3D printing is the conversion of a digital model into a physical model and there are 2 different technologies that predominate, namely FDM vs SLA. FDM is another name for Fused Deposition Modeling, also known as Fused Filament Fabrication (FFF). SLA means StereoLithography Apparatus. These methods are both popular but very different. They both have their own techniques, advantages and disadvantages, results and specific applications. In this article we will explain the differences of FDM vs SLA.
When you watch a video about 3D printing you will probably see an FDM printer. FDM is the most popular technique. It is a reliable, user-friendly and affordable method of creating layers that adhere to each other to form an object. Let’s explain how that works.
First, the printer needs to get the right information. This is done using a 3D model file that contains information on how an object is “cut” into layers. Cura, Slic3r and Simplify3D are all good examples of cutting tools that can be used to create these files. This program “cuts” the object into individual layers and creates a gcode that tells the printer what to do. The FDM 3D printer then knows which layers to create one by one. Of course, the more complex or smaller the object, the finer these layers should be.
The computer file (usually a .STL or .OBJ) gives the 3D printer all the information it needs to start. However, the layers must of course be created with material. With FDM printers we call this material filament. FDM printers can print a large number of (strong) plastic-like materials. This filament is introduced in the form of a wire. The 3D printer heats the material making it semi-liquid. The material is then extruded through the nozzle as it moves back and forth. The next layer is repeatedly placed on the previous layer until the 3D object is complete.
SLA is the abbreviation for Stereolithography Equipment, or just stereolithography. Like FDM, SLA is an additive method: models are built layer by layer. Instead of using plastic filament, Stereolithography uses a liquid resin material. When exposed to the right type of light, the resin permanently hardens to a new shape.
SLA printers also print layer by layer, but instead of extruding material, they zap a tank full of resin solution.The process begins with the resin solution and a lightsource that can be carefully targeted at the lower resin layer. The SLA printer uses a 3D file with instructions for targeting that light source. The printer usually contains a base for the 3D object to build on. The base moves through the tank (the photopolymer box) with liquid as the object is built layer by layer. Each layer is then hardened to a solid layer. The print bed then rises slightly to allow the next layer to harden, causing the object to gradually rise from the depth.
However, there is a difference in layers in SLA vs FDM. SLA allows you to print a model with extremely fine details. The layers are less than one hundred microns thin and form very quickly. Instead of fusing FDM wires, these layers chemically connect with each other. In this way, the object becomes essentially one uniform material. After the print is completed, it undergoes a chemical bath to remove the excess resin and is then placed in UV light to harden.
The disadvantage is that SLA 3d printers usually have smaller construction plates than FDM printers, so no larger objects can be created. Also, fewer different materials can be used. In fact, SLA printers should be handled with care as the resin used to make your hi-def prints is highly toxic and is not recommended for inexperienced users.
When we compare SLA vs FDM we also have to take into account the materials and especially the costs. FDM technology is the most popular method and therefore many different materials have been developed for it. FDM printers can print on a variety of materials, including the most popular ones: ABS, PETG and PLA. Other filaments such as nylon, TPU and PVA, TPU, PEEK, Ultem and mixtures of wood, ceramics, metal, carbon or fibres can also be processed. There are many colors filament to choose from and they can also be custom made. A typical FDM printer uses filaments with a diameter between 1.75 mm and 2.85 mm.
With SLA printing, the materials are exclusive: they cannot be used in a SLA printer from another manufacturer. Each manufacturer designs its resin box so that it will only fit on its printer. The choice of material color is also very limited from yellow, black, white, magenta to cyan. There are different types of resin available and they are often very good presenting materials making them suitable for industrial use. The resin used in SLA printing is also quite expensive compared to equal amounts you get with filaments.
As with any machine, there are operating costs and these differ for SLA vs FDM printers.
The usage costs for FDM printers are mainly related to the nozzles and filaments. As mentioned before, most FDM printers use the same standardized materials and you are not dependent on a particular manufacturer. The prices for these materials have decreased in recent years. 1 kg PLA filament can be purchased for $25. Specialized materials cost more.
The usage costs for SLA printers are higher and do not only include the material. After printing 2-3 liters of resin, the resin tank needs to be replaced. This is because the tank will stain inward over time, making it impossible for the light source to project the image precisely into the resin. The result is a drastic depreciation on the printing quality. Depending on the manufacturer and the model, a resin tank costs about $40 to $80.
The construction platform also needs to be replaced from time to time. This is because it is often damaged when the user removes the printed model. A platform costs around $100.
The resin is also expensive: 1 liter of standard resin costs between $80 and $150.
Of course you want to calculate which 3D printing technology is most economically appropriate. An FDM printer costs about $2000 while the SLA variant with the same construction volume should cost minimal three times more.
One of the most important differences between SLA vs FDM is the print quality.
With FDM printers, the precision of the machine is determined by the nozzle size and the accuracy of the extruder movements both vertically and horizontally (X/Y axis).
This means that it is of the utmost importance to calibrate the machine properly. Often the quality varies depending on the machine. FDM printers operate from the ground up, which means that the weight of the upper layers compresses the lower layers. This can lead to a number of design errors and printing problems (e.g. warping, misalignment of the layers, shift of the layers and shrinking of the lower parts). This also depends on the material used. There are some thermoplastics that can provide very accurate and strong parts. The layer thickness of an FDM printer varies from 0.5 to 0.127 mm.
It is possible to achieve extra accuracy and rigidity of the objects with SLA printers because no nozzle is used to create the layers. The resolution is mainly determined by the optical dot size of the lightsource – which is very small. Less force is also applied to the model during printing, as light is used for polymerisation. This results in much smoother surfaces with a layer thickness of 0.05 to 0.01 mm.
We often forget that once we have finished printing, there is still some work to be done to remove the object. This should also be taken into account when talking about the differences between SLA vs FDM 3d printing. Adhesion refers to how easily the object can eventually be removed. With FDM this is relatively simple. If it sticks, there is nothing a decent palette knife can’t do.
With SLA printers it is exactly the opposite. The object sticks to the base like glue. It is therefore usually difficult to remove the 3D printed model from the bed. Often a lot of resin remains on the platform that you have to remove with a palette knife. This takes a lot more effort than an FDM printer so get ready for some hard work there.
As with all technologies, there is continuous innovation so there are a number of companies that have come up with new ideas to prevent this accumulation of resin. Carbon3D for instance uses oxygen to keep the resin on the surface and prevent hardening.
All 3D printing technologies require finishing. This can vary from removing the object to hours of work.
With FDM technology, as described above, removing the object is very easy. After removal, the next step is to reconstruct the design errors in the final print. You can fill holes with epoxy resin or ABS-acetone compound. You will also need to polish the surfaces by sanding the surfaces or smoothing them with vapour.
As written before, the removal of the model is a bit more complicated with SLA than with FDM because resin residues may be left behind. The hard residues must also be removed from the object itself. This can be done by placing them in a bath of isopropyl alcohol. This should be done carefully with gloves to protect the model from corrosive substances. The resulting waste should be disposed of in special containers. To obtain a smoother surface, you can sand or polish the surface. You can also use some mineral oil to hide any discoloration.
FDM can be set to print faster than SLA. However, it is a trade-off between print speed and print quality. To speed up the building process, you can choose to print thicker layers, for example. The faster you want to print, the lower the quality of the final object will be.
FDM printers emit a lot of heat, and it usually requires the user to take time to cool and cure the material. Of course, the type of material determines the time needed to heat the material and then cool it down again.
SLA machines are fast because they use lightsources aimed at specific target areas. The use of photopolymer allows the UV light to cure the material in a short period of time. The stronger the lightsource, the faster the curing process. There is also less heat emitted in the process.
It all depends on the use case. Due to the difference in prices and quality of SLA and FDM, their use is concentrated in different sectors. Jewelry or Dental need high quality and accurate detailing and SLA is the most suitable for this. However, it is not smart to use SLA to create objects that can be exposed to lighting or heat, as they can change when exposed to sunlight.
FDM is used in many different industries for design, rapid prototyping and even the production of functional components.
It all depends on the use case which is the most suitable technique. Both methods have their own advantages and disadvantages, results and specific applications. Time for an overview of all the positive and negative aspects.