## 3 Results and Discussion
### Main Influencing Variables and Interactions

Table 6: Results of the SPD with the effects of the factors and interactions on the width of the HAZ (- no indication of difference, * indifferent, ** significant difference, *** highly significant difference). \begin{table}
\begin{tabular}{c c c c} \hline
**Factor** & **Effect (\(\upmu\)m)** & \(p\)**-Value** & **Significance** \\ \hline Block & - & 0.226 & - \\ A & \(-154.0\) & 0.000 & *** \\ B & \(330.3\) & 0.000 & *** \\ C & \(-234.2\) & 0.000 & *** \\ AB & \(-127.8\) & 0.000 & *** \\ AC & \(71.7\) & 0.013 & * \\ D & \(173.9\) & 0.000 & *** \\ E & \(-270.6\) & 0.000 & *** \\ F & \(22.2\) & 0.350 & - \\ BD & \(2.2\) & 0.927 & - \\ BE & \(-51.7\) & 0.031 & * \\ CF & \(-49.5\) & 0.038 & * \\ DE & \(-62.0\) & 0.010 & * \\ AEF & \(-56.1\) & 0.019 & * \\ BDF & \(-83.3\) & 0.001 & ** \\ ABEF & \(-52.7\) & 0.028 & * \\ ACDF & \(-55.0\) & 0.022 & * \\ \hline \end{tabular}
\end{table} 
Table 7: Results of the SPD with the effects of the factors and interactions on the depth of the HAZ (- no indication of difference, * indifferent, ** significant difference, *** highly significant difference). * The change from a planar to a convex fibre nozzle (A) causes a reduction in the width and depth of the HAZ on average. Accordingly, a planar fibre nozzle should be used for a higher width and a convex fibre nozzle for a smaller width of the HAZ;
* The effect of the nozzle diameter (B) for \(\mathrm{b_{HAZ}}\) was 2247.31 \(\mathrm{\SIUnitSymbolMicro m}\) and for the depth \(\mathrm{t_{HAZ}}\) 330.30 \(\mathrm{\SIUnitSymbolMicro m}\). This means that, ceteris paribus, for every millimetre increase in the nozzle diameter, the HAZ becomes, on average, 1123.65 \(\mathrm{\SIUnitSymbolMicro m}\) wider and 165.15 \(\mathrm{\SIUnitSymbolMicro m}\) deeper. This is also in the expected direction since, according to Equation (3), the transferred heat energy increases with an increasing surface area. Therefore, for small values of \(\mathrm{b_{HAZ}}\), the smallest possible nozzle diameter should be used;
* The effects of the nozzle distance (C) were \(-\)549.25 \(\mathrm{\SIUnitSymbolMicro m}\) for the width and \(-\)234.17 \(\mathrm{\SIUnitSymbolMicro m}\) for the depth of the HAZ. Increasing the nozzle distance, therefore, causes a reduction in \(\mathrm{b_{HAZ}}\) and \(\mathrm{t_{HAZ}}\). This effect seems logical and can be explained by increasing the nozzle distance using Equation (3) and the associated reduced heat flux;
* The effects of the nozzle temperature (D) on the depth and width were 748.13 \(\mathrm{\SIUnitSymbolMicro m}\) and 173.89 \(\mathrm{\SIUnitSymbolMicro m}\), respectively. An increase in temperature by 1 K, ceteris paribus, causes an average increase in \(\mathrm{b_{HAZ}}\) by 24.94 \(\mathrm{\SIUnitSymbolMicro m}\) and 4.35 \(\mathrm{\SIUnitSymbolMicro m}\) for \(\mathrm{t_{HAZ}}\). This effect can also be explained by Equation (3);
* The effect of the feed rate of the fibre nozzle (E) was \(-\)958.22 \(\mathrm{\SIUnitSymbolMicro m}\) for \(\mathrm{b_{HAZ}}\) and \(-\)270.58 \(\mathrm{\SIUnitSymbolMicro m}\) for \(\mathrm{t_{HAZ}}\). Thus, ceteris paribus, increasing the feed rate reduces the width of the HAZ by 31.94 \(\mathrm{\SIUnitSymbolMicro m}\) and the depth by 9.02 \(\mathrm{\SIUnitSymbolMicro m}\) on average. The direction of the effect can be explained by the shorter heat transfer time with an increasing speed. The feed rate is suitable for achieving a deeper HAZ without becoming significantly wider. However, this means a speed reduction. As a high process speed is required, a compromise must be found for this trade-off;
* While the other main factors were rated \"highly significant\", the temperature of the additional heat source (F) was rated \"indifferent, collect more data if possible\" for width and \"no indication of difference\" for depth. However, the additional heat source seems to have had a positive effect. This statement should be interpreted cautiously since the effect is not statistically significant.