Improving minimum quantity lubrication in CBN grinding using compressed air wheel cleaning

The application of minimum quantity lubrication (MQL) in grinding has emerged as an alternative for reducing the abundant flow of cutting fluids, thus achieving cleaner production. Although considered an innovative technique in grinding operations, its widespread application is hindered due primarily to the high heat generation and wheel pore clogging caused by machined chips, harming the final product quality and increasing tool wear on the machine. This study sought to improve MQL use in grinding. In addition to the conventional MQL injected at the wheel/workpiece interface, a compressed air jet was used to clean the mixture of MQL oil and machined chips from clogged wheel pores. Experiments were conducted using external cylindrical plunge grinding on AISI 4340 quenched and tempered steel, and a vitrified cubic boron nitrite (CBN) wheel. The cooling-lubrication methods employed were the conventional flood coolant application, MQL (without cleaning), and MQL with a cleaning jet directed at the wheel surface at different angles of incidence. The main goal of these experiments was to verify the viability of replacing the traditional abundant flow of cutting fluid with MQL and wheel cleaning. The analyses were conducted by measuring the following output variables of the process: workpiece surface roughness and roundness errors, diametrical wheel wear, acoustic emission generated by the process, and metallographic images of the ground surface and subsurface. Results show the positive effects of implementing the cleaning jet technique as a technological improvement of minimum quantity lubrication in grinding in order to reduce the usage of cutting fluids. The MQL technique with cleaning compressed air jet, for a specific angle of incidence (30°), proved to be extremely efficient in the improvement of the surface quality and accurate workpiece shape; it also reduced wheel wear when compared to the other cooling-lubrication methods that were tested (without a cleaning jet).     

Useful coolant flowrate in grinding

A model has been developed for flowrate between a rotating grinding wheel and a workpiece. It was found that the useful flow that passes through the contact zone is a function of the spindle power for fluid acceleration, wheel speed and delivery-nozzle jet velocity. Two loss coefficients having values less than 1 are required to be calibrated for the particular grinding wheel and fluid delivery type. The model is then valid for a range of nozzle flowrates for the particular wheel and nozzle conditions. The flowrate delivered is related to unit width of the delivery nozzle assumed to be unit width of grinding contact. The model makes it possible to determine a suitable value of nozzle outlet gap to achieve a required fluid film thickness in the grinding zone. A guide is given to optimisation of the jet velocity in relation to the power required to accelerate the fluid and the particular velocity of the wheel. The model has been validated experimentally. Its simplicity and accuracy allow application to a wide range of grinding situations.     

面向绿色制造的快速点磨削磨削液供给参数计算

高速／超高速磨削条件下,砂轮边缘的高速空气带会阻碍磨削液注入磨削区。空气带压力与砂轮速度的平方成正比。快速点磨削是一种新型高速／超高速磨削技术,接触区很小,实际磨削功率低,冷却及散热效果好。在分析了高速／超高速磨削砂轮周围旋转空气带动压力及速度分布特点的基础上,根据热力学原理及快速点磨削特点,分析并建立了磨削液的供给流量和供液速度的理论模型。在此基础上,建立了面向绿色制造的快速点磨削的磨削液喷嘴直径及供液压力的工程计算公式。     

Experimental simulation of the efficiency of high speed grinding wheel cleaning

The grinding of certain materials such as ductile material which are hard to grind implies particular conditions of work. Maintaining the cutting ability of the wheel is necessary and wheel cleaning is one of these conditions. In this paper, the parameters which are influential in maintaining a clean wheel are identified. A cleaning criterion is proposed to estimate the efficiency of the cleaning process. Using an experimental setup, the significant of the influence of the nozzle position, the flow rate and pressure, the boundary layer of air around the rotating wheel and the particle rate contained in the fluid are assessed. It is observed too that the fluid temperature has no significant effect. Lastly, the best method to clean a wheel when high speed grinding is discussed.     

脉冲射流式岩屑床清理工具的研究

针对大斜度及水平井段,岩屑极易沉积在井筒底部形成一定高度的岩屑床,使得钻杆被埋没,造成钻杆摩阻增大、钻具断裂等问题,设计一种射流式岩屑床清洁工具,基于液固两相流理论,建立三维射流式清洁工具与普通携岩钻杆的仿真模型,并利用Fluent分析射流式清理工具的喷嘴喷射角度、喷嘴流速、岩屑粒径、钻井液排量等参数变化对环空井筒内岩屑体积分数及岩屑质量的影响规律。结果表明：增加脉冲射流式工具后,环空内的岩屑沉积量明显减少,在钻杆转速为80 r/min时,最佳的喷嘴角度为90°;增加喷嘴流速及钻井液排量都可以降低环空内的岩屑量;随着岩屑粒径的增加,环空内岩屑沉积更多。该工具能够降低沉积在环空内的岩屑质量,提高岩屑的运移能力。     

Optimisation of fluid application in grinding

This paper addresses the quantity of fluid required for grinding and the method of application. Results from this research suggest that supply flowrate needs to be 4 times the achievable ‘useful’ flowrate. Extra flowrate is wasted. It is shown that jet velocity and jet flowrate can be separately specified. Improved system design allows ‘actual’ useful flowrate to approach ‘achievable’ useful flowrate. Achievable useful flowrate depends on wheel porosity and wheel speed whereas actual useful flowrate depends on nozzle position, design, flowrate and velocity. Experimental methods are complemented by computational fluid dynamics (CFD) simulations.     

Improving grinding fluid delivery using pneumatic barrier and compound nozzle

Grinding fluid is commonly applied to control grinding defects caused by high grinding zone temperature. Delivery of fluid to the grinding zone is obstructed by the formation of a stiff air layer around the grinding wheel. This results in huge wastage of grinding fluid. In the present paper, results of using a pneumatic barrier and a compound nozzle are discussed with respect to delivering fluid deep into the grinding zone. Grinding fluid passing through the grinding wheel contact zone is measured under different modes of fluid delivery using a flood cooling, or a compound, nozzle, with or without the application of a pneumatic barrier. It is found that the system using a pneumatic barrier with flood cooling nozzle, and that employing a compound nozzle perform better than the flood cooling nozzle. A compound nozzle along with a pneumatic barrier renders substantially less wastage of grinding fluid even at a low flow rate of grinding fluid. Above a fluid discharge of 475 ml/min, the compound nozzle alone shows effective penetration of grinding fluid through the grinding zone. Reduction of grinding force, specific energy and roughness of ground surface are obtained after using compound nozzle fluid delivery system. Compound nozzle may be used instead of flood cooling nozzle as it improves grinding performance even using 52.5 % less discharge of grinding fluid.     

Strategies for optimal use of fluids in grinding

The increased concern for environment and sustainability are pushing machining operations towards the reduction or even complete elimination of cutting fluids. Grinding is not excluded from this objective, but greater difficulties appear due to the nature of the material removal mechanisms. In this work, two approaches aiming at the optimization of fluid application in grinding are presented. First, the influence of nozzle design on the development of velocity and pressure fields is studied using CFD tools. A new nozzle design that optimizes the characteristics of the jet is introduced, analyzed and manufactured. Grinding experiments show that improvements in wheel life and surface finish are possible using the new nozzle. Second, the performance of a new grinding technology that combines MQL with low-temperature CO₂ is evaluated trough industrial grinding tests. Results show an increased performance in terms of friction conditions and surface finish.     

汽车变速器齿轮高精度磨齿机床研究

面向汽车变速器行业对高精度齿轮的需求,开发一种蜗杆和成型砂轮复合磨削的双工件主轴磨齿机床。该机床具备全自动更换刀具和全自动装卸被加工齿轮功能,可使用通用修整器同时修整蜗杆砂轮和成形砂轮;采用双工件主轴结构,节省了上下料装载时间,加工效率大幅提升,比单主轴效率高出30%左右;在合适的粗磨和精磨砂轮颗粒的作用下,蜗杆砂轮和成形砂轮磨削的结合使磨削时间减少了50%左右;自带齿轮检测设备,能够在线检测齿轮磨削加工量是否达到加工工艺要求,实现了齿轮磨削高效、高精度、节能环保加工。     

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).     

砂轮刚性对磨削性能及产品加工质量的影响

通过测量不同砂轮磨削时机床功率、磨削区温度、刀具的表面粗糙度和刃口质量,分析砂轮刚性改变对砂轮磨削性能和刀具质量的影响。研究发现:在一定范围内降低砂轮的刚性可以提高砂轮的磨削性能,改善刀具的加工质量。其中,加入体积分数10%的尼龙制备的砂轮对其刚性改善比较明显,在相同的磨削条件下,其磨削区的平均温度较普通砂轮磨削区的平均温度低50℃左右;累计磨削相同工件后,机床负载约为使用普通砂轮时的30%~50%;磨削得到的刀具表面粗糙度降低,可以达到R_a0.02μm以下,且磨削纹路规则;在×500倍显微镜下,观察不到刀具崩刃等缺陷,刃口质量得到明显改善。      

聚酰胺1212在印刷电路板刀具磨削用金刚石砂轮中的应用

选用微米级聚酰胺1212(PA1212)对聚酰亚胺树脂结合剂金刚石砂轮进行改性。通过磨削测试,对改性前后树脂砂轮的耐用度、寿命以及磨削PCB加工用刀具的表面质量等进行了研究。结果表明:PCB刀具磨削用金刚石砂轮经过PA1212改性,耐用度提升59.5%,寿命提升71.2%;使用该砂轮加工的刀具刃口崩口概率降低,表面纹路更加均匀。      

高压水射流在铝板带清洗设备上的应用

介绍了铝板带清洗原理及高压水射流喷射距离的选择,通过对打击力进行理论分析,建立了打击力的计算公式,从而找到提高清洗效果的途径;对清洗机组设备结构与工艺过程进行了介绍,总结了铝板带的高压清洗系统节水、节能、提高洗净率的方法;文中给出了入射角、压力、喷嘴结构、喷射距离、喷流角度等实用参数选择的原则和方法,具有实用价值。     

基于CFD的清洗用扇形喷嘴清洗参数研究

扇形喷嘴因其均匀的扁平射流能提供其较大的清洗面积而被广泛应用在工业清洗中。打击力和动压是衡量清洗效果的重要参数,合理的匹配喷嘴直径、压力、流量,能更有效、更节能地进行清洗作业。在建立了扇形喷嘴及其外流场的三维模型的基础上,运用FLUENT的VOF两相流模型对不同出口直径的扇形喷嘴在不同压力下的打击力、动压进行了比较分析。结果表明:喷嘴直径和压力的增大都会使打击力增大,但不是二者越大打击力的增大的幅度就越大;同一个扇形喷嘴,射流压力在1~21 MPa之间,打击力会随着压力的增大而增大,但增大的幅度会随之减小,如3 mm喷嘴射流压力从1 MPa提升到2 MPa射流打击力增加率为101%,但从20 MPa提升到21 MPa射流打击力增加率只有5%;相同的射流压力下,扇形喷嘴出口直径在1~3 mm之间,打击力会随着出口直径的增大而增大,但增大的幅度会随之减小,如射流压力为2.5 MPa喷嘴出口直径从1 mm提升到1.5 mm射流打击力增加率为118%,但从2.5mm提升到3 mm射流打击力增加率只有42%。     

高速超高速磨削工艺及其实现技术

高速超高速磨削加工是先进制造方法的重要组成部分，集粗精加工与一身，达到可与车、铣和刨削等切削加工方法相媲美的金属磨除率，而且能实现对难磨材料的高性能加工。本文主要论述了高速超高速磨削工艺技术的特点；分析了电主轴是高速超高速磨削主轴系统的理想结构，介绍了陶瓷滚动轴承、磁浮轴承、空气静压轴承和液体动静压轴承在主轴单元中的应用；超高速砂轮主要用电镀或涂层超硬磨料(CBN、金刚石)制成，介绍了超硬磨粒的特点和砂轮的修整，分析了在高速及超高速磨床上得到广泛应用的德国Hofinann公司生产的砂轮液体式自动平衡装置；介绍了高压喷射法，空气挡板辅助截断气流法，气体内冷却法，径向射流冲击强化换热法磨削液供给系统的特点；最后介绍了直线电机进给系统和声发射智能监测系统等实现高速超高速磨削的关键技术。     

Laser surface preparation of vitrified grinding wheels

A new method for surface cleaning loaded grinding wheels is introduced by applying CO₂ laser irradiation onto the grinding wheel surface. It was demonstrated that effective cleaning can be achieved by selection of the laser power flux and the duration of the irradiation. Fusion and evaporation of clogged metal chips play important roles in the laser cleaning process. It is suggested that high laser power irradiance and short irradiation duration are essential for effective grinding wheel cleaning. This paper was presented at the fourth International Surface Engineering Congress and Exposition held August 1–3, 2005 in St. Paul, MN.     

低温冷风磨削加工替代传统磨削的试验研究

利用自行研制的低温冷风发生装置进行绿色磨削试验研究,试件材料是40Cr。测试喷嘴出风温度、砂轮粒度、磨削进给量和砂轮线速度对试件表面加工质量的影响。与传统磨削的加工结果进行对比分析,表明:在该试验条件下,低温冷风磨削的加工质量可以达到传统磨削的精密标准,能够替代传统磨削。该研究对于推广低温冷风磨削技术的应用具有重要的参考意义。     

Laser Dressing of Metal Bonded Diamond Wheel

In this study, a laser beam is used as a non-contact thermal dressing tool for a bronze bonded diamond wheel. The pulsed-Nd:YAG laser beam is irradiated on the wheel surface and the bond material partially removed by laser irradiation only. In order to efficiently remove the bond material, it is necessary to direct an air jet on the spot irradiated by the laser so as to blow away the molten binder before it solidifies again. Less damage of diamond particles such as micro-cracks or graphitization occurs. In grinding with a laser-dressed wheel, the grinding forces are almost the same as those for a conventionally dressed wheel. Consequently, effective laser dressing can be expected with the associated dressing conditions.     

磨料用量与喷嘴直径相关关系的实验研究

本研究以实验为基础,利在回归分析法建立了磨料用量与喷嘴直径之间的相关关系,为工程应用中地喷砂清理提供了理论指导。     

Influence of oil mist parameters on minimum quantity lubrication – MQL grinding process

Promising alternatives to conventional dry and fluid coolant applications are minimum quantity lubricant (MQL) or near dry grinding. Despite several researches, there have been a few investigations about the influence of MQL parameters on the process results, such as oil flow rate, air pressure, MQL nozzle position and distance from the wheel–workpiece contact zone. The current study aims to show through experiment and modeling, the effects of the above parameters on grinding performance such as grinding forces and surface roughness. The results show that the setting location of the nozzle is an important factor regarding the effective application of MQL oil mist. It has been shown that optimal grinding results can be obtained when the MQL nozzle is positioned angularly toward the wheel (at approximately 10–20° to the workpiece surface). In addition, it is found that the efficient transportation of oil droplets to the contact zone requires higher mass flow rate of the oil mist towards the grains flat area and longer deposition distance of an oil droplet. Applying the new setup, considerable reduction in the grinding forces and surface roughness has been achieved.