Approaches to Creating Colorful 3D-Printed Parts and Reliefs ^†

Abstract

The present article aims to examine different approaches and technologies for producing multi-color 3D printed parts and reliefs using FDM/FFF printing technology. Several examples of parts used in the fields of technology, architecture, marketing and art are presented. The innovative HueForge software version 0.8.1 is used to create a multi-color relief. The process of establishing the Transmission Distance parameter of a given filament, which is key to creating colored reliefs with HueForge, is also examined.

1. Introduction

The various 3D printing technologies have undergone rapid development over the past two decades. FDM/FFF, SLA, and DLP/LCD, have become the most common 3D printing methods due to their accessibility, with the former using a polymer filament as the input material, and the latter and third using a photopolymer [1,2]. Over the past few years, several budget-friendly and yet sufficiently reliable multi-color FDM/FFF printing systems have been developed [3,4], which are reviewed in this study. There are many other technologies, such as Multijet Fusion, which allows multi-color 3D printing, but they strictly reserved for industrial use, due to the high material costs involved and complex and expensive 3D printers required [5,6]. Due to the limited availability of such machines, these specific technologies are not addressed in this study.

In addition to machines that allow multi-color 3D printing, special software is also needed for the generation of multi-color 3D model files that store information about the colors and geometry to be produced, and can pass this information to the slicer (the software used to slice the 3D model into layers and generate the controlling G-code for the slicer) [7,8].

2. Materials and Methods

There are several main technological options for multi-color printing with FDM/FFF 3D printers, which are discussed in the article.

2.1. Pausing at a Specific Layer Height with a Single-Nozzle Printer

When pausing at a certain height, the filament is manually replaced and printing continues with the new filament color (with a pause at the layer in the slicer software). In this way, various two-color emblems, logos, architectural ornaments, etc., can be produced. With this approach, no additional preparation of the 3D model is required [9].

Three-dimensional-printed parts for retro cameras are shown in Figure 1a, and Figure 1b shows an architectural ornament. The elements were produced using the specified method with a Creality Ender 3 printer from Creality, Shenzhen, China.

2.2. Using a Printer with Two or More Nozzles

In this type of 3D printer, a different color material is loaded into the extruder of each nozzle and the active nozzle is switched at a certain layer height or a certain preset color in the model [10]. There are two options for preparation depending on the printed model—if repeated layer-by-layer color changes are required, this can be performed again by changing the settings of the slicer, which allows different layers to be printed with a different nozzle. If a part is being manufactured and there should be two colors in one layer, two models can be used, superimposed on each other in the slicer; a 3D model can be prepared in a parametric 3D modeler (for example, SolidWorks); or a relief can be created with the specialized HueForge software, which is discussed below.

A test 3D model for two-color 3D printing is shown in Figure 2a, and Figure 2b shows the printed part produced on an Ultimaker 3 Extended printer manufactured by Ultimaker in 2018 from Sofia, Bulgaria.

2.3. Using Multi-Material Units

This method involves installing an additional unit that allows a change of materials. An example of such a device is the Prusa Multi Material Upgrade 3 (MMU3). It allows a printer with a single extruder to print with up to 5 colors (filaments) simultaneously. Through separate motors, the system feeds filament to a common material path, and from there it is fed to the extruder. This system also allows for automatic material change when a filament runs out. When changing the material, the extruder needs to be cleaned to avoid mixing different materials. The MMU3 has several options for this—an intelligent cleaning tower (“wipe tower”), cleaning into fill (“wipe into infill”) or cleaning into an object (“wipe into object”). Another popular external device that can be used to print several different materials is the Bambu Lab Automatic Material System (AMS), Sofia, Bulgaria, 2024. It can hold up to 4 different materials, and up to 4 AMSs can be connected to one printer, i.e., up to 16 colors can be changed in one print. The AMS is hermetically sealed, which helps minimize the amount of moisture in the material. There is also an open version AMS Lite, which is designed to be compatible with the budget series of Bambu Lab printers. At the end of 2024, Anycubic launched the Anycubic Color Engine Pro (ACE Pro)—a system that again allows for four-color changing, as well as drying the filaments loaded in it. There are other similar systems—the Chinese company Creality has also started selling one [11]. With this type of device, additional settings have to be adjusted in the slicer in order to 3D print successfully. Below in the text, there is a practical example of creating a file for multi-color printing—a logo, created using Bambu Studio for Bambu Lab X1C, and subsequent printing.

Bambu Studio is a slicer developed for Bambu Lab printers, which allows the post-processing of models for color printing. For this purpose, it is necessary to add a ready-made three-dimensional model (for example, in STL format), which can be “colored” with the colors loaded in AMS. A test model suitable for this purpose has been created—the logo of Sofia Tech Park is modeled in the Autodesk Fusion environment, as shown in Figure 3.

The created logo model is then exported to STL and imported into Bambu Studio for further processing. The logo is composed of three colors—a white base, blue color for the main logo, and a black inscription “Sofia Tech Park”. For this purpose, the three colors and the material—PLA—are set in the virtual AMS in Bambu Studio. Bambu X1C is used for 3D printing. The height of the printed layer is 0.2 mm. These basic settings are shown in Figure 4.

Using the various tools in the Color Painting submenu, the different parts of the model are gradually colored according to the color they will be made of, as shown in Figure 5a. Figure 5b shows the final appearance of the logo in Bambu Studio.

Figure 6a shows the logo after slicing. The figure shows the printing time, the amount of material used, and the number of layers. The model during printing on the Bambu Lab X1C printer is shown in Figure 6b.

2.4. Creating a Color Printing Model with HueForge

HueForge is a software that uses a technique similar to filament painting to prepare two-dimensional images for color printing on FDM/FFF 3D printers. One of the advantages of the software is that it can also be used on single-nozzle 3D printers without an additional multi-material unit. However, printing a color model is much easier with an AMS or other type of multi-color printing system. The software was created by Steve Lavedas (Manassas, United States) and offers several license plans—from one for hobbyists and amateurs, who are allowed to create models for personal use without selling them, to a professional lifetime license, which allows the user to use the software for commercial purposes [12].

HueForge has a library of printing materials from some manufacturers, in which the Transmission Distance is preset. In cases in which a filament that is not in the library is used, it is necessary to determine the TD parameter, as it is of key importance for a good printing result. There are two main ways to do this—with the TD-1 device from the AJAX-3D company [13] or by means of printed samples, in which a black filament with a thickness of about 1 mm is printed as a substrate, and then rectangles with different layer heights of the tested color are printed on the black base—in this example, the first one is 0.08 mm high (1 layer), the second one is 0.16 mm high (2 layers), the third one is 0.24 mm (3 layers), etc. [14]. The Blending Distance parameter is determined by counting the rectangles up to and including the first opaque one. The resulting number is multiplied by the layer height. To obtain an approximate value of Transmission Distance, BD is multiplied by ten. Figure 7 shows the printed test samples used to determine the BD and TD for the colors used, and Figure 8 shows the main printing parameters that are key to obtaining satisfactory results when printing relief color models in Bambu Studio.

The materials are entered into the HueForge library with the corresponding values for the RGB color model and visually determined TD values from the samples, as shown in Figure 9.

The image used to prepare the colorful three-dimensional model of the NAO robot is shown in Figure 10. The background of the photo is removed and saved in PNG format.

Figure 11 shows the HueForge working screen with the loaded NAO image and the model being prepared. The sliders in the lower left part of the screen are used to adjust the height of the layers for the respective material color. Sliders with a value of zero are inactive.

After adjusting the settings and saving the project, three files are saved in the working directory—one with the extension “hfp”, which stores information about the entire project and can be reopened in HueForge; one text document with the extension “txt”, which contains instructions for slicer settings (when to change the filament color, fill, layer height, etc., as shown in Figure 12); as well as an “stl” file, which contains the generated 3D model.

Figure 13a shows the generated “stl” file in the Bambu Studio slicer after slicing and adding a color change to the given layers. The model during printing is shown in Figure 13b.

3. Results and Discussion

The printed three-color logo of Sofia Tech Park is shown in Figure 14.

The final printed color relief of the NAO robot is shown in Figure 15a. Figure 15b shows a side view, in which the relief nature of the printed model is clearly visible.

The paper examines various multi-color 3D printing technologies suitable for application in FDM/FFF technology. Experiments have been conducted with different software and machines, with each of the applied methods showing satisfactory results. With the development of affordable FDM/FFF 3D printers, allowing multi-color printing using multiple nozzles or with an additional multi-color printing system, software solutions such as HueForge are also being developed, which allow engineers, designers and artists to use these technologies to solve a variety of problems—creating logos, paintings, printing with different materials in order to achieve certain properties of a given part, etc. [15,16].