# Assessment of Laser Joining Quality by Visual Inspection, Computer Simulation, and Deep Learning
## 2 Experiments  
### Experimental Setup  
A diode laser was used as the heat source in the experiments because these lasers are widely used for polymer bonding due to their excellent efficiency and ease of control. As shown in Figure 1, a laser beam resonated by the diode laser (c) was transmitted through fiber optics. The specimen was placed on the working table controlled by a computer numerical control (CNC) machine (a), and integrated control was achieved using a laptopcomputer (b). The delivered laser beam was focused on the specimen through a focusing lens installed at the head of the CNC.  
The laser beam was transferred to the CNC head, and the distance between the workpiece and focus lens (FL = 50 mm) could be adjusted to obtain the desired beam size. In the experiments, the focused spot diameter was set to 5 mm based on the preliminary experimental results. A 3-axis-controlled CNC machine (SME3030; SME Trading) was used for the precise transfer of specimens by G-code, and both the laser and specimen transfers were controlled using the laptop. The laser generated a continuous waveform (CW) with a wavelength of 980 nm, and the output was set in the range of 3-17 Watts. The welding speed was set in the range of 60-250 mm/min depending on the output power. A total of 15 combinations of laser power and welding speed were used to achieve an input energy per unit length of 3-5 J/mm; the detailed welding schedules are summarized in Table 1.  
The irradiated laser beam passed through the transparent PC material and was absorbed on the boundary by the ABS material (through transmission). The absorbing layer was heated to the glass transition temperature, which is approximately 135 and 110 \({}^{\circ}\)C for PC and ABS, respectively [19]. Then, the absorbed heat energy on ABS transferred to the contact PC layer, which resulted in a crosslinking of polymer chains at the contact boundary.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{1}{c}{**Input Energy (J/mm)**} & \multicolumn{1}{c}{**Power (Watt)**} & \multicolumn{1}{c}{**Welding Speed (mm/min)**} \\ \hline \#1-1 & 3 & 3 & 60 \\ \hline \#1-2 & 3 & 5.5 & 110 \\ \hline \#1-3 & 3 & 8 & 160 \\ \hline \#1-4 & 3 & 10.5 & 210 \\ \hline \#1-5 & 3 & 13 & 250 \\ \hline \#2-1 & 4 & 5 & 75 \\ \hline \#2-2 & 4 & 7.5 & 112.5 \\ \hline \#2-3 & 4 & 10 & 150 \\ \hline \#2-4 & 4 & 12.5 & 187.5 \\ \hline \#2-5 & 4 & 15 & 225 \\ \hline \#3-1 & 5 & 7 & 84 \\ \hline \#3-2 & 5 & 9.5 & 114 \\ \hline \#3-3 & 5 & 12 & 144 \\ \hline \#3-4 & 5 & 14.5 & 174 \\ \hline \#3-5 & 5 & 17 & 204 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Matrix of welding schedule.  
Figure 1: Experimental setup.  
For the experiments, the specimens on the joining jig were prepared, and the materials were cut to dimensions of 42 \(\times\) 100 \(\times\) 6.5 mm for ABS and 42 \(\times\) 100 \(\times\) 3 mm for PC. The specially designed jig shown in Figure 2 was used to hold the weld specimens. Precision mold springs and wrench bolts were used to maintain a precise and constant pressing force on the specimens via pressure plates made of aluminum. The mold springs had an inner diameter of 6 mm, an outer diameter of 12 mm, a free length of 40 mm, and a spring constant of 0.7 kg\({}_{\text{f}}\)/mm. The wrench bolts were tightened in four places to yield a force of 22.4 kg\({}_{\text{f}}\) in total.