Material Extrusion - FDM

What is FDM Printing?

FDM stands for Fused Deposition Modeling, and is sometimes also known as Fused Filament Fabrication (FFF). It is a 3D printing technology commonly found in many consumer-level machines.

 

FDM machines are known for using material extrusion technology. A 3d project is built through layers of melted material being stacked on top of each other. Common FDM materials that are used include thermoplastic polymers that come in filaments.

 

As the technology that is most commonly installed in all printers worldwide, FDM is the first technology that newcomers learn about. In this article, we will cover everything there is to know about FDM.

 

This will help many of you hobbyists who have the intention of designing your own 3D models. Through your understanding of how FDM works, you can decide if this is the right printing technology for certain builds you want to create.

How does the FDM Process work?

How does the FDM process actually work in detail?

A spool of plastic filament has to be loaded into the printer first. The nozzle of the machine then has to reach a certain temperature. The print process is then started when the filament is fed through the extrusion head and starts to melt as it passes through the nozzle.

There is a 3 dimensional axis system that the extrusion head is attached to. This allows the melted thermoplastic to be extruded in thin strands which are then placed out in layers. These layers then start to cool and become solid. For some machines, there will be cooling fans attached to the extrusion head which help to speed up the cooling process of the plastic.

When solid objects are forming, this requires many layers to fill up a certain space. This means that the extrusion head will have to make multiple movements before many layers are stacked on top of each other.

FDM Printer FDM Parameters?

Here are some of the parameters that can be adjusted for the FDM printing process.

  1. Temperature of Nozzle
  2. Temperature of the Build Platform
  3. Build Speed
  4. Layer Height
  5. Cooling Fan Speed

These are parameters that come with most FDM printers, and are usually quite easy to learn on how to adjust. For aspiring 3D designers, the parameters that will apply mostly to you would be the build size and layer height.

Build size refers to the 3D printing capacity that each machine is capable of creating 3D objects in. Consumer-level machines tend to have a smaller build size of around 200 x 200 x 200mm. Whereas for industrial machines, the build size can go up to 1000 x 1000 x1000 mm. 

Some establishments even buy a big printer and separate it into smaller parts if they don’t want a build size that is that large.

Depending on how you expect your printer to perform, different layer heights can also affect the 3D objects that you print. For example, a smaller layer height tends to print smoother parts and is more suited for curved geometric objects. Whereas for larger layer heights, there is a faster printing time and this can help to reduce costs.

What is Warping?

Warping is the most common downside when it comes to FDM printing. When the melted plastic cools and starts to solidify, the size of the object will decrease.

It is a common thing to have different areas of the object to be cooling at different rates. Because of this, the dimensions of each separate area will change at different rates. 

Warping happens when different cooling rates causes an increase in stress to underlying material layer and pulls it upward. This leads to a damaged and unsuccessful build process.

How can newcomers learn to prevent this kind of defect in their 3D objects? One good habit to set is to learn how to closely monitor the temperature of your FDM printer. Another pointer is to increase the adhesion of the plastic model with the build platform.

Here are some other pointers that you can follow to prevent the chances of your object from warping:

  1. Builds with large flat surfaces, (e.g. a big box) are more likely to experience warping.
  2. For objects that have a thin protruding feature, these will be prone to warping as well. If you add material that connects the edge of the thin feature to the build platform, this will reduce your chances of warping as well.
  3. Sharp corners tend to warp more compared to rounded objects.
  4. ABS plastic tends to warp more compared to other plastics like PLA or PETG.

What is Layer Adhesion

When layers of material are stacked on top of each other during the FDM process, how the layers hold together is really important. This is what we call layer adhesion.

 

As highly heated thermoplastic is being fed out of the nozzle, it is laid down on top of the previous layer. The high temperature and pressure of the material melts the surface of the previous layer which allows the new layer to bond together with it.

What is a Supportive Structure?

For many objects that are created through FDM, a support structure is needed as melted thermoplastic layers can’t be deposited on thin air. This is common for some geometric builds, as they need a support structure in order for the object to be printed in full. 

When there are objects that require a support structure, the areas that need support tend to be of lower surface quality. With that said, it is always important to design an object that requires as little support as possible.

When it comes to printing the support structure, the same material used for the actual object will also be used for the support structure.

Some support structure materials that dissolve in liquid are also used, but they tend to be utilized for higher-end or industrial-grade machines. These dissolvable materials may help to improve the overall print quality of the actual object being supported, however, this would increase the overall cost of the print as these dissolvable materials can be very costly.

What is Infill & Shell Thickness?

Objects printed through FDM are usually not printed to be solid. Instead, there is an outer perimeter that is created which is called the shell. Afterwards the interior is filled with a structure called the infill.

Based on the parameters you choose for your object’s shell and infill, this will impact the final strength of the object that solidifies.

10% Fill

20% Fill

30% Fill

Common FDM Materials

One of the main reasons why FDM is so popular is because of the wide range of filament materials that is compatible with this type of printing technology.

First of all we have our common thermoplastics such as PLA and ABS. Moving on from that there are engineering-level materials such as PA, TPU and PETG. 

For creators that require more high-performing materials, you can consider materials such as PEEK and PEI.

Based on the type of material that you use, this will affect the mechanical properties, cost price and overall success of the print.

Pros & Cons of FDM

PRO

  1. FDM is the most affordable way to produce customized 3D thermoplastic objects.
  2. FDM have one of the fastest print times compared to other technologies
  3. There is a huge number of thermoplastic materials that are compatible with FDM printing.

CONS

  1. FDM technology has the lowest dimensional accuracy compared to all the other 3D printing technologies. For 3D models that have a lot of minute details, FDM machines might not be the solution for you.
  2. FDM printed 3D models might have layer lines that are quite visible. This requires a process of smoothening out the surface area after the print is done.