• Design & Manufacturing
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• 제15권3호
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• pp.39-44
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• 2021

In molding of continuous fiber-reinforced thermoplastic composites, it is very difficult to impregnate between the reinforcements and the matrix since the matrix has a high melting temperature and high viscosity. Therefore, most of composite molding processes are divided in the manufacturing processes of intermediate materials called prepreg and the forming of products from intermediate materials. The divided process requires additional facilities and thermoforming, and they increase the cycle time and cost of composite products. These problems can be resolved by combining the continuous fiber-reinforced composite molding process with injection molding. However, when a composite material is manufactured by inserting woven fabric into the injection mold, poor impregnation occurs on the surface of the molded product. It affects the properties of the composites. In this paper, through an impregnation experiment using cores with different heat transfer rates and pore densities, the reason for the poor impregnation was confirmed, and molding experiments were conducted to produce composite with improved surface impregnation by inserting the mesh. And also, the surface impregnation and deformation of composites molded using different types of mesh were compared with each other.

• Design & Manufacturing
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• 제16권3호
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• pp.50-57
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• 2022

The qualities of the products produced by injection molding are strongly influenced by the process variables of the injection molding machine set by the engineer. It is very difficult to predict the qualities of the injection molded product considering the stochastic nature of the manufacturing process, since the processing conditions have a complex impact on the quality of the injection molded product. It is recognized that the artificial neural network(ANN) is capable of mapping the intricate relationship between the input and output variables very accurately, therefore, many studies are being conducted to predict the relationship between the results of the product and the process variables using ANN. However in the condition of a small number of data sets, the predicting performance and robustness of the ANN model could be reduced due to too many input variables. In the present study, the ANN model that predicts the length of the injection molded product for multiple combinations of process variables was developed. And the accuracy of each ANN model was compared for 8 process variables and 4 important process inputs that were determined by the feature selection. Based on the comparison, it was verified that the performance of the ANN model increased when only 4 important variables were applied.

• Design & Manufacturing
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• 제16권3호
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• pp.39-43
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• 2022

In this study, we designed an vibration cutting tool that can achieve improvements such as low cutting force, interrupted chip evacuation and better surface quality of cutting performance to obtain high-quality surface roughness and improvement of tool wear, which is an issue in the machining of high-hardness mold steel. Among the resonance frequency modes of the vibration cutting tool, the bending mode was used to maximize the driving amplitude of the vibration tool tip, and the resonance frequency was confirmed through the finite element method. After measuring the actual resonant frequency of the designed tool using an optical fiber sensor, the cutting force and machining surface of vibration cutting and conventional cutting were compared and analyzed in the turning process of high hardness mold steel (STAVAX). As a result of the experiment, the cutting force was reduced by about 20 % compared to the conventional cutting process, and the surface roughness was also improved by about 60 %. This study suggested that the tool wear and surface quality of high-hardness steel can be improved through the vibration cutting method in the machining of high hardness mold steel.

• Design & Manufacturing
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• 제16권4호
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• pp.46-51
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• 2022

The piercing process of creating holes in sheet metals for mechanical fastening generates high shear force. Real-time monitoring technology could predict tool damage and product defects due to this severe condition, but there are few applications for piercing high-strength aluminum. In this study, we analyzed the load signal to predict the punch's wear level during the process with a piezoelectric sensor installed piercing tool. Experiments were conducted on Al6061 T6 with a thickness of 3.0 mm using piercing punches whose edge angle was controlled by reflecting the wear level. The piercing load increases proportionally with the level of tool wear. For example, the maximum piercing load of the wear-shaped punch with the tip angle controlled at 6 degrees increased by 14% compared to the normal-shaped punch under the typical clearance of 6.7% of the aluminum piercing tool. In addition, the tool wear level increased compression during the down-stroke, which is caused by lateral force due to the decrease in the diameter of pierced holes. Our study showed the predictability of the wear level of punches through the recognition of changes in characteristic elements of the load signal during the piercing process.

• Design & Manufacturing
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• 제16권2호
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• pp.1-6
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• 2022

As environmental regulations are strengthened, automobile manufacturers continuously research lightweight structures based on carbon fiber reinforced plastic (CFRP). However, it is difficult to see the effect of strength reinforcement when using a single CFRP material. To improve this, a hybrid laminate in which CFRP is mixed with the existing body structural steel was proposed. In this paper, CFRP patch reinforcement is applied to each compression/tensile action surface of a 22MnB5 metal sheet, and it was evaluated through a 3-point bending experiment. Progressive failure was observed in similar deflection on bending deformation to each one-sided reinforced specimen. After progressive failure, the tensile reinforced specimen was confirmed to separate the damaged CFRP patch and 22MnB5 sheet from the center of the flexure. The compression reinforced specimen didn't separate that CFRP patch and 22MnB5, and the strength reinforcement behavior was confirmed. In the compression reinforced specimen, damaged CFRP patches were observed at the center of flexure during bending deformation. As a result of checking the specimen of the compression reinforcement specimen with an optical microscope, It is confirmed that the damaged CFRP patch and the reinforced CFRP patch overlapped, resulting in a concentrated load. Through the experimental results, the 22MnB5 strength reinforcement characteristics according to the reinforcement position of the CFRP patch were confirmed.

• 한국산학기술학회논문지
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• 제17권11호
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• pp.223-229
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• 2016

본 연구에서는 엔진의 밸브트레인에 적용되는 롤러 태핏 하우징의 냉간단조 공정을 개발하였다. 시제품을 제작하였으며, 태핏 하우징의 내구성 평가를 통하여 작동성을 확인하였다. 소재 시편의 압축시험을 통하여 태핏에 사용되는 소재의 물성을 확보하고 상용 소프트웨어인 Deform-3D을 이용하여 단조해석을 수행하였다. 해석결과를 바탕으로 냉간단조 공정을 설계하였으며, 실제 금형을 제작하고 시제품을 제작하였다. 제작한 시제품의 평가를 위하여 치수정밀도, 표면조도, 평행도, 동심도를 확인하였으며, 목표한 항목에 모두 부합하는 결과를 확인하였다. 또한 제품의 작동성 및 내구성 평가를 수행하기 위하여, 엔진 밸브트레인의 구동을 모사하는 별도의 시험장치 개발을 완료하였다. 디젤엔진의 아이들 상태를 가정하여 작동성을 평가하고, 엔진의 최고 회전수를 가정하여 내구성 시험을 진행하였다. 시험결과 태핏하우징의 마모는 시험 전, 후 외경 치수 0.002 mm 감소로, 미소한 마모를 보였다. 본 연구를 통하여 정밀 냉간단조 기술을 이용한 제품개발 프로세스를 정립하였다. 또한 본 연구에서 개발한 작동성 평가 시험기를 통해 밸브트레인용 부품의 작동성 및 내구성 평가 시험이 가능할 것으로 사료된다.

• 전자공학회논문지
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• 제50권11호
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• pp.130-137
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• 2013

본 논문은 생체신호 측정을 위한 저전력/저면적 AFE(analog front-end)에 관한 것이다. 제안된 AFE는 계측증폭기(IA), 대역 통과 필터(BPF), 가변 이득 증폭기(VGA), SAR 타입 A/D 변환기로 구성된다. 전류 분할 기법을 이용한 작은 gm (LGM) 회로와 고 이득 증폭기로 구성된 Miller 커패시터 등가 기술을 이용하여, 외부 수동소자를 사용하지 않고 AC-coupling을 구현하였다. 응용에 따른 BPF의 고역 차단 주파수 변화는 전압 조절기(regulator)를 이용한 출력 전압 변화를 이용하여 $g_m$을 변화하여 구현 시켰다. 내장된 ADC는 커패시터 분할 기법을 적용한 이중 배열 커패시터 방식의 D/A변환기와 비동기 제어 방식을 이용하여 저 전력과 저 면적으로 구현하였다. 일반 CMOS 0.18um 공정을 이용하여 칩으로 제작하였고, 전체 칩 면적은 PAD등을 모두 포함하여 $650um{\times}350 um$이다. 제안된 AFE의 전류 소모는 1.8V에서 6.3uA이다.

• 대한전자공학회논문지SD
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• 제40권8호
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• pp.598-609
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• 2003

본 논문에서는 CMOS IF PLL 주파수합성기를 설계하였다. 설계된 주파수합성기는 칩 외부에 LC 공진 회로를 원하는 값에 맞게 바꿈으로써 다양한 중간 주파수에서 동작 가능하다. VCO는 자동진폭조절 기능을 갖도록 설계하여 LC 공진회로의 Q-factor에 무관하게 일정한 진폭의 출력을 발생한다. 설계된 주파수분주기는 8/9 또는 16/17 dual-modulus prescaler를 포함하며, 다양한 응용분야에 적용 가능하도록 외부 직렬데이터에 의해 동작 주파수를 프로그램할 수 있도록 하였다. 설계된 회로는 0.35㎛ n-well CMOS 공정을 사용하여 제작되었으며, 제작된 IC의 성능을 측정한 결과 260㎒의 동작주파수에서 위상잡음은 -114dBc/Hz@100kHz 이고 lock time은 300㎲보다 작다. 설계된 회로는 3V의 전원전압에서 16mW의 전력을 소모하며, 칩 면적은 730㎛×950㎛이다.

• 산업경영시스템학회지
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• 제41권4호
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• pp.248-255
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• 2018

Ensuring the quality of molds is one of the major issues in mass production. In general, securing the quality of the molds is achieved by repeating grinding and die spotting after machining the molds based on engineer's decision. However, this heuristic method is affected by the engineer's skill and working environment. Therefore, a lot of time and resources are needed in order to ensure quality. In this study, ensuring the quality of molds using grinding map which is generated using automatic measurement is proposed. An automatic measuring system based on CMM (Coordinate Measuring Machine) is developed for measuring the molds. This system generates the measurement path automatically using the 3D CAD model of products. CAD (ComputerAided-Design), CAM (Computer-Aided-Manufacturing), and CAQ (Computer-Aided-Quality) technology is integrated using DMIS (Dimensional Measuring Interface Standard) format in the automatic measuring system. After measuring the molds, a grinding map is generated using the gap between the CAD model and measured values of mold. The grinding map displays the machining tendency and the required amount of grinding with values on a 3D map. Therefore, the quality of molds can be ensured with exactness and quickness based on the grinding map. This study shows that integrating the planning, measuring, and analyzing based on computer technology can solve the problem of quality assurance of mold using the proposed method, therefore the productivity can be increased.

• 한국산학기술학회논문지
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• 제22권2호
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• pp.593-601
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• 2021

축류팬은 여러 산업분야에서 사용되며, 환기 및 제연을 목적으로 사용하는 송풍기의 핵심 요소이다. 유체 운동을 이용하는 축류팬의 연구는 공력성능에 대한 연구가 많이 진행되어 왔다. 본 연구 대상은 100마력의 송풍기에 사용되는 축류팬이며, 직경 1800 mm의 대형 송풍기이다. 송풍기의 축류팬은 블레이드, 허브, 허브 캡, 보스로 구성되어 있으며, 블레이드와 허브는 중요한 구성부품이다. 공력성능에 많은 영향을 미치는 블레이드에 대한 설계는 공력성능 예측 프로그램을 이용해 3차원 점 데이터를 추출하여 이를 3D 모델링 형상을 생성하게 된다. 중요 구성부품이 절삭가공을 이용해 가공하게 되면 제품의 수정이 용이하다. 하지만, 블레이드와 허브는 다이캐스팅이나 중력주조를 통해 제작하는 환경으로 인해 금형 제작 전에 구조안전에 대한 연구가 필요하게 되었다. 본 연구에서는 축류팬 정격운전속도와 그 이상의 운전속도에서 주요 구성부품에 대한 구조안전성에 대한 특성과 취약부위에 대한 해석결과는 최대응력과 안전계수를 통해 검증하고 설계시 반영된 여유간극은 블레이드의 회전과 다른 부품과의 간섭 여부를 확인하기 위해 변위 결과를 도출하여 축류팬의 구조안전성에 대해 검증하고자 한다.