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.     

Flow visualization and characterization for optimized MQL machining of composites

Limited information is available on the effect of Minimum Quantity Lubrication (MQL) parameters (oil flow rate OFR, air flow rate AFR, nozzle orientation and distance from the cutting zone) on flow characteristics. ‘Particle Image Velocimetry’ and ‘Phase Doppler Anemometry’ flow visualization methods were used to define the optimal MQL jet for better penetration and cooling/lubrication; coherent, small magnitude/number of vorticities, and small droplets of high velocity. Effect of flow characteristics on cutting forces, temperature, tool wear and geometric errors was examined in CFRP milling. Optimum AFR, OFR and nozzle distance from the cutting zone were established and compared to flood, pressurized air, and dry machining.     

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。     

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.     

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).     

Modelling of high velocity, loose abrasive machining processes

In the recent years the interest in loose abrasive machining processes as efficient, flexible processes is rising. This paper describes the development of a ‘coherent set of models’ for a category of these processes, namely those which use high velocity of the particles to obtain the necessary energy to machine a workpiece surface. The usability of this ‘coherent set of models’ will be explained with its application in the field of high-pressure abrasive waterjet cutting. At the end of this paper a forecast to the application of this modelling technique to other loose abrasive machining processes as Micro-Abrasive Air Jet Machining is given.     

On the formation of laser induced self-organizing nanostructures

Laser induced self-organizing rippled nanostructures on steel are formed by femtosecond laser pulses. They are applied as hydrophobic surfaces. A low fluence results in ‘regular ripples’ with a spatial repetition of 300-500 nm, orientated perpendicular to the laser polarization direction. In twinned areas ‘pre-ripples’ with much smaller wavelength (about 150 nm) are observed, with a different orientation. We found indications that the energy absorption depends on the crystal orientation and that pre-ripples are only formed at very low fluence. Pre-ripples initiate on secondary carbides or on grain boundaries. At higher energy, regular ripples initiate in areas with pre-ripples; at even increasing fluence disordered structures are obtained.     

Effect of deformation speed on the microstructure and mechanical properties of AA6063 during continuous extrusion process

Experiments and numerical simulations were conducted to analyze the continuous extrusion of AA6063 aluminum alloy under extrusion wheel angular velocities of 0.52, 0.78, 1.04 and 1.3 rad/s. Simulation results indicate that variations in extrusion wheel velocity directly affect material deformation and significantly influence the maximum extrusion temperature. This work also reveals that deformation and temperature have opposing effects on the microstructure of the resulting product. A greater wheel velocity causes a higher strain rate and extrusion temperature. Increasing the wheel velocity, at an initially low speed, causes a large increase in strain rate. This results in a decrease in grain size. In contrast, at high wheel velocities, further increases to wheel velocity have much less effect on the strain rate, leading to an increase in grain size as the increased extrusion temperature dominates the mechanics of grain growth. Tensile test results demonstrate that the tensile strength of the resulting aluminum extrusions mainly depends on the exit temperature, which is decided by the deformation speed. Tensile strength and hardness slightly increase with increased deformation speed. Extremely high extrusion temperature results in brittle failure and low mechanical properties of the resulting product when the extrusion speed reaches 1.3 rad/s. This paper suggests that an optimum extrusion wheel velocity, which will generate products with good mechanical properties, exists.     

Influence of gas flow on argon microwave plasma jet at atmospheric pressure

Many kinds of an atmospheric-pressure plasma jet have been developed and used for widespread applications such as a surface treatment and modified. This study focused on the argon atmospheric-pressure microplasma jet generated by discharging of RF power of 2.45 GHz microwave. The plasma jet shows sensitivity to surrounding environment: pressure, temperature and gaseous species. It is therefore absolutely imperative that a nature of atmospheric-pressure plasma jet should be understood from a point of fluid dynamics. This study, therefore, focused on the interrelationship between the plasma jet and the working gas. Motion of the plasma jet and the working gas was evaluated by velocity measurement and fast photography. As a result, the unsteady sinusoidal waving motion in the radial direction of a torch was observed. Advection velocity of the plasma in just downstream region of the torch exit increases with the supplying flow rate, and the velocity ratio is in the range of 0.75-0.87.     

Assessment of Grinding Fluid Effectiveness in Continuous-Dress Creep Feed Grinding

Creep feed grinding is a high-productivity abrasive removal process that is often limited by thermal damage and high wheel wear. A review of current industrial practices in the area of fluid supply optimisation in grinding shows that very little knowledge of the pressure, flowrate and method of application exists in industry. This paper presents an experimental procedure to evaluate fluid supply conditions in grinding on a continuous-dress creep feed grinder. Using tapered workpieces, the authors have evaluated the influence of wheel speed and material removal rate on grinding fluid effectiveness, based on the material removal rate at the position of the wheel along the ramp when burn starts to occur and the corresponding spindle power surge. Correlations are investigated between visible discoloration, metallurgical examinations and change in spindle power, in order to establish the onset of grinding burn. This procedure serves to determine the upper limit of material removal rate or - respectively - the lower limit of fluid flow rate for given grinding systems consisting of specified wheel type, material type, fluid type and fluid supply nozzle. The advantage of the presented method is its easy and time saving application in industry, but it is also of help to researchers who need to optimise fluid supply conditions prior to their grinding tests.     

A Novel Digital Enterprise Technology Framework for the Distributed Development and Validation of Complex Products

The development of complex products Involves considerable risk In terms of meeting target delivery dates, controlling life-cycle costs and establishing an efficient production network. This paper describes a new methodology for complex product design and development that utilises the recently proposed framework of ‘Digital Enterprise Technology’ (DET). The methodology Involves utilising the five technical strands of DET and In particular focuses in developing novel methods and tools for aggregate modelling, knowledge management and laser measurement planning to ‘bridge’ the gap that exists between conceptual product design and the organisation of the corresponding manufacturing and business operations. A pilot system has been created for simulating the distributed development and validation of complex aerospace products.     

Resource-Aware Aggregate Planning for the Distributed Manufacturing Enterprise

The realization of ‘intelligent and resource aware’ distributed enterprises requires substantial development of the underpinning modelling, information management and knowledge representation technologies. This paper deals with the ‘resource-aware, aggregate planning’ of manufacturing operations at early design stages. The term ‘resource aware’ indicates the creation of a dynamic inter-relationship between the planning entities and the enterprise resources, humans and machines. The technologies employed for implementing the pilot methods include; a web-centric co-development environment, unique methods for enriching planning entities with knowledge, and a flexible engine supporting planning scenarios by using evolutionary computing for optimisation and capability analysis techniques for feedback evaluation.     

Electrochemical characterization and computational fluid dynamics simulation of flow-accelerated corrosion of X65 steel in a CO2-saturated oilfield formation water

The flow-accelerated corrosion (FAC) of an X65 pipeline steel was investigated in a CO₂-saturated formation water by electrochemical measurements and computational fluid dynamics (CFD) simulation on micro-electrodes installed on an impingement jet system. The surface morphology of the electrodes after corrosion test was characterized by scanning electron microscopy. Results demonstrated that the role of fluid hydrodynamics in FAC of the steel depends on its effect on the carbonate corrosion scale formed on the electrode surface. An increasing flow velocity and shear stress would thinner, degrade or even remove completely the scale, increasing corrosion of the steel. An oblique impact of fluid would generally result in a high corrosion rate of the steel. The effect of impact angle on corrosion of the steel is attributed to the distribution of fluid flow field and shear stress on the electrode surface. At the normal impact, a low flow velocity and shear stress and thus a low mass transfer rate would be generated at the centric region. Consequently, a compact corrosion scale can be formed on the electrode surface to protect the steel from corrosion. The highest corrosion rate is observed on micro-electrodes that are adjacent to the center, with the highest flow velocity and shear stress. At the oblique impact angles, the fluid flow velocity and shear stress, and the corrosion rate of the micro-electrodes are higher at the side far away from the nozzle than those at the side close to nozzle. The corrosion activity of the steel electrode located at the center of the sample holder generally increases with the decreasing impact angle due to the enhancing shear effect on the corrosion scale.     

Prevention of wheel clogging in creep feed grinding by efficient tool cleaning

This paper is dealing with the identification of efficient cleaning nozzle configuration to prevent the wheel from loading in creep feed grinding. The properties of different cleaning nozzles types were analyzed in terms of jet velocity and jet impact on the wheel surface using high speed imaging and pressure sensitive sheets. In grinding experiments the cleaning efficiency of each nozzle configuration was evaluated by optical measurement of wheel clogging inside the machine tool. With this newly developed procedure of tool cleaning optimization a significant reduction of grinding forces (up to 30%) and of the tool wear (up to 20%) was achieved.     

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。     

Composition changes around sulphide inclusions in stainless steels, and implications for the initiation of pitting corrosion

We report high-resolution SIMS microscopy measurements, which show that many ‘MnS’ inclusions have surrounding them a narrow ‘halo’ of half-width typically 100 nm that is strongly enriched in Fe, forcing consideration of the electrochemistry of FeS as a determinant of the behaviour of the inclusion boundary. We suggest that on exposure to water a very thin and porous metal-deficient polysulphide skin forms between the bulk of the inclusion and the steel, within which a pit can be triggered. The results resolve a controversy concerning the composition of the boundary region around inclusions in stainless steel and re-emphasise its potential significance.     

黏性流体液滴撞击超疏水壁面奇异射流的试验与模拟

液滴在特定条件下撞击超疏水壁面会形成奇异射流现象，该现象产生机理及调控机理有待进一步研究。基于高速显微数码摄像技术，研究不同黏度（0.9～27.7m Pa·s）牛顿流体液滴撞击超疏水壁面（静态接触角为158°）的动态行为，归纳奇异射流发生的相图。通过水平集相界面追踪法，建立液滴撞击超疏水壁面的有限元数值模型。研究结果表明：对于中低黏度（甘油质量分数小于67wt.%）的液滴，奇异射流现象发生在特定的We数区间。随着液滴黏度的增大，发生奇异射流的We数阈值提高。当液滴的黏度大于14.2 mPa·s后，即使继续提高液滴撞击速度（We>100），奇异射流现象不再出现。奇异射流的产生与回缩阶段液滴内空腔的形成有关，且发生射流时空腔底部有很大的压力集中区。黏度的改变会影响液滴内空腔底部气液交界处的界面形态。随着黏度增加，空腔底部气液相界面将由上凸形转变为下凹形，无法形成向上的射流。奇异射流主要发生于Re在700～1 000的区域，且在该区间内奇异射流发生的We数区域较宽，可为液滴动力学行为调控提供理论依据。     

The Impact of fluid supply on energy efficiency and process performance in grinding

An approach is presented to evaluate the energy efficiency of grinding processes by the total specific energy in relation to the process limits, e.g. starting thermal damage at a certain specific removal rate. The paper deals with grinding experiments on hardened steel workpieces covering a broad range of different types of fluid supply nozzles, fluid flowrates, and removal rates with and without high pressure tool cleaning. In the investigations, process configurations were identified leading to high energy efficiency in combination with highest achievable removal rates. Furthermore, the results confirm that the process limit is significantly influenced by specifically adapted fluid supply conditions e.g. flowrate and jet speed.     

吹氩板坯连铸结晶器内双循环流的形成条件

利用Lagrange两相流模型定量研究了吹氩板坯结晶器内双循环流形成条件,并用水模型检验了数值模拟结果.在此基础上考察了吹氩量、钢流量,结晶器宽度、水口浸入深度以及下倾角度对双循环流形成的影响规律.结果表明:选择与其它工艺参数匹配的吹氩量是保证双循环流型的重要条件,且维持此流型的临界吹氩量随钢流量的增加而增加.当钢液质量流量较大(qm＞2.5 t/min)时,减小结晶器宽度和增加水口浸入深度均有助于扩大临界吹氩量范围,而水口下倾角度对其影响较小;当钢液质量流量较小(qm≤2.5 t/min)时,以上工艺参数的影响均不明显.     

Erosion–corrosion resistance of microcrystalline and near-nanocrystalline WC–17Co high velocity oxy-fuel thermal spray coatings

Cermet based coatings are being increasingly used to combat erosion–corrosion in oil sands pipelines and pumps where the degradation is caused by a slurry mix of sand particles and aqueous solution. This research assesses the erosion–corrosion resistance of cermet composite coatings obtained by HVOF thermal spraying of microcrystalline and ‘duplex cobalt coated’ near-nanocrystalline WC–17Co feedstock powders. Electrochemical measurements, surface characterization, and the extent of weight loss were studied through an impingement jet system. Results suggest that the erosion–corrosion mechanism in the coatings was dominated by pure erosion in the microcrystalline coating and corrosion-enhanced erosion in the near-nanocrystalline coating.