• 수산해양기술연구
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• 제17권2호
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• pp.85-91
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• 1981

평판 강괴를 연속적으로 주조할 경우에 초기주조 상태에서 Mold 내부의 Support bar 및 용강자중, 주조속도, 용강두께, 이를 지지하는 제어 Roller, 유압기구, 구동 Motor, 그리고 주조조직의 응고 등이 용강의 인발력을 유도하는 Pinch Roller와의 사이에서 동력학적 부평형을 일으켜 Slip 현상을 초래하므로 본 논문에서는 이상의 제요인들을 근거로 Slip 현상을 규명하는 식을 유도하고 강괴의 주조속도, 비중량, 두께의 변화에 대한 Slip Force 거동을 규명하였다. 그 결과 1. 본 논문의 해석식에 의하여 평판강괴 연속주조용 Pinch Roller의 적정압을 설계할 수 있다. 2. 비중량은 순수히 자중만 증가시키는 요인이며 Slip Force는 주조속도변화에 대해서 포물선적으로 증가한다. 3. 주조두께 및 비중량의 변화에 대한 Slip Force는 이에 비례하여 증가하나 특히 두께의 값이 소폭보다 대폭에서 그 변화 값이 크게 나타났다.

• Journal of Ceramic Processing Research
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• 제19권6호
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• pp.445-449
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• 2018

Chromium plating is a common surface treatment technique extensively applied in industry due its excellent properties which include substantial hardness, abrasion resistance, corrosion resistance, surface color, and luster. In this study, the effect of $MoS_2$ particles of the composite coating was investigated. To improve the lubrication of mold, $Cr-P-C/MoS_2$ composite plating was studied by varying the $MoS_2$ content. The current efficiency of the composite plating incorporated $MoS_2$ particles was increased at $MoS_2$ contents of 0.5 and 1.0 g/l due to the incorporation of fine particles. On the other hand, when the content of $MoS_2$ is 1.0 g/l or more, the current efficiency is lowered due to an increase in impact on the cathode surface. In order to evaluate the mechanical properties of Scratch test were conducted. Scratch test confirmed the lubricity and abrasion resistance characteristics revealed that the composite plating with added $MoS_2$ had relatively low surface roughness and uniform surface modification to improve its properties.

• 한국기계가공학회지
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• 제21권5호
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• pp.91-97
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• 2022

The Directed Energy Deposition (DED) is a representative metal additive manufacturing method. Owing to its strong point of repairment, its application is gradually spreading in aerospace applications, power generation, military components, and mold making. 5-axis cladding is needed to repair damage, such as wear and scratches on cylindrical surfaces to circular-shaped parts, including sleeves and liners. Furthermore, the condition of cladding on inclined parts must also be considered to prevent interference between the nozzle and the part. In this study, the effects of changes in scanning speed due to the 5-axis control system and differences from the height of laser beam irradiation due to inclination are evaluated among the items that should be additionally considered in 5-axis cladding compared to 3-axis cladding. Moreover, the trends of the width and height of the clad are identified by different tilting angles via single line cladding. Lastly, cladding methods on cylindrical surfaces at various angles are proposed to enhance the clad quality and post-processing efficacy. These results can be applied with 5-axis cladding on inclined surfaces, including cylindrical surfaces.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2021년도 가을 학술논문 발표대회
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• pp.154-155
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• 2021

Appearance finish is important for amorphous buildings to maximize amorphousness, and GFRC, glass, and metal are mostly used as exterior materials for amorphous buildings currently applied. However, the existing exterior materials showed limitations in amorphous expression, texture, and color expression. In this study, a 3D stereoscopic panel mold was manufactured using the FDM method, one of the 3D printing technologies, and 3D stereoscopic panel production was reviewed using Ultra High Performance Concrete (UHPC), which has excellent physical and mechanical performance and expression. In order to overcome the limitations of unstructured expression, a UHPC 3D stereoscopic panel using the FDM method, one of the 3D printing technologies, was manufactured. Unlike steel molds, FRP molds, and EPS molds, the FDM method can be applied to various materials, and complex shapes are implemented. If it is used using recyclable materials as well as PLA filaments used in the FDM method, it will overcome the limitations of amorphous expression and activate the production of 3D stereoscopic panels that have secured eco-friendliness.

• 대한치과보철학회지
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• 제57권2호
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• pp.95-101
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• 2019

목적: 레진 시멘트와 코발트 크롬 합금 간의 미세인장결합강도에 다양한 프라이머들이 미치는 영향을 평가하기 위한 것이다. 재료 및 방법: 본 실험에서는 4개의 프라이머(Universal primer, Metal primer II, Alloy primer, and Metal/Zirconia primer)와 2개의 레진 시멘트(Panavia F2.0, G-CEM LinkAce)를 사용하였고, 길이 6 mm, 폭 1 mm, 두께 1 mm의 150개의 코발트 크롬 빔들이 캐스팅 과정을 통해 제작되었다. 150개의 코발트 크롬 빔들을 프라이머와 레진 시멘트의 종류에 따라 프라이머 처리를 하지 않은 대조군을 포함하여 10개 그룹으로 나누었다. 금속과 레진시멘트를 산화알루미늄($125{\mu}m$ 크기)으로 샌드블라스팅 처리한 후 실리콘 틀을 이용하여 접착시켰다. 실험 전에, 입체현미경(stereomicroscope)을 이용하여 모든 금속-레진 빔들을 검사하였고, 미세인장결합강도 실험을 시행하였다. 통계적인 평가에는 one-way ANOVA와 Tukey's test를 사용하였다. 결과: 모든 그룹들의 평균 미세인장결합강도는 20 - 28 MPa이었으며, 그룹 간에 통계적으로 유의한 차이는 없었다. Panavia F2.0과 G-CEM LinkAce 그룹 모두에서 접착 파절과 응집 파절이 동시에 나타나는 혼합 파절이 가장 흔하게 일어난 파절 양태였다. 결론: 모든 실험군들의 미세인장결합강도는 상대적으로 높았지만, 본 실험에서는 프라이머의 사용이 Panavia F2.0 및 G-CEM LinkAce 레진시멘트와 코발트 크롬 합금 사이의 미세인장결합강도를 증가시키지 않았다.

• 한국식품위생안전성학회지
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• 제28권1호
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• pp.69-74
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• 2013

본 연구는 식초절임 무의 HACCP (Hazard Analysis Critical Control Point)시스템 구축을 위하여 생물학적 위해요소분석을 위한 목적으로 2012년 2월 1일~6월 31일까지 약 150일 동안 수행하였다. 일반적인 식초절임 무 제조업체의 제조공정을 참고로 하여 공정도를 작성하였으며, 식초절임 무의 원료 농산물(무), 용수, 첨가물과 포장재료에 입고, 보관, 정선, 세척, 표피제거, 절단, 선별, 충진, 내포장, 금속검출, 외포장, 보관 및 출하공정에 대하여 작성하였다. 원료 무의 세척 전, 세척 후의 Coliform group, Staphylococcus aureus, Salmonella spp., Bacillus cereus, Listeria Monocytogenes, E. coli O157:H7, Clostridium perfringens, Yeast 와 Mold를 측정한 결과 Bacillus cereus는 세척 전 $5.00{\times}10$ CFU/g이었으나, 세척 후 검출되지 않았으며, Yeast 와 Mold 는 세척 전 $3.80{\times}10^2$ CFU/g, 세척 후 10 CFU/g로 감소되었으며 나머지 병원성균은 검출되지 않았다. 조미액의 pH(2~5)별 미생물의 변화를 시험한 결과 모든 균이 검출되지 않은 pH 3~4를 조미액의 pH로 결정하였다. 작업장별 공중낙하균 (일반세균수, 대장균, 진균수) 시험결과 내포장실, 조미액가공실, 세척실, 보관실의 미생물수는 10 CFU/Plate, 2 CFU/Plate, 60 CFU/Plate 그리고 20 CFU/Plate 가 검출되었다. 종사자 손바닥 시험결과 일반세균수 346 $CFU/Cm^2$, 대장균군 23 $CFU/Cm^2$로 높게 나타나 개인위생관리에 대한 교육 및 훈련이 요구 되었다. 제조설비 및 기구의 표면오염도를 검사한 결과 모든 시료에서 대장균군은 검출되지 않았고, 일반세균은 PP Packing machin과 Siuping machine (PE Bulk)에서 가장 많은 $4.2{\times}10^3CFU/Cm^2$, $2.6{\times}10^3CFU/Cm^2$ 검출되었다. 위의 위해분석 결과 병원성미생물을 예방, 감소 또는 제거할 수 있는 조미액 가공 공정이 CCP-B (Biological)로 관리되어야 하고, 한계기준은 pH 3~4로 결정하였다. 따라서 전통한과생산에의 HACCP 모델 적용을 위한 미생물학적 위해도 평가에서와 같이 조미액 가공 공정의 관리기준 및 이탈시 조치방법, 검증방법, 교육 훈련과 기록관리 등 철저한 HACCP 관리계획이 필요할 것으로 생각된다.

• 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.

• Design & Manufacturing
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• 제14권1호
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• pp.1-7
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• 2020

In this study, the variation of the shrinkage in the thickness direction of the molded parts according to the gate size of the polymer core fabricated through the 3D printer using the SLS method was studied. The polymer cores are laser sintered and the powder material is nylon base PA2200. The polymer cores have lower heat transfer rate and rigidity than the metal core due to the characteristics of the material. Therefore, the injection molding test conditions are set to minimize the deformation of the core during the injection process. The resin used in the injection molding test is a PP material. The packing condition was set to 80, 90 and 100% of the maximum injection pressure for each gate size. The runner diameter used was ∅3mm, and the gates were fabricated in semicircle shapes with cross sections 1, 2, and 3 ㎟, respectively. Thickness measurement was performed for 10 points at 2.5 mm intervals from the point 2.5 mm away from the gate, and the shrinkage to thickness was measured for each point. The shrinkage rate according to the gate size tends to decrease as the cross-sectional area decreases as the maximum injection pressure increases. The average thickness shrinkage rate was close to 0% when the packing pressure was 90% for the gate area of 1mm2. When the holding pressure was set to 100%, the shrinkage was found to decrease by 3% from the standard dimension due to the over-packing phenomenon. Therefore, the smaller the gate, the more closely the molded dimensions can be molded due to the high pressure generation. It was confirmed that precise packing process control is necessary because over-packing phenomenon may occur.

• Design & Manufacturing
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• 제12권2호
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• pp.40-45
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• 2018

Recently, in construction equipment machinery production, development has focused on environmentally-friendly functions to improve existing production capacity. For excavators as well, emphasis has been placed on response to environmental regulations, miniaturization, and noise reduction, while technology is being developed considering cost reduction and safety.Accordingly, the front support, an inner reinforcement part of the excavator, as well as high-strength steel plates to improve safety and reduce weight, are being applied.However, in the case of high-strength materials, Springback occurs in the final formed part due to high residual stress during product forming. Derivation of a forming or product shaping process to reduce springback is needed. Accordingly, regarding the front support, an inner reinforcement part of the excavator, this study derived a method to improve springback and secure shape stiffness through analysis of the springback occurrence rate and springback causes through a forming analysis.As for the results of analyzing the springback occurrence rate of existing products through forming analysis, springback of -22.6 mm < z < 27.35 mm occurred on the z-axis, and it was confirmed that springback occurred due to the stiffness reinforcing bead of the upper and middle parts of the product.To control product residual stress and springback, we confirmed a tendency of springback reduction through local pre-cutting and stiffness reinforcement bead relocation.In the local pre-cutting model, springback was slightly reduced by 5.3% compared with the existing model, an insignificant reduction effect. In the stiffness reinforcement bead relocation model, when an X-shaped stiffness reinforcement bead was added to each corner portion of the product, springback was reduced by at least 80%.The X-shaped bead addition model was selected as the springback reduction model, and the level of stiffness compared to the existing model was confirmed through a structural analysis.The X-shaped bead additional model showed a stress springback of 90% and springback reduction of 7.4% compared with the existing model, indicating that springback and stiffness will be reinforced.

• Design & Manufacturing
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• 제12권1호
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• pp.52-57
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• 2018

With the recent strengthening of environmental regulations and the need for cost reduction, excavators, a type of construction equipment, are being miniaturized while components are being developed in consideration of stability. In the case of excavator press parts, mainly high-strength steel sheets are being used to enhance stability and reduce weight. However, in the case of high-strength materials, there is a need to research product forming methods to reduce Springback in defects arising in parts assembly due to Springback that result from the internal residual stress that occurs in press forming being released after product forming. Accordingly, regarding the tank cover, an excavator press-forming part, this study selected a method to reduce distortion through analysis of the Springback occurrence rate and Springback causes through a forming analysis. A forming analysis was conducted for the Springback of the tank cover. Deformations of 13.714 mm in the upper part and 6.244 mm in the inner part of the product occurred, while wrinkles occurred on the sides of the product due to uneven thickness. A forming analysis was conducted for the major shapes of the product to investigate the causes of Springback. Distortion deformation due to the bead in the center of the product was confirmed to be a large factor. A Springback reduction method of correcting uneven thickness in the product sides, a Springback reduction method of removing the bead, and a correction method of restriking after the final forming were used in a forming analysis to determine the degree of Springback reduction. For the forming method to correct uneven thickness in the sides, deformation was reduced by 12% in the upper side compared to the existing model, but deformation in the inner side increased by 1%. For the restriking forming method, deformation decreased by 25% in the upper side and 13% in the inner side. For the bead removal method, deformation decreased by 28% in the upper side and 13% in the inner side, the largest Springback correction results. This indicates that the bead has a large affect on Springback.