Ceramic Response to High Speed Grinding

Material response was investigated with respect to normal grinding forces, surface roughness, and removal mechanisms in grinding of alumina, silicon carbide, silicon nitride, and zircona with a resin-bond 160 μm grit diamond wheel at the grinding speeds of upto 160 m/s. The results reveal that the normal grinding forces decreased significantly with an increase in grinding speed; they also increased substantially with an increase in a complex relation of the ceramic hardness and toughness. High speed grinding produced a reduction in surface roughness for silicon carbide and alumina but gave no improvement for zirconia and silicon nitride. Also the surface roughness in high speed grinding was found to be material-dependent that the ground silicon nitride exhibited much smoother than the other ground ceramics. The influence of grinding speed on material removal mechanisms was analyzed in terms of grinding geometry and ceramic material properties.     

On the grindability of low-carbon steel under dry, cryogenic and neat oil environments with monolayer brazed cBN and alumina wheels

Grinding of low-carbon steel often exhibits severe wheel loading due to the formation of long chips and high adhering tendency of the work material with the grits. Conventional composite-type alumina wheels are commercially utilised for grinding low-carbon steel. However, the actual nature of grit wear cannot be truly understood in a composite wheel. The truing and dressing conditions also have some influences on the wear mechanism. Therefore, in order to explore the wear pattern on a single layer of grits, monolayer brazed cBN, white and grey Al₂O₃ wheels were used in the present study. The grindability of AISI 1020 steel was evaluated under dry, liquid nitrogen and neat oil environments. The surface profile of the workpiece after being ground in each environmental condition was traced with a surface profilometer to reveal the mechanism of grit wear. The post-grinding conditions of the wheels were observed using scanning electron microscopy. The cBN wheel was found to outperform the alumina wheels in terms of grinding forces and grit wear. The wear of the cBN wheel was remarkably arrested with the application of neat oil. On the other hand, large-scale adhesion and breakage of grits in white alumina wheel were observed under cryogenic environment. In fact, the beneficial role of liquid nitrogen could not be realised in reducing grinding forces and grit wear with all the three types of wheel. A lubricating agent like neat oil appeared to be more suitable than cryogenic cooling when grinding low-carbon steel.     

Heat generation and heat transfer in cylindrical grinding process -a numerical study

Grinding is the most common abrasive machining process and in many cases the last of the series of machining operations. Compared to other machining processes grinding requires very high-energy input per unit of volume of material removal. The chip removal process consists of rubbing, plowing and metal removal. The frictional resistance encountered between work material, the tool, and the chip tool interface and the resistance to deformation during shearing of chips contributes to a rise in temperature and the cutting zone. The temperature generated is not only quite high but the temperature gradients are also severe. Under abusive grinding conditions, the formation of the heat-affected zone was observed which damages the ground surfaces of the workpieces. The present work aims at optimizing the amount of heat generation and modeling the temperature rise between wheel and work contact zone in a cylindrical grinding process so as to achieve better surface integrity in AISI 3310, AISI 6150, and AISI 52100 steel materials. Taguchi’s methodology a powerful tool in design of experiments for quality is used for optimization process.     

Subsurface crystal lattice deformation machined by ultraprecision grinding of soft-brittle CdZnTe crystals

Cd_0.96Zn_0.04Te (111) single crystals were ultraprecisely ground by #1500, #3000, and #5000 diamond grinding wheels, and the corresponding surface roughness Ra is 49.132, 18.746, and 5.762 nm. High-resolution field emission scanning electron microscope and transmission electron microscope were employed to investigate the surface and subsurface damage. After ultraprecision grinding by three kinds of diamond wheels, the subsurface can achieve ultra-low damage layer with thickness of 1–2 nm made of amorphous state material and lattice distortion layer. For the #1500 precision grinding, the subsurface damage is mainly multi-nanocrystal with diameter in the range of 5–20 nm. While for the #3000 precision grinding, the subsurface damage is made of amorphous state material containing nanocrystals with diameter mainly in the range of 2–5 nm, and the bending deformation is mainly conducted through dislocation pleat formation. For #5000 ultraprecision grinding, the subsurface damage is mainly amorphous state material, and nanocrystals with diameter in the range of 2–5 nm enrich adjacent to the ground surface. Moreover, the size of nanocrystal ground by #5000 diamond grinding wheel is mainly 2 nm. Fracture mechanism ground by #5000 diamond grinding wheel firstly turns onto thin amorphous state film, then fracture.     

Effects of Abrasive Types on Grinding of Chopped Strand Mat Glass Fiber-Reinforced Polymer Composite Laminates

A grindability study of chopped strand mat glass fiber reinforced polymer laminates (CSM GFRP) has been carried out to evaluate the effects of abrasive types on grinding force ratio and area roughness at varying grinding parameters such as speed, feed and depth of cut. Performances of alumina (Al₂O₃) and cubic boron nitride (CBN) wheels were compared. Both wheels delivered the maximum grinding force ratios at low speed, high feed and low depth of cut. Alumina wheel produced smoother surface when grinding at low speed, low feed and high depth of cut. CBN wheel, on the other hand, gave smoother surface at high feed and low depth of cut conditions, regardless of speed. With CBN wheel, it is likely that a single grinding condition exists that maximizes grinding force ratio and minimizes area roughness. The findings indicate that CBN wheel exhibited higher grinding force ratio than alumina grinding wheel in general. CBN grinding wheel also outperformed alumina grinding wheel by producing smoother ground surface in most cases.     

Experimental study of time-dependent performance in superalloy high-speed grinding with cBN wheels

The time-dependent performance of grinding is expressed as the change of process output measures as a function of time during grinding. Although the wheel capability will be restored by dressing, the time-dependent performance of grinding during one dressing skip is the determinant on the grinding quality variation in terms of surface integrity and workpiece geometric accuracy. Therefore, understanding of grinding time-dependent performance in relation with the wheel–workpiece microscopic interaction is critical for wheel and process development to achieve stable grinding processes. In this article, the grinding of superalloy with cubic boron nitride (cBN) grinding wheels is performed. The time-dependent performance is recorded to represent the characteristic features, and the microscopic wheel topography is measured under scanning electron microscope (SEM) throughout the grinding process, so as to reveal the root cause for the time-dependent performance and its impact on the workpiece quality variation. The experiment results indicate that during the grinding process, there exist three characteristic stages, namely, initial wheel wear stage, severe wheel wear stage, and wheel resharpening stage. Moreover, the change trend of spindle power consumption, workpiece quality on surface hardness and roughness, wheel wear condition, and G ratio are consistent with the wheel topography evolution reflected by SEM photos, which can be used to present the three grinding stages. The wear and replacement of the efficient grain cutting edges result in the time-dependent performance during superalloy high-speed grinding with cBN wheels.     

OPTIMIZING GRINDING PERFORMANCE BY THE USE OF SOL-GEL ALUMINA ABRASIVE WHEELS AND A NEW TYPE OF AQUEOUS METALWORKING FLUID

The purpose of this study was to optimize the grinding process by the use of different types of metalworking fluids and grinding wheels. The four most important variables in the grinding process are the grinding machine, the grinding wheel, the metalworking fluid, and the type of material being ground (the part). This study limited the material ground to two different grades of steel. In most machine shops today, the grinding machine is a fixed component, as modification or replacement is too expensive. However, the metalworking fluid and the grinding wheel are relatively inexpensive and easy components to change. Therefore, this paper will only consider changes in the metalworking fluid and the grinding wheel when attempting to optimize the grinding process. Furthermore, this study will limit these two components to aqueous metalworking fluids and non-superabrasive grinding wheels.     

Grindability of high-temperature alloy with ceramic alumina wheels

The grindability of high-temperature alloy by using ceramic alumina wheels is studied on the basis of extensive analysis of the grinding force, grinding temperature, surface roughness and topography of ground surfaces, residual stress, hardness distribution of surface layer, and morphology of the surface layer from a metallographic point of view. The grinding burn mechanism of high-temperature alloy is unveiled and the feasible grinding parameters to avoid burning are analyzed. Some conclusions are obtained as follows. Increasing the grinding depth or the wheel velocity makes grinding temperature and residual tensile stress of the surface rise, which deteriorates the surface topography. Appropriate liner velocity of the wheel is 18–22 m/s and the depth of grinding should not exceed 0.02 mm in grinding GH2132 alloy with ceramic alumina wheels to assure the surface quality. When a_p increases enough to cause grinding burn, the strengthening effect of particles ?′ in ? base decrease and the micro-hardness of the surface is obviously lower than that of the base material, which deteriorates the mechanical properties and heat resistance of GH2132 alloy. Results provide a theoretical and experimental basis for technical optimization in the grinding of high-temperature alloy with high efficiency and high quality.     

An experimental study on the grinding of alumina with a monolayer brazed diamond wheel

A monolayer diamond grinding wheel was fabricated by brazing in vacuum. The wheel was then used to grind alumina at three different grinding speeds. The horizontal and vertical grinding forces, and the grinding temperatures were measured during grinding. SEM observations were made for the ground workpiece surfaces. The influences of the peripheral wheel speed on the grinding forces, specific grinding energy and grinding temperatures were analyzed under different combinations of depth of cut and workpiece velocity. The dependence of the average grinding force per grain and specific grinding energy on the maximum undeformed chip thickness was discussed respectively. It was found that an increase in the peripheral wheel speed reduced grinding force, but increased force ratio, specific grinding energy, and grinding temperature.     

杯形砂轮磨削高硬度球面砂轮磨损的研究

采用分块杯形砂轮磨削高硬度球面,磨削过程中砂轮磨损不仅影响砂轮磨削性能,而且造成工件和砂轮实际接触面积不断产生变化,影响磨削力和磨削质量。为此,基于展成法磨削原理研究砂轮块磨损后的形状变化,分析了分块砂轮的磨损形式,揭示了进给过程中砂轮块磨损形状的变化规律,推导了砂轮磨损量和砂轮工件接触面积的计算公式,分析了砂轮磨损速度的变化趋势及其影响因素,试验最后研究了砂轮磨损量的变化规律,并验证了砂轮磨损量的计算模型。     

Vibro-impact dynamics of material removal in a robotic grinding process

This paper studies the vibratory dynamics governing material removal performed by a compliant robot. The objective is to understand whether metal removal at a target rate or to a target depth of cut is possible given the unavoidable significant and sustained vibrations inherent to the process. Robotic grinding by the SCOMPI robot developed at Hydro-Québec’s research institute for field maintenance work on hydroelectric equipment is studied. A test rig is developed to investigate the instantaneous process of material removal. The setup employs the methodology of angular analysis to detect and locate the discrete cutting events with respect to the instantaneous angular position of the spindle. Test results confirm that the grinding wheel exhibits cyclic impacting oscillations while removing material. This vibro-impact behavior is explained by the nonsmooth nature of the system arising from the substantial difference between process stiffness and stiffness of the robot. Grinding force and power are formulated based on the impacting dynamics of material removal (impact cutting). Parameters of the impact-cutting model are determined experimentally. The impact-cutting model is found well-suited to predicting the grinding power required to remove metal at a target rate. The conclusion is reached that metal removal to a target depth and with acceptable surface waviness is possible despite high-amplitude vibro-impacts between the grinding wheel and workpiece.     

非球面模芯ELID磨削系统的研制

针对非球面模芯超精密磨削加工问题,研制了在线电解修锐(ELID)磨削系统。该系统应用平行法磨削原理,用整形后的球头砂轮进行非球面模芯的超精密磨削加工;利用非球面模芯工件本身的导电性能,以铸铁结合剂CBN砂轮作为阳极,以模芯本身作为阴极,通过ELID电源参数(电流、电压、占空比)的合理选择,解决了CBN球头砂轮的修锐,稳定地实现了小口径非球面模芯的ELID超精密磨削加工。     

Grindability of high-temperature alloy with ceramic alumina wheels

The grindability of high-temperature alloy by using ceramic alumina wheels is studied on the basis of extensive analysis of the grinding force, grinding temperature, surface roughness and topography of ground surfaces, residual stress, hardness distribution of surface layer, and morphology of the surface layer from a metallographic point of view. The grinding burn mechanism of high-temperature alloy is unveiled and the feasible grinding parameters to avoid burning are analyzed. Some conclusions are obtained as follows. Increasing the grinding depth or the wheel velocity makes grinding temperature and residual tensile stress of the surface rise, which deteriorates the surface topography. Appropriate liner velocity of the wheel is 18–22 m/s and the depth of grinding should not exceed 0.02 mm in grinding GH2132 alloy with ceramic alumina wheels to assure the surface quality. When a _p increases enough to cause grinding burn, the strengthening effect of particles γ′ in γ base decrease and the micro-hardness of the surface is obviously lower than that of the base material, which deteriorates the mechanical properties and heat resistance of GH2132 alloy. Results provide a theoretical and experimental basis for technical optimization in the grinding of high-temperature alloy with high efficiency and high quality.     

Some observations on profile wear in creep-feed grinding

Tests were performed to investigate the effect of various parameters on the wear of a profiled grinding wheel when creep-feed grinding a nickel-base alloy. The wear of a number of different radii, angles and profile heights was monitored. It was found that this wear was strongly influenced by the total distance travelled by an individual grit while in contact with the workpiece and by the workpiece feed rate. In addition, using a neat oil grinding fluid resulted in less wear than a water-based fluid and a 120 grit wheel wore less than a 60–80 grit wheel. A simple theoretical model was developed for predicting the effect of stock removal rate on profile wear in the creep-feed grinding of a “difficult-to-grind” material and this gave good correlation with the experimental trends.     

Roughness due to workpiece wear generated in surface grinding of metals

Assuming the grinding wheel surface to be fractal in nature the maximum envelope profile of the wheel and contact deflections are estimated over a range of length scales. This gives an estimate of the ‘no wear' roughness of a surface ground material. Four test materials, aluminium, copper, titanium and steel are surface ground and their surface power spectra estimated. The departure of this power spectra from the ‘no wear' estimates is studied in terms of the traction induced wear damage of the surfaces.     

拟稳态条件下AA6061铝合金和TC4钛合金的电化学清理磨削

电化学清理磨削工艺（ECCG）可有效解决延塑性金属磨削时的砂轮黏附问题，该工艺成功应用的关键是使砂轮表面黏附物的形成率与其电解率相平衡。基于电化学原理和磨削机理分析，提出一种利用电解电流定量评估砂轮黏附率的新方法，确定了不同磨削参数下ECCG工艺所需的工作电压。在拟稳态条件下，利用该工艺对AA6061铝合金和TC4钛合金工件进行磨削加工。研究结果表明，ECCG工艺具有较强的可扩展性，可用于加工大型延塑性金属零件。     

用普通磨料砂轮对陶瓷工件超精磨削及去除机理的实验研究

在大量实验基础上,提出一种用普通磨料砂轮对优质赛隆（Sialon）陶瓷工件超精加工方法。分析了工艺参数及砂轮现场平衡技术对超精磨削过程的影响及其磨削力特征。通过对工件表面的扫描电镜观察,研究了超精磨削的去除机理,指出陶瓷超精表面的形成依赖于材料的塑性流动型去除方式。     

光学自由曲面反射镜模芯的镜面成型磨削

采用精密修锐修整的圆弧形粗金刚石砂轮在CNC精密磨床上进行了数控成型磨削加工,实现了高效镜面磨削。分析金刚石砂轮圆弧形轮廓的成型修整原理,建立了圆弧形修整的数控模式。通过建立曲面数控成型磨削的行走轨迹算法,实现了自由曲面的圆弧包络成型磨削加工。分析了磨削工艺参数和砂轮出刃形貌参数与超光滑表面形成的作用机制,进行了镜面磨削试验并检测表面微观形貌和粗糙度,分析实现镜面磨削的脆/塑性磨削转换机理。理论分析表明,降低砂轮行走速度,提高砂轮转速以及改善出刃形貌可以获得纳米级粗糙度的超光滑磨削表面。试验结果显示,先将砂轮修锐修整再控制砂轮行走速度小至15 mm/min时,表面粗糙度小于10 nm以下,且微观加工表面没有发生脆性破坏,形成镜面。加工高速钢自由曲面时,面形误差(PV值)可以达到10 μm以下,表面粗糙度R_a可以达到约16 nm。实验结果表明:利用数控技术和粗金刚石砂轮可以实现自由曲面模芯的高效镜面磨削加工,保证了高精度的光学自由曲面反射镜注塑模芯。     

Si_3N_4陶瓷材料的磨削试验研究

通过用树脂结合剂金刚石砂轮对Si3 N4陶瓷进行磨削试验 ,从磨削过程中的磨削力、磨削比能、磨削温度及磨削表面的微观形貌变化等方面 ,综合探讨Si3 N4材料的磨削加工机理。研究结果表明 :Si3 N4在磨削加工中在磨粒切深较大时主要以脆性断裂方式去除 ,其磨削温度与材料去除机理有着密切联系。     

多孔复合结合剂立方氮化硼砂轮制备与磨削性能

针对高温合金高效磨削用砂轮气孔率不高、砂轮耐磨性差等问题,基于空心球造孔与高温钎焊技术,提出多孔复合结合剂立方氮化硼(Cubic Boron Nitride,简称CBN)砂轮制备方法。从砂轮结构设计、砂轮节块制备工艺、砂轮粘接与修整等方面加以阐述,最后对该砂轮高效磨削高温合金磨削性能进行评价。在磨削速度为80m/s、磨削深度为0.2 mm的工艺条件下,多孔CBN砂轮最大材料去除率可达50 mm3/mm·s,这表明该新型多孔CBN砂轮在镍基高温合金高效深切磨削中具有应用潜力。