Flexible Filaments for 3D Printing Explained

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.

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.

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.

A smooth surface is essential for many applications, such as aerospace, automotive, and medical devices, where surface quality is critical.

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.

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.

A lower Ra value indicates a smoother surface. Other methods of measuring surface roughness include visual inspection, tactile testing, and optical scanning.

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.

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. 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. Post-processing steps like sanding, chemical smoothing, or coating are often required to achieve a smoother finish. 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. SLA is often used in applications where fine details and excellent surface quality are crucial.

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.

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.

Post-Processing Options and Surface Finishing Techniques

• Sanding and Polishing: These mechanical methods reduce surface roughness, particularly for FDM and SLS parts. The sanding process typically starts with coarse sandpaper to remove major imperfections and progresses to finer grits for a smoother finish. Sanding is often followed by polishing to achieve a high-gloss finish. Polishing can further enhance the part, creating a shiny, aesthetically pleasing, and functional surface.

• Chemical Smoothing: This process involves exposing the part to a solvent vapor and is commonly used for polymer prints, especially with ABS. It smooths the surface by partially dissolving the outer layer of the part, reducing both Ra and Rz values.

• 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.

• Read more about MakerVerse’s finishing options here.

Start Your Additive Manufacturing Project

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.

Get a quote today and discover how MakerVerse can support your next manufacturing project.