• Structural Engineering and Mechanics
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• 제75권3호
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• pp.369-376
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• 2020

The life of conventional steel plastic injection molds is long but manufacturing cost and time are prohibitive for using these molds for producing prototypes of products in limited numbers. Commonly used 3D printers and rapid prototyping methods are capable of directly converting the digital models of three-dimensional solid objects into solid physical parts. Depending on the 3D printer, the final product can be made from different material, such as polymer or metal. Rapid prototyping of parts with the polymeric material is typically cheaper, faster and convenient. However, the life of a polymer mold can be less than a hundred parts. Failure of a polymeric mold during the injection molding process can result in serious safety issues considering very large forces and temperatures are involved. In this study, the feasibility of the inspection of 3D printed molds with the surface response to excitation (SuRE) method was investigated. The SuRE method was originally developed for structural health monitoring and load monitoring in thin-walled plate-like structures. In this study, first, the SuRE method was used to evaluate if the variation of the strain could be monitored when loads were applied to the center of the 3D printed molds. After the successful results were obtained, the SuRE method was used to monitor the artifact (artificial damage) created at the 3D printed mold. The results showed that the SuRE method is a cost effective and robust approach for monitoring the condition of the 3D printed molds.

• Design & Manufacturing
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• 제12권3호
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• pp.36-41
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• 2018

Metal 3D printing is very useful for making the injection molds containing complex conformal cooling channels. The most important issue of the 3D printed molds is cost and life cycle. However, powder bed fusion (PBF) methods are vulnerable to fatigue loading because of the presence of pores and rough surfaces. In the present study, the fatigue test was performed to obtain fatigue analysis input data for predicting the durability of a 3D printed injection mold core. The metal 3D printer used to manufacture the specimen was OPM250L from Sodick, and the metal powder material was maraging steel. The ultrasonic fatigue testing method was adopted for the fatigue test. A key advantage of the ultrasonic fatigue method is that $10^8{\sim}10^9$ long cycle test data or more could be obtained within a relatively short period. Based on the results of the experiment, the effect of heat treatment was negligible. However, there was an apparent difference in durability depending on the presence or absence of the surface treatment.

• Design & Manufacturing
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• 제14권1호
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• pp.49-55
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• 2020

In this study, the fatigue behavior and fatigue life characteristics of PA2200 specimens fabricated by SLS 3D printer were studied. Fatigue tests were performed according to the standard specification (ASTM E468) and fatigue life curves were obtained. In order to perform the fatigue test, mechanical properties were measured according to the test speed of the simple tensile test, and the self-heating temperature of the specimen according to the test speed was measured using an infrared temperature measuring camera in consideration of heat generation due to plastic deformation. There was no significant difference within the set test speed range and the average self-heating temperature was measured at 38.5 ℃. The mechanical strength at the measured temperature showed a relatively small difference from the mechanical strength at room temperature. Fatigue test conditions were established through the preceding experiments, and the loading conditions below the tensile strength at room temperature 23 ℃ were set as the cyclic load. The maximum number of replicates was less than 100,000 cycles, and the fracture behavior of the specimens with the repeated loads showed the characteristics of Racheting. It was confirmed that SLS 3D printing PA2200 material could be applied to the Basquin's S-N diagram for the fatigue life curve of metal materials. SEM images of the fracture surface was obtained to analyze the relationship between the characteristics of the fracture surface and the number of repetitions until failure. Brittle fracture, crazing fracture, grain melting, and porous fracture surface were observed. It was shown that the larger the area of crazing damage, the longer the number of repetitions until fracture.

• 한국의학물리학회지:의학물리
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• 제30권1호
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• pp.32-38
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• 2019

Purpose: The objective of this study is to evaluate the geometrical accuracy of a patient-specific bolus based on a three-dimensional (3D) printed mold and casting method. Materials and Methods: Three breast cancer patients undergoing treatment for a superficial region were scanned using computed tomography (CT) and a designed bolus structure through a treatment planning system (TPS). For the fabrication of patient-specific bolus, we cast harmless certified silicone into 3D printed molds. The produced bolus was also imaged using CT under the same conditions as the patient CT to acquire its geometrical shape. We compared the shapes of the produced bolus with the planned bolus structure from the TPS by measuring the average distance between two structures after a surface registration. Results and Conclusions: The result of the average difference in distance was within 1 mm and, as the worst case, the absolute difference did not exceed ${\pm}2mm$. The result of the geometric difference in the cross-section profile of each bolus was approximately 1 mm, which is a similar property of the average difference in distance. This discrepancy was negligible in affecting the dose reduction. The proposed fabrication of patient-specific bolus is useful for radiation therapy in the treatment of superficial regions, particularly those with an irregular shape.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2021년도 가을 학술논문 발표대회
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• pp.168-169
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• 2021

A hydrophobic surface increases the contact angle between water and cement paste. There are two methods to increase water contact angle, i.e. lowering the surface energy and adjusting the surface roughness of concrete. The hydrophobicity of concrete can be quantitatively evaluated according to the chemical and physical properties of the solid surface. So far, researches have shown the chemical properties of hydrophobic concrete, however it has not covered how to control surface. This study demonstrated the hydrophobic cement paste prepared by low-resolution molds printed with a 3D printer that exhibit rough surface. Thus, we presented the most hydrophobic characteristics of mold.

• 대한소아치과학회지
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• 제43권4호
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• pp.427-434
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• 2016

본 연구에서는 최근 개발된 교합면 수복용 bulk-fill resin인 Filtek Bulk Fill Posterior Restorative (FBF)와 $Tetric^{(R)}$-N-Ceram Bulk Fill (TBF)의 물성을 기존 복합레진($Filtek^{TM}$ Z-350 XT, 이하 Z-350)과 비교하여 그 효용성을 평가하고자 하였다. 재료의 중합도를 반영할 수 있는 미세경도 및 중합수축을 반영하는 미세누출 양을 염료침투실험으로 측정하였다. 실험오차를 줄이기 위하여 정형화 된 3D 프린팅 몰드에 충전하여 미세경도를 측정하고, 우치를 대상으로 미세누출을 평가하였다. 측정된 미세경도와 미세누출정도는 Kruskal-Wallis test와 Mann-Whitney test를 이용하여 95%의 신뢰도로 각 군별 유의성을 평가하였다. 하면 미세경도에서 광중합 시행 1시간 이내에는 FBF와 TBF가 Z-350에 비해 유의하게 낮은 미세경도를 보였으나(p < 0.05), 24시간 후에는 FBF의 미세경도가 Z-350과 유의한 차이를 보이지 않을 만큼 현저히 증가하였다(p > 0.05). 하면을 제외한 미세경도는 Z-350, FBF, TBF 순으로 유의한 차이를 보였으며(p < 0.05) 미세누출실험에서는 TBF가 다른 두 군에 비해 유의하게 작은 미세누출을 보였다(p < 0.05). Bulk-fill 레진의 임상적 적용을 위해서는 중합 역학의 특성 상 수복 후 24시간 동안 저작력에 대한 주의가 필요하며 미세누출량을 감소시키기 위한 추가적 연구가 필요할 것으로 사료된다.

• 한국산학기술학회논문지
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• 제22권2호
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• pp.632-637
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• 2021

현재 미래의 건설 산업 기술을 발전시키고자 최근 미래 산업으로 각광받고있는 3D 프린팅을 이용한 콘크리트의 시공기술을 활용하여 구조물을 건설하는 연구가 국내외 건설업계 및 학계에서 활발히 진행되고 있다. 하지만 현재 개발되고 있는 3D 프린팅 기술은 적합한 시공기술, 콘크리트 재료 자체의 물성이 사용기준에 미치지 못하고 실제 현장에서 적용하기가 어려운 상황이다. 또한 시공된 구조물에 대한 내구성 관리 및 유지관리를 위한 연구가 필요한 실정이다. 본 연구에서는 Material extrusion 방식으로 출력한 3D 프린팅 콘크리트를 각각의 적층 방향 X, Y, Z축으로 나누어 측정한 압축강도와 휨강도를 기존의 몰드에 제작한 시험체와 비교 분석하였다. Test direction II Z축의 시험체의 압축강도가 나머지 Test direction I, III Y축, X축의 시험체에 비하여 8~10%의 높은 강도를 발현하였고 몰드 제작 시험체와 비교하였을 경우 4%가량 낮은 강도를 발현하였다. 휨강도 측정결과 재령 28일 기준으로 Test direction II Z축 방향의 시험체의 휨강도가 Test direction I, III Y축, X축의 시험체에 비하여 5~7%의 높은 강도를 발현하였고 몰드 제작 시험체와 비교하였을 경우 2%가량 낮은 강도를 나타내었다.

• 정보과학회 논문지
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• 제43권5호
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• pp.516-523
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• 2016

노역분장을 위해서는 석고로 연기자의 얼굴 모형을 만들고, 그 위에 주름을 조소작업한 후 다시 석고로 음각 몰드를 제작하여 얼굴에 붙일 실리콘 피부 패치를 만들게 된다. 이러한 처리 과정은 며칠이 걸리며 연기자나 분장사에게 어려움을 주고 있다. 최근에 3D 프린팅 및 스캐닝 기술이 발전하여, 얼굴을 스캔하여 실물로 제작하는 것이 쉬워지고 있다. 본 논문에서는 석고나 조소작업 없이 노역분장용 실리콘 마스크를 간편하고 효율적으로 제작하기 위해, 얼굴 스캐닝, 인터랙티브 주름 모델링, 몰드 프린팅으로 이루어진 새로운 파이프라인을 제안한다. 고해상도 얼굴 모델에서도 주름을 실시간에 생성하기 위해 노멀맵 기반의 직관적인 스케치 인터페이스를 제시한다. 그리고 최종적인 주름의 기하를 깊이맵을 이용하여 복원하고, 주름진 얼굴의 음각 몰드를 프린팅한다. 또한 완성된 음각 몰드에 실리콘을 부은 뒤 원래의 양각 얼굴을 겹쳐 실리콘 마스크를 제작함으로써, 제안 파이프라인이 기존 방식보다 노역분장용 마스크를 간편하게 제작할 수 있음을 보인다.

• 대한소아치과학회지
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• 제44권1호
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• pp.82-88
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• 2017

본 연구의 목적은 0.2% 클로르헥시딘이 함유된 $Peak^{(R)}$ Universal Bond (PUB)의 우치 상아질에서의 전단결합강도를 알아보는 것이다. 30개 우치의 상아질 시편을 10개씩 세 군으로 나누어 I군에는 $Adper^{TM}$ Single Bond Universal (SB)를 적용하였고 II군에는 $Consepsis^{(R)}$를 처리한 이후 SB를 적용하였고 III군에는 PUB를 적용하고 $Filtek^{TM}$ Z-350 XT B3 shade를 충전후 각각의 전단결합강도를 비교 평가하였다. 그 결과 산부식 후 $Consepsis^{(R)}$를 사용하는 것은 상아질의 전단결합강도에 있어 통계학적으로 유의한 차이를 보이지 않았다(p > 0.05). SB에 $Consepsis^{(R)}$를 적용하거나 적용하지 않은 것의 전단결합강도와 PUB의 전단결합강도는 통계학적으로 유의한 차이를 보였다(p < 0.05).

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2023년도 봄 학술논문 발표대회
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• pp.91-92
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• 2023

With the development of technology, interest in the implementation of free-form buildings is increasing, and research on producing free-form panels is being conducted accordingly. Since free-form buildings are curved and consist of geometric shapes, there are many problems with the production technology of free-form panels that implement them. Due to the inability to reuse molds, the cost of disposal of construction waste and waste of manpower for assembly increase the construction period and construction cost. To improve these limitations, a 3D printed concrete nozzle for FCP production was developed. However, this technology is not quantitatively extruded according to the shape of the panel, and there is a problem that residues are generated. Therefore, an free-form panel extrusion experiment was conducted to analyze the limitations of existing nozzles and to analyze the requirements for the development of new concrete extrusion nozzles. Existing nozzles were unable to be quantitatively extruded, resulting in errors. Due to the weak pressure of the screw and the inability to adjust the internal pressure, detailed extrusion speed control was impossible, and residue generation in the opening and closing device seemed to be the cause. Therefore, a pump capable of quantitative concrete pressure transfer and a pressure control device for easy extrusion of concrete are required. In addition, it is judged that it is necessary to develop an opening and closing device and an extrusion device that do not generate residues. The results of this study are expected to provide information for FCP production and production and to be a basic study of technologies necessary for the production of free-form building panels.