• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.1
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• pp.90-94
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• 2022

Metal 3D-printing technology enables the manufacture of complex features or internal structures, which is not possible in fabrication by conventional cutting methods. The most successful types of metal 3D printing have been powder bed diffusion and directed energy deposition, which use laser heads exploiting high-power laser sintering metal powder. In this study, a cost-effective optical design was proposed for a 2-kW-level fiber laser head. Only two commercial lenses, a beamsplitter and a window, are used in the laser head, satisfying the technological requirements. According to the optical design, the spot size was 2.54 mm, and the stand-off distance from the laser head was 295 mm. The intensity distribution was Gaussian. Thus, smooth power sintering was possible without any laser spot marks. Monte Carlo analysis was employed to verify the consistency of the optical performance under conventional assembly tolerance.

• Journal of Dental Rehabilitation and Applied Science
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• v.32 no.3
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• pp.246-254
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• 2016

Nowadays, 3 dimentional (3D) printing, especially Direct Metal Laser Sintering (DMLS) system is used in dentistry. DMLS system has recently been introduced for fabrication metal framework for metal ceramic crowns to overcome the disadvantages of the casting method and computer aided design/computer aided manufacturing (CAD/CAM) milling system. DMLS system uses a high-temperature laser beam to selectively heat a substructure metal powder based on the CAD data with the framework design. A thin layer of the beamed area becomes fused, and the metal framework is completed by laminating these thin layers. Utilizing DMLS system to fabricate fixed prostheses is expected to achieve free-from shaping without mold and limitations from cutting tools, fabricate prostheses with complex geometry, prevent distortion and fabrication defects that inherent to conventional fabrication methods. The purpose of this case report is to demonstrate various fixed prostheses such as long span fixed prostheses, post to achieve satisfactory results in functional and esthetic aspects.

• Journal of the Optical Society of Korea
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• v.7 no.4
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• pp.230-233
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• 2003

This study describes the conceptual design of a soft x-ray microscope system based on a laserbased source for biomedical application with high resolution (${\leq}$50nm). The laboratory scale soft x-ray microscope consists of high power laser plasma x-ray source and grazing incidence mirrors with high reflectivity. The laser plasma source used for developing this system employs Q-switched Nd-YAG pulsed laser. The laser beam is focused on a tantalum (Ta) target. The Wolter type I mirror was used as condenser optics for sample illumination and as objective mirror for focusing on a detector. The fabrication of the Wolter type I mirror was direct internal cutting using ultraprecision DTM. A hydrated biological specimen was put between the two silicon wafers, the center of which was $Si_3N_4$ windows of 100㎚ thickness. The main issues in the future development work are to make a stable, reliable and reproducible x-ray microscope system.

• Proceedings of the IEEK Conference
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• 2002.06e
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• pp.91-94
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• 2002

SFFS(Solid Freeform Fabrication System) is commercializing to rapid prototyping concept in foreign some corporations including the U.S.A, have much technological problems yet and need new mode for agile prototyping. In this paper, we design algorithm that the cutting path of laser beam, on the SFFS(Solid Freeform Fabrication System), is controlled with constant speed. The designed algorithm for constant-speed path control is implemented and experimented in the CAFL$\^$VM/ (Computer Aided Fabrication of Lamination for Various Material) system, the new SFFS which was developed in this paper.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1253-1256
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• 2005

An Experiment was carried out to study burr minimization in drilling on the inclined exit surface. Several different drills, exit surface angles and cutting conditions were selected to determine their influences on burr formation. In drilling operation, there are not only flat exit surfaces but also inclined exit surfaces which is described as inclination angle. Inclination of exit surface causes a quiet different burr formation when comparing with flat surface. Burr formation mechanisms are analyzed according to the drill geometries and cutting conditions. Several schemes for burr minimization on inclined exit surface were proposed. Burr geometry in each drill and cutting condition are measured by laser measurement system.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.1137-1140
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• 2005

Automatic welding has been used frequently on pipeline projects. The productivity and reliability are most essential features of the automatic welding system. The mechanized GMAW process is the most widely used welding process and the carriage and band system is most effective welding system for pipeline laying. This application-oriented paper introduces new automatic welding equipment for pipeline construction. It is based on cutting-edge design and practical welding physics to minimize downtime. This paper also describes the control system which was designed and implemented for new automatic welding equipment. The system has the self diagnostic function which facilitates maintenance and repairs, and also has the network function via which the welding task data can be transmitted and the welding process data can be monitored. The laser vision sensor was designed for narrow welding groove in order to implement higher accuracy of seam tracking and fully automatic operation.

• Journal of Welding and Joining
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• v.25 no.3
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• pp.78-84
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• 2007

Laser Material Processing has been replaced the conventional machining systems - cutting, drilling, welding and surface modification and so on. Especially, LTH(Laser Transformation Hardening) process is one branch of the laser surface modification process. Conventionally, some techniques like a gas carburizing and nitriding as well as induction and torch heating have been used to harden the carbon steels. But these methods not only request post-machining resulted from a deformation but also have complex processing procedures. Besides, LTH process has some merits as : 1. It is easy to control the case depth because of output(laser power) adjustability. 2. It is able to harden the localized and complicated a.ea and minimize a deformation due to a unique property of a localized heat source. 3. An additional cooling medium is not required due to self quenching. 4. A prominent hardening results can be obtained. This study is related to the surface hardening of the rod-shaped carbon steel applied to the lathe based complex processing mechanism, a basic behavior of surface hardening, hardness distribution and structural characteristics in the hardened zone.

• Journal of the korean academy of Pediatric Dentistry
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• v.28 no.4
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• pp.683-693
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• 2001

The purpose of this study was to evaluate the effects of Er:YAG laser on cutting efficacy and its histologic findings. Dentin specimens of human premolars and molars were used and irradiated by Er:YAG laser with noncontact handpiece type delivery system under different treatment condition of irradiation time. Cavity pattern and volume were evaluated to determine the cutting efficacy and following results were obtained. 1. Cutting volume of sound dentin was getting larger with time immersed in water increase 2. With the condition of irradiation (150mJ, 10Hz, 30sec), surface irregularity was more increased in sound dentin comparing to carious dentin. For the light microscopic examination, dentinal tubules were opened and ash flecks and cracks were noted with inconsistence of dentinal tubules. 3. In case of 30 sec. irradiation in carious dentin, dark zone was limited to small focus whereas 1 min. irradiation, more wider, and cracks were noted in the perpendicular to direction of dentinal tubules. For the 2 min. irradiation, cavity was the widest and more cracks were found.

• Proceedings of the KAIS Fall Conference
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• 2002.11a
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• pp.260-262
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• 2002

제품의 소재를 미리 테입 형태로 만들어 단면의 경계면을 따라 레이저로 절단하여 적층하는 방식은 제품의 표면에 계단 모양의 무늬가 생기므로 정밀한 제품을 제작하는데 어려움이 있었다. 이를 극복하기 위하여 단면의 경계선을 절단할 때 수직으로 절단하는 것이 아니라 경사면을 따라 절단하여 전체적인 제품의 옆면이 부드럽게 연결되는 경사절단형 임의형상가공시스템을 개발하였다. 이를 위하여 레이저 5축 경사절단기를 개발하였는데, x축과 y축은 상용화되어 있는 x-y table을 이용하였고 z축은 한 개의 z축 이송대를 이용하였다. 롤과 피치를 위하여는 서보모터 두 개를 이용하여 작업대가 회전할 수 있도록 하였다. 이와 같은 레이저 5축 경사절단기를 개발함으로써 시편의 어느 위치에서든 어느 각도로도 절단이 가능하게 할 수 있었다.

• Proceedings of the KOSOMBE Conference
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• v.1996 no.11
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• pp.192-196
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• 1996

[ $1.06/1.32{\mu}m$ ] dual-wavelength medical laser was developed and preliminary clinical comparisons at these two wavelengths were performed for dental application. We could develop a compact laser system 1) by lasing two wavelengths from the same Nd:YAG rod, and 2) by introducing high-voltage switching power supply modules. Experiment on gingiva of pig jaw showed higher thermal damage at $1.32{\mu}m$. Depending on particular procedures, each wavelength has its own advantages and disadvantages. For cutting, however, using conical tips rather than bare fibers provided better results with low threshold of cutting energy and less surrounding thermal damage. Appling light-absorbing dye on target area appeared to induce more damage during laser irradiation. However, histological studies showed no significant difference whether dye was applied or not.