In this post we take a look at and explain the differences between the current competing 3D printing technologies FDM and SLA and see which may suit your needs better.
Before we start let us take a look what these acronyms stand for:
- What does SLA stand for?: StereoLithoGraphy
- What does FDM stand for?: Fused Deposition Modelling
- 1 FDM vs SLA: Explained
- 2 What Are The Print Quality Differences?
- 3 How Do Print Times Vary Between FDM & SLA?
- 4 FDM vs SLA: What Are The Running Cost Comparisons?
- 5 FDM vs SLA: When To Use Which?
- 6 FDM vs SLA: Materials, Colours & Availability
- 7 FDM vs SLA: Removal After 3D Printing
- 8 F.A.Q About FDM & SLA
FDM vs SLA: Explained
For a true comparison it is important to explain what the main characteristic differences are between FDM & SLA? So we take a look at how these two technologies work!
What is FDM and how does it work?
FDM is essentially a type of “additive manufacturing”, meaning that the 3D model is not created in one whole process such as molding, but rather by means of adding continuous layers of the melted material (typically a type of plastic) to build up the final solid 3D model from the bottom up. The model then cools down to one solid piece.
FDM printers are made up of components that move in all three axes, the x-axis, y-axis and z-axis to create the 3D object (logical, right?).
The printer must read a 3D generated model (usually in .STL format) created using a 3D package such as Blender and then start to print it out. However, because FDM 3D printers are designed to created things by means of layering, it means that the 3D generated model (which is essentially solid) must then be sliced up into layers using a Slicer Software.
What is SLA and how does it work?
SLA works very differently to FDM inasmuch as it does not build up layers of heated plastic materials to create the finish product after cooling. However it is still an “additive manufacturing” process where UV light is used to harden liquefied resin to create the finish product.
The process of reading and slicing up the model using slicer software is the same though!
A vat is filled with a photo-curable resin and an ultraviolet laser beam shines onto the layer of resin. The laser beam traces a pattern on the surface of the liquid resin which ultimately solidifies the pattern. The process continues, and each layer that hardens, solidifies to the next layer in order to create the final product. Essentially, this process works in reverse order to FDM, inasmuch as it builds the 3D model from the top down… although some printers do allow for printing from the “bottom up” which has a huge advantage, the printed model can can be much bigger than the vat itself.
What Are The Print Quality Differences?
The above title in itself suggests there is competition between FDM and SLA printing techniques, and that statement is becoming even more true as SLA are hitting the market even harder than ever before due to their increased affordability.
However, what makes SLA printers even more attractive is their ability to produce prints that are ultimately more detailed and smoother in finish compared to their plastic layer building friends. This is due to being able to print at smaller layer heights (Z-axis) and more importantly a higher XY-resolution.
FDM Print Quality Factors To Consider
- Nozzle size affects resolution / print quality
- Weight of layers may squeeze lower layers and deform print
- Warping caused when plastics such as PLA & ABS cool after heating
- Missing layers are common when the printer fails to provide the correct amount of plastic
- Stringing happens when some material drops from the nozzle onto unwanted parts of the print
- Nozzle blockage is common
- More mechanical and software tinkering / calibration for optimal printing
Check this out for a truly great overview on FDM printing problems
SLA Print Quality Factors To Consider
- Consistently creates higher resolution prints with fewer flaws
- Creates more accurate prints (closer in dimensions, shape and size to the actual CAD file)
- Less force applied to model during print (improved surface finish)
- As resin is photo-curable by UV light, long terms exposure to sunlight can reduce models mechanical strength.
- Resin is sticky and completed prints need to be cleaned out with alcohol to remove stickiness
- Printing from the “top down” means the model’s height can not be greater than the depth of resin in the vat.
- Tied to purchasing resin from manufacturer (currently no to few third party suppliers)
- Post-finishing required – removal of support structures after print
How Do Print Times Vary Between FDM & SLA?
Desktop 3D printer technology is getting faster, but some may argue it is not quite at the stage were most would like. So naturally you would want to know which prints out faster before forking out the bill on your brand new hardware.
Deep down, I think we all know there is going to have to be some form of compromise between quality against speed of print and it is up to you to decide which way to go depending on your printing requirements.
Yet an other “well it depends” answer? That was not very helpful!
You are absolutely correct, so what we decided to do is contact various experts on using 3D printers and ask them what they thought.
Asking The Experts About Printing Technology Speeds
Question 1: Generally speaking, which technology can be set to print the fastest, FDM or SLA?
Question 2: Can you describe why this technology is able to printer quicker than the other?
Question 3: Which printing technology would you generally pick and why?
Pierre-Antoine is Co-Founder of Aniwaa and 3D printing expert, who has dedicated his time in creating a true comparison portal on all things that are 3D, using unique data sets to determine the “best of”. These include comparison guides on 3D printers, 3D scanners and filaments / resins.
After reading the 10 best resin printers article, I thought it was time to get in touch and ask some further questions to get the answers that you may be looking for!
Answer 1: As often with 3D printing, there is not one good answer and it all depends on what you’re trying to achieve. The short answer is FDM can be set to print faster than SLA for desktop 3D printers under $5,000. Typically, it’s a trade off in the 3D printer settings between print speed and print quality: the faster you print, the lower the quality for the final object.
Answer 2: For a long time, FFF (also known as FDM, an acronym patented by Stratasys) was a much faster 3D printing process than SLA. That was mainly due to the fact that it was possible to increase the nozzle size in order to extrude more material at a faster rate, at the expense of the accuracy and layer thickness.
Stereolithography, on the other hand, relies on a light source, like a laser beam, to polymerize a liquid resin, which is a quite slow process. However, a number of innovations made SLA faster. For instance, many 3D printers today leverage the DLP technology, which uses a projector as a light source instead of a laser, thus making it possible to polymerize a wider area in one go. But FFF remains able to print faster in many cases because it’s quite easy to set up the 3D printer extrude more material and form thicker layers to accelerate the build process.
Answer 3: It all depends on the use case. For applications such as Jewelry or Dental where high precision is required, SLA and DLP are the best fits. SLA is also very interesting for casting applications (which requires specific resins, “castable resin”). For design, prototyping, and even producing functional parts, FFF remains the best option. The choice of available material is wider (ABS, PLA, Nylon, Ultem, Flex, mix of thermoplastics and exotic materials (aluminum, bronze, wood, …) and the technology is much easier to manage, especially for non-advanced users.
Chris McAndrew is a product development and product management expert who has used 3D printing to create everything from children’s toys to nanoscale electrodes for biological computing. He writes about the new product development process at 3DNPD.com which focuses on the tools and skills needed to bring ideas to market.
Answer 2: SLA machines should be fast, fundamentally, since they are typically lasers focused on a very specific area. They use photopolymers and light exposure cures the resin almost immediately and there should be a lot less heat and energy waste to the surrounding materials. FDM printers heat up a lot of material but and must control the temperature so there can be dwell time required as you wait for the material to cool back down, attach, and harden. In practice this really depends on how fast you can physically move the laser focus, or the nozzle, and how much wait time is controlled in between. Stronger lasers and larger light sources can cure a layer of material in an instant, but they come at a cost.FDM printers are a more crude but accessible method of combining materials. In order to fuse a material heat is used to raise it near a melting temperature where the material properties allow it to be combined. As noted above this is not entirely efficient since it requires heating all areas of the material. This also heats the surrounding area, the nozzle, the air, and things nearby. The time it takes to heat the material, and then cool it back down, is dependent on the material type, it’s change point temperature and the surrounding environment. This can extend the time it takes a great deal if you need precision but can also be done crudely often to the detriment of the appearance of the final print.The scale of the print also matters. Technologies exist that enable “3d printing” on a nanoscale. Using photon polymerization a laser is used to excite the state of individual atoms and molecules and cure them together. We can only achieve this through SLA type activity since there is no other technology that can fuse and deposit material on this scale. Of course this process can be very time intensive, creating a structure only a micron wide may take hours or even days. In this case FDM technology may take a century to do such a job since we do not yet even have the technology to compete.
FDM vs SLA Printing Times
- FDM Standard Setting: 0.3-1.7 in/hr
- SLA Built In Rate: 0.3 – 0.7 in/hr
FDM vs SLA: What Are The Running Cost Comparisons?
It is important to note that here we are not talking about maintenance cost of each technology (something I will need to look into in the future) or the power consumption comparison, but rather the cost of materials and other directly related factors.
FDM 3D Printing Cost
Fused Deposition Modeling has the advantage of having only one consumable, which are the filament rolls. They are by in large the same standarized rolls that can be used on all FDM printers. As a results many third party providers selling the product which increases competition and therefore reduces cost, particularly during recent years.
A simple filament can cost as little as $25 for one kilo (1Kg) of roll, however, some specialized rolls can cost more!
Tip: It is important to try and find a supplier that provide a uniform diameter of filament throughout its entire length. This allows for better quality prints and reduces the chances of blockage and machine maintenance.
If this is not feasible for the time being, you can then try extrusion calibration to compensate for the varying diameters throughout a filament’s length.
SLA 3D Printing Cost
StereoLithoGraphy unfortunately has a few more consumables than Fused Deposition Modeling. SLA technology uses resin to print out a model and this is considerably more expensive than filaments. One liter (1L) of standard resin can cost anywhere between $150-$250 depending on which printer you have. This price should start to drop when third party suppliers start offering their compatible versions for each printer, but having said that, it will most likely still remain more expensive than filaments.
The tank or vat also has to be replaced after about 3-4 liters of resin has been printed. In time the build up of resin smudges the tank’s transparent walls and interferes with the UV light passing through and can no longer precisely project the image which in turn effects print quality. A resin tank can cost about $60 to buy new.
The other consumable is the build platform (the area the printed models rests on during printing). This does not need to be replaced so often, but in time when the model is removed, the surface gets spoiled and somewhat ruined. One platform can cost up to $100.
FDM vs SLA: When To Use Which?
If we look at asking the experts section and read Answer 3 provided, you will get an idea of which technology suits which conditions and/or requirements.
FDM vs SLA: Materials, Colours & Availability
Like any machine there are running costs, and for 3D printers the main one is consumables (essentially the materials needed to create the 3D print). One of the advantages that FDM has over SLA is the variety of materials and colors that are on offer, general lower cost of the materials, and just as importantly the variety of third party consumerables (ability to shop around).
Having said that one advantage SLA has over FDM is the accuracy of prints that can be used for anatomical regions of patients and for accurate prototyping for businesses to access design and functionality of their product or for advertising the final product.
One of the major disadvantages of SLA however is the limited choice of resins which cannot be exchanged between printers… essentially (at least for the time being) each manufacturer will design their resin vat to fit only their printer(s)
3D Printer Filament Material Types (FDM): Overview
|Filament Type||Color Variety||Printing Temp.|
|ABS||Yes||230 - 240|
|PLA||Yes||180 - 220|
|Flexible (TPU)||Yes||195 - 230|
|Nylon||Yes||240 - 280|
|PET||Yes||230 - 250|
|PC Polycarbonate||Yes||250 -320|
|Wood||200 - 260|
Check this out for an even more comprehensive list of filament types on offer.
With SLA, the resin is quite expensive compared to equal quantities you get with filaments, not to mention a limitation of materials & colors too and you are (at least for the time being) tied to purchasing the resin from the same company you bought the printer from. However there are different types of resin available for purchase to allow your final prints to have different physical properties.
FDM vs SLA: Removal After 3D Printing
We often forget that once your print is complete, there is still a bit of work to be done and the is removing your print from the print bed.
In general, removing FDM prints is relatively easy and may require a little assistance with a knife to release those stubbornly stuck ones… but all in all, it is relatively easy to do.
SLA, however, does pose some potential difficulties in comparison. Resin will reside on the platform in large quantities which first has to be removed before being able to get to your print. This requires the use of a knife / palette knife and takes a lot more effort.
Note: Like all technology things are constantly improving. Companies such as Carbon3D and WASP have come up with some new ideas to prevent this accumulation of resin:
- Carbon3D use oxygen to keep the resin at the surface and preventing it from hardening. This eliminates the build up around your model.
- WASP claim by moving their projector to the top of the bath has solved this problem.
Info source on FDM vs SLA removal after 3d printing
F.A.Q About FDM & SLA
We have compiled some of the most common asked questions regarding StereoLithoGraphy & Fused Deposition Modeling with answers for you consideration.
Are There Other 3D Printing Technologies Besides FDM & SLA?
“Yes”! There are in fact several types of printing technologies, each of which have their advantages and disadvantages. Even though some of these are similar or related to FDM & SLA in some ways, they do have their differences too!
Let us take a small peek at what they are!
- Selective Laser Sintering (SLS):
Essentially works on the same principle as SLA, but rather than using resin, a powder is used. A laser heats up the powder to just below melting temperature causing it to sinter. Then a roller comes along and rolls an other layer of powder on top only for the laser to sinter it too.
Essentially each layer is stuck together because the laser heats them up enough to fuse, but not too much to cause them to melt.
- Digital Light Processing (DLP):
- Continuous Liquid Interface Production (CLIP):
- Binder Jetting
- Selective Deposition Lamination (SDL)
For an even more comprehensive understanding of 3D Technologies check out Sculpteo’s website.
When Was StereoLithoGraphy Printing Invented?
Chalres W. Hull (AKA Chuck Hull) is credited for inventing StereoLithoGraphy and is considered to be the father of 3D printing which has shaped the technology to what it is today. Hull knew it would probably take about 30 years before the technology reached the homes of everyday people.
The concept of SLA printing emerged to Hull when working for a small business that made tough coatings for tables using ultraviolet lights. He quickly realized that this same process could be used to create three dimensional parts.
He created his printer back in 1983, but it was not until 8th of August 1984 that he coined the term stereolithography in his patent Apparatus for production of three-dimensional objects by stereolithography
How Accurate Is StereoLithoGraphy Printing?
SLA is quite possibly the preferred 3D printing technology for accurate prototyping for designers of any niche where tolerances of parts are paramount.
Being able to create accurate formed prototypes (particularly dynamic / moving parts) enables verification that the design will or will not work before committing to any production route.
Not only is stereolithography one of the most accurate printing methods, it also provides good durability, along with a clean surface finish.
One other factor to note, the size of the print can affect accuracy. For example conventional FDM printing starts to struggle when printing smaller / tiny objects. However, the resolution of SLA is determined by the spot size of the UV lazer and therefore can handle smaller prints with more accuracy.
How Does StereoLithoGraphy 3D Layering Works?
In case you’d missed it, we did actually answer this question of how stereolithography works above!
How Does Additive Manufacturing Work?
Additive manufacturing refers to the process of extracting data from a digital file, such as a 3D CAD file created using 3D packages. This data is then transferred to a PC that then uses an other type of software to slice up the file in layers. Slicing up the file into layers is a language that the printer understands as this is the same process the printer uses to print the complete part…by means of adding layers on top of each other, hence the term “Additive Manufacturing”.
What we now term as “3D Printing” should in fact be termed “Additive Manufacturing” as the latter more accurately describes the production technique used to create the final product.