What's in a name? Some thoughts on stereolithography terminology

Author Jim Reitz is general manager of Union Tech

While speaking to attendees at the Additive Manufacturing Users Group (AMUG) earlier this year, I observed that the term SLA has become synonymous with a wide range of additive manufacturing (AM) processes that utilize a UV light source to cure, layer by layer, a photopolymer formulation to translate a computer aided design (CAD) into a three-dimensional part. People use SLA to describe a range of processes, from laser-based industrial and desktop systems to a variety of digital light processing (DLP)- based systems.

So, what's the significance of SLA semantically transitioning to a catch-all description? 

Is it important to make a distinction between SL and SLA as a descriptor of the stereolithography process?

Stereolithography was the first widely used process in what has become the 3D printing and AM industry. SLA was, and remains to my knowledge, a registered trademark of 3D Systems. Any student of 3D printing history understands SLA as the abbreviation for StereoLithography Apparatus, similar to PCA as the commonly used abbreviation for Post-Cure Apparatus. SL is an easily understood and generic abbreviation for stereolithography as a process, distinct from any particular equipment.

There is, however, an even bigger issue than distinguishing SL as a generic process descriptor. Consider how commonly used industrial SL equipment works: powerful, lower wavelength lasers draw an image from overhead onto a platform accurately positioned in a vat of photopolymer with mechanical re-coating between layers and the platform traveling downward. Now, consider the significant differences in the various processes referred to as SLA, namely:

  • imaging can be effected from beneath the vat through a UV transparent platform with the imaged part connected to a platform that raises into the air;
  • support requirements can vary by process;
  • differences in light source from laser type to DLP lamp;
  • imaging by drawing each layer versus projecting the entire layer instantaneously;
  • variations in UV light sources, wavelength and energy;
  • formulation chemistry tailored to a particular wavelength and available curing energy;
  • differences in re-coating capability and practical layer thicknesses; and
  • significant variations in post-cure requirements ranging from a UV cure to an elevated temperature bake. 

Compared with traditional industrial SL, these variations can translate to significant practical differences regarding part size, build speed, accuracy, precision, finishing requirements and physical and mechanical properties. This is why it is so critical to use accurate terminology and avoid the muddling of process attributes. As the AM user base expands rapidly, we must develop strong foundations of understanding relative to the benefits and limitations of the available processes. Re-introducing technical distinctions between these photopolymer processes will ensure better end-user understanding and satisfaction when choosing the process and materials that best serve their needs.

Can we abandon the word-mush and potential issues of using the trade-marked term SLA and use reasonable descriptors that clearly delineate these AM processes? For instance: 355 nm SL, 405 nm desktop SL, and (wavelength specific) DLP are all good starting points to allow potential users to recognize differences in process type and the implications of the process. Let's avoid allowing search engine optimization or broad-brush marketing considerations to dictate technical process descriptors that aid in the proper communication of technology capabilities.

About Jim Reitz

Jim Reitz is general manager of Union Tech and is a 16-year veteran of the AM industry. His plastics industry experience of over 35 years encompasses product development, marketing and general management. Jim was recognized as an Additive Manufacturers User Group distinguished innovator/operator (DINO) in 2014.