PET-CF 3D Printing: What Does Nozzle Size Change?

In FDM 3D printing, nozzle diameter can affect both the mechanical performance of a printed part and how long it takes to make. That trade-off matters when a component needs to be strong and stiff without unnecessary production time. A study by Adi Pandžić, PhD, compares PET-CF specimens printed with 0.4 mm and 0.6 mm nozzles and reports changes in strength, stiffness, deformation before failure and print time.

Key findings

• A 0.6 mm nozzle increased tensile strength by up to 21.6% compared with a 0.4 mm nozzle.
• Flexural strength increased by up to 14.8% with the 0.6 mm nozzle.
• Elastic modulus rose by up to 17.6% in tension and up to 21% in flexure.
• Strain before failure fell by 4.5% in tension and by up to 20% in flexure.
• Printing time for test specimens decreased by up to 31% with the 0.6 mm nozzle.
• The findings point to a trade-off: higher strength and stiffness, but less deformation before failure.

Why nozzle diameter matters

Fused Deposition Modeling, or FDM, is an additive manufacturing process in which a 3D printer deposits melted filament in successive layers. Nozzle diameter affects how material is extruded and can influence the geometry of deposited roads and the time required to print a part. It can therefore matter to mechanical performance as well as to production efficiency.

The study focuses on PET-CF: polyethylene terephthalate reinforced with chopped carbon fibers. The paper describes it as retaining the printability of PETG while offering greater stiffness and improved temperature and chemical resistance. The manufacturer lists tooling, functional prototyping and manufacturing aids among its potential uses. These are relevant contexts for engineers choosing a material and print setup, but the results in this paper apply to the specific PET-CF material and printing conditions tested, not automatically to every part made from the same filament.

What the study tested

The paper reports a comparison of PET-CF test specimens made with two CC Core nozzle diameters: 0.4 mm and 0.6 mm. The specimens were designed in Solidworks 2023 in accordance with ISO 527-2 for tensile testing and ISO 178 for flexural testing. CURA 5.6.0 was used to prepare the prints, and the specimens were printed flat on the build plate.

The reported settings were held constant for both nozzle sizes: a layer height of 0.15 mm, 100% infill density, a printing temperature of 270 °C, a build plate temperature of 80 °C, a print speed of 30 mm/s and a fan speed of 10%. Printing was carried out on an Ultimaker S5 Pro. Testing used a Shimadzu AGS-X universal testing machine with a 10 kN capacity. The test speed was 5 mm/min, following the cited standards. Ten replicate specimens were printed for each type of test, and CURA software calculations were used to determine specimen printing time.

Tensile strength describes the maximum stress a specimen withstands when pulled. Flexural strength is measured under bending. Elastic modulus indicates stiffness: how strongly a material resists elastic deformation. Strain before failure describes how much it deforms before breaking or failing. These measures capture different aspects of behaviour. A material can be stronger and stiffer while deforming less before failure, which is why the results should be considered together.

Results: strength, stiffness and printing time

Compared with the 0.4 mm nozzle, the 0.6 mm nozzle increased tensile strength by up to 21.6% and flexural strength by up to 14.8%. The elastic modulus also increased: by up to 17.6% in tension and up to 21% in flexure. In the tested setup, the larger nozzle was therefore associated with improvements in both strength and stiffness, as well as faster specimen production.

Strain before failure moved in the opposite direction. With the 0.6 mm nozzle, strain before failure decreased by 4.5% in tensile testing and by up to 20% in flexural testing. This distinction is important when interpreting the strength figures. A higher strength value does not, by itself, mean that a material can deform more before failure. Designers need to consider whether a part’s requirements emphasize strength and stiffness, or the ability to tolerate deformation.

The larger nozzle also reduced the time needed to print a test specimen by up to 31%. The paper reports that printing time affects the cost of a final product. However, the paper does not quantify a monetary saving, so the reported reduction in print time should not be treated as a specific percentage reduction in product cost.

What the findings mean in practice

For engineers and product designers, the comparison shows why nozzle diameter should be treated as a meaningful process choice rather than simply a way to alter speed. Under the conditions tested, the 0.6 mm nozzle was associated with higher tensile and flexural strength, a higher elastic modulus and shorter printing time. Its lower strain-before-failure results also deserve attention if a component must deform before failure rather than remain relatively stiff.

For students, the study is a useful example of why mechanical properties should not be reduced to a single number. Strength describes resistance to failure under a particular loading test; stiffness describes resistance to elastic deformation; and strain before failure records deformation before failure. Here, the larger nozzle improved the first two measures but reduced the third. The different outcomes help explain why a process setting that benefits one design requirement may not suit another.

The findings are specific to FDM printing of PET-CF using the printer, nozzle sizes and parameter settings reported in the paper. They should not be assumed to apply unchanged to other filaments, print orientations, layer heights or machines. The research tests FDM; it does not test SLA, so its results should not be applied to that technology.

Limitations and next steps

The experiment compares only two nozzle diameters, 0.4 mm and 0.6 mm, for one material and a defined set of printing conditions. It does not establish an ideal nozzle diameter for every PET-CF application or show how the results would change with other combinations of settings. The paper reports several differences as “up to” values, so they should be presented as the reported maximum changes, not as guaranteed improvements for every printed component.

The paper recommends investigating other mechanical properties, including compressive strength, hardness and impact toughness. It also identifies surface quality and dimensional accuracy as areas for further study. Examining these additional outcomes could help characterize the effects of nozzle diameter beyond the tensile and flexural properties measured here.

Conclusion

Published in the Proceedings of the 35th DAAAM International Symposium in 2024, this study by Adi Pandžić, PhD, compared PET-CF specimens printed with 0.4 mm and 0.6 mm nozzles. Under the tested conditions, the 0.6 mm nozzle increased tensile and flexural strength and elastic modulus, and reduced printing time by up to 31%. At the same time, strain before failure decreased. For PET-CF FDM printing, the practical lesson is to select nozzle diameter in light of both production time and the required balance between strength, stiffness and deformation.

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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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