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Post-Processing CFR Composite Parts with AMT PostPro 3D

Wait, Onyx parts can get even smoother?

Fresh off of the print bed, Markforged parts are not only the strongest in extrusion-based 3D printing, they also have the most uniform surface finish in the game. Continuous Fiber Reinforcement materials give parts strength and stiffness, while the finely-balanced blend of short carbon fibers used in Onyx delivers accuracy, durability, and its characteristic silky-smooth surface finish.

Based on a nylon matrix polymer, Onyx also has strong resistance to solvents and petrochemicals. This is a boon for our manufacturing customers whose parts are often exposed to lubricants and cleaners, but also means that even hazardous chemical post-processing techniques like acetone vapor smoothing will not work.

Processes Compared

In certain applications, an even finer surface finish may be desirable to aid fluid flow over the part, to seal surfaces, or to improve aesthetics.
For those looking to further enhance the surface finish of Onyx parts, the only options until recently were:

1. Mechanical post-processing with abrasives, like glass bead blasting or sanding. This yields nice results, but is generally labor-intensive and can also make quite a mess. As a result of the skilled labor requirement, it can also be a costly service.
2. Chemical post-processing with harsh solvents, like vaporized nitric acid or acetic acid. The harsh chemicals often require specialized facilities preparations which are not practical for the average customer. Since acid breaks down nylon, this also tends to degrade parts, causing embrittlement and loss of strength. Realistically, this is not an option unless you already have access to a facility which performs this service.

When AMT showed us a part that was processed in their PostPro 3D system, which boasts a simple, automated process, we had to dig in to find out more.

Our initial testing used a limited test suite of ASTM standard dogbones. The results indicate that in addition to reducing surface roughness, the AMT's chemical vapor smoothing did not compromise mechanical properties. In some cases, parts became more elastic or even slightly stronger on average after undergoing the AMT process. Your results may vary depending on geometry.



    Onyx XY Tensile Stress at Yield


    Onyx XY Young's Modulus


    Onyx XZ Young's Modulus


    Average reduction in surface roughness across all tested surfaces.

AMT explains the process behind their PostPro 3D technology and the vapor smoothing process, which is a combination physical-chemical process that can smooth Onyx, as well as a variety of other thermoplastic polymers.

How it works

The following is a description of the process, provided by AMT.

AMT's PostPro 3D uses their patented chemical vapor smoothing process to effectively and efficiently post-process additively manufactured thermoplastics. PostPro 3D achieves reproducible, smooth parts, without compromising the part's geometry or mechanical properties. The surface imperfections are erased from parts with no line of sight issues, and effectively seals even complex geometries with internal cavities.

Parts are suspended in the processing chamber where they are exposed to a controlled amount of solvent vapor. The vapor condenses on the parts, interacting with the polymers at the surface and causing the surface to re-flow. After time, the machine heats back up, causing the solvent to re-vaporize and then it is extracted from the parts and the processing chamber. The parts are then thoroughly dried in the processing chamber, leaving behind just a newly smoothed surface.

The Onyx parts we have run turned out amazing and exceeded any expectations I had. It essentially eliminates any layer lines which allows us to run parts faster by printing them at 200 microns and still achieve a great surface finish."
– Pete Kootstra, Re3DTech Director of Engineering