What is Fused Deposition Modeling (FDM)?

FDM, or Fused Deposition Modelling, is a layer additive manufacturing process where the print material, or filament, are put together layer by layer in a specific sequence. This sequence is determined by the shape of the desired part, which is provided using CAD designs and STL files. 

FDM was introduced by S. Scott Crump in 1988. The term ‘Fused Deposition Modelling’ is trademarked by Stratasys, so it is also known as an alternative term called Fused Filament Fabrication (FFF) and is the most used 3D printing method in the world. We will look into how it works and what characteristics make it the most preferred choice in the 3D printing world.

How it Works?

FDM printers use thermoplastic filaments to make the desired parts. It is melted just above its glass transition temperature and the flow and temperature of the melted filament is controlled by an extrusion system and hot nozzle. This nozzle moves around the printing platform/bed according to the model provided to it.

FDM printing starts with a 3D design made using CAD softwares. However, 3D printers don’t understand these CAD models and are converted into STL file as the 3D CAD design is sliced into layers. These STL files describe the surface geometry of a 3D object without any information on the colour, texture and other attributes of the part.

Support structures may also be added, according to the design. Since the support structures are made from different material than the thermoplastic filament, 3D printers with dual extrusion capability is required for the FDM process. This means the printer can extrude two types of materials simultaneously.

Extrusion

Once all the processes are complete, the actual part starts to get printed. This starts with the extrusion of the filament. Thin thread-like spools of thermoplastic and support material are used to make each cross section/layer of the part. They are continuously unwound from their coil and fed into the extrusion system, which lay down the materials on the build platform. The extrusion system is made up of two hot nozzles, one of the build materials and another for the support material. It is ensured that a continuous and constant rate of support and build material is supplied from the spools to the nozzles to prevent any blob formation or deformation.

The part is built bottom up in FDM with the extrusion nozzle moving in the x-y direction i.e. horizontal movement and the build platform moving in z-direction i.e. vertical movement. These movements are repeated and the part is created layer by layer. The resolution of the vertical movement plays a big role in determining the accuracy, strength and printing time of the finished product.

As each layer is deposited, it cools down and binds to the layer beneath it. This also hardens the hot filament, which provides a solid support to the following layers. This cycle is repeated continuously, as per the resolution, complexity and size of the design, as the part takes shape.

Working of an FDM Printer:

Post Processing

When the printing is completed, the finished part is removed from the build platform and the support materials are removed. Support materials can be removed easily although, different techniques can be used to remove them depending in the support material used. Raw, unprocessed FDM parts have visible layer lines which make the surface uneven, which often require post processing. However, there are multiple finishing options to smooth the surface. The most common finishing option is hand sanding and polishing. Cosmetic paints can also be used to provide smooth and even surface.

Characteristics

FDM prints are generally considered to be durable and dimensionally accurate. It may not be as accurate or have smooth finish as the SLA or PolyJet printing methods but its compact design and ease of use are fair compensation.

The resolution of FDM printers can also be varied by the user and can vary from 50 to 400 μm. High resolution can help increase the accuracy of the print for complex models but it also means more layer lines leading to uneven surface and will take longer to print. Higher resolution also leads to reduce strength of the finished product. 

Another characteristic of FDM is the temperature required. The usual temperature range in FDM is from 150 to 230 C, depending on the build and support material used. For instance, Polylactic Acid (PLA) prints optimally at around 205 C while Acrylonitrile Butadiene Styrene (ABS) prints optimally at around 230 C.

A number of other materials can be used in FDM such as Polycarbonate, High-Density Polyethylene (HDPE), Polyphenylsulfone (PPSU), high conductive filaments, transparent filaments etc.

Advantages

FDM technology is preferred over other 3D printing technologies mainly due to its ease of use, accuracy and repeatability. Development of new compact printers with ease of installing has further increased its adoption by the masses along with reduced cost of printing as compared to other printing methods.

With the mass adoption of FDM, there is a plethora of support materials for new users to learn easily making it very accessible to the average person. This has also resulted in many choices for the filament material, from PLA, ABS to more stylish metal-infused filaments and glow in the dark filaments and more.

Limitations

As mentioned earlier, this printing method is not the most accurate out there which makes it not suitable for complex designs which require high accuracy. Also, the added post processing increases the time required to make a ready-to-use products. Not to mention the reduced strength of the product with the increase in resolution of printing.

Conclusion

FDM printing is the most popular and preferred 3D printing method in the world. It may not be the strongest or the most accurate method of printing but the compact design, ease of use and installation along with the plethora of filament materials available in the market make it stand out among the rest.

With its increasing applications and popularity, FDM is only set to evolve and improve over time in the future and it seems difficult for any other printing method to take the spot from FDM. 

FDM is utilized in a number of industries such as Aerospace, Automotive, Industrial and Medical etc. With so many applications and continuing increase in popularity, we foresee FDM technology as evolving further in the future.  At this point, it’s very unlikely for another 3D printing technology to take the top spot – FDM printing is here to stay.

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Additional Information:

https://3dinsider.com/what-is-fdm/