실시간 면외변형 제어를 위한 무구속 용접기법에 관한 수치해석적 연구

Abstract

ABSTRACT

Simulation based study on jig free in-situ control of welding induced out of plane deformation

Jong-heon Hong Advisor : Prof. Sung-min Joo, Ph.D. Department of Welding and Joining Science Engineering, Graduate School of Chosun University

Welding residual stress and deformation cause various problems in the fabrication of welded structures. Welding residual stresses reduce the fatigue strength of the welded structure and facilitate the development of brittle cracks and stress corrosion cracks, and welding deformation may damage the appearance of the welded structure or cause a mismatch of the joints in the assembly process To mitigate the residual stress and deformation that occurs in the welding process, many conventional welding processes are designed to minimize the heat input of the welded structure and have used a process of applying heat load and mechanical force. However, the pre and post welding process for correcting welding deformation and residual stress is costly and time consuming. In order to solve the problem, this study applied jig free in-situ control technique. Al5083-O, which has three times higher heat conductivity than iron and twice the thermal expansion coefficient of iron, was selected. Cooling temperature (Temp), the radius (R) of the cooling heat source and Standoff Distance (SOD) between the welding heat source and the cooling heat source were set as variables. Out of plane deformation, residual stress, and temperature distribution are observed through numerical analysis and then Bead On Plate (BOP) welding and Heat sink welding (HSW) were compared. BOP welding occurred 6.557mm deformation, but the HSW was 0.857mm at SOD = 10mm, R = 6mm, temp = -56.6 ℃. By applying HSW, the deformation was reduced by 86.92%. HSW showed less deformation as SOD was smaller. From SOD = 30mm or more, application of cooling heat source tends to intensify weld deformation. As the SOD was lowered, the tensile residual stress decreased and then changed to the compressive residual stress. As the lower cooling temperature was applied, it changed from tensile residual stress to compressive residual stress. It is possible to control the welding residual stress and deformation through the finite element analysis using jig free in-situ control technique of welding induced out of plane deformation in Al5083-O thin plate welding. Using jig free in-situ control technique is expected to increase the fatigue strength of welded structures. In addition, it is expected that it will improve productivity and lower the production cost because it does not perform pre and post-treatment after welding.