Feature first published in the May/June 2021 issue of 3D ADEPT Mag, then online in December 2021. Equipment, contributors’ roles and process settings refer to that period and the specific processes discussed.
In the textile industry, dyeing is acknowledged as a pivotal process that provides colour to fabrics. In the additive manufacturing industry on the other hand, the ultimate goal remains the same: provide colour to ready-made 3D printed products but the technological process that enables to deliver these end-products is not always well depicted.
Bath dyeing involves immersing parts in a mixture of water and dye at a controlled temperature, then rinsing them. In a manual setup, dye selection, bath control and batch handling raise several questions:
- Handling time and available capacity for large batches.
- Repeatability for the geometry, wall thickness, material and bath agitation used.
- Colour durability under light, heat and operating conditions.
- Product compatibility with the part and operator protection, to be determined from supplier instructions and safety data sheets.
This feature examines automated dyeing solutions, their applications and preparation stages. A general process certification cannot establish the suitability of every dye, material and use combination.
Which processes and materials are suitable for dyeing?
Depending on the AM process leveraged and on the manufacturing goal of a given part, some post-processing tasks may be favoured over others.
Post-print dyeing is used notably for polymer parts made by SLS or Multi Jet Fusion (MJF). It is neither mandatory for these processes nor applicable without verification to all powder-bed fusion materials, including metals.
Colouring changes a part’s appearance; it does not improve the geometric resolution of printing. This finishing step should be distinguished from functional dyes investigated in research, which can contribute to material properties when incorporated into a suitable formulation.
“Modifying elastic moduli upon light irradiation, inducing optical and emitting properties in the matrices or conferring temperature responsivity are just few examples of innovative stimuli-responsive materials that can be produced by combining well-designed dyes with the appropriate 3DP printed matrices”, a research on “Functional Dyes in Polymeric 3D Printing” reads.
The examples examined in that research concern specific formulations and processes, including photopolymerisation and extrusion. Dyes may then be incorporated before or during printing. These functions should not automatically be attributed to bath dyeing applied after manufacture.
For post-print colouring, suppliers presented in this feature include DyeMansion, CIPRES and Girbau. OmegaSonics also offered a dye tank for certain polymer parts. In every case, compatibility needs to be checked for the material and printing system involved, not simply for a machine brand.
DyeMansion’s founders first launched Trindo in 2013 to produce 3D printed smartphone cases. DyeMansion was founded in 2015, focusing on industrial post-processing and colouring solutions.
In 2004 when it was founded, CIPRES was a manufacturer of laser sintering prototypes. In 2006, the company has decided to deliver serial production of 3D printed parts, and since then, has also been focusing its activities on the development of colour techniques, colour units and solutions for surface finishing.
Girbau, founded in 1960 and based in Vic, Spain, is known for industrial laundry equipment. Its experience in water management and temperature control provided a starting point for developing dyeing equipment for 3D printed parts.
An exchange with José Maria Maristany, responsible for the Girbau program in the AM industry, enabled us to discover that the company started developing a dyeing solution for AM in 2018, thanks to a partnership project between Girbau lab (Girbau open innovation platform) and Hewlett Packard (HP).
The project gave life to DY130, primarily intended for HP Jet Fusion 3D 4210/4200 Printing Solutions, an only dyeing solution dedicated to AM in the company’s portfolio. “We have decided to focus on dyeing solution because of the synergies between Girbau traditional know-how in [water management and temperature control]. We are currently working on adjacent products and services to complete our dyeing solution and enhance our value proposition”, Maristany told 3D ADEPT Media.
References to equipment and ongoing developments in this interview describe the 2021 offering.
Dyeing within the post-processing workflow
As often mentioned in our dossiers, the post-processing stage is a long phase that comprises many different tasks that operators can perform to deliver the desired end-product.
For the polymer powder-bed parts discussed here, cooling, unpacking and depowdering precede dyeing. Appropriate cleaning limits residues that could cause stains. It does not, by itself, guarantee the part’s functional properties.
Bead blasting or shot peening can form part of a validated route to achieve the desired finish. It is not a mandatory treatment after every dyeing operation; its effect on surface and colour needs to be assessed.
So, normally, right after the cleaning phase, the dyeing process is relatively simple to achieve and consists of two main phases. “In the first phase, parts are immersed into a dyeing bath with specific temperature conditions for a prescribed period of time. In the second phase, [the operator] rinses parts with water”, Maristany explains.
| Stage | Reported operator time | Reported process time |
|---|---|---|
| Placing parts in laundry bags | 5 min per batch | 5 min per batch |
| Dyeing | 0 min per batch during the cycle | 2.5 h per batch |
| Drying | 10 min per batch | 2–3 h per batch |
| Sandblasting or shot peening (optional) | 30 s–5 min per part | 30 s–5 min per part |
| Preparing dye solution | 5 min for 5 batches | 40 min for 5 batches |
These values reproduce the Girbau diagram in this 2021 feature. The reported reduction to about 45 minutes with a hot-water supply concerns the dyeing phase, not the entire workflow: drying remains separate. Times depend on installation, program and batch; zero operator time during a cycle does not mean zero process time. Girbau and HP present the DY130 as a batch-processing solution. Colour uniformity and repeatability need to be checked for the materials and geometries involved.
However, two main recommendations are worth noting:
The first one is that “to avoid the physical marks produced by movement of the pieces during the drying process, the use of laundry bags to separate pieces (with different weights) in the same batch is strongly recommended.” And, “as the process takes place in water, it is important to keep in mind that, as parts absorb some water during the process, their dimensional and mechanical properties may change slightly. Warpage of thin and flexible parts could be affected.”
Programs presented for the DY130 include bath mixing and conditioning, dyeing at 60 °C, bath disposal and cleaning. These settings belong to the solution described; they are not a universal recipe for other materials, dyes or machines.
Speaking of materials their solution can process, Girbau’s expert states that “HP has validated [their] solution for PA11 and PA12 materials. DY130 could be used to dye parts produced with similar Industrial 3D printing solutions such as SLS.”
The cited validation does not automatically extend to another technology, a new colour or a new use. Process documentation and qualification of the selected combination remain necessary.
A machine dedicated to each colour is a process-organisation recommendation for the solution presented. Colour changes may be considered according to supplier cleaning instructions, with checks for contamination of the next bath.
Applications and outlook
Dyeing can support the appearance or identification of consumer products, eyewear, watches, figurines and industrial parts. Models used for medical training may also be coloured; that use does not establish qualification for a patient-contact device.
For prolonged skin contact or another demanding use, qualification needs to cover the part, material, dye and treatment together. Choosing between a manual bath and an automated solution also depends on volume, repeatability, handling and cost. Manufacturer documentation remains the reference for configuring the process.
This feature was first published in the May/June 2021 issue of 3D ADEPT Mag. Featured image: bracelets coloured by CIPRES. Image: CIPRES.
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