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.     

Pin-plate micro assembly by integrating micro-EDM and Nd-YAG laser

This paper presents a novel technology that applies the principle of Molten-Separation Joint (MSJ) from the micro-part back to perform precise micro assembly. This has been realized by using a hybrid process that integrates micro-EDM and Nd-YAG laser welding on a single machine to fabricate micro parts and complete precise micro assembly. To demonstrate this novel technology, we used this hybrid process to assemble a product, which is referred as a pin-plate. It consists of a micro pin with down to 50 μm in diameter jointed to a thin plate with 200 μm thick, and is made of SUS304.A tensile mechanism has been designed to measure the strength of the pin-plate after micro assembly. The results on SUS304 show that the joint strength is higher than that of the substrate for a micro pin with 200 μm in diameter. In addition, the pin-plate perpendicularity can be measured with a micro probe and a short sense discharge circuit specially installed in the micro-EDM. The detected results were quite satisfactory. This was further assured by observing the assembled joint cross section through a microscope.     

Automation of centered micro hole drilling using a magnetically levitated table

This paper presents the automation of centered micro hole drilling, using a magnetically levitated table. Centered micro hole drilling, an example of which is nozzle outlet hole drilling, has previously been performed manually by skilled craftsmen. If a micro hole is drilled when the center line of the drill and the center line of the guide hole are not aligned, the misalignment may cause drill breakage. By using a magnetically levitated table, a workpiece can be aligned frictionlessly. When the horizontal support stiffness of the table is set small, by lowering the drill slowly, centering can be performed due to the contact force between the drill tip and the conical surface of the nozzle. Spinning nozzles were used as experimental workpieces, and 0.1–0.5 mm diameter drills were used.     

Modeling of minimum uncut chip thickness in micro machining of aluminum

Micro mechanical machining operations can fabricate miniaturized components from a wide range of engineering materials; however, there are several challenges during the operations that can cause dimensional inaccuracies and low productivity. In order to select optimal machining parameters, the material removal behavior during micro machining operations needs to be understood and implemented in models. The presence of the tool edge radius in micro machining, which is comparable in size to the uncut chip thickness, introduces a minimum uncut chip thickness (MUCT) under which the material is not removed but ploughed, resulting in increased machining forces that affect the surface integrity of the workpiece. This paper investigates the MUCT of rounded-edge tools. Analytical models based on identifying the stagnant point of the workpiece material during the machining have been proposed. Based on the models, the MUCT is found to be functions of the edge radius and friction coefficient, which is dependent on the tool geometry and properties of the workpiece material. The necessary parameters for the model are obtained experimentally from orthogonal cutting tests using a rounded-edge tool. The minimum uncut chip thickness (MUCT) is then verified with experimental tests using an aluminum workpiece.     

Investigation into micro abrasive intermittent jet machining

In the machining of small holes by the conventional micro abrasive jet machining, the colliding abrasives accumulate in the bottom of the hole, preventing the direct impact of successive abrasives onto the workpiece. As a result, the machining efficiency decreases as the machining progresses. This paper introduces a new method of micro abrasive jet machining, called micro abrasive intermittent jet machining (MAIJM), in which there exists a period of time during which no abrasive is injected into the gas stream from the nozzle so that the continuous flow of gas without abrasives from the nozzle could blow away any abrasives that have accumulated in the hole. Empirical models are developed for evaluation of the effect of MAIJM process parameters on the shape of the machined holes by proper design of experiments based on a Taguchi orthogonal array and by multi-variable linear regression. Further experiments are conducted to confirm the validity of the developed statistical model by comparing the model predictions with the experimental results.     

Modelling and analysis of micro scale milling considering size effect, micro cutter edge radius and minimum chip thickness

This paper presents mechanisms studies of micro scale milling operation focusing on its characteristics, size effect, micro cutter edge radius and minimum chip thickness. Firstly, a modified Johnson–Cook constitutive equation is formulated to model the material strengthening behaviours at micron level using strain gradient plasticity. A finite element model for micro scale orthogonal machining process is developed considering the material strengthening behaviours, micro cutter edge radius and fracture behaviour of the work material. Then, an analytical micro scale milling force model is developed based on the FE simulations using the cutting principles and the slip-line theory. Extensive experiments of OFHC copper micro scale milling using 0.1 mm diameter micro tool were performed with miniaturized machine tool, and good agreements were achieved between the predicted and the experimental results. Finally, chip formation and size effect of micro scale milling are investigated using the proposed model, and the effects of material strengthening behaviours and minimum chip thickness are discussed as well. Some research findings can be drawn: (1) from the chip formation studies, minimum chip thickness is proposed to be 0.25 times of cutter edge radius for OFHC copper when rake angle is 10° and the cutting edge radius is 2 μm; (2) material strengthening behaviours are found to be the main cause of the size effect of micro scale machining, and the proposed constitutive equation can be used to explain it accurately. (3) That the specific shear energy increases greatly when the uncut chip thickness is smaller than minimum chip thickness is due to the ploughing phenomenon and the accumulation of the actual chip thickness.     

Boring and face grooving using micro turning tools

Micro turning tools with outside diameters of 25–50 μm were fabricated using cemented tungsten carbide by electrical discharge machining and used for micro boring and micro face grooving. The new process used could improve the hole circularity down to 0.25 μm and provide smooth-finished surfaces. From a set of experiments, the limit depth of cut and feed rate that can prevent tool breakage were determined. Compared with previous studies, the current study paved the way for applying removing processes with micro tools to boring and face grooving.     

Straightening of micro wires using the direct wire heating and pulling method

In this study, we have developed a novel micro wire straightener using the direct wire heating and pulling (DWHP) method. The straightener can remove the bend of the micro wire (< 200 μm) by heating it with the direct current, which flows through the wire in the glass chamber and simultaneously giving it the appropriate tension. A tension meter was attached to control the tension of the micro wire (tungsten). In order to avoid surface oxidization of the wire, we supplied inert gas (argon) into the glass chamber during the heating process, and examined the effect of the gas flow rate. The effects of the tension and the current applied to the micro wires (tungsten) were investigated experimentally. With Results from various experiments and parametric studies, we could obtain desired straightness (≈1 μm/1000 μm) with a tension of 500–600 gf and an approximate electric current of 1.5 A.     

Micro electrochemical machining for complex internal micro features

In this paper, the application of micro electrochemical machining (ECM) for the micromachining of internal features is investigated. By controlling pulse conditions and machining time, micro features are machined on the side wall of a micro hole. These methods can easily machine a micro hole with larger internal diameters than the entrance diameter, which is very difficult to do by the conventional processes. A micro disk-shaped electrode with an insulating layer on its surface is also introduced to machine microgrooves inside the hole. This method is similar to the turning lathe process. The purpose of this study was to confirm the various possibilities of making complex internal structures in a micro hole by micro ECM.     

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.     

Micro cutting in the micro lathe turning system

As an application of cutting for the manufacture of micro mechanical parts and as a trial of the development of a miniature machining system matching the micro size of the work piece, a micro lathe turning system has been developed. A work material 0.3 mm in diameter is clamped and cut to a minimum of 10 μm in diameter with a rotation speed up to 15,000 rpm. The whole size of the equipment is about 200 mm which can be set under an optical microscope. A micro diamond single point tool has been applied to the cutting of various shapes, and the usefulness of such a micro cutting tool for the various forms has been confirmed. Cutting force has been investigated using a three directional force sensor and the possibility of the reduction of resistant force to improve working accuracy and to apply to micro parts has been examined.     

混粉电火花镜面加工技术及应用

利用自行研制的混粉电火花镜面加工装置，对混粉电火花镜面加工影响因素，加工表面性能等进行了深入研究，找出了粉末特性，工件材料，粉末浓度及放电参数等对混粉电火花镜面加工的影响规律，给出了合理的混粉电火花镜面加工工艺条件，以文中确定的加工工艺条件对铸造和压铸模具进行混粉电火花镜面加工，结果表明，该技术能提高模具制造质量，降低工人劳动强度，缩短模具制造周期。     

Machining accuracy for shearing process of thin-sheet metals—Development of initial tool position adjustment system

In the shearing process, clearance has a significant effect on machining accuracy. However, the relationship between uneven clearance caused by misalignment of tool position and machining accuracy remains unclear. This is attributed to the fact that, previously, the effect was small because the thickness of the workpiece was not so thin, and a method for precisely measuring and adjusting the tool position had not been established. Therefore, in the present study, a new method of adjusting the initial tool position is developed. In addition, punching experiments are conducted under the condition that the initial tool position is adjusted to an accuracy of 2 μm or better, and the effects of clearance on machining accuracy, shape of cross-section, and diameter of hole, are investigated in three types of materials. From these results, the importance of adjusting the initial tool position is clarified.     

A study of EDM and ECM/ECM-lapping complex machining technology

EDM (electrodischarge machining) and ECM (electrochemical machining)/ECM-lapping complex machining is investigated in this paper. First, EDM shaping and ECM finishing technology are investigated. These processes are carried out in sequence on the same machine tool with the same electrode (copper) and the same machining liquid (water). Two types of EDM and ECM complex machining are investigated. One is with a formed electrode, and the other is with simple-shape electrode scanning. The complex machining with electrode scanning is applied to produce small and various-shaped components without making a formed electrode. The EDM surface of 1 μm Ra is improved to 0.2 μm Ra by applying ECM. Second, in order to get a smoother surface, a new EDM and ECM-lapping complex machining technology is developed. The surface roughness of a machined hole is improved to 0.07 μm Ra by applying 2 min of ECM lapping. The surface finishing of a hole shape is demonstrated with the complex machining technology.     

Numerical simulation and experimentation of a novel micro scale laser high speed punching

A novel process technology for micro punching of thin sheet metals is presented in this paper. The laser induced shock waves act as the micro punch. The forming speed can be controlled by adjusting the laser energy. Micro holes of 250 μm in diameter were successfully punched on sheet metal of 10 μm in thickness by single pulse, and good edge quality was obtained. The micro die-opening is produced by electrical discharge machining (EDM) using the copper electrode of φ=220 μm. In the experiment, a sacrificial coating is used to generate high-pressure plasma under a laser pulse, so no signs of melting, burning, or ablation were observed on the workpiece. The novel process of micro scale laser high speed punching is also numerically studied. In addition, this method can be used to fabricate noncircular micro holes on thin sheet metals with noncircular micro die-openings. With further development, laser high speed punching may become an important micro punching technology, which is characterized by non-contact, low cost, and high efficiency.     

Chatter suppression in micro end milling with process damping

Micro milling utilizes miniature micro end mills to fabricate complexly sculpted shapes at high rotational speeds. One of the challenges in micro machining is regenerative chatter, which is an unstable vibration that can cause severe tool wear and breakage, especially in the micro scale. In order to predict chatter stability, the tool tip dynamics and cutting coefficients are required. However, in micro milling, the elasto-plastic nature of micro machining operations results in large process damping in the machining process, which affects the chatter. We have used the equivalent volume interface between the tool and the workpiece to determine the process damping parameter. Furthermore, the accurate measurement of the tool tip dynamics is not possible through direct impact hammer testing. The dynamics at the tool tip is indirectly obtained by employing the receptance coupling method, and the mechanistic cutting coefficients are obtained from experimental cutting tests. Chatter stability experiments have been performed to examine the proposed chatter stability model in micro milling.     

Size effects of micro drilling in steel

The main objective of this research work is to investigate size effects by downscaling the twist drilling process into the micro range (diameter: d = 50 μm to 1 mm). Therefore, experimental micro drilling tests in steel AISI 1045 (normalized and full-annealed) are performed with different cutting conditions (drill diameter, feed, cutting speed) and compared with data obtained from conventional drilling. Various size effects and its significant influence on the micro cutting process are characterized with help of the experimental results. Additionally, the formula of Victor–Kienzle is adjusted to model the feed force in micro drilling operations.     

Wear behaviour in a combined micro blanking and deep drawing process

A one stroke micro blanking and deep drawing process is used to produce micro cups in a high quantity (200 strokes per minute) with an outer diameter of 1 mm. For cutting and deep drawing one single hollow punch is used. The outer diameter punches the circular blank while the inner diameter serves as drawing ring. Investigations regarding the tool life show that the punching edge wears out quicker than the rest of the tool. Furthermore it is shown that the positioning of the tool has a high influence on the wear behaviour.     

微细倒锥孔在线加工参数调控的电火花加工工艺

基于微细孔电火花加工中观测到的“腰鼓”现象,进行了微细倒锥孔的在线加工参数调控电火花加工工艺的研究.实验研究了开路电压、进给深度、变压深度、放电电容等加工参数对微孔加工孔形的影响.通过对工艺参数的优化选择,加工得到出入口直径平均相差18.6 μm、锥度为1.16°的倒锥孔,可用于柴油发动机倒锥喷孔的加工.进一步实验了工...     

High surface quality micro machining of monocrystalline diamond by picosecond pulsed laser

In micro machining of monocrystalline diamond by pulsed laser, unique processing characteristics appeared only under a few ten picosecond pulse duration and a certain overlap rate of laser shot. Cracks mostly propagate in parallel direction to top surface of workpiece, although the laser beam axis is perpendicular to the surface. This processed area can keep diamond structure, and its surface roughness is smaller than R_a = 0.2 μm. New laser micro machining method to keep diamond structure and small surface roughness is proposed. This method can contribute to reduce the polishing process in micro machining of diamond.