在磨削工艺和二维超声振动的多参数共同作用下,材料去除机理产生复杂变化,表面微观形貌创出过程变得极其复杂。为此,提出一种超声振动螺线磨削加工表面数值仿真方法。基于超声振动螺线磨削几何映射关系,建立磨粒相对工件的空间螺旋线切削运动模型,进而给出超声振动螺线磨削加工表面生成模型,模拟出普通磨削和超声振动磨削的三维表面微观形貌,对比分析了超声振动对表面形成过程的影响规律。最后将仿真表面与磨削试验表面对比,发现两者微观形貌特征规律基本一致,验证了仿真方法的正确性和有效性。     

Mathematical modeling of the cylindrical grinding process

This paper proposes a dynamic model of cylindrical grinding with a tool owning specified distribution of abrasive grains. Cutting forces have been calculated, the surface geometry formed after a grinding wheel pass has been determined, the influence of the process dynamics on cutting forces and machined surface geometry has been taken into account, and the effects of cutting condit on vibrations being generated in the process of grinding have been investigated.     

Image processing of grinding wheel surface

Identifying the situation of grinding wheel wear and loading is a very important issue for high efficiency grinding operations. This paper presents a new method that detects and identifies the chip loading and cutting edge wear of a grinding wheel using the image processing toolbox of MATLAB. The different optical characters of the metal chips and the abrasive grains are analysed. The Sobel operator is adopted to make edge detection. A sensitivity threshold based on the global condition is used to decrease the noise. Image dilation and erosion processes are used to ensure the edge of each loaded chip is covered by a continuous section. The ratios of chips are calculated and displayed to monitor the wheel surface working status.     

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     

基于球切多面体和光密度的砂轮建模与测量

针对金刚石砂轮磨粒形状的不规则性、尺寸的变化性以及空间位置随机分布的特点,采用基于球坐标的随机点产生的空间平面切分实体的方法,建立更接近实际的虚拟多面体磨粒,并建立金刚石砂轮模型;从类似机床刀具切削刃的磨刃二面角出发,运用仿生物学中光密度以及计算机数字图像处理的方法,提出了基于光密度、积分光密度、平均积分光密度的一种新的砂轮形貌评价方法,并通过试验测量研究了磨刃二面角与积分光密度值之间的关系。研究结果表明,磨刃二面角越大,积分光密度值越大,在0~200之间变化。最后结合砂轮表面面积密度、磨粒平均个数、出刃高度、积分光密度值等参数验证了所建立的虚拟多面体磨粒和砂轮模型的有效性。     

Image processing of the grinding wheel surface

Identifying the situation of grinding wheel wear and loading is a very important issue for high-efficiency grinding operations. This paper presents a new method that detects and identifies the chip loading and cutting edge wear of a grinding wheel using the image processing toolbox of the MATLAB package. The different optical characters of the metal chips and the abrasive grains are analysed. The Sobel operator is adopted to make the edge detections. A sensitivity threshold based on the global condition is used to lower the noise. Image dilation and erosion processes are used to ensure that the edge of each loaded chip is covered by a continuous section. The ratios of chips are calculated and displayed to monitor the wheel surface working status.     

Simulation and assessment of diamond mill grinding wheel topography

The topography of grinding wheel has a remarkable effect on grinding process. In this paper, the topographies of two mill grinding wheels with different grain sizes were measured by using an Olympus confocal scanning laser microscope. Kolmogorov–Smirnov normality tests were carried out to obtain distribution characteristics of abrasive grains. The test results indicate that the surface of grind wheel is of non-Gaussian nature. Consequently, a non-Gaussian statistical model was proposed to simulate the mill grinding wheel topography. Simultaneously, some parameters of “Birmingham 14” were introduced to assess the grinding wheel surface quantitatively. Simulated profile of the grinding wheel is found to correspond well in appearance with that of the actual grinding wheel.     

基于凸多面体碰撞检测的虚拟砂轮建模研究

虚拟砂轮建模时大多采用包围球对磨粒进行碰撞检测,而包围球相互接触时凸多面体磨粒之间仍存在间隙,导致虚拟砂轮表面与实际砂轮表面差异较大,影响后续磨削过程仿真的准确性.针对这一问题,提出了一种基于凸多面体碰撞检测的虚拟砂轮建模方法.推导了砂轮表面磨粒随机位置的数学模型,基于凸多面体碰撞检测判断磨粒干涉状况,最终生成虚拟砂轮...     

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。     

磨削加工过程建模的研究进展

综述了磨削加工过程的几何建模过程中砂轮几何模型的建立方法、磨粒去除工件材料机制的研究进展,指出了其中存在的一些问题;阐述了磨削加工过程的物理建模过程中磨削力机理解析建模、经验公式建模的研究动态,分析了这些建模方法的局限性,简要介绍了磨削温度场建模中能量分配和热源形状的研究进展;讨论了对磨削加工过程进行数值模拟所存在的一些难点。     

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.     

Lubrication by Grinding Fluids at Normal and High Wheel Speeds

An investigation is described of the lubricating effects of various grinding fluids at both normal and high wheel speeds under geometrically similar conditions. Grinding fluids include air (dry), water, soluble oil in two concentrations, and cutting oil. Results indicate that the specific cutting energy and the attritious wear of the abrasive grains are reduced by lubrication, but the rubbing friction between the workpiece and the wear flats on the grains is not. With high wheel speed, the specific cutting energy is lower with all grinding fluids than with normal wheel speed, but the attritious wear rate is greater. These lubricating effects are related to results for G-ratio, surface finish, and burning conditions.     

金刚石砂轮中磨粒出刃的分形分析

针对金刚石砂轮微观出刃形貌复杂的问题,提出分形维数和等价出刃尺寸的评价指标。目的是利用分形维数和等价出刃尺寸分别评价砂轮磨粒的破碎程度和砂轮磨粒出刃的均匀程度。试验和分析结果表明,进给深度越大,砂轮出刃的分形维数就越大,表明砂轮磨粒的破碎程度越大,会给加工表面造成较大的粗糙度或划伤表面。进给深度对磨粒出刃的等价出刃尺寸的影响不大。     

钢轨砂带打磨与砂轮打磨综合性能对比实验研究

基于自主研发的锂电驱动钢轨砂带打磨机和砂轮打磨机,以60N型钢轨廓形作为实验对象,全面对比了新型钢轨砂带打磨技术和传统砂轮打磨技术的性能。结果表明：当打磨压力在45～75 N范围内时,砂带打磨的材料去除率约为砂轮打磨的15～30倍,而当压力增大到90 N时,砂带打磨的材料去除率高达砂轮打磨的102倍;砂带打磨的振动加速度、噪声和能耗均小于砂轮打磨;砂带打磨切屑为带状,而砂轮打磨则表现为高温熔融状,同时当打磨压力增大到105 N时,砂轮打磨后钢轨表面会出现发蓝现象,而砂带打磨不会;此外,砂带打磨的横向表面粗糙度大于砂轮打磨,最高可达8 μm,但满足中国铁路钢轨养护要求的最大值10 μm。综上,钢轨砂带打磨技术在材料去除率、振动、噪声、能耗和温度等方面显著优于传统砂轮打磨技术,预期将成为工程实际中解决钢轨严重病害问题的有效方法之一。