PLA 3D Printing: How Nozzle Size Affects Strength and Time

Choosing settings for FDM 3D printing can affect both the properties of a finished part and the time needed to make it. That trade-off matters to engineers developing products and to students learning how manufacturing parameters influence test results. In a study by Adi Pandžić, PhD, this relationship was examined using PLA specimens printed with four nozzle diameters.

Key findings

• The study tested nozzle diameters of 0.25 mm, 0.4 mm, 0.6 mm and 0.8 mm, with a fixed layer height of 0.15 mm.
• The highest measured tensile strength was 44.60 MPa, and the highest tensile elastic modulus was 2.80 GPa, both with the 0.8 mm nozzle.
• Flexural strength reached 114.89 MPa and flexural modulus reached 6.30 GPa with the 0.8 mm nozzle.
• The greatest measured strains at break occurred with the 0.4 mm nozzle: 2.70% in tension and 3.09% in flexure.
• Printing one tensile-test specimen took 163 minutes with a 0.25 mm nozzle and 36 minutes with a 0.8 mm nozzle.

Why nozzle diameter matters

Fused deposition modeling, or FDM, is an additive manufacturing process in which thermoplastic filament is heated and extruded through a nozzle. The printer deposits material layer by layer along paths defined in G-code. Nozzle diameter is one of several process settings that can be selected, alongside layer height, print speed and infill pattern. Infill is the material structure inside a printed part; changing infill was not the focus of this experiment.

Nozzle diameter is worth investigating because it can be related to how material is deposited and how many passes are needed to build a part. Here, the paper reports measurements of more than surface appearance: tensile and flexural properties were tested and print time was recorded. Production time affects planning and the cost of making a part, so the study addresses a practical question for product development and laboratory teaching: what changes in measured properties when one FDM setting is varied?

The paper places the question in the broader context of additive manufacturing, which can produce prototypes and products without dedicated tooling. However, it does not compare FDM with SLA printing or test specific applications in medicine or other specialized fields. Its scope is focused: black PLA, four nozzle diameters and the mechanical properties of printed test specimens.

Materials, printer and test methods

The paper reports that black Ultimaker PLA filament with a diameter of 2.35 mm was used. PLA is a thermoplastic polymer commonly used in FDM printing. Tensile specimens were designed according to ISO 527, while flexural specimens followed ISO 178. Five replicas were printed for each specimen and nozzle-diameter combination.

G-code was prepared in Ultimaker Cura using the default “Normal” profile for the specified filament. The four nozzle diameters were 0.25 mm, 0.4 mm, 0.6 mm and 0.8 mm. Layer height remained at 0.15 mm for every sample, allowing the nozzle diameter to be compared without also changing that setting. Printing was performed on an Ultimaker S5.

Tensile and flexural tests were conducted on a Shimadzu AGS-X universal testing machine at a test speed of 5 mm/min. A tensile test loads a specimen by pulling it, measuring how it responds to stretching. A flexural test evaluates how it responds to a bending load. Tensile strength is the highest stress recorded during tension, while elastic modulus describes stiffness in the elastic region. Strain at break indicates how much a specimen deformed before it failed.

Results: tensile and flexural properties

The highest tensile strength and tensile elastic modulus were measured with the 0.8 mm nozzle. Tensile strength was 36.10 MPa for 0.25 mm, 41.90 MPa for 0.4 mm, 42.00 MPa for 0.6 mm and 44.60 MPa for 0.8 mm. The tensile elastic modulus rose from 2.40 GPa with 0.25 mm to 2.50 GPa, 2.60 GPa and 2.80 GPa as the nozzle diameter increased.

Flexural strength measured 85.74 MPa with 0.25 mm, 102.83 MPa with 0.4 mm, 100.61 MPa with 0.6 mm and 114.89 MPa with 0.8 mm. Flexural modulus increased across the four settings, from 5.20 GPa to 5.70 GPa, 5.80 GPa and 6.30 GPa. The highest flexural strength was therefore recorded with the largest nozzle, but the values did not rise at every step: the 0.6 mm result was lower than the 0.4 mm result. This distinction matters when reading the paper’s overall statement about an increasing trend alongside the individual measurements.

Strain at break did not follow the same pattern as strength and modulus. Tensile strain values were 2.40%, 2.70%, 2.30% and 2.00% for nozzle diameters of 0.25 mm, 0.4 mm, 0.6 mm and 0.8 mm, respectively. Flexural strain values in the same order were 2.86%, 3.09%, 2.41% and 2.40%. The greatest measured strain in both test types occurred with the 0.4 mm nozzle.

Print time and practical implications

The reported time refers to printing one specimen for tensile testing. It was 163 minutes with a 0.25 mm nozzle, 81 minutes with a 0.4 mm nozzle, 48 minutes with a 0.6 mm nozzle and 36 minutes with a 0.8 mm nozzle. The paper describes the 0.25 mm nozzle’s print time as up to four times longer than that of the other tested nozzle diameters. These figures show a substantial time reduction under the study’s specific conditions; they should not automatically be assumed for every part geometry or printer setup.

For an engineer or product designer, the results illustrate a choice among measured strength, strain and production time. In this dataset, the 0.8 mm nozzle had the highest tensile and flexural strength and modulus, along with the shortest print time. If strain at break is the priority, the highest values were obtained with the 0.4 mm nozzle. The study does not identify one universally best setting for every printed part. The appropriate choice depends on the properties and production constraints relevant to a particular task.

For students and researchers, the comparison also demonstrates a controlled experimental approach: nozzle diameter changed while layer height and material were held constant, and the specimens were tested using defined procedures. This helps make the selected parameter easier to discuss, but it does not establish that the same pattern will hold for a different PLA, printer or set of printing parameters.

Limitations and future work

The experiment covered one material, black Ultimaker PLA, one printer and four nozzle diameters. Every specimen was printed with a 0.15 mm layer height, and the mechanical tests ran at 5 mm/min. The findings describe the tested specimens and conditions, not every geometry or end use. The results table does not provide measures of variation, so this article does not make additional claims about the statistical significance of differences.

The paper suggests repeating the analysis with other materials and examining further mechanical properties and characteristics of FDM-printed materials. Such work could show how consistently the observed relationship between nozzle diameter, material properties and print time applies beyond this experiment.

Conclusion

For the FDM-printed PLA specimens in this study, changing the nozzle from 0.25 mm to 0.8 mm was associated with higher measured tensile and flexural strength and modulus at the largest diameter, as well as a shorter print time. The highest tensile strength was 44.60 MPa, the highest flexural strength was 114.89 MPa, and printing one tensile specimen took 36 minutes with the 0.8 mm nozzle. The greatest strains at break, however, were measured with the 0.4 mm nozzle. Nozzle selection should therefore follow the needs of the part and be verified for the specific combination of material and printing settings.

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Author: Adi Pandžić, PhD in Mechanical Engineering

This article summarises a published research paper; please refer to and cite the original paper. About the author

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