• 구강회복응용과학지
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• 제36권4호
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• pp.254-261
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• 2020

목적: 본 연구의 목적은 서로 다른 제작 방법인 절삭 가공과 적층 가공 기술로 제작된 임시 보철물의 변연 및 내면 적합도를 평가하는 것이다. 연구 재료 및 방법: 상악 우측 제1대구치를 도재 수복을 위한 지대치 모형으로 준비하였다. 석고를 이용하여 총 40개의 실험 모형으로 복제하였고, 각각의 실험 모형을 구강 스캐너를 사용하여 스캔 데이터를 획득하였다. 3종의 3D 프린터(Meg-printer 2; Megagen, Zenith U; Dentis 그리고 Zenith D; Dentis) 및 1종의 밀링 장비(imes-icore 450i; imes-icore GmbH)를 사용하여 각 그룹당 10개의 임시 보철물을 제작하였다. 임시 보철물의 내면에 실리콘을 채우고 모형에 적합하여 중합이 완료된 후, 실리콘으로 내면이 복제되어 있는 실험 모형을 구강 스캐너를 사용하여 스캔 데이터를 획득하였다. 3차원 검사 소프트웨어(Geomagic control X; 3D Systems)를 이용하여 변연 간격, 절대 변연 간격, 섐퍼, 축벽, 교두, 교합 영역의 적합도를 분석하였다. 통계 분석은 제작 방법의 차이를 비교하기 위해서 Kruskal-Wallis test를 사용하여 검증하였으며, 사후 검정을 위해서 Mann-Whitney U-test and Bonferroni correction method을 사용하였다(α = 0.05). 결과: 3종의 3D 프린터와 1종의 밀링 장비에서 제작된 임시 보철물의 절대 변연 간격은 유의한 차이를 보이지 않았다(P = 0.812). 축벽, 교합 간격에서 밀링 장비와 3D 프린터 사이에 유의한 차이를 보였다(P < 0.001). 결론: 3종의 3D 프린터로 제작된 임시 보철물의 변연 적합도는 모두 임상적 허용 범위(< 120 ㎛)에 있었으므로, 적합도 측면에서 본다면 임시 보철물 제작을 위해서 충분히 사용될 수 있다.

• 한국세라믹학회지
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• 제49권4호
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• pp.337-341
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• 2012

Mechanochemical processing (MCP) involves several high-energy collisions of powder particles with the milling media and results in the increased reactivity/sinterability of powder. The present paper shows results of mechanochemical processing (MCP) of silicon nitride powder mixture with the relevant sintering additives. The effects of MCP were studied by structural changes of powder particles themselves as well as by the resulting sintering/densification ability. It has been found that MCP significantly enhances reactivity and sinterability of the resultant material: silicon nitride ceramics could be pressureless sintered at $1500^{\circ}C$. Nevertheless, a degree of a silicon nitride crystal lattice and powder particle destruction (amorphization) as detected by XRD studies, is limited by the specific threshold. If that value is crossed then particle's surface damage effects are prevailing thus severe evaporation overdominates mass transport at elevated temperature. It is discussed that the cross-solid interaction between particles of various chemical composition, triggered by many different factors during mechanochemical processing, including a short-range diffusion in silicon nitride particles after collisions with other types of particles plays more important role in enhanced reactivity of tested compositions than amorphization of the crystal lattice itself. Controlled deagglomeration of $Si_3N_4$ particles during the course of high-energy milling was also considered.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.402-407
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• 2002

Laminate tooling process is a fast and simple method to make metal tools directly for various molding processes such as injection molding in rapid prototyping field. Metal sheets are usually cut, stacked, aligned and joined with brazing or soldering. Through the joining process, all of the metal sheet layers should be rigidly joined. When joining process parameters are not appropriate, there would be defects in the layers. Among various types of defects, non-bonded gaps of the tool surface are of great importance, because they directly affect the surface quality and dimensional accuracy of the final products. If a laminate tool with defects has to be abandoned, it could lead to great loss of time and cost. Therefore a repair method for non-bonded gaps of the surface is essential and has important meaning for rapid prototyping. In this study, a rapid laminate tooling system composed of a CO2 laser, a furnace, and a milling machine was developed. Metal sheets were joined by furnace brazing, dip soldering and adhesive bonding. Joined laminate tools were machined by a high-speed milling machine to improve surface quality. Also, repair brazing and soldering methods of the laminates using the $CO_2$ laser system have been investigated. ill laser repair process, the beam duration, beam power and beam profile were of great importance, and their effects were simulated by [mite element methods. The simulation results were compared with the experimental ones, and optimal parameters for laser repair process were investigated.

• Carbon letters
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• 제12권4호
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• pp.243-248
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• 2011

Two different types of graphite, such as flake graphite (FG) and spherical graphite (SG), were used as anode materials for a lithium-ion secondary battery in order to investigate their electrochemical performance. The FG particles were prepared by pulverizing natural graphite with a planetary mill. The SG particles were treated by immersing them in acid solutions or mixing them with various carbon additives. With a longer milling time, the particle size of the FG decreased. Since smaller particles allow more exposure of the edge planes toward the electrolyte, it could be possible for the FG anodes with longer milling time to deliver high reversible capacity; however, their initial efficiency was found to have decreased. The initial efficiency of SG anodes with acid treatments was about 90%, showing an over 20% higher value than that of FG anodes. With acid treatment, the discharge rate capability and the initial efficiency improved slightly. The electrochemical properties of the SG anodes improved slightly with carbon additives such as acetylene black (AB), Super P, Ketjen black, and carbon nanotubes. Furthermore, the cyclability was much improved due to the effect of the conductive bridge made by carbon additives such as AB and Super P.

• 한국정밀공학회지
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• 제18권2호
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• pp.199-205
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• 2001

Burr makes troubles on manufacturing process due to deburring cost, quality of products and productivity. This paper described the results of experimental study on the influence of the cutting parameters on the formation of exit burrs in face milling. Using the results of experimental study, burr types are classified and data bases are developed to predict burr formation result. From the CAD file for work geometry and the NC data for tool path, the exit angles are calculated at every edges. This program predicts the burr geometry at exit edges using the prediction algorithm and data bases which are developed experimentally. Simulation results on deformation strain and temperature are also available in specific 2-dimensional cutting conditions. Also algorithm which can determine the exit angle is proposed.

• 한국세라믹학회지
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• 제55권4호
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• pp.352-357
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• 2018

The slip casting process is widely used to make green bodies from ceramic slips into dense compacts with homogeneous microstructure. However, stress may be generated inside the green body during drying, and can lead to cracking and bending during sintering. When starting from the spherical powders with mono-size distribution to make the close packed body, interstitial voids on octahedral and tetrahedral sites are formed. In this research, experiments were carried out with powders of three size types (host powder (H), octahedral void filling powder (O) and tetrahedral void filling powder (T)) controlled for average particle size by milling from two commercial alumina powders. Slips were prepared using three different powder batches from H only, H+O or H+O+T mixed powders. After manufacturing green compacts by solid-casting, compacts were dried at constant temperature and humidity and sintered at $1650^{\circ}C$. Alumina samples fabricated from the multi-sized powder mixture had improved compacted and sintered densities.

• 한국분말재료학회지
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• 제3권3호
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• pp.181-187
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• 1996

Cobalt and VC powders were ball milled with M2 grade high speed steel powders under various ball to powder ratios. The powders milled under higher ball to powder ratio become finer, more irregular and have a broader size distribution, and thus possess a lower compressibility and a better sinterability regarding densification. Increasing the ball to powder ratio lowered the sintering temperature to obtain the density level necessary to isolate all the pores. Lowering the sintering temperature is very critical to maintain fine microstructure since grain and carbide coarsening are accelerated by higher sintering temperature due to more liquid phase formation. The powders obtained by ball milling at 20 to 1 ratio has the lowest compressibility but has the best sinterability, almost compatible to unmilled pure M2 powders. A sintered body over 97% theoretical density with fine microstructures having average grain size of ~10 microns was obtained from the powder by sintering at 1260 $^{\circ}C$ for 1 hour in vacuum. XRD results indicate that two types of carbides are mainly present in the sintered structure, MC and $M_{6}C$ type. The MC type carbides are more or less round shaped and mainly located at the grain boundaries whereas the $M_{6}C$ type are angular shaped and mainly located inside the grains.

• 한국수산과학회지
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• 제46권2호
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• pp.139-146
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• 2013

Surimi products are among the most prominent seafoods in Korea. Together with fish meat, wheat flour is a major ingredient in the preparation of surimi products. Rice flour, however, can be an effective ingredient in enhancing the rheological characteristics of surimi products. In this study, we evaluated the potential of rice flour as an agent to replace wheat flour in surimi products. The effects of rice flour milling types and addition methods on the rheological and sensory properties of surimi products were investigated. Among different addition methods, the surimi product containing non-treated rice flour showed better gel strength and sensory properties than products containing paste (1:1.3 rice flour/water, w/v) and steamed paste (steamed at $100^{\circ}C$ for 30 min). According to the gel strength results for surimi products with added roll-mill (40 mesh) and jet-mill (180 mesh) rice flours, the roll-mill rice flour shows good potential as a replacement for wheat flour. When considering gel strength and sensory properties, an effective amount of rice flour to add was 10-15% (w/w). In conclusion, the rheological and sensory properties of surimi products containing rice flour were comparable with those of a premium commercial surimi product. Therefore, rice flour might be an effective alternative to wheat flour for premium surimi products.

• 한국환경농학회지
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• 제30권4호
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• pp.409-413
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• 2011

곡류의 도정별 지방산 함량을 분석, 비교하였다. 지방산의 조성비는 시료 전체에서 0.01~54.0%범위의 분포를 보였다. 알곡에서는 총 지방산의 함량은 평균적으로 알곡에서는 23.6 mg/g, 도정곡에서는 18.3 mg/g인 것으로 나타났다. 포화지방산은 대체적으로 일부 시료를 제외하고는 도정곡보다 알곡에서 더 높은 경향을 보였으며, 반대로 불포화지방산은 알곡보다 도정곡에서 더 높은 경향을 보였다. 포화지방산량과 불포화지방산량을 비교 시 거의 모든 시료에서 불포화 지방산 이 더 많은 비율을 차지하고 있었다. 총 지질의 지방산 조성은 linoleic acid가 44.5%로 가장 높았고, 다음이 palmitic acid로 26.1%, 그리고 oleic acid가 17.7%를 차지했다. 이 세 가지 지방산은 총 지방산량의 약 89%를 차지하고 있었다. 총 지방산량은 대부분의 시료에서 알곡이 도정곡보다 더 높은 반면, 새쌀보리와 피에서는 도정곡에서 더 높게 나타났다.

• The Journal of Advanced Prosthodontics
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• 제10권5호
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• pp.388-394
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• 2018

PURPOSE. To measure axial displacement of different implant-abutment connection types and materials during screw tightening at the recommended torque by using a contact scanner for two-dimensional (2D) and three-dimensional (3D) analyses. MATERIALS AND METHODS. Twenty models of missing mandibular left second premolars were 3D-printed and implant fixtures were placed at the same position by using a surgical guide. External and internal fixtures were used. Three implant-abutment internal connection (INT) types and one implant-abutment external connection (EXT) type were prepared. Two of the INT types used titanium abutment and zirconia abutment; the other INT type was a customized abutment, fabricated by using a computer-controlled milling machine. The EXT type used titanium abutment. Screws were tightened at $10N{\cdot}cm$, simulating hand tightening, and then at the manufacturers' recommended torque ($30N{\cdot}cm$) 10 min later. Abutments and adjacent teeth were subsequently scanned with a contact scanner for 2D and 3D analyses using a 3D inspection software. RESULTS. Significant differences were observed in axial displacement according to the type of implant-abutment connection (P<.001). Vertical displacement of abutments was greater than overall displacement, and significant differences in vertical and overall displacement were observed among the four connection types (P<.05). CONCLUSION. Displacement according to connection type and material should be considered in choosing an implant abutment. When adjusting a prosthesis, tightening the screw at the manufacturers' recommended torque is advisable, rather than the level of hand tightening.