A 3D print path algorithm with carbon fiber thermoplastics


In a recent article published in the journal Additive manufacturing, the authors proposed a path planning algorithm for the printhead of Fused Deposition Modeling (FDM) 3D printer to generate a path in one shot and continuously print the shape without need to cut repetitive filaments for each layer. The fabricated samples were also characterized by the authors using X-ray computed tomography (CT).

Study: A new single-shot path planning algorithm for 3D printers using continuous carbon fiber reinforced thermoplastics. Image Credit: Sergi Lopez Roig/Shutterstock.com

Three-dimensional (3D) printers applying continuous carbon fiber have received considerable attention from researchers and have been used to construct complex shapes. However, the use of carbon fiber filament in a 3D printer remains unexplored due to the need for additional steps to cut the carbon fiber filament multiple times.


The excellent mechanical properties of continuous fiber composites have enabled their application in 3D printing materials. The conventional method of their use involves their manufacture as an intermediate.

The operation of FDM 3D printers using resins or short fibers as material is different from 3D printers using continuous fibers. However, the major disadvantage of using continuous fibers is that an intersection point in the same layer can break the fiber bundle due to excess material deposition in these areas, thus limiting the movement of the nozzle. In this context, limiting the distribution of fibers at intersections without altering the impression of the remaining parts can conditionally solve the problem.

Limiting fiber distribution can be done either by using the nozzle impregnation method or by creating a path using slicing software and making multiple cuts at intersections or other points. However, the nozzle impregnation method limits the maximum fiber volume fraction, and the application of slicing software causes discontinuity in the fibers and weakens the strength of the bundle.

About the study

In the present study, the authors proposed an algorithm to print the target geometry in a single stroke. They created an Eulerian graph based on target structures and generated a path using Hierholzer’s algorithm with constraints.

The algorithm generated a single-stroke path inside the contour, which was then transformed into an undirected graph further into an Eulerian graph to form the single-stroke path. Calculating the Eulerian circuit from the Eulerian graph can determine the closure of the trait. Finally, this path was adjusted at all intersections and transformed into a geometric code (G-code).

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In the present study, the authors used honeycomb and triangular models as inputs, and the constructed samples were observed in the upper middle using ScanXmate-L080TT, an X-ray scanner.

The results revealed that the small gaps generated at the bent part of the vertices were due to fiber discontinuity and non-attachment to the resin. These gaps significantly reduced the stiffness and strength of the specimen. Moreover, the construction of the same complexes with PLA made it possible to compare the reproducibility of the shapes. The results showed no gap generation with PCA, and the reproducibility at vertex corners was very high.

The gaps formed were due to three shape reproducibility issues. The first problem is due to the stiffness of filaments containing continuous carbon fibers and the inability to bend to bends resulting in poor reproducibility. Additionally, the filament’s moment of inertia significantly affected the reproducibility of print curves at severe bends.

The second problem was the twist at the bends of the network which can cause errors in the print path. Although an accurate prediction of twists is possible, it can practically not be zero. The third reproducibility issue is the continuity of the filament in the newly printed path. The difference between the direction of the previous print and the direction of the nozzle at the bends caused misalignment. This misalignment was compensated by adjusting the parameters.


In this study, the authors used continuous carbon fibers as a material in FDM-based 3D printers and proposed a trajectory planning method for the printer printhead. The proposed method generated a single stroke print path for each layer. Each step of the algorithm was a single stroke path.

The proposed method applies to the filling of periodic patterns (of variable thickness) and complex patterns without periodicity. Although the present study deals with the application of the algorithm to network geometry, it can also be applied to generate single stroke paths for other geometries.

The proposed algorithms work best for printing complex geometric patterns. Thus, the authors anticipate the combination of the proposed algorithm with the patterns obtained from the topology optimization. Furthermore, the practical implementation of these algorithms to print complex 3D structures presents two challenges. The first is to develop a technology that considers the characteristics of continuous fibers to print target geometries with 3D intersections. The second challenge is to modify the constraints of the algorithm according to the limitations inherited from the 3D geometry of the complex structure and to produce a suitable path to print the target geometry.

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Yamamoto, K., Luces, JVS, Shirasu, K., Hoshikawa et al. A new single-shot path planning algorithm for 3D printers using continuous carbon fiber reinforced thermoplastics. Additive manufacturing (2022). https://www.sciencedirect.com/science/article/pii/S2214860422002160

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