This review analyses different approaches used to study selective laser sintering (SLS) technology of polymer materials. These main approaches concern: thermal behaviour, fatigue and surface roughness.Regarding the first behaviour, researchers extensively studied the impact of process parameters, including scan speed, laser, power and laser energy density, on the thermal behaviour of 3D printed parts. Numerical and experimental analyses are used to conduct process parameter evaluations.Laser power and scan speed are the most significant parameters of the laser energy density. For the second, according to test protocols and quantitative analysis performed, the authors concluded that the combination of small and large laser energy density particles generates higher sintering and better fatigue resistance. Moreover, tensile analysis in different environments showed that testing in the water decreased the fatigue life of polymer samples. The influence of process parameters on the mechanical properties and surface roughness of 3D parts is also analysed. In addition, the investigators found that the additives increase the surface roughness of 3D printed parts.This review shows that researchers can focus on creating a combination of these approaches to expand the use of this process for industrial part production.All these investigations have made it possible to determine the optimal process conditions to ensure higher quality, optimal surface quality and better fatigue strength.

The presented article analyzes the impact of internal defects on the modal responses of polyamide parts subjected to bending. Samples with defects of various sizes (0, 3, 5, 7, and 10 mm) located at the neutral bending line were tested. Modal properties were measured via an acoustic and a vibration sensor, using impulse excitation and fast Fourier transform (FFT) analysis. Modal properties include peak frequency, damping and amplitude. Non-defective samples show lower peak frequency and stronger amplitude for both detectors. Moreover, defects larger than 3 mm have minimal impact on peak frequency. The vibration detector is more sensitive to delamination presented at 7 and 10 mm defects. In addition, elevated peak frequency at 3 mm is the result of local hardening at the defect edge. Moreover, a neutral line position reduces damping when the defect size approaches 5 mm. Conversely, acoustic detectors ignore delamination and reveal lower damping and amplitude at 7 and 10 mm defects. Furthermore, internal sound diffusion from 3 and 5 mm defects enhances air losses and damping. Acoustic detectors only evaluate fault size and position, whereas vibrational detectors may detect local reinforcement and delamination more easily. These results highlight the importance of choosing the right detector according to the location, size, and specific modal characteristics of defects.

Humidity has a negative effect on the 3D printing quality of polyamide 12 (PA12) components. The influence of humid powder on 3D printed materials has been the subject of several investigations. Nevertheless, there has been limited investigation into how process variables affect the moisture content of 3D parts. Therefore, the work investigates the impact of processing parameters, such as layer thickness and laser power, on the humidity content of 3D-printed PA12 specimens.The humidity rate was determined by comparing the mass change percentage before and after the oven test, in accordance with ASTM standard D6980.Consequently, the humidity rate is reduced because higher heat is generated by an enhanced laser power ratio, particularly at lower layer heights, which evaporates any remaining moisture during sintering. On the other hand, a thinner layer reduces humidity by keeping moisture out of the print output. Combining the effects of laser power and layer thickness reveals that configurations with a low laser power ratio and an elevated layer height are associated with higher humidity rates. Therefore, compared with layer height, laser power has a greater impact on humidity rate, according to ANOVA analysis.Overall, this experiment demonstrated the role of changing process variables in lowering moisture content and suggested future studies to understand better the combined impact of humidity on their mechanical and porosity properties.The originality of the study lies in the examination of how processing parameters, including laser power and layer thickness, affect the moisture content of PA12 manufactured parts.