• Journal of the Korean Society for Precision Engineering
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• v.10 no.1
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• pp.126-133
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• 1993

Conventional cutting(CC) and Ultrasonic Vibration Cutting(UVC) of 20[KHz] are practised with standard lathe for fine ceramics(A1$_{2}$O$_{3}$. UVC is suggested to good cutting method for difficult-to-machine-materials and it is known to excellent cutting method to super precision cutting and elevation of productibility for general, nonferrous matals. In this research, main results to be obtained are as follows: 1. From the CC and UVC results by general lathe with sintering diamond tool, the surface roughness and roundness are improved in UVC. Also tool life is longer in UVC than CC. From the observation of machined surface, it is found that brittle fracutural material remove occured in fine ceramics cutting. 2. It is verified that the thrust force is the biggest in fine ceramics cutting, principal force is the next, and feed rate force the third and it is appear a little, on the other hand the principal force is the biggest in metal cutting, feed rate frece is the second, and thrust force is the next.

• Journal of the Korean Academy of Esthetic Dentistry
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• v.26 no.2
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• pp.68-83
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• 2017

With the increasing popularity of dental CAD / CAM, the kinds of materials that can be used and the range that can be utilized are also increasing. One of the biggest advantages of a dental CADCAM is that you can make a final prosthesis with one visit, but in case of zirconia or a complex aesthetic prosthesis, it is often difficult to make it in one day. In this case, temporary PMMA material can be used to provide a temporary crown with aesthetic and functional properties to the patient and can be used as a test crown or template for the final prosthesis. And if you are with a 5-axis milling machine in a clinic, you can make a temporary crown precisely to a large extent in a short time. In this article, various applications and clinical cases of PMMA temporary crown in the clinic will be presented.

• International Journal of Precision Engineering and Manufacturing
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• v.9 no.2
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• pp.63-68
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• 2008

Hard and brittle materials, such as Ni- and Ti-based alloys, glass, and ceramics, are very useful in aerospace, marine, electronics, and high-temperature applications because of their extremely versatile mechanical and chemical properties. One Ni-based alloy, Inconel 718, is a precipitation-hardenable material designed with exceptionally high yield strength, ultimate tensile strength, elastic modulus, and corrosion resistance with outstanding weldability and excellent creep-rupture properties at moderately high temperatures. However, conventional machining of this alloy presents a challenge to industry. Ultrasonic vibration cutting (UVC) has recently been used to cut this difficult-to-machine material and obtain a high quality surface finish. This paper describes an experimental study of the UVC parameters for Inconel 718, including the cutting force components, tool wear, chip formation, and surface roughness over a range of cutting conditions. A comparison was also made between conventional turning (CT) and UVC using scanning electron microscopy observations of tool wear. The tool wear measured during UVC at low cutting speeds was lower than CT. UVC resulted in better surface finishes compared to CT under the same cutting conditions. Therefore, UVC performed better than CT at low cutting speeds for all measures compared.

• Journal of Electrochemical Science and Technology
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• v.15 no.2
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• pp.220-241
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• 2024

Due to its unique advantages, electrochemical machining (ECM) is playing an increasingly significant role in the manufacture of difficult-to-machine materials. Most of the current ECM research is conducted at room temperature, with studies on ECM in a cryogenic environment not having been reported to date. This study is focused on the electrochemical dissolution characteristics of typical iron and nickel base alloys in NaNO₃ solution at low temperature (-10℃). The polarization behaviors and passive film properties were studied by various electrochemical test methods. The results indicated that a higher voltage is required for decomposition and more pronounced pitting of their structures occurs in the passive zone in a cryogenic environment. A more in-depth study of the composition and structure of the passive films by X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy showed that the passive films of the alloys are modified at low temperature, and their capacitance characteristics are more prominent, which makes corrosion of the alloys more likely to occur uniformly. These modified passive films have a huge impact on the surface morphologies of the alloys, with non-uniform corrosion suppressed and an improvement in their surface finish, indicating that lowering the temperature improves the localization of ECM. Together with the cryogenic impact of electron energy state compression, the accuracy of ECM can be further improved.

• Computers and Concrete
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• v.19 no.6
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• pp.651-658
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• 2017

High-performance concrete, besides aggregate, cement, and water, incorporates supplementary cementitious materials, such as fly ash and blast furnace slag, and chemical admixture, such as superplasticizer. Hence, it is a highly complex material and modeling its behavior represents a difficult task. This paper presents an evolutionary system for the prediction of high performance concrete strength. The proposed framework blends a recently developed version of genetic programming with a local search method. The resulting system enables us to build a model that produces an accurate estimation of the considered parameter. Experimental results show the suitability of the proposed system for the prediction of concrete strength. The proposed method produces a lower error with respect to the state-of-the art technique. The paper provides two contributions: from the point of view of the high performance concrete strength prediction, a system able to outperform existing state-of-the-art techniques is defined; from the machine learning perspective, this case study shows that including a local searcher in the geometric semantic genetic programming system can speed up the convergence of the search process.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.12 no.2
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• pp.23-30
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• 2003

It is very important to detect and evaluate the surface or subsurface flaws because of their influences on mechanical properties of materials. Rayleigh wave and creeping wave are commonly used for the detection of surface and subsurface flaws. These techniques, however, have following problems. Each amplitudes are remarkably affected by the surface condition and evaluation of echo pattern is usually difficult because shear wave mode propagate in the material at the same time. On the other hand, surface SH-wave which is horizontally polarized shear wave traveling along near surface layer is an attractive technique for the surface or subsurface material characterization and this technique is useful to solve the problems mentioned above. In this paper, The stability and transmission coefficient of SH waves through a viscous fluid layer is theoretically studied and simulated. Its results agreed well with the theoretical expectation for the experimental verification. These experimental results show that viscosity of couplants, thickness of couplant and surface roughness are closely related to transfer efficiency in surface SH angle beam method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.383-386
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• 2005

Low frequency heavy-weight impact noise is the most irritating noise in Korean high-rise reinforced concrete apartment buildings. This low frequency noise is generated by foot traffic due to the fact that Koreans do not wear shoes at home. The transmission of the noise is facilitated by a load bearing wall structural system without beams and columns which is used in these buildings. In order to control low frequency heavy-weight impact noise, floating floors using isolation materials such as glass-wool mat and poly-urethane mat are used. However, it was difficult to control low frequency heavy-weight impact sound using isolation material. In this study, reinforcement of concrete slab using beams and plate was conducted. Using the FEM analysis, the effect of concrete slab reinforcement using FRP(fiber-glass reinforced plastic) on the bang machine impact vibration acceleration level and sound were conducted at the standard floor impact sound test building. The $3{\sim}4dB$ floor impact vibration acceleration level and impact sound pressure level were reduced and the natural frequency of slabs were changed.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.10a
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• pp.89-94
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• 2003

Hard coatings are known to improve the performance of cutting tools in aggressive machining applications, such as high speed machining. New superhard Ti-Al-Si-W films, characterized by a nanocomposite nano-sized (Ti,Al,Si)N crystallites embedded in amorphous $Si_3 N_4$ matrix, could be successfully synthesized on WC-Co substrates by a hybrid coating system of arc ion plating(AIP) and sputtering method. The hardness of Ti-Al-Si-N film increased with incorporation of Si, and had the maximum value ~50 GPa at the Si content of 9 at.%, respectively. And the X-ray diffraction patterns of Ti-Al-Si-N films with various Si content is investigated. In this study, Ti-Al-Si-N coatings were applied to end-mill tools made of WC-Co material by a hybrid coating system. Cutting tests fir the high-hardened material (STD11,$H_R$)C62 and their performances in high speed cutting conditions were studied. Also, the tool wear and tool lift of Ti-Al-Si-N with various si(6, 9, 19) contents were measured.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.2
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• pp.48-58
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• 1995

A micro positioning system using piezoelectric actuators have very wide application region such as ultra-precision machine tool, optical device, measurement systen. In order ro keep a high precision displacement resolution, they use a position sensor and feedback the error. From the practical point of view, a high-resolution displacement sensor system are very expensive and difficult to guarantee such sensitive sensors work properly in the hard opera- tion environment of industry. In this study, a micro-positioning grinding table which does not require position sensor but uses piezoelectric voltage feedback, has been developed. It is driven by hystersis-considering reference input voltage which calculated from computer and then uses actuator/sensor characteristics of piezoelectric materials. From the result of experiments we proved a fast and stable response of micro-positioning system and suggested efficient technique to control the piezoelectric actuator. And through grinding experiments, it is revealed that a characteristics of ground surfaces transient to plastic deformation as extremely small depth of grinding.

• Journal of the Korea Convergence Society
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• v.8 no.12
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• pp.39-47
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• 2017

The Internet have increased the number of digital web documents related to the history and traditions of Korean Culture. However, users who search for creators or materials related to traditional cultures are not able to get the information they want and the results are not enough. Document classification is required to access this effective information. In the past, document classification has been difficult to manually and manually classify documents, but it has recently been difficult to spend a lot of time and money. Therefore, this paper develops an automatic text classification model of traditional cultural contents based on the data of the Korean information culture field composed of systematic classifications of traditional cultural contents. This study applied TF-IDF model, Bag-of-Words model, and TF-IDF/Bag-of-Words combined model to extract word frequencies for 'Korea Traditional Culture' data. And we developed the automatic text classification model of traditional cultural contents using Support Vector Machine classification algorithm.