## 4 Results and Discussion
### Analysis of Influencing Factors on Resistivity
#### 4.1.2 Extrusion Temperature, Speed and Flow Rate
However, this effect does not occur at flow rate of 95% and 105% so that defects owing to under- or overextrusion are presumed. Whereas at a raster angle of 90\({}^{\circ}\) both speed and flow rate solely slightly influence the resulting resistivity, these parameters for orientations of 0\({}^{\circ}\) and \(\pm\)45\({}^{\circ}\) provide possibilities for adjusting electrical resistance. At a raster angle of \(\pm\)45\({}^{\circ}\), a flow rate of 95% tends to result in a lower resistance. Figure 13 represents the results of the experimental investigations regarding M3D. The resulting resistivity is significantly lower than of the other characterized materials. However, an increase of extrusion temperature results in a higher resistivity, which is contrary to the results of the other experimental investigations. This is due to oxidation of the copper nanowires that are used as filler in the M3D material. According to the manufacturer of the material, the problem of filler oxidation is known, and further development of the material by an additional coating is already planned. Consequently, as extrusion speed is decreased at raster angles of \(\pm\)45\({}^{\circ}\) and 90\({}^{\circ}\) owing to machine's acceleration at the turnaround points, both the thermal damage of the filler and the resistivity increases. In general, lower speeds and lower flow rates negatively influence resistivity due to thermal damage or voids among the beads. In addition, at these flow rates, thermal conductivity of the additively manufactured structures is higher due to internal porosity because the oxidation is likely to be intensified. The range of electrical resistance at \(\pm\)45\({}^{\circ}\) regarding flow rate and extrusion speed is very high. Since PCL has a low melting point and thermal conductivity of the composite polymer is increased due to the filler, an overextrusion results in dense layer bonding and, thus, generally in lower resistivity independent of the raster angle orientation. A low extrusion temperature and a high extrusion speed with few turnaround points (e.g., raster angle of 0\({}^{\circ}\)) results in less thermal damage, but can also lead to defects due to insufficient flowability of the material (see Figure 3). These defects result in an increase in resistance and a reduction in current density. Figure 12: Dependencies of the resistivity of FFE regarding temperature, extrusion speed and flow rate structured by raster angle. Overall, it can be stated that electrical resistance or resistivity of additively manufactured structures can be adjusted by means of the raster angle orientation as well as the process parameters extrusion temperature, speed and flow rate. Raster angle orientation has the biggest influence on resistivity, followed by extrusion temperature. In general, a raster angle of 0\({}^{\circ}\) results in the lowest resistivity, whereas a higher extrusion temperature also leads to decreased resistance except for M3D. Flow rate and speed have a lesser influence; however, a variation of these parameters can also be utilized for an adjustment of resistivity of additively manufactured structures. However, it has to be noted that only three specimens per batch were manufactured and both reproducibility and dependency on geometry have to be investigated in more detail, for example, regarding standard deviation.