## 3 Results and Discussion
### Optimisation of Target Variables
For this range, a width of the HAZ below 2700 \(\mathrm{\SIUnitSymbolMicro m}\) and above 2600 \(\mathrm{\SIUnitSymbolMicro m}\) was predicted. Figure 11: Response surface plot (a) and contour plot (b) for the width of the WEZ with the influence of roving integration. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Factor** & \(-\boldsymbol{\alpha}\) & \(-\boldsymbol{1}\) & \(\boldsymbol{0}\) & \(\boldsymbol{1}\) & \(\boldsymbol{\alpha}\) \\ \hline \(T_{\mathrm{D}}\) (\({}^{\circ}\)C) & 335 & 338 & 345 & 352 & 355 \\ \(v_{\mathrm{D}}\) (\(\mathrm{mm}/\mathrm{min}\)) & 92 & 99 & 116 & 133 & 140 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Factor levels used for the CCD with abbreviations. Equation (7) shows the regression function generated by Minitab to describe the depth of the HAZ with the influence of the roving integration. \[\mathrm{t_{HAZ}}=39,969-224.5\mathrm{T_{D}}-18.14\mathrm{v_{D}}+0.33\mathrm{T_{D} ^{2}}+0.0651\mathrm{v_{D}^{2}} \tag{7}\]  
The standard error of the regression, S, for the depth of the HAZ was also low at 35.6891 \(\upmu\)m. Therefore, the predicted deviation from the actual value was only 35.6891 \(\upmu\)m. The coefficient of determination of R\({}^{2}\) = 0.7178 was lower than that for the width model, but it is acceptable. The surface response and contour plot for t\({}_{HAZ}\) is shown in Figure 12.  
It can be seen that the depth of the HAZ also decreased with the decreasing nozzle temperature and increasing nozzle feed rate. This is also consistent with the findings of Study 1. In addition, an increasing effect with an increasing nozzle temperature and decreasing nozzle feed rate can also be seen for the depth. This effect can be attributed to the same causes as for the width. The optimum range for depth is also shown at the top left of the contour diagram (b). In this case, the point was at a nozzle temperature between 335 \({}^{\circ}\)C and 345 \({}^{\circ}\)C and a feed rate between 130 mm/min and 140 mm/min. For this range, the depth of the HAZ was predicted to be below 540 \(\upmu\)m and above 520 \(\upmu\)m.  
To investigate the roving integration's influence on the HAZ's width and depth, the same factor levels were chosen in the FE model as in Table 8[21]. Equation (8) shows the regression function for the FE model results to describe the HAZ depth without the influence of the roving. \[\mathrm{t_{HAZ}}=63,424-369\mathrm{T_{D}}-1\mathrm{v_{D}}+0.541\mathrm{T_{D}^{ 2}}+0.0008\mathrm{v_{D}^{2}} \tag{8}\]  
In addition, the central composite design's central point without roving integration was repeated five times on the developed LS machine to quantify the influence of roving integration on the HAZ experimentally. In the following Figure 13a, the surface response plot according to Equation (8) of the FE model (lower surface response plot, without the influence of the roving) and of Equation (7) (upper surface response plot, with the influence of the roving) were compared. Figure 13b shows the experimental comparison of the central point with and without roving integration. It can be seen that with roving integration, the depth of the HAZ was more significant compared to without roving integration. In addition, Figure 13b shows that roving integration mainly affects the depth (+100 \(\upmu\)m) and only marginally the width of the HAZ (+32 \(\upmu\)m). The overlapping of the scatter bars also shows this. The reason for the increase in depth is the heat transferred from the heated  
Figure 12: Response surface plot (**a**) and contour plot (**b**) for the depth of the WEZ with the influence of roving integration. fibre nozzle to the roving. The intrinsic heat generated by the roving caused additional melting, increasing the HAZ's depth by an average of 110 \(\upmu\)m.  
For the evaluation of the roving overlap above the part level in which the roving was integrated (process reliability), no significant influence of the nozzle feed was found on the nozzle feed rate in the range between 92 mm/min and 140 mm/min.