A study on micro machining of e-glass–fibre–epoxy composite by ECSM process

The paper presents the result of an experimental investigation on the micro machining of electrically non-conductive e-glass–fibre–epoxy composite during electrochemical spark machining using specially designed square cross section with centrally micro hole brass tool and different diameter round-shaped micro tools made of IS-3748 steel. A micro electrochemical spark machining (ECSM) setup has been designed, fabricated and used for conducting the experiments. According to the Taguchi method-based design, the specific numbers of experiments have been carried out to investigate the influence of the fabricated ECSM parameters on the material removal rate and overcut on generated hole radius. Test results show that the material removal rate is maximum when machining was performed at higher setting value of D.C. supply voltage (e.g. 70?V), moderate setting value of electrolytic concentration (e.g. 80?g/l) and 180-mm gap between electrodes. Taking significant machining parameters into consideration and using multiple linear regression, mathematical modes for material removal rate and overcut on hole radius are established to investigate the influence of cutting parameters during micro-ECSM. The influence of machining parameters on machined hole and special shape contour quality are also analysed through different scanning electron micrographs. Confirmation test results established the fact that the developed mathematical models are appropriate for effectively representing the machining performance criteria.     

Manufacture of micro sized threads for micro actuator of laser grating mount

This work presents the fabrication of micro threads of pitch less than 100?μm for micro components. The micro sized threading tool having a tool nose radius less than 40?μm is manufactured by micro wire electric discharge machining (μWEDM) process. This μWEDM process overcomes the difficulties in conventional machining process for production of threading tools and helps in achieving a corner radius as small as 15?μm with specialized wire tool path strategies. This method also helps in fabrication of special micro tools from commercially available or worn-out tungsten carbide tool inserts.     

选择性激光烧结设备管式辐射加热数值建模与计算

为了分析选择性激光烧结系统预热温度场分布不均的成因,对HRPS系列选择性激光烧结系统采用的管式辐射加热系统进行了数学建模,通过数值计算获得了不同安装高度下辐射热源对工作腔内各点的热量分布情况及均匀度变化曲线,也获得了最优的安装高度。这种数值建模的量化分析方法为开发辐射加热预热装置提供了有益的借鉴和分析思路。     

Built-up edge effects on process outputs of titanium alloy micro milling

Built-up edge (BUE) is generally known to cause surface finish problems in the micro milling process. The loose particles from the BUE may be deposited on the machined surface, causing surface roughness to increase. On the other hand, a stable BUE formation may protect the tool from rapid tool wear, which hinders the productivity of the micro milling process. Despite its common presence in practice, the influence of BUE on the process outputs of micro milling has not been studied in detail. This paper investigates the relationship between BUE formation and process outputs in micro milling of titanium alloy Ti6Al4V using an experimental approach. Micro end mills used in this study are fabricated to have a single straight edge using wire electrical discharge machining. An initial experimental effort was conducted to study the relationship between micro cutting tool geometry, surface roughness, and micro milling process forces and hence conditions to form stable BUE on the tool tip have been identified. The influence of micro milling process conditions on BUE size, and their combined effect on forces, surface roughness, and burr formation is investigated. Long-term micro milling experiment was performed to observe the protective effect of BUE on tool life. The results show that tailored micro cutting tools having stable BUE can be designed to machine titanium alloys with long tool life with acceptable surface quality.     

A study on the micro tooling for micro/nano milling

Many researches have studied the micro tools either by simulations or experiments showing that the micro tools play very important roles in micro/nano machining, and micro tool geometries have a direct impact on the final machining quality. Commercially available micro milling tools are usually simply made from downsizing of macro milling tools, which may not be able to be accurately fabricated. Custom micro milling tools have been created by some researchers, but no design criteria for micro milling tools have been introduced. The above factors constrain the development of effective micro milling tools and consequently constrain the researches on micro/nano milling. Based on former researcher??s work, this paper tries to introduce the design criteria for the custom micro tooling. Firstly, the extent typical micro milling tools are studied, and their drawback/limitations are summarized. Secondly, experimental evaluations of the key drawback/limitations are processed. Thirdly, the design criteria for custom micro milling tools are proposed, and corresponding design process is introduced. Then, a new micro hexagonal end mill has been designed based on these criteria. Finally, a polycrystalline diamond micro hexagonal end mill with a diameter of 0.5?mm was fabricated by wire electrical discharge machining, and the evaluation experiments for the hexagonal end mill have been processed on a nano milling center. Experimental results show the newly designed hexagonal end mill can achieve submicron level surface roughness and has simultaneously high-accuracy side and bottom machining capabilities.     

Design and development of PCD micro straight edge end mills for micro/nano machining of hard and brittle materials

One of the biggest challenges for mechanical micro/nano milling is the design and fabrication of high precision and high efficiency micro milling tools. Commercially available micro milling tools are either too expensive (around several hundred US dollars) or simply made from downsizing of macro milling tools, which is sometimes not appropriate for the specific micro/nano milling requirements. So the design and fabrication of custom micro milling tools are necessary. In this paper, a micro straight edge endmill (SEE) is designed. Static and dynamic FEM analyses have been done for the SEEs with different rake angles trying to identify their stiffness and natural frequencies. By wire electrical discharge machining (WEDM), the SEEs made of polycrystalline diamond (PCD) with three different rake angles have been fabricated. The evaluation milling on tungsten carbide (WC) and silicon wafer have processed on a nano milling center. Experimental results show the SEEs have a good ability to simultaneously micro/nano milling of both the side and bottom surfaces with submicron surface roughness, and the SEE has high accuracy for large aspect ratio thin wall machining. The milling experiments on silicon wafer have successfully demonstrated that ductile mode machining was achieved and the coolant played an important role in silicon wafer milling.     

Micro wire electrode electrochemical cutting with low frequency and small amplitude tool vibration

For removing electrolysis products and renewing electrolyte, the low frequency and small amplitude micro-tool vibration which direction is parallel to wire electrode axis is adopted. A wire electrochemical micro-machining system with micro-tool vibration unit has been developed. A mathematical model of overcut is presented. The micrometer scale wire electrodes of 10, 5, and 2???m in diameter have been electrochemically in situ fabricated. The influence of micro-tool vibration on processing stability, overcut, machining accuracy, and repeatability accuracy of micro wire electrode electrochemical cutting is investigated. With electrodes in various diameters, influence of electrode diameter on overcut is experimentally studied. To investigate the influence of machining parameters and work-piece thickness on the machining, comparative experiments are carried.     

Micro wire electrochemical machining with an axial electrolyte flow

Micro wire electrochemical machining is a useful technique to produce high-aspect-ratio slit micro-structures. To improve processing stability, the axial electrolyte flow is adopted to renew electrolytes in the machining gap. A wire electrochemical micro-machining system with an axial electrolyte flow unit is developed. A mathematical model of tool feed rate is presented. To investigate the influence of electrolyte flow on processing stability and machining efficiency, comparative experiments were carried out. The influence of applied voltage and electrolyte concentration on machining accuracy is studied and the parameters such as electrolyte flow rate and applied voltage are optimized. Low initial machining gap is applied to decrease the stray current machining in the initial machining period. With the optimal parameters, the high-aspect-ratio micro spline and curved flow channel with the slit width of 160?μm have been fabricated on 5-mm-thick stainless steel (0Cr18Ni9). The width of the slit is uniform and the aspect ratio is 31.     

Design of micro square endmills for hard milling applications

In experiments of machining hardened tool steels (such as AISI H11, H13, and D2, up to 56 HRC) by commercial ? 0.5?mm square endmills, it is observed that the tested micro endmills showed severe wear at an early stage of the process due to chipping off around cutting edge corners, resulting in unsatisfactory tool life and product appearance (burr formation). Detailed examination of current tool geometry shows that it is mainly inherited from that of macro endmills, making the cutting edge corners the weakest part on the tool. As the micromilling process is characterized by small values of machining parameters, the cutting edge corners of the micro endmill are the most loaded part of the cutting edges. New design rules are studied for improving the stiffness and strength of micro endmills used in micro hard milling applications. Analytical modelling and finite element method analysis are used to aid the design of tool geometry. By using a larger neck angle, optimizing tool core geometry, and choosing a negative rake angle, tool stiffness and cutting edge strength are improved. The new endmill designs, both two-flute and four-flute, are tested in experiments on hardened tool steels and showed considerable lower tool wear and increased tool life. Furthermore, the geometrical accuracy and appearance of the workpiece (burr formation) has been improved drastically.     

Fabrication of various shaped tungsten micro pin arrays using micro carving technology

This paper describes a state of the art in micro-structuring high strength metallic materials. Tungsten micro pin arrays in a variety of shapes are fabricated using a micro carving technology, which combines laser beam machining and electrochemical etching processes. First, micro pin arrays were rough-shaped by laser beam machining along a pre-defined scanning path to control their structural shape. The micro pin array in this stage had near-conical shape of structures due to a recast layer. Next, the genuine shape of micro pin arrays came to the surface via electrochemical etching process to elute the recast layer into electrolyte. Quantitative elemental analysis with energy-dispersive spectroscopy (EDS) was implemented to characterize the formation of recast layer on a micro pin structure after the laser beam machining process. The atomic percentage EDS maps indicated that higher percentage of tungsten was detected on the core micro pin structure, whereas relatively large percentage of oxygen was found on the recast layer (O 9%, W 91% in the center area, and O 53%, W 47% in the outer area).     

Study of micro ball end mill geometry and measurement of cutting edge radius

Cutting edge radius plays an important role in conventional micro machining process, as it is of the same order as uncut chip thickness. Therefore it is important to measure the edge radius accurately. There is no recommended methodology, as of now, to measure edge radius of a ball end mill. An attempt is made in this paper to study edge radius of ball end mill at normal and transverse planes on a virtual ball end mill generated using kinematic relations in CAD environment. In the present study, non-destructive methods using confocal microscope and stereo microscope are used to measure edge radius. These measurements capture the edge radius on the transverse plane. For confirmation, the tool sectioned in the transverse plane by a low speed diamond saw is examined under scanning electron microscope and the radius is assessed using suitable software. Among the non-contact approaches proposed in this work, confocal method appeared to be more reliable considering the reproducibility aspect.     

An experimental investigation on micro machining of fine-grained graphite

Industrial applications of the micro milling process require sufficient experimental data from various micro tools. Research has been carried out on micro milling of various engineering materials in the past two decades. However, there is no report in the literature on micro milling of graphite. This paper presents an experimental investigation on micro machinability of micro milling of moulded fine-grained graphite. Full immersion slot milling was conducted using diamond-coated, TiAlN-coated and uncoated tungsten carbide micro end mills with a uniform tool diameter of 0.5 mm. The experiments were carried out on a standard industrial precision machining centre with a high-speed micro machining spindle. Design of experiments (DoE) techniques were applied to design and analysis of the machining process. Surface roughness, surface topography and burrs formation under varying machining conditions were characterized using white light interferometry, SEM and a precision surface profiler. Influence of variation of cutting parameters including cutting speeds, feedrate and axial depth of cut on surface roughness and surface damage was analysed using ANOVA method. The experimental results show that feedrate has the most significant influence on surface roughness for all types of tools, and diamond tools are not sensitive to cutting speed and depth of cut. Surface damage and burrs analysis show that the primary material removal mode is still brittle fracture or partial ductile in the experimental cutting conditions. 3D intricate micro EDM electrodes were fabricated with good dimensional accuracy and surface finishes using optimized machining conditions to demonstrate that micro milling is an ideal process for graphite machining.     

Fabrication accuracy analysis of micromilling tools with complicated geometries by wire EDM

The micromilling tool is one of the key factors affecting micromilling performance. The design and fabrication of micromilling tools are still behind the increasing requirements in miniature component fabrication. How to estimate the fabrication accuracy of a newly designed micromilling tool is one of the urgent issues for micro tooling. This paper introduces an accuracy analysis method in the fabrication of micromilling tools by wire electrical discharge machining (WEDM) process. Taking two typical micro ball end mills into consideration, the micro tool fabrication process is kinematically modeled and analyzed. Analytical results show that the final fabrication accuracy has a close relationship with the designed micro tool geometry. The fabrication procedures can be arranged based on the kinematical analysis, and the final fabrication accuracy also is affected by it. The radius errors of the fabricated micro ball end mill prototype are within ±2μm, which is higher than that of commercially available similar ones. It verifies the proposed accuracy analysis method.     

Numerical simulation of orthogonal machining process using multilayer and single-layer coated tools

The tool edge radius significantly affects material deformation and flow, tool?Cchip friction, and a variety of machining performance measures (such as the cutting forces and tool wear) in mechanical micro/meso-scale machining. The tool edge-related research, either theoretically or experimentally, has been only focused in machining cases in which no built-up edge (BUE) is generated. To close this research gap, a comparative study of sharp and round-edge tools in orthogonal machining with BUE formation is conducted, including both experimental investigations and theoretical modeling. The experimental results show that the variations of the cutting forces are more stable in machining with a sharp tool than those in machining with a round-edge tool. A round-edge tool produces higher vibration magnitudes than does a sharp tool. The cutting vibrations do not necessarily have the same varying pattern as that of the cutting forces in machining with either a sharp tool or a round-edge tool. A neural network-based theoretical model is developed to predict three distinct regions of BUE formation (namely BUE Initiation Region, Steady BUE Region, and Unsteady BUE Region) in machining with a round-edge tool. The developed neural network model has been proven valid using a separate set of cutting experiments under different cutting conditions from those used for network training and testing.     

三维微细电解铣削加工的实时控制与检测

为了实现三维微细电解铣削加工过程的实时监测,建立了基于Labwindows/CVI软件平台的控制与检测系统。对该系统所采用的三维轨迹生成及控制策略,数据采集及抗干扰算法,加工时间误差补偿算法等进行了研究。首先,根据微细电解铣削加工的特点,分析了加工控制与检测系统的需求。接着,搭建了高精度的三维微细铣削加工实验硬件平台。然后,利用虚拟仪器平台建立了基于分层铣削加工方式的三维轨迹进给控制模块,并对刀具轨迹的优化进行了讨论。最后,介绍了数据采集及反馈控制模块以及实时控制的时间补偿函数。基于上述控制与检测系统,实验并成功加工出了单层尺寸为15μm×55μm×15μm的三层阶梯结构,结果表明,本系统可以满足微细电解铣削加工的高精度、快响应、稳定可靠等要求。     

Development of microelectrodes for electrochemical micromachining

Electrochemical micromachining (EMM) has become more and more important in micro machining in recent years. Microelectrode as the tool of EMM is an essential cell in the machining process. In this study, microelectrodes with various end shapes are fabricated by different processing techniques. First, the different end shape forming methods for microelectrode, such as electrochemical etching, single electric discharge, and electrochemical micromachining are investigated. Second, microelectrodes with various end shapes fabricated above are simulated, analyzed, and then used in EMM process. At last, micro holes array with diameter of less than 10???m, three micro holes with no taper and a 3D microstructure are machined on metallic materials by above three types of microelectrodes.     

UV-LIGA制作超高微细阵列电极技术

采用UV-LIGA技术制作了超高金属微细阵列电极,并利用电解置桩的方法辅助去除SU-8胶。通过单次涂胶和提高前烘温度、降低后烘温度的方法制作了厚度达1mm的SU-8胶结构;采取反接电极法在金属基底上电解得到微坑,增强电铸金属电极与金属基底的结合力,保证去胶后电铸金属的完整性。选取优化的工艺参数:单次注射式涂胶,前烘110℃/12h,适量曝光剂量,分步后烘50℃/5min、70℃/10min、90℃/30min,反接电极电解10V/15min等,获得了高900μm、线宽300μm的金属微细阵列电极结构。试验表明,UV-LIGA技术是一种高效、经济的制造超高微细阵列电极的有效手段。     

Research of micro EDM/ECM method in same electrolyte with running wire tool electrode

A micro rod machining method which can switch between electrical discharge machining (EDM) and electrochemical machining (ECM) by attaching/detaching a diode to/from a bipolar pulse generator in parallel to the working gap was newly developed using a wire electrode made of tungsten. The problem of the wire electrode wear was eliminated by the use of the wire electrochemical turning (WECT) method in which the tungsten wire electrode is continuously running. The ultra-short bipolar pulse current was generated by the electrostatic induction feeding method where a pulse voltage is coupled to the working gap through a feeding capacitance. The machining characteristics of three types of wire guide; disk-shaped WC guide, laminated wire guide and cylindrical acrylic guide, were studied. The experimental results showed that the cylindrical acrylic guide has the best machining characteristics without the influence of guide wear and with less stray current flowing through the working gap. Using the cylindrical acrylic guide, the influences of the feeding capacitance C₁, and the total amplitude of the pulse voltage on the machining characteristics were studied. Finally, a stainless steel SUS 304 micro-rod with a high aspect ratio of 14 was fabricated efficiently by using the EDM and ECM modes for rough and finish machining in sequence with the same setup, pulse generator, and neutral electrolyte.     

UV-LIA制作超高微细阵列电极技术研究

超高金属微细阵列电极在微细加工领域和生命科学领域有广泛应用。本文采用UV-LIGA技术制作超高金属微细阵列电极,并利用电解置桩的方法辅助去除SU-8胶。通过单次涂胶、提高前烘温度、降低后烘温度的方法制作了厚度达1mm的SU-8胶结构;采取反接电极法在金属基底上电解得到微坑,增强电铸金属电极与金属基底的结合力,保证去胶后电铸金属的完整性。选取优化的工艺参数：单次注射式涂胶;前烘110℃/12h;适量曝光剂量;分步后烘50℃/5min、70℃/10min、90℃/30min;反接电极电解10V/15min等,获得了高900μm、线宽300μm的金属微细阵列电极结构。试验表明,UV-LIGA技术是一种高效、经济的制造超高微细阵列电极的有效手段。     

An improved cutting force model for micro milling considering machining dynamics

Micro milling, as a versatile micro machining process, is kinematically similar to conventional milling; however, it is significantly different from conventional milling with respect to chip formation mechanisms and uncut chip thickness modelling, due to the comparable size of the edge radius to the chip thickness, and the small per-tooth feeding. Considering tool runout and dynamic displacement between the tool and the workpiece, the contour of the workpiece left by previous tool paths is typically in a wavy form, and the wavy surface provides a feedback mechanism to cutting force generation because the instantaneous uncut chip thickness changes with both the vibration during the current tool path and the surface left by the previous tool paths. In this study, a more accurate uncut chip thickness model was established including the precise trochoidal trajectory of the cutting edge, tool runout and dynamic modulation caused by the machine tool system vibration. The dynamic regenerative effect is taken into account by considering the influence of all the previous cutting trajectories using numerical iteration; thus, the multiple time delays (MTD) are considered in this model. It is found that transient separation of the tool-workpiece occurring at a low feed per tooth, caused by MTD and the existing cutting force models, is no longer applicable when transient tool-workpiece separation occurs. Based on the proposed uncut chip thickness model, an improved cutting force model of micro milling is developed by full consideration of the ploughing effect and elastic recovery of the workpiece material. The proposed cutting force model is verified by micro end milling experiments, and the results show that the proposed model is capable of producing more accurate cutting force prediction than other existing models, particularly at small feed per tooth.