Gradient printing

Seam defect

For multi-material closed curves, the original seam in a single-material Toolpath is naturally replaced by one of the material changes in the Multi-Material Toolpath to minimize the number of single-material segments. Consequently, the curve starts and ends with different materials, which introduces a visible multi-material seam defect without gradient transition. This defect can be replaced with gradient transition by having the seam of the multi-material curve at the middle of any of the single-material segments.

Wipe units

Now the nozzle will enter and exit with the same material, called the transit material. When the nozzle travels between two curves of different transit materials, a wiping stop is needed. The nozzle typically extrudes somewhere off the print body to complete the material transition. For each transition, we place a rectangle curve known as a wipe unit whose length should be greater than the transitional length \(L_{2}\), preferably with a factor. To place the wipe units, a Multi-Material Print Bed should be used.

Reorder for continuous printing

Cross-layer continuous printing of branching, porous geometry requires a slender, long nozzle, which is incompatible with multi-material filament extrusion as the mixing chamber must stay close to the outlet to prevent clogging. Sequential planning thus aims to minimize multi-material seam defects and the number of accompanying wipings. Reorder Multi-Material Toolpath uses a greedy algorithm that replaces the seam points to reduce seam defects, reorders the multi-material curves of each layer, and generates necessary wipe units.

Print scheme of two cells of Schwartz P TPMS on a \(300 \times 300\text{ mm}\) print bed, showing the wipe units. This 90-layer print uses 8 wipe units, saving 91% of the wiping material, 11% of the total material

Example Files

9. Multi-Material Printing → (6) Reorder
9. Multi-Material Printing → (7) Comprehensive Example

Bed Adhesion

We can add Multi-Material Bed Adhesion (skirt or brim) to a Multi-Material Toolpath to prime the nozzle and enhance stability and adhesion. It should be added before Reorder Multi-Material Toolpath.