# A Comparative Study on the Laser Welding of Ti6 Al4V Alloy Sheets in Flat and Horizontal Positions
## 3 Results  
### Weld Profile Defects  
The cross sections of the laser welds produced with the two sets of laser welding parameters used are shown in Figures 4 and 5, respectively. The dimensions of weld profile defects measured for these laser welds are listed in Tables 4 and 5. Table 4 lists the undercuts of welds, from which it can be found that, for flat welds, the face undercut is greater than the root undercut. Undercuts on the left side and the right side are essentially the same, i.e., symmetrical about the weld centerline. A decrease in heat input (i.e., using 2.5 kW and 20 mm/s, instead of 2.2 kW and 8 mm/s) results in a noticeable increase in face undercut, while the root undercut is less affected. For horizontal welds, the undercuts on the left side and the right side are no longer symmetrical. The left side (which is on the top side during horizontal welding) is notably larger than the right side (which is on the bottom side during welding). A decrease in the heat input results in an increase in the face undercut but decrease in the root undercut. On the whole, flat welding leads to larger face undercuts but smaller root undercuts than horizontal welding. With regard to the sum of the face and root undercuts on the same side (i.e., left side or right side), it can be found that the sum on the left side for the horizontal welds is notably larger than that on the right side, and is also larger than both the left and right side for the flat welds. The excess weld metal and excess penetration values are presented in Table 5. Among all welds produced in this study, the flat welds have the least excess weld metals but noticeable excess penetrations. Large differences exist between the excess weld metal and the excess penetration for flat welds. The horizontal welds have larger excess metal values than excess penetration values. The differences between the excess weld metal values and the excess penetrations are smaller than the differences for the flat welds. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Welding Position**} & \multirow{2}{*}{**But Weld**} & \multirow{2}{*}{**Face Undercut**} & \multicolumn{2}{c}{**Root Undercut**} & \multicolumn{2}{c}{**Sum of Face and Root Undercuts**} \\ \cline{3-8}  & & & **Left Side** & **Right Side** & **Left Side** & **Right Side** & **Left Side** & **Right Side** \\ \hline \multirow{2}{*}{Flat} & F01 & 71.1 & 75.8 & 0 & 0 & 71.1 & 75.8 \\  & F02 & 116.1 & 101.9 & 0 & 23.7 & 116.1 & 125.6 \\ \hline \multirow{2}{*}{Horizontal} & H01 & 81.0 & 0 & 111.9 & 25.0 & 192.9 & 25 \\  & H02 & 116.0 & 32.9 & 46.5 & 0 & 162.5 & 32.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Undercuts of welds produced under different welding conditions (unit: \(\upmu\)m). Figure 5: Cross sections of laser welds (laser power: 2.5 kW; traveling speed: 20 mm/s). (**a**) Flat welding; (**b**) Horizontal welding. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \begin{tabular}{c} **Welding Position** \\ \end{tabular} & \begin{tabular}{c} **But Weld** \\ **Identity** \\ \end{tabular} & \begin{tabular}{c} **Excess** \\ **Weld Metal** \\ \end{tabular} & \begin{tabular}{c} **Excess** \\ **Penetration** \\ \end{tabular} & \
\begin{tabular}{c} **Face Weld** \\ **Width** \\ \end{tabular} &
\begin{tabular}{c} **Root Weld** \\ **Width** \\ \end{tabular} \\ \hline \multirow{2}{*}{Flat} & F01 & 11.8 & 252.4 & 6194.3 & 6111.4 \\  & F02 & 86.1 & 314.0 & 3784.4 & 3265.4 \\ \hline \multirow{2}{*}{Horizontal} & H01 & 255.8 & 100.3 & 6546.6 & 6339.7 \\  & H02 & 199.1 & 173.8 & 4169.0 & 3470.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Excess weld metals, excess penetrations, face and root weld widths for different welding conditions (unit: \(\upmu\)m). The face and root weld widths of welds are also given in Table 5. For both sets of welding parameters, the face and root widths for the flat welds are slightly smaller than those for the horizontal welds. Face weld widths are larger than root weld widths for both flat welds and horizontal welds.