## 4 Heat Transfer Analysis for the Full-Frame Structure  
The material properties of AL6063-T5 (the main material of the structure) such as density, specific heat, and thermal conductivity are required for heat transfer analysis. This study used material properties including nonlinear temperature history information, as shown in Figure 12, to conduct the analysis more accurately [14]. As shown in Figure 13, the 3D design geometry of the full-frame structure was also simplified before performing the simulation. The overall shape was simplified by removing negligible geometric elements such as the chamfer and round of corners, the holes for inserting bolts and positioning pins, and the protrusions on the bottom frame to improve the mesh quality. As shown in Figure 12, the 3D design geometry of the full-frame structure was simplified before conducting the simulation. The overall shape was simplified by removing negligible geometric elements such as the chamfer and round of corners, the holes for inserting bolts and positioning pins, and the protrusions on the bottom frame to improve the mesh quality. Figure 14 shows mesh for heat transfer analysis consisting of triangular elements, and Table 8 shows the mesh properties such as the conditions, method, size, quality, and the number of nodes and elements. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Item** & **Unit** & \multicolumn{5}{c}{**Measuring Point**} \\
**Distance** & **mm** & **\(\mathbf{-50}\)** & **\(\mathbf{-40}\)** & **\(\mathbf{-30}\)** & **\(\mathbf{-30}\)** & **40** & **50** \\ \hline
**Experiment** & \({}^{\circ}\)C & 58.3 & 84.1 & 110.7 & 146.1 & 196.1 & 168.3 \\
**Analysis** & & 46.8 & 72.2 & 132.6 & 194.2 & 194.2 & 132.6 \\
**Deviation** & \% & 19.8 & 14.2 & \(-19.8\) & \(-32.9\) & 1.0 & 21.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Comparison of maximum displacements in y-direction [mm]. Figure 12: AL6063-T5 material properties required for heat transfer analysis: (**a**) Density; (**b**) specific heat; (**c**) thermal conductivity. Figure 13: Simplify the design geometry of the full-frame structure. The simulation was performed by transient analysis to investigate the history of temperature according to time. The welding process sequence was in the order of front, rear, right, and left, as shown in Figure 15a, to conduct the pre-process of heat transfer analysis. To enter the temperature of the heat source derived through test correlation into the center of the weld, this study created an area to enter the heat source in the welding direction of the 3D model as shown in Figure 15b. The area to enter the heat source was divided into 50 mm sections from 2, 5, and 10 mm from the welding center line. The temperature entered in this range was determined by averaging the temperatures derived through the specimen unit test correlation as shown in Table 9. The movement of the heat source under optimal process conditions (80 mm/min welding speed) was implemented by configuring time steps to enter temperatures every 37.5 s in the temperature input area divided into 50 mm sections. The heat source application time (welding time) was 1 h, 21 min, and 40 s, and the cooling time to lower the temperature of the structure to room temperature was 1 h, so the total time step was set to 2 h, 21 min, and 40 s. In terms of the convection heat transfer coefficient, which is a factor that affects the cooling of the structure, this study applied 20 for areas in contact with air and 200 W/m\({}^{2.\circ}\)C for areas in contact with metal by jigs [15; 16]. Figure 16 shows the temperature distribution history of the full-frame structure as the result of heat transfer analysis. The figure shows the distribution of temperature drops as the tool moves from the previous weld zone to the next weld zone and the temperature distribution for a total of 2 h and 30 min including the welding time around 1 h and 30 min and the time it takes to cool down the structure to room temperature.