Automated Filament Pigmenting for Multi-color 3D Printing

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Fig. 1. 3D printing using the automated filament pigmenting mechanism (left). Filament passes through the mechanism (blue)

mounted at the top of the printer frame. White filament can be seen pigmented magenta. Results of a gradient print to test reproducible

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colors using three alcohol ink markers (middle). Two test prints showcasing color gradients possible with proposed method (right).

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The test print on top uses four markers corresponding to CMYK color scheme, while the bottom print makes use of three: cyan,

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magenta, and black.

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24 Automated Filament Pigmenting for Multi-color 3D Printing

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26 EAMMON LITTLER, Dartmouth College,

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28 BO ZHU, Dartmouth College,

29 WOJCIECH JAROSZ, Dartmouth College,

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1 INTRODUCTION

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Multi-color 3D printing for traditional FFF desktop 3D printers has long been a challenge for the industry. Existing solutions are often

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limited in color palette and require precise tuning and calibration unique to each system. Dual extruder printers, for example, makes

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use of two separate extruder and hotend assemblies to extrude filament independent of each other. This allows for printing with two

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colors at the cost of added weight to the gantry and a reduced build volume to account for offsets between the two nozzles. Attention

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must be paid to the alignment of the nozzles to prevent collisions with a print. Single nozzle multi-color enabling attachments have

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gained attention in recent times, opting to swap between colors by completely unloading and reloading filament. This step, while

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necessary, is the weakest link of the process, being susceptible to failures if the proper calibration steps are not taken. In the case of

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printer errors, extensive time can be taken to troubleshoot and restart a print. This puts multi-color 3D printing outside of the realm of

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possibility for the majority of consumers.

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made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components

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redistribute to lists, requires prior specific permission and/or a fee. Request permissions from permissions@.

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? 2018 Association for Computing Machinery.

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Manuscript submitted to ACM

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SCF '21, October 28?29, 2021,

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2 METHODS

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We propose a novel hardware solution in the form of a low-cost attachment for existing desktop 3D printers, greatly increasing the

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available color palette options while requiring little maintenance beyond what a typical 3D printer requires. The coloring method is

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achieved by pigmenting white PLA filament using alcohol-based inks prior to extrusion. Our custom attachment has been designed

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to house four alcohol ink markers, actuated by a rack and pinion system controlled by servo motors. The filament is fed from one

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end, inked and air-dried by a fan, and exits into the 3D printer extruder inlet. The attachment dispenses ink directly onto filament

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programmatically through the use of custom G-code commands. G-code is read by an Octoprint instance running on a Raspberry

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Pi 3, intercepting the custom command and running the pigmenting tool in parallel, leaving the printer undisturbed. This greatly

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reduces the chance of prints failing as a result of the filament swapping process as seen in other approaches. At worst, a print will

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complete without proper coloring while still providing useful insight to its form. Up to four inks, based on the CMYK color scheme, are

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dispensed onto filament at varying pressures or frequency to achieve the desired color. Pigmented filament mixes naturally as part of

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the extrusion process, producing consistent colors in the print. G-code is generated using PrusaSlicer under a multi-extrusion profile.

67 A post-processing script is used to remove any unloading and reloading commands that would normally take place between nozzles,

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as well as the addition of our custom color change command. The issue of color bleeding is handled by the use of a purge tower, akin

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to most single nozzle approaches. In effect, a 3D print can have limitless color options given nozzle purges are conducted between

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each color change. This has implications beyond coloring filament, giving users options beyond market offerings while keeping 3D

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printer modifications to a minimum.

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3 DISCUSSION

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Being a work in progress, there are many improvements planned in the pipeline of the project. For future additions, G-code parsing

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and post-processing will be improved to color only the perimeters and walls of prints, reducing the use of inks to just the exterior.

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Though untested, the possibility of compromising the structural integrity of pigmented prints cannot be ignored. Coloring only the

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exterior should serve to improve the strength and durability of a print. Mixing colors automatically and color reproducibility is yet

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untested and will be determined heavily by the accuracy of the mechanism. In testing this, the desired color will be specified as a

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parameter in the custom G-code command represented as CMYK percentage values. This will allow for per basis color changing

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control rather than being limited to a set palette, as well as understanding the true color range of the system.

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ACM Reference Format:

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Eammon Littler, Bo Zhu, and Wojciech Jarosz. 2018. Automated Filament Pigmenting for Multi-color 3D Printing. In . ACM, New York,

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NY, USA, 2 pages.

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