3D laser investigation on micron-scale grain protrusion topography of truncated diamond grinding wheel for precision grinding performance

A grain tip (GT) truncation is proposed to truncate grain protrusion tips of #270 diamond grinding wheel in plunge grinding of hard and brittle material. In this study, a 3D laser microscopy was employed to measure the wheel working surface and parameterize its 3D grain protrusion topography. The objective is to investigate how micron-scale grain protrusion parameters influence grinding performance such as grinding force and surface roughness. First, the GT truncation was performed after dressing of diamond grinding wheel in grinding experiment of quartz glass; then its 3D grain protrusion topography was constructed by smoothing 3D measured noise, matching measured point cloud, transferring protrusion frame and extracting 3D diamond grains; finally, the grain protrusion parameters such as grain protrusion number, grain protrusion height, grain protrusion volume, grain rake angle, grain clearance angle, etc. were investigated in connection with ground surface and grinding force. It is shown that GT truncation averagely decreases grain protrusion number, grain protrusion height, grain protrusion volume, grain rake angle and grain clearance angle by about 44%, 74%, 75%, 24% and 70% on whole wheel surface, respectively. However, it greatly increases active grain number by about 32 times and active grain volume by about 181 times in actual grinding with the depth of cut in 1 μm, thus leading to a decrease (about 80%) in surface roughness and an increase (about 40 times) in grinding force. It is also found that truncated diamond grain tips are mostly shaped with nanometer-scale tip wedges along grain cutting direction, leading to about 75% very large negative grain rake angles and about 75% large grain clearance angles, thus contributing to ductile-mode grinding. It is confirmed that the active grain number and active grain volume for the actual depth of cut may be regarded as main grain protrusion parameters to evaluate and predict the precision grinding performance of a coarser diamond grinding wheel.     

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 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.     

硬脆材料超声辅助磨削技术研究现状及展望

硬脆材料具有高强度、高硬度、低密度等特点,用传统方式加工时损伤大、效率低,而超声辅助磨削具有磨削力小、加工质量优等优点,在硬脆材料加工领域具有独特优势。从不同振动维数及振动方向与磨削表面位置关系的角度出发,总结了不同类型超声辅助磨削加工的机理及特性,在此基础上探讨了硬脆材料超声辅助磨削的延性域加工机理、超声振动参数与磨削用量匹配性的研究现状,并对今后超声辅助磨削领域应重点关注的研究方向进行了展望。      

复杂曲面硬脆材料零件磨削加工数值模拟

建立了大型复杂形面薄壁石英纤维复合材料的树脂金刚石磨削过程传热学模型,并基于有限元方法,利用工程数值模拟软件ANSYS对石英纤维材料磨削时的热传递过程进行了数值计算,得出工件的温度场分布规律及温度变化历程。研究表明：以现行磨削用量干磨削后,磨削最高温度达到316℃,热量主要分布在表层2 mm深范围内,对工件表面材料性能影响不大;同时得到了温度场分布随热源的移动而变化的规律及工件表面某位置下不同深度的温度变化历程。借助有限元方法对工件表层的温度场进行仿真,可以预测整个磨削过程,优化磨削参数,减少试验次数与成本,为解决磨削表面热损伤和热变形等问题提供了依据。     

金刚石砂带超精密研磨细长脆硬材料的工艺参数研究

基于线性磁带开放协议的第三代磁头的关键部件之一是一种由复合脆硬材料组成的具有特殊外形轮廓的微小细长杆件,由于其长径比大,弯曲变形要求严,使得加工较为困难。本文用固着磨料研磨方法进行外形轮廓研磨,通过测量工件的直线度误差、材料去除率和表面粗糙度,研究研磨压力、速度、磨料粒度以及夹紧力等工艺参数对研磨质量和效率的影响。结果表明,当研磨压力为4.59kPa、速度80次/min、夹紧力9.8N、用粒径1μm的金刚石砂带时效果最优,同时表明工件变形随研磨压力及夹紧力的增大而增大。     

脆性材料平面磨削温度场的测量及分析

磨削温度直接影响砂轮寿命、加工成本和工件质量,一直是磨削加工领域研究加工过程及其本质的重点.获得磨削弧区温度及工件实际的温度场分布是研究磨削热机理的基础.本文采用NEC TH31-110红外热像仪,测量了平面干磨削脆性材料时的热像图,获得了工件整体温度场分布及沿层深的温度分布数据,确定了工件磨削接触区的最高温度及其准确...     

Ultra precision grinding of spherical convex surfaces on combination brittle materials using resin and metal bond cup wheels

This paper reports on a parametric investigation on ultra precision grinding of combination materials of zirconia and silica. Rotational grinding was adopted for the generation of spherical convex surfaces using metal and resin bonded cup wheels. The wheels have grit sizes ranging from 4 to 20 μm. A simplified geometrical model was used to analyse the effects of wheel wear on ground dimensional accuracy. Besides, a new truing and dressing technique of the cup wheel using loose abrasives was introduced. This new truing and dressing technique enables the precision profile truing of cup wheels. With the well prepared cup wheel, high form accuracy (average PV 0.25 μm) with mirror/near-mirror surface finish for silica and zirconia was achieved.     

硬脆金属的超声电解复合加工研究

硬脆金属材料采用普通切削加工相当困难。本文对硬脆金属材料进行了超声电解复合加工工艺试验与研究，该复合加工方法使加工速度、精度有表面质量较单一工艺有显著改善。     

Experimental study on brittle–ductile transition in elliptical ultrasonic assisted grinding (EUAG) of monocrystal sapphire using single diamond abrasive grain

This study is carried out to investigate the material removal characteristics in elliptical ultrasonic assisted grinding (EUAG) of monocrystal sapphire using single diamond abrasive grain. The scratching experiments are performed to develop a fundamental understanding of the ductile–brittle transition mechanism during EUAG of monocrystal sapphire. An elliptical ultrasonic vibrator attached with a sapphire substrate was set up on a multi-axis CNC controlled machining center equipped with a single point diamond tool. The vibrator was constructed by bonding a piezoelectric ceramic device (PZT) having two separated electrodes on a metal elastic body, and an elliptical ultrasonic vibration was generated on the end-face of the metal elastic body when two phases of alternating current (AC) voltages with a phase difference are applied to their respective electrodes on PZT. In scratching experiments, the effects of ultrasonic vibration on the critical depth of cut a_c for the ductile–brittle transition region and the material removal ratio, i.e., the ratio of the removed material volume to the machined groove volume, f_ab, are investigated by the examination of the scratching groove surfaces with SEM and AFM. The obtained results show that the critical depth of cut in EUAG is much larger than that in conventional grinding without vibration (CG), and even the bigger vibration amplitude leads to a greater improvement. Although the values of f_ab in the ductile–brittle transition region in both EUAG and CG are less than 1, that in EUAG is bigger than that in CG. Furthermore, as the vibration amplitude increases, the value of f_ab is increased to eventually be close to 1. These show that it is prone to achieve a ductile mode grinding in greater vibration amplitude. It was also found that in the process there are two kinds of material removal modes, i.e., continuous cutting and discontinuous cutting modes, which are determined by the relationship between values of vibration amplitude and depth of cut. This study validates that the elliptical ultrasonic assisted grinding method is highly effective in ductile mode machining of hard and brittle materials.     

Study on the system matching of ultrasonic vibration assisted grinding for hard and brittle materials processing

Ultrasonic vibration assisted grinding (UAG) is an effective processing method for hard and brittle materials. Compared with common grinding (CG), both of grinding force and workpiece surface quality is improved by UAG, but the principle of improvement is still unclear. In order to reveal the mechanism of grinding force reduction and grinding quality improvement in UAG, this paper presents a mathematical model for system matching in UAG of brittle materials. Assuming that brittle fracture is the primary mechanism of material removal in UAG of brittle materials, the system matching model is developed step by step. On the basis of this mathematical model, the mechanism of grinding force reduction and surface roughness forming are discussed. The advantage of UAG processing brittle materials is pointed out in theory. Using the model developed, influences of input variables on grinding force are predicted. These predicted influences are compared with those determined experimentally. This model can serve as a useful foundation for development of grinding force models in UAG of brittle materials and models to predict surface roughness in UAG.     

硬脆材料的电镀金刚石线锯超声切割锯切力研究

基于冲量理论和振动加工理论,采用叠加原理建立了电镀金刚石线锯超声切割锯切力数学模型.从理论上分析了电镀金刚石线锯施加超声振动后锯切力与普通锯切力的区别,并进行了超声振动与普通锯切力对比试验研究.结果表明:锯切力的大小随线锯往复频率的提高而降低,随侧向压力的增加而增大.通过比较发现,超声振动锯切力比普通锯切力减小20%～30%.同时,对超声振动锯切过程中单颗金刚石磨粒切削运动轨迹进行了仿真分析,进一步解释了施加超声振动后锯切力减小的原因.     

金刚石钻磨头超声振动钻磨硬脆材料表面质量的试验研究

硬脆材料以其优良的性能在生产实践中得到了广泛应用，但其低塑性、易脆性及不导电性等使得加工十分困难，尤其是超精密表面制作更加困难。为此，本文将超声振动引入普通钻磨中，介绍了超声振动切削原理，通过超声与普通两种方式下的表面粗糙度试验和微观形貌观察得出以下结沦：1）不同加工参数时，超声振动钻磨时的工件表面粗糙度值均低于普通钻磨时的表面粗糙度值；2）随着进给量、工件转速和输入功率的增加，超声和普通钻磨时的表面粗糙度均呈上升趋势；3）普通钻磨加工后孔壁表面有宽度和间距不均匀的沟槽，并且沟槽较宽，而超声钻磨加工后表面沟槽（划痕）较浅且均匀。     

Surface and subsurface integrity in diamond grinding of optical glasses on Tetraform ‘C’

In order to investigate the surface and subsurface integrity of diamond-ground optical glasses, a Tetraform ‘C’ machine tool featuring high close-loop stiffness was used to conduct the ultra-precision machining of fused silica and fused quartz assisted with electrolytic in-process dressing (ELID). An acoustic emission (AE) sensor and a piezoelectric dynamometer were used to monitor the grinding process to correlate the processing characteristics with the generated surface and subsurface integrities, which were characterized by atomic force microscope (AFM), scanning electronic microscope (SEM), and nano-indentation technique. Experimental results showed that for optical glasses the fracture toughness value can be used to predict the machinability while its bigger value always means a better surface and subsurface integrity. During the grinding process of optical glasses, the smaller amplitude and RMS values of AE signal, as well as the smaller grinding forces and the ratio of normal force to tangential force, correspond to a better surface and subsurface integrity. With selected machining parameters and a 6–12 μm grain-sized diamond-grinding wheel, nanometric quality surfaces (Ra<5 nm) with minimal subsurface damage depth (< 0.5 μm) can be generated for fused quartz on Tetraform ‘C’.