Purge calibration: How to reduce filament waste in multicolor FFF 3D printing

Multicolor FFF printing often generates large amounts of waste when changing colors. When changing colors, the printer pulls the current filament out of the hot end and pushes in new material. However, residues of the previous color remain in the melting chamber, so the extruder continues to feed until the extrusion is visually “clean.” This extruded material is considered purge and ends up as unusable waste. With unfavorable settings, the cleaning waste can significantly exceed the actual component requirements. In some cases, the waste percentage for multicolor printing is over 90 percent.

There are basically two ways to reduce this percentage. One option is to switch to systems that clean less or differently. Newer multicolor systems that reduce the purge process are considered alternatives. Examples include current solutions from SnapMaker and Prusa Research. Those who continue to use their existing hardware can adjust the purge process in the slicer. Many slicers offer adjustment options for this, but the optimal amount depends heavily on the specific color combination. A change from light gray to dark gray typically requires less flushing material than the transition from red to white. This results in a matrix of values for each direction, i.e., A to B and B to A, as well as all other combinations.

Slicers often work with conservative default values. These ensure clean transitions, but cost material and time. The lowest usable values can only be determined by testing. This involves printing sequences with varying purge amounts and visually evaluating the result. Two tests are required for two colors, twelve for four colors.

A less complex variant is described by the MakerWorld model “AMS Purge Calibration V2.” It combines the test object and sequence and uses numbered lines based on the BambuLab calibration pattern. The model can be downloaded free of charge from MakerWord.