Researchers at the University of Hamburg in Germany have introduced a unique way of slicing 3D printed objects to create smoother results. They 3D print nonplanar layers close to the horizontal, this slicing method removes the stair-stepping effect typical to FDM surfaces. Besides providing a smoother result, objects 3D printed this way have proven to be significantly stronger than their conventional counterparts.

The problem of stair-stepping

At times due to their discretized layer structured 3D printed objects can have approximation errors from the original model like stair-stepping. These artifacts can especially occur on surfaces with a horizontal slope. The surface quality for any layer-by-layer 3D printing process can be impaired by this phenomenon.

The intensity of the stair-stepping artifacts can be decreased by reducing the layer thickness. This can be done on all layers evently, or on layers where it’s necessary. Since FDM printers have somewhat thick layers, this fix does not completely eliminate stair-stepping and additional manual post-processing is required to smooth layers. Common techniques involve chemical or a CNC milling. 

Including curved nonplanar layers can get rid of stair-stepping on the surface of objects. Instead of spreading the surface of the object over different layers and creating a stair-stepping effect, nonplanar layers follow the surface. As a result, the combination of nonplanar and planar layers is much smoother surfaces for FDM objects.

A novel slicing algorithm for nonplanar 3D printing

Researchers seek to create a method to 3D print nonplanar layers on top of planar layers in any object. The team achieved its goal by adjusting open-source slicing software Slic3r. Adding the ability to print nonplanar surfaces to an open-source slicer increase the usability and provides a general-purpose approach. The algorithm in the study is specifically developed for the Ultimaker 2.

Because of the new algorithm, the areas that should be printed with nonplanar are detected automatically. The algorithm also checks for possible collisions while printing. Collision prevention sees to it that the printhead does not crash into previously printed structures while printing nonplanar layers.

The area below the nonplanar surfaces is printed with a regular planar structure. First, toolpaths are generated as 2D toolpaths and the projected downwards along with the original mesh which creates a nonplanar 3D toolpath that can be visualized in Slic3r. With Slic3r to ensure that the path looks as intended, 3D printing is carried out by moving the planar layers upwards to form a new nonplanar layer. 

The surface quality of objects with nonplanar layers is increasingly better than with planar layers only. In addition, print time for an object with nonplanar layers is comparable to that for the object with planar layers. 

3D Printing of Nonplanar Layers for Smooth Surface Generation” is the master thesis of Daniel Ahlers, Visiting Scientist at the University of Hamburg. Ahler’s implementation in this work is open-source and can be found on GitHub


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