3D printed parts are usually not ready to be sent directly from the printer. Generally, like most manufactured parts, it must go through one or more post-processing steps before shipping. These range from sanding and tumbling to machining and electropolishing. So, what are the specific methods for processing parts after 3D printing?
This method is commonly used for post-processing of plastic and metal parts that are 3D printed by a powder bed fusion process. For example, all components made by selective laser sintering (SLS) are media-blasted to remove excess unsintered powder adhering to the workpiece.
Media blasting is usually carried out in a closed cabinet equipped with air nozzles and gloves passing through the cabinet wall. Compressed air is mixed with grinding media such as sand-like glass beads and shot directly at the part.
Different media produce different results. Glass beads will produce a rough surface and can be used to clean and prepare painting surfaces. The ceramic medium will produce tiny dents, making the parts feel smooth. Small metal balls are used for shot peening of metal parts to remove unsintered materials and improve the mechanical properties of fine parts by smoothing the surface.
Currently, there is no sandblasting method that can bring 3D printed parts to a fully polished state without some kind of manual intervention (such as sanding).
- Grinding And Media Tumbling.
In many cases, the goal of post-processing is to smooth or polish parts or part features. Rolling sandpaper and abrasive media is a typical method to reduce surface roughness.
There are many grades of sandpaper, depending on the size and number of sand particles. The lower the value, the rougher the sandpaper. For example, sanding to a finish close to polishing can start with 300 grit sandpaper applied during wet sanding (sanding under running water). From there, operators gradually use finer sandpaper: 600, 800, 1,200, and finally 2,000+ coarse sand.
It is important to note that sanding is a manual process, and the associated costs (mainly labor) may exceed the price of the part.
Analysis of the method and process of 3D printed parts post-processing
Media tumbling is another grinding method. Unlike grinding, it is an automated technology. The tumbling equipment is a vibrating plastic bucket, a ceramic bucket or a metal medium. Their size and geometry vary, depending on the finished part. 3D printed parts with tumbling media usually have a smooth or satin appearance.
The disadvantage of media tumbling is that it may damage thin walls or delicate features and discolor some parts, depending on the media conditions. And, like grinding, grinding a part to a polishing medium usually requires multiple steps and operations.
- Dyeing Plastic.
When using a powder bed fusion process like SLS to 3D print parts from nylon, the parts are white or natural. Dyeing them is a relatively simple way to change their appearance and make them unique.
Dyeing involves mixing acid dyes in a hot water bath. Since many parts can be immersed in water at once, dyeing is an inexpensive post-processing option.
So far, due to the versatility of pigments in different applications, black parts that are dyed are the most common. Black can give the appearance a uniform appearance, where the dyes of some colors may vary from batch to batch due to saturation and exposure.
Since nylon parts are solid, the dye will not penetrate completely. This means that if the part is severely scratched or cut, the natural color of nylon will be visible.
Machining is most commonly used for 3D printed metal parts that require certain surfaces or tolerances. Machining usually involves the use of manual or CNC milling cutters to remove material through drills, end mills or other cutting tools.
Post-processed parts benefit from improved mechanical properties because their continuous smooth surface has fewer micro-stress points. However, post-processing is usually expensive and requires custom settings and test runs.
- The Steam Is Smooth.
This non-contact process takes advantage of material incompatibility. For example, acetone will dissolve ABS plastic because these materials are chemically incompatible. If properly controlled, the acetone vapor smoothing process will only liquefy the exterior of the ABS 3D printing and stop the dissolution before the parts are damaged.
Like machining, steam smoothing can enhance the mechanical properties and appearance of parts. It can also seal porous materials that are impermeable to water.
One of the disadvantages of steam smoothing is that it denatures brittle parts. After the process is completed, these functions may be rounded.
- Electrolytically Polished Metal.
This technology can reduce surface roughness and increase brightness. The process involves immersing the material in a conductive solution and allowing the ions of the material to be removed from the surface, which increases the smoothness.
Electropolishing is usually the last step of polishing because it can only remove very fine layers of material. Certain processes will boldly polish parts to remove sharp corners and subtle parts.