Co-authors​ :

 Zsolt KÁLLAI (GERMANY), Johann KIPPING (GERMANY), Thorsten SCHÜPPSTUHL  

3D printing with pre-impregnated, continuous carbon fiber reinforced polymer filament (CFF) has created new opportunities for producing complex and individual parts with the advantageous properties of carbon fiber (CF). CFF is not only an active field of research but also a commercially available application, according to current manufacturing trends. However, many printers are limited to planar printing, which restricts the placement of CF and prevents the full potential of the fibers from being utilized. To address this issue, non-planar CF placement and non-uniform layer height are necessary. These requirements have been successfully implemented in non-fiber strengthened 3D printing by varying the material deposition point-to-point during the printing process. However, it is important to note that pre-impregnated continuous carbon fiber filament can only be placed with a constant layer height. Reducing the layer height compacts the fibers in the placed filament with a force that damages or breaks the embedded carbon fibers. Conversely, increasing the distance to the previous layer results in insufficient compaction between the layers in the build direction, causing delamination in the finished part.
The paper presents two approaches for creating non-planar CF parts with the constant layer height requirement. The example used is curved pipes, which are divided into straight and curved (non-planar) segments. Only the CF filament will be used in the straight sections, but in the curved sections, the print material will be varied between two filaments: the CF and the Matrix filament. The proposed approaches will be tested on a dual-robot experimental setup capable of printing with two materials in turns.
The first method involves a cut and place process to create a non-uniform layer. This is achieved by iteratively placing multiple segments of CF filament on top of each other to form a layer in the curvature. The calculations are based on the length of the smallest placeable CF filament, which is a geometrical constraint derived from the distance between the cutting mechanism and the nozzle's outlet. The Matrix filament is then applied to fill any gaps or unfilled areas.
The second approach aims to compensate for the distance between two CF layers by using the Matrix filament. This involves creating a layer in the curvature from two sub-layers. Firstly, the constant CF layer is placed, and then the space between the next CF layer is filled with the Matrix. It is important to note that the Matrix is not fiber reinforced, so the amount of material placed can be varied from point to point.
A teaser video from the non-fiber reinforced, 3D printed, curved pipes with non-uniform layer height can be found here: https://www.youtube.com/watch?v=mbRxhiaj1ck