• 대한기계학회논문집A
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• 제20권10호
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• pp.3031-3037
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• 1996

In cold forming processes, due to high working pressure action on the die surface, failure mechanics must be considered before die design. One of the main reasons of die failure in industrial application of metal forming technologies is wear. Die wear affects the tolerances of formed parts, metal flow and costs of process etc. The only way to control these failures into devlop methods which allow prediction of die wear and which are suited to be used in the design state in order to optimize the process. In this paper, the forming propcesses that involve cold forward extrusion and wire drawing were simulated by rigid plastic finite element method and its output were used for predicting die wear by Archard wear model. The simulation results were compared with the measured worn dies.

• 소성∙가공
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• 제22권6호
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• pp.323-327
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• 2013

In this paper, the flow lines as a function of product design as well as the forging process design are explored using typical application examples. The prediction of flow lines using metal forming simulation technology is introduced along with their characterization. Experimental studies have shown that the metal flow lines have a strong influence on the structural rigidity of the final product. In this study we present several typical applications. One example is the case of severely cut metal flow lines during machining, especially in the region where periodic contacting forces are applied. Another example is the case of abnormal distortion of flow lines which can cause too much elongation or hot shortness due to viscous heating in the region of distortion. A third example is the case of a macrosegregation region which needs to be controlled so it is not adjacent to the region where the force is applied in the use of the final component. An example of weight reduction for an automobile component with improved flow lines is also introduced. These typical applications can provide process engineers with the insight in designing automobile or mechanical components as well as in designing the manufacturing methods to produce various parts.

• 한국산업융합학회 논문집
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• 제23권4_1호
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• pp.541-547
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• 2020

This paper relates a rheo die casting using electromagnetic force, which is one of the representative semi-solid methods for aluminum. The most important factors in electromagnetic stirring would be the melt temperature, sleeve temperature, electromagnetic force, and input time. The effect of the temperature of molten alloy on the direct rheo-casting is assessed in this study. The temperature of the molten alloy is set to 590 ℃ with a solidification of 40%, 600 ℃ with 30%, and 610℃ with less than 20%. Under the condition of 590 ℃ with a solidification of 40%, the whole molten alloy is solidified, causing non-forming during forming process. Meanwhile, under the condition of 600 ℃, where the solidification was 30%, appropriate amount of molten alloy is solidified, filled well into the mold, resulting in good forming, while at 610 ℃ with the solidification of 20%, the molten alloy is not sufficiently solidified and scattered away. The investigation of the defects inside the product with the help of the X-ray equipment shows that the electromagnetic stirring at 590 ℃ with a solidification of 30% produces many air-pores inside the product.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.589-590
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• 2006

Based on the comparison of structures and properties of the HS6-5-2 high speed steels made with the powder injection moulding method, pressureless forming, compacting and sintering, and commercial steels made with the ASEA-STORA method, fine carbides spread evenly in the steel matrix were found in the structure of all tested high-speed steels in the sintered state. The steels made with the pressureless forming method are characteristic of the lowest sintering temperature and the highest density, resulting from the high carbon concentration coming from the binding agent degradation.

• 한국자동차공학회논문집
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• 제9권3호
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• pp.131-142
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• 2001

A wrinkling is the instability phenomenon influenced by material properties, shape geometry, forming conditions, stress state, etc. The wrinkling is considered as a critical defect in appearance of product. Many wrinkling prediction methods using thickness strain distribution and farming analysis have been proposed. The wrinkling, however, is not easily predicted precisely by these methods. In this study, the region in the biaxial plane stress state is modeled with a rectangular plate introducing the effective dimension, and critical stress values for the wrinkling are calculated. Prediction index for the wrinkling is then evaluated by normalizing the actual stress with respect to the critical stress. In order to show the validity and efficiency of the method proposed, the wrinkling prediction for a squared sheet in the uniaxial tensile stress and auto-body front finder panel is performed.

• 패션정보와 기술
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• 제13권
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• pp.74-80
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• 2016

• 한국산학기술학회논문지
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• 제18권2호
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• pp.704-710
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• 2017

본 연구팀은 프레스 공정의 협소공간에서 작업이 가능한 6자유도 로봇을 개발하고 있으며, 본 논문은 개발된 로봇의 작업 시간을 최소화하기 위한 작업 시퀀스 최적화 방법을 제안하였다. 우선 6 자유도 로봇의 기구학을 모델링하고 작업 시간 예측 방법을 기술하였다. 그리고 작업 시퀀스 최적화를 위하여 수학적 모델을 제시하고, 이를 바탕으로 개미 집단 시스템(ant colony system), 시뮬레이트 어니일링(simulated annealing), 유전자 알고리즘(genetic algorithm)의 세 가지 최적화 방법을 적용하고 결과를 비교 분석하였다. 시뮬레이션 결과 유전자 알고리즘이 가장 좋은 결과를 보임을 확인할 수 있었으며, 계산 속도 측면에서도 가장 빨리 최적값에 수렴하였다. 또한, 개미집단시스템과 시뮬레이티드 어니일링의 경우 여러 파라미터 값들의 설정에 따라 수렴된 최적값의 편차가 비교적 큰 것에 비하여, 유전자 알고리즘은 파라미터 값에 상관없이 안정적으로 근사 최적값을 찾을 수 있었다. 마지막으로, 로봇의 작업시퀀스 최적화 방법을 시각적으로 검증하기 위하여 Mathworks 사의 Matlab과 Coppelia Robotics 사의 V-REP (virtual robot experimentation platform)를 사용한 시뮬레이션을 수행하였다.

• 대한조선학회논문집
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• 제52권1호
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• pp.70-76
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• 2015

The ship hull is accomplished by assembling various curved surfaces. There are numerous existing methods for ship hull processing, which need certain appropriate processing methods to enable it to be more efficient. The curved hull plates can be divided into convex region and saddle region. It is common to use line heating method to form a saddle region, when it comes to a convex region, it will be triangle heating method to be utilized. A precise analysis for curvature domain is required for the application of proper processing method. There exist various problems on existing calculation methods of curvature domain. Therefore, a more powerful method is demanded to it more accurately. In this study, a method called Dual Contouring is applied to extract curved surfaces, which is able to improve accuracy of extracted area. Based on all above, a best-suited heat processing method should be selected.

• Asian Pacific Journal of Cancer Prevention
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• 제17권10호
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• pp.4735-4739
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• 2016

Background: Intrahepatic cholangiocarcinoma (IHCCA) is an aggressive tumor for which surgical resection is a mainstay of treatment. However, recurrence after resection is common associated with a poor prognosis. Studies regarding recurrence of mass-forming IHCCA are rare; therefore, we investigated the pattern with our dataset. Methods: We retrospectively reviewed the medical and pathological records of 50 mass-forming IHCCA patients who underwent hepatic resection between January 2004 and December 2009 in order to determine the patterns of recurrence and prognosis. All demographic and operative parameters were analyzed for their effects on recurrence-free survival. Results: The median recurrence-free survival time was 188 days (95%CI: 149-299). The respective 1-, 2-, and 3-year recurrence-free survival rates were 16.2% (95%CI: 6.6-29.4), 5.4% (95%CI: 1.0-15.8) and 2.7% (95%CI: 0.2-12.0). There was an equal distribution of recurrence at solitary and multiple sites. Univariate analysis revealed no factors related to recurrence-free survival.Conclusion: The overall survival and recurrence-free survival after surgery for mass-forming IHCCA were found to be very poor. Almost all recurrences were detected within 2 years after surgery. Adjuvant chemotherapy after surgery may add benefit in the affected patients.

• 한국산학기술학회논문지
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• 제12권6호
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• pp.2777-2784
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• 2011

본 논문에서는 비변수 추정 알고리즘을 토대로 선형배열 안테나와 원형배열 안테나로부터 수신되는 다중신호의 DOA와 적응 빔성형 알고리즘을 연구하고 분석하였다. 비변수 추정 알고리즘에서는 입사각의 함수로써 신호에너지를 추정하기 위하여 고분해능과 잡음억압을 도출하도록 비이차놈을 사용하여 규칙화 목적함수를 최소화하였다. 그리고 나서, 신호와 잡음공간 조정벡터로부터 DOA를 추정하였고, 공간벡터에 의하여 도출된 가중치 벡터를 적용하여 적응 빔성형 패턴을 개선하였다. 특히, 안테나 배열방법과 배열소자의 수에 따라 입사되는 다중신호의 방향성 판별 능력과 적응빔을 성형하는 능력을 비교하고 고찰하였다.