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。     

基于TRIZ理论的微量润滑喷嘴设计北大核心

针对目前传统微量润滑喷嘴冷却润滑效率低的问题,根据微量润滑喷嘴雾化的问题分析,定义微量润滑喷嘴雾化技术冲突,提出一种基于发明问题求解理论(theory of inventive problem solving,TRIZ)的微量润滑高效冷却润滑喷嘴的创新设计方法,建立基于TRIZ冲突解决理论的微量润滑喷嘴创新设计过程模型,分析超音速雾化理论,提出超音速微量润滑喷嘴结构模型,利用数值模拟方法对所提出的结构模型进行超音速可行性研究。研究结果表明,所提出的喷嘴在进气口压强为0.2 MPa时,出口速度先增大后减小,最终处于亚音速状态;在进气口压强达到0.4 MPa时,出口速度一直增大,实现超音速;随着进气口压强继续增大,出口速度可实现超音速,但最大速度提升不明显。可为微量润滑系统的高效冷却润滑喷嘴设计提供新思路。     

镍基单晶高温合金磨削润滑方式对表面完整性的影响

为提高镍基单晶高温合金DD5的磨削表面质量,采用单因素试验探究3种磨削加工方法（干磨削、传统浇注式、微量润滑（minimum quantity lubrication, MQL））对其表面完整性的影响。结果表明：在不同冷却条件下,DD5磨削表面粗糙度从低到高依次为MQL、传统浇注式、干磨削方式下的。当砂轮线速度较小时,磨削表面质量较差,存在较深划痕和沟槽;当砂轮线速度较大时,磨削表面质量较好,磨痕较小,且分布均匀。在距磨削表面为5～15μm时,DD5亚表面显微硬度随着深度的增加而急剧下降;在距磨削表面为20～150μm时,DD5亚表面显微硬度趋于平衡,其在540 HV附近波动。     

最小量润滑装置的设计与应用

为了符合绿色制造的发展方向,微量润滑技术逐步取代传统浇注式技术,而应用该技术的前提是设计出优良的微量润滑装置。在研究微量润滑技术以及国内常见微量润滑装置的基础上,设计一种新型微量润滑装置,并阐述精密雾化喷嘴、密封式缸体、润滑油循环系统等设计原理,最后通过切削实验与干切削和传统微量润滑装置进行对比。实验结果表明此装置在工业切削领域的可应用性,并且相比传统微量润滑装置有更好的切削效果。     

静电雾化机理及微量润滑铣削7075铝合金表面质量评价

目的 针对传统气动雾化微量润滑雾化性能差、环境气雾浓度高以及参数化可控性差的技术难题,设计了静电雾化微量润滑铣削供给系统。研究了铣刀工件约束界面的气流场并进行了静电雾化微量润滑(Electrostatic Minimum Quantity Lubrication,EMQL)机理分析与7075铝合金铣削表面质量评价。方法 通过分析铣刀工件约束界面气流场的分布情况,对气流场中的涡流场速度分布情况进行了理论建模,基于圆周涡流与进入涡流的动力学特征建立了喷嘴最佳射流位姿模型。研究了EMQL的荷电与雾化机理,在此基础上,进行了不同润滑条件下的铣削7075铝合金实验,包括干切削、浇注式、EMQL。测量了不同润滑条件下的铣削力、铣削表面粗糙度(Ra、Rsm),此外,对2种参数条件下EMQL获得的加工表面轮廓进行了自相关分析。最后,分析了荷电润滑剂在切削区的微观作用机制。结果 在实验铣削参数条件下,进入涡流的诱导半径为0.007 m,最佳位姿参数设定如下:射流点到工件表面的距离lz=9.7 mm,射流点到铣刀边缘的距离ly=11.5 mm,喷嘴与工件水平方向的夹角γ≈40°。与干切加工相比,EMQL获得的铣削力降低了15%、18.6%;此外,与干切削相比,30 kV条件下的EMQL获得的Ra、Rsm分别降低了15.5%、25%,并且相比于20 kV的电压,30 kV的EMQL铣削表面轮廓自相关分析曲线显示出更优异的表面质量;浇注式润滑获得了最佳的表面质量(Ra=0.221 μm、Rsm=0.037 μm)。结论 荷电液滴能够提升摩擦界面毛细管的渗透性能,并且毛细渗透长度可以在提升电压的条件下增加,在高电压条件下的EMQL相比于低电压条件下的EMQL展现出更好的铣削性能。     

周峰研究员受邀在Tribology Frontiers大会上作主旨报告

<正>2015年10月25~27日美国摩擦与润滑工程师协会(STLE)主办的第二届摩擦学前沿(Tribology Frontiers)会议在美国丹佛举行。周峰研究员受邀在大会上作主旨报告(Keynote)。作为4个受邀主旨报告之一,周峰研究员就仿生润滑作了题为"Bioinspired lubrication:how far we can go and beyond"的报告,介绍了课题组在仿生润滑研究方面的最新进展和未来的发展     

纳米生物润滑剂微量润滑磨削性能研究进展

微量润滑是针对浇注式和干磨削技术缺陷的理想替代方案，为了满足高温高压边界条件下磨削区抗磨减摩与强化换热需求，进行了纳米生物润滑剂作为微量润滑的雾化介质探索性研究。然而，由于纳米生物润滑剂的理化特性与磨削性能之间映射关系尚不清晰，纳米生物润滑剂作为冷却润滑介质在磨削中的应用仍然面临着严峻的挑战。为解决上述需求，本文基于摩擦学、传热学和工件表面完整性对纳米生物润滑剂的磨削性能进行综合性评估。首先，从基液和纳米添加相的角度阐述了纳米生物润滑剂的理化特性。其次，结合纳米生物润滑剂独特的成膜和传热能力，分析了纳米生物润滑剂优异的磨削性能。结果表明，纳米生物润滑剂优异的传热和极压成膜性能显著改善了磨削区的极端摩擦条件，相比于传统微量润滑，表面粗糙度值（Ra）可降低约10%～22.4%。进一步地，阐明了多场赋能调控策略下，磨削区纳米生物润滑剂浸润与热传递增效机制。最后，针对纳米生物润滑剂的工程和科学瓶颈提出了展望，为纳米生物润滑剂的工业应用和科学研究提供理论指导和技术支持。     

使用雾化液的K9光学玻璃化学机械磨削

根据K9光学玻璃的物理化学特性,在干式化学机械磨削（chemical-mechanical grinding,CMG）的基础上,用超声雾化方法产生NaHCO₃雾化液参与磨削,研制了适合湿式CMG的磨具,对K9光学玻璃试样进行了化学机械磨削试验,得到了雾化环境下磨削结果最优的CeO₂型磨具。在此基础上,采用正交试验法,对比分析工件转速、磨具转速以及雾化液的pH值对K9光学玻璃表面粗糙度和材料去除率的影响。结果表明:工件表面粗糙度受雾化液的酸碱度的影响最强,磨具转速次之,工件转速最弱;对材料去除率的影响,雾化液的酸碱度最强,工件转速次之,磨具转速最弱。使用适量的雾化液可提高加工质量和速度,消除干式CMG产生的粉尘污染,这种方法适于对K9光学玻璃的精加工。      

不同制粉工艺对NiAlW粉末及涂层组织性能的影响

对大气雾化和真空大气雾化工艺制备的两种不同的NiAlW合金粉末,进行了粉末物性对比、粉末及粉末剖面结构的形貌对比、粉末化学成分对比,结果表明,真空雾化工艺制备的NiAlW合金粉末对比大气雾化工艺制备的NiAlW合金粉末具有更好的流动性、更高的松装密度、更好的球形度及更低的氧含量,粉末性能对比结果显示真空雾化工艺制备的粉末性能较好;采用大气等离子喷涂制备了涂层,分析了两种涂层SEM形貌和孔隙率,对比了涂层的显微硬度、结合强度和耐磨损性能。结果表明:用真空大气雾化工艺制备的NiAlW涂层孔隙率低、显微硬度低、结合强度高、耐磨损性好,显示出更好的综合性能。粉末初始形貌及化学成分的差异可导致喷涂层性能的差异,球形度好、氧含量低且杂质含量低的粉末经喷涂后更易形成高致密的涂层。     

快速冷却条件下Cu-Co合金的凝固

利用气体雾化方法研究了Cu-20%Co(质量分数)合金的快速凝固行为,获得了富Co相以微细球形粒子形式分布于基体的合金粉末.建立了Cu-Co雾化液滴快速凝固过程模型,模拟分析了雾化液滴凝固的动力学细节.结果表明:所建模型能很好地描述Cu-Co合金雾化液滴冷却凝固过程;液一液相变过程中组织演变是弥散相液滴形核、长大,碰撞凝并和空间迁移共同作用的结果;雾化液滴尺寸越大,冷却越慢,富Co相液滴的形核速率越低,凝固后富Co相的弥散度越差.     

An investigation of graphite nanoplatelets as lubricant in grinding

Cooling and lubrication are very critical to ensure workpiece quality in grinding due to the high friction and intense heat generation involved in the process. Liquid lubricants have traditionally been used in flood form or minimum quantity lubrication (MQL), raising however, major environmental and economic concerns. The focus of this study is to evaluate the performance of graphite nanoplatelets as a lubricant in surface grinding. The role of graphite's characteristics such as form, size and concentration; and the effect of the carrying medium and the graphite's application method are determined based on an experimental study. The results indicate that graphite nanoplatelets significantly reduce the grinding forces, specific energy, and improve surface finish during surface grinding of hardened D-2 tool steel. A comparison with results obtained in conventional MQL grinding is also provided. The proper selection of graphite, carrying medium and application method can lead to a low cost, nontoxic and simple alternative to solid lubrication or MQL grinding.     

Experimental evaluation of the lubrication performance of MoS2/CNT nanofluid for minimal quantity lubrication in Ni-based alloy grinding

A nanofluid minimum quantity lubrication with addition of one kind of nanoparticle has several limitations, such as grinding of difficult-to-cutting materials. Hybrid nanoparticles integrate the properties of two or more kinds of nanoparticles, thus having better lubrication and heat transfer performances than single nanoparticle additives. However, the use of hybrid nanoparticles in nanofluid minimum quantity lubrication grinding has not been reported. This study aims to determine whether hybrid nanoparticles have better lubrication performance than pure nanoparticle. A hybrid nanofluid consisting of MoS₂ nanoparticles with good lubrication effect and CNTs with high heat conductivity coefficient is investigated. The effects of the hybrid nanofluid on grinding force, coefficient of friction, and workpiece surface quality for Ni-based alloy grinding are analyzed. Results show that the MoS₂/CNT hybrid nanoparticles achieve better lubrication effect than single nanoparticles. The optimal MoS₂/CNT mixing ratio and nanofluid concentration are 2:1 and 6 wt%, respectively.     

氧化铝空心球对树脂结合剂金刚石磨盘磨削蓝宝石的影响

为改善蓝宝石研磨效果,在树脂结合剂金刚石磨盘中添加氧化铝空心球。通过力学性能测试、SEM扫描观测和实际磨削实验,研究空心球粒径及体积分数对树脂结合剂强度和磨盘性能的影响。研究表明:试样抗折强度随空心球粒径和比例的增大而降低;当添加空心球的体积分数为30%时,空心球粒径对试样抗折强度的影响基本消失。磨削实验证明:添加氧化铝空心球可提高蓝宝石磨削时的效率,并改善蓝宝石的表面粗糙度。添加体积分数为20%的空心球的磨盘在磨削过程中具有最好的综合磨削性能,与不加空心球的磨盘相比,磨削效率提高82.6%,表面粗糙度降低至R_a 0.249μm。      

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).     

Grinding of nanostructured ceramic coatings: surface observations and material removal mechanisms

Surface grinding of thermally sprayed nanostructured WC/12Co and Al₂O₃/13TiO₂ (n-WC/12Co and n-Al₂O₃/13TiO₂) coatings has been undertaken with diamond wheels and under various grinding conditions. This paper investigates the effects of the grinding parameters such as depth of cut, feedrate, wheel grit size and bond materials on grinding forces, surface finish and surface topography. Different from their consolidated counterparts, the coatings have large quantities of defects inherited from thermal spray process, which greatly influence the grinding process and ground coatings. The competing phenomenon between the effects on surface finish from both the thermal spray process and the grinding process is studied. Different surface topographies are observed and their relationship with grinding conditions and material properties is investigated. Furthermore, the material removal mechanisms in grinding are explored. The effects of grinding parameters, material properties and the defects from thermal spray process on material removal mechanisms are discussed.     

基于MQL的碳纤维复合材料制孔表面质量及切削力试验

目的 减少碳纤维增强复合材料(CFRP)制孔表面毛刺及边缘凸起等缺陷。方法 对比研究在干切削和微量润滑(MQL)2种加工条件下碳纤维增强复合材料(CFRP)的制孔,在切削速度一定时,探究切削方式、进给速度对制孔尺寸精度、表面质量、切削力的影响。采用方差分析对各影响因素及其权重进行分析。结果 得出了切削方式和工艺参数对制孔尺寸精度、切削力、表面质量的影响规律。试验结果表明,在微量润滑条件下,由于润滑和降温的影响,表面毛刺得到有效去除,纤维断面平整,剪切作用明显,抑制了由温升所引起的边缘隆起膨胀现象,试样的表面质量得到显著提高,切削力整体降低。在干切削和微量润滑条件下对制孔尺寸精度影响最大的是切削方式。对于切削力,在干切削时受到切削方式的影响最大,在微量润滑条件下受到进给速度的影响最大,随着进给速度的增大而增大。结论 在现有试验条件下,微量润滑的加工质量总体上优于干切削的加工质量,其制孔尺寸的精度整体更高,其切削力最大降低了84.26%。     

TiH2对Cu60Zn40合金结合剂结构和性能的影响

以Cu60Zn40合金粉末为原料,加入TiH₂,研究TiH₂的体积分数与烧结温度对Cu60Zn40结合剂力学性能与微观结构的影响。结果表明:TiH₂起到活化烧结作用,可以提高Cu60Zn40的力学性能。当烧结温度为680 ℃,TiH₂的体积分数从0增大到10%时,抗弯曲强度从225 MPa提高到445 MPa,抗冲击强度从28.3 kJ/m2提高到54.3 kJ/m2。当烧结温度为560 ℃,TiH₂体积分数从0增大到5%时,硬度由46 HRB提高到88 HRB。气孔率随着TiH₂体积分数的增大而增大,当TiH₂体积分数为20%时,气孔率为6.2%。TiH₂的加入可以提高Cu60Zn40结合剂金刚石磨具磨削性能。当TiH₂体积分数从0增大到10%时,磨耗比由28.50提高到61.67,同时减少工件表面烧伤。      

Microstructure and electrochemical properties of mechanically ground Ce2Mg17 + x wt.% Ni (x = 0, 50, 100, 200) composites

The effects of mechanical grinding with or without nickel powder on microstructure and electrochemical properties of Ce₂Mg₁₇ hydrogen storage alloy in 6 M KOH solution were investigated. The microstructure and electrochemical properties depend greatly on the amount of nickel powder introduced during mechanical grinding. For the alloy ball-milled with nickel powder, the more nickel powder added, the more advantageous it is for the formation of a homogeneous amorphous structure, and the larger discharge capacity obtained. After 90 h ball-milling, the Ce₂Mg₁₇ + 200 wt.% Ni composite exhibited a large discharge capacity of 1014 mAh g(Ce₂Mg₁₇)⁻¹[338 mAh g(Ce₂Mg₁₇ + 200 wt.% Ni)⁻¹] at 303 K. The improvement of electrochemical capacity can be attributed to the formation of a homogeneous amorphous structure as well as the modification of the surface state by Ni addition.