• The Journal of Korean Academy of Prosthodontics
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• v.54 no.3
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• pp.226-233
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• 2016

Purpose: The purpose of this study was to evaluate the adaptation of lithium disilicate crowns fabricated by CAD-CAM (computer aided design-computer aided manufacturing) and heat-press technique to compare two different measurement methods in assessing fit of the ceramic crowns: micro CT and cross-section technique. Materials and methods: A prepared typodont mandibular molar for ceramic crown was duplicated and ten dies were produced by milling the PMMA (polymethylmethacrylate) resin. Ten vinyl polysiloxane impressions were made and stone casts were produced. Five dies were used for IPS e.max Press crowns with heat-press technique. The other five dies were used for IPS e.max CAD crowns with CAD-CAM technique. Ten lithium disilicate crowns were cemented on the resin dies using zinc phosphate cement with finger pressure. The marginal and internal fits in central buccolingual plane were evaluated using a micro CT. Then the specimens were embedded and cross-sectioned and the marginal and internal fits were measured using scanning electronic microscope. The two measurement methods and two manufacturing methods were compared using Mann-Whitney U test (SPSS 22.0). Results: The marginal and internal fit values using micro CT and cross-section technique were similar, showing no significant differences. There were no significant differences in adaptation between lithium disilicate crowns fabricated with CAD-CAM and heat-press technique. Conclusion: Both micro CT and cross-section technique were acceptable methods in the evaluation of marginal and internal fit of lithium disilicate crown. There was no difference in adaptation between lithium disilicate crowns fabricated with CAD-CAM and heat-press technique except occlusal fit.

• Design & Manufacturing
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• v.12 no.2
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• pp.46-50
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• 2018

Recently, as machine components and products are getting smaller, it is demanded to develop superprecision production technologies multilaterally. Along with the advancement of production technology, people are paying keener attention to the development of eco-friendly technology and efficient processing technology. Particularly, in many industries related to automobiles, shipbuilding, or airplane components, it is demanded to obtain technology to process multiple micro-holes. On account of this trend, micro-hole processing employing high-power electron beams is rising nowadays, and more interest is being shown in it, too. In Korea, however, the process of manufacturing vaporized amplification sheets influencing high-power electron beam processing technology and the processability considerably has not been developed sufficiently yet. Therefore, this study has applied vaporized amplification sheets manufactured to analyze the processability of high-power electron beams and examine necessity for vaporized amplification sheets.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.5
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• pp.773-777
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• 2012

Recently UV laser micromachining processes is widely introduced to meet the needs of advanced components of IT, BT and ET industries. Due to the characteristics of non-contact and high-speed laser processing, UV laser micromachining is applied to manufacture very thin substrate such as polymer, metals and composite. These minimum line width obtained by UV laser micromachining is generally determined from laser wavelength, optical lens and its numerical aperture. In this paper we will show the lens effect of water droplet on the surface of workpiece to reduce the line width when UV laser light is irradiated and focused through the water droplet. Because of the refraction effect generated by the semi-spherical or spherical shape of water droplet, we can find smaller line width. And water droplet could not only protect thermal deformation, but also carry away burr around micro dent. Firstly fundamental theory of minimum line width was derived from relationship between the geometry of water droplet and laser light trace, and then experimental and simulation results will be finally compared to verify the effectiveness of water droplet lens effect of UV laser micromachining process.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.7
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• pp.8-13
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• 2019

As increasing demand for precise machining in advanced disciplines, especially in semi-conductor, aeronautical and automotive industries, the magnetic abrasive deburring(MAD) which is able to eliminate micro-sized burr on complex surface in less time has drawn the attention in the last decades. However, the performance of MAD is subject to shape and size of a tool. Therefore, this study aim to identify deburring behavior of MAD in U-type flow channel by measuring the length rate of burr removal in radial distance of the cylindrical tool under four process factors. In order to evaluate the deburring effect of MAD on the surface, finishing regions are divided based on center of the circular cutting tool. As a results, it was defined that the amount of burr removal in a downward direction moving toward flow channel from the top surface was higher than upward direction. This is because the magnetic abrasives were detached from magnetic lines of force due to geometrical shape.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.4
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• pp.97-103
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• 2018

Force is a crucial element to be measured in various industries, especially the machine tool industry. Mega units of force are required in fields such as the heavy and ship industries. Micro/nano units of force are required for microparticles. The detection of force generates a physical transformation due to the force imposed from the outside, atlrnd electrical voltage signals are obtained from the system. For the detection of force, an octagonal ring load cell based on circular ring theory is designed and produced. To design the octagonal strain ring, theoretical values with data from the ANSYS program are compared to determine the size of the octagonal strain ring. An octagonal strain ring of the chosen size is made with the SCM415 material. The strain gauges are attached to the octagonal strain ring, designed to construct a full Wheatstone bridge. The LabVIEW program is used to measure the data, and strain values are found. With the octagonal ring load cell completed in this way, experiments are conducted by imposing forces on the tangential axis and radial axis. Experiments are performed to verify if the octagonal ring load cell conducts measurements properly, and theoretical values are analyzed to find any differences. The data will later be used in further research to develop a machine-tool dynamometer.

• The Journal of Korean Association of Computer Education
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• v.14 no.1
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• pp.175-185
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• 2011

Recently RFID systems have been introduced in place of barcode systems to industries such as logistics, distribution, and manufacturing. Due to security vulnerabilities in wireless communication between the reader and tags, however, the authentication protocols for the communication have also been researched extensively. In order to solve the vulnerability of previously proposed protocols, this paper thus proposes an authentication protocol that satisfies the security requirements in the RFID system and minimizes the quantity of computation such as random number generation, transmitting the micro-time of databases. In addition, it is expected that the proposed cross authentication protocol is safe against replay attack, spoofing attack, traffic analysis, and eavesdropping attack when it is applied to the RFID system. Also, it has advantages such as providing a high level of security at a lower manufacturing cost.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.314-317
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• 2006

Electroformed part is widely used in modem manufacturing industries, especially semi-conductor division. It is basically a specialized form of electroplating. So, it has very similar parameters with electroplating. The object of this study is development of the fine metal mask by electroforming process. In this paper considered two parameters. The first is relationship of UV exposure and soft baking time. The other one is thickness uniformity of electroformed parts by distance of between electrodes. This paper presents the fabrication method of fine metal mask by electroforming process.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.10 no.4
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• pp.97-103
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• 2001

The study on the high-speed machine tool is very important for the improvement of productivity since it can shortens cutting and non-cutting time. Especially, high speed of feed drive system is the major research field. In the industries of the advanced countries, the feed drive systems at the speed of 60 m/min have been already developed based on the high lead ball screws. In this study, a high speed feed drive system at the speed of 60 m/ min has been developed, and its movements characteris-tics are investigated. As the movement characteristics, positioning accuracy, angular accuracy, straightness and micro step-response are measured. Thermal characteristics of the system is also discussed. For measuring the movement characteris-tics, a laser interferometer, a memory-based Hi-coder and a cooling device are used. The experimental results confirm that the movement characteristics and the thermal behavior of the system are satisfactory in the aspect of accuracy and stability.

• KDI Journal of Economic Policy
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• v.43 no.4
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• pp.1-21
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• 2021

This paper aims to investigate whether there is empirical evidence supporting the learning-to-export hypothesis, which has received little attention in the literature. By taking full advantage of plant-product level data from Korea during 1990-1998, we find some evidence for the learning-to-export effect, especially for the innovated product varieties with delayed exporters: their productivity, together with research and development and investment activity, was superior to their matched sample. On the other hand, this learning-to-export effect was not significantly pronounced for industries protected by import tariffs. Thus, our empirical findings suggest that it would be desirable to implement certain policy tools to promote the learning-to-export effect, whereas tariff protection is not justifiable for that purpose.

• The Journal of the Korea institute of electronic communication sciences
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• v.8 no.7
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• pp.979-986
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• 2013

Recently, in the electric, electronic, robotic, and medical industries, a great attention has been paid to the development of MEMS-based smart devices with a compact size and highly intelligency. The MEMS technology is very effective in designing into a compact size and lightweight by combining into one the complex electrical, mechanical, chemical, and biological features which are required by smart devices, and at the same time, in bulk batch manufacturing. Therefore, this study, to prepare for upcoming new MEMS-based technological paradigm, analyzes MEMS processes and then considers its Applications.