• Bulletin of the Korean Chemical Society
• /
• 제29권4호
• /
• pp.833-841
• /
• 2008

Principal component-genetic algorithm-multiparameter linear regression (PC-GA-MLR) and principal component-genetic algorithm-artificial neural network (PC-GA-ANN) models were applied for prediction of melting point for 323 drug-like compounds. A large number of theoretical descriptors were calculated for each compound. The first 234 principal components (PC’s) were found to explain more than 99.9% of variances in the original data matrix. From the pool of these PC’s, the genetic algorithm was employed for selection of the best set of extracted PC’s for PC-MLR and PC-ANN models. The models were generated using fifteen PC’s as variables. For evaluation of the predictive power of the models, melting points of 64 compounds in the prediction set were calculated. Root-mean square errors (RMSE) for PC-GA-MLR and PC-GA-ANN models are 48.18 and $12.77{^{\circ}C}$, respectively. Comparison of the results obtained by the models reveals superiority of the PC-GA-ANN relative to the PC-GA-MLR and the recently proposed models (RMSE = $40.7{^{\circ}C}$). The improvements are due to the fact that the melting point of the compounds demonstrates non-linear correlations with the principal components.

• 한국정밀공학회지
• /
• 제18권8호
• /
• pp.71-78
• /
• 2001

In GMA(Gas Metal Arc)Welding, the weld size that is a locally melted area of a workpiece is one of the most important considerations in determining the strength of a welded structure. Variations in the weld power and the welding heat flux may affect the weld pool formation and ultimately the size of the weld. Therefore, an accurate prediction of the weld size requires a precise analysis of the weld thermal cycle. In this study, a model which can estimate the weld bead geometry and a method for thermal analysis, including the model, are suggested. In order to analyze the weld bead geometry, a mathematical model was developed with transformed coordinates to apply to the horizontal fillet joints. A heat flow analysis was performed with a two dimensional finite element model that was adopted for computing the base metal melting zone. The reliability of the proposed model and the thermal analysis was evaluated through experiments, and the results showed that the proposed model was very effective for predicting the weld bead shape and good correspondence in melting zone of the base metal.

• 대한용접접합학회:학술대회논문집
• /
• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
• /
• pp.151-155
• /
• 2002

In GMA(Gas Metal Arc)Welding, the weld size that is a locally melted area of a workpiece is one of the most important considerations in determining the strength of a welded structure. Variations in the weld power and the welding heat flux may affect the weld pool formation and ultimately the size of the weld. Therefore, an accurate prediction of the weld size requires a precise analysis of the weld thermal cycle. In this study, a model which can estimate the weld bead geometry and a method for thermal analysis, including the model, are suggested. In order to analyze the weld bead geometry, a mathematical model was developed with transformed coordinates to apply to the horizontal fillet joints. A heat flow analysis was performed with a two dimensional finite element model that was adopted for computing the base metal melting zone. The reliability of the proposed model and the thermal analysis was evaluated through experiments, and the results showed that the proposed model was very effective for predicting the weld bead shape and good correspondence in melting zone of the base metal.

• 대한기계학회논문집B
• /
• 제26권5호
• /
• pp.648-657
• /
• 2002

This paper presents a numerical analysis on the solidification characteristics in twin-roll strip casting. Unstructured fixed-grid system was employed to deal with phase change. Melting of pure gallium was analyzed to confirm the validity of present program in both structured and unstructured grid systems. An algorithm for simultaneous calculation of the temperature in the roll and the molten metal pool was developed. The flow field in the pool and heat transfer features between pool and roll were shown. The effect of process parameters was also studied. Since the geometry of the molten metal Pool significantly deforms along the casting direction, unstructured grid system is more efficient. The unstructured grid system gives almost the same accuracy, even though the number of grids is only 60% of the structure done.

• Journal of Welding and Joining
• /
• 제27권2호
• /
• pp.44-50
• /
• 2009

The characteristics of arc pressure, current density and heat flux distribution are important factors in understanding physical arc phenomena, which will have a marked effect on the penetration, size and shape of a weld in TIG welding. The purpose of this study is to find out the effect of the heat flux on the melting efficiency and penetration shape in TIG welding using the results of the previous investigators. The conclusions obtained permit to draw a proper method which derived the heat flux distributions by arc pressure distribution measurements, but previous researchers calculated heat flux and current distribution with the heat intensity measurements by the calorimetry. Heat flux of Ar gas arc was concentrated at the central part and distributed low from the arc axis to the radial direction, that of He mixing arc was lower than that of Ar gas, and it was wide distributed to radial direction. That showed a similar characteristic with the Nestor's by calorimetry calculated values. Throughout heat flux drawn in this study was discussed melting efficiency and penetration shape on Ar gas and He mixing gas arc.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 1996년도 추계학술대회 논문집
• /
• pp.474-478
• /
• 1996

Process monitoring in laser welding is essential for automation and quality control of products. Various signals from laser welding, such as plasma, sound, optical signals, etc., are utilized for monitoring the process and detecting abnormal weld conditions. In this study, both W light from plasma formed above the weld pool and IR signal from the melting pool are detected with photodiodes and PC-based A/D board, and analyzed to give a guidance about the weld quality. Experimental results show the possibility of using the signals for predicting and evaluating the weld qualify and adapting into the system for on-line process monitoring.

• 한국원자력학회:학술대회논문집
• /
• 한국원자력학회 1997년도 춘계학술발표회논문집(1)
• /
• pp.489-494
• /
• 1997

A comparative transient analyses were performed for oxide and nitride cores or a large (3000 MWt), pool-type, liquid-metal-cooled reactor (LMR). The study was focused on three representative accident initiators with failure to scram : the unprotected loss-of-flow (ULOF), the unprotected transient overpower (UTOP), and the unprotected fast transient overpower (UFTOP). The margins to fuel melting and sodium boiling have been evaluated for these representative transients. The results show that there is an increase in safety margin with nitride core which maintains the physical dimensions of the oxide core.

• 대한용접접합학회:학술대회논문집
• /
• 대한용접접합학회 2005년도 춘계학술발표대회 개요집
• /
• pp.217-219
• /
• 2005

In the conventional GMAW of 9% Ni steel, Inconel wire has been employed. The major problem of the Inconel GMAW is that arc stability and fluidity of weld pool is poor. Lack of fusion and convex weld bead is liable to occur in case of 9% Ni steel because of low melting point of Inconel wire. In this study the effect of shielding gases on the Inconel 625 GMA weldability was investigated.

• 대한기계학회논문집A
• /
• 제35권12호
• /
• pp.1655-1662
• /
• 2011

본 연구는 레이저를 이용한 스테인리스강의 용접성 평가에 대한 연구이다. 사용된 금속인 스테인리스 스틸은 녹 및 열적변형이 우수하여 다양한 적용 분야를 가지고 있다. 본 연구는 50 W 레이저 열원에 자기장을 적용하여 스테인리스 스틸에 기계적 성질을 향상 시키는데 목적을 두고 있다. 이에 따른 기계적 성질을 분석하기 위하여 수치적 해석, 인장강도, 형상 및 미세조직, 경도 시험 등을 수행하였다. 결과적으로 수치적 해석을 통한 금속 용융점에서의 속도 증가, 인장강도 약 16 MPa 상승, 용융부에 섞임, 경도 약 7 Hv 상승으로 기계적 성질이 향상 되었다.

• 소성∙가공
• /
• 제28권1호
• /
• pp.21-26
• /
• 2019

Direct Laser Melting (DLM) of $Ti-xTiH_2$ (mixing ratio x = 2, 5, 10 wt.%) blended powder is characterized by producing porous titanium parts. When a high energy laser is irradiated on a $Ti-TiH_2$ blended powder, hydrogen gas ($H_2$) is produced by the accompanying decomposition of the $TiH_2$ powder, and acts as a pore-forming and activator. The hydrogen gas trapped in a rapidly solidified molten pool, which generates porosity in the deposited layer. In this study, the effects of a $TiH_2$ mixing ratio and the associated processing parameters on the development of a porous titanium were investigated. It was determined that as the content of $TiH_2$ increases, the resulting porosity density also increases, due to the increase of $H_2$ produced by $TiH_2$. Also, porosity increases as the scan speed increases. As fast solidified melting pools do not provide enough time for $H_2$ to escape, the faster the scan speed, the more the resulting $H_2$ is captured by the process. The results of this study show that the mixing ratio (x) and laser machining parameters can be adjusted to actively generate and control the porosity of the DLM parts.