微坑阵列掩膜电解加工试验研究微坑阵列掩膜电解加工试验研究

为了解决机械零件表面织构的加工问题,并充分利用电解加工的优势,本文基于COMSOL Multiphisics软件进行了微坑阵列掩膜电解加工过程的仿真分析,开展了电解加工零件表面微织构的工艺试验研究,得到了具有微米级别直径与深度的表面阵列微坑,总结了普通直流加工电压与加工时间、脉冲电流加工频率与占空比、不同掩膜孔直径对微坑加工的工艺规律。试验结果表明:在加工时间12 s,脉冲电压12 V,占空比30%,脉冲频率3 000 Hz,掩膜孔径200μm的参数下,能得出表面质量最优的微坑。     

扫描射流掩膜电解加工微坑阵列试验研究

表面织构在摩擦学、热能交换以及生物医学等许多领域发挥重要作用,其中微坑阵列是常用的表面织构.为了能在金属表面制造出微坑织构,对掩膜电解加工微坑阵列的文献进行了研究与分析,在分析了射流掩膜电解加工技术的基础上,提出使用一种扫描射流掩膜电解加工的方法,利用光刻胶做掩膜,成功地在不锈钢上加工出海量微坑阵列.设计实验,探究了电...     

轴套内表面微结构掩膜电解加工模拟及试验研究

掩膜电解加工是金属基底表面织构化的有效手段,为了实现在轴套内表面阵列微结构的加工,进行了活动掩膜电解加工方法的仿真与试验研究。建立了活动掩膜电解加工有限元计算模型,通过数值计算分析了图形分布均匀性及掩膜厚度影响电流密度分布的规律和机理。结果表明:采用掩膜和阴极一体化的这种特殊电极结构形式,加工非均匀占空比图形时更有利于得到一致的加工深度;通过控制掩膜厚度与图形特征尺寸的关系,可以控制所加工的微结构底部形状。以仿真计算结论为依据进行了掩膜电解试验优化,并采用优化的工艺参数在轴套的内表面加工出了直径为100μm的微坑阵列。     

回转体表面掩膜微细电解加工有限元分析及试验研究

针对在回转体零件表面加工微织构的难题,文中建立了回转体表面微细电解加工的多物理场耦合数学模型,利用COMSOL Multiphysics软件进行了仿真求解。设计了掩膜电解加工专用夹具和电解液系统,优化了电解液的流道结构,在较低加工电压和较短加工时间的条件下,开展了工艺试验。通过对比分析微坑深度的仿真值和测量值,验证了加工过程多物理场耦合仿真模型的准确性,得到了形状精度高、均匀排布的直径为φ200μm的微坑阵列,为在回转体表面加工微织构提供了一种合理有效的方法。     

掩膜电解加工气缸套微造型摩擦性能研究

优化电解参数对气缸套进行掩膜电解加工,同时采用数控铣床对缸套试件加工出相同或相近尺寸微坑,然后对不同加工方式的缸套进行往复摩擦磨损实验。结果表明:在富油工况下,掩膜电解加工微造型缸套摩擦系数比机械珩磨缸套试样减小了11.35%、比机械加工微造型减小了6.41%,磨损量比机械珩磨缸套试样减小了32.75%、比机械加工微造型缸套试样减小了4.56%;在贫油工况下,掩膜电解加工微造型缸套比机械珩磨缸套试样抗黏着磨损时间延长了48.52%,比机械加工微造型缸套试样延长了9.57%;通过对试样磨损前后表面形貌进行微观检测分析,微造型形貌和电化学协同作用造就了其优异的抗磨减摩性能。     

阵列微沟槽的场域离散脉冲电解加工技术

针对难加工金属材料表面阵列非贯穿型微沟槽的高效高质量加工难题,提出一种场域离散脉冲电解加工方法,所加工沟槽具有表面质量好、尺寸微小、槽数多、沟槽前后非贯穿的特点。使用绝缘栅栏隔板作为活动掩模板对各微沟槽加工区进行离散,同时遮蔽非加工区,从而实现流场隔离和非加工区电场屏蔽等效果,有效提高沟槽的加工稳定性、精度和一致性。通过设计专用夹具,对影响加工精度的关键因素进行了单因素工艺实验研究,并利用Comsol Multiphysics软件对电解加工的流场和电场进行了仿真分析。仿真和试验结果显示:场域离散加工方法的流场和电场都比传统的掩膜电解加工、电解转印加工好。成功地在1min内加工出9条宽538.76μm,深25.78μm,过切量为19.38μm的阵列微沟槽,证实了该方法的有效性。采用短加工时间、低脉冲电压幅值、高脉冲频率、小脉冲占空比等工艺参数,有利于提高沟槽的加工精度。通过场域离散电解加工技术,可以实现对非贯穿型微沟槽的高效率、高质量、低成本加工。     

钛合金表面微结构激光加工及参数优化

针对钛合金种植体与人体组织的结合问题,提出利用激光加工方法在钛合金表面加工微结构,并对激光加工的参数进行优化。首先,对材料进行预处理;然后,分别改变电流和Q频率等参数,在钛合金表面进行激光加工试验,寻找一组能在材料表面加工出理想微凹坑形貌的参数,最后使用优化参数在钛合金表面加工微结构。结果表明:激光加工钛合金微结构阵列的最佳电流为13A,Q频率为3k Hz;采用优化后的激光加工参数可以得到形貌规则的微凹坑阵列。     

基于电场和流场耦合的微坑电解加工数值研究

表面织构技术能够有效降低摩擦副表面摩擦和磨损。以方形微坑电解加工为对象,充分考虑加工中电场与流场相互关系建立了耦合场理论模型,采用数值计算方法得到了耦合场电势分布、电流密度分布和体积分数分布等,探讨了入口压力与出口最大氢气体积分数的影响关系,研究结果可为方形微坑电解加工提供一定的参考。最后开展了方形微坑电解加工实验,得到了方形微坑实验件。     

摩擦副表面气膜屏蔽微细电解加工微织构及摩擦性能分析

采用气膜屏蔽微细电解加工方法在金属平面副、圆柱副表面加工不同阵列形貌微织构。通过试验将该方法与微细电解加工的微织构尺寸精度、表面质量、摩擦性能进行对比，研究结果表明，气膜屏蔽微细电解加工的微织构相比微细电解加工方法加工的微织构平面副及圆柱副凹槽深径比分别提高了约45.6%和25.8%，改善了加工的定域性，提高了加工精度。进一步的摩擦磨损试验结果表明，相较于微细电解加工方法，气膜屏蔽微细电解加工出的平面副及圆柱副微凹槽的表面摩擦因数分别减小了13.6%与16.2%，表面摩擦性能得到了提高。     

光纤激光掩膜微细电解复合加工装置研发

微小型金属工件的高效微细加工技术是困扰现代制造业的一个难题。采用光纤激光器在304不锈钢表面以直写方式进行表面改性处理,在不锈钢表面生成金属氧化层,形成抗腐蚀性保护掩膜,再将激光表面改性技术与微细电解加工技术相结合,利用简单片状工具电极通过微细电解加工,完成复杂微结构加工。为此研制了一套激光掩膜微细电解加工装置,开发了专用激光掩膜微细电解电源,并加工出典型微结构型腔样件,为进一步探索激光掩膜微细电解加工新工艺奠定基础。     

电解转印法加工凹坑阵列结构试验研究

为得到降低摩擦副表面磨损所需的微小凹坑阵列结构,提出电解转印法加工凹坑阵列的工艺方法。对电解转印法加工过程进行有限元仿真,分析光刻胶膜厚度对凹坑尺寸和形状的影响。用光刻的方法制作尺寸均一,单个孔径为100μm的阴极平板。进行微细电解加工试验,试验分析脉冲电源频率和脉冲占空比对加工结果的影响。结果表明,采用电解转印法加工微小凹坑阵列结构,可以获得平均直径为200μm,深度10μm的凹坑阵列。     

Fabrication of Superhydrophobic Micro Post Array on Aluminum Substrates Using Mask Electrochemical Machining

Surfaces with controllable micro structures are significant in fundamental development of superhydrophobicity. However,preparation of superhydrophobic surfaces with array structures on metal substrates is not effective using existing methods. A new method was presented to fabricate super-hydrophobic post arrays on aluminum(Al) substrates using mask electrochemical machining and fluoridation. Electrochemical etching was first applied on Al plates with pre-prepared photoresist arrays to make the post array structures. Surface modification was subsequently applied to reduce the surface energy, followed by interaction with water to realize superhydrophobicity. Simulation and experimental verification were conducted to investigate how machining parameters affect the array structures. Analysis of the water contact angle was implemented to explore the relationship between wettability and micro structures.The results indicate that superhydrophobic surfaces with controllable post structures can be fabricated through this proposed method, producing surfaces with high water static contact angles.     

复合工艺制备的表面微凹坑织构的摩擦性能研究

在构建的激光电化学复合微加工系统上,采用皮秒脉冲激光辐照与电解刻蚀复合加工方法在7075铝合金表面制备出不同尺寸的阵列凹坑微织构。采用共聚焦显微镜观测复合加工织构试样表面形貌,采用MFT-5000型RTEC摩擦磨损试验机研究润滑条件下凹坑织构的摩擦学性能,并探讨直径、深度、面积密度对减摩性能的影响。结果表明:复合加工工艺制备的表面微织构具有良好的表面形貌;润滑条件下材料表面的凹坑型织构能显著改善其摩擦学性能,相比光滑表面最高可降低摩擦因数30%;在实验参数范围内,凹坑的直径与面积密度对材料表面摩擦性能影响较大,凹坑深度对摩擦性能影响较小。     

Research on ECM process of micro holes with internal features

Micro holes with internal features are widely used as spray holes and cooling holes nowadays, which are usually required to be with high aspect ratio and shape accuracy, as well as good surface quality. An electrochemical machining (ECM) process is presented to machine these micro holes with diameter <200 μm. A quantitative relation between micro-hole diameter and machining parameters including voltage, duty ratio and feedrate is obtained through orthogonal experiments. According to the designed shape of internal features, change rules of machining parameters for varied diameters in different depth are obtained, and then micro holes with internal features are shaped precisely. Taking reverse tapered hole as an example, ECM experiments by varying parameters of voltage, duty ratio and feedrate (called varying voltage machining, varying duty ratio machining and varying feedrate machining, respectively) are carried out. Micro holes with inlet diameter of 178 μm and taper angle of 1.05° are shaped on a 1.0 mm-thick workpiece of 18CrNi8. The deviation of inlet is <3 μm and the taper-angle error is <0.1° in varying voltage machining. The corresponding dimensional accuracy of taper angle is improved by 51% than that of varying duty ratio machining under the same efficiency. The machining efficiency of varying voltage machining is increased by 36% compared to the efficiency in varying feedrate machining. In addition, the micro holes with complex features of funnel shape and bamboo shape are machined.     

Mathematical modelling of superhydrophobic surfaces for determining the correlation between water contact angle and geometrical parameters

Water-repellent surfaces have recently become an active area of research due to the desire to achieve self-cleaning, anti-sticking, and non-wetting properties on surfaces. These surfaces are required for different engineering applications. A superhydrophobic (SHP) surface achieves a water contact angle (CA) of 150° or greater. The physical understanding of the process by which surfaces attain superhydrophobicity is still limited, making it difficult to fabricate such surfaces by machining due to the hierarchical scale of the features involved. This work, therefore, aims to shed light on the physical understanding of the behaviour of a water droplet as it rests on a micro textured surface. In the first part of the work, a mathematical model is developed that follows a basic and novel approach of force balance considering a water drop sitting on a surface under static conditions. The various forces responsible for equilibrium are individually evaluated. The model used to describe a surface's interaction with water establishes the relationships between various parameters in the force balance system. From these relationships, the water contact angle (CA) required for superhydrophobicity was found through a simulation. In the second part of this work, arrays of projected micro-features were fabricated on different materials using deep X-Ray lithography (DXRL), micro wire EDM, and the wire wound method. The measured values of the CA on the fabricated surfaces were similar to the values obtained from the model. The proposed model, therefore, helps in designing SHP surfaces (SHSs) on large-scale arrayed micro-features based on several geometrical parameters.     

电解线切割加工技术试验研究

分析了应用电解线切割加工工艺在厚不锈钢板上加工高深宽比结构的可行性。为解决加工高深宽比结构时的排屑问题,在分析该工艺特点的基础上,采用了轴向冲液的方法。在自行搭建的加工系统中,进行了不同加工参数的一系列试验,以研究加工电压、电极丝进给速度、电解液浓度和冲液速度对该工艺的影响。最后,对电解线切割加工参数进行优化,加工出了缝宽为160μm、深宽比高达30的微型花键。     

Prediction of aspect ratio of a micro hole drilled by EDM

Micro electrical discharge machining (EDM) has the ability to drill micro holes with high accuracy in metallic materials. The aspect ratio of a micro hole generated by micro EDM is usually higher than those by other processes such as etching, mechanical drilling, and laser. However, it was found that the drilling speed of micro EDM slows down and even stops when the aspect ratio of a micro hole reaches a certain value. To understand this phenomenon, a theoretical model is proposed based on the fluid mechanics and surface tension. Experiments under different machining conditions are carried out to verify this model. Experimental results agree with the theoretical values, which indicate the validity of the proposed model. The difference between the theoretical values and the real values might be caused by debris, temperature and rotating of electrode in the discharge gap, which are ignored in the model.     

OPTIMAL MQL AND CUTTING CONDITIONS DETERMINATION FOR DESIRED SURFACE ROUGHNESS IN TURNING OF BRASS USING GENETIC ALGORITHMS

The evolving concept of minimum quantity of lubrication (MQL) in machining is considered as one of the solutions to reduce the amount of lubricant to address the environmental, economical and ecological issues. This paper investigates the influence of cutting speed, feed rate and different amount of MQL on machining performance during turning of brass using K10 cemented carbide tool. The experiments have been planned as per Taguchi's orthogonal array and the second order surface roughness model in terms of machining parameters was developed using response surface methodology (RSM). The parametric analysis has been carried out to analyze the interaction effects of process parameters on surface roughness. The optimization is then carried out with genetic algorithms (GA) using surface roughness model for the selection of optimal MQL and cutting conditions. The GA program gives the minimum values of surface roughness and the corresponding optimal machining parameters.     

Fabrication of PDMS micro through-holes for electrochemical micromachining

Surface texture has played a fundamental role in the development of many advanced fields. Through mask electrochemical micromachining (TMEMM) is a feasible alternative for fabricating surface textures. In this paper, polydimethylsiloxane (PDMS) is firstly employed as a mask in TMEMM due to its chemical resistance, low cost, flexibility and high moulding capability. A simple method for fabricating PDMS micro through-holes is proposed. A vacuum-aided process was introduced to fill a PDMS gel into an SU-8 mould, and the PDMS gel was solidified in an oven. Then, the cured PDMS micro through-holes were peeled off of the SU-8 mould. PDMS micro holes with a minimum diameter of 50 μm and a thickness of 200 μm were obtained. Furthermore, the PDMS micro through-holes were then used as a mask to prepare a micro dimple array by TMEMM. Experiments were conducted to verify the feasibility of the proposed approach, and the effect of applied voltage and machining time on the diameter and depth of the micro dimple was investigated. Finally, an array of micro dimples 109 μm in diameter and 9.7 μm deep was successfully fabricated by using PDMS.     

Vibration assisted electrochemical micromachining of high aspect ratio micro features

The most used processes for generation of high aspect ratio microchannels are Nd: YAG laser technology on silica substrate and ultra violate lithography (UV-LIGA) process on metals. There are a few micromachining technologies such as micro mechanical milling, micro electro discharge machining (EDM) and electrochemical micromachining (EMM) for production of high-aspect-ratio micro features on highly stressed and anticorrosive metal like stainless steel. This paper discusses the micro fabrication of high aspect ratio micro features at the intended location on high strength stainless steel sheet of very small thickness to high thickness with highest average aspect ratio 14.33 achieved during microchannel generation by EMM with the help of coated microtool. Mathematical model relating aspect ratio with various parameters and machining conditions is derived to explore the ways to increase the aspect ratio of micro features. Experimental investigations were carried out to know the effect of vibration of microtool, frequency of pulsed voltage, microtool tip shape, thickness of work piece and non-conducting layer coated microtool on high aspect ratio micro features. Vibration of microtool with very small amplitude improved the stability of micromachining due to improved flow of electrolyte.