SLA vs. PolyJet [Technology Review]

By Samantha Bild on

What is PolyJet printer

Every company aims to print parts that have the look and feel of a finished product. However, if you’re more than a hobbyist it is important to understand the different types of precision 3D printing technologies available. This blog discusses the differences between Stereolithography Apparatus (SLA) from 3D Systems and Triple Jetting Technology (PolyJet) from Stratasys. Understanding the differences between how SLA vs. PolyJet impact your application will help determine your current and future needs from a 3D printer.

With both SLA and PolyJet technologies, you need to start with a 3D model in STL format from CAD software like SOLIDWORKS. It is recommended that you check your STL file before sending it to the slicing software to prevent errors such as reversed normal, bad edges, holes in the mesh and noise shells. After errors are removed, the printer specific software slices the file and sends it to your 3D printer. SLA requires a fully-sliced STL file to be completed prior to starting the printing process. PolyJet slices on the fly, so printing starts immediately.

How does SLA work?

Unlike PolyJet, SLA uses a vat of resin and ultraviolet laser beams to build parts. The laser beam traces a pattern on the surface of the liquid resin. This exposure to Ultra Violet light cures and solidifies the pattern and joins the material to the layer below as the build platform goes down to create to next layer. After the 3D printed part is formed, it is immersed in a chemical bath for cleaning. During SLA post-processing, supports are removed, and the part is placed in an ultraviolet oven.  Once this is complete, the part is ready for use.

It is important to note that SLA is a single-material vat-based technology. Therefore, every component of the 3D printed part is made from the same material, including support structures. Another important note is that SLA models are partially cured out of the printer, making post-curing an essential step before using your 3D printed part.

SLA’s Strengths:

  • High-resolution parts with very fine features and a smooth surface finish (as long as support structures are not touching part surface)
  • Very detailed parts by enabling high XY resolution
  • Accuracy planned vs. actual dimension variances are small (great for fit tests)

SLA’s Weaknesses:

  • Minimum layer thickness is 50um
  • Part blemishes due to removal of support structures
  • Parts can become weak when support structures are removed
  • SLA process is not as stable as PolyJet leading to variation in duplicate prints
  • With all vat-based resin technologies, the post-process is long, labor-intensive, and not suitable for office environments
  • No flexible or mixed material capability
  • Limited color capability
  • Due to interaction with uncured resin, Haz-mat handling and disposal requirements are required.

How does PolyJet work?

A PolyJet 3D printer works like an inkjet printer. Instead of jetting drops of ink, the printer  jets drops of photopolymer that solidify when exposed to UV light.  These layers accumulate on the build tray until the part is complete. For complex geometries with overhangs, the 3D printer jets a removable gel-like support material. PolyJet materials properties vary, ranging from rigid to rubber-like. This technology can also mix multiple materials together to achieve unique material properties and colors. PolyJet materials are best suited for applications where accuracy, surface finish, and detail are essential components of the printed part.

PolyJet’s Strengths:

  • Faster build times
  • High-resolution parts with detailed features that simulate final-product aesthetics
  • Minimum layer thickness of 16um due to better Z-resolution
  • Multi-material technology allows mixed trays, mixed material parts, and digital material printing
  • Colored and diverse material options for greater versatility
  • Good tensile strength

PolyJet’s Weaknesses:

  • Requires manual support removal
  • Water jet is recommended means of removing support (requires plumbing)
  • Where support material is needed, gloss finish is not achieved until post processing

When mechanical properties are an important factor to your design, TriMech recommends FDM technology with the Fortus 3D printer line over SLA and PolyJet technology.

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