FDM vs SLA

August 25th, 2017
Eljay Bernabe

In the 3D printing world, there are numerous types of 3D printing processes to choose from. There's FDM, SLA, SLS, DLP, and much more. A question that often comes up is, "what type of 3D printing process should I use?" The answer to that question depends on what you are looking to accomplish. This post will provide a quick breakdown of two of the most popular 3D printing processes currently being used by industries all across the world: Fused Deposition Modeling and Stereolithography.

Source: Loughborough University

Fused Deposition Modeling (FDM)

Fused Deposition Modeling (FDM) is one of the most popular forms of 3D printing and by far likely the most popular form of 3D printing on a commercial basis. FDM 3D printing arguably can also be considered the current face of 3D printing due to the hundreds, if not thousands of manufacturers selling FDM 3D printers. You might even consider the possibility that if you were to ask a random individual in public how they think 3D printing works, they might be able to describe the entire FDM process.

So how does the FDM process work? With FDM 3D printing, there are three main elements: an extruder, a printhead, and filament material. The FDM process begins with filament material being fed through a tub that runs through an extruder component. The extruder component melts the filament material to a specific point making the filament easily mold-able. The melted filament is then passed through a printhead (which is attached to the extruder) and the printhead gradually layers the filament layer by layer, slowly building a 3D model. FDM filament material over the course of more than a decade has grown in both variety, reliability, and capability. FDM filament comes in a variety of materials that include ABS plastic, PLA, Polypropylene, TPU, and more. Many filaments have been engineered to mimic polycarbonate plastics for real world applications. Historically, FDM 3D Printers have been a popular choice among engineers, manufacturers, prototypers, schools, and numerous industries!

Stereolithography (SLA)

Stereolithography, or SLA, builds models layer by layer just like FDM 3D printing. However, SLA utilizes a different form of technology to print 3D models. Some would even say that SLA is a step into a Star Wars - Star Trek type of future, even though the technology has been around for more than a decade. SLA technology uses UV light lasers, and liquid resin material. Don't worry, while it is a lot more futuristic, we'll break it down easy for you.

SLA uses focused/UV light to build 3D models. In just about every SLA 3D printer is a guided laser system. The guided laser system systematically guides the UV light to cure (or harden) the resin material. It is important to note that just like FDM, every 3D print is built layer by layer. With SLA, each layer is also more accurately completed due to the advanced guided laser technology.

Source: University of Leeds

Liquid resin material comes in various property formulas with many formulas being created for real world application use. One detail to keep in mind is, once a print has been completed on a SLA 3D printer, the print needs to be place inside a UV curing oven if it contains a special property formula. The reason being is, the property formula requires an extensive amount of UV light and heat to fully extract it's properties. SLA 3D printers use only enough UV light and heat to complete a print.

For example, resin from the company Formlabs comes in various versions such as high temp (for high temperature resistance use), tough (for high-impact resistance use), durable (for long term, rigidity & chemical resistance), and flexible (prints that have a flexible/soft TPU feel). When a print is completed on a Formlabs Form 2, the print is nothing more than a regular print off any SLA 3D printer because the amount of UV light and heat used from the Form 2 was not enough to fully extract the respective properties. Thus a UV curing oven (which uses a higher amount of heat and UV light) will be able to fully extract the properties of the intended print.

While SLA has been around for quite some time as well, advances in technology have gradually helped SLA 3D printing become a power house option among architects, dentists, designers, engineers, jewelers, manufacturers, prototypers, schools, and much more!

SLA 3D Print Sample
(via Formlabs Form 2)
FDM Print Sample
(via Ultimaker 3)

FDM vs SLA

Between FDM and SLA, there are many different factors between these the two printing process. For FDM printing, the immediate pro is the fact that there are hundreds, if not thousands of different FDM 3D printers currently on the market. This means that you can find a FDM 3D printer for as little as $100. However, the lower the price of course comes with the territory of the hardware being very minuscule. While you can find options for a very low price, to achieve industrial standard quality will run you around the $1,500 to $4,000 range. SLA 3D printers on the other than are natural in the $2,000 to $4,000 territory because of the extensive hardware each 3D printer contains. 

The second immediate difference and most important difference is performance. FDM 3D printers are more limited in ability to produce intricate details. FDM 3D printers are often great for quick prints that are often used for prototyping purposes to perfect a design or for educational purposes. SLA 3D printers are more on the industrial, intricate detail side. SLA is often used to print final designs or print designs that no longer need to be prototyped. As a result, a lot of prints that come from a SLA 3D printer are actually used.  

To further expand on performance, SLA prints have a chemical bond between layers that are created by connecting photopolymers during the SLA process. These chemical bonds create a much stronger part that is water-tight. As a result, SLA prints look more professional, more smooth, and more detailed as compared to a FDM print. With a FDM print, instead of a smooth surface finish, often times FDM prints will have a smooth texture but individual lines are still visible. Thus as mentioned before regarding pricing range, because SLA creates better, more defined prints, the value of the hardware is more expensive to acquire, run, and maintain than FDM printers. However, judging from the end print results, there is no question as to why each 3D printing process is priced the way it is.

So Which Is Option Do I Choose?

After going through the explanations, the answer still is: what are you trying to achieve? If you're looking to do extensive prototyping or need a fast, quick model created with no concern regarding detail, then FDM is your best bet. If you're looking to create highly intricate detailed work, then SLA is your only choice. Both options use different technology and at the end of the day, in order to decide which option is best for you depends on primarily your objective.