## 3 Experimental
### Preliminary Investigations on Electrical Bonding  
To determine the influence of electrical bonding on the resulting resistance, different concepts for applying electrical bonding were investigated. The dimensions of the test specimen were chosen as 60 \(\times\) 20 \(\times\) 0.8 mm\({}^{3}\) (see Figure 2). However, the area of electrical bonding was restricted to an area of 5 \(\times\) 20 mm\({}^{2}\) on both sides on the upper side of the specimen; the length varied slightly between the individual concepts. The different concepts of electrical bonding are represented in Figure 6, whereas Table 4 shows an overview of the investigated variants in comparison to the test specimen without any additional electrical bonding concept. FFE was exemplarily tested by using the following process parameters for manufacturing: a raster angle of 0\({}^{\circ}\), an extrusion temperature of 230 \({}^{\circ}\)C, a speed of 40 mm/s, a layer height of 0.2 mm and a flow rate of 100%. It is worth noting that the pressed-in electrical bonding concepts (no. a-c) and the specimen without electrical bonding showed a high dependence of the resulting resistance on the applied pressure during the measurement. Therefore, these variants were not suitable for the following experimental investigations as the varying resistance of the electrical bonding would significantly falsify the measurements. The results represented in Table 4 show a vast range of resulting resistance from 50.5 \(\Omega\) (silver paste) to 1504 \(\Omega\) (copper wire) depending on the utilized concept of electrical bonding due to the contact resistance. In comparison to the different variants of electrical bonding, the specimen without electrical bonding had significantly higher resistance and scattering. Hence, the selection of the electrical bonding variant is a key factor in additively manufactured conductive structures, since it influences the resistance decisively. Thus, for the experimental investigation presented in Section 4, the silver paste (e) was used due to the very low bonding resistance and its easy application. \begin{table}
\begin{tabular}{c c c} \hline \hline
**No.** & **Name of Electrical Bonding Variant** & **Resistance (\(\Omega\))** \\ \hline  & Without electrical bonding & 6850–8500 1  \\ (a) & Crimp connector (round); pressed in & 403–597 1  \\ (b) & Crimp connector (flat); pressed in & 845–1209 1  \\ (c) & Copper wire (\(\Omega\) 1.3 mm); pressed in & 963–1504 1  \\ (d) & Copper tape (width 5.5 mm); inlaid during manufacturing process & 791 \\ (e) & Silver paste (EMS 12640); deposited after manufacturing process [ENDFOOTNOTE] & 50.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Different concepts of electrical bonding examined using Functionalize F-ElectricTM PLA. Figure 6: Illustration of the different investigated variants of electrical bonding: (**a**) crimp connector (round), pressed in; (**b**) crimp connector (flat), pressed in; (**c**) copper wire, pressed in; (**d**) copper tape, inlaid during printing; and (**e**) silver paste, applied after printing. To analyze the influence of the silver paste on the resulting resistivity, the feedstock materials of the used materials PPC, 3 dk, FFE and M3D were bonded along the filament strand. The distance between the measuring points was selected as 20 mm and the total measurement distance was set to 270 mm. A total of three filament strands per material were examined to determine the mean value and the standard deviation. Figure 7 shows the results of the experimental investigations. It can be seen that the electrical bonding positively influences resistivity of the feedstock material, with M3D being an exception. Furthermore, the determined resistivity of PPC, 3 dk and FFE is lower than the manufacturer information suggests, while M3D's resistivity is significant higher (see Table 2). For PPC and FFE, the influence of the electrical bonding on the resistance is very low above a measuring length of 40 mm, whereby its influence on PPC is lower as the resistivity is higher compared to FFE.