## 3 Experimental
### Experimental Set-Up
#### 3.1.2 Machine and Manufacturing of Test Specimens  
Material extrusion was chosen for the manufacturing of the test specimens, since multi-material MEX allows a combination of multiple materials for incorporation electrically conductive structures. MEX uses thermoplastic polymers as feedstock materials that are directed into an extruder unit where the material is melted. The plasticized material is applied to a build platform or previous layer according to the individual cross section of the generated part. Due to thermal fusion, the applied layer bonds with the surrounding already solidified material. In this way, the part is generated layer by layer [8]. The process of multi-material MEX was shown and described in more detail, for example, by [PERSON] et al. (2018) [29]. For manufacturing of the specimens, the pro-consumer machine X400 by German RepRap GmbH (Feldkirchen, Germany) with a dual extruder system was used. The printer comes with a heated build platform and a direct extruder with a nozzle diameter of 0.4 mm. For the preparation of the build job, the slicing software Simplify3D (version 4.0) was used. Table 2 gives an overview of the utilized process parameter sets. In addition, the line width was set to 0.4 mm and no perimeter shells were used. The material was directly processed on object slides that were positioned in recesses in a sheet metal (see Figure 5). In the sheet metal, three object slides can be positioned. On each object slide, three test specimens were printed with the same set of process parameters. In one build job, three batches were manufactured one specimen after another to ensure repeatable process conditions. In addition, solely the extrusion speed varied in one build job, whereas extrusion temperature, flow rate, and raster angle orientation were equal. All specimens were manufactured by using the identical calibration set-up and the same environmental conditions (ambient temperature of \(23\pm 1\)\({}^{\circ}\)C and a relative humidity of 45-50%).  
Due to this experimental set-up, the specimens did not have to be removed from the build table after the manufacturing process, thus damage due to the removal was avoided. Further, the electrical bonding and the measurement of the electric resistance was conducted without detaching the specimens from the object slides. Thus, the repeatability of both the manufacturing process and the characterization of the specimen's resistance was improved. The specimens for analyzing heat radiation capacity were also directly processed on object slides.  
Before starting the manufacturing process, the materials were dried: the materials based on PLA at 45 \({}^{\circ}\)C and M3D at 30 \({}^{\circ}\)C, for 4 h each. To ensure equal environmental conditions during the printing process, the materials were stored in a box during the manufacturing process that regulates relative humidity at about 20%. Before testing, all specimens were stored at an ambient temperature of \(23\pm 1\)\({}^{\circ}\)C and a relative humidity of 45-50% for at least one week in the laboratory.  
Figure 5: Representation of the additive manufacturing process of test specimens for characterization of resistivity on object slides exemplarily shown based on preliminary investigations with different raster angle orientations.