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유중돈,Yoo, Choong-D. 대한용접접합학회 2008 대한용접·접합학회지 Vol.26 No.1
초음파 용접용 혼의 설계에 대한 기본적인 방법과 절차를 설명하였다. 그러나 아직까지 혼의 최적 형상을 구하는 방법은 시행착오(trial-and-error) 방법과 실험 및 설계자의 경험에 많이 의존해야 한다. 또한, 혼의 해석 결과로서 다양한 진동 모드를 얻을 수 있기 때문에 설계자는 이를 분석하고 원하는 진동 모드를 얻을 수 있도록 설계하여야 한다.
Modification of pinch instability theory for analysis of spray mode in GMAW
Park, Ah-Young,Kim, Sun-Rak,Hammad, Muhammad A,Yoo, Choong D Institute of Physics [etc.] 2009 Journal of Physics. D, Applied Physics Vol.42 No.22
<P>While the pinch instability theory (PIT) has been widely used to analyse the spray mode in gas metal arc welding (GMAW), it assumes an infinite cylinder and no current leakage on the cylinder surface. The PIT is modified in this work to predict the spray mode more accurately by considering reduction of the molten tip radius, the finite cylinder geometry and current leakage. The effective cylinder radius is formulated as a function of current to consider the tapered cone shape of the molten tip, and the critical wavelength of the modified PIT is derived considering a finite cylinder with a hemispherical end and current leakage. The effective radius is found to have most significant effects on drop transfer followed by the finite cylinder geometry and current leakage, and the predicted results of the modified PIT are in reasonable agreement with the experimental data of the spray mode.</P>
CD 스터드 용접의 해석 및 결함 분석 Part 1 : 공정 모델링과 해석
오현석,유중돈,Oh Hyun-Seok,Yoo Choong-D. 대한용접접합학회 2006 대한용접·접합학회지 Vol.24 No.3
The CD (Capacitor Discharge) stud welding utilizes the arc heat and pressure to attach the stud to the workpiece, which consists of the arc. ignition, arcing and pressure welding stages. In order to predict the dynamic behavior of the CD stud welding process, mechanical and electrical models are employed in this work. While the mechanical model estimates the duration of each stage, the electrical model predicts the voltage and current waveforms using the RLC circuit. Effects of process parameters such as the electric components and spring force are analyzed through simulation. It is found that the contact resistance and gap between the stud and base metal influence the tip fusing and arcing duration. The calculated results showed reasonably good agreements with the experiment results.
CD 스터드 용접의 해석 및 결함 분석 Part 2 : 기공 제어
오현석,유중돈,Oh Hyun-Seok,Yoo Choong-D. 대한용접접합학회 2006 대한용접·접합학회지 Vol.24 No.3
Since the voids occur at the CD stud welds, the mechanism of void formation and void reduction method are investigated in this work. It is speculated that the voids are formed because of high short-circuit current above 1000A. When the simple flow model is used to estimate the void trapping condition, the most voids are trapped at the weld mainly due to fast cooling rate of the CD stud weld. Since it is almost impossible to remove the voids completely, a method is proposed to reduce the void by decreasing the short-circuit current at the end of the arcing time. The experimental results show that the void is reduced by decreasing the short-circuit current to 1000A.
김선락,이재학,유중돈,Kim, Sun-Rak,Lee, Jae-Hak,Yoo, Choong-D. 대한용접접합학회 2009 대한용접·접합학회지 Vol.27 No.4
The cylinder horn is designed to increase uniformity of the displacement on the output face through simulation and experiments for the simple cylinder, spool and step horns. The modal analysis is conducted numerically to calculate the vibration mode and stress distribution of the cylinder horn, and the design of experiment (DOE) technique is employed to determine the optimum configuration of the spool horn. Displacement of the cylinder horn was measured using the Laser Doppler Vibrometer (LDV), and experimental results show good agreements with the predicted results. It appears that uniformity higher than 95% can be achieved with the spool horn when the proper dimension of the groove is used.
용적 내부의 유동에 의한 모멘텀을 고려한 GMA 용접의 입상용적 이행에 대한 해석
이승현,강문진,유중돈,Lee, Seung-H.,Kang, Moon-J.,Yoo, Choong-D. 대한용접접합학회 2008 대한용접·접합학회지 Vol.26 No.4
The static force balance model (SFBM) has been used to analyze drop transfer in gas metal arc welding. Although the SFBM is capable of predicting the detaching drop size in the globular mode with reasonable accuracy, discrepancy between the calculated and experimental results increases with current. In order to reduce discrepancy, the SFBM is modified by considering the momentum of the molten metal flow, which is generated by the pinch pressure. The momentum increases with smaller drop size and becomes compatible to the electromagnetic force. The modified force balance model (MFBM) predicts the experimental results more accurately, and extends its application to the projected mode.
김선락,이재학,유중돈,Kim, Sun-Rak,Lee, Jae-Hak,Yoo, Choong-D. 대한용접접합학회 2009 대한용접·접합학회지 Vol.27 No.5
The bar horn is designed to increase uniformity of the displacement on the output face through simulation and experiments. Three-dimensional modal analysis is conducted using the finite element method to calculate the vibration mode and displacement on the output face, and the design of experiment (DOE) technique is employed to determine the optimum dimensions of the groove and slot so that the high amplitude uniformity of the bar horn is produced. Displacement of the bar horn was measured using the Laser Doppler Vibrometer (LDV), and the experimental results show good agreements with the predicted results. High uniformity of the bar horn is achieved with the dimensions of the groove and slot determined using the design equations.
박아영,김선락,유중돈,Park, Ah-Young,Hammad, Muhammad A.,Kim, Sun-Rak,Yoo, Choong-D. 대한용접접합학회 2009 대한용접·접합학회지 Vol.27 No.5
While the pinch instability theory (PIT) has been widely employed to analyze the spray transfer mode in the gas metal arc welding (GMAW), it cannot predict the detaching drop size accurately. The PIT is modified in this work to increase the accuracy of prediction and to simulate the molten tip geometry to be more physically acceptable. Since the molten tip becomes a cone shape in the spray mode, the effective wire diameter is formulated that the effective diameter is inversely proportional to current square. Modifications are also made to consider the finite length of the liquid column and current leakage through the arc. While the effective diameter influences drop transfer significantly, the current leakage has negligible effects. The effects of modifications on drop transfer are analyzed, and the predicted drop diameters show good agreements with the experimental data of the steel wire.