• Journal of the Korean Society for Precision Engineering
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• v.20 no.7
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• pp.227-232
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• 2003

In order to make a deep and precise micro-hole, electrode wear and clearance between the electrode and the workpiece are important parameters using micro-electrical discharge machining. In this study, experiments were carried out to show the characteristics of electrode wear and radial clearance with respect to the depth of machined hole. Electrode wear varied with respect to the depth of hole. With deeper machined hole, bigger clearance was observed. Also it was found that the diameter of electrode influences machining characteristics of deep holes.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.1
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• pp.117-129
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• 1998

Micro-hole drilling (holes less than 0.5 mm in diameter with aspect ratio larger than 10) is recently having more attention in a wide spectrum of precision production industries. Alternative methods such as EDM. laser drilling, etc. can sometimes replace the mechanical micro-hole drilling but are not acceptable in PCB manufacture because of the inferior hole quality and accuracy. The major difficulties in micro-hole drilling are related to small signal to noise ratios, wandering motions of the inlet stage, high aspect ratios, high temperatures and so forth. Of all the difficulties. the most undesirable one is the increase of drilling force as the drill proceeds deeper into the hole. This is caused mainly from the chip effects. Peck-drilling is thus widely used for deep hole drilling despite that it suffers from low productivity. In the paper, a method of cutting force regulation is proposed to achieve continuous drilling. A PD and a sliding mode control algorithms were implemented through controlling the spindle rotating frequency. Experimental results show that the sliding mode control reduces the nominal cutting force and the variation of the cutting force better than the PD control. The advantages of the regulation, such as increase of drill life, fast stabilization of a wandering motion, and the precise positioning of the hole are verified in experiment.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2004.04a
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• pp.48-52
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• 2004

Ultrasonic machining is effective for machining of extreme hard and brittle materials, including glass, ceramic, carbide, graphite. The major machining principle involves the direct hammering as well as the impact of abrasive panicles on the workpiece. Also, it involve cavitation erosion. The general workpiece is flat side. This study attempted micro hole machining of a curved surface of glass tube. Ultrasonic machining is fault of the slow machining speed. An experiment does and got 16 seconds validity machining time as increasing the processing speed. Moreover, entrance crack and surface roughness was similar both machining speed is slow and fast. Several micro hole of glass tube machined using one micro tool, but tool wear is infinitesimal.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1052-1058
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• 2003

The possibility of micro/nano machining through electro-chemical process is discussed in this research. Electro-chemical dissolution region is localized within 1 ${\mu}m$ by applying ultra short pulses with tens of nanosecond duration. The effects of voltage, pulse duration, and pulse frequency on the localization distance are investigated. Localization distance can be manipulated by controlling the voltage and pulse duration, and various hole shapes are produced including stepped holes and taper free hole. High quality micro-hole with 8 ${\mu}m$ diameter with 20 ${\mu}m$ depth and micro-groove with 9 ${\mu}m$ width with 10 ${\mu}m$ depth are machined on 304 stainless steel.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.202-205
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• 2002

The micro-extruding die is a die for manufacturing of fine-wire by extruding process. The fine-wire made from the micro-extruding can be effectively applied to fields of semiconductor parts and medical parts etc. It is predicted that the demand of fine-wire in industry is more and more increasing. In this study $\Phi$ 50${\mu}{\textrm}{m}$ micro-drill which is coated with diamond is used for drilling of super micro-hole sues. For the machining of taper parts of entrance and exit, drill having $\Phi$ 9mm inclination angle 20$^{\circ}$ is used. This is useful for anti tool-breakage in drilling process. After micro-drilling, the polishing process by abrasive is carried out for increasing surface roughness.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1147-1154
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• 1990

Micro-hole drilling by EDM and production of fine rods for the tool electrode or other purpose have become very important in industry. This paper suggests a new method for production of very fine rods by ultrasonic-assisted chemical machining and describes the machining characteristics of micro-hole drilling by EDM. For fine rods, copper wires of initial diameter of 250.mum are used and successfully machined into a diameter of less than 30.mum with good repeatability. The ultrasonic agitation not only accelerated the material removal rate uniformly, but also produced smooth surfaces of fine rods. To drill the micro-hole, kerosene and pure water is used as a dielectric. From the experiment, water is superior to kerosene with respect to surface roughness of inlet and outlet of hole and machined surface as well as electrode wear. However, due to the electrochemical reaction of water, small pits are remained on the workpiece surface.

• Journal of ILASS-Korea
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• v.21 no.1
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• pp.58-63
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• 2016

This study presents the dynamic characteristics of an impinging droplet on hydrophobic and hydrophilic surfaces with various texture area fractions. The flat surface was fabricated by using the drilling technique to make micro-meter hole-patterned surfaces, which shows hydrophobic textured surfaces. Moreover, the hydrophilic textured surfaces were manufactured by anodizing technique on the micro-meter hole-patterned surfaces to generate multi-layer surfaces. Impinging droplet experiments were conducted for various hole-patterned surfaces, with changing impact velocity and texture area fractions. It is observed that an anodizing technique increases wettability by decrease in hole diameter on the textured surfaces. However, micro-drilled surfaces decreases wettability because the hole diameter was so large that air can be trapped under the holes. In addition, the maximum spreading diameter decreases with the texture area fraction for the micro-drilled surfaces because of decrease in wettability.

• Journal of the Semiconductor & Display Technology
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• v.20 no.3
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• pp.77-82
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• 2021

This numerical study focuses on the analysis of fume particle dispersion characteristics over the surface of target workpiece in laser micro-hole machining process. The effects of oblique stagnation flow over fume generating machining point are examined by carrying out a series of three-dimensional random particle simulations along with probabilistic particle generation model and particle drag correlation of low Reynolds number. Present computational model of fume particle dispersion is found to be capable of assessing and quantifying the fume particle contamination in precision hole machining which may influenced by different types of air flow patterns and their flow intensity. The particle size dependence on dispersion distance of fume particles from laser machining point is significant and the effects of increasing flow oblique angle are shown quite differently when slot blowing or slot suction flows are applied in micro-hole machining.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.5
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• pp.842-849
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• 1997

The aim of this study is an investigation of the interaction of two micro hole defects affecting fatigue crack initation life and propagation behavior. The locatio of two micro hole defects was considered as an angle of alignment and the distance between the centers of two micro hole defects. The fatigue cracking behavior is experimented under bending. When micro defects are located close to each other, the fatigue crack initiation lives are varied with their relative locations. In the experiments, the area of local plastic strain strongly played a role in the fatigue crack initiation lives. Therefore we introduce a parameter which contains the plastic deformation area at stress concentrations and propose a fatigue crack initiation life prediction curve. In addition, the directions and propagation rates of fatigue cracks initiated at two micro hole defects are studied experimentally.

• Journal of Mechanical Science and Technology
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• v.14 no.10
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• pp.1021-1027
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• 2000

In this study, fatigue tests were performed to examine the effects of micro drill hole on fatigue limit of as cast and austempered ductile cast iron (ADI) using the rotary bending fatigue tester. As results, micro drill holes ($diameter{\leq}0.4mm$) did not influence the fatigue limit of ADI, compared to annealed ductile cast iron; the critical defect size of crack initiation, in ADI was larger than as cast. If the ${\sqrt{area}}$ of micro drill hole and graphite nodule in ADI are comparable, crack initiates at the graphite nodule. When the ruggedness developes through austempering treatment process, microstructure on crack initiation at micro drill hole is tougher than that of as cast ductile cast iron.