Modeling and simulation of useful fluid flow rate in grinding

This research established a mathematical model of the useful grinding fluid flow rate of a rough grinding wheel. The abrasive distribution matrix of the grinding wheel surface topography was programmed on the MATLAB software platform to obtain the grinding wheel porosity φ at different particle sizes. The grinding fluid flow field was simulated and studied by using the volume of fluid multiphase flow model of FLUENT. Results showed that given a certain circular velocity of the grinding wheel, a larger grinding fluid jet velocity resulted in greater useful grinding fluid flow. When the grinding fluid jet velocity was set, the useful grinding fluid flow increased with increasing circular velocity of the grinding wheel. With the increasing velocity of the grinding wheel, as affected by the airbond layer, the increasing rate of the useful grinding fluid flow decreased, and the flow likewise showed a tendency to decrease. With a certain grinding fluid jet velocity, the useful flow rate of the grinding fluid was positively proportional to the useful flow. When the grinding fluid jet velocity changed and grinding wheel velocity was set, the grinding fluid jet velocity increased as the useful flow rate decreased. When the grinding fluid jet velocity was equivalent to the grinding wheel velocity, the useful flow rate of the grinding fluid was positively proportional to the useful flow. When the minimum clearance of grinding zone h increased, the useful grinding fluid flow and useful flow rate likewise increased. When the grinding fluid jet velocity was equivalent to the grinding wheel velocity, a larger nozzle gap width increased the flow supply for the grinding fluid and the useful grinding fluid flow. However, the increase in the useful flow rate of the grinding fluid was significantly smaller than that of the nozzle flow. This condition decreased the useful flow rate of the grinding fluid.     

磨削过程中磨削液的有效利用及其实现技术

在磨削加工过程中,一般都是利用向磨削区供给充分冷却液的方法来抑制零件表面温度升高和解决热损伤。但是由于砂轮的高速旋转,会在砂轮的表面形成一个高压空气边界层,阻止磨削液有效的进入磨削区,使加工条件恶化,磨削区温度升高,影响了工件的表面质量和完整性。通过合理的选择供液压力、流量和供液方式及喷嘴形式来提高进入磨削区有效磨削液的比例,进而更好的发挥磨削液的冷却作用,降低磨削区温度,保证工件表面质量和表面完整性,同时也有利于实现绿色磨削加工。     

陶瓷空心球形复合超硬磨料低温磨削特性实验研究

针对空心球形复合超硬磨料的多微孔结构对磨削温度影响问题,研究了空心球形复合超硬磨料的结构,建立了空心球形磨料砂轮的磨削模型.从理论上分析了多微孔结构对砂轮的切削锋利度和携带冷却液能力的影响机制;运用温度测量系统,进行了陶瓷空心球形复合超硬磨料砂轮在不同磨削切深和不同冷却液供给量条件下的平面磨削温度实验研究,并分析了磨削温度随不同切深和冷却液供给量的变化趋势.研究结果表明,空心球形磨料砂轮的磨削温度明显低于传统超硬磨料砂轮,验证了空心球形磨料砂轮具有较锋利的切削刃和更好的携带冷却液能力,可有效降低磨削温度,是实现低温磨削的一种新途径.     

磨削加工时磨削液的流体动压效应

根据流体动压润滑理论,分析了平面砂轮磨削液的流体动压效应,并考虑砂轮渗透度的影响,推得了有限宽线接触条件下磨削液三维流动的Ｒｅｙｎｏｌｄｓ方程,用数值分析方法,得出了砂轮磨削区内磨削液动压力的分布曲线和液膜举起力。然后进一步分析讨论了砂轮渗透度、砂轮与工件间的相对速度及相对间隙对液膜举起力的影响。数值计算结果与实测数据基本吻合。     

Investigation of a heat pipe cooling system in high-efficiency grinding

The high grinding temperature is one of the problems restricting on the further development of high-efficiency grinding due to the workpiece burnout and excessive wheel wear. An original method about enhancing heat transfer in the contact zone based on heat pipe technology is put forward to reduce the grinding temperature in this paper. Drawing on the structure of rotation heat pipe, one heat pipe cooling system, heat pipe grinding wheel (HPGW) applied to high-efficiency grinding, is developed and its heat transfer principle is illustrated. Besides, the cooling effect in the contact zone using HPGW is simulated through a three-dimensional heat transfer model in grinding, and the influence of different parameters of the wheel speed, cooling condition, and heat flux input on the grinding temperature is analyzed. Eventually, preliminary grinding experiments with HPGW were carried out to verify the cooling effect by comparing with non-HPGW in grinding of 0.45 wt.% C steel and titanium alloy Ti-6A1-6V. Results show that using HPGW can significantly reduce the grinding temperature and prevent the burnout.     

加压内冷却砂轮的研制及磨削性能研究

针对高温合金材料在磨削加工过程中存在磨削烧伤问题,为避免气障效应并强化冷却液在磨削弧区的换热效果,提出采用加压式内冷却断续磨削方法。利用数值模拟方法和3D打印技术对砂轮基体、加压内冷却系统和密封结构等进行设计和验证,制备了用于平面磨削的加压内冷却开槽CBN砂轮。在相同的磨削加工参数条件下,使用加压内冷却方法与外部喷射冷却方法进行镍基高温合金磨削对比试验,分析了砂轮速度、磨削深度和工件进给速度等加工参数对磨削温度、加工表面粗糙度和表面形貌的影响规律,验证了加压内冷却断续磨削方法对磨削弧区的强化换热效果。结果表明：在相同试验参数条件下磨削镍基高温合金,加压内冷却法比外部喷射冷却法的换热效率更高,得到的磨削温度更低,表面粗糙度更小,加工表面更为光滑细腻。     

An application of lubrication theory to predict useful flow-rate of coolants on grinding porous media

By considering both hydrodynamic pressure and ram pressure effects on flow through the grinding zone, we construct a predictive model for calculating the useful flow-rate of coolants on grinding porous media. The hydrodynamic pressure is computed by means of a modified Reynolds equation for porous media, with upstream boundary conditions supplied by the ram pressure. To find the tangential velocity, the radial velocity, the depth of fluid penetrating into the wheel, and the flow-rate through the grinding zone, we solve momentum and continuity equations for flow through a porous wheel. Numerical results indicate that for a lower porosity of workpiece, the hydrodynamic pressure is higher and the fluid penetrating into the pores of wheel is deeper. Also, the useful flow-rate increases as the porosity of workpiece increases.     

The influence of spraying parameters on grinding performance for nanofluid minimum quantity lubrication

To reduce the usage of grinding fluid, nanofluid has recently been applied to grinding process with minimum quantity lubrication (MQL) technique. In this study, surface grinding of hardened AISI 52100 steel under different spraying parameters was carried out. Grinding performance was investigated and compared in terms of grinding forces, surface roughness, and grinding temperature. Experimental results show that the MQL nozzle spraying direction has important effects on the application of the nanofluid mist, and then on the lubrication and cooling of the grinding zone. It is found that an optimal grinding performance can be obtained when the nozzle is positioned angularly toward the grinding wheel. Furthermore, it is shown that air pressure and spraying distance are also critical in order to enhance the nanofluid mist to be penetrated into the grinding zone. Grinding forces, surface roughness, and grinding temperature are decreased with the increase of air pressure, and grinding performance in shorter spraying distance is better than that in longer spraying distance. The influence mechanism of the spraying parameters on the grinding performance was discussed.     

ENERGY PARTITION FOR GRINDING OF NODULAR CAST IRON WITH VITRIFIED CBN WHEELS

An investigation was undertaken to determine the energy partition to the workpiece for grinding of an automotive nodular cast iron with a vitrified CBN wheel. The energy partition is a critical parameter which is needed for calculating grinding temperatures and predicting the occurrence of thermal damage to the workpiece. Straight surface grinding experiments were conducted over a wide range of removal rates to measure the workpiece temperature response and spindle power. Temperature matching analyses were then applied in order to obtain the energy partition. Values for the energy partition were found to range from 3 to 6% when the temperature at the grinding zone was maintained below the fluid burnout limit. Such low energy partitions indicate cooling of the workpiece by the fluid at the grinding zone. Higher energy partitions up to 60% were obtained by reducing or eliminating the fluid, which also raised the temperature above the burnout limit.     

开槽砂轮缓进给深切磨削时工件表层温度场解析

采用热源法推导出开槽砂轮缓进给深切磨削时磨削弧区工件表层温度分布的理论解析式，并利用理论计算公式结合磨削实验完成了施加水射流冲击条件下工件表层温度场的推演计算，计算结果与实验结果基本吻合，证实了开槽砂轮辅以弧区定向高压水射流冲击强化换热的确具有良好的冷却效果。     

An investigation on surface grinding of hardened stainless steel S34700 and aluminum alloy AA6061 using minimum quantity of lubrication (MQL) technique

In grinding process, the abrasives plunge and slide against the workpiece during material removal with high specific energy consumption and high grinding zone temperature. To improve process efficiency, lubrication becomes an important requirement of the grinding fluids, along with chip removal and cooling the grinding zone. Grinding fluids have negative influences on the working environment and machining cost in terms of the health of the machine operator, pollution, the possibility of explosion (for oil), filtering, and waste disposal. The use of minimum quantity of lubrication (MQL) with an extremely low consumption of lubricant has been reported as a technologically and environmentally feasible alternative to flood cooling. This paper deals with an investigation of the grindability of hardened stainless steel (UNS S34700) and aluminum alloy AA6061 using dry, MQL, and conventional fluid techniques. One type of SiC and five types of Al₂O₃ wheels (corundum) as well as vegetable and synthetic ester MQL oils have been tested. The influences of wheel and coolant–lubricant types have been studied on the basis of the grinding forces, surface topography, and surface temperature. Synthetic ester MQL oil was found to give better grinding performance than the vegetable MQL oils. It was argued that the improved performance of the ester oil is caused by the formation of tribo-films on the abrasives and the workpiece, which enhances lubrication by inhibiting metal–abrasive interaction. Also, the grindability of the machined specimens was found to increase substantially by using the MQL grinding process with soft and coarse wheels. In MQL grinding of AA6061 alloy, the use of vegetable oil resulted in the lowest surface roughness, whereas using synthetic ester additives lead to highest surface roughness because of higher chip loading on the grinding wheel and consequently more redeposited material on the workpiece surface.     

Surface grinding of carbon fiber reinforced plastic (CFRP) with an internal coolant supplied through grinding wheel

Carbon fiber reinforced plastic (CFRP) is widely used in the aerospace industry due to its high specific strength and elastic modulus. When cutting CFRP with tools such as an endmill, problems such as severe tool wear, delamination, and burrs in the CFRP can arise. Grinding, on the other hand, is supposed to improve the quality of the machined surface and tool life, according to its machining property. However, the amount of heat generated during grinding is still a considerable problem in that it is significantly higher than the temperature with conventional cutting. In order to achieve the high performance machining of CFRP, this study aims to show the effect of supplying an internal coolant through the grinding wheel on the surface of the CFRP. Face grinding of CFRP using a cup-type grinding wheel was conducted. Vitrified aluminum oxide grinding wheel was used. Three different coolant supply systems were tested: dry grinding, coolant supply using an external nozzle, and coolant supplied internally through the grinding wheel. The results showed that matrix resin loading on grinding wheel was significantly reduced by the internal coolant supply. Hence, the grains of the grinding wheel were able to cut the fibers sharply, without delamination or burr formation on the ground surface, and surface roughness was reduced compared to the machined surface with endmill. The internal coolant supplied through the grinding wheel showed greater cooling ability, and markedly reduced grinding temperature, keeping it lower than the glass-transition temperature of the matrix epoxy resin of CFRP. Because the coolant was supplied to the grinding point directly through pores in the grinding wheel, chips were eliminated from the pores, and coolant supply was sufficient to cool the ground surface.     

A NEW TECHNOLOGY ON ENHANCING HEAT TRANSFER AT GRINDING ZONE THROUGH JET IMPINGEMENT DURING CREEP FEED GRINDING

This paper presents a jet-impingement technology to enhance heat transfer at the grinding zone. The jet-impingement technology uses a new apparatus developed to spray grinding fluid onto the workpiece surface at the grinding zone from the radial holes of an electroplated CBN wheel. Because the fluid is sprayed normally on the workpiece surface at the grinding zone, the heat transfer to the fluid is significantly improved as compared to the conventional fluid delivery methods. Experimental results, obtained under both imitated grinding tests and actual creep-feed grinding of titanium alloys, show that the jet-impingement technology lowers grinding temperature significantly. Much higher material removal rates are possible with jet-impingement without workpiece burn.     

叶轮式内喷润滑剂砂轮的流场分析及实验研究

提出了一种叶轮式内喷润滑砂轮结构及其磨削加工的方法。基于FLUENT软件模拟分析了叶轮式内喷润滑砂轮的内腔固体颗粒流场,设计出了叶轮式内喷润滑砂轮,并通过内喷润滑砂轮磨削TC4钛合金实验,分析了内喷润滑砂轮的磨削加工性能。结果表明：叶轮式固体内喷润滑砂轮中的润滑剂在离心力的作用下,通过砂轮外缘微孔直接析出到砂轮表面,能够实现抑制钛合金黏附、降低磨削区温度和摩擦因数的目的。     

基于Reynolds 方程的磨削流体动压特性的研究

由于旋转砂轮与工件表面之间存在楔形间隙,当磨削液进入楔形区域后,就会产生磨削流体动压力。以流体动压润滑理论的Reynolds方程为依据,推导出描述平面磨削时磨削流体动压力方程。采用VB和MATLAB混合编程开发出磨削时磨削流体动压力场的计算软件GRWHP。该仿真软件可用于计算磨削流体动压力的分布及磨削流体动压力对砂轮的法向作用力,且仿真结果与实验结果相符。仿真结果表明:最大磨削流体动压力产生于最小间隙附近,且位于磨削引入区内;最大磨削流体动压力随着砂轮转速的提高而增大,随着最小间隙的减小而增大。     

Grinding with directionally aligned SiC whisker wheel-loading-free grinding

A new grinding wheel has been developed, wherein very fine SiC whiskers are aligned normally to the grinding surface. However, the grinding wheel exhibits a tendency toward loading. In this study, a method to improve grinding efficiency was proposed. The loading of the grinding wheel could be remarkably reduced by the addition of a small amount of very fine abrasive grains to the grinding fluid. The experimental results showed that alumina of 0.6-μm grain size is most suitable, and a concentration of 0.25% wt is sufficient to prevent the loading. The grinding efficiency and grinding ratio were remarkably improved by this method.     

基于FLUENT的热管砂轮换热能力仿真分析

采用CFD软件FLUENT建立了热管砂轮的三维有限体积传热模型,通过改变砂轮外圆面热流密度和砂轮转速,得出对应参数条件下热管砂轮的温度场分布,并分析各参数对砂轮换热能力的影响.仿真实验结果表明:随着热源面热流密度的增大,砂轮外圆面温度越高;在冷端条件一定的情况下,提高砂轮转速能降低砂轮外圆面温度.     

石英玻璃的热辅助高效塑性域干磨削

为了提高大口径石英玻璃光学元件的加工效率,提出了热辅助塑性域超精密磨削石英玻璃的新方法。分析了石英玻璃的热辅助塑性域磨削机理,通过理论推导得出磨削深度对磨削区表面最高温升的影响规律。采用陶瓷结合剂立方氮化硼(CBN)砂轮对石英玻璃进行干磨削,利用磨削热改善磨削区石英玻璃的力学性能,实现了石英玻璃的高效塑性域磨削。通过磨削实验研究了不同磨削深度对石英玻璃表面粗糙度(Ra)和亚表面损伤深度的影响。实验结果表明,随着磨削深度的增加,Ra和亚表面损伤深度反而降低。当磨削深度为5μm,大于粗磨表面的裂纹深度时,获得了Ra值为0.07μm的光滑无裂纹的塑性域磨削表面。通过扫描电镜观察研究了砂轮的磨损机理,结果显示陶瓷结合剂CBN砂轮塑性域干磨削石英玻璃时,砂轮以磨耗磨损为主,该结果为研究新型的陶瓷结合剂CBN砂轮提供了依据。     

加压内冷却方法在高温合金磨削中的应用

针对镍基高温合金在磨削加工中大量磨削热的冷却问题,提出采用加压内冷却与断续磨削结合的冷却方法,实现磨削过程中充分冷却磨削弧区高温的目的。设计制备磨粒有序排布的加压内冷却砂轮,采用Fluent有限元软件建立砂轮磨削GH4169高温合金的温度场模型,模拟分析砂轮转速和冷却液压力对砂轮散热性能的影响。开展加压内冷却砂轮磨削GH4169实验研究,分别对磨削温度、表面粗糙度以及表面微观形貌进行对比和分析。结果表明：在相同的磨削参数条件下,相对外冷却方式,内冷却方式能获得更优良的加工表面质量,磨削温度和表面粗糙度均明显降低;在其他磨削参数相同时,冷却液压力越大,磨削温度越低且表面粗糙度越小,表面形貌更加规则、完整。     

Application of self-inhaling internal cooling wheel in vertical surface grinding

There is less research on vertical sculptured grinding technology. Especially in high vertical surface grinding process with the cup abrasive wheel, the thermal damage is prone to happen and undermine the grinding surface integrity. This problem limits to improve the grinding efficiency and the grinding ratio greatly. Through the analysis of vertical surface grinding process and features in depth, this paper revealed the inherent mechanism of higher grinding temperature in the process of vertical sculptured grinding using the cup wheel. Based on the previous research achievements, the grinding experiments on TC4 （Ti-6A1-4V） and GH4169 are carried out utilizing the self-inhaling internal cooling wheel. The experimental results show that the self-inhaling internal cooling wheel can efficiently reduce the grinding surface temperature. Moreover, the inherent mechanism of reducing the grinding temperature using the internal cooling method is revealed. Meanwhile, under the same grinding conditions, the grinding ratio during the experiments on GH4169 using self-inhaling internal cooling method is about 3 times as high as using conventional external cooling method. And the grinding forces can be reduced by about 20%. This research revealed the inherent mechanism of higher grinding temperature in the process of vertical sculptured grinding using the cup wheel, which provides theoretical basis for the design and application of self-inhaling internal cooling wheel. At the same time, an efficient and non-invasive surface grinding method of TC4 and GH4169 is presented.