10 Techniques For Post-Processing FDM Printed Pieces
3D printing is believed to be a mostly automated digital workflow; a process that is fast, simple, and machine-driven. That notion, for the most part, is accurate. However, once the device churns out the print, the automation is shifted to manual operation, called ‘post-processing.’ 3D model post-processing affects the time, cost, and quality of the final print. Usually, different 3D printing technologies have distinct variations, but ‘post-processing’ is something common. It is always needed once an object is done printing. This article will highlight ten ways for post-processing FDM printed pieces.
FDM technology is ideal for 3D printing cost-efficient prototypes. They can be created with brief lead time. As FDM 3D prints tend to have visible layer lines, it makes the post-processing a necessary measure to smoothen the surface, if required. Certain post-processing processes can also increase the strength of the prints. It helps in mitigating the anisotropic nature of FDM objects.
POST-PROCESSING FDM PRINTED PIECES
The following are the different post-processing steps required for FDM 3D printed items.
1. SUPPORT REMOVAL
Removing supports is usually the first post-processing step in all 3D printing technologies where accurate pieces are produced. They can be divided into two types; standard supports and dissolvable supports. The standard ones can quickly be scrapped with a little effort. Different types of tools are available for this task, even if they are in hard-to-reach places. As for the dissolvable supports, they can be removed by dunking the printed piece into a solution of material-specific solvent, until the supports disappear.
Once the supports are taken care of, the next phase is sanding. It is intended to smoothen the piece, and get rid of any visible blemishes. With sanding, blobs, support marks, layer lines, etc. can be graded. The initial grit of the sandpaper is determined by the print quality and layer height. For blemish-less prints and layers under 200 microns height, they can be scrubbed with a 150 grit sandpaper. In case of visible spots, or the items with a layer height over 300 microns, they can be sanded with 100 grit sandpaper.
3. COLD WELDING
Cold welding is one of the techniques for post-processing FDM printed pieces. Sometimes, when the scale of a model is over the max volume of the device, it is divided into smaller pieces. These parts are then printed individually and arranged later. The assembly or cold welding requires gluing the printed parts to get the final form of the model. For PLA or similar plastics, appropriate glue can be used. Incase of ABS, acetone is used to cold weld the different pieces together.
4. GAP FILLING
Sometimes, following sanding or removing supports, prints can appear on the prints. These gaps are caused by the layers that are sometimes left incomplete because of toolpath constraints. For filling small voids and gaps, epoxy would be enough to fix them. As for larger gaps and spaces left after assembling a multipart print, an autobody filler would do an excellent job. It will, however, require additional sanding and painting once cured. Autobody fillers also strengthen the areas and joints where they are applied.
Usually, after sending and removing any blemishes from the print, it is ready for polishing. For filaments such as PLA and ABS, the plastic polish can be used to give them a shiny finish. After sanding a piece with a 2000 grit sandpaper, wiping it to clean any dust, and brushing it using a small brush and warm water, the polish can be applied. Once the paint is fully dry, you can apply the polish either by hand with a microfiber cloth or a buffing wheel.
Priming is required before painting a printed piece. The aerosol primer should be used for this purpose. Aerosol primers are designed for model painting, and they do not obscure the details before the model could be painted. The first coat should be sprayed with short quick strokes, from a distance of 15 to 20 centimeters. If required, use a 600 grit sandpaper to take care of any imperfections after the primer has dried. The final coat should be applied similarly in quick light strokes to make sure that the chemical does not pool on the printed item.
After priming, the model is ready to be painted. Artist acrylic paints can be used, although airbrush or aerosol sprays, made specifically for model paintings tend to leave a smoother finish. Start by painting the item with very thin coats. The initial few layers of the paint will appear translucent, and once an opaque layer comes out, let the piece sit for about half an hour to set the paint. After that, use nail sticks to softly polish the painted parts. This process should be repeated for each color, followed by polishing.
8. VAPOR SMOOTHING
Vapor smoothing is used to create a shiny finish on the print. This process starts by warming acetone up on a heated surface, and an airtight container is recommended for this task. Then, place the piece in the container, so that they could come into contact with the acetone vapors. This will cause them to slightly melt to give the piece a shiny finish. There are also commercial grade vapor smoothing stations available in the market. One thing to keep in mind is that as acetone is a toxic substance, there should be adequate ventilation.
Dipping is another one of the techniques for post-processing FDM printed pieces. It is used to smoothen the print using a particular solvent. Acetone should be dipped in ABS, and while THF or MEK can be used for dipping PLA. As PLA is relatively resistant to dipping solvents, it may take a few attempts to get the desired finish.
10. EPOXY COATING
In order to coat the printed item with epoxy, it has to be sanded first. It will produce much better results. Add the specific levels of resin to the hardener, as per the instructions on the bottle. Make sure that you measure everything accurately. Bear in mind that as epoxy resins are exothermic, containers made from low melting point materials should be avoided.