Effects of Printing Angle, Infill Density and Cryogenic Pre-Treatment on the Tensile and Flexural Properties of FFF-Printed PLA

Additive manufacturing of polymer materials, also known as 3D printing, is becoming a key technology for the production of functional parts with the ability to customize the structure and properties according to the application requirements. Polylactide (PLA) is one of the most commonly used materials in this field due to its biodegradability, ease of processing, and adequate strength for lightweight functional components. An important factor that affects the resulting properties of parts is not only the filler structure and density but also the angle at which the material is deposited during the printing process. This article focuses on investigating the influence of the printing angle (0°, 30°, 60° and 90°) and the bulk density of the filler (20%, 40%, 60% and 80%) on the mechanical properties of PLA samples. Two series of samples were prepared—the first was subjected to direct mechanical tests, and the second series was first exposed to freezing conditions and then tested to evaluate the effect of freezing on the material behavior. The samples were tested for tensile strength according to ASTM D638 and for bending strength according to ASTM D790. The results showed that the highest values were achieved in tensile strength in the 60°/80% configuration with a strength of 39.27 MPa, which represents more than a twofold improvement over the weakest configuration (0°/20%–19.58 MPa). In the bending test, the best results were achieved by the 90°/80% sample with a strength of 58.89 MPa, approximately 18% higher than 0°/20%. Cryogenic treatment caused a deterioration of all monitored parameters, especially at low infill densities and at an angle of 0°, where the decrease in strength reached up to 10–13%. These results confirm that the combination of a higher printing angle and a higher infill density is key to optimizing the mechanical properties of PLA parts, while cryogenic treatment has a negative impact on their behavior.