
To obtain excellent surface quality in metal 3D printing, post-processing is a crucial technique. A printed part frequently has an uneven, layered, and rough surface. The appearance and performance of printed parts can thus be greatly enhanced by post-processing, which entails actions including support removal, heat treatment, surface cleaning, machining, sandblasting, polishing, and coating.
Enhanced surface finish not only gives the parts a professional look but also improves durability, reduces friction, ensures better fit for assemblies, and can even enhance biocompatibility for parts meant for medical applications. Furthermore, post-processing can optimize the mechanical properties of parts, boosting hardness, wear resistance, or fatigue strength, and specific procedures can improve the fluid dynamics in components designed for fluid flow.
Thus, post-processing plays a vital role in ensuring metal 3D printed parts meet the desired specifications and performance criteria, extending their practical applications in various industry sectors.
Advantages of post-processing in metal 3D printing
The post-processing will hugely influence the functionality, durability, and even the aesthetic appeal of the end-product. Here are some advantages of applying surface finish treatments to metal 3D printed parts.
1. Improved Aesthetics: Surface finishing processes smooth out the layer lines commonly associated with 3D printed parts, resulting in a polished and more professional look. This is particularly important for consumer-facing products or prototypes.
2. Increased Durability: Some surface finishes can enhance the part's endurance to wear, tear, and environmental conditions, extending its lifespan and use. For instance, coating or plating can provide a harder surface or offer more corrosion resistance.
3. Reduced Friction: If parts need to slide or move against each other, a smooth, well-finished surface can reduce friction and improve the part's operational efficiency.
4. Better Fit and Function: Parts intended to fit seamlessly together will do so better if they have a uniform and smooth surface finish. This understanding can lead to better assembly, reduce wear in mating components, and improve product performance.
5. Enhanced Biocompatibility: In the field of medical implants, a better surface finish ensures the part is smooth and free of microscopic cracks or crevices where bacteria could reside. This is crucial for implants to be biocompatible and not present any health risks.
6. Greater Sealing Ability: For parts required to hold fluids (such as piping or fluid systems), a smooth interior surface finish can improve flow characteristics and reduce leakage risk.
7. Improved Mechanical Properties: Some surface finishing techniques can improve a part's mechanical properties, enhancing hardness, wear resistance, or fatigue strength.

the processes of post-processing for metal 3D printed parts
While these advantages are substantial, it's also essential to consider the additional time and cost associated with surface finishing. Therefore, the benefits of surface finish should be balanced against the part's intended use and the performance requirements.
After a part has been printed using Selective Laser Melting (SLM), there are several post-processing steps that can be taken to improve the finish of the object. Here are some of the most common post-processing techniques and steps for parts produced by SLM.
Support Removal
Support removal is a critical post-processing step in metal 3D printing, particularly for manufacturing processes like Selective Laser Melting (SLM) and Direct Metal Laser Sintering (DMLS). During the printing process, support structures are often necessary to hold the part in place, prevent warping due to thermal stress, or support overhanging geometries. Once the printing is completed, these support structures must be removed carefully in order to deliver the final product. This removal can be done manually with cutting tools, pliers, or grinding tools for simpler structures. However, for complex designs or when precision is needed, machine-based methods like Wire Electrical Discharge Machining (EDM) may be used, which provide greater accuracy and leave a cleaner finish. High precision removal methods are particularly critical as any leftover support material or damage done during the removal process can compromise the final product's function or necessitate additional refining steps. Hence, expert handling is key during support removal to ensure that the part's integrity and finish quality are not compromised.
Heat Treatment
Heat treatment is a significant post-processing procedure in additive manufacturing that plays a vital role in refining and enhancing the mechanical and physical properties of printed parts. Upon printing, metal parts may contain stresses introduced during the layer-by-layer buildup of material, and these residual stresses can negatively impact the part's performance and could potentially lead to part distortion or cracking. Heat treatment includes processes such as annealing, quenching, tempering, and aging, depending on the metal used and the required characteristics of the part. For instance, annealing, which involves heating the part and allowing it to cool slowly, can be used to relieve these internal stresses, increase ductility, and improve the part's toughness. Similarly, a process like solution annealing or aging can be used to precipitate a phase that enhances the hardness or yield strength of the part. Furthermore, heat treatment can also help reduce the part's porosity, thus improving its density. Ultimately, these heat treatment processes help to optimize the mechanical properties of the 3D printed metal parts, making them suitable for their intended applications in a variety of sectors such as aerospace, automotive, or medical.
Abrasive Blasting
Abrasive blasting, also known as sandblasting, is a frequently adopted post-processing method in metal 3D printing. This process involves forcibly propelling a stream of abrasive material under high pressure against a 3D printed part's surface to refine its finish or change its properties. Abrasive blasting is highly effective in removing surface irregularities, such as the stepped effect common in 3D prints, leading to a smoother finish. Depending on the hardness and granulation of the blasting materials and the pressure used in the process, different surface finishes can be achieved, varying from matte to semi-glossy. Additionally, abrasive blasting can help to eliminate residual sintered powders, support structures, or other particulates stuck to the metal part's surface. Moreover, this process can also impart compressive stresses on the part's surface, improving resistance to fatigue and stress corrosion. However, it's important to consider the part's geometry as abrasive blasting could lead to material removal in detail areas or difficulties in effectively processing small, internal channels. So, while it's a versatile and effective technique, it requires careful control and understanding of the impact on the final part.
Sanding and Polishing
Sanding and polishing can be applied for metal 3D printing where parts often come out of the printer with a rough, layered exterior. Sanding serves to eliminate or minimize these layers and provide an even surface. This process can be conducted manually using sandpaper of varying grit sizes or mechanically with automated sanding machines, starting with a coarse grit to remove more significant layer lines or imperfections, followed by progressively finer grit sizes for smoother finishes. After sanding, polishing comes into play. Polishing enhances the smoothness and sheen of the metal part, offering an impressive final aesthetic. Tools like polishing wheels, buffing pads, or polishing compounds might be utilized in this step. In certain cases, electropolishing could be employed. This electrolytic process not only removes a thin layer of material to smooth and brighten the surface but also helps in removing burrs and stresses from the metal part. Both sanding and polishing can significantly enhance the part's visual appeal, improve its tactile feel, and potentially provide functional benefits like improved part fit or reduced friction.
Coating/Plating
Coating or plating can enhance the final properties and usability of the printed parts. Coatings, which can include a variety of materials such as ceramics, polymers, or metals, are applied to the part's surface to improve its mechanical, thermal, electrical, or chemical properties. Plating, a subset of coating, typically involves depositing a thin layer of metal onto the part's surface. This not only aids in improving the aesthetic appeal of the part but also provides functional benefits like increased corrosion resistance, electrical conductivity, or thermal stability. Certain coatings or platings can enhance wear resistance, which is vital for parts in high-friction environments. For biocompatible applications, such as medical implants, coatings can provide an interface that promotes proper interaction with biological systems.
Moreover, for parts intended for food processing or other sensitive applications, coatings improve cleanliness and prevent contamination. Depending on the specific requirements of the application, various coating and plating techniques can be employed, such as physical or chemical vapor deposition, electroplating, thermal spray, and others. However, the choice of coating and its application method should factor in the part's geometry, material, and intended function to ensure a desirable outcome.
CNC Machining
CNC machining is another crucial post-processing after 3D printing, especially when high-precision dimensions and polished surfaces are necessary. Often metal 3D printed parts require additional machining to meet tight tolerances or fitment requirements that may not be achievable directly from the printer due to the layer-wise additive process. CNC machining, standing for Computer Numerical Control machining, is a subtractive manufacturing process where material is removed from the part using various cutting tools controlled by a computer program. When applied as a post-process to 3D printed parts, CNC machining can help achieve high accuracy and excellent surface finish on critical features or mating surfaces. This is particularly valuable for industries such as aerospace, automotive, or medical devices where parts often have strict dimensional requirements.
Furthermore, CNC machining allows for creation of threads, deep drilled holes, or other complicated geometries that might be challenging to 3D print directly. It's important to remember, though, the addition of CNC machining as a post-process increases the time and cost of a part, so its use should be balanced with the overall benefits it brings to the final part's quality or function.
Wire brushing
Wire brushing is another post-processing method frequently encountered in the world of 3D printing, particularly when it comes to metal parts. This technique involves cleaning and finishing the surface of the print using a brush with wire bristles. These brushes can be used manually or attached to power tools for automated brushing. Wire brushing is highly effective at removing loose or adhered material residues, such as support structures' remnants and sintered powder. Furthermore, it can help to smoothen the print’s surface texture and eliminate minor surface inconsistencies. One key advantage of wire brushing is that it can be performed without significantly altering the part's dimensions—as it doesn’t remove significant excess material. In addition to surface improvement, wire brushing can also be employed to prepare parts for subsequent finishing steps like painting or coating by creating a better adhesion surface. Despite these benefits, it's important to note that wire brushing might not always offer the highest level of finish, especially for parts with extremely tight dimensional tolerances or needing a mirror-like smooth finish.
Quality Control & Inspection
This final stage often involves verifying that the finishing process has achieved the desired results and that the part meets all the required specifications. This could include microscopy, profilometry or non-destructive techniques.
Keep in mind that the type and amount of post-processing done will depend on the specific requirements of the part being produced, including its intended function, the required level of precision, and the desired appearance. It's also important to understand that each step may add cost and time to the production process, so careful planning and optimization are key to achieving the best results. If you have any question to metal 3D printing and its post-processing, please contact us, LUSHI's experts will give you more details about your project.