• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 춘계학술대회논문집
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• pp.131.2-135
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• 1999

This study focuses on part quality and cycle times under gas-assisted injection molding(GIM) of housing molded parts. The position of the gas channel was estabished near to parting line at the end of last locations to fill. Applied hot runner and valve gates the gas was introduced directly into the mold cavity via gas pin. As GIM was applied the introduced directly into the mold cavity via gas pin. As GIM was applied the conclusion reached as follows. I) The quality of appearance was improved by reducing sink marks and scratches of texture ii) The realibility was improved by preventing warpages and reinforcing rigidity through optimum gas channel layout iii)It is enable to use small size of injection molding machine step by step as GIM was accomplished low pressure and reduced clamp forces against CIM iv)The productivity were improved by reducing cycle times.

• 한국전기전자재료학회논문지
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• 제16권6호
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• pp.515-521
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• 2003

There are now many theoretical investigations and real manufactures for numerous applications of photonic crystals (PCs) associated with photonic band gap and photonic integrated circuits. However, there are some difficulties to design and fabricate the desired pattern quality. It is not easy to satisfy accurate critical dimension (CD) for patterns with arbitrary shapes and pitch sizes aligned in various directions. In this work, we report the optimum conditions to better fabricate and design, and greatly improve pattern quality in delineating two-dimensional (2D) PCs in the nanometer range using single- step e-beam lithography system with conventional exposure mode.

• 소성∙가공
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• 제8권3호
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• pp.276-283
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• 1999

This study focuses on part quality and cycle times under gas-assisted injection molding (GIM) of box shape molded parts. The position of the gas channel was established near to parting line at the end of last locations to fill. Applied hot runner and valve gates, the gas was introduced directly into the mold cavity via gas pin. As GIM was applied, the conclusion reached as follows. I) The quality of appearance was improved by reducing sink marks and scratches of texture. ii) The reliability was improved by preventing warpages and reinforcing rigidity through optimum gas channel layout. iii) It is enable to use small size of injection molding machine step by step as GIM was accomplished low pressure and reduced clamp forces against CIM. iv) The productivity were improved by reducing cycle times.

• 한국공간구조학회논문집
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• 제3권3호
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• pp.67-74
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• 2003

The purpose of this study is to improve convergence speed of topology optimization procedure using the existing ESO method and to deal with topology decision of the truss structures according to a boundary condition, such as cantilever type. At the existing ESO topology optimization procedure for the truss structures, the adjustment of member sizes according to target stress has been executed by increasing or reducing a very small value from each member size. In this case, it takes too much iteration till convergence. Accordingly, it is practically hard to obtain optimum topology for a large scale structures. For that reason, it is necessary to improve convergence speed of ESO method more effectively. During the topology decision procedure, member sizes are adjusted by calculating approximate solution for member sizes corresponding to the target stress at every step, the new member sizes are adjusted by such method are applied in FEA procedure of next step.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1994년도 추계학술대회 논문집
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• pp.141-148
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• 1994

In order to improve the productivity of cold forging at low production cost, an integrated system's approach is necessary in handling the material preparation and the optimum process design, considering the forming machines, tooling, and operation including quality control. As the first step toward this approach, an expert system for multi-stage cold forging process design for fasteners with various head geometries is developed using Prolog language on IBM 486 PC. For effective representation of the complex part geometries, the system uses the multiple element input, and the forward inference scheme in determination of the initial billet size and intermediate forging steps. In order to determine intermediate steps, the basic empirical rules for extrusion, heading, and trimming were applied. The required forming loads and global strain distributions at each forging step were calculated and displayed on the PC monitor. The designed process sequence drawing can be obtained by AutoCAD. The developed system will be useful in reducing trial and error of design engineers in determining the diameter and height of the initial cylindrical billet from the final product geometry and the intermediate necessary sequences.

• International Journal of Reliability and Applications
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• 제17권1호
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• pp.85-105
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• 2016

In this paper accelerated life testing is incorporated in quality control technique of acceptance sampling plan to induce early failures in high reliability products.Stress under accelerated condition can be applied in constant-stress, step-stress and progressive-stress or combination of such loadings. A ramp-stress results when stress is increased linearly (from zero) with time. In this paper optimum failure-censored ramp-stress accelerated life test sampling plan for log-logistic distribution has been formulated with cost considerations. The log-logistic distribution has been found appropriate for insulating materials. The optimal plans consist in finding optimum sample size, sample proportion allocated to each stress, and stress rate factor such that producer's and consumer's interests are safeguarded. Variance optimality criterion is used when expected cost per lot is not taken into consideration, and bilevel programming approach is used in cost optimization problems. The methods developed have been illustrated using some numerical examples, and sensitivity analyses carried out in the context of ramp-stress ALTSP based on variable SSP for proportion nonconforming.

• 한국세라믹학회지
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• 제29권10호
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• pp.779-784
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• 1992

In producing cordierite glass-ceramics by sintering, following experiments were conducted in order to determine the optimum heat-treatment schedule for high-crystallinity and dense sintered body. The glass composition of 11.67MgO-29.46Al2O3-52.88SiO2-5P2O5-1B2O3 (wt%) was selected on the basis of the early experiment. The 3-step heat treatment schedule was determined by the results of DTA, Dilatometric measurement and high-temperature XRD, where the particle-size-controlled glass powder was used. The degree of densification and the crystallinity were evaluated by the measurement of the bulk density and X-ray scattering intensity. The specimen fired with the optimum conditions showed ${\alpha}$-cordierite phase, relative density ∼98%, crystallinity ∼92%, thermal expansion coefficient ∼30${\times}$10-7/$^{\circ}C$, dielectric constant ∼5.5 and resistivity ∼1.0${\times}$1012 {{{{ OMEGA }}cm, respectively.

• 한국통신학회논문지
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• 제34권8C호
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• pp.756-763
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• 2009

LMS알고리즘은 잡음이 섞인 신호로부터 원 신호를 복원하는데 자주 사용된다. 이 LMS알고리즘의 주된 결점은 음성 신호 파워에 따라 선형적으로 EMSE(Excess Mean Square Error)가 증가한다. 그 결과 최적의 값에서 큰 EMSE 때문에 성능의 효율성이 떨어진다. 이러한 결점은 적은 스텝사이즈를 선택함으로서 해결 할 수 있지만, 수렴율이 늦어지는 단점이 있어, 빠른 수렴율과 낮은 EMSE를 동시에 만족할 수 있는 값이 필요하다. 본 논문에서는 IGC(lnstantaneous Gain Control) 알고리즘을 음성신호가 존재하는 경우에서 제안한다. 시뮬레이션은 음성신호와 가우시안 잡음을 이용하여 수행하였고, 수렴율, 잡음제거, 그리고 EMSE에서 LMS알고리즘보다 IGC알고리즘이 우수하다는 것을 보인다.

• Journal of Ship and Ocean Technology
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• 제5권2호
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• pp.14-26
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• 2001

This paper presents a novel design approach that could generate structural design alternatives having different topologies and then, select the optimum structure from them with simulataneously determining its optimum design variables related to geometry and the member size subjected to the multiple objective design environments. For this purpose, a specialized genetic algorithm, called StrGA_DeAl + MOGA, which can handle the design alternatives and multi-criteria problems very effectively, is developed for the optimal structural design. To validate the developed method, method, plain truss design problems are considered as illustrative example. To begin with, some possible topological of the truss structure are suggested based on the stability criterion that should be satisfied under the given loading condition. Then, with the consideration of the given multi-criteria, several different topology forms are selected as design alternatives for the second step of the conceptual design process. Based on the chosen topolgy of truss structures, the sizing or shaping optimization process starts to determine the optimum design parameters. Ten-bar truss problems are given in the paper to confirm the above concept and methodology.

• 접착 및 계면
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• 제3권2호
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• pp.9-16
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• 2002

자가유화방식의 수분산 폴리우레탄의 경우, 이온성 그룹이 포함된 프리폴리머를 중화시켜 수분산시킨 후 분자량을 증가시키기 위해 사슬연장을 하게 된다. 본 연구에서는 아민계 사슬연장제를 사용하여 사슬연장 시 연속상의 pH의 변화를 관찰하였으며, 이온성 그룹의 함량, 사슬연장제의 사슬 길이와 투입 속도 등과 같은 공정 변수에 따른 최적의 사슬연장 정도와 사슬연장 시 평균 입도 변화를 분석하였다. 투입되는 사슬연장제의 농도가 증가함에 따라서 연속상의 pH가 증가하게 되고, 사슬연장 정도에 따른 pH 변화곡선의 변곡점으로부터 최적의 사슬연장제 함량을 결정하였다. 사슬연장제 투입 속도에 따른 평균 입도 크기 변화의 경우, 초기 사슬연장전의 평균 입자 크기는 거의 비슷하다가 최종 사슬연장이 끝난 후에 사슬연장제 투입 속도가 빠른 쪽의 평균 입도 크기가 증가한다는 사실이 관찰되었다. 이온성 그룹의 함량이 증가할수록 친수성기의 농도가 증가하므로 평균 입도 크기는 감소한다. 사슬연장제의 사슬 길이의 영향이 최적의 사슬연장 정도를 결정하는데 큰 영향은 미치지 않고, 사슬의 길이가 긴 아민류를 사용하였을 시 입자와 입자 사이에서 사슬연장 반응을 통해 입자의 크기가 크게 증가하는 경향이 관찰되었다.