An investigation of redeposition effect for deterministic fabrication of nanodots by focused ion beam

Focused ion beam machining is a powerful technique for micro/nanofabrication. However its machined surface form accuracy will be degrade due to atoms redeposition in the nanofabrication process. In this paper, a 3D surface topography model and associated simulation program are developed to study redeposition effect for precise and deterministic fabrication of nanodots by focused ion beam. The simulation is implemented by level set method. The angular dependence of sputtering yield is calculated by a Monte Carlo simulation program - TRIDYN. The simulation results have been evaluated by focused ion beam fabrication of nanodots experiment on a silicon substrate. It demonstrates that the simulation method can precisely describe the generation of 3D surface in focused ion beam machining process (with less than 10% simulation error). Redeposition has made significant contribution to the surface generation in nanoscale fabrication by reducing more than 1/3 of intended depth. The model and simulation program developed has approved to be a good tool to determine proper machining parameter to achieve deterministic nanofabrication by focused ion beam.     

Manufacturing process of copper microgrooves utilizing a novel optical fiber-based laser-induced etching technique

A new approach for the fabrication of copper microgrooves with near triangular cross-sectional profile is introduced. For manufacturing the microgrooves, a laser-induced thermochemical etching technique based on an optical fiber as an optical waveguide and machining tool is proposed, which significantly reduced the complexity of a conventional laser etching set up. It is explained that the possible problem of fiber damage during laser etching with the proposed method can be solved by appropriately controlling the gap between the sample surface and fiber tip. The fabrication of copper microgrooves with 100 ∼ 300 μm in depth and 100 ∼ 150 μm in width is accomplished with the proposed technique. The grooves fabricated in the optimal process condition have smooth surfaces and clear edge. The angle of triangular groove is measured to be in the range of 30 ∼ 50 degree and the aspect ratio of grooves is about 1 ∼ 2. The overall etching results such as etch width, depth, and aspect ratio variation are reported in detail with respect to process variables.     

Nanofabrication of arbitrary patterns by nano plastic forming and etching (NPFE)

In this paper, flexibility of nano plastic forming and etching, an ultra-high resolution nanofabrication process developed recently by the authors, in terms of fabrication of arbitrary patterns as well as applicability to various work materials is demonstrated. First, a thin layer of nickel (Ni) is deposited on a silicon (Si) substrate. Then, it is directly patterned by nano plastic forming. Next, the patterned Ni mask is slightly etched by direct current sputter etching to transfer the pattern into the entire mask thickness and expose the surface of the substrate in the individual patterned areas. Afterward, the pattern is transferred onto the substrate by reactive ion etching. Finally, the remained Ni layer is removed from the substrate, and nanostructures fabricated on the surface of the substrate are revealed. Fabrication of grid patterns with various pitch settings on the surface of Si substrates is demonstrated. The experimental results indicate that the depth and width of the nanostructures can be controlled by the etching time. Also, it is confirmed from the results that the depth and width are not influenced by the pitch setting.     

A method to include plastic anisotropy to orthogonal micromachining of fcc single crystals

Micro-abrasive jet machining (μ-AJM) is a fast and flexible technique for micro-patterning of brittle materials and can be combined with patterned mask made from a material with excellent photolithographic properties. Here, we demonstrate a fabrication method for the realization of a passive micromixer with third-dimensional feature by using a μ-AJM process with employing photopolymer as a mask on a glass slide target. We fabricated the mask using SU8, a photosensitive polymer, applied as a micro-pattern for μ-AJM process. The design and fabrication of the proposed micromixer is the first reported for such a device. Three glass layers were successfully bonded in a single step using a direct bonding method. These three bonded glass layers with micro-patterns etched on them were the realization of third-dimension feature on the micromixer design.     

Hybrid (LASER + CNC) process for lubricant groove on linear guides

A novel hybrid process [LASER?+?computer numerical control (CNC) machining] is used to fabricate a linear motion guide. A 20-W pulsed fiber laser and a three-axis CNC machining center were combined to fabricate microscale lubrication grooves on a 5-mm wide linear guide contact surface made of SCM-440H material. Ablation fabrication speed was increased up to 1,000 mm/min (or 16.7 mm/s) with a great ablation quality without any tool wear. The mean values of patterned sizes of lubrication grooves were measured to be between 40 and 80?μm in width and between 150 and 275?μm in depth with a laser pulse repetition of 25 kHz. A specially designed optical device was compact enough to be installed on CNC machine. It was mounted on the CNC spindle and proved to be flexible enough to deliver the laser beam on to the work piece. The microscale ablation quality of the surface was of sufficient quality to be adopted on most linear motion related applications.     

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。     

Development of rapid mask fabrication technology for micro-abrasive jet machining

Micro-machining of a brittle material such as glass or silicon is important in micro fabrication. Particularly, micro-abrasive jet machining (μ-AJM) has become a useful technique for micro-machining of such materials. The μ-AJM process is mainly based on the erosion of a mask which protects brittle substrate against high velocity of micro-particles. Therefore, fabrication of an adequate mask is very important. Generally, for the fabrication of a mask in the μ-AJM process, a photomask based on the semi-conductor fabrication process was used. In this research a rapid mask fabrication technology has been developed for the μ-AJM. By scanning the focused UV laser beam, a micro-mask pattern was fabricated directly without photolithography process and photomask. Therefore, rapid and economic mask fabrication can be possible for the micro-abrasive jet machining. Two kinds of mask patterns were fabricated by using SU-8 and photopolymer (Watershed 11110). Using fabricated mask patterns, abrasive-jet machining of Si wafer was conducted successfully. This paper was recommended for publication in revised form by Associate Editor Dae-Eun Kim Seung Pyo Lee is a research engineer of GM Daewoo Auto & Technology. He receives his Ms degree in Precision Mechanical Engineering at the Chungbuk National University in 2007. Hyun-Wook Kang is currently a Ph.D. candidate in the Department of Mechanical Engineering at POSTECH, Korea. He received his B.S. degree in the Department of Mechanical Engineering from POSTECH. His current research interests are in the solid freeform fabrication technology for the engineered tissue construction. Seung-Jae Lee received the M.S. degree from the Dept. of Me-chanical Engineering from the POSTECH in 2002, and his Ph.D. degree in Dept. of Mechanical Engineering from POSTECH in 2007. His Ph.D research is the study of Microfabrication and Tissue engineering. In Hwan Lee is a professor of School of Mechanical Engineering at Chungbuk National University, Korea. He receives his Ph.D. degree in Mechanical Engineering from the POSTECH in 2003. His research is focused on micro-manufacturing and bio-system. Tae Jo Ko is a professor of mechanical engineering at Yeungnam University, Korea. Also, he is responsible for the Gyoungbuk Hybrid Technology Institute that is regional research innovation center and initiates the idea for hybrid manufacturing. He earned Ph.D in mechanical engineering from POSTECH, Korea, in 1994. He worked for Doosan Infracore Co. Ltd. (formerly Daewoo) from 1985 to 1995. His research interests include machine tools, metal cutting as well as nontraditional machining. Dong-Woo Cho is a professor in the Department of Mechanical Engineering at the POSTECH. He received his Ph.D. degree in Mechanical Engineering from the University of Wisconsin-Madison in 1986. His research focuses on the manufacturing system for Tissue Engineering.     

Investigation into fabrication of microslot arrays by electrochemical micromachining

Maskless electrochemical micromachining (EMM) is a prominent and unique surface texturing method to fabricate the arrays of microslots. This article investigates the generation of microslot arrays using maskless EMM method. The developed prototype maskless EMM setup consists of EMM cell, power supply connections, electrode holding devices and constricted vertical cross flow electrolyte system for the fabrication of microslot arrays economically. One textured cathode tool with SU-8 2150 mask is used to produce 22 microslot arrays. Influences of EMM process parameters including voltage, electrolyte concentration, inter electrode gap, flow rate and machining time on the machining performance that is, width overcut, depth and surface roughness (R_a) of microslot arrays are investigated. For lower width overcut, controlled depth, and lower surface roughness, machining with lower voltage, lower electrolyte concentration, lower inter electrode gap, higher flow rate and lower machining time are recommended. From the analysis, it is observed that the best machining conditions including inter electrode gap of 50?μm, applied voltage of 6 V, electrolyte concentration of 20?g L^?1, flow rate of 5.35 m³ hr^?1 and machining time of 1?min fabricate regular microslot array with mean width overcut of 24.321?μm, mean machining depth of 10.7?μm and mean surface roughness of 0.0101?μm.     

Biochemical machining — biochemical removal process of plastic

Plastic products are now ubiquitos; however, home and industrial plastic waste cannot be degraded. Hence, disposal of such wastes is now a large problem in maintining a clean environment. Some biodegradable plastics have been developed in response to demands for waste-free plastic products. Biodegradable Editorial Board plastics can be degraded by microorganism or enymes by means of cutting down the molecular chains. Taking note of the bio-degradation process of biodegradable plastic by microorganisms, biochemical machining, using a mold as a new biochemical microremoval process, has been developed.     

A theoretical and experimental investigation of orthogonal slow tool servo machining of wavy microstructured patterns on precision rollers

Precision cylinders, or rollers, with patterned microstructures on the surface are the key tooling component in the Roll-to-Roll and Roll-to-Plane fabrication process for precision manufacturing of microstructured plastic films. These films are widely used in optical applications such as the backlight guide and brightness enhancement films in LCD and LED displays. Compared with other fabrication processes, such as lithography, Single-Point Diamond Turning (SPDT), using a Fast Tool Servo (FTS) or Slow Tool Servo (STS) process, is an enabling and efficient machining method to fabricate microstructures. Most studies of the tool servo machining process focus on either machining microstructures in the axial direction for face machining of flat parts or in the radial direction on the surface of a precision roller. There is relatively little research work found on the machining of patterned microstructures on the surface of precision rollers using the tool servo in the axial direction. This paper presents a pilot study on the development of a tool path generator for machining wavy microstructure patterns on precision rollers by using an Orthogonal Slow Tool Servo (OSTS) process. The machining concept of OSTS is first explained, and then the tool path generator is developed in detail for machining wavy microstructure patterns on a roller surface. Modelling and simulation of pattern generation for different microstructures with different wavy patterns and grooves are presented based on the proposed tool path generator. Preliminary experimental work using SPDT on a 4-axis ultra-precision machine tool is presented and clearly shows the generation of unique wavy microstructure patterns on a precision roller. The machined wavy microstructures on the roller surface are measured and analyzed to evaluate the validity of the proposed tool path generator.     

Simulation-based fabrication of micro-helical grooves in a hydrodynamic thrust bearing by using ECMM

In hydrodynamic thrust bearing, common micro-grooves with helical or herringbone forms are generally to ensure the bearing load capacity and reduce leakage of lubricant, consistent with the design or size requirements of grooves. In this investigation, the electrical field distribution and anodic dissolution of helical grooves in electrochemical micro-machining process can be predicted by using COMSOL Multiphysics^TM software. The processing equivalent is based on the chemical composition of the workpiece. The micro-helical grooves are hollowed out of hydrodynamic thrust bearing using a DC and pulse power supply, and experiment results are compared with simulation results. The experimental results demonstrate that the fine surface of helical grooves can be obtained with a depth of 4.9 μm in machining time of 3 s by using a pulse power supply of 5 kHz. To eliminate the effect of such factors as flush flow, temperature difference between workpiece and tool, and formation of hydrogen bubble barriers, the k values of these factors are considered for amendment to get more accurate simulation results.     

Direct 3D mask modeling for nonplanar workpieces in microabrasive jet machining

Recently, a new microengraving technology, microabrasive jet machining, has been studied as a machining technology for highly brittle materials. The technology implements the machining by using an abrasive jet and it uses mask structures to achieve microscale geometrical accuracy. The mask structure selectively blocks the abrasive jet at the portions of the surface that are not to be machined. Modeling and fabrication of the mask structure are thus key processes in microabrasive jet machining. Microstereolithography is believed to be a better means of mask fabrication for general planar and nonplanar workpieces. However, it is not easy to model a precise 3D mask structure from a given pattern image. Because of inconsistencies between the computer-aided design (CAD) model and the actual workpiece, mask structures modeled from workpiece CAD models often fall off. We therefore propose an automated modeling algorithm for the corresponding 3D nonplanar mask structure by using measured geometry directly. The algorithm takes the workpiece geometry as section images acquired from computer tomography and generates the CAD mask model directly from the section and mask images. Application software was developed to verify the algorithm and was tested by verification and actual cases.     

Ultra-precision nano-structure fabrication by amplitude control sculpturing method in elliptical vibration cutting

This paper studies the nano-structure fabrication on hardened steel by means of elliptical vibration cutting equipped with the ultra-precision amplitude control sculpturing method. Machining performance of the amplitude control sculpturing method is investigated, and the limitation in nano-scale machining is explored. In this proposed method, machinable part geometry is essentially restricted by vibration conditions and tool geometry. In addition, a considerable error between the amplitude command and the envelope of the tool trajectory is generated when the slope of the machining part geometry becomes steep. To overcome this error, a compensation method for the amplitude control command is proposed. In order to clarify the machining performance of the proposed technology, a series of analytical and experimental investigations are conducted. Furthermore, by applying the proposed command compensation method, nano-structures with a large ratio of structure height to wave length are machined accurately. The proposed sculpturing method is subsequently applied to the machining of nano-textured grooves and a three-dimensional grid surface, which verifies the feasibility of the proposed amplitude control sculpturing method.     

Abrasive water and slurry jet micro-machining techniques for fabrication of molds containing raised free-standing micro-features

The demand for metallic micro-molds that can be used for inexpensive mass production of polymeric microfluidic chips is increasing. Existing manufacturing techniques such as soft-lithography and photolithography can require multiple time-consuming steps, especially when the aim is to create three-dimensional features. In this study, the feasibility of using abrasive water jet machining (AWJM) and abrasive slurry jet machining (ASJM) to fabricate such micro-molds in Al6061-T6 and SS316 was studied. Jet raster scans under various combinations of process parameters were used in order to machine micro-pockets containing free-standing structures, representing molds for casting microfluidic chips with channel networks. As expected, for both materials and using both ASJM and AWJM, the pocket roughness decreased as the distance between adjacent raster scans (step size) decreased, but the lowest waviness occurred at an intermediate step size. The best quality pockets were achieved on SS316 using ASJM with the intermediate step size and the highest possible slurry mass flow rate. Unmasked machining could not be used to fabricate molds with sharp-edged intersecting features, and a novel hybrid AWJM/ASJM masked machining technique was thus introduced. An undercut and an undesirable erosion near the edges of the mask formed if the position of the last raster scan closest to the mask was not carefully controlled. Possible reasons for these phenomena were discussed in terms of the likelihood of jet deflection off the machining kerf and mask, and the resulting erosion due to secondary slurry flow. By careful selection of the process parameters, it was demonstrated that high quality molds with both single and intersecting free-standing structures at multiple heights could be fabricated, thus making three-dimensional microfluidic chip mold fabrication feasible.     

Abrasive jet machining for the microprofile control patterning of herringbone grooves

Fluid bearings have features of high speed and high rotation accuracy, and therefore, they are used in spindle motors of hard disk drives, cooling fans of central processing units, and other devices. Further, these bearings have microherringbone grooves on the shaft or sleeve inner surface that help generate dynamic pressure in the lubricant fluid around the shaft. Although the depth of the groove is constant, dynamic pressure can be increased by decreasing the depth from both ends to the central corner of each groove on a micron scale. This study aims to verify the effect of sloped herringbone grooves using computational fluid dynamics (CFD) analysis and to develop a new microfabrication method for manufacturing microsloped herringbone grooves on the shaft surface using abrasive jet machining. The generated dynamic pressure is analyzed using CFD; the results indicated that the sloped herringbone grooves result in an increase in the dynamic pressure at the groove tips and cause a decrease in the fluctuations in dynamic pressure in the circumferential direction.     

V型毛细微沟槽犁切-挤压成形试验研究

采用犁切—挤压一次成形加工工艺,在0.5mm厚的铜带表面加工出V形毛细微沟槽结构。对所加工的V型微沟槽进行电镜扫描,观察其特征,并用显微镜测量其几何参数。分析了不同加工参数和刀具结构参数对沟槽翅高和槽深度的影响。研究结果表明:在V型微沟槽成形过程中,受到加工参数和刀具结构参数的联合影响。     

型腔类零件的数控加工

在普通铣削加工中,型腔类零件大都是使用成形刀具直接成形出来的。但是切削时刀具处于满刃状态、切削受力大、排屑差,零件的精度与表面粗糙度难以控制和达到要求。利用数控铣削加工此类零件均可通过走刀轨迹加工并能达到零件图要求。但在实际加工时(比如深槽加工、内腔转角圆弧小且内腔深度较大)都应在工艺上做相应的处理。通过对圆腔、方腔、带孤岛的腔体类零件的分析与数控加工可知加工工艺的确定非常重要。     

A thick SU-8 mask for microabrasive jet machining on glass

This work presents the implementation of a thick SU-8 layer as a mask in the microabrasive jet machining (μ-AJM) process. A microchannel with an aspect ratio of 0.33, which was obtained in this work, had an arc-shape with a width of 190 μm and a depth of 70 μm. The process phenomena that are important for achieving a qualified microchannel for microfluidic applications are discussed. By using the repeated sequence of steps proposed in this paper, three-dimensional microchannels on a single glass slide can be fabricated.     

Fabrication of micro rods by twin-mirroring-wire tangential feed micro electrical discharge grinding

In micro electrical discharge machining (micro-EDM), the precision fabrication of cylindrical micro rods is difficult to achieve with a high processing efficiency. In order to overcome this challenge, this paper proposes a new processing method, which is denoted as twin-mirroring-wire tangential feed micro electrical discharge grinding (TMTF-WEDG). The machining principle, characteristics, and realization of the new method are firstly introduced. Then, the advantages of TMTF-WEDG in terms of machining efficiency and accuracy are demonstrated. The experimental results have shown that the machining efficiency can be increased to more than 70% in comparison with conventional tangential-feed wire electrical discharge grinding. It has also been proved that a minimum removal of material corresponding to a reduction of less than 1 μm in the diameter of a micro rod can be obtained by TMTF-WEDG. This considerably helps in improving the accuracy and repeatability of the machining process. A deviation of less than 1 μm on the diameter of a micro rod has been obtained in a length range of 800 μm. The process repeatability in machining five micro rods has been established to be below 2 μm. The proposed method is therefore of great significance for improving the machining efficiency and ensuring a high precision in the shaping process of cylindrical micro rods.     

Generating micro-dimples array on the hard chrome-coated surface by modified through mask electrochemical micromachining

It has been recently identified that micro-dimples can act as fluid reservoirs and promote the retention of a lubricating film to reduce friction between mechanical components. Various techniques are employed to produce micro-dimples on the surface of friction pair. In this study, a modified through mask electrochemical micromachining (TMEMM), in which the insulation layer was directly attached to the cathode, was developed to produce micro-dimples on the hard chrome-coated surface. By controlling machining parameters, micro-dimples array, with hundreds of micrometers in diameter and several micrometers in depth, were produced. Compared with the traditional TMEMM, the modified method can both reduce cost and improve machining efficiency. Friction experiments show that the friction coefficient of the surface with appropriate micro-dimples array is obviously lower than that with nondimples.