Finishing SLS Parts: A Selective Laser Sintering (SLS) Guide
Several post-processing options are available after printing a part via Selective Laser Sintering (SLS). Some of these options are standard and applied to every part. Others are optional but can significantly impact the look, feel, and functionality.
So, which post-processing option is suitable for your SLS components? This guide explains the different options and when to consider each one.
Understanding SLS Finishes
SLS finishes refer to the various surface treatments and post-processing techniques applied to SLS 3D-printed parts to enhance their appearance, functionality, and durability.
SLS post processing is a comprehensive workflow that includes multiple finishing processes such as cleaning, smoothing, coating, and coloring, all aimed at achieving professional-grade results and tailored material performance.
These finishes are crucial because the finishing process not only improves the appearance of SLS parts but also enhances material properties such as strength, chemical resistance, and durability. These processes are essential steps to produce parts suitable for end-use production, not just prototypes. Coatings applied during post-processing can further enhance UV protection, chemical resistance, and wear/water resistance, thereby increasing the part’s lifespan and function. By understanding the different types of SLS finishes, you can select the most appropriate option for your specific needs, ensuring that your parts look good and perform well.
Media Blasting
This standard process is included in any order from the MakerVerse platform. Parts printed via SLS typically contain loose powder and a grainy finish, but media blasting remedies this. Common types of media blasting for finishing SLS parts include bead blasting and plastic bead blasting, which are used to achieve a smooth, matte surface finish. An abrasive media (such as sand, glass beads, or plastic beads) is applied to the part under high pressure.
Before or during media blasting, compressed air is used to remove remaining powder from the part’s surface. Media Blasting utilizes high-pressure compressed air and media to create a uniform, matte finish while removing residual powder. Media blasting’s benefits are functional (gaining a specific surface roughness) and optical (a clean, polished surface). Once media blasting has finished, the component might be produced completely, or the additional post-processing options detailed below might take place.
When to use this: Always. Media blasting is a standard process that improves surface quality and removes excess powder.
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Media Tumbling
Media tumbling is a smoothing process beyond what’s possible with media blasting. During the tumbling process, the parts are placed in a tumbler filled with small ceramic chips, which vibrate against the surface to remove roughness and achieve a smooth finish on rough SLS parts. This process, also known as vibro polishing or vibratory tumbling, can be used to process multiple parts simultaneously, improving efficiency and cost-effectiveness. Vibro polishing smooths the surface of the part via a tumbler filled with small media, and can reduce surface roughness by up to 80%, resulting in a smooth and slightly shiny appearance similar to injection molded parts. However, media tumbling and vibro polishing will slightly alter part dimensions and will also round off sharp edges.
However, media tumbling is not recommended for parts with fine details and intricate features, as the process can alter dimensions and round edges and potentially damage smaller components. The part loses some material during this process. This could impact the look and mechanical properties of the part. For example, if the part has sharp edges or fragile features, media tumbling can adversely affect the final result.
When to use this: If a satin-like finish is needed and the part is not fragile.
Vapor Smoothing
Vapor smoothing is a chemical process that bathes SLS 3D printed parts in vaporized chemical solvents to create a controlled chemical melt of the 3D printed material. During vapor smoothing, the top layer of the part is dissolved in a vapor chamber.
Vapor smoothing is suitable for complex parts with internal channels or negative features and is often used to prepare final parts for end use. Vapor smoothing does not create a polished surface, and the part’s surface topology will still be visible. Chemical vapor smoothing enhances part performance and aesthetics by sealing surfaces.
Maintaining dimensional accuracy during vapor smoothing is crucial, as the process can significantly impact the precision and performance of the final part. The result is a smooth and even surface that retains the part’s mechanical properties.
When to use this: When the surface needs to be smoothed and evened but is too fragile for media tumbling.
Color Dyeing
The dye process is a popular post-processing method for adding color to SLS 3D printed parts. In this process, the SLS component is immersed in a dye bath, allowing the dye to penetrate both internal and external surfaces due to the porous nature of SLS parts. This ensures even and vibrant coloration, especially for complex geometries. Dyeing is a cost-efficient and quick method for adding color, and multiple parts can be dyed at once, making it ideal for batch production. Importantly, dyeing does not affect the dimensions of SLS parts, so the original part geometry is maintained. The dye usually only penetrates to a depth of around 0.5 mm, so over time, wear and tear could erode the color on the part’s surface. SLS 3D printed parts are quite porous, making them well suited for dyeing and offering a wide range of color options. For painting or lacquering over dyed parts, applying multiple thin coats is recommended for better adhesion and a smoother finish.
When to use this: When only a single color is needed or if the part has a complex geometry.
Painting
In painting, spray paint is used as a post-processing technique for SLS parts. A professional spray painting system adds additional colors to the printed part. Spray painting and lacquering can provide a wide range of finishes, including semi-gloss, glossy finish, and metallic sheen, enhancing both appearance and surface durability. Spray painting provides the most even coverage and is scalable for batch processing. Before applying the final paint coat, filler primers can be used to seal the porous SLS surface and fill in layer lines. The part is cleaned, and a clearcoat is applied to protect the paint. While painting offers a nearly infinite range of colors, it can be challenging if the part’s complex geometry. Note that spray painting may chip with abrasion or heavy use, while dyeing results in a more consistent, semi-permanent color.
When to use this: When multiple colors or a range of colors are needed. Ideal for evaluating a printed prototype.
Quality Measurements
Quality measurements don’t change a part’s properties, but they can be invaluable in ensuring that the part is printed exactly as expected. Several quality measurements are available on the MakerVerse platform.
Optical 3D Scan: High-quality stereo cameras compare the original design geometry with the finished part. The scan provides a false-color image that allows users to spot geometric deviations from the original design. This option is ideal for a quick evaluation of dimensional stability.
Surface Roughness: A sensitive stylus measures the roughness of a part’s surface. It is best performed when the statistical deviations of a surface from the ideal form are required.
When to use this: Whenever in-depth quality control is needed. It can be helpful before sourcing a larger batch of parts.
Next Steps
SLS 3D printed parts offer a range of benefits, including high accuracy, complex geometries, and fast production times. The finishing process for SLS printed parts involves a series of post-processing steps that enhance surface quality, surface hardness, and overall functionality.
Standard SLS finishes result in a matte, grainy surface finish, similar to medium grit sandpaper, which is suitable for further finishing like painting or lacquering. These standard finishes provide accurate overall geometry and have lower cost factors, but offer limited color options as the color of the powder determines the final appearance.
Coatings such as powder coating, ceramic coatings, and metal coatings are important for enhancing UV protection, chemical resistance, corrosion resistance, surface hardness, and water tightness. Watertight coatings like silicone and vinyl-acrylate can significantly improve the water resistance of SLS parts, while polyurethane is not effective for waterproofing. Metal plating and nickel plating add a metallic finish, improve wear resistance, and provide chemical and corrosion protection. Electroplating can increase structural strength and provide electrical conductivity by coating parts in metals such as nickel or copper. Ceramic coatings can be applied to improve mechanical strength and chemical resistance, and they offer a variety of color options.
Maintaining a minimum wall thickness of 1.5 mm is essential for reliable results in SLS components, as thin walls and small features may be affected or damaged by certain post-processing techniques. SLS components require specific post-processing steps to achieve a smooth finish due to their grainy, ‘sugar-like’ texture. Additionally, parts must cool in the build chamber to avoid warping before de-powdering, which removes excess unsintered powder.
Understanding the different types of SLS finishes and design considerations allows you to select the most suitable post-processing technique for your specific application. Whether you require a standard or an advanced finish, MakerVerse offers a range of options to enhance your parts’ functionality and aesthetic appeal.
