Beyond production: the dyeing of 3D printed parts

Aesthetic or functional. The use of dye in additive manufacturing has been greatly forgotten in the post-processing of parts. Partially, because of its difficulty in dyeing certain components. But also, because it is usually seen as an aesthetic purpose or as the improvement of the resolution of objects.

However, the latest advances in this field have revealed that the tinting of 3D parts also provides functional properties. According to the research "Functional Dyes in Polymeric 3D Printing: Applications and Perspectives" of the American Chemical Society, there are innovative materials able to react to stimuli, such as light and temperature.

Dyes can provide specific properties, such as modification of mechanical behavior, sensitivity to light or permeability. However, to achieve these properties, colorants are generally used during the printing process, which means that they cannot be considered a post-processing step.

What is the post-processing of 3D parts?

The manufacturing process does not end when the part is withdrawn from the 3D printer. After printing, the components undergo a fairly long post-processing work, depending on the technology used, which lengthens production times. That is why many manufacturers are looking for faster, more accessible and automated solutions.

While talking about the post-processing functions of the parts, it is important to highlight:

Cleaning

When 3D printers finish producing a part, it is not usually delivered as is. Although there are machines that deliver functional final parts, in general, the excess material is cleaned. What’s more, in some cases, the print media must also be removed. When it comes to polymers-based components, the withdrawal is done by hand, but in metallic processes a specific machine is used.

Surface finish

This process ensures that each part meets your specifications. Through the Surface Finish, details such as roughness or consistency are adjusted. At the same time, the details of the printed part are kept untouched.

Dyeing

Generally, the third step of post-processing is dyeing of 3D printed parts. Although, as already mentioned, the coloration can be applied during the printing process, especially tinting with functional properties.

Types of dyeing of 3D printed parts

Most 3D printing machines can only print in one color. So, if a manufacturer wants to get a multi-color part, they must resort to painting or other post-processing techniques to add other colors after manufacturing.

However, on complex components, post-painting is usually not an option. In these cases, the part must be printed in color from the beginning. There are different dyeing techniques, such as filament exchange, dual extrusion or supported technologies to achieve this.

Resin Color Kit

By using tinted resin, manufacturers can print parts in color. Conventionally, only a limited number of colors were available, thus limiting designers and engineers. As a result, designs did not have the same visual appearance as the final parts.

However, with new technological advances, more colors have been obtained. With a white resin base, to which the primary colors are added, mixtures can be achieved that generate a full spectrum of colors.

Filament exchange

Filament exchange allows different colors to be used on each layer of the part. It is a simple process, used mainly in fused deposition modeling (FDM) printing. To change color in the process, you must pause the print and change the filament of the desired color.

It is the best method for printing logos or plates with extruded text, with a three-dimensional appearance. The color change to highlight certain parts of the component can be done as many times as desired. However, it can be a tedious process and it is difficult to get good results.

Filament dyeing

Like filament swapping, this technology allows different layers of a part to be colored. It is usually used with nylon threads, since, thanks to its permeability, it can easily absorb the dye.

This technique consists of introducing the filament into a solution made of boiling water and the dye for about 10 minutes. As a result, the threads of material that will be used to manufacture the part will absorb the color and be dyed. Optimal results can be achieved, but the control when placing the different colors in the part is limited.

Multi-extrusion

Printers with multiple extruders have been around for a long time, but they faced two challenges: reliability and ease of use. However, technology has improved, and it is one of the solutions for tinting 3D parts.

Dual extrusion printers color parts by inserting colored filaments into a hotend, the part responsible for heating the material for deposition. There are two main techniques:

1. The most popular technique includes two or more extruders (the part that pushes the filament to the nozzle) and two or more hotends. Each extruder feeds filament to a single hotend, which is used to print a section of the part. The number of extruders varies depending on the number of colors or materials to be used.
2. A newer and less common technique is one that involves a hotend and multiple extruders. One by one, the extruders feed the hotend. To combine colors, each extruder is activated with the change of color.

Filament splicing

This technique allows selective color prints, using a single extruder and hotend. For this type of tinting, the palette is used, a component of the machine that can take up to 4 different colors to 'splice' them into a continuous thread.

The splicing technique is similar to filament swapping and dyeing, but the palette is self-contained. This means more detailed selection when deciding which parts of the component to be colored. However, filament splicing is not the ideal technique for printing on different materials.

Supported technologies

Although only available on professional machines, there are some printing technologies that allow you to obtain multicolored parts by default:

1. PolyJet: droplets of photopolymer resin are injected into an object to cure them with ultraviolet light. Some machines can color the droplets before deposition, obtaining full color parts.
2. Binder jet: a glue-like substance, in this case colored, is deposited onto a powdery substrate. This technique produces fewer sharp results because the dye permeates the surrounding powder.

Beyond production

Whether it is for aesthetic or functional purposes, the dyeing of 3D parts is an essential part of additive manufacturing. On a visual level, thanks to technological advances in the coloring process, engineers and designers can create final parts the way they sketched them.

However, going one step further, coloring with smart materials can give printed components a series of characteristics that make them suitable for the specific function they are to perform. Changes in temperature, light and the stress to which the parts are subjected cease to be a problem with functional coloring.