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Vapor-smoothing 3D prints to get the ‘ugly’ out of their parts

Vapor smoothing is a hands-off process for improving the finish of polymer parts

vapor smoothing eliminates stairstep effect in 3d printing: before and after

These before-and-after closeups illustrate the goal behind all vapor smoothing technologies: eliminate the stairstep effect common to most 3D-printed parts. Zortrax

Let’s face it: Many 3D-printed parts come out of the machine looking layered, rough, and ... well, a bit ugly. It’s possible to remove much of this stairstepped ugliness via sanding, beadblasting, filling, and other manual processes. But these techniques are time-consuming and error-prone. And, often, they can’t reach into the nooks and crannies of complex part geometries.

Fortunately, a far less labor-intensive method exists—for certain polymers, at least—that intrepid souls can attempt using common household items.

YouTube followers of Czech 3D printer manufacturer Josef Prusa know that “acetone smoothing” of ABS and ASA parts—two common materials used in the fused filament fabrication (FFF) process—requires nothing more than a loosely covered Rubbermaid bin, a small quantity of acetone (nail polish remover) in the bottom of the bin, and a platform that holds the parts above the acetone. Place the parts on the platform, close the bin, and let the vapors do their work. In just a few minutes, the objects will be smooth and shiny. No sanding necessary.

Similarly, Prusa describes how PVB parts can be smoothed with isopropyl alcohol, and other YouTube contributors show these processes performed over an electric stove and suggest that parts made from PLA—another common material—might be vapor-smoothed in this manner. Exercise caution, however, as both these compounds are highly flammable and, if used improperly, can be harmful to humans and 3D-printed parts.

Easy Does It

Such vapor smoothing tactics are fine in a hobbyist’s well-ventilated workshop. But for additive manufacturers with delivery schedules to keep, a safer, more accurate, and predictable solution is needed.

According to Jacek Krywko, technology solutions specialist at Zortrax S.A., an Olsztyn, Poland, supplier of 3D printers, filaments, and other additive products, one such solution is the company’s Apoller desktop “smart vapor” smoothing device. In operation, the multistage process begins by lowering the pressure within a sealed smoothing chamber containing the printed part or parts, he explained. Solvent is then pumped into a heated tray at the bottom of the chamber, and an air-circulation system draws the resulting vapor up and around the workpiece, condensing on its surface.

“By precisely controlling the airflow and temperature, we can achieve very predictable results without any oversmoothing or part distortion,” said Krywko.

The automated process takes three hours, regardless of part size or quantity, and it uses acetone or butanone. The chamber generates a slight vacuum and is locked during operation, which alleviates safety concerns, said Krywko, and the condensed, unused solvent falls to the bottom of the tank for reuse.

It is intended for parts made of ABS, ASA, and high-impact polystyrene, but it can also be used with polycarbonate and other polymers that react with (can be melted by) either of the two solvents.

Beyond FFF When Vapor Smoothing 3D Prints

The vapor smoothing discussed so far has been in the context of FFF-printed parts. The main reasons are because FFF, or extrusion-based, printing is among the widest used AM processes, it generally produces the roughest surface finishes, and it employs materials reactive with the solvents mentioned.

3d printed computer fans

The Zortrax Apoller smoothed this large batch of computer fans in less than three hours. Zortrax

That said, available systems can smooth parts built by other additive technologies.

One is from Additive Manufacturing Technologies (AMT) Inc., Cedar Park, Texas. The company was founded in 2017 with the goal of producing an automated smoothing system that makes 3D-printed parts as aesthetically pleasing as injected-molded ones and does the job quickly and safely, said AMT Executive Vice President Luis Folgar.

The result is the company’s PostPro 3D and PostPro 3D Mini chemical vapor smoothing systems. Their capabilities include delivering postprocessed part surface finishes down to 1 μm Ra; dimensional degradation of no more than 0.4%, regardless of the target surface finish; improved mechanical properties, which, depending on the material and printer technology, can include greater elongation at break, higher tear resistance, and improved ultimate tensile strength; reduced surface porosity and cracking; and a sealed surface that resists bacterial growth and eliminates liquid or gas absorption.

The list of proven AM materials the PostPro 3D smooths includes polyamides (nylons such as PA6 and PA12) and its many filled variants, Ultem, PMMA (acrylic), TPU, and TPE. “We’re also quite close to a solution for PEEK and PAEK, polymers that are especially challenging to smooth,” said Folgar.

Vapor Smoothing 3D Prints on the Shop Floor

Digital manufacturing company DI Labs, Willmar, Minn., recently purchased one of AMT’s larger systems. And seeing that it runs “pretty much nonstop,” according to the company’s president and co-owner, Carl Douglass, he’s considering buying a second unit.

“Many of our parts require ultrasmooth surfaces,” he said, adding that the process is quite fast, taking anywhere from 20 minutes to an hour or two depending on the part complexity, material, and desired surface finish. And because it’s a closed system, DI Labs personnel don’t have to handle hazardous waste. Every few weeks operators remove canisters of spent chemicals, which are returned to AMT, and replace them with fresh canisters.

As with additive manufacturing itself, however, developing the correct vapor smoothing “recipe” of processing parameters is not a plug-and-play affair. For polymer parts production, DI Labs uses FFF, SLA, Multi Jet Fusion (MJF), and digital light synthesis printers, with which it prints roughly four dozen materials and thousands of unique workpieces annually. For each part and material combination, an operator must determine the best way to place the part in the smoothing chamber, how long to process it, what temperature to use, and other variables that can result in a perfect part, one that doesn’t meet specifications, or in extreme cases, a melted pile of goo.

“We’ve even seen where the same material from two different suppliers produces different smoothing results,” Douglass said. “But the same can be said about AM in general. With MJF, for example, we have to make sure that the right heat profile is being applied for the part and that there’s consistent energy distributed through each of the Z-planes. Some of that same philosophy applies to vapor processing, where we typically make sure that all the parts in a smoothing run have similar features and wall thicknesses so that they heat and cool at roughly the same rate.

“That’s just the nature of the additive game, though,” he laughed. “There’s a lot more to it than the equipment.”

About the Author

Kip Hanson

Kip Hanson is a freelance writer with more than 35 years working in and writing about manufacturing. He lives in Tucson, Ariz.