Researchers from the University of Duisburg‐Essen have developed a novel powder resin that enables color parts to be 3D printed using desktop Laser Powder Bed Fusion (LPBF) machines.
By introducing small amounts of plasmonic silver nanoparticles into a conventional thermoplastic powder, the research team were able to incorporate a yellow color into a range of printed objects. Given that current desktop LPBF systems are only capable of fabricating components in white or black, the team’s new resin could bring a splash of color to a number of existing printers.
“The use of inexpensive and compact diode lasers for LPBF in the visible or near‐infrared range is highly desired, but at present, only black objects can be printed by desktop laser printers,” stated the researchers in their paper. “In this study, we have presented a new way for colored parts to be produced through laser 3D printing.”
The need for new LPBF 3D printing polymers
With the growing popularity of desktop systems and the increased number of hobbyist adopters of 3D printing, the demand for new, more effective, polymer-based materials has never been higher. Currently, around 90 percent of available thermoplastic powders are polyamide-based, which emphasizes the potential headroom for innovation in this area.
Although several alternatives materials have been brought to market in recent years, they have often lacked the flowability, optical absorption, and melting features of existing resins. Thermoplastic Polyurethane (TPU) for instance, is a versatile material with high-resistance qualities, but its unfavorable thermal properties have prevented its wider adoption by the users of desktop systems.
At present, in terms of process parameters, TPU’s limitations have only been overcome using CO2 lasers, which are more complicated and expensive than existing laser-based systems. With regard to potential alternative materials, previous research has also identified carbon‐based photothermal sensitizers, such as carbon black, graphene, or nanotubes, as a material alternative to TPU.
Carbon’s strong absorption in the near-infrared spectrum makes it compatible with a number of cheaper diode laser sintering methods, albeit at the cost of being black in color. As a result, unlike those that use binder jetting or material extrusion systems, desktop LPBF users can only add color to parts in post-processing, which is a real drawback.
The Duisberg team’s novel silver-infused powder
In order to overcome the color limitations of desktop LPBF, the team hypothesized that nanosized photothermal sensitizer could be added to TPU printing powder. Although prior research has shown that gold is effective within this role, silver is 40 times cheaper and less prone to agglomeration and a lack of dispersion.
As a result, the team adopted silver colloidal nanoparticles (NPs), and mixed them with polymer microparticles in a Laser Synthesis and Processing of Colloids (LSPC) process. The resulting polymeric powders featured a high level of dispersion, with only minor aggregation. Additionally, because silver NPs generated via LSPC have a Surface Plasmon Resonance (SPR) peak of 397 nm, the resulting colloid was yellow in color rather than black or white.
Due to the fact that almost no plasmonic particles were absorbed onto the surface of the polymer, the team observed no significant change in its color after drying and sifting. In order to fully investigate the suitability of their novel powder for LPBF printing, the research team subsequently carried out a series of evaluations using a diode laser at 445 nm.
Testing revealed that the powder featured a 20 percent lower bulk density than commercial TPUs, indicating that its flowability might be slightly poorer as a result. Despite the powder’s poor flow behavior, the team pressed ahead with 3D printing a series of sample objects. Although the process proved reliable, yielding a number of yellow parts, it did require five times more energy to achieve than printing conventional black TPU.
In conclusion, the mixed testing results showed that a balance still needs to be struck between effectively heating powdered polymers, and adding color to them. According to the researchers, further research could yet see their production technique being developed in order to produce parts in colors other than yellow.
“The additional coloring of the plasmonic Ag‐TPU powders could still be possible, but not if carbon black is used,” concluded the team in their paper. “Silver nanoparticle‐polymer composites also show a high level of potential for applications in the fields of biology, catalysis, and electronics.”
Perfecting the LPBF 3D printing process
LPBF additive manufacturing is widely-used, especially within desktop systems, and a number of organizations are working to optimize the process for heavier duty applications.
Dutch metal 3D printer supplier Additive Industries is working with the Fraunhofer Institute to accelerate the implementation of LPBF for industrial series production. Based at the University of Twente, the partnership is analyzing all aspects of the process, with the aim of encouraging LPBF’s integration into existing industrial process chains.
Fabrisonic, the solid-state metal 3D printing specialist, has partnered with EWI, and Luna Innovations to build a Smart Baseplate for LPBF additive manufacturing processes. The device is designed to prevent parts from debonding or delaminating from the build-up of residual stress on the build plate during printing.
Global standards developer ASTM International is currently developing a specific standard for the LPBF 3D printing method. The prospective certification will seek to assess the quality of fabricated parts, as well as the performance of the LPBF systems that manufacture them.
The researchers’ findings are detailed in their paper titled “Plasmonic Seasoning: Giving Color to Desktop Laser 3D Printed Polymers by Highly Dispersed Nanoparticles,” which was published in the Advanced Optical Materials journal. The report was co-authored by Tim Hupfeld, Andreas Wegner, Meik Blanke, Carlos Doñate‐Buendía, Vladyslav Sharov, Simon Nieskens, Markus Piechotta, Michael Giese, Stephan Barcikowski and Bilal Gökce.
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Featured image shows some of the yellow 3D printed objects that the researchers produced using their novel polymeric powder. Image via the Advanced Optical Materials journal.