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.     

A fundamental study on the mechanism of electrolytic in-process dressing (ELID) grinding

Demands for high quality surface finish, dimensional and form accuracy are required for optical surfaces and it is very difficult to achieve these using conventional grinding methods. Electrolytic in-process dressing (ELID) grinding is one new and efficient method that uses a metal-bonded diamond grinding wheel in order to achieve a mirror surface finish especially on hard and brittle materials. However, studies reported so for have not explained the fundamental mechanism of ELID grinding and so it has been studied here by conducting experiments to establish optimal grinding parameters to obtain better surface finish under various in-process dressing conditions. In this research the results show that the cutting forces are unstable throughout the grinding process due to the breakage of an insulating layer formed on the surface of the grinding wheel; however, a smoother surface can be obtained using a high dressing current duty ratio at the cost of high tool wear. ELID grinding is efficient for feed rates of less than 400 mm/min, and surface cracks are observed when it exceeds this limit.     

精密轴承磨削金刚滚轮修整工艺优化研究

目的 通过对轴承套圈表面修整工艺优化的研究,实现对轴承套圈表面优质高效的磨削加工.方法 首先基于金刚滚轮修整原理和力学原理,建立修整过程系统简化模型,根据模型求得系统固有频率,再根据频响函数曲线图确定主轴最佳转速.然后建立砂轮与滚轮的运动轨迹方程,根据方程求得曲率半径,再根据曲率半径求得使砂轮表面粗糙度较低的修整速比.接着引入一个新的物理量干涉角,根据经验确定一个较优的干涉角,将修整速比代入,求得最后的滚轮进给速度.最后通过间接获得的磨削力大小来优化整个修整过程,若磨削力偏大,则重新选择主轴转速.结果 根据该方法得到优化结果,选用砂轮转速为23994 r/min、滚轮转速为5473 r/min、修整进给速度为1.77 mm/min、磨削力为37.2 N时,轴承套圈表面能获得较高的质量.对比优化前后轴承套圈沟形,由优化前的不合格变为优化后的合格,有了显著的改善.结论 将修整参数运用多个方法进行确定,并通过磨削力进行最后的优化.根据加工产品表面呈现出的问题,可以找到对应的参数,进而对参数进行单独优化,为企业优化轴承套圈表面质量提供了一套科学有效的方法.     

D杯形砂轮修整碟形金刚石砂轮试验研究

本文采用了D杯形砂轮与碟形砂轮对磨法来修整大直径树脂结合剂碟形金刚石砂轮。在分析研究杯形砂轮修整碟形砂轮的修整原理及修整方式的基础上，用自行研制的专用修整装置，从主轴转速、修整深度、修整工具结合剂类型等方面进行了对比工艺试验研究，总结了杯形砂轮修整碟形砂轮的不同工艺参数与修整效率、修整质量之间的工艺规律。试验结果表明，在本试验条件下主轴转速500r／min，修整深度0．02mm的修整效率较好；细粒度、中等浓度的青铜结合剂杯形金刚石砂轮与粗粒度、高浓度的杯形砂轮修整碟形砂轮相比，后者具有较好的修形效果和修整效率；D杯形砂轮与GC杯形砂轮交替配合使用可以大大提高碟形金刚石砂轮的修形效率和修锐效果。     

Influence of dressing feed on the performance of laser dressed Al2O3 wheel in wet grinding

The influence of dressing feed on the performance of a laser dressed Al₂O₃ wheel in surface grinding under wet, plunge grinding conditions is discussed. The performance of a grinding wheel dressed with different feed rates was evaluated by means of several grinding parameters such as grinding forces, wheel wear against work material removed (G-ratio), worksurface finish and its integrity. The performance of a laser dressed wheel was compared with that of a diamond dressed wheel. Analysis of the results clearly indicated the satisfactory performance of the laser dressed Al₂O₃ wheel in wet grinding, especially when dressed with a feed of 0.35 mm/rev and with an intensity of 4.0 × 10¹⁰W/m2. Further, this particular analysis suggests the selection of smaller feed rates for dressing grinding wheels with a laser in order to modify the wheel surface topography considerably, so as to produce effective grinding results with laser dressed grinding wheels.     

细粒度金刚石砂轮椭圆超声振动修整试验研究

针对硬脆材料精密加工中细粒度金属结合剂金刚石砂轮修整精度低、修整速度慢、成本高的难题,开发了基于局部共振设计方法的新型单驱动椭圆振动超声修整装置,设计了专用试验砂轮.修整试验结果表明:与普通机械修整方式比较,椭圆超声振动修整后的砂轮表面磨粒分布均匀、静态磨粒数增加;磨粒表面平滑完整,多个棱边有完整锋利的磨刃;同时,结合剂三角洲面积减小,磨粒突出高度增大,延性修整痕迹明显.随着修整切深增加,单位面积上砂轮突出磨粒数减少,砂轮的承载率下降,磨粒锋利性降低;随着修整导程增加,各截层的磨粒数逐步减少,但是承载率增加,磨粒变得锋利;砂轮转速增加,椭圆超声振动修整的效果减弱,砂轮磨粒锋利性降低,而超声功率增大有利于改善修整效果.选择合理参数,采用椭圆振动超声复合修整技术,可以实现细粒度金刚石砂轮的低成本快速修整.     

陶瓷CBN砂轮修整参数的量化分析研究

采用正交试验方法量化分析了陶瓷CBN砂轮的修整参数对工件表面质量的影响。研究结果表明:进给速度对工件表面粗糙度和支承长度率均有明显的影响;修整量对表面粗糙度影响较小,但对支承长度率却有较为明显的影响,且修整时往复次数越少,砂轮越锋利;修整速差对表面质量影响较小。因此,可以通过加大进给速度、降低单次深度和增大往复次数的方法,来达到提高首件表面粗糙度、增加修整间隔、提高砂轮使用寿命的目的。      

Ground surface integrity of granite by using dry electro-contact discharge dressing of #600 diamond grinding wheel

Dry electro-contact discharge (ECD) dressing of metal-bonded #600 diamond grinding wheel is proposed for grinding of various granites. As compared to mechanical GC dressing, Dry ECD dressing can not only protrude fine diamond grains from wheel metal-bond without any damage, but also eliminate bond-tail behind the protruded grain. The objective is to understand how the synthetic factors including granite structure, grinding parameters and dressing method influence the ground surface integrity of multi-crystal granite such as surface roughness and surface crack appearance in contrast to homogeneous optic glass. First a micron-scale indentation experiment was carried out to display the growth mechanism of micro-cracks on polished surface, then Dry ECD dressing and mechanical GC dressing were carried out in grinding experiment, respectively, finally surface roughness and micro-surface crack were investigated in connection with granite crystal size, work speed and dressing method. It is found that in almost all cases the multi-crystal granite has always worse ground surface than homogeneous optic glass even if grinding parameter is changed. Moreover, the improvement of ground surface for granite is more sensitive to grain protrusion feature than that for optic glass. Although it is very difficult to find out obvious relationship between surface roughness and grinding parameter such as work speed, it has a good correlation with granite structure such as granite crystal size: it decreases with the increase of the granite crystal size. It is concluded that Dry ECD dressing may more greatly improve the ground surface integrity of various granites than mechanical GC dressing.     

Optimization of multi-pass face-milling via harmony search algorithm

This study presents a harmony search (HS) algorithm to determine the optimum cutting parameters for multi-pass face-milling. The optimum value of machining parameters including number of passes, depth of cut in each pass, speed and feed is obtained to minimize total production cost while considering technological constraints such as allowable speed, feed, surface finish, tool life and machine tool capabilities. An illustrative example is used to demonstrate the ability of the HS algorithm and for validation purpose, the genetic algorithm (GA) is used to solve the same problem. Comparison of the results reveals that the HS algorithm converges to optimum solution with higher accuracy in comparison with GA.     

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。     

金刚石微粉烧结棒和D、GC杯型砂轮修整碟型金刚石砂轮对比研究

通过对D，GC杯型砂轮和金刚石微粉烧结棒修整大直径树脂结合剂碟型金刚石砂轮的对比实验，以反映砂轮平面度的周向跳动变化率和径向跳动变化率作为修整效率的评价依据，以被修砂轮加工出硬质合金插齿刀的齿形误差作为修整质量的评价依据，从修整原理及修整模型上分析了影响修整效率和修整质量的主要因素，分析结果表明：被修砂轮金刚石颗粒微切削频率以及修整力方向对修整效率有很大的影响；修整质量与作用在被修砂轮上的修整运动有关，磨削，单用GC杯型砂轮法修整后的碟形金刚石砂轮适合于粗磨和半精磨；D，GC杯型砂轮组合修整法既具有高的修整效率也具有高的修整质量，是一种可广泛应用的修整方法。     

改变立方氮化硼磨具修整方向的研究

树脂结合剂CBN磨具的磨削性能取决于磨具的修整效果,磨具修整的效果关键在于其修整方向。本丈通过不同的修整方向的对比试验和磨削试验,分析用不同的修整角所修整出的磨具表面,找出了CBN磨具修整的最佳方法。     

微晶陶瓷刚玉砂轮对微电机转子轴的磨削性能评价

针对目前微电机转子轴无心外圆磨过程中砂轮修整频繁的问题,采用微晶陶瓷刚玉砂轮替代传统刚玉砂轮磨削微电机转子轴。通过搭建平面磨削工艺平台,参考无心磨砂轮修整及其磨削加工参数,从磨削温度、工件表面粗糙度、表面微观形貌、磨削比等方面,对比分析微晶陶瓷刚玉砂轮与传统刚玉砂轮的磨削性能。结果表明:相对传统刚玉砂轮,微晶陶瓷刚玉砂轮不仅有效改善磨削温度（降低38.5％）,提高工件表面加工质量（表面粗糙度降低78.6％）,还具有较高的砂轮磨削比（提高2.2倍）。选用微晶陶瓷刚玉砂轮对微电机转子轴进行无心磨生产线验证,结果表明:微电机转子轴无心磨样件的各项检测结果均满足实际生产指标要求,且较传统刚玉砂轮延长了1.6倍的修整周期,在提高加工质量的同时,显著提高了生产效率。      

修整参数对陶瓷cBN砂轮磨削效果的影响

本研究采用陶瓷cBN砂轮加工冷激合金铸铁凸轮,采用金刚石滚轮对砂轮进行在线修整。通过改变修整量、滚轮与砂轮的相对移动速度、修整速比,得出修整参数对砂轮磨削效果的影响规律。研究结果表明,当修整量从5μm×4降低到5μm×3时,工件表面粗糙度从0.25μm增大0.27μm,但仍可满足加工表面粗糙度要求,而砂轮修整量减少1/4,砂轮使用寿命延长;滚轮与砂轮的相对移动速度从0.1 mm/r增大到0.15 mm/r时,工件表面粗糙度值Ra从0.354μm上升到0.452μm,砂轮耐用度从750个工件降低到480个;修整速比增大,工件磨削表面粗糙度增大,当修整速比从0.61增大到1.35时,工件表面粗糙度值Ra从0.2μm增大到0.63μm。     

The effect of ELID grinding on the flexural strength of silicon nitride

Advanced structural ceramics, such as silicon nitride-based materials, are of significant interest due to their excellent physical and mechanical properties. However the cost of grinding these ceramics, an integral part of their fabrication, is very high and can result in surface and subsurface damage to the material. These defects can significantly reduce the strength and reliability of the finished component and are sensitive to grinding parameters. In this investigation, the effect of finish electrolytic in-process dressing (ELID) grinding on the flexural strength of silicon nitride specimens were studied. Kyocera's silicon nitride SN 235, in the form of Modulus of Rupture (MOR) specimens, were ground using the application of ELID grinding with a # 6000 grit sized cast iron bonded diamond (CIB-D) grinding wheel. A significant improvement in the strength of the Si₃N₄ specimens was noted when finish ELID grinding was performed. This was the result of ductile regime grinding using the application of finish ELID grinding. Another method to improve the flexural strength of silicon nitride specimens will also be addressed in this paper.     

Application of shallow circumferential grooved wheels to creep-feed grinding

A single-point diamond dressing tool was used to cut shallow circumferential groove on aluminum oxide grinding wheels. Creep-feed grinding experiments were then carried out to compare the performance of these grooved wheels with a non-grooved wheel. The results showed that, for the conditions used in this research, a grooved wheel could remove twice as much material as a non-grooved wheel before workpiece burn occurred. The results also showed that a grooved wheel can improve grinding efficiency by reducing the consumed power by up to 61%. Although the use of grooved grinding wheels caused the workpiece surface roughness to increase slightly when compared to a non-grooved wheel, the grooved wheel enabled up to 37% more material to be removed while still maintaining workpiece surface roughness values below 0.3 μm (“fine quality” surface finish), and up to 120% more material to be removed while still maintaining workpiece surface roughness values below 1.6 μm (“average quality” surface finish).     

磨削区内气流场速度和压力分布规律的研究进展

在高速旋转的砂轮表面形成一层空气附面层，即气流场。气流场的存在，不仅影响工件的加工精度和加速砂轮的磨损，而且还阻止磨削液有效地注入磨削区，使加工条件恶化，磨削力上升，磨削温度升高，严重影响了工件的加工质量和表面完整性。本文综合分析了在磨削区速度和压力的分布规律及影响因素，为今后工业生产中进一步控制、利用气流场进行磨料流光整加工奠定基础。     

A study on the mirror-like grinding of die steel with optimum in-process electrolytic dressing

In recent years, grinding techniques for the precision machining of brittle materials used in die, mold and optical parts have been improved by using super-abrasive wheels and precision grinding machines. The completion of the optimum dressing of a super-abrasive wheel makes possible the effective precision grinding of die steel STD-11. However, the present dressing system cannot have control of the optimum dressing of the super-abrasive wheel.In this study, a new system and the grinding mechanism of optimum in-process electrolytic dressing are proposed. This system can carry out the optimum in-process dressing of a super-abrasive wheel. Therefore, optimum in-process electrolytic dressing is a good method to for obtaining the efficient and mirror-like grinding of STD-11.     

钎焊砂轮精密磨削K9玻璃的实验研究

K9玻璃广泛应用于高端光学元件,但K9玻璃是具有难加工性质的脆性材料。为了提高磨削效率,尽量减少磨削损伤以及减轻后加工工序的难度,降低加工成本,许多研究者都在开展K9玻璃的加工技术研究。钎焊砂轮具有磨粒出露高度大、磨粒易排序等特点,采用钎焊金刚石砂轮对K9玻璃进行精密磨削,研究砂轮在修整过程中的变化,并观察K9磨削表面质量随磨削工艺参数的变化。实验结果表明:砂轮修整时磨粒会出现平台磨损、棱边钝化等形态变化,磨削K9玻璃表面会出现有磨痕纹理的光泽区域和剥落破碎的坑点。     

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.