3D graphical evaluation of micron-scale protrusion topography of diamond grinding wheel

A new graphical evaluation of micron-scale wheel protrusion topography is proposed by using 3D coordinate data derived from contact measuring of 180 diamond grinding wheel. The objective is to quantify 3D distribution of grain protrusion height, gain rake angle and grain relief angle on wheel working surface in dressing. First adaptive measuring was conducted on the base of topographical curvature to identify grain cutting edge in 3D space, second grain protrusion mode was established by polar coordinate transfer so as to ascertain datum plane of grain protrusion, then linear approximation graphics was conducted to display wheel protrusion topography, finally distributions of gain rake angle and grain relief angle were investigated with reference to grain protrusion height. Analytical results show that higher outer grains have more and shaper cutting edges, but lower layer grains retain approximately original crystal forms. In wheel protrusion topography, grain protrusion heights, grain rake angles and grain relief angles are dispersedly distributed in the range 0–28 μm, −45.0° to −89.1° and 1.2–73.1°, respectively, which can be increased by dressing. It is concluded that 3D grain protrusion attitudes distributed on wheel working surface can be quantified by 3D graphical evaluation method.     

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.     

Study on micro-topographical removals of diamond grain and metal bond in dry electro-contact discharge dressing of coarse diamond grinding wheel

A coarse diamond grinding wheel is able to perform smooth surface grinding with high and rigid grain protrusion, but it is very difficult to dress it. Hence, the dry electro-contact discharge (ECD) is proposed to dress #46 diamond grinding wheel for dry grinding of carbide alloy. The objective is to understand micro-topographical removals of diamond grain and metal bond for self-optimizing dressing. First, the pulse power and direct-current (DC) power were employed to perform dry ECD dressing in contrast to mechanical dressing; then the micro-topographies of diamond grains and metal bond were recognized and extracted from measured wheel surface, respectively; finally, the relationship between impulse discharge parameters and micro-topographical removals was investigated with regard to grain cutting parameters, dry grinding temperature and ground surface. It is shown that the dry ECD dressing along with spark discharge removal may enhance the dressing efficiency by about 10 times and dressing ratio by about 34 times against the mechanical dressing along with cutting removal. It averagely increases grain protrusion height by 12% and grain top angle by 23%, leading to a decrease 37% in grinding temperature and a decrease 46% in surface roughness. Compared with the DC-25V power along with arc discharges, the Pulse-25V power removes the metal bond at 0.241 mm³/min by utilizing discharge energy by 73% and diamond grain at 0.013 mm³/min through surface graphitization, respectively, leading to high and uniform grain protrusion. It is confirmed that the impulse discharge parameters are likely to control the microscopic grain protrusion topography for efficient dressing according to their relations to the micro-removal of metal bond.     

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.     

Ordered diamond micro-arrays for ultra-precision grinding—An evaluation in Ti-6Al-4V

The surface topography of a conventional diamond grinding wheel can be characterised as having a perplexity of abrasive particles with random crystallographic orientations resulting in different heights of protrusion from the bond and inherent varying inter-particle spacing. The number and effectiveness of the abrasive particles during grinding depends on factors such as the abrasive concentration, the crystallographic shape and the extent of particle protrusion from the wheel’s surface. The consequence of this random layout inhibits the optimal performance of individual abrasives in the process of material removal, and where particles are clustered, chip flow is negatively affected. This paper reports on the evaluation of purpose designed precision diamond micro-arrays for the grinding a case-study material, Ti-6Al-4V and compares their performance against conventional diamond electroplated micro-cutting elements of D91 and D46 abrasive size in an imitated grinding setup. The precision diamond micro-arrays, produced from thick film CVD diamond utilising energy beam ablation offer an optimised layout of abrasive elements, each having a cutting width of 100 μm of identical crystallographic orientation, protrusion height and regular spacing to provide chip flow paths. In addition, the primary/secondary rake angles γ=−32°/+1° and clearance angle α=4.5° of each abrasive cutting element have been controlled in order to provide an enhanced cutting action. The precise layout of the abrasive cutting elements of the micro-arrays produced superior chip flow compared with the diamond electroplated grinding elements; this has been proven by in-depth scanning electron microscopy of the clogged workpiece material on the studied abrasive elements. The results show a 3.5 times improvement to surface finish and a 21.5 times improvement to flatness of the Ti-6Al-4V workpieces when ground with the proposed innovative diamond micro-arrays.     

钎焊金刚石砂轮修整实验研究

单层钎焊金刚石砂轮的圆度轮廓精度由于受磨料粒径和钎焊结合剂层高度不均匀等因素的影响而使其难以在工程陶瓷等硬脆材料精密磨削中应用.然而单层钎焊金刚石砂轮的修整是直接对金刚石磨粒进行微量的磨损,修整难度大、效率低,因此,探讨快捷且精密的整形方法就成了解决其应用问题的关键技术之一.在本文研究中,分别采用铁基金刚石烧结磨块、钎焊细粒度金刚石板和氧化铝磨块三种整形工具对钎焊金刚石砂轮进行了磨削法整形实验研究,实验结果表明利用氧化铝磨块进行磨削修整效率极低;钎焊金刚石板磨削修整虽然效率高,但是对砂轮表面金刚石磨粒造成大量破碎磨损;铁基金刚石烧结磨块在整形过程中可稳定地以磨平方式磨损砂轮表面金刚石磨粒,经精密整形后的砂轮圆度轮廓精度较高,用其磨削工程陶瓷时工件表面的犁沟和裂纹明显减少.     

细粒度钎焊金刚石砂轮磨削花岗石的磨削力特征分析

通过测量磨削力,研究细粒度钎焊金刚石砂轮磨削花岗岩过程磨削力随加工参数的变化特征。结果表明:磨削力是随着砂轮线速度的增大而减小,随着工件进给速度的变大而增大,随着磨削深度的增大而增大。回归分析表明,磨削力受磨削深度的影响程度最大。不同加工条件下,法向磨削力与切向磨削力之间存在良好的线性关系,比值约为7.6。磨削过程中,金刚石与花岗石之间的运动符合Coulomb定律描述的滑动摩擦方式。     

基于SPH法的钢轨打磨单颗磨粒磨削仿真

为研究钢轨打磨过程中材料的去除机理,采用光滑粒子流体动力学（SPH）的方法,仿真模拟钢轨打磨过程中单颗磨粒的切削过程,分析单颗磨粒几何形状、切削深度、负前角对打磨磨削过程中切削力、切削力比的变化规律及工件材料应力、变形情况的影响。结果表明:由于单颗磨粒的推挤作用,工件材料流动后形成毛刺和磨屑,而棱锥形磨粒可以获得较好的磨削加工表面;切削力随磨粒切削深度的增加而增大;磨粒负前角增大时,切削力和切削力比都随之增大,且负前角越大磨屑呈越明显的锯齿状。      

Study on the grinding of advanced ceramics with slotted diamond wheels

Slotted diamond wheel grinding is a new machining technology. In this paper, an experimental study on the cutting force and the grinding temperature for ceramic face grinding using slotted diamond wheels is presented. Moreover, the empirical relationships related with the material removal rate, the surface roughness, the depth of cut, the wheel speed and the grain size are discussed. With these relationships, a temperature field for face grinding has been built. The work contributes to the fundamental theories for optimal design of slotted diamond wheels.     

金刚石砂轮的ECD修锐和整形研磨及其对硬脆材料的加工

为研究金属结合剂金刚石砂轮切削刃修锐整形对硬脆材料加工表面形态的影响,先通过接触放电法对SD600金属结合剂砂轮切削刃进行修锐,再用整形研磨方法对砂轮表面金刚石磨粒的不同切削刃高度进行整形研磨,最后用修整好的砂轮磨削加工用于光学设备的硼硅玻璃、石英玻璃、石英晶体和蓝宝石等几种硬脆材料。结果表明:硬脆材料粗糙度的改善程度取决于材料的种类,硼硅玻璃、石英玻璃、石英晶体、蓝宝石的最大粗糙度R_y比砂轮整形前的分别减少了44%、34%、30%、26%,且石英晶体材料几乎可以实现延性磨削。      

激光结构磨削在氮化硅陶瓷中的磨削行为

为提高氮化硅陶瓷的加工精度，用激光辅助复合加工技术在氮化硅表面烧蚀出4种具有相同表面积的结构化图案，然后用金刚石砂轮对氮化硅表面进行磨削，研究图案结构对磨削效果的影响，并分析砂轮转速、进给速率等参数对磨削力的影响。结果表明:激光烧蚀能够在氮化硅表面产生凹槽并降低表面氮化硅的强度，从而有利于磨削液进入并降低磨削力，最高降幅达63%。同时，金刚石砂轮磨损也有效降低。磨削结构化的氮化硅表面时，砂轮转速和进给速率对磨削力的影响规律同磨削普通氮化硅时的规律一致。      

钢轨打磨用钎焊金刚石砂轮研究

为解决传统树脂砂轮打磨钢轨时存在的打磨效率低、易烧伤钢轨和粉尘污染大等问题,分析利用钎焊金刚石技术的优势制备新型钢轨打磨用砂轮的可行性。结合磨粒有序排布工艺,制备具有开槽结构的新型钎焊金刚石砂轮,并对U71Mn钢轨钢进行打磨对比试验。结果表明:相较于树脂锆刚玉砂轮,新型钎焊金刚石砂轮能提高50%左右的打磨效率,并有效降低磨削温度,避免钢轨烧伤。在钢轨打磨过程中,新型钎焊砂轮排屑效果显著,基本不发生磨屑黏附现象;但砂轮开槽导致磨削振动增大,加剧金刚石磨粒破碎,并增大钢轨表面粗糙度。新型砂轮磨屑多为带状,磨屑体积大且无熔融小球。      

氧化铝增韧陶瓷的高效ELID精密磨削实验研究

氧化物增韧陶瓷是一种高技术陶瓷材料，具有高强度、高韧性以及良好的耐磨、耐腐蚀性能。在一般的加工过程中，采用普通树脂砂轮对硬度较高的氧化铝增韧陶瓷材料进行磨削时，磨料的消耗比较快，磨削比较低，仅为8，10左右。通过ELID磨削对氧化铝陶瓷进行高效磨削实验，从砂轮速度、进给速度、砂轮粒度和砂轮电解活化钝化趋势等因素中，找到合适的加工工艺参数，使效率和精度达到最优。实验表明，砂轮速度和进给速度对磨削比影响较大；砂轮粒度和砂轮电解活化钝化趋势对表面质量影响较多。使用优化后的ELID磨削工艺使氧化铝陶瓷材料的加工效率提高了50％。磨削比增大到60～100。     

粗磨粒金刚石砂轮精密磨削工程陶瓷的试验研究

为了实现粗磨粒金刚石砂轮延性域磨削加工SiC陶瓷材料,采用碟轮对粒径为297~420μm的粗磨粒金刚石砂轮进行了精密修整。然后,使用经过修整好的粗磨粒金刚石砂轮对SiC陶瓷进行磨削加工。在此基础上,对不同的砂轮线速度、工件进给速度、磨削切深对SiC陶瓷表面粗糙度和表面形貌的影响进行了研究。试验结果表明:经过精密修整的粗磨粒金刚石砂轮是能够实现SiC陶瓷材料的延性域磨削的,表面粗糙度值Ra达到0.151μm;随着砂轮线速度增大、工件进给速度和磨削切深减小,SiC陶瓷表面的脆性断裂减小,塑性去除增加。     

A study of grinding silicon nitride and cemented carbide materials with diamond grinding wheels

This paper presents selected results of the grinding of silicon nitride and cemented carbide materials with diamond grinding wheels, which will in later research be extended to the grinding of ceramic-cemented carbide compound drill tools. In these fundamental experiments four different types of diamond grinding wheels were used in face grinding processes. The diamond grinding wheels vary by the grain size, the grain concentration and the bonding material. The relevant influencing variables such as the cutting and feed speed and the coolant supply method were varied to investigate the effect on grinding of the two different workpiece materials, the brittle silicon nitride workpiece material and the ductile cemented carbide workpiece material. Some factors, which have significant effects, like the radial wear of the grinding wheel, the components of the grinding forces, the normal and the tangential grinding force, and the surface quality of the ground workpieces are discussed in detail.     

55钢CBN砂轮平面磨削的磨削力模型研究

本文建立了基于未变形磨屑厚度的磨削力计算模型。根据55号钢的CBN砂轮平面磨削实验,首先采用随机方向搜索法对切向力模型进行优化拟合,再根据拟合的参数对法向力模型进行优化,得出了CBN砂轮与工件之间的摩擦系数和磨粒顶锥角。分析了摩擦力在磨削力中所占比重的影响因素,结果表明:当切深不变时,随着vs/vw比值的增加,磨削力以及摩擦力在磨削力中所占的比重均下降,但当磨粒间距增加时,磨削力减小,而摩擦力在磨削力中所占比重增加。     

非球面磨削过程中圆弧形砂轮的磨损分析

针对砂轮磨损会严重影响非球面磨削质量的问题，基于非球面磨削的运动方式，解析了非球面磨削过程中的材料去除体积和砂轮磨损体积公式，并结合砂轮磨损实验，探究非球面磨削用圆弧形金刚石砂轮的磨损规律。结果表明:圆弧形金刚石砂轮在磨削非球面过程中由于磨损会导致其径向尺寸减小，在砂轮失效前其直径变化主要存在3个阶段:即直径快速变化阶段、缓慢变化阶段和微量变化阶段。圆弧形砂轮表面的结构特性，使得砂轮圆弧顶端的结合剂对顶端区域的磨粒把持力要低于其他磨粒的，导致该区域的磨粒和结合剂被快速磨损，直至圆弧形金刚石砂轮的几何结构不再影响其结合剂对磨粒的把持力，此后其磨损过程与平面金刚石砂轮磨损类似。      

磨粒半径对金刚石研磨加工影响机制的仿真研究

为解析金刚石磨粒尺寸变化对金刚石材料研磨质量的影响机制,利用分子动力学方法建立球形刚性金刚石磨粒研磨金刚石工件的模型,研究不同磨粒半径下的磨削力变化规律和应力、相变分布。结果表明: 磨粒半径从6a增大到20a(a为金刚石晶格常数),磨削平均法向力和平均切向力均线性增加,但平均法向力增量为平均切向力的3倍;磨粒与工件间的剪切作用相对挤压和摩擦的作用越来越小,且磨削力波动幅度变大表明工件的位错形成更剧烈;同时,磨粒前下方形成的强压应力区和磨粒后方由摩擦引起的集中拉应力区增大,非晶相变区域增大,研磨区后方缺陷增多,工件的加工表面质量变差。当半径为10a、15a和20a的磨粒压入深度为2 nm时,磨粒刻划后的工件表面显微硬度比未刻划时的有所降低,分别减少2.8%、9.6%和18.3%,即磨粒半径增大会显著降低工件表面力学性能。      

A survey of recent grinding wheel topography models

This paper provides a survey of grinding wheel topography models. Recent 1D, 2D, and 3D models are reviewed, and the important model components for a state-of-the-art 3D topography model are identified. Future directions for topography modeling are recommended and, based on this survey, a general modelling approach using grain size, shape, arrangement, and wheel dressing is proposed.     

单颗磨粒的平面磨削三维动态有限元仿真

将磨粒简化为圆锥形,利用Deform-3D软件,进行了单颗磨粒的平面磨削的三维动态有限元仿真。分析了砂轮与工件表面之间的摩擦系数相同而磨削速度不同时对磨削力产生的影响,以及磨削速度相同而摩擦系数不同时对磨削力产生的影响。结果表明：未变形磨屑厚度不变时,单位磨削力随着砂轮速度的增加而增大,在砂轮速度的低速区,单位磨削力增加较快,而在砂轮速度的高速区,单位磨削力增加得较慢;在磨削速度不变时,单颗磨粒的磨削力随着摩擦系数的增加而增加。