Prediction of Laser Welding Deformation of Sandwich Panel in 3D Thermal Elasto-Plastic Analysis

摘要

The use of I-Core sandwich panel has increased in cruise ship deck structure since it can provide similar bending strength with conventional stiffened plate while keeping lighter weight and lower web height. It also has other merits of high insulation and good crashworthiness. However, due to its thin plate thickness, i.e. about 4～6 mm at most, it is assembled by high power CO_2 laser welding to minimize the welding deformation. Laser is shot on face sheet plate at the joint of the face sheet plate and web plate (I-core). The laser penetrates the face sheet plate and reaches upper part of the web plate. The penetrated part melts and becomes plasma status and it forms a shape like keyhole. In this paper, a heat source assumption is newly suggested in heat transfer analysis to realize the keyhole phenomenon, heat distribution around the keyhole part. For its verification, the melting zone and keyhole zone are compared with experimental result and generally known keyhole shape, respectively. An additional suggestion is made to consider negative defocus, which is known to provide deeper penetration than 0 or plus defocus. The proposed heat source is also verified through a 3D thermal elasto-plastic analysis to compare welding deformation with experimental results. Temporary welding restraints used in the laser welding experiment are also taken into account in the thermal elasto-plastic analysis.