FDM vs. SLS 3D Printing - What They Mean and When to Use Them

3D Printing or Additive Manufacturing refers to a group of technologies used to build three-dimensional objects. Depending on your project's characteristics, the object you need to print, and the quality and cost required, one 3D printing technology might be more suitable than the others.

Currently, the most used technologies are FDM (Fused Deposition Modelling) and SLS (Selective Laser Sintering)   but.. What are the main differences between FDM and SLS processes?

Although there are professional and industrial FDM Printers, most printers of this type are consumer-grade printers, meaning that they are the most affordable kind of 3D printers and are mostly oriented towards a moderate printing frequency for one or a few users. On the other side, most SLS printers are professional or industrial printers. Their cost represents a significant investment but they can handle thousands of high quality prints per week on uninterrupted production.

If you're curious about 3D printing but don't own a 3D printer, you might be wondering if investing in a 3D printer is worth it. If you do, you are probably also thinking about the printing quality, the costs involved and the main characteristics of these two completely different technologies. For those of you who are in that situation, here you will find a side-by-side comparison of what you can get with each type of printer!


FDM vs SLS - The Showdown

As mentioned above, Fused Deposition Modelling technology allows you to land in the 3D printing world in an affordable way, which is a big advantage specially for individuals than usually don't have a company's budget. The core reason for this lies in the relatively simple concept behind FDM printers, which is to melt a plastic filament while positioning it in a structured way. That simple fact turned FDM into the most popular printing technology and flooded the market with inexpensive and relatively easy-to-use desktop 3D printers. 

On the other corner, Selective Laser Sintering technology allows to 3D print an object by selectively sintering (forming a solid mass of material by heat but without reaching liquefaction) sections of successive layers of powder using a powerful laser beam. The process most notably discards the need of support material (as there is unsintered powder all around the object being printed) facilitating the creation of complex and interlocking forms. This significantly more complex technology will set the owner back between 150 000 and 500 000 euros. Thankfully, everyone can still have access to the benefits of SLS technology without the need to purchase a printer by using a 3D printing online service like Sculpteo.

 

If you want to discover more about these technologies you can have a look to our 3D Printers and 3D Printing: Technologies, Processes and Techniques page.

 

The capabilities of FDM and SLS can be analyzed and compared separately for three gradually increasing object complexities: 

  1. Minimum complexity is a simple shaped object with small or no overhangs.  A spinning top will be our example object for this category.

  2. Middle complexity can be an object with a a few overhangs or articulated parts that needs to be printed all at once already assembled. For this category we have chosen a 3D fabric similar to the ones used by the fashion industry, as Danit Peleg did with her 3D printed collection.

  3. High complexity is an object that may have many large overhangs, thin sections, overhangs in places where is difficult to access to remove support material or may not have a stable standing position to be printed on. For this case we went with a Springy ball, which almost checks all characteristics on our list. 

The head-to-head comparison done below was completed with the following machines, materials and settings:

FDM: Stratasys MOJO and Makerbot Replicator Printers, with a layer thickness between 150 and 200 microns,  printing with P430 ABS PLUS and SR-30 Soluble material on the Mojo and PLA on the Makerbot.

SLS: EOS P110 Printer with a layer thickness of 150 microns, printing white Polyamide (also known as Nylon). This is the most commonly used material for SLS printing.

 

Minimum complexity - The Tippe Top

 
FDM TOP.jpg   SLS TOP.jpg
                              The FDM Top                                                                             The SLS Top 

The FDM Top : Due to the curved bottom of the design the top was split into two pieces with the purpose of simplifying the printing. It could have been printed in several ways using support material, hence avoiding the use of glue altogether but doing that would render it impossible to print for the majority of the desktop 3D printers, that don't have dual extruder and consequently cannot use support material. The top took one hour to print and it was doing its magic right after the two sides were glued together.


The SLS Top : It took 2 days to have the top in our hands using the SLS printer. The printing itself didn't take two days but the whole process did as while the top was being printed, hundreds of other objects were being printed too (it wouldn't be practical to print one single object at once, but if it was done, it would take about an hour too). After printing, the top was polished and dyed, which accounted for about 4 extra hours of post processing. 


For this level of complexity, the main difference between the two tops is the aesthetic appearance. The layering on the SLS print is barely visible (and only on small angles), and even before polishing the surface comes out pretty smooth. On the other side, the FDM print shows an attractive shiny color but also its layers are visible for every angle, on every surface (even vertical ones). Disregarding the juncture and the poorly executed gluing, the text on the inside is hardly readable and the small overhang looks notably different than the rest of the print. On the plus side, for some people printing it at home can be a lot of fun.

Also you may want to consider the cost associated with using these technologies, either at home with a full investment in your own printer or the cost of single print using a 3D printing service. It all comes down to how often do you print, you can learn more about this with our Should You Buy a 3D Printer or Use a 3D Printing Service? analysis.


Medium Complexity - The ChainMesh

 
FDM Chain_1.jpgSLS chain 2.jpg
 
                                          FDM Chainmesh                                                                              SLS Chainmesh

 
 

The FDM ChainMesh : The ChainMesh with all its individual parts was printed all at once already assembled, in almost 4 hours. The finish is rough and not really aesthetically pleasing to use for fashion purposes. The mobility between the components is good for a prototype and this allows to test multiple iterations in a short period of time.

 

The SLS ChainMesh: This ChainMesh was also printed in one single run, in the same way the Tippe Top above was produced, but without post processing. The finish is smooth and its appearance would go well for fashion purposes and dyeing, if required. The mobility of the components was smoother than on the FDM print, allowing more fluent movements of the entire mesh. This ChainMesh could have also been used for prototyping purposes but at the same time you are definitely getting closer to the final appearance you are probably looking for.

 
On both the FDM and SLS ChainMesh the freedom of movement is pretty much the same although you do have to push harder on the FDM print due to the rougher surface. On the picture above you can clearly see the layers on the FDM object on the left, which is not the case on the SLS one on the right.


SLS Chain.jpg


You can observe that the last layer on the FDM model left some lumps on the top. This detail might be a problem depending on what you are using the piece for. If you wanted to dye it, the SLS piece would be the best choice, but you can also print in multiple colors and materials on an FDM printer.

 

High complexity: The Springy ball

 
SLS SPRINCY BALL.jpg

The SLS Springy Ball : The SLS Springy Ball that would be a real challenge for any 3D printer that requires support material, was nothing too special for our SLS printer. As we commented before, on a SLS printer the objects being printed are simultaneously being "buried" in unsintered powder, so any overhang can easily rest on this powder that acts as building material and support at the same time. This on top of the high strength of Polyamide gave us a bouncy and amusing 4" Springy Ball. The printing time was the same as usual, and although a unique print could be done in about 3-4 hours including cleaning, it took us about 2 days to have it ready for the same reasons aforementioned.

 

The FDM Springy Balls : This print was not successful. It took 19 hours to print it using support material, a lot of it (about 3 times as much as ABS itself when using Stratasys automatic support tool). We run into problems when we tried to dissolve it though, as the time required to dissolve all that amount of support was too long, and the very same solvent started attacking and weakening the ABS itself. This wouldn't be that problematic if we didn't have really thin sections, as we have on the springs. End result, by the time the support looked almost gone, we took out the part out of the solvent and it literally fell apart, with only the middle sphere and discs remaining. 

Despite most of the support material not being easily accessible to remove it mechanically, we printed this object again but trying to get rid of as much support as possible by manually breaking it off, in order to minimize the time required on the solvent. Unfortunately, we still needed a few hours (but not 7 like the first time) which was too long for the springs to withstand, ending with similar results once again. Bear in mind that we are using the official solvent manufactured by Stratasys for this printer and this support material.

Finally, we agreed that this design was particularly difficult for a FDM printer. It may not be impossible, but for sure quite challenging. We were left wondering how the springs would have behaved and/or if they would have been strong enough, due to the strong layering effect visible on FDM prints.

 
 

SLS Sprincy ball 1.jpg
SLS Sprincy ball 2.jpg SLS Sprincy ball 3.jpg
 
 

When to use FDM or SLS?

 

If you own a FDM 3D printer and you want to print objects of minimum to medium complexity, FDM may be the best choice: it's quicker, cheaper, and offers good results. On top of that, you made it yourself, which is pretty cool.

That being said, you might want to consider our SLS printers for your more advanced projects, or if you need a lot of copies and you don't want to spend a week by the 3D printer. Remember that depending on the shape, size and finish of your object, you can get up to 80% off for large quantities.

For those middle ground objects, you should ask yourself:

What is the purpose of this object? 

What technical properties do I need?

What finish quality do I need?

Based on the answers to these questions, you can choose one printing technology or the other. Objectively, SLS prints tend to look a bit more as an actual product, since the layers are rarely visible. On the other side, FDM printers are so popular that there is a humongous variety of filaments, colors, textures, etc. Luckily, we also offer a wide range of materials, colors and finishes that can make give your object a finished product look, and we are constantly seeking to offer more materials, finishes and colors.

 

If you want to have a first idea of how a 3D printing online service works, upload your 3D file !