The purpose of the investigation was to attempt to determine the correlation between the growth of the side value of the cellular structure and the maximum force set for each of the samples. With reference to Table 4, it can be seen that the weight of the models printed from the PLAG material is slightly higher than the models made from the other two materials. This fact can be observed for each model of the hexagonal structure, even though they were manufactured from the same stereolithographic file and with constant printing parameters.
Table 4
Characteristics of hexagonal samples
Type of Material | PA2200 | PLAB | PLAG | PLAW |
Type of Sample | Mass, g | Max Load, N | Mass, g | Max Load, N | Mass, g | Max Load, N | Mass, g | Max Load, N |
5Hex1 | 0.93 | 226.52 | 0.92 | 82.40 | 1.01 | 103.65 | 0.97 | 128.43 |
5Hex2 | 0.92 | 222.46 | 0.93 | 87.79 | 1.02 | 72.82 | 0.96 | 84.09 |
5Hex3 | 0.93 | 228.48 | 0.93 | 87.59 | 1.02 | 94.02 | 0.95 | 100.72 |
5Hex4 | 0.94 | 227.59 | 0.94 | 55.55 | 1.02 | 101.85 | 0.94 | 124.40 |
5Hex5 | 0.93 | 219.72 | 0.93 | 90.42 | 1.03 | 80.06 | 0.93 | 117.99 |
\(\stackrel{-}{X}\) | 0.93 | 224.954 | 0.93 | 80.750 | 1.02 | 90.480 | 0.95 | 111.126 |
σ | 0.007 | 3.722 | 0.007 | 14.384 | 0.007 | 13.562 | 0.016 | 18.452 |
6Hex1 | 1.12 | 143.78 | 1.23 | 71.41 | 1.29 | 68.52 | 1.21 | 71.59 |
6Hex2 | 1.11 | 159.44 | 1.23 | 78.39 | 1.28 | 71.48 | 1.21 | 67.9 |
6Hex3 | 1.11 | 157.41 | 1.22 | 72.20 | 1.29 | 73.83 | 1.20 | 65.2 |
6Hex4 | 1.11 | 152.00 | 1.21 | 74.51 | 1.28 | 72.47 | 1.21 | 61.37 |
6Hex5 | 1.13 | 148.61 | 1.23 | 75.59 | 1.29 | 64.34 | 1.21 | 64.58 |
\(\stackrel{-}{X}\) | 1.116 | 152.248 | 1.224 | 74.420 | 1.286 | 70.128 | 1.208 | 66.128 |
σ | 0.009 | 6.391 | 0.009 | 2.79 | 0.005 | 3.778 | 0.004 | 3.836 |
7Hex1 | 1.31 | 105.39 | 1.44 | 60.42 | 1.54 | 57.63 | 1.45 | 57.87 |
7Hex2 | 1.30 | 113.12 | 1.42 | 70.18 | 1.55 | 62.43 | 1.44 | 57.01 |
7Hex3 | 1.31 | 108.26 | 1.41 | 75.13 | 1.54 | 57.99 | 1.43 | 55.41 |
7Hex4 | 1.33 | 101.42 | 1.41 | 68.28 | 1.54 | 61.11 | 1.44 | 56.48 |
7Hex5 | 1.27 | 97.52 | 1.41 | 69.23 | 1.53 | 58.67 | 1.44 | 59.67 |
\(\stackrel{-}{X}\) | 1.304 | 105.142 | 1.418 | 68.648 | 1.540 | 59.566 | 1.440 | 57.288 |
σ | 0.022 | 6.029 | 0.013 | 5.304 | 0.007 | 2.099 | 0.007 | 1.602 |
Models manufactured from the PLAB material exhibited the lowest force decrease. The maximum force set for models with hexagonal structures made from this material oscillated between 60–90 N, even though the mass of the models was slightly less than that of models made from the other materials. In the case of the PLAW material, it was noted that the highest values of Maximum Force for the length of the side a1 = 5mm. However, the maximum force values for the a2 and a3 sides were in the 55–72 N range. A similar situation was observed with the PLAG material, where, despite the slightly higher mass of each of the cellular structure models, a higher standard deviation for maximum force was recorded for the a1-sided structure, however, the force adopted values for in the range 72–104 N. According to the determined characteristics, it can be concluded that for PLAB material the values are clustered closest in the case of side a1 and a2. In the case of side a3, the values are most closely clustered for models manufactured from PLAW material. The maximum force value for the samples manufactured from PA2200 material was 228.48 N. For all samples manufactured from PA2200 material, the maximum forces were higher than those from PLA materials, but for the 6 and 7mm side models the standard deviation was twice as high as for the 5mm side samples.
Figure 4Plots Load – Displacement – Side a1 = 5mm:
A) FFF-PLAB; B) FFF-PLAG; C) FFF-PLAW; D) SLS-PA2200.
In contrast to PLA samples, the samples manufactured from PA2200 showed a higher compressive strength, the results were more concentrated around a single value and the load-displacement plots showed that the samples had a similar behaviour in spite of the increase in side length, as shown in the plots in Fig. 4. The maximum strength for models manufactured by SLS technology is almost twice as high as for FFF technology.
Figure 5 Plot Load – Displacement – Side a 2 = 6mm:
A) FFF-PLAB; B) FFF-PLAG; C) FFF-PLAW; D) SLS-PA2200.
Models manufactured from PLA materials showed similar maximum force values. However, each sample from this range of materials had a different behaviour when a compressive force was applied. In the case of the PLAB material samples, there was a partial collapse of the upper part of the model which is characterised in Fig. 5 by the A diagram between 2-2.5 mm. In the case of the PLAG material samples, it was noted that the models collapsed after reaching the maximum force in the range
of 1.5-2 mm with a very short displacement of 2 to 3 mm. In the case of the PA2200 material samples shown in Fig. 5, graph D, it was shown that the SLS-made models exceeded, also by almost double the maximum force in comparison to the PLA material models, and the graphs did not show any particular localised jumps or significant decrease in the force acting on the models, or as in the case of the PLAW material graphs for samples 1 and 4 in the range of 2.25-3 mm the collapse of the upper part of the model.
Figure 6 Plot Load – Displacement – Side a 3 = 7mm
A) FFF-PLAB; B) FFF-PLAG; C) FFF-PLAW; D) SLS-PA2200.
The PLAG and PLAW material specimens showed multiple arm kinks in the
1–3 mm range as indicated by graphs B and C in Fig. 6. In contrast to the previous samples with 5 mm and 6 mm side values, the samples manufactured from PLAB material showed that, for a given compressive force, the samples reached at 3 mm strain closer to the 5 mm side values and did not show a significant effect on the shoulders, i.e. kinking as in the case of the 6 mm side samples. A similar situation occurred, i.e. for the other samples manufactured from the PA2200 material by SLS technology.