Laser dressing of alumina grinding wheels

High-power lasers are being explored as a non-contact-type dressing tool for alumina grinding wheels. The alumina grinding wheel surface underwent melting and/or vaporization on the surface when laser-dressed, forming a modified layer on the surface. Refinement of the grain size took place. The individual particles that formed on the surface had well-defined faceted structures. Microcutting edges were generated on the individual grains and particles, which can act as cutting edges for efficient grinding. The results of x-ray diffraction and pole figure analysis suggested that the formation of these faceted structures was due to the preferential orientation of the grains after dressing. This paper was presented at the fourth International Surface Engineering Congress and Exposition held August 1–3, 2005 in St. Paul, MN.     

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.     

Stochastic modeling of grain wear in geometric physically-based grinding simulations

Grinding processes can be optimized by simulating the influence of individual grains on process forces and surface topographies. However, the process results are significantly influenced by tool wear. Simulating this effect allows, e.g., the prediction of necessary tool changes when manufacturing large forming tools. Therefore, a new point-based approach for modeling arbitrarily shaped grains in different states of tool wear was developed. Based on a small amount of representative wear investigations, a flexible tool model was defined, which can be used for various tool shapes without further experiments. This model can be applied for grinding processes with varying engagement situations.     

New tool concept for grinding a plateau-like surface for tribological applications

One of the most important factors for energy efficiency is the reduction of friction in machine elements. The grinding process is often the final machining process in machining hardened steel parts and the resulting surface finish influences the tribological behavior. The combination of grinding with a honing process can generate a plateau-like surface to reduce friction and create an oil reservoir to decrease abrasive wear and improve the fluid film stability. Additional processes like laser machining, micro milling or etching are able to generate micro dimples to improve the reduction of friction. Today, grinding processes are limited to machine plateau-like surfaces. Within this paper, a new tool concept will be presented, composed of a grinding tool with two different grain sizes and a metallic bonding. The use of small abrasive grains generates a smooth surface with low roughness values. A few additional larger grains induce stochastic scratches and create the plateau-like surface. Grinding experiments are conducted to analyze the effect of feed rate, feed angle and ratio between small and large grains on the resulting surface.     

Analysis and simulation of the grinding process. Part I: Generation of the grinding wheel surface

This paper is in three parts describing the analysis and simulation of the grinding process. This first part is concerned with the generation of the wheel surface by single point diamond dressing. In grinding, the grinding wheel has to be dressed periodically to restore wheel form and cutting efficiency. Understanding the process of generating the grinding wheel surface is important for the control of the grinding process. Generation of the wheel surface is simulated as a single diamond dressing process on a computer generated wheel. The wheel is simulated by grains randomly spaced in the wheel volume. The topography of the wheel cutting surface is generated by simulating the action of an ideal dressing tool as it dresses the wheel. The simulation of the wheel topography takes account of the motion of the dressing tool, grain size, grain spacing, grain fracture and grain break-out. The simulated cutting surface is used for further simulations of grinding. The simulation of grinding using the simulated grinding wheel surface is described in Sections 2 and 3 where a comparison is made of results predicted from simulation with results obtained from experiments. By matching simulated and experimental results, it is possible to explain the relative importance of dressing and grinding parameters.     

磨粒有序排布曲面砂轮设计及磨削性能实验研究

提出一种曲面砂轮表面磨粒有序化排布的设计方法,制备磨粒有序排布和无序排布的2种曲面砂轮.通过磨削实验,从磨削力、砂轮磨损及工件加工形状误差等3个方面对比研究.结果表明:在整个磨削过程中,磨粒有序排布的曲面砂轮的磨削力总体上小于磨粒无序排布的曲面砂轮的磨削力.磨粒有序排布曲面砂轮的磨粒磨损一致性优于无序排布曲面砂轮的.整...     

石英粒度及其级配对陶瓷结合剂磨具性能的影响

研究了石英粒度及其级配对陶瓷结合剂磨具性能的影响。实验结果表明,在传统生产工艺和生产成本基本不变的情况下采取以下措施,磨具性能方可得到不同程度的提高：（1）磨料采用混合粒度时磨具性能比采用传统单一粒度时性能好,抗折强度由19,85提高到21．62,提高了8．92％;抗拉强度由8．61提高到9．57,提高了11．15％;（2）粘土、长石和石英一起球磨不同时间,结合剂对磨具性能影响不明显,只有采用将硬质石英分别球磨不同时间后,再与其它成分混合,磨具性能才有明显的不同程度的提高;（3）在一定烧成制度下,石英粒度控制在一定范围内有利于磨具性能的提高。最佳粒度范围是在250—320目之间;（4）石英粒度级配选择合适时磨具性能比选择单一细粒度石英时有一定程度的提高。     

Characterization of N-doped polycrystalline diamond films deposited on microgrinding tools

Chemical vapor deposited diamond films have many industrial applications but are assuming increasing importance in the area of microengineering, most notably in the development of diamond coated microgrinding tools. For these applications the control of structure and morphology is of critical importance. The crystallite size, orientation, surface roughness, and the degree of sp ³ character have a profound effect on the tribological properties of the films deposited. In this article, we present experimental results on the effects of nitrogen doping on the surface morphology, crystallite size, and wear of microgrinding tools. The sp ³ character optimizes at 200 ppm nitrogen, and above this value the surface becomes much smoother and crystal sizes decrease considerably. Fracture-induced wear of the diamond grain is the most important mechanism of material removal from a microgrinding tool during the grinding process. Fracture occurs as a consequence of tensile stresses induced into diamond grains by grinding forces to which they are subjected. The relationship between the wear of diamond coated grinding tools, component grinding forces, and induced stresses in the model diamond grains is described in detail. A significant correlation was found between the maximum value of tensile stress induced in the diamond grain and the appropriate wheel-wear parameter (grinding ratio). It was concluded that the magnitude of tensile stresses induced in the diamond grain by grinding forces at the rake face is the best indicator of tool wear during the grinding process.     

马氏体合金钢3J33b磨削力热载荷–晶粒尺寸演变的动态迭代作用机制研究

目的 探究微磨削过程中微磨削力热–晶粒尺寸演变的动态迭代作用机制,构建考虑动态迭代作用的磨削力热模型,提高微磨削力热的预测精度。方法 基于金属材料再结晶理论,探究磨削各阶段弹塑性变形作用下材料晶粒尺寸的演变规律。基于微观组织增强理论,分析微磨削加工过程中材料的流动应力,揭示多颗磨粒重复加载作用下晶粒尺寸演变–微磨削力热的动态迭代作用机制,通过微磨削实验进行实验验证。最后基于灵敏度分析,探究不同工艺参数组合下马氏体合金钢塑性变形和材料去除机理。结果 考虑动态迭代作用的磨削力预测模型的预测值在切向力的平均相对误差为31.51%,法向上的平均误差为27.40%,传统模型磨削力预测值切向力平均相对误差为40.82%,法向力平均相对误差为39.54%。考虑微磨削力热–晶粒尺寸演变的动态迭代作用的磨削温度最大温度预测值的平均相对误差为12.97%,而传统的磨削温度预测值的平均相对误差为16.14%。磨削力随着线速度的增大而减小,随着进给量、磨削深度和晶粒尺寸的增大而增大。磨削温度随着线速度和磨削深度的增大而增大,随着进给量和晶粒尺寸的增大而减小。结论 考虑微磨削力热–晶粒尺寸演变的动态迭代作用的磨...     

基于DEFORM3D的伺服阀芯端面磨削毛刺形成仿真

为研究磨粒不同排布方式对磨削毛刺形成的影响，对伺服阀阀芯材料端面磨削过程进行简化，利用DEFORM3D对单颗磨粒在叶序、错位和随机3种排布形式下的磨削过程建模并进行磨削有限元仿真，分析3种不同磨粒排布方式下的侧边毛刺形成过程，比较其磨削毛刺高度。结果表明:在叶序排布下，2颗磨粒中间接触边处存在高度较为稳定的毛刺；在错位排布下，2颗磨粒的磨削轨迹基本重合，耕犁的工件表面两侧形成毛刺；在随机排布下，2颗磨粒的磨削轨迹存在重叠，2颗磨粒接触边处材料挤压隆起特征更显著，容易形成二次毛刺。使用叶序排布的砂轮更有利于加工中控制毛刺的高度。      

Simulation of grinding processes using finite element analysis and geometric simulation of individual grains

The wear-resistance of sheet metal forming tools can be increased by thermally sprayed coatings. However, without further treatment, the high roughness of the coatings leads to poor qualities of the deep drawn sheet surfaces. In order to increase the surface quality of deep drawing tools, grinding on machining centers is a suitable solution. Due to the varying engagement situations of the grinding tools on free-formed surfaces, the process forces vary as well, resulting in inaccuracies of the ground surface shape. The grinding process can be optimized by means of a simulative prediction of the occurring forces. In this paper, a geometric-kinematic simulation coupled with a finite element analysis is presented. Considering the influence of individual grains, an additional approximation to the resulting topography of the ground surface is possible. By using constructive solid geometry and dexel modeling techniques, multiple grains can be simulated with the geometric-kinematic approach simultaneously. The process forces are predicted with the finite element method based on an elasto-plastic material model. Single grain engagement experiments were conducted to validate the simulation results.     

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。      

Grain mill test for sintered microcrystalline aluminum oxide abrasive grains

In this contribution results from physical and technological testing of different sintered microcrystalline aluminum oxide abrasive grains are presented. For the physical testing an innovative test stand based on a grain mill was used. Significant differences of the measured friction forces were obtained for two different sintered microcrystalline abrasive grain types. In the technological testing vitrified grinding wheels were used for an external cylindrical profile grinding process. In the values of the grinding forces, the surface roughness and the profile deviation good correlations to the results from physical testing showed up. Also at grinding with a higher load coincident tendencies of the grinding force values were detectable. Drawing conclusions it can be declared that the results from the physical testing allow evaluating the grinding performance of the tested grain types. In further experiments the impact of different percentages of the microcrystalline grit was analyzed. It turned out that the friction forces in the physical testing increased accordingly with the percentage of microcrystalline grit while the grinding forces in the technological testing showed a non-linear interdependency to the percentage of microcrystalline grit. To give reasons for these effects an advanced approach for modeling the interdependencies of microcrystalline grit percentage was formulated.     

Study on axial-feed mirror finish grinding of hard and brittle materials in relation to micron-scale grain protrusion parameters

An axial-feed mirror finish grinding of hard and brittle materials is proposed by controlling grain protrusion parameters. In this grinding, the grinding wheel feed is along the wheel axial direction rather than in the traditional wheel cutting direction. The objective is to understand how micron-scale grain protrusion parameters influence ductile-mode grinding and ultimately to realize efficient mirror finish grinding using a coarse diamond grinding wheel. In this study, the grain tip truncation (GT-truncation) was performed after dressing to improve grain protrusion topography. First, a formation model of axial-feed ground surface was constructed to analyze the effect of grain protrusion parameters and grinding parameters on the critical cutting depth transferred from brittle-mode removal to ductile-mode removal; then GC dressing and GT-truncation of #180 diamond grinding wheel were experimentally performed to investigate surface roughness and ductile-mode grinding behavior with reference to grinding parameters and grain protrusion parameters; finally, a truncated coarser #60 diamond grinding wheel was employed for mirror finish grinding to observe active grain number and grain protrusion angle. Theoretical analysis shows that this ductile-mode grinding is dominated by active grain number, active grain protrusion angle, wheel rotating speed and axial-feed speed, but it does not depend on the depth of cut assumed to be less than the grain protrusion height. Experimental results indicate that the GT-truncation may increase active grain number and grain protrusion angle for ductile-mode grinding when the axial-feed speed decreases to some extent. Moreover, the micro tip radius of diamond grain also influences the ground surface. It is confirmed that by increasing active grain number and grain protrusion angle synchronously, a truncated #60 diamond grinding wheel can be applied for efficient mirror finish grinding of the SiC ceramic plate at the axial-feed speed of 50 mm/min and the tool path interval of 0.1 mm.     

Electrochemical discharge dressing of metal bond micro-grinding tools

Micromachining using miniature metal bond grinding tools is widely used in microelectromechanical systems. However, dressing of these micro-tools is time-consuming and likely to damage the abrasives. In this paper, a novel dressing technique called electrochemical discharge dressing (ECDD) is presented. A dull micro-end grinding bit and an auxiliary electrode are connected to the cathode and anode of a power supply, respectively. The auxiliary electrode is immersed in an electrolyte, and the grinding face of the tool is in contact with the electrolyte surface. During dressing, metal bond on the tool-electrolyte interface is progressively removed subjected to electrochemical discharge effect, thus creating grain protrusion. Experiments were conducted to evaluate the dressing performance of ECDD in terms of surface morphology of the tool, grinding force and surface roughness of the workpiece. Experimental results show that abrasive grains on the tool protrude without observable damage. The normal grinding force and the surface roughness of the workpiece are reduced by half after dressing.     

An Investigation of Grinding with Electroplated CBN Wheels

Grinding of hardened bearing steel with electroplated CBN wheels was Investigated with particular attention to how the wear of the abrasive grains affects the wheel topography and grinding performance during the wheel ire. Power, surface roughness, and wheel topography data were obtained throughout the wheel life for internal cylindrical grinding. Dulling of CBN gratis by attrition was found to cause an increase in the grinding power, but the degree of dulling was restricted mainly by grain fracture and also by grain pullout. Grain fracture and pullout had a much smaller effect on the progressive increase in active grain density, which caused the surface roughness to progressively decrease. Wheel failure tended to occur by stripping of the abrasive layer when the radial wear reached about 70% - 60% of the grain dimension     

工程陶瓷圆弧成形磨削力预测与实验研究

圆弧成形磨削是难加工零件复杂型面的加工方法,对其磨削力的研究有利于改善工程陶瓷的表面质量。基于圆弧砂轮的结构特点及尺寸趋近思想对陶瓷材料圆弧成形磨削力进行预测。通过研究磨粒对工程陶瓷的去除机制,提出建立单颗磨粒滑擦、塑性及脆性去除磨削力模型。基于砂轮磨粒尺寸与分布差异,利用概率统计方法对磨削中不同去除方式的有效磨粒数进行探讨,进而实现圆弧成形磨削力理论模型的构建。最后通过磨削力实验对理论模型进行验证。结果表明：法向磨削力和切向磨削力理论值与实验值平均误差分别为8.793%和9.986%;磨削力随着磨削深度及进给速度的增加而增加,随着砂轮速度的增加而减小。     

自锐性金刚石树脂砂轮磨削性能的研究

本文通过对比磨削试验，研究了自锐性金刚石(CSD)树脂砂轮的磨削性能。试验结果表明，由于CSD形状小规则，有许多凹入角和粗糙表面，树脂结合剂对CSD的把持力较普通金刚石强，所以在磨削各参数相同的条件下，自锐性金刚石砂轮与普通金刚石砂轮相比，其磨削比提高60％以上。且由于CSD的内部为许多单个亚晶粒所组成的镶嵌的颗粒，因此在应力作用下，只有很小的不规则的碎片崩掉，从而在每个颗粒的表面上留下许多新的小切削刃，故其加工工件的表面粗糙度值较低。     

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。      

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.