FDM or SLA?
Intro | FDM | SLA | Conclusion
Can't decide what 3D printing process is right for your part? Let's explore the pros and cons of each
If you are new to 3D printing and unsure which process to choose when making a part, hopefully this quick rundown will help in your decision making.
3D printing typically works by taking a model (.stl or some other 3D file format) and "slicing" it into discrete layers that are then built up, layer by layer, in the printer. However, each process achieves this in different ways.
Similarly, due to the difference of how the object is printed, different materials are suitable for different processes and end goals. Due to this, the process you choose may depend more on the desired material characteristics of the object than other considerations, such as scale or dimensional accuracy.
Let's take a look at each 3D printing technology in more detail.
FDM
FDM
or Fused Deposition Modelling
FDM, or Fused Deposition Modelling, also known as FFF (Fused Filament Fabrication), is a 3D printing process that produces objects by extruding molten filament through a small nozzle onto a (usually heated) bed. As the molten filament leaves the nozzle, it quickly cools and solidifies. The print head follows a path defined by the slicing process. This path will complete each layer successively, until the object is finished.
Materials
FDM produced parts can be made with many, diverse materials. These include, but are not limited to:
PLA (PolyLactic Acid)
ABS (Acrylonitrile Butadiene Styrene)
PETG (PolyEthylene Terephthalate Glycol-modified)
TPU (Thermoplastic PolyUrethane)
Metal Composites (PLA with metal particles, such as copper, dispersed throughout)
Fiber Composites (PLA with fibres, such as carbon fibre, dispersed throughout)
ePa Nylon
Pros
FDM is ideal for quick, functional prototyping. Depending on the choice of material, it can be hard and rigid (e.g. PLA or PETG) or flexible (TPU). It provides good dimensional accuracy and a moderate surface finish, which can be further processed for enhancement.
It is the more inexpensive of the two processes.
FDM machines are also currently easier to scale up in size, so larger prints are more viable with this process.
Cons
While the dimensional accuracy is good enough for most functional parts, for very finely detailed parts, or parts requiring a very smooth surface finish, such as busts and other aesthetic pieces, it may not provide as good a solution as SLA.
SLA
SLA
or StereoLithography
SLA, or StereoLithography Apparatus, is a 3D printing process that creates an object by selectively exposing a liquid photopolymer (also known as resin) that reacts to certain (usually UV) wavelengths of light in a layer-wise fashion.
In the original incarnation of SLA, the image that forms each layer was drawn out with a laser. While this method is still in use, it has been joined by other methods of image formation that can display the all the pixels of each layer simultaneously.
One such method is DLP (Digital Light Processing) where the image is formed by shining the light onto a controllable set of mirrors, a DMD (Digital Micromirror Device), which direct the light as pixels towards the resin.
Another is by use of an LCD (Liquid Crystal Display), where the light shines through a screen which selectively allows light to pass through pixels and onto the resin.
CALT Dynamics has created a process called PMC (Physical Mask Curing) where the image is formed by passing UV light through a high resolution photo-mask. This process has advantages for large engineering parts and components requiring exceptional resolution.
Materials
While the makeup of the resins used in SLA printers is complex and subtle in its differences from variety to variety, at their base they are usually colourless liquids that are often pigmented and form a hard material when cured. The main difference between different types are the hardness of the cured material, with some having hardness similar to ABS for example, and others being soft and flexible.
Pros
SLA provides excellent dimensional accuracy and surface finish and for this reason is ideal for the most intricate of parts.
Cons
While SLA prints perform well while under compression, they are generally not as well suited to high stress situations as FDM printed parts.
It is also more expensive than FDM printing. However, the price of resins has been steadily decreasing in the last few years.
Due to certain issues with scaling, SLA prints are currently restricted to smaller prints (about the footprint of an A4 page) although this is likely to grow in the future.
Conclusion
To sum up, the differences between FDM and SLA, in general, are cost and level of detail. Where cost is important, FDM is probably your best bet. Where dimensional accuracy and surface finish are critical, SLA is what you want.
If you are still unsure about which process or material is best for your part, get in contact with us and tell us a bit more about it and we'll help you pick the best solution.
Intro | FDM | SLA | Conclusion