In this study, a spray dryer is used to make granules of Y2O3 and YF3, and then Y5O4F7 is synthesized following heat treatment of them under Ar gas atmosphere at 600 oC. Single and binary monomer mixtures are compared and analyzed to optimize photocurable monomer system for DLP 3D printing. The mixture of HEA and TMPTA at 8:2 ratio exhibits the highest photocuring properties and low viscosity with shear thinning behavior. The optimized photocurable monomer and synthesized Y5O4F7 are therefore mixed and applied to printing process at variable solid contents (60, 70, 80, & 85 wt.%) and light exposure times. Under optimal light exposure conditions (initial exposure time: 1.2 s, basic exposure time: 5 s), YOF composites at 60, 70 & 80 wt.% solid contents are successfully printed. As a result of measuring the size of the printed samples compared to the dimensions of the designed bar type specimen, the deviation is found to increase as the YOF solid content increases. This shows that it is necessary to maximize the photocuring activity of the monomer system and to optimize the exposure time when printing using a high-solids ceramic slurry.

Recently, the demand for atypical structures with functions and sculptural beauty is increasing in the construction industry. Existing mold-based structure production methods have many advantages, but building complex atypical structures represents limitations due to the cost and technical characteristics. Production methods using molding are suitable for mass production systems, but production cost, construction period, construction cost, and environmental pollution can occur in small quantity batch production. The recent trend in the construction industry calls for new construction methods of customized small quantity batch production methods that can produce various types of sophisticated structures. In addition to the economic effects of developing related technologies of 3D Concrete Printers (3DCP), it can enhance national image through the image of future technology, the international status of the construction civil engineering industry, self-reliance, and technology export. Until now, 3DCP technology has been carried out in producing and utilizing residential houses, structures, etc., on land or manufacturing on land and installing them underwater. The final purpose of this research project is to produce marine structures by directly printing various marine structures underwater with 3DCP equipment. Compared to current underwater structure construction techniques, constructing structures directly underwater using 3DCP equipment has the following advantages: 1) cost reduction effects: 2) reduction of construct time, 3) ease of manufacturing amorphous underwater structures, 4) disaster prevention effects. The core element technology of the 3DCP equipment is to extrude the transferred composite materials at a constant quantitative speed and control the printing flow of the materials smoothly while printing the output. In this study, the extruding module of the 3DCP equipment operates underwater while developing an extruding module that can control the printing flow of the material while extruding it at a constant quantitative speed and minimizing the external force that can occur during underwater printing. The research on the development of 3DCP equipment for printing concrete structures underwater and the preliminary experiment of printing concrete structures using high viscosity low-flow concrete composite materials is explained.

Metal three-dimensional (3D) printing is an important emerging processing method in powder metallurgy. There are many successful applications of additive manufacturing. However, processing parameters such as laser power and scan speed must be manually optimized despite the development of artificial intelligence. Automatic calibration using information in an additive manufacturing database is desirable. In this study, 15 commercial pure titanium samples are processed under different conditions, and the 3D pore structures are characterized by X-ray tomography. These samples are easily classified into three categories, unmelted, well melted, or overmelted, depending on the laser energy density. Using more than 10,000 projected images for each category, convolutional neural networks are applied, and almost perfect classification of these samples is obtained. This result demonstrates that machine learning methods based on X-ray tomography can be helpful to automatically identify more suitable processing parameters.

Additive manufacturing technology, 3D printing, has been applied to various industrial fields. This production method is a production method with less material, cost and time savings, and less restrictions in shape, and is also making a leap forward in the field of eco-friendly product production. In particular, FDM (fused depositon modeling) method of extrusion lamination manufacturing is widely applied in products and medical fields. And as an alternative to mold manufacturing, it is widely used in manufacturing plastic products and parts. Therefore, this paper quantitatively and qualitatively analyzes the mechanical properties according to the processing factors of the specimen through the processing of the ABS tensile specimen printed by the FDM type 3D printer and derives the optimum value.

The 3D printing process provides a higher degree of freedom when designing ceramic parts than the conventional press forming process. However, the generation and growth of the microcracks induced during heat treatment is thought to be due to the occurrence of local tensile stress caused by the thermal decomposition of the binder inside the green body. In this study, an alumina columnar specimen, which is a representative ceramic material, is fabricated using the digital light process (DLP) 3D printing method. DTG analysis is performed to investigate the cause of the occurrence of microcracks by analyzing the debinding process in which microcracks are mainly generated. HDDA of epoxy acrylates, which is the main binder, rapidly debinded in the range of 200 to 500oC, and microcracks are observed because of real-time microscopic image observation. For mitigating the rapid debinding process of HDDA, other types of acrylates PETA, PUA, and MMA are added, and the effect of these additives on the debinding rate is investigated. By analyzing the DTG in the 25 to 300oC region, it is confirmed that the PETA monomer and the PUA monomer can suppress the rapid decomposition rate of HDDA in this temperature range.

본 연구에서는 초음파 처리가 fused deposition modeling 방식으로 젤리를 3D 프린팅 하는데 요구되는 소재 필요 요건에 미치는 영향을 연구하였다. 젤리 제형은 젤라틴 16 wt%, 설탕 40 wt%, 그리고 구연산 1 wt%이었다. 젤라틴 제형(1,300 g)을 초음파 처리(700 W, 30 분)한 후 25 ℃에서 젤리 제형의 유변학적 특성을 측정하였고, 제형으로부 터 형성된 젤의 젤 강도를 측정하였다. 젤리 제형의 프린팅 필요요건은 G’, tan δ, yield stress (τ0), phase angle (δ), flow consistency (k), relaxation exponent (n), 그리고 gel strength로 나타내었고, 각각의 값은 5410.13 Pa, 0.09, 283.09 Pa, 5.04°, 4615.61, 0.046, 그리고 17.25 N였다. 초음파 처리는 G’과 k를 각각 8634.03 Pa와 7421.97로 증가시켰고, tan δ, δ, n, 그리고 젤 강도를 각각 0.044, 2.50°, 0.025, 그리고 16.96 N으로 감소시켰다. 이로써 초음파 처리가 젤리 3D 프린팅의 소재 필요 요건 중 fidelity, solidarity, 그리고 extrudability에 영향을 미치는 것을 확인할 수 있었다. 3D 프린팅에 적합하지 않은 젤리 제형을 초음파 처리하였을 때, G’과 k값이 각각 6569.24 Pa, 4656.41로 증가하여 3D 프린팅에 적합한 소재 필요요건 범위를 만족시키는 것을 알 수 있었다. 또한 tan δ, δ, 그리고 n값은 각각 0.04, 2.05°, 그리고 8.37 N으로 감소하여 3D 프린팅 필요요건에서 벗어난 결과를 나타냈지만 각각의 필요요건 값에 근 접하는 경향으로 변화함을 알 수 있었다. 따라서 본 연구에서는 초음파 처리가 젤리를 3D 프린팅 하는데 요구되는 소재 필요요건에 미치는 영향을 확인할 수 있었고, 이로써 초음파 처리가 젤리를 3D 프린팅 하기 위한 소재의 물 성 조절 방법으로서 사용될 수 있음을 확인할 수 있었다.

젤리 제형에 대한 소르비톨의 첨가가 젤리를 fused deposition modeling 방식으로 3D 프린팅 하기 위해 요구되는 소재 필요 요건에 미치는 영향을 연구하였다. 연구에 사용된 젤리 제형은 젤라틴(10 wt%), 펙틴(7 wt%), 설탕 또는 소르비톨(30 wt%), 그리고 구연산(1 wt%)이었다. 제형의 유변학적 특성은 cup & bob geometry를 장착한 레오미터를 이용하여 25 ℃에서 frequency sweep test (0.1-100 rad/s)와 strain sweep test (0.1-100%)를 수행하여 측정하였고, gel strength는 cylinder measuring probe (p/0.5HS)가 장착된 texture analyzer를 이용하여 측정하였다. 소르비톨이 첨가된 소 재의 유변학적 특성과 gel strength는 기존의 설탕이 첨가된 소재(tan δ: 0.67, phase angle: 33.96, n: 0.40, gel strength: 5.91 N)와 비교하였을 때 tan δ, phase angle, flow behavior index (n), 그리고 gel strength가 각각 0.49, 26.02°, 0.28, 그 리고 1.92 N으로 감소하여 설탕을 대신한 소르비톨의 첨가가 젤리 3D 프린팅의 소재 필요 요건 중 fidelity, solidarity, extrudability, 그리고 gel strength에 영향을 미친다는 것을 확인하였다. 소재 필요요건에서 벗어난 제형(젤라틴(10 wt%), 펙틴(5 wt%), 설탕(30 wt%), 그리고 구연산(1 wt%))에 소르비톨을 첨가하였을 때 tan δ, phase angle, n, 그리고 gel strength가 각각 0.43, 23.08, 0.24, 그리고 1.08 N으로 감소하여 소르비톨의 첨가가 소재 필요요건에 벗어난 제형 을 소재 필요요건에 만족 시키는 방향으로 변화 시킴을 알 수 있었다. 본 연구를 통해 젤리 제형에 대한 소르비톨의 첨가를 이용한 소재 물성 조절 방법이 젤리를 프린팅 하는데 요구되는 소재 필요 요건에 미치는 영향을 확인할 수 있었고, 소르비톨 첨가가 젤리의 3D 프린팅에 사용되는 소재의 물성 조절 방법으로 사용될 수 있음을 확인할 수 있 었다.

FDM 3D printing structures have rough surfaces and require post-treatment to improve the properties. Fumigation is a representative technique for removing surface unevenness. Surface treatment by fumigation proceeds by dissolving the surface of the protruding structure using a vaporized solvent. In this study, 3D printed PVB outputs are surface-treated with ethyl-alcohol fumigation. As the fumigation time increases, the surface flattens as ethanol dissolves the mountains on the surface of PVB and the surface valleys are filled with dissolved PVB. Through the fumigation process, the mechanical strength tends to decrease, and deformation rate increases. Ethanol vapor permeates into PVB, widening the distance between chains and resulting in weak bonding strength between chains. In order to confirm the effect of fumigation only, an annealing process is performed at 80 oC for 1, 5, 10, 30, and 50 minutes and the results of the fumigation are compared.

Sand casting 3D printing uses a binder jetting method to produce a mold having complicated shape by spraying a binder on sand coated with activator. Appropriate heat treatment process in sand mold fabrication can increase the degree of polymerization to improve flexural strength. However, long heat treatment of over 24 hours decreases flexural strength and reliability due to chemical bond decomposition through thermal degradation. The main role of the activator is to control the reaction rate between the polymer chains. As a result, when the activator composition is increased from 0.15 wt% to 0.25 wt%, the flexural strength is increased by 218 N/cm2. However, excess activator (0.40 wt%) has been shown to decrease reliability without increasing flexural strength. The main role of the binder is to control the flexural strength of the specimen. As the binder composition is increased from 2.00 wt% to 4.00 wt%, the flexural strength increases to about 255 N/cm2, indicating the maximum flexural strength increase. Finally, the reliability of the flexural strength of the fabricated specimens is evaluated by a Weibull plot. Weibull modulus calculations are used to evaluate the flexural strength reliability of the specimens, and maximum reliability value of 11.7 is obtained at 0.20 wt% activator composition. Therefore, it is confirmed that this composition has maximum flexural strength reliability.

In the development of advanced ceramic tools, material improvements and design freedom are critical in improving tool performance. However, in the die press molding method, many factors limit tool design and make it difficult to develop innovative advanced tools. Ceramic 3D printing facilitates the production of prototype samples for advanced tool development and the creation of complex tooling products. Furthermore, it is possible to respond to mass production requirements by reflecting the needs of the tool industry, which can be characterized by small quantities of various products. However, many problems remain in ensuring the reliability of ceramic tools for industrial use. In this study, alumina inserts, a representative ceramic tool, was manufactured using the digital light process (DLP), a 3D printing method. Alumina inserts prepared by 3D printing are pressurelessly sintered under the same conditions as coupon-type specimens prepared by press molding. After sintering, a hot isostatic pressing (HIP) treatment is performed to investigate the effects of relative density and microstructure changes on hardness and fracture toughness. Alumina inserts prepared by 3D printing show lower relative densities than coupon specimens prepared by powder molding but indicate similar hardness and higher fracture toughness values.

When 3D printing is used practically at construction sites, there is a serious lack of studies on the conflict with construction-related laws and expected operational problems. Accordingly, the purpose of this study is to present obstacles and directions for improvement in construction-related laws (Building Act, Construction Technology Promotion Act, Housing Act, Construction Machinery Management Act, etc.) for practical operation of 3D printing. The important results are as follows. Amending existing construction-related laws for 3D printing is irrational and inefficient in terms of structure and material. This study proposed a method of satisfying performance required by laws or standards based on the performance design method presented in existing laws and systems through structure and material performance certification procedure. In addition, inclusion of 3D printing equipment in the Construction Machinery Management Act results in various restrictions such as equipment inspection and certification of machine parts. As such restrictions can block vitalization of 3D printing, a long-term and step-wise approach was suggested.

3D 프린팅의 적층제조를 위한 시멘트 모르타르의 이용은 시멘트의 유동 특성을 개질하기 위한 시멘트 혼화용 폴리 머의 혼입이 필수적이다. 시멘트 모르타르는 점성이 높고 수축이 크기 때문에 적층제조를 위해서는 유동성, 경화속도, 시공성 및 적층특성의 개선이 필요하다. 시멘트 혼화용 폴리머 디스퍼젼을 혼입한 시멘트 모르타르는 시멘트 수화물과 공극 사이에 폴 리머 필름이 상호 형성되어 인장강도와 취성이 개선되며 우수한 접착성, 기밀성, 내약품성을 보인다. 최근, 사용편리성이 우수한 Ethylene-vinyl acetate 재유화형 분말수지가 널리 사용된다. 하지만 화재와 같은 고온에서는 재유화형 분말수지를 혼입한 경우에 는 성능저하가 더 크다. 재유화형 분말수지가 시멘트 수화물과 공극에 폴리머 필름을 형성하고 충전하지만 고온에 의해 열분해 되기 때문이다. 본 연구에서는 3D 프린팅의 적층제조를 위해 내열성이 개선된 Ethylene-vinyl chloride 재유화형 분말수지의 혼입률을 달리하여 고온에서의 특성과 열분해에 따른 공극특성을 검토하였다. 연구결과, EVCL 재유화형 분말수지를 혼입한 경우 고온에서 약간의 성능개선을 보였지만 열분해하여 공극률이 커지며, 밀도, 강도가 감소한다. 따라서, 사용조건에 적합한 배합조절 등이 필요하다.

In this study, a process is developed for 3D printing with alumina (Al2O3). First, a photocurable slurry made from nanoparticle Al2O3 powder is mixed with hexanediol diacrylate binder and phenylbis(2,4,6- trimethylbenzoyl) phosphine oxide photoinitiator. The optimum solid content of Al2O3 is determined by measuring the rheological properties of the slurry. Then, green bodies of Al2O3 with different photoinitiator contents and UV exposure times are fabricated with a digital light processing (DLP) 3D printer. The dimensional accuracy of the printed Al2O3 green bodies and the number of defects are evaluated by carefully measuring the samples and imaging them with a scanning electron microscope. The optimum photoinitiator content and exposure time are 0.5 wt% and 0.8 s, respectively. These results show that Al2O3 products of various sizes and shapes can be fabricated by DLP 3D printing.