## 4 Composite Blade Manufacturing  
After the sections of the two moulds are 3D printed (Figure 6a), they are assembled using a rubber hammer and a polyamide punch and placed on a flat plane. The sections are bonded together (Figure 6b) using a polyurethane adhesive, which has the advantage that as it hardens, the volume of the adhesive increases, thus ensuring the tightness of the mould and filling any gaps that may occur. The assembly of the mould is followed by the adjustment of the active surfaces. These are sanded and, where necessary, filled with putty to fill in low areas and even out the surface. Next, the mould is coated with a layer of 2K primer (Figure 6c), which serves as a separation layer between the composite (blade) and the 3D-printed mould. The manufacture of the anti-torque blade begins with the preparation of the parts that are to be used and the preparation of the moulds. Thus, the first step is to manufacture the blade core by 3D printing (Figure 6d). To do so, the following were of great importance: the walls should be as thin as possible and the infill density as low as possible. The blade core takes the place of a structure for which traditionally, various materials are used [56,57], namely PVC foam (polyvinyl chloride), moltoprene, Nomex honeycomb, and metallic honeycomb. The advantage of a 3D-printed core allows the construction of a hollow cavity which decreases the overall mass of the finished part. The core is manufactured on a Prusa MK2 3D printer (Prusa Research a.s., Prague, Czech Republic) from PLA filament, it has an outer wall of 0.3 mm and 4 inner stiffening ribs of the same thickness (Figure 6d); additionally, it has two perforated bores allowing the insertion of carbon rods. As shown in Figure 6e, the anti-torque blade is built from the outside to the inside from a carbon fibre shell, which encloses a structural box girder made of two unidirectionally-arranged fibreglass spars, the direction of lamination being in the blade span. In the mid-section, the blade box girder is made up of a 3D-printed core through the middle of which two 4 mm diameter carbon rods pass. These rods are used to join the core structure, which is made up of six sections. The tips of the rods are inserted into the end section of the blade core and pass through the perforated bores of the core. These rod tips are embedded in the carbon section called the monoblock section of the blade. Additionally, after the \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Mould**} & \multirow{2}{*}{**3D-Printed Section**} & \multicolumn{2}{c}{**Manufacturing Time [h]**} & \multirow{2}{*}{**Filament Consumption [g]**} \\  & & & **Time [g]** & & **[m]** \\ \hline  & 1 & 49 & 874 & 110.52 \\  & 2 & 27 & 473 & 59.8 \\  & 3 & 33 & 578 & 73.08 \\ MAT-COMP V3-FEMALE & 4 & 33 & 578 & 73.03 \\  & 5 & 32 & 575 & 72.7 \\  & 6 & 34 & 616 & 77.82 \\  & 7 & 46 & 834 & 105.49 \\ SUBTOTAL MAT-COMP V3-FEMALE & 254 & 4528 & 572.44 \\  & 1 & 49 & 874 & 110.52 \\  & 2 & 32 & 653 & 82.56 \\  & 3 & 34 & 678 & 85.75 \\ MAT-COMP V3-MALE & 4 & 33 & 637 & 85.07 \\  & 5 & 34 & 686 & 86.71 \\  & 6 & 33 & 667 & 84.26 \\  & 7 & 33 & 641 & 81.02 \\ SUBTOTAL MAT-COMP V3-MALE & 248 & 4836 & 615.89 \\  & TOTAL & 502 & 9364 & 1188.33 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The printing time and filament consumption needed to manufacture the anti-torque blade mould. lamination of the monoblock structure, two layers of Kevlar are laminated to the leading edge. The Kevlar layers are added for reinforcement of the structure in case of impact or to prevent premature wear of the blade. In order to obtain a roughness of the active surfaces of the two moulds (upper and lower), two models of the upper surface (Figure 7a) and lower surface (Figure 7b) of the blade were manufactured by the thermoplastic extrusion process, this time being positive shapes of the mould section. The active surface of the mould is sanded with the help of these and abrasive paper of different grits.