Three-dimensional (3D) printing technology has evolved tremendously over the last decade to the point where it is now viable for mass production in industrial settings. Also known as "additive manufacturing," 3D printing allows one to create arbitrarily complex 3D objects directly from their raw materials. In fused filament fabrication, the most popular 3D printing process, a plastic or metal is melted and extruded through a small nozzle by a printer head and then immediately solidifies and fuses with the rest of the piece. However, because the melting points of plastics and metals are very different, this technology has been limited to creating objects of either metal or plastic only--until now.
In a recent study published in Additive Manufacturing, scientists from Waseda University, Japan, developed a new hybrid technique that can produce 3D objects made of both metal and plastic. Professor Shinjiro Umezu, who led the study, explains their motivation: "Even though 3D printers let us create 3D structures from metal and plastic, most of the objects we see around us are a combination of both, including electronic devices. Thus, we thought we'd be able to expand the applications of conventional 3D printers if we managed to use them to create 3D objects made of both metal and plastic."
Their method is actually a major improvement over the conventional metallization process used to coat 3D plastic structures with metal. In the conventional approach, the plastic object is 3D-printed and then submerged in a solution containing palladium (Pd), which adheres to the object's surface. Afterwards, the piece is submerged in an electroless plating bath that, using the deposited Pd as a catalyst, causes dissolved metal ions to stick to the object. While technically sound, the conventional approach produces a metallic coating that is non-uniform and adheres poorly to the plastic structure.
In contrast, in the new hybrid method, a printer with a dual nozzle is used; one nozzle extrudes standard melted plastic (acrylonitrile butadiene styrene, or ABS) whereas the other extrudes ABS loaded with PdCl2. By selectively printing layers using one nozzle or the other, specific areas of the 3D object are loaded with Pd. Then, through electroless plating, one finally obtains a plastic structure with a metallic coating over selected areas only.
The scientists found the adhesion of the metal coating to be much higher when using their approach. What's more, because Pd is loaded in the raw material, their technique does not require any type of roughening or etching of the ABS structure to promote the deposition of the catalyst, unlike the conventional method. This is especially important when considering that these extra steps cause damage not only to the 3D object itself, but to the environment as well, owing to the use of toxic chemicals like chromic acid. Lastly, their approach is entirely compatible with existing fused filament fabrication 3D printers.
Umezu believes that metal-plastic hybrid 3D printing could become very relevant in the near future considering its potential use in 3D electronics, which is the focus of upcoming Internet-of-Things and artificial intelligence applications. In this regard, he adds: "Our hybrid 3D printing method has opened up the possibility of fabricating 3D electronics so that devices and robots used in healthcare and nursing care could become significantly better than what we have today."
This study hopefully paves the way for hybrid 3D printing technology that will enable us to get the best of both worlds--metal and plastic combined.