Which of the 10 most commonly used FDM 3D printing parts post-processing method should I choose?

Brief

The post-processing of 3D printing can improve the aesthetic of the printed pieces, as well as the strength and other properties. Most 3D printed works require post-processing after printing. This blog introduces the 10 most commonly used post-processing methods of FDM printing process and the results that can be achieved by using these post-processing methods.

 

Intro: Cleaning and pretreatment 
Cleaning and pretreatment techniques include basic work such as support removal and grinding. Depending on the requirements of the project application, these techniques are often the first step in post-processing, but depending on what effect you want to achieve, these can be the last step as well. 

1. Remove support (manually remove and dissolve)

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Support removal is the most basic post-processing. Usually, it doesn't take a lot of effort to remove support, unless it's in a tight corner or other hard-to-reach place. Depending on their material, supports can be insoluble or soluble (able to dissolve in water or other liquids).
Insoluble supports are made of the same material as the main components. FDM 3D printers with a single extruder can only use this type of support because the parts and support are printed from the same coil of filament. Insoluble supports are usually removed by breaking them by hand or cutting them off with pliers.
Of course, you can also use a 3D printer with a dual extruder so that you can use soluble supports. Insoluble supports can be tricky in corners, while soluble supports dissolve by simply immersing the part in water or other liquids, leaving almost no traces of support or residue. The two most common soluble support materials are HIPS and PVA.HIPS is used for ABS and is soluble in D-limonene, while PVA is well suited for PLA and is soluble in water.

2. Sanding (sandpaper)

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Sanding is the most common form of post-processing, in addition to support removal. Typically, FDM 3D prints will have a slightly rough surface, and sanding is the easiest way to make the surface smooth.
Parts may have spots left on the surface after printing, or there may be some marks after you remove the support. The ideal way to eliminate this blemish is to use sandpaper. It is best to start with a low grit sandpaper (150-400) and move to a high grit sandpaper (up to 2000) during several stages of grinding.
Several key techniques for sanding are wet sanding and circular motion. When you grind a part, the friction between the sandpaper and the surface generates heat, which can negatively affect the fine features of the print, especially for heat-sensitive materials. To avoid this, simply wet the part before grinding to absorb any excess heat.
Especially for FDM parts, where lamination is easy to see, it is important to grind the parts in circular motion. If you grind a part parallel to or perpendicular to the layers, you may damage the visual appearance of the part.

3. Splicing (acetone)

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If you want to 3D print a large object using ABS, but your 3D printer's build is too small, splicing is the perfect solution for you.
In FDM 3D printing, splicing refers to the use of acetone to connect ABS parts. Acetone has the ability to melt ABS, so this means ABS parts can be joined with acetone splices.
The process is quite simple. Apply a little acetone to the part you want to "glue". This will cause the plastic to melt slightly, at which point, attach another part to the edge of the melt to stitch them together.

4. Cement (glue)

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While splicing is a great way to combine multiple 3D-printed parts, it only works with parts printed with ABS. Fortunately, 3D-printed pieces made from other materials can still be attached with glue. Similar to splicing, this is often used in cases where single-piece printing is not possible due to printer size limitations. 
PLA and PETG are adhesives such as super glue that can be used. 

Fine finishing
Finishing technology is the last step in 3D printing post-processing. Common methods include painting, smoothing, polishing and impregnating FDM 3D prints. By applying these techniques, you will be able to eliminate lamination and create as smooth a surface as possible. You can't even tell that your parts were printed by a 3D printer!

5. Spray paint (model paint)

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Priming is a post-processing technique used to prepare for painting. Apply a primer or spray primer to a part as a base for the paint to be applied later.
It is a good idea to sand your parts with low and medium grade sandpaper before applying the primer. This will remove the lamination and make the surface smooth. After polishing, apply two coats of primer. 

6. Surface smoothing (acetone)

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Smoothing is a popular post-processing technique, especially for ABS printed models. Acetone has the ability to melt ABS, smoothing the surface of the parts. 
The easiest way to do this is to pour acetone into a large container (plastic can be used, but glass is recommended) and place your print on a platform on top of the acetone. Close the lid of the container for 10-20 minutes to allow the steam to melt the outer layer of the part. If you want steam to escape from the container, drill holes in the lid beforehand. 
If you don't have a suitable container, you can use a brush to apply a small amount of acetone to the surface of the 3D-printed piece. But it's important to note that acetone is highly flammable and explodes. Therefore, appropriate precautions should be followed when performing both procedures. Even just smoke can be harmful if inhaled, causing irritation and poisoning. Work in a well-ventilated area at all times and make sure gloves and a mask are worn. 
As for PLA, it cannot be smoothed with acetone as it will not melt the acetone and may even make the whole print "gelatinous", thus damaging it. PLA can be smoothed with chemicals such as THF or MEK, but the results will not be as good as ABS smoothed with acetone. 
If you have some 3D printed pieces made with PVB filament, you can use isopropyl alcohol to smooth them out. 

7. Polishing (polisher)

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This 3D-printed post-processing technique is used to achieve the smoothest possible surfaces. Polishing 3D-printed pieces can be done with plastic polishers and tools that are available at almost every hardware store. A microfiber cloth and a plastic polisher are all you need. 
Before a part can be polished, it needs to be properly polished with the finest sandpaper. After polishing, rinse your parts and make sure no particles are left. If you are using cloth, apply a polisher to the polished part and move the cloth in a circular motion until you are satisfied with the result. 

8. Hydrographics transfer printing

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While typically used on a large scale for industrial products, small-scale water transfer printing can easily be applied to 3D-printed parts to make them look very nice. Water transfer printing is the process of applying a design pattern to a solid object using special water transfer paper. One side of the paper is made from PVA, on which graphics are printed using an inkjet printer. 
Start by finding a container large enough to hold your parts and filling it with hot water. Remove the back of the paper so that you are left with the transparent PVA printed with the graphics. Carefully place it in the water, and when the PVA dissolves, your figure will float on its own. 
Then, slowly dip the part into the figure at a 45 degree Angle. You can hold it in one hand or with a stick to be able to work from a distance. Once the part is completely submerged, give it a few shakes and you can pull the finished part out of the container. 
Water transfer printing is only used to enhance the aesthetic of the object, does not change the feel or any size attributes. However, the possibilities of the graphics you can add to parts are endless, so this is one of the best ways to make your 3D-printed creations stand out. 

9. Epoxy paint

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The epoxy coating can improve the strength of your 3D-printed piece, but it can also seal the porous parts of the printed piece and act as a protective layer. Epoxy coatings are composed of two different chemicals: the epoxy itself and the hardener. 
When you buy chemicals for epoxy coating applications, your brand of choice will provide blending instructions. The ratio of hardener to resin has to be right for good results, or you could end up with a coating that will never dry and can be applied to the 3D-printed part once you have the mixture ready. 
We recommend using a foam applicator or sponge to apply the coating. When you're done with the first layer, let the parts dry and then sandpaper them with grade 1000 or 2000. Once done, you can apply the second and final layer of epoxy. 
If you want to try epoxy coating, there are some epoxy coating products for 3D printing, such as XTC-3D. 

10. Electroplating

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Electroplating is the process of adding metal coatings to other metals or components with conductive surfaces. This is a great post-processing technique that can greatly improve strength and visual appearance. The process itself may seem complicated at first, but it's not as technical as it seems. 
Electroplating is basically the transfer of a metal coating from one metal to another (or a component with a conductive surface). Electroplating is made possible by a chemical process called electrolysis. The two main tools for electrolysis are a power supply (battery or rectifier) and an electrolyte. 
An electrolyte is a mixture of a metal salt (the metal you want to coat your parts with), acid and water. An electric current is needed to start the reaction between the cathode (the negative pole connected to the power supply) and the anode (the positive pole). 
The anode is made of the metal you want to use as a coating, and the part to be electroplated serves as the cathode.Both the anode and cathode are then immersed in the electrolyte. 
The salts in the electrolyte contain cations and anions (positively and negatively charged ions) that need to be moved to the cathode and anode for the metal to transfer. Turning on the power supply and applying a current to the electrolyte causes the anion to move to the anode and the cation to the cathode. 
Let's say you want to coat your 3D-printed parts with copper, so the electrolyte you'll use is copper sulfate (CuSO4). Once the current starts, the Cu2+ cation moves to the cathode and coats your part. 
The most common metals used in this process are copper and nickel, but materials such as brass, gold, silver, and chromium can also be used. 
Since 3D-printed parts are plastic and non-conductive, you'll need to properly polish them and apply conductive paint before attempting electroplating. 

Conclusion

The above are the 10 most commonly used post-processing processes for FDM 3D printed parts, mainly for polymer plastic parts, and the post-processing processes for FDM printed metal parts are not included. Readers can choose which post-processing process to use according to the results they want to achieve. 

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