A new metal-plastic hybrid 3D printing technology
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2021-08-06
Figure 1: A method to extend the use of 3D printers to 3D electronics, enabling future robotics and IoT applications while allowing simultaneous printing of both metal and plastic.
3D printing technology has seen tremendous advancements over the past decade, now enabling large-scale production in industrial settings. Also known as "additive manufacturing," 3D printing allows people to create 3D objects of any complexity directly from raw materials. In the most popular 3D printing process—fused deposition modeling—plastics or metals are melted and extruded through a small nozzle by the printer head, where they instantly solidify and fuse with the rest of the part. However, due to the significant differences in melting points between plastics and metals, this technology has so far been limited to producing either metal or plastic objects.
In a recently published study in the journal *Additive Manufacturing*, scientists from Japan’s Waseda University have developed a new hybrid composite technique capable of producing 3D objects made from both metal and plastic. Leading the research, Professor Shinjiro Umezu explained their motivation: "While 3D printers already allow us to create 3D structures using metals and plastics separately, most everyday objects around us—such as electronic devices—are actually composed of these two materials combined. That’s why we believe that by leveraging conventional 3D printers to fabricate 3D objects out of metal and plastic, we can significantly broaden the range of their practical applications."
Their method represents a significant improvement over the traditional metallization process used for coating 3D-printed plastic structures with metal. In the conventional approach, the plastic object is first 3D-printed and then immersed in a solution containing palladium (Pd), which adheres to the surface of the object. Next, the part is placed into a chemical plating bath, where the deposited Pd acts as a catalyst, enabling dissolved metal ions to bond firmly to the plastic. While this technique is technically sound, it often results in uneven metal coatings and poor adhesion to the plastic structure.
Figure 2: A: Conventional method for metalizing 3D-printed plastic structures. This approach requires wet pre-treatment to activate the surface of the workpiece. Pd colloids are first deposited onto the surface, after which the Pd-catalyzed part is immersed in a chemical deposition bath, enabling the coating of the desired metal onto the surface. The Pd catalyst facilitates electroless deposition. However, since the plastics used in 3D printers—such as ABS in this study—are predominantly hydrophobic, the deposited metal exhibits poor adhesion to the surface, resulting in an uneven coating. B: The method proposed in this paper for selectively depositing metal onto specific areas of 3D-printed plastic structures. In addition to using pure ABS filament for the base structure of the workpiece, a special ABS filament containing PdCl₂ is also employed. During 3D printing, the main structural components of the workpiece are fabricated using pure ABS filament, while the selected areas of interest (highlighted in yellow in the figure) are coated with the PdCl₂-containing ABS filament. Because the workpiece is already Pd-catalyzed in these targeted regions, it can be directly immersed in the chemical plating bath—effectively skipping the catalytic step shown in Figure A.
Figure 3 shows 3D-printed ABS structures obtained using different catalytic methods. (A) The conventional method illustrated in Figure 1A: immersion in a Pd ion solution. Double-headed arrows indicate the immersion depth. (B) Region-selective catalysis: An ABS and PdCl₂ mixture dissolved in acetone is applied via a nozzle under pneumatic pressure. (C) Region-selective catalysis: PdCl₂-containing ABS filament is fed into an FFF 3D printer, where it bonds with another layer of PdCl₂-treated ABS. The left image depicts the structure after 3D printing and catalysis, while the right image shows the result after chemical deposition.
An overview of traditional methods for metalizing 3D-printed plastic structures, along with the approach proposed in this paper. Unlike conventional techniques, the dual-nozzle method introduced here selectively produces 3D objects with a uniform and firmly adhered metal coating—precisely where it’s needed.
In contrast, the new hybrid method employs a printer equipped with dual nozzles: one nozzle extrudes standard molten plastic—acrylonitrile-butadiene-styrene (ABS)—while the other nozzle dispenses ABS mixed with palladium chloride (PdCl₂). By selectively printing layer-by-layer using either nozzle, specific areas of the 3D object are enriched with Pd. Finally, through chemical plating, these regions are transformed into plastic structures fully coated with metal—precisely where it was initially deposited.
Scientists have discovered that when using this method, the adhesion of the metal coating is significantly higher. More importantly, because the raw materials already contain Pd—unlike traditional approaches—their technique eliminates the need for any type of roughening or etching of the ABS structure to promote catalyst deposition. This is particularly crucial, as these additional steps not only risk damaging the 3D object itself but also pose serious environmental hazards due to the use of toxic chemicals like chromic acid. Finally, their method is fully compatible with existing filament-based 3D printers.
Umezu believes that, given the potential applications of metal-plastic hybrid 3D printing in 3D electronics, this technology could become increasingly important in the near future—particularly as the focus shifts toward emerging IoT and AI-driven applications. In this regard, he added: "Our hybrid 3D printing approach opens up new possibilities for creating advanced 3D electronic devices, enabling innovations in healthcare and caregiving tools, as well as robotics, potentially making these technologies far more sophisticated than anything we have today."
This research is poised to pave the way for advanced 3D printing technologies, enabling us to fully leverage the advantages of both metals and plastics.
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