Why Need Post Processing for 3D Printing?
3D printing can get fast and complicated prototypes, but they have a low surface finish. Which leads to stress concentrations and cracks that can reduce fatigue resistance and fracture toughness. Even by improving the quality of the metal powder and optimizing the molding direction or printing parameters, the surface quality of 3D printed workpieces can enhanced to a certain extent, but it still can’t meet the requirements of the industry for surface roughness. However, post-processing after 3D printing can reach an ideal surface
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Defects of 3D Printing
High Cost for Raw Material
Initially, the difficulty of developing material for additive manufacturing caused a higher manufacturing cost for 3D printing. (generally over $10-100 per gram)
Manufacturing Efficiency
Additionally, 3D printing manufacturing with low efficiency, especially in metal molding, is around 100-3000 grams per hour.
Accuracy
Lastly, in the current situation, 3D printing technology is not very mature, so the manufacturing accuracy can’t be compared with the traditional ultra-precision machining technology.
What Are the Post-processing Finishing Techniques?
Overall post-processing techniques mean after the initial manufacturing or production processes are completed. Then through other procedures and methods, refine and enhance the part’s surface appearance, quality, and functionality. So these techniques are crucial in various industries, especially in 3D printing.,
Types of Polishing and Their Applications
I. Hand Polishing
Significantly hand polishing is the simplest and earliest post-processing method. However, component quality depends on the operator’s proficiency and experience level, resulting in parts with poor repeatability and consistency. Plus, the dust pollution generated in the polishing process will also cause damage to the human body.
2. Sandblasting Polishing
Through the compressed air to form a high-speed jet beam, the spray material (quartz sand, emery, etc.) sprayed to the surface of the workpiece to be processed, due to the impact of the spray material on the surface of the workpiece and the cutting effect, so that the surface obtains a certain degree of smoothness and different roughness. Eventually used for polishing the outer surface of the workpiece, removing oxidized layers, etc.
3. CNC Grinding and Polishing
Relative to the workpiece, the grinding wheel of the CNC machine tool rotates at high speed, causing the abrasive grains to rub strongly against the workpiece. At the same time generating a large amount of heat, the thickness of the cutting layer is in micrometers, so that the surface of the workpiece obtains high surface accuracy and low surface roughness.
4. Laser Polishing
A new polishing method that uses a high-energy laser beam to reduce surface roughness by re-melting the material on the part surface. So far, the surface roughness of laser-polished parts is Ra 2–3 μm.
However, the equipment for laser polishing is expensive, so this technique has not been widely used.
5. Chemical and Electrochemical Polishing
Through the etching effect of chemical reagents, the selective dissolution of the uneven areas on the surface of the part can eliminate abrasion marks and pits to achieve a leveling effect. This technique is especially suitable for small hollow features or array structures of the part.
Chemical polishing mainly removes the adhering metal spherical powder on the surface, while electrochemical polishing further reduces the surface roughness on this basis.
6. Grain Flow Polishing
Under a certain pressure reciprocating flow through the processed area, the use of abrasive media in the micro-cutting action of the abrasive particles removes the roughness of the surface.
Also, abrasive flow polishing technology is suitable for polishing, deburring, chamfering, etc. Furthermore, parts with complex internal cavities, free-form surfaces, and irregular shapes. Obviously, this technique can process almost all metal materials.
7. CNC Machining
Additionally, some 3D-printed parts need machining services to achieve the required dimensional accuracy and surface finish.
What Post Processing Steps in 3D Printing?
Since the main steps in 3D printing post-processing include powder removal, stress relieving, removing parts, heat treating, hot isostatic pressing, machining, mold removal, de-supporting, cleaning, blow drying, secondary curing, and sanding. Thus post-processing steps for metal 3D printing are relatively complex and involve multiple steps to ensure the final quality and performance of the printed part.
Powder Removal
Since 3D-printed part is built in a powder bed fusion system and is buried in the powder when finished. So we need to remove it and sieve/filter/recycle it for future use.
Stress Relieving
To remove internal stresses caused by heating and cooling of the metal. Stress-relieving is usually done in an oven or furnace and is recommended to be performed in an oven with an inert environment to minimize oxidation.
Heat Treatment
Also, heat treatment is a necessary step for almost all 3D-printed metal parts and can effectively improve the microstructure and mechanical properties of the part.
Hot Isostatic Pressing (HIP)
In some cases, HIP is used to improve the fatigue life of castings. And if performed HIP process, usually heat treatment is not required
Machining
To ensure the dimensional accuracy of the finished part, including CNC machining of surfaces, threads, support structures, and more.
Post-processing Steps For Light-Cured 3D Printing
Model and Support Structure Removal
After the model is printed, firstly, remove the model and the support structure to obtain a smooth surface.
Cleaning and Dry-blowing
Then, remove any uncured material that is left on the surface, and blow drying is to allow the alcohol and moisture to evaporate further.
Secondary Curing and Sanding
Besides the above, apply secondary curing and sanding to enhance the physical quality and aesthetic features of the model.
Conclusion
The post-processing steps may need to be handled differently. Also depending on the 3D printing technology and material to ensure that the final quality of the print is as expected.
3D Printing Finishing Techniques: 5 Ways to Apply Coloring
Hand Colored
Hand coloring is the easiest to learn and work with which is the cheapest way as well, but the quality can be inconsistent due to the varying skill levels of the workforce.
Spray Painting Color
So far, spray painting is one of the main coloring processes for 3D-printed products, known for its high adhesion of paint. Hence, it is widely applicable; thus, the gloss achieved is only comparable to electroplating and nanospraying. However, the color options are relatively limited, making multi-color spraying difficult.
Dipping
Dip-dyeing is another coloring process for 3D-printed products, but it is limited to nylon materials and specific colors. While the process is faster, taking around 30 minutes to complete, it is more expensive than hand coloring and spray painting and offers the lowest level of gloss.
Plating
Electroplating involves using electrolytic principles to apply a thin layer of other metals or alloys on the surface. This technology enhances wear resistance, conductivity, reflectivity, corrosion resistance, and aesthetics. However, it is limited to chrome, nickel, and gold colors and is only applicable to metal and ABS plastic. Furthermore, the cost is high, and the process is restricted by part size and shape, but it delivers an exceptional mirror-like gloss.
Nano-plating
Nanospray plating uses specialized equipment and advanced materials to apply a chemical coating directly. That method achieves a mirror-like high-gloss effect in various colors, including gold, silver, and chrome. Nanoplating is currently the most cutting-edge technology globally, offering flexibility in materials and colors without limitations of volume or part shape. It allows for simultaneous applications of multiple colors with extremely natural transitions. Despite being a high-tech solution, the cost is relatively low, and with excellent results. You can also customize the equipment according to the production capacity.
| Technical Processing | Hand Coloring | Painting | Dipping | Plating | Nanoplating |
|---|---|---|---|---|---|
| Material Applicable | All Types of Material | All Types of Material | Nylon | Metal and ABS | All Types of Material |
| Part Volume /Shape | Limited | Limited | No Limitation | Limited | No Limitation |
| Color | Variety of Colors | Variety of Colors | Variety of Colors | Chrome, Nickel, Gold | Variety of Colors |
| Environmental Friendly | No Emission of 3 Wastes | With 3 Wastes Emission | With 3 Wastes Emission | With 3 Wastes Emission, Contains Heavy Metals | No Emission of 3 Wastes |
| Recycling | Not Allowed | Not Allowed | Allow | Not Allowed | Allow |
| Equipment Investment | Small | Can be Large Or Small | Can be Large Or Small | More Than 300,000RMB Need Wastewater Treatment Equipment | Can be Large Or Small |
| Partial Processing or Color Interspersed Treatment | Can | Can | Can | Can't | Can |
| Pre-treatment Such As Conductive Layer | Need | No Need |