Understanding Surface Roughness in 3D printing
Surface roughness significantly impacts the functionality, aesthetics, and overall quality of 3D-printed parts. Engineers and designers must understand how to measure, control, and optimize surface roughness within the manufacturing process to achieve desired project outcomes.
Achieving optimal surface smoothness is often the primary goal when optimizing surface roughness in 3D printing, as it enhances both the look and feel of finished parts. Parts produced using fused deposition modeling (FDM) technology typically exhibit layer lines that can impact both the tactile feel and visual appeal of the part.
This article explores critical metrics for measuring surface roughness, Ra and Rz,how various 3D printing technologies affect surface finish, the factors influencing surface roughness, and how to adjust and improve it.
What is Surface Roughness in 3D Printing?
Surface roughness in 3D printing refers to measuring the texture and irregularities on the surface of a 3D-printed part. The quality of the first layer and the top surface plays a crucial role in achieving a smooth surface finish, as precise first layer settings and careful attention to the top surface can significantly improve the final appearance and quality of the part.
It is a critical aspect of 3D printing, as it can affect the part’s aesthetic appeal, functionality, and overall performance. Various factors, including 3D printing, material properties, and post-processing techniques, can cause surface roughness. Additionally, the rough and porous surface of 3D printed parts can become a breeding ground for bacteria and is prone to absorbing liquids, which may compromise the part’s integrity.
A smooth surface is essential for many applications, such as aerospace, automotive, and medical devices, where surface quality is critical. However, a smooth finish may not always be necessary and is often more about the aesthetics of the part, but it can enhance comfort and experience when using the part.
Understanding Ra and Rz Values
Ra (Roughness Average) and Rz (Average Maximum Height) are commonly used to quantify surface roughness.
- Ra measures the average deviation of surface irregularities from the mean line, providing a general sense of the surface’s smoothness. Lower Ra values indicate smoother surfaces, often preferred in applications requiring aesthetic appeal or precise fitting.
- Rz measures the average height difference between the five highest peaks and the five deepest valleys over a sampling length. While Ra provides an average roughness, Rz captures the extremes, offering a more detailed understanding of the surface texture.
Ra and Rz are essential in assessing the quality of 3D printed surfaces, particularly when selecting the right technology and post-processing methods to achieve specific surface requirements. Measuring these values is typically done through a surface roughness test, where a sensitive stylus is used to collect measurements.
Measuring Surface Roughness
Measuring surface roughness is crucial to determining the quality of a 3D-printed part. Extrusion calibration ensures the printer extrudes the exact amount of plastic requested to prevent over- or under-extrusion.
The most common method is using a profilometer, which measures the deviation of the surface from its ideal plane. The Ra (average roughness) value is the most widely used measure of surface roughness, calculated by averaging the absolute values of the surface deviations. The condition and calibration of the print bed can also affect surface roughness measurements and overall print quality.
A lower Ra value indicates a smoother surface. Other methods of measuring surface roughness include visual inspection, tactile testing, and optical scanning.
MakerVerse is your platform for sourcing industrial parts, providing instant access to a vetted supply chain and a full range of manufacturing technologies. With AI-powered quoting, order management, and fulfillment, MakerVerse helps with everything from initial prototypes to full-scale production.
Start Your Manufacturing Project with MakerVerse
MakerVerse is a platform for sourcing industrial parts. It provides instant access to a vetted supply chain and a full range of manufacturing technologies. With AI-powered quoting, order management, and fulfilment, MakerVerse helps with everything from initial prototypes to full-scale production.
How Different 3D Printing Technologies Affect Surface Roughness
Surface roughness varies significantly depending on the 3D printing technology used. Each method has distinct advantages and limitations in achieving a smooth finish. The effectiveness of surface finishing techniques can also depend on different materials and part geometry, as complex shapes or specific material properties may require tailored approaches.
Laser Powder Bed Fusion (LPBF)
LPBF, commonly used for metal 3D printing, tends to produce parts with relatively rough surfaces due to partially melted powder particles adhering to the surface. Typical Ra values range between 5 to 15 µm, but these can be reduced with post-processing techniques such as machining or polishing. At MakerVerse, all LPBF parts are media blasted to minimize surface roughness.
PolyJet
PolyJet technology is known for producing some of the smoothest surfaces in 3D printing. The process involves jetting layers of liquid photopolymer cured by UV light onto a build tray. This fine resolution and smooth layer deposition result in high-quality surface finishes, ideal for prototypes and models that require excellent visual quality. The condition of the build plate is important for achieving optimal surface quality in PolyJet prints. Applying a thin layer of sandable epoxy can further enhance the smoothness of PolyJet prints, filling in any minor imperfections.
Fused Deposition Modeling (FDM)
FDM is widely used for prototyping and functional parts but can produce rough surfaces due to visible layer lines, with Ra values typically ranging from 10 to 25 µm. The roughness depends on layer height, nozzle size, and material. Maintaining a stable temperature and enclosing the printer can prevent warping caused by uneven cooling, especially with materials like ABS and PETG. Adjusting the layer height between 0.12mm and 0.2mm can improve the smoothness of the top layer. Post-processing steps like sanding, chemical smoothing, or coating are often required to achieve a smoother finish, and the choice of technique should be matched to different materials such as ABS, PLA, or PET for best results. However, maintaining dimensional accuracy during post-processing can be challenging, especially when using aggressive techniques like chemical smoothing. MakerVerse offers free media blasting to reduce surface roughness.
Selective Laser Sintering (SLS)
SLS, often used for durable nylon parts, can have high surface roughness due to the sintered powder, with Ra values ranging from 10 to 20 µm. Unsintered powder sticking to the part during printing contributes to this roughness, making post-processing necessary for applications requiring a smoother surface. Surface blasted is included with all orders through MakerVerse.
Multi Jet Fusion (MJF)
MJF offers a smoother surface finish than SLS, with typical Ra values ranging from 5 to 10 µm. Using a fusing agent and infrared lamps helps create a more uniform surface, though some post-processing may still be required for parts needing a very smooth finish. Media blasting is included for free through MakerVerse.
Stereolithography (SLA)
SLA produces high-quality, smooth surfaces with low Ra values. This technology uses a laser to cure liquid resin layer by layer, resulting in highly detailed and smooth surfaces. The condition and calibration of the build plate are crucial for achieving the best possible surface finish in SLA prints. SLA is often used in applications where fine details and excellent surface quality are crucial.
When considering 3D printing smooth surface finish, keep in mind that other materials and technologies may require specific post-processing approaches, such as the use of resins, paints, or custom composites, and that part geometry can influence the effectiveness of these methods.
Factors Affecting Surface Roughness in 3D Printing
In addition to the type of manufacturing used, several factors influence the surface roughness of 3D-printed parts:
Material Choice: The type of material used in 3D printing significantly affects surface roughness. Materials with finer grain sizes or smoother extrusion characteristics generally produce smoother surfaces. For example, PLA in FDM printing often results in a smoother finish than ABS due to its lower printing temperature and reduced warping. Materials with coarser grain sizes can produce a rough surface, which may require additional finishing steps.
Layer Height and Resolution: Layer height is directly correlated with surface roughness. Smaller layer heights produce finer details and smoother surfaces because the steps between layers are less noticeable. However, reducing layer height increases printing time, which is a trade-off to consider. Print settings and slicer settings, such as layer height and top layer line width, play a critical role in determining surface quality and roughness. Proper Z-axis calibration is essential for achieving even layers and a smooth top surface.
Post-Processing Techniques: Post-processing plays a crucial role in enhancing the surface finish of 3D printed parts. Techniques such as sanding, polishing, chemical smoothing, and media blasting can significantly reduce surface roughness, improving both Ra and Rz values. Post-processing is essential for addressing uneven surfaces that result from the layer-by-layer nature of 3D printing. Various surface finishing techniques, such as sanding and chemical smoothing, can significantly improve the final appearance and functionality of the printed part.
Top layer quality is crucial for a professional appearance and can be improved by adjusting slicer settings, such as top layer line width and pattern, as well as monitoring and fine-tuning print settings throughout the process.
Post-Processing Options and Surface Finishing Techniques
- Sanding and Polishing: Sanding is one of the most widely employed techniques in the post-processing of 3D-printed parts and is often labor intensive and time consuming. These mechanical methods reduce surface roughness, particularly for FDM and SLS parts. The sanding process typically starts with coarse sandpaper, such as 220-grit, to remove major imperfections and progresses to finer grits up to 2000-grit for a glass-like finish. Using a sanding block helps apply even pressure during sanding, and finer sandpaper is essential for the final stages to refine the surface.
Wet sanding is crucial for PLA to prevent it from heating up, melting, and sticking to the paper. It is important to use lint free cloths to clean the surface before and after sanding to avoid dust and contaminants. Sanding is often followed by polishing to achieve a high-gloss finish, and applying a polishing compound after sanding can further enhance surface shine. Polishing can further enhance the part, creating a shiny, aesthetically pleasing, and functional surface.
- Chemical Smoothing: Chemical treatments are property-changing post-processing methods that modify the surface and mechanical properties of 3D printed parts. This process involves exposing the part to a solvent vapor and is commonly used for polymer prints, especially with ABS. Acetone vapor smoothing is a common method for smoothing ABS prints, where the part is sealed in a container with acetone vapor to melt and level the surface. Acetone vapor smoothing is highly effective for ABS prints but poses health risks if not handled properly. Isopropyl alcohol can be used for smoothing certain filament types like PVB and PolySmooth™ PLA. Chemical dipping involves submerging parts in a chemical bath that eats away the surface. Chemical vapor smoothing is a sophisticated post-processing method for achieving a polished finish.
Hazards of chemical smoothing methods include flammability and toxicity, so it is essential to wear proper safety gear, including gloves and a dust mask, and to perform these processes in a well ventilated area. Local melting is an easy way to reduce the appearance of surface scratches from damage or support removal, but it is not effective for deep scratches.
- Vapor Smoothing is a specific type of chemical smoothing for materials like ABS. In this process, the surface is exposed to a vapor that melts and smooths the top layers, resulting in a smoother finish.
- Media Blasting: This technique involves blasting the part with abrasive media to smooth the surface texture. It’s effective for reducing roughness in SLS and MJF parts.
- Electropolishing: Electropolishing is a standard method for metal 3D-printed parts to reduce surface roughness. It removes a thin material layer, improving both the Ra and Rz values and the part’s overall appearance. Other materials and coatings can also be used for finishing.
Additive post-processing is another method for smoothing and strengthening parts by adding material directly onto the printed surface. Primers prepare 3D-printed parts for the addition of subsequent layers by pre-treating the surface for better adhesion. Spray coatings, including spray paint, varnish, resin, plastics, and rubbers, are available as finishing options. Foiling or vinyl wrapping involves wrapping an adhesive foil made of light metals or plastic onto an object for surface finishing.
- Heat Treatment: Heat treatment can smooth surface imperfections by using a heat gun or an oven at low temperatures. A heat gun works at low temperature (around 75°C) and should be used at a distance of 15-20 cm to smooth surface imperfections without causing warping. For PLA, heat treatment in an oven at low temperature (around 40°C) helps avoid deformation. Gentle sanding is important for specialty materials. Removing excess material during printing helps avoid rough surfaces. Achieving better adhesion between layers, by using primers and slowing print speed, improves surface finish. Certain materials are easily smoothed with specific methods, so selecting the right smoothing method based on material and part geometry is crucial. Manual post-processing methods are often time consuming and labor intensive.
- Read more about MakerVerse’s finishing options here.
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Surface roughness is critical in 3D printing, affecting the final product’s functionality and aesthetics.
MakerVerse, your platform for sourcing industrial parts, offers a wide range of manufacturing technologies and post-processing options to meet your surface finish requirements. Whether you’re producing prototypes or full-scale production parts, MakerVerse provides the tools and expertise to ensure high-quality results.
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