PSI - Issue 42

Manuel Sardinha et al. / Procedia Structural Integrity 42 (2022) 1274–1281 M. Sardinha et al. / Structural Integrity Procedia 00 (2022) 000–000

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2(a), the higher the bed temperature, the less likely it is for the part to warp, and the temperature chosen to promote consistent warping was 74ºC. Bed coating also significantly impacts warping; therefore, three di ff erent coatings were tested: solid UHU glue, Isopropyl alcohol, and glass cleaner, and as shown in Figure 2(b), exclusively properly cleaning the build platform with isopropyl alcohol provided the most consistent warping.

Fig. 2: Results of tests concerning the: (a) bed temperature; (b) bed coating;and (c) specimen’s grading by printing temperature.

Finally, the printing temperature is also a key factor when evaluating the warping phenomena. The higher the printing temperature, the minor warping can be expected [7, 13, 15]. The tested printing temperatures are shown in Figure 2(c), where the authors assign a qualitative classification (0-5) of the appearance of the parts, based on visible deformations. For temperatures below 210ºC, the nozzle was not hot enough to partially melt the leftover material on the tip which often potentiated a clogged nozzle; on the other hand, a higher printing temperature led to increased material ’draining’ and a visually worse the final product. Reports can be found with suggestions of increasing the temperature to reduce warping, as well as statements advising it should not be lower than 215ºC for ABS [11, 18]. According with the results shown in Figure 2(c), the used printing temperature for all specimens was 220ºC. In prismatic samples, the most warped regions are the vertices of each specimen [15]. For this reason, four of the six measuring points were located on those vertices. An analogue comparator was used to measure the height di ff erences, as shown in Figure 3, and a mobile set was used to assemble it. This last included a vernier height gauge, an adaptor for the comparator and a moving handle. Note that the specimen is flipped upside down during the measurements. Notably, since there is a constant relation between the points of specimens and their relative location while being produced (equal in all samples), points 5 and 6 always displayed the highest geometrical distortions. Such a conclusion suggests that regardless of calibration precision, there is always a level of inclination of the build platform or an uneven distribution of build platform temperature, hence the observed tendency of pronounced warping in the sides of the cuboid. Using the height measured by the analog comparator, the absolute and relative warping can be calculated, as shown in Table 2. 2.2. Distortion measurements

Fig. 3: Illustration of the measuring setup and points.