# Thermal Layer Design in Fused Filament Fabrication
## 2 Materials and Methods
### Material Testing  
The procedure for the manufacturing and testing of material specimens is given in Figure 1. All of the samples were manufactured and tested using the ISO-527 standard [16] as a guideline, which was also used in the manufacturer's technical datasheet [14]. Specimens were printed in the Z-direction to investigate the influence of the layer deposition temperature on material properties. When investigating the effect of layer temperatures, more target temperatures are considered a higher priority than the number of samples at each temperature to create a trendline. Therefore, three samples were considered the minimum as the process is time-consuming. The printer used to produce test specimens is a modified Creality CR-10 [12]. The filament used was a commercial grade PolyMide PA6-CF from Polymaker [14] with a diameter of 1.75 mm. The filament contains 20 wt% chopped carbon fibers [14]. The filament had been stored at room temperature for six months in vacuum bags filled with  
Figure 1: Shows steps 1 through 6 for the production, measurement, and testing of specimens, with symbols representing temperature and time. In step 2: E—extruder; C—chamber; and B—bed. silica. Before the manufacturing of the specimens, the filament was dried at 75.6 \({}^{\circ}\)C for 24 h and continuously kept at this temperature during printing. The specimen geometry is based on ISO 527 and was adapted to reduce printing time due to the large number of samples needed. 3D models of the specimens were created by computer-aided design (CAD) using Solidworks and exported to STL using the maximum resolution. The thickness was increased and the width was slightly reduced, as thinner geometries tend to overflow and create variable geometries. The cross-sectional area of the gauge section is 50 mm\({}^{2}\). Figure 2 shows the nominal dimensions of the test specimen model. SuperSlicer, a forked open-source version of Prusa Slic3r, was used to modify the settings for the printing process [16]. The specimens were printed with several fixed parameters, using the printing speed to manipulate the layer temperatures. The fixed parameters are listed in Table 1. Table 2 lists the used printing speeds and approximate values of the effects on volumetric flow and time to complete each layer in the gauge section, calculated in the slicer. The specimens were printed three at a time sequentially, completing individual objects before starting the next one. Placing the samples with the wide side perpendicular to the x-axis on the bed allowed for higher print speeds with fewer geometrical defects. To minimize moisture exposure, the specimens were removed from the heated chamber and placed in individual zip-lock bags. After organizing all of the finished prints, the lengths, widths, and thicknesses of the specimens were measured using calipers and micrometers. Measurements were taken at several places on the specimen, and the most-significant deviation was documented. As the geometrical details of the specimens change with the printing speeds, the average centerline roughness of the surface, Ra, was measured using a Mitutoyo SJ-301 surface roughness profilometer. After all of the geometric measurements were made, the specimens were annealed at 100 \({}^{\circ}\)C for 6 h, following the manufacturer's recommendations [14]. The specimens were placed on a salt bed in a preheated oven to ensure an even heat distribution during annealing. After the heat treatment, the specimens were placed back into individual zip-lock bags. Tensile testing was performed 30 min to 3 h after annealing, as the specimens were annealed in batches. Tests were performed using MTS Criterion Electromechanical Load Systems, the model of which was C42.503, 5 kN.