Polylactic Acid, commonly known as PLA, is a widely embraced material in 3D printing. Its popularity stems from its plant-based origins, derived from renewable resources like corn starch or sugarcane, making it an environmentally conscious choice. Hobbyists and professionals favor PLA due to its straightforward printing process, minimal warping, and ability to produce models with fine detail and a smooth finish. This ease of use makes PLA an accessible starting point for exploring additive manufacturing.
Understanding PLA’s Material Properties
Understanding PLA’s material properties helps gauge its capabilities. Tensile strength measures a material’s resistance to being pulled apart, and PLA exhibits a good range, between 35.6 to 52.5 megapascals (MPa). This characteristic makes PLA quite rigid, similar to a wooden ruler that resists bending but can snap under enough force. However, PLA has lower impact strength, meaning it can be brittle and prone to shattering when subjected to sudden, sharp forces, much like glass. It also possesses flexural strength, indicating its ability to bend under pressure before breaking, with values often ranging from 52.5 to 72 MPa.
How Print Settings Affect Strength
A 3D printed object’s strength is heavily influenced by how it is printed, not solely by the material itself. Print orientation is one of the most significant factors, as layer lines inherently create weak points in a part. When designing for strength, it is usually better to orient a part so that anticipated forces are applied across these layers, distributing the load along the filament strands, rather than attempting to split the layers apart. For example, printing a hook lying flat on the build plate often results in a stronger part than printing it standing upright, as the layers are better aligned to resist the pulling force.
Infill percentage and pattern also play a substantial role in a print’s overall strength. Increasing the infill percentage directly enhances rigidity. While 100% infill provides the highest theoretical strength, a range of 50-70% often offers a good balance for functional parts without excessive material use or print time. Certain infill patterns, such as triangular or gyroid, distribute stress more effectively than simple grid patterns, contributing to a stronger part. The gyroid pattern, in particular, provides more balanced strength across all three axes.
Increasing the number of outer walls (perimeters or shells) can be more effective for strength than increasing infill alone. These solid outer layers form the structural backbone of the print; for functional components, three or more perimeters are commonly recommended. Smaller layer heights can also improve adhesion between layers, leading to a stronger part. When a thinner layer is extruded, the molten plastic is squished more, promoting better bonding with the layer below and enhancing the part’s integrity.
Strength Comparison with Other Filaments
To understand PLA’s strength, it’s helpful to compare it to other common 3D printing filaments like ABS and PETG. PLA exhibits higher tensile strength, resisting stretching or pulling forces well. However, ABS (Acrylonitrile Butadiene Styrene) offers superior toughness and impact resistance, making it less prone to shattering under sudden forces. ABS also offers higher temperature resistance, maintaining structural integrity up to 98°C, considerably higher than PLA’s softening point of 55-60°C.
PETG (Polyethylene Terephthalate Glycol) often serves as a middle ground between PLA and ABS. It provides improved toughness and impact resistance compared to PLA, absorbing shocks without breaking easily. PETG also has excellent layer adhesion, contributing significantly to the strength and durability of printed parts. With a heat deflection temperature around 70°C, PETG offers better temperature resilience than PLA while being easier to print than ABS.
Improving Strength After Printing
Annealing is a post-processing technique that can further enhance a PLA print’s strength. It involves carefully heating a printed PLA part in a controlled environment, such as an oven, to a temperature below its melting point (60°C to 100°C). This process encourages the plastic’s molecular chains to rearrange and form more crystalline structures, known as recrystallization. The slight melting during annealing helps layers fuse more effectively, reducing weak points associated with layer lines.
After heating, the part cools slowly, often by turning off the oven and letting it return to room temperature gradually. This controlled cooling helps relieve internal stresses and enhances the material’s properties. Annealed PLA parts can see increased stiffness and heat resistance, with some studies indicating a 10-20% gain in strength and reduced brittleness. Annealing can lead to trade-offs like part shrinkage or warping, particularly with complex geometries or inconsistent wall thicknesses. These effects can be minimized by ensuring uniform infill during printing and supporting the part during annealing, sometimes with materials like sand or uncooked rice.