Engineers at Rutgers University in New Jersey have developed a new efficient, automated post-processing method for painting complex 3D printed objects. The spray coating process can reach the most inaccessible areas of a component. The new method, which can potentially save manufacturers time and money in the post-processing stages of production, can also provide new opportunities to create “smart skins” for 3D printed parts.

Using electrospray deposition (ESD), a spray coating process, Rutgers engineers have devised a technique that possesses the ability to conformally coat complex 3D objects without changing the location of the spray needle or orientation of the object, making them ideal for post-processing additive manufactured parts.

Senior author on the study, Jonathan P. Singer, an assistant professor in the Department of Mechanical and Aerospace Engineering in the School of Engineering at Rutgers University–New Brunswick, comments:

Our technique is a more efficient way to coat not only conventional objects, but even hydrogel soft robots, and our coatings are robust enough to survive complete immersion in water and repeated swelling and de-swelling by humidity.

A hydrogel lattice without (left) and with (right) coating. Photo via Jonathan P. Singer/Rutgers University–New Brunswick.

Developing the self-limiting electrospray deposition technique

Traditional means of coating and painting 3D printed objects via conventional sprays and brushes are limited in that they are unable to reach all nooks and crannies of a complex component. This can prove troublesome for many industries, like aerospace and medical for example, where the geometrical design freedom of 3D printing is a key benefit.

Rutgers engineers have identified a modified ESD technique for coating any exposed surfaces on a 3D printed object. ESD, they explain in their research paper, is a micro/nanoscale spray coating method that utilizes a high voltage to atomize a flowing solution into charged microdroplets. Often, the process is used mainly for analytical chemistry, however in recent years ESD has been leveraged in lab-scale demonstrations of coatings that deliver vaccines, light-absorbing layers of solar cells and fluorescent quantum dots for LED displays.

The engineers’ modified version of ESD minimizes its charge dissipation, enabling the deposition of thickness-limited film that grows in area over time, which they have named self-limiting electrospray deposition (SLED). Explaining the benefits of the process, the authors of the paper wrote: “Our results on SLED-sprayed wires demonstrated that the final coating thickness on all surfaces depended only on the distance to the spray needle (i.e., the field strength).” This means that location of the needle on the object, or the orientation of the object itself, did not have an effect on the coating process of SLED.

(a) Schematic of 3D coating with the SLED process where built up charge redirects the spray. (b) Steel-bronze 3D lattice before (left) and after (right) coating with a blue dyed. Photo via ACS Applied Materials & Interfaces

Compared to traditional fluid sprays, the SLED process was also more capable of tracking the features of 3D printed statues the engineers used for testing: “This trend was demonstrated on more complex 3D statues […] It was clear that the conformal nature of the spray tracked these features within the statues, not filling or bridging recesses as might occur with fluid sprays. For this reason, there is an opportunity to apply SLED to structures produced through additive manufacturing as a complementary postprocessing method.”

As such, the Rutgers team is currently building a SLED accessory for 3D printers that will allow automated coating of 3D printed parts with functional, protective or aesthetic layers of paint. The accessory will potentially enable much thinner and better-targeted paint application, according to the tests, while also using fewer materials than traditional methods.

Moving forward, the engineers are looking to create surfaces that can adapt their properties or trigger chemical reactions to generate paints that can sense their environment and report stimuli to onboard electronics. The Rutgers team hope to commercialize their SLED technique as a rapid coating tool that can be used immediately on a component immediately after 3D printing.

Research from Rutgers University

Rutgers University has demonstrated a significant output of research in the area of 3D printing, as researchers and engineers at the university seek to advance the technology and its capabilities.

As well as post-processing, recent 3D printing from Rutgers has revolved around bioprinting and 4D printing. In February, we reported on a research paper from the university about a bio-ink for 3D printing that enables the construction of scaffolds to support growing human tissues.

Additionally, in that same month, researchers from Rutgers also created bioinspired, programmable 4D printed microneedles that enhance tissue adhesion using Projection micro-stereolithography (PµSL). This follows a previous study from the university in 2018 where researchers developed a new method of 4D printing.

The paper discussed in this article, “Self-Limiting Electrospray Deposition for the Surface Modification of Additively Manufactured Parts,” is published in ACS Applied Materials & Interfaces. It is written by Dylan A. Kovacevich, Lin Lei, Daehoon Han, Christianna Kuznetsova, Steven E. Kooi, Howon Lee, and Jonathan P. Singer.

This article was originally published HERE

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