电火花摇动加工微细阵列轴和孔的试验研究

针对微细阵列轴和孔的电火花加工,提出了利用数控电火花加工机床摇动功能的摇动加工微细阵列轴和孔的方法.此法是基于电火花反拷贝加工的原理,先用丝电极在薄平板(中间电极)上按要加工的阵列轴和孔间距或数倍间距加工阵列小孔(直径0.1 mm以上),然后用加工的薄平板(中间电极)作电极,电火花摇动加工微细阵列轴(电极),最后用此微细阵列电极加工阵列孔.进行了电火花摇动加工微细阵列电极试验,得到了单电极直径为50 μm、长径比为16的3×3阵列电极,并用此电极在70 μm厚的不锈钢板上加工出单孔直径为70 μm的3×3微细阵列孔.试验结果表明,电火花摇动加工方法可实现微细阵列轴和孔的加工.     

群孔的微细电火花加工技术研究

对微细电火花群孔加工工艺进行了分析和研究。用微细电火花加工机床加工出单电极,并用该电极加工出2×2直径约100μm的阵列孔,在此过程中采用加大加工长度和适度欠补偿的方法,获得了质量较好的阵列孔。用此阵列孔作为工具加工出了2×2直径约100μm的群电极,然后用此群电极一次加工出2×2直径约100μm的群孔,从而实现了微细电火花阵列孔的加工。     

微细电加工应用技术研究

微细电加工要达到工业应用的目的,需兼顾加工效率和加工精度两方面的要求.以微细孔、微细三维结构的加工为目标,进行了微细孔电火花加工、三维微细结构电火花伺服扫描加工及微细电化学加工技术的研究开发.设计出微细电极的损耗补偿进给和导向机构,开发出三维微细结构的电火花伺服扫描加工工艺,研究了采用阵列微细电极的微细电化学加工方法.微细孔电火花加工可连续加工直径小至100 μm的孔.伺服扫描电火花加工可便捷地在小于1 mm2区域内加工出三维微细结构.提出的微细电化学加工技术路线拟将微细电解加工应用于阵列微细孔和三维微细结构的加工.     

微细阵列方形轴孔的电火花和电化学组合加工工艺研究

对微细阵列轴孔的电火花、电化学组合加工工艺进行了分析和研究.用微细电火花线切割机加工出3×3至10×10系列方形阵列电极,宽度在25～90 μm, 加工中采用降低加工电压、加工电流、进给速度和减小工作液冲击等方法,获得了质量较好的阵列电极,并分别利用微细电化学加工和微细电火花加工两种工艺方法进行阵列孔加工.在加工过程中通过适度间歇抬刀、超声振动、循环流动工作液等方法,较好地解决了微弧放电、排屑、加工区温度过高等加工难题,获得了质量较好的大小在30～100 μm相应的阵列孔,从而实现了微细阵列轴孔的电火花、电化学组合加工,为大规模微细阵列轴孔的加工开辟了高效、可行的新工艺方法.     

微细孔电火花加工设备及其加工实验研究

开发了一种电极丝辅助激振微细孔电火花加工设备,主要由微细电极丝伺服进给与导向模块、加工状态监测与控制模块、高频脉冲电源、微细电极丝辅助激振模块以及工作液循环系统等组成.采用拉拔微细钨丝作为工具电极,可加工直径100～300 μm的微孔及阵列微细孔.实验结果表明,使用直径0.07 mm的电极丝可连续稳定地进行阵列微孔的加工(孔径为100 μm,16×16阵列).加工使用的微细电极丝最小直径为50 μm.     

组合式微细电火花电极制作工艺试验研究

针对块电极磨削效率高和线电极磨削(WEDG)精度高的优点,采用块电极磨削和线电极磨削相结合的方法,在多模式脉冲电源下制定了块电极磨削作为粗磨削、线电极磨削作为中、精磨削的微细电火花电极制作工艺流程。采用去离子水作为工作液,分别对块电极磨削和线电极磨削进行了电源模式和电参数试验,分析试验结果,总结出一组适合于粗、中、精磨削的电参数组合,研究出一套加工效率高、精度高且直径一致性高的电极制作工艺方法。并通过试验验证了该工艺方法能稳定加工出长径比大于16的微细电极,利用其加工出了256个直径小于50μm、直径偏差在2μm内的微细阵列孔。     

微细孔、阵列孔及微细三维型腔的超声加工研究

利用自行开发的微细电火花与微细超声复合加工装置,对微孔超声加工中效率随孔深的变化、磨料颗粒尺寸对精度的影响等进行了实验研究,并采用恒加工力控制方式,在单晶硅100晶面实际完成了直径18μm圆孔和28μm×28μm方孔的超声加工、微细十字孔与阵列孔的超声反拷加工以及微细三维型腔的工具均匀损耗补偿分层铣削超声加工.     

基于高速铣削的微细电极加工方法

微模具型腔的高效、高精密加工,一直是制约微模具制造技术发展的瓶颈问题.以微细 电火花加工用的圆柱阵列结构微细电极为对象,研究了应用高速铣削加工技术,实现微细电极的高效、高精密加工方法.通过优化分析微细电极结构和高速铣削加工参数及刀具路径,获得了尺寸和形状精度及表面质量均满足要求的阵列结构微细电极,并以制得的微细电极进行...     

用块电极轴向进给法电火花磨削微细轴

对电火花磨削微细轴中的关键问题进行了分析，提出并研究了利用块状电极轴向进给磨削微细轴的方法。在自行研制的多功能微细加工装置上，用该方法加工出了直径10μm的微细轴，并用此轴加工出了直径20／μm的微细孔。实验中发现：令伺服响应延时，可改善微细轴的圆度。用此方法得到的微细轴，根部强度高，有利于微细轴的加工和工作。     

微细阵列型孔的冲压与电火花复合加工技术研究

提出一种微细冲压加工和微细电火花加工交叉结合的微细阵列型孔复合加工方法。尺寸较大的过渡型腔采用微细冲压加工，以提高加工效率和保证加工尺寸的一致性；型孔喷口的最小特征尺寸采用微细电火花逐层扫描加工得到。设计制作了专用的微小型腔冲压实验装置，从机构设计上保证加工工艺对微小型腔冲压深度的精确控制。进行了非圆截面阵列微细型孔的加工实验，验证了所提出的工艺方法的可行性和合理性。     

Study of precision micro-holes in borosilicate glass using micro EDM combined with micro ultrasonic vibration machining

Because of its excellent anodic bonding property and surface integrity, borosilicate glass is usually used as the substrate for micro-electro mechanical systems (MEMS). For building the communication interface, micro-holes need to be drilled on this substrate. However, a micro-hole with diameter below 200 μm is difficult to manufacture using traditional machining processes. To solve this problem, a machining method that combines micro electrical-discharge machining (MEDM) and micro ultrasonic vibration machining (MUSM) is proposed herein for producing precise micro-holes with high aspect ratios in borosilicate glass. In the investigations described in this paper, a circular micro-tool was produced using the MEDM process. This tool was then used to drill a hole in glass using the MUSM process. The experiments showed that using appropriate machining parameters; the diameter variations between the entrances and exits (DVEE) could reach a value of about 2 μm in micro-holes with diameters of about 150 μm and depths of 500 μm. DVEE could be improved if an appropriate slurry concentration; ultrasonic amplitude or rotational speed was utilized. In the roundness investigations, the machining tool rotation speed had a close relationship to the degree of micro-hole roundness. Micro-holes with a roundness value of about 2 μm (the max. radius minus the min. radius) could be obtained if the appropriate rotational speed was employed.     

Fabrication of a micro-pin array with high density and high hardness by combining mechanical peck-drilling and reverse-EDM

To fabricate circular cross-section micro-pin array with high hardness and high density in a fast and efficient way, a combined method of mechanical peck-drilling and reverse electrical discharge machining (reverse-EDM) is proposed in this research. First, a ball-cone-hole-magnet (BCHM) method is applied in high vibration cantilevered platform (HVCP) and quick release holder/jig to produce highly precise, fast and elastic positioning. Second, a micro-hole array with high density and different types of holes on a workpiece (brass material) is produced by a vibration-assisted mechanical peck-drilling (VAMPD), which includes the high vibration of workpiece created by HVCP and mechanical peck-drilling of micro-drill. This VAMPD can drill up to 1600 single-stage or multi-stage micro-holes, and the aspect ratio of the drilled one-stage micro-holes of Ø60 μm is up to ten. Finally, reverse-EDM is used to fabricate the micro-pin array made of tungsten carbide. In this process, the effects of the chip removal mechanism, the various micro-hole types, and the density of the micro-holes on the electrodes are investigated. The results indicate that the combination of multi-stage micro-hole electrodes and three chip removal methods (working fluid spraying, vibration-assisted electrode and shake-down type workpiece) can produce a 1600-micro-pin array with an average diameter below Ø30.00 μm, a length of 625.0 μm, and a pitch of 100 μm. Consequently, the proposed method of combining mechanical peck-drilling and reverse-EDM can fabricate a micro-pin array with high hardness, high density, high quantity, and uniform diameter in a fast and efficient way.     

Fabrication of micro-hole arrays using precision filled wax metal deposition

This study presents a low-cost hybrid fabrication process that produces micro-holes of less than 200 μm in diameter. First of all, a micro-EDM hole-drilling is employed to perforate micro-holes through the mirror-like substrate (SUS304), which is cylindrical in shape. The oily wax also known as “sacrificial material” is extruded and formed onto the SUS304 substrate, resulting in a precision cylindrical micro-wax pillar mould. A precision electroforming is then conducted to deposit a thick nickel metal layer onto the substrate, and subsequently the wax mould is completely removed and revealed a perforated micro-hole array after releasing from the substrate. Experimental results show that the wax mould has an excellent duplication capability. The finished micro-hole array has an average hole-diameter of 165.3 μm and demonstrates ideal geometric accuracy. The proposed approach can significantly cost down and contribute to the precision machining industry.     

Study on vibration-EDM and mass punching of micro-holes

In this research vibration-EDM is realized by the vibrating worktable designed, which is employed in the micro-punching machine we had already developed. It is found that larger feed and better surface finish can be achieved in micro-EDM with vibration machining. Circular and noncircular micro-electrodes of diameter below 200 μm were fabricated with vibration-EDM and the setup of u-axis. Experiments to punch micro-holes of diameter 200 μm on SUS304 stainless steel and brass strips were carried out. Mass punching of micro-holes on brass strip was performed successfully, using the automatic feeding system developed. The capability of micro-punching and effects of parameters on the quality of punched micro-hole are studied.     

Effect of surface roughness of tool electrode materials in ECDM performance

Electrochemical discharge machining (ECDM) is an emerging non-traditional machining process that involves high-temperature melting assisted by accelerated chemical etching. In this study, the tool electrode (200 μm in diameter) is fabricated by wire electrical discharge grinding (WEDG). After the tool electrode is machined, the surface roughness of tool electrode materials (stainless steel, tungsten carbide, and tungsten) is different because of the physical properties. However, the surface roughness affects the wettability on tool electrode, and also changed the coalesce status of gas film in ECDM. Hence, this study explores the wettability and machining characteristics of different tool electrode materials and their impact on gas film formation. Their machining performance and extent of wear under gravity-feed micro-hole drilling are also examined. Experimental results show that the optimal voltage of different tool electrode can shed light on the machining performance. Moreover, wettability of tool electrode is determined by surface roughness of tool material, which in turn affects the coalesce status of gas film, machining stability and micro-hole diameter achieved. In addition, differences in tool material also results in variations in machining speed. Significant tool wear is observed after repeated gravity-feed machining of 50 micro-holes.     

Debris and consequences in micro electric discharge machining of micro-holes

The tip shape of a blind micro-hole produced using micro electrical discharge machining varies with respect to the process parameters used during machining. The usual tip shape is a blunt geometry within the common range of applications, however, under specific machining conditions and machining depths, the tip shape changes drastically to an inverted concaved shape. The origin of such tip deformation in micro electric discharge machining of blind micro-holes was investigated. It was observed that debris particles produced during machining accumulated at the tip, formed a hill and functioned as a tool electrode especially when using fine machining conditions. The phenomena is elaborated experimentally with the affecting parameters to describe the wear mechanism. Open gap voltage, pulse energy and tool rotation speed are examined as varying parameters during the experiments.     

Application of micro-EDM combined with high-frequency dither grinding to micro-hole machining

This research presents a novel process using micro electro-discharge machining (micro-EDM) combined with high-frequency dither grinding (HFDG) to improve the surface roughness of micro-holes. Micro-EDM is a well-established machining option for manufacturing geometrically complex small parts (diameter under 100 μm) of hard or super-tough materials. However, micro-EDM causes the recast layer formed on the machined surface to become covered with discharge craters and micro-cracks, resulting in poor surface quality. This affects the diameter of the micro-hole machined and undermines seriously the precision of the geometric shape. The proposed method that combines micro-EDM process with HFDG is applied to machining high-nickel alloy. As observed in SEM photographs and surface roughness measurement, HFDG method can reduce surface roughness from 2.12 to 0.85 μm Rmax with micro-cracks eliminated. Our results demonstrated that micro-holes fabricated by micro-EDM at peak current 500 mA followed by HFDG at 40 V can achieve precise shape and good surface quality after 6–8 min of lapping.     

A new tool wear compensation method based on real-time estimation of material removal volume in micro-EDM

Owing to the reduced tool area and poor flushing conditions in deep holes, tool wear in micro-electrical discharge machining (EDM) is more significant than in macro-EDM. In micro-EDM drilling, the z-axis of the tool position is monitored as machining progresses. However, due to significant electrode wear, the machined hole depth is not identical to the programmed depth of the hole, and thus this will result in geometrical inaccuracy. This paper presents a new micro-EDM drilling method, in which the material removal volume is estimated as machining progresses. Compensation length is calculated and adjustment is made repeatedly along the tool path until the targeted material removal volume is reached. A real-time material removal volume estimator is developed based on the theoretical electro-thermal model, number of discharge pulse and pulse discrimination system. Under various energy input and machining depth settings, the experimental and estimated results are found to be in satisfactory agreement with average error lower than 14.3% for stainless steel, titanium, and nickel alloy work materials. The proposed drilling method can compensate the tool wear and produce more accurate micro-holes as compared to other methods. Experimental work also shows that the proposed method is more reliable as compared to the uniform wear method. In drilling micro-holes of 900 μm depth, the depth error can be reduced to 4% using the proposed method.