## 3 Results and Discussion
### Optimisation of Target Variables  
To simplify this analysis, the nozzle diameter, nozzle curvature, nozzle distance and temperature of the additional heat source were kept constant. According to Study 1, the nozzle diameter should be as small as possible to obtain a small value of b\({}_{\text{HAZ}}\). As in Study 1, an outer diameter of 2 mm was used in this analysis. This value represents the smallest diameter that can be manufactured. In addition, a planar nozzle was used since the influence of the nozzle curvature was negligible with decreasing nozzle diameters, according to the findings from Study 1. As mentioned in Study 1, a nozzle spacing of 0.4 mm resulted in increased powder adhesion to the fibre nozzle. In preliminary tests, this value was increased to 0.6 mm. At this nozzle distance, rovings can be repeatedly integrated without powder adhesion [26]. According to Study 1, increasing the nozzle distance leads to widening the HAZ. Since this effect was not desired, the nozzle distance was kept constant at 0.6 mm. The temperature for the additional heat source at the fibre integration unit was set to 185 \({}^{\circ}\)C to avoid the premature crystallisation of the part and, thus, curling during roving integration. Therefore, the nozzle temperature and the nozzle feed rate remained as factors in this analysis. The result was a two-dimensional model. For the analysis of the nonlinear effects, the predicted operating point from the FE model in COMSOL Multiphysics formed the starting point--see in [21]. In this simulation-based optimisation, it was assumed that the depth of the HAZ must be at least as thick as the roving thickness to place the roving completely into the generated HAZ and, thus, avoid contact between the roving and the recoater. With a measured roving thickness (1K) of 0.4 mm, the FE model predicted a nozzle feed rate of approx. 110 mm/min at a nozzle  
Figure 10: Interaction diagram for the interaction AB for the depth of the HAZ. Figure 9: Interaction diagram for the interaction AB for the width of the HAZ. temperature of 345 \({}^{\circ}\)C. The factor levels for the CCD listed in Table 8 were used to analyse the region around this identified point. Equation (6) shows the regression function generated by Minitab to describe the width of the HAZ. \[\mathrm{b}_{\mathrm{HAZ}}=222,195-1275\mathrm{T}_{\mathrm{D}}-41.8\mathrm{v}_{ \mathrm{D}}+1.878\mathrm{T}_{\mathrm{D}}^{2}+0.1377\mathrm{v}_{\mathrm{D}}^{2} \tag{6}\]  
The standard error of the regression was 108.54 \(\mathrm{\SIUnitSymbolMicro m}\). The model can, therefore, predict the width values with an accuracy of 108.54 \(\mathrm{\SIUnitSymbolMicro m}\). The coefficient of determination was R\({}^{2}\) = 0.8051 and was close to one. The model can, thus, explain a large part of the variance. The model is illustrated in Figure 11 as a surface response (a) and contour plot (b) for interpretation. Figure 11 shows that the HAZ's width decreases with a decreasing nozzle temperature and increasing nozzle feed. It can be seen that the effect of nozzle temperature increased with higher nozzle temperatures. This can be explained by the fact that heat conduction is the dominant effect on the amount of heat transferred, but heat radiation also has an influence. Since heat radiation increases proportionally with the fourth power of temperature according to Equation (3), this can explain the increasing effect of nozzle temperature with increasing temperature. Since the heat flow is a function of the heat energy and the heat transfer period, a higher feed rate will result in a lower heat flow [23]. The effect of the nozzle feed decreased with an increasing feed rate. The surface response with the narrowest HAZ can be seen in the contour diagram (b) in the top left. The nozzle temperature, in this case, was between approx. 335 \({}^{\circ}\)C and 342 \({}^{\circ}\)C with a nozzle feed rate between approx. 135 \({}^{\circ}\)C and 140 \(\mathrm{mm}\)/\(\mathrm{min}\).