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.     

Computer fluid dynamics analysis for efficient spraying of oil mist in finish-turning of Inconel 718

A compressible turbulence analysis of the flow of oil mist in MQL finish-turning of Inconel 718 was conducted using a finite volume method for optimizing the spraying conditions of oil mist and reducing the oil consumption. First, a domain of the analysis including a rotating workpiece and a single point cutting tool with a spraying nozzle was discretized, and then, changes in the velocity, pressure and vorticity of compressed air, and mass flow rate of oil mist near the cutting edge were calculated for three types of spraying nozzles. It was found that when the distance from the outlet of a nozzle to the tool tip was decreased using cover-type nozzles, mass flow rate of oil mist to near the cutting edge increased drastically. Among the three types of nozzles, the mass flow rate was the largest for a cover-type nozzle for oblique spraying. These results were consistent with the performance of the nozzles in cutting experiments. Finally, the flight of an oil droplet and the lubrication mechanism in MQL machining were investigated using analysis results.     

Experimental evaluation of minimum quantity lubrication in near micro-milling

This paper presents the performance of the minimum quantity lubrication (MQL) technique in near micro-milling with respect to dry cutting on the basis of tool wear, surface roughness and burr formation. The effects of tool materials, oil flow rate and air flow rate on tool performance in MQL cutting are also studied. It is found that the application of MQL will significantly improve the tool life, surface roughness and burr formation compared to those in dry cutting based on slotting tests with micro-end mills on a meso-scale machine tool. It is also observed that the values of surface roughness are close related to the tool-wear conditions in micro-cutting. Based on the experimental results, it is presumed that the maximum allowable tool flank wear of the 600-μm micro-tool is 80 μm while the surface finish quickly deteriorates after the tool flank wear reaches 80 μm and the tool breaks soon after the tool wear reaches 100 μm. The optimal lubrication conditions in this study are oil flow rate of 1.88 ml/h and air flow rate of 40 l/min. It is also found that the air flow rate has a more significant influence on tool life than the oil flow rate under MQL conditions in this study.     

High-speed grooving with applying MQL

The performance of minimum quantity lubrication (MQL) in high-speed cutting was evaluated in grooving 0.45%C carbon steel with a carbide tool coated with TiC/TiCN/TiN triple coating layers. MQL with supplying vegetable oil at a small and constant rate of 7 ml/h reduced the corner and flank wears more effectively than a solution type of cutting fluid at high cutting speeds of 4 and 5 m/s. In MQL grooving, the wears decreased drastically with increasing the pressure of air supply. This suggested that the air supply took an important role in transporting the oil mist to the interface between the flank wear land and machined surface. Then, a controlled oil mist direction (COD) tool was devised and its performance was proved to be high at a reduced rate of oil supply.     

微量润滑赋能雾化与供给系统关键技术研究进展

传统金属切削液会对环保、人体健康及制造成本产生负面影响,难以满足绿色制造的发展需求。微量润滑是一种介于浇注式和干式加工的润滑剂绿色供给技术,利用压缩空气将少量可降解的生物润滑剂雾化,形成微液滴,从而起到润滑和抗磨减摩的作用。然而,尚无相关研究针对雾化微液滴精准输运技术的规律进行总结,无法为微量润滑供给参数提供科学指导。为此,综述了微量润滑赋能雾化和供给系统关键技术的研究进展。揭示了微量润滑两相流气动雾化液滴粒径和雾化锥角随供给参数的演变规律,提出了静电雾化微量润滑赋能供给新方法,分析了静电赋能雾化性能调控机制和荷电流体渗透特性,阐述了超声赋能雾化液滴均一化机理和工艺参数优化策略。进一步分析了基于流体动力学模型的刀具/砂轮–工件界面流场分布规律,阐明了喷嘴结构对液滴输运的影响规律,为喷嘴位姿参数的选取提供了理论支撑。此外,论述了喷嘴位姿参数化调控装置的研究进展,解决了润滑介质参数化供给难题。最后,展望了微量润滑复合增效和智能供给关键技术,以期为微量润滑技术的工程应用提供理论支持和技术指导。     

内置式MQL喷射特性对车削GCr15轴承钢的影响

微量润滑(MQL,Minimum Quantity Lubrication)加工作为绿色切削技术,其应用逐渐广泛。相对于外置式MQL,内置式MQL具有渗透性好、切屑影响小、效率高等特点。为了寻求出内置式MQL的喷射特性对加工的影响规律,开发了车削内置式MQL系统,设计了四因素三水平的正交实验。以切削力和表面粗糙度为评价指标,切削液流量、空气流量、可生物降解润滑油及切削速度为变量,沿后刀面喷射,进行了车削GCr15轴承钢的正交实验,分析了喷射参数对加工的影响规律,并得到了优化的喷射参数,对机械加工工程应用具有参考意义。     

Effect of cooling and lubrication conditions on surface topography and turning process of C45 steel

At present coolants and lubricants are increasingly recognized as harmful factors for environment and machine operators’ health. Industry and research institutions are looking for new means of reducing or eliminating the use of cutting fluids, both for economical and ecological reasons. This can be done if quality properties of machined surfaces and process parameters in dry and wet machining are comparable. This paper presents an investigation into the influence of cutting zone cooling and lubrication on surface roughness, waviness, profile bearing ratio and topography after turning C45 steel. Dry cutting and minimum quantity lubrication (MQL) results are compared with conventional emulsion cooling. Cutting forces and their components were put under examination as well. The experimental outcomes indicate that the cooling and lubrication conditions affect significantly the investigated process and surface properties. However, the impact of the cooling and lubricating technique depends to a large extent on the applied cutting parameters, namely the cutting speed and feed rate. Turning dry or with MQL with properly selected cutting parameters makes it possible to produce better surface topography characteristics than turning with conventional emulsion cooling. Apart from improving the surface properties the MQL mode of cooling and lubrication also provides environmental friendliness.     

A new hybrid minimum quantity lubrication system for machining difficult-to-cut materials

A newly designed and manufactured hybrid MQL system is reported. Vegetable oil and tungsten disulphide suspension are mixed in an additively-manufactured nozzle and delivered through pressurised air as a coolant/lubricant spray. Cooling capability of the system is improved. Lubrication and the impact on machinability is assessed in high speed milling Ti6Al4V. Tool life and cutting forces with the new system are compared to those with air and with flood cooling and with commercial MQL. Over the reported practical range of cutting speeds, tool life is more than 2 times longer than with the commercial system and from 4 to 11 times longer than with air cooling.     

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).     

Cutting performance of different coatings during minimum quantity lubrication drilling of aluminum silicon B319 cast alloy

Cutting performance of cemented carbide drills with various coatings was investigated in detail under minimum quantity lubrication (MQL) conditions. An advanced dual-channel Bielomatik MQL system was installed in an Okuma machining center. A specially designed Mapal drill was selected for the studies to eliminate voids between the tool and the MQL tool holder that can interfere with mist delivery. Using this design, a mist flow rate of 25 mL/min was achieved through the drills.Progressive frictional/wear studies were performed. Coated drills were tested in three stages (50, 500, and 7000 holes). During short term drilling tests (50-hole level), cutting performance was comprehensively evaluated for a range of coatings by measuring several in-situ frictional characteristics of the cutting process, such as cutting forces, and related characteristics including, chip type and undersurface morphology. Wear patterns of the cutting tools were indentified as well. Selected coatings were tested further. The best cutting performance based on the 500-hole testing was found with the diamond coating. However, excessive brittleness of the entire coating/substrate system led to premature failure of the drill after 4300 holes. The low-hydrogen DLC coating that also showed promising cutting performance based on the 500-hole test was selected as the next candidate for further testing. Drills with low-hydrogen DLC coating achieved 7200 drilled holes with a flank wear of only 110 μm and moderate intensity of workpiece material pickup. This results in a better surface finish of drilled holes.Based on this study, the Mapal drills with the low-hydrogen DLC coating provided comparable machining performance to that possible with traditional wet machining, but with the environmental and cost advantages possible with MQL.     

Experimental evaluation on the effect of minimal quantities of lubricant in milling

Implementation of stricter Environmental Protection Agency (EPA) regulations associated with the use of ample amount of flood coolant has led to this study on minimal quantities of lubrication (MQL) technique on milling of ASSAB 718 HH steel at 35 HRc with uncoated carbide inserts while the MQL amount and flood coolant flow rate were 8.5 ml h⁻¹ and 42,000 ml min⁻¹, respectively. Unlike fracture in flood cooling or flaking in dry cutting the MQL used aided inserts were still in serviceable condition despite the presence of higher width of flank wear. Analyses of the cutting force, surface roughness, chip shape and EDX findings reveal that MQL may be considered as an economical and environmentally compatible lubrication technique for low speed, feed rate and depth of cut.     

Effects of cooling air temperature on cryogenic machining of Ti-6Al-4V alloy

This paper presents experimental investigations on influence of different coolant strategies such as dry, wet, minimum quantity lubrication (MQL) and MQL with cooling air on performance in milling of the Ti-6Al-4V alloy with uncoated cemented carbide inserts. Cutting force, tool wear, surface roughness and chip morphology are experimentally studied to compare the effects of different cooling air temperatures. The results showed that minimum quantity lubrication (MQL) with cooling air significantly reduces cutting force, tool wear and surface roughness. Unfortunately, MQL (without cooling air) condition cannot produce evident effect on cutting performance, and flaking wear on the flank surface of the insert has been found under this condition. Four different cooling air temperatures are used to investigate the effects of cooling air temperature on the machinability characteristics of Ti-6Al-4V alloy. Based on the experimental results, MQL with cooling air of −15 °C provides more favourable effects compared to other cooling air temperatures (0 °C, −30 °C,−45 °C). Short chips are produced under MQL with cooling air conditions due to the high velocity of cooling air enhances the chip brittleness for easy chip breaking, and the effective penetration of lubricant to the chip-tool interface results in lower friction. However, due to the dramatic increase in chip hardness at lower temperature, MQL with cooling air environments cannot promote chip curl to some extent.     

切削参数对碳钢微量润滑切削温度的影响

为了了解切削参数影响碳钢微量润滑切削温度的规律,通过45钢的车削实验,利用自然热电偶测温,探明在干切削、传统浇注润滑和微量润滑条件下,不同切削参数对切削温度的影响及原因。实验结果表明:MQL切削温度随切削参数增大而上升,切削速度对MQL温度影响最大,切削深度影响最小;在低切削速度时,MQL冷却效果优于传统浇注润滑,在中、高速时,MQL冷却效果比浇注润滑差;MQL冷却能力随切削速度和进给量增大而减弱,不随切削深度而变化。     

A study on droplets and their distribution for minimum quantity lubrication (MQL)

A better understanding in the application of minimum quantity lubrication (MQL) or near dry machining (NDM) is needed for its effective use in practical industrial applications. This paper presents the combination of confocal laser scanning microscopy (CLSM) and image processing techniques including wavelet transform to characterize the droplet sizes and the droplet distribution after MQL oil has been sprayed onto a polished silicon wafer. The raw droplet topographies captured with CLSM have been wavelet-filtered to purge the noise and artifacts and then the droplets themselves were isolated using wavelets multi-resolution analysis in order to measure the volume of each droplet. In addition, the empirical droplet size estimation equation was introduced for extremely small droplets which are difficult to measure. The distribution of the droplets has been also studied to determine the MQL optimal nozzle–workpiece distance and the nozzle discharge pressure. The procedures developed in this paper can be used to determine optimal conditions for various applications of MQL processes.     

The effects of liquid-CO2 cooling,MQL and cutting parameters on drilling performance

An investigation is made into the effects of liquid carbon dioxide (LCO₂) cooling, minimum-quantity lubrication (MQL) and cutting speed in drilling. Experimental measurements of torque, thrust force and temperature are made over a wide range of process and operating conditions. The resulting empirical models are used to quantify the individual contributions of the controlled parameters on drilling performance, and to facilitate temperature-based process optimization. Of particular interest is the need to carefully adjust the LCO₂ flow rate for any combination of MQL flow rate and cutting speed. The optimization is validated both in simulation and actual drilling tests.     

微量润滑系统参数对加工残余应力影响试验

微量润滑(MQL)切削是一种绿色加工技术。为了解MQL系统对加工残余应力影响,通过45钢车削正交试验,研究MQL系统的空气压力、润滑液用量、喷射距离、油雾温度对加工残余应力的影响。试验结果表明:油雾温度对加工残余应力的影响最大,润滑液用量也有一定的影响,空气压力和喷射距离的影响不显著;油雾温度降低,残余(拉)应力变小;润滑液用量增加,残余(拉)应力变小;MQL系统对加工残余应力的影响机制是通过改变油雾的冷却能力和渗透性,改变残余应力热力耦中的热效应。     

Effects of minimum quantity lubrication on turning AISI 9310 alloy steel using vegetable oil-based cutting fluid

This paper presents the effects of minimum quantity lubrication (MQL) by vegetable oil-based cutting fluid on the turning performance of low alloy steel AISI 9310 as compared to completely dry and wet machining in terms of chip–tool interface temperature, chip formation mode, tool wear and surface roughness. The minimum quantity lubrication was provided with a spray of air and vegetable oil. MQL machining was performed much superior compared to the dry and wet machining due to substantial reduction in cutting zone temperature enabling favorable chip formation and chip–tool interaction. It was also seen from the results that the substantial reduction in tool wears resulted in enhanced the tool life and surface finish. Furthermore, MQL provides environment friendliness (maintaining neat, clean and dry working area, avoiding inconvenience and health hazards due to heat, smoke, fumes, gases, etc. and preventing pollution of the surroundings) and improves the machinability characteristics.     

Cooling techniques for improved productivity in turning

The past century has witnessed significant advancements in turning process, cutting tools, machine controls and coolant/lubricant chemistry. These developments have particularly enhanced the machining of difficult-to-cut materials, which are used for aerospace, steam turbine, bearing industry, nuclear and automotive applications. In turning operation, friction and heat generation at the cutting zone are the frequent problems, which affect the tool life and surface finish apart from other machining results. This mechanism of heat generation plays quite a negative role during the turning of modern materials due to their peculiar characteristics such as poor thermal conductivity, high strength at elevated temperature, resistance to wear and chemical degradation. A good understanding of the methods of lubrication/cooling at the cutting zone, reduction of heat generation will lead to efficient and economic machining of these modern materials. This paper presents an overview of major advances in techniques as minimum quantity lubrication (MQL)/near dry machining (NDM), high pressure coolant (HPC), cryogenic cooling, compressed air cooling and use of solid lubricants/coolants. These techniques have resulted in reduction in friction and heat at the cutting zone, hence improved productivity of the process. A brief survey of modeling/FEA techniques is also performed.     

微磨料空气射流加工玻璃微流道结构研究

采用微磨料气射流加工技术(MAJM),对普通硅酸盐玻璃进行微流道槽加工.对通过掩膜加工与非掩膜加工效果相比较,得出在掩膜加工过程中,由于磨料的二次反弹冲蚀作用,所加工出的槽,槽壁较陡;在掩膜加工过程中,改变喷射距离、喷射压力、喷嘴移动速度和磨料流量四个加工参数,对加工槽的轮廓、加工过程中的材料去除率、磨料的流量效应进行研究,得出当喷射距离为4 mm,喷射压力为0.5 MPa,喷嘴移动速度为1.0 mm/s,磨料流量为0.117 g/s时,加工效果最好.通过倾斜喷射与掩膜加工相结合,研究了磨料磨粒的二次反弹冲蚀现象,为复杂三维微结构的加工,提供了一种新方法.     

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.