Flashback to episode 2

How is “FDM” different from “SLA (resin)”? A deep comparison of these two popular technologies!

From the previous article, we have seen that 3D printers are widely used in everything from prototyping to medical applications. However, in reality, even though they are all called "3D printers," there are actually a variety of "product creation methods" to choose from.

In this article, we'll take a closer look at two of the most popular technologies: FDM (layer-by-layer filament melting) and SLA (light curing resin) along with their working principles and the differences in output quality. This will allow you to decide which one best meets your business and work needs.

1. What is FDM?

FDM is one of the most familiar and widely used 3D printing technologies, from casual users looking to create simple parts to industry experts.

The heart of this technology is the heating of plastic filament until it melts and then injects it layer by layer to form a three-dimensional shape. Imagine squeezing soft-serve ice cream into the desired shape, but the machine works with tens of times more precision.

Working principle

This method uses a small plastic filament called a filament that is heated until it melts through a nozzle and prints a thin line, similar to squeezing soft cream. The machine then gradually deposits the material layer by layer until it becomes the finished product.

Advantages of FDM

• low cost
  Both the machine and the filament material are affordable, making it the easiest technology to get started with.
  
• Various materials
  It can use plastics like ABS or PC, which are materials actually used in industrial parts, and are both strong and affordable.

FDM limitations

• Rough surface
  Due to the principle of laying down material layers one at a time, layer lines, also known as “Layer Lines,” are clearly visible and are a major weakness of this system.
  
  
• Resolution
  The smoothness of the surface and the ability to capture small details are inferior to the photoresist system discussed in the next section.

2. What is SLA?

SLA is one of the oldest 3D printing technologies and is also a technology that Formlabs specializes in.

Working principle

This system uses a material called photopolymer resin, a liquid that hardens when exposed to UV light. The machine shoots a laser beam or uses a high-resolution LCD screen to shine through the bottom of the resin tank, causing the resin to harden layer by layer until it becomes a complete piece.

SLA advantages

• Ultra high resolution
  Because it is a process of solidifying liquid with light, it makes the surface of the workpiece smooth, detailed and almost invisible. The quality of the workpiece is similar to that of workpieces produced by injection molding.
  
• High dimensional accuracy
  Resin material has very little heat shrinkage, so it can keep its shape close to the CAD model with precision.

SLA limitations

• Post-processing is required.
  After printing, the uncured resin must be washed off and the piece must be UV-cured again to fully harden. This step is essential.
  
  
• Material costs are higher than FDM.
  Resin is more expensive than regular filament, resulting in a higher cost per piece.
  
  
• Lower UV resistance
  It depends on the type of resin, but generally, photocured materials tend to deteriorate easily when exposed to sunlight or UV for long periods of time.

3. Comparison of FDM and SLA

Both technologies have their own advantages and limitations.
So, the “best answer” will depend on your intended use case and what you need most.

Below is a comparison of each key point:

Comparative topics	FDM	SLA
Working principle	The plastic filament is melted with heat and then printed layer by layer.	Use light to harden the liquid resin layer by layer.
Surface	The skin is rather rough, with visible wrinkles.	The skin is very smooth, barely visible wrinkles.
Resolution / Accuracy	Low to medium level	Very accurate, sharp details
Material costs	Affordable price	Higher price
Post-processing	Remove Support as a priority	Additional washing and drying is required.
What kind of work is it suitable for?	Simple shape checking, making jigs and fixtures	Check design work, detailed prototypes, and dental work.

Cases where FDM systems are suitable

1. Want to start using a 3D printer with the lowest possible budget and want to try it out first.
2. Focus on testing the strength and durability of materials like ABS more than the beauty of the surface.
3. It is used to make jigs or equipment that are only important for their “functionality”, so the surface finish or detail is not too serious.

Cases where it is suitable to use a photoresist (SLA) resin system

1. Want to make a design model to present to clients
2. Want a workpiece with a smooth surface that is close to the actual product.
3. The fit of various parts (Fit/Assembly) must be checked, which requires micron-level accuracy.
4. Focuses on work that requires very high detail, such as figures, jewelry, or dental models.

Conclusion: Decision points for business work

For hobby use or just basic shape verification, FDM printers are a good choice. But for real-world product development, where both design accuracy and a beautiful finish are required to present to customers, a superior technology is the Light-Lasting Resin (SLA) system.

Formlabs' commitment to SLA technology delivers professional-grade resolution, stability, and reliability, making it the trusted choice for engineers, designers, and medical users worldwide.

It delivers quality, precision, and value—so if you're looking for a tool that can truly elevate your workflow, Formlabs' SLAs are the answer to take you further.

Next article

In part 4, we'll explore industrial-grade technology that FDM or SLA simply can't deliver. Print durable, ready-to-use nylon parts with SLS, the same technology used by the Formlabs Fuse 1+. Get ready for innovation that will change the way we look at manufacturing and usher in a new era for industrial applications.

References

1. What does SLS mean?
   https://www.yam-sls-3dprinter.com/post/blog-20241023-sls-technology

2. 3D Japanese traditional medicine (SLA方式) is a Japanese traditional Chinese medicine.
   https://make.dmm.com/blog/modelingmethod/stereolithographyapparatus/

3.  https://www.3d-printer.jp/knowledge/classification/fdm.html#:~:text=FDM%E3%83%86%E3%82%AF%E3%83%8E%E3%83%AD%E3%82%B8%E3%83%BC%EF%BC%88Fused%20Deposition%20Modeling,%E9%80%A0%E5%BD%A2%E3%81%8C%E8%A1%8C%E3%81%88%E3%82%8B%E3%81%93%E3%81%A8%E3%81%A7%E3%81%99%E3%80%82

4. 3D has a long history of 3D animations,
   https://i-maker.jp/blog/select-3dprint-method-33992.html

5. 3D games will be released in 2025.
   https://www.3d-printer.jp/knowledge/classification/

6. What is 3D printing? How does it work? https://www.3d-printout.com/study3d/study1/

7. 3D characters that are used in the game | 3D design, 3D design, 3D design, i-MAKER,
   https://i-maker.jp/blog/select-3dprint-make-33988.html

8. 【22 Pages of Images】3D Images and Images of Images at https://www.dent3d-navi.com/