• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.499-500
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• 2006

The electrode wear in micro-EDM significantly deteriorates the machining accuracy. In this regard, electrode wear needs to be compensated in-process to improve the product quality. Therefore, there are substantial amount of research about electrode wear. In this study a control method for micro-EDM using discharge pulse counting is proposed. The method is based on the assumption that the removed workpiece volume is proportional to the number of discharge pulses, which is verified from experimental results analyzing geometrically machined volume according to various number of discharges. Especially, the method has an advantage that electrode wear does not need to be concerned. The proposed method is implemented to an actual micro-EDM system using high speed data acquisition board, simple counting algorithm with 3 axis motion system. As a result, it is demonstrated that the volume of hole machined by EDM drilling can be accurately estimated using the number of discharge pulses. In EDM milling process a micro groove without depth variation caused by electrode wear could be machined using the developed control method. Consequently, it is shown that machining accuracy in drilling and milling processes can be improved by using process control based on the number of discharge pulses.

• 드라이브 ㆍ 컨트롤
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• 제14권4호
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• pp.1-8
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• 2017

The Down-the-Hole hammer is one of the pneumatic drill equipment used for grinding, drilling, and mining. One the advantages of which is that a reduction work efficiency at deep site are relatively small compared to other drilling methods. Due to the large vibration in the underground area, it is difficult to measure the performance of the hammer, and hammer testing requires substantial production cost and operating expenses so research on the development of the hammer is insufficient. Therefore, this study has developed a dynamic simulation model that apprehends the operating principles of an 8-inch DTH hammer and calculates performance data such as performance impact force, piston speed, and BPM. By using the simulation model, design factors related to strike force and BPM were selected, and the influence of each design factors on performance was analyzed through ANOVA analysis. As a result, be the most important for BPM and the strike force are position of upper port that push the piston in the direction of the bit and in BPM, the size of the empty space between the bits and the piston is the second most important design factor.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.1466-1469
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• 2004

Micro spherical lens mold processing method based on mechanical one completes a spherical shape by setting a diamond tool of hundreds $\mu$m radius on spins with high speed and then using Z-axis vertical feeding motion like the fabrication of micro drilling. In this method, we can see unprocessed parts shaped like cylinder and cone and check increasing chatter marks and burrs by setting errors of the central axis of rotation on the edge of the tool. That is why this method doesn't suit for the optical lens mold. In this paper presents unprocessed parts are disappeared and chatter marks and burrs are decreased from centre of the lens after using Run-out measuring and setting system on run-out occurred from setting tool. Also the fabrication characteristics of 6：4 Brass, A1601, PMMA are compared and analyzed, establishing the optimum machining condition on each material.

• 한국기계가공학회지
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• 제11권3호
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• pp.62-67
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• 2012

To realize 2-dimensional vibrational micro cutting in milling and drilling, etc. where the tools rotate, it could be a promising way to vibrate a workpiece instead of a rotating tool itself. In this study, an excitation work-table was developed using two piezoelectric materials orthogonally arranged. The trochoidal trajectory of a cutting tool which is necessary for 2D vibrational cutting is enabled in the excitation condition of higher excitation frequency and larger amplitude of vibration and the cutting condition of smaller diameter of cutting tool and lower spindle speed. The various trochoidal trajectories of a cutting tool could be generated in the excitation work-table by adjusting the input voltages to two piezoelectric materials and the phase between the two voltages and the trajectories could be readily used for the 2D vibrational micro cutting.

• 한국레이저가공학회지
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• 제11권1호
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• pp.25-31
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• 2008

The characteristics of femtosecond laser ablation of $Al_2O_3$ for prescision microfabrication are studied experimentally. Specifically, the process time during femtosecond laser drilling of microholes with $sub-100{\mu}m$ diameter are investigated for varying laser fluence, scan speed and beam path designs like trepanning with continuously changed start points. The accumulation of sub-micrometer size particles within the hole and the deterioration of edge clarity and roundness for decreasing hole diameter are examined and through process optimization the microdrilling with good hole quality is achieved using a femtosecond laser system (repetitionrate 1 kHz, wavelength 785 nm, pulse duration 185 fs)

• 대한산업공학회지
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• 제26권2호
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• pp.165-170
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• 2000

In order to perform a successful material cutting process, the operators are to select the suitable machining tools and cutting conditions for the cutting environment. Up to now, this has been a complicated procedure done by the data in the tool manufacturers' paper catalog and the operator's experiencial knowledge, so called heuristics. This research is motivated by the fact that using computer techniques in processing vast amount of data and information, the operator can determine the tool and cutting condition easily. In the developed program, the selection of milling cutter, insert, and components are combined to provide optimal cutting speed, depth of cut, feed rate, rpm, and power. This program also provides the selection routine for end mill, drilling, turning, and grinding where the suitable tools are selected by workpiece, holder type, cut type, and insert shape.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1991년도 춘계학술대회 논문집
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• pp.321-327
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• 1991

High power laser beams are used in a wide variety of materials processing applications such as cutting, welding, drilling and surface treatment. The CO$\sub$2/ laser is increasingly used in laser beam welding because of the highly potential advantages. High power laser welding is a high energy density, no filler metals and low heat input process to join metals. As the comparison with the conventiona welding, precision work and good fit-up to join the metals are required and maintenance is expensive at present. The principal variables of laser beam welding are the laser beam power, travel speed and bean spot size. The penetration depth during laser beam welding is directly related to the power density of the laser beam. Generally, for a constant beam size, the penetration depth increases with increasing laser beam power.

• 한국기계가공학회지
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• 제9권5호
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• pp.1-6
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• 2010

The wavelet transform is a popular tool for studying intermittent and localized phenomena in signals. In this study the wavelet transform of cutting force signals was conducted for the detection of a tool failure in turning process. We used the Daubechies wavelet analyzing function to detect a sudden change in cutting signal level. A preliminary stepped workpiece which had intentionally a hard condition was cut by the inserted cermet tool and a tool dynamometer obtained cutting force signals. From the results of the wavelet transform, the obtained signals were divided into approximation terms and detailed terms. At tool failure, the approximation signals were suddenly increased and the detailed signals were extremely oscillated just before tool failure.

• 설비공학논문집
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• 제18권4호
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• pp.370-376
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• 2006

The paper concerns an experimental study of fully developed laminar flow of a Newtonian and non-Newtonian liquid in concentric annuli with combined bulk axial flow and inner cylinder rotation. Pressure losses and skin friction coefficients have been measured for Newtonian fluid, water and non-Newtonian fluids, 0.2% aqueous of sodium carboxymethyl cellulose (CMC) and 5% bentonite solutions, when the inner cylinder rotates at the speed of $0{\sim}500$ rpm. The influences of rotation, radius ratio and working fluid on the annular flow field are investigated. And the new correlations among the skin friction coefficient, the Reynolds number and the Rossby number are presented with reasonable limits of accuracy in laminar flow regime.

• 한국기계기술학회지
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• 제20권6호
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• pp.894-900
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• 2018

Among the soft ground improvement methods, PBD is the most common construction method because it is cheap and construction is fast. However, if the ground is rigid, additional work is required. In this study, the structural safety, natural vibration, and safety angle of the steel vertical tower structure were evaluated in the development of the PBD composite perforator which can be combined with drilling work and PBD construction. Structural safety was assessed when the wind load of 20 m/s was simultaneously applied to the PBD construction load of 20 tons, the perforating operation of 25 tons, and the wind speed of 50 m/s was applied only to the wind load. The natural frequencies were evaluated up to the sixth mode, and the safety angle was evaluated for static and dynamic safety angles.