# Thermal Layer Design in Fused Filament Fabrication
## 4 Discussion  
### Method and Results  
The main variable investigated in this study was layer temperature, controlled by adjusting the printing speed. Here, it is important to point out that the print speed and the resulting layer temperature are not transferable to other geometries and were only used to obtain the specimen test data. A print speed of 50 mm/s was used for the component, as it was the highest speed that could be used with the hardware to produce a component without any large defects. Due to the larger cross-section of the component, the temperature in the component with added mass had a temperature range from 71 to 156 \({}^{\circ}\)C. In future component studies, the combination of printing speed, chamber temperature, and even additional energy sources is needed to achieve the optimal layer temperature of PA6-CF. Due to acceleration and deceleration, the actual speed in certain print areas would be lower in areas of starts/stops. Using TLD, the mass of the component was increased in the thin edges and the center profile, which had the lowest temperatures. As seen in Figure 12, the increased mass led to the layer retaining more heat in the modified areas. By adding mass, more energy is transferred to the local region, and, depending on the local geometry, the area affected by TLD will cool down slower. Although this was the highest reliable printing speed, it did not produce the same temperatures as within the material test samples. The selected component even had a small cross-section relative to the printing bed, and to achieve the optimal layer temperature additional hardware designs need to be explored. The layer temperature was measured using a thermal camera, where the temperature reading was found in the first frames of a stable temperature reading. This manual reading may vary with the person using the camera. The nozzle used 1 s to move away from the specimen to be completely out of the frame of the thermal camera, necessary to obtain a correct reading, and the camera provided continuous data at 8.7 Hz. As seen in Figure 11, the samples disperse heat by approximately 2 degrees per second. Therefore, the measured temperature 1 s later will provide a temperature of some degrees lower compared to the produced specimens. There might also be a variation within each layer, as the temperature is a function of location and time, but we observe in Figure 10 that the temperature is almost evenly distributed. All of the samples were also manufactured identically, so a potential deviation would be constant through all of the samples. Another source of uncertainty is the emissivity of the deposited material changing with temperature. A study on acrylonitrile butadiene styrene (ABS) found that this effect led to a misread of 36 \({}^{\circ}\)C at a 240 \({}^{\circ}\)C readout temperature [21]. However, this is above the melting temperature of ABS, and a finished layer of a print will have cooled down when being measured. Because the increase in the layer temperature is caused by an  
Figure 12: Thermal distribution mid-printing and as the layer is completed: (**a,b**) for the original component, (**c,d**) for the component with added mass, respectively. increase in the speed and stays well below the melting temperature for PA6-CF, the trend should be intact. Although temperature measurements were recreated several times during testing, improved setups for monitoring the layer temperature of printed specimen should be investigated, preferably during the production to gather more accurate estimations of actual in situ temperature. Figure 5 shows that the peak UTS is reached in the layer temperature range from 167 to 175 \({}^{\circ}\)C. This range also resulted in the smallest deviation between specimens. The UTS results reach the higher end of the reported 67.7 \(\pm\) 4.7 MPa by the manufacturer [14]. The UTS in this study is based on the nominal cross-section, although the true area of the specimen cross-section does contain voids with an increased printing speed.