What is FDM (fused deposition modeling) 3D printing?

Fused filament fabrication (FFF) or Fused Deposition Modeling (FDM) is a material extrusion additive manufacturing (AM) process. It produces objects by selectively depositing melted material in a predetermined path layer by layer with thermoplastic polymers that are supplied in filaments.

FDM is the technology with the largest installed base of 3D printers in the world. It is widely used across most industries and is likely the first process that comes to mind when thinking of 3D printing.

In this article, we explain the fundamental principles and essential features of this common additive technology. We also differentiate between FDM machines intended for prototyping (desktop) and industrial applications and offer advice to engineers on achieving optimal results with FDM 3D printing.

How does FDM 3D printing function? #

An FDM 3D printer deposits melted filament material on a build platform in layers until a finished part is produced. FDM relies on digital design files, which are uploaded to the machine and translated into physical measurements. Threadlike polymers, including ABS, PLA, PETG, and PEI, are fed through a heated nozzle to serve as the FDM materials.

To operate an FDM printer, load a spool of thermoplastic filament and wait for the nozzle to reach the desired temperature.

The printer will then extrude the filament through a nozzle attached to a three-axis system that can move across the X, Y, and Z axes. The melted material is deposited layer by layer along a path specified by the design. After deposition, the material cools and solidifies. You can attach fans to the extrusion head to speed up cooling in certain situations.

To fill an area, multiple passes are necessary, similar to filling in a shape with a marker. When the printer completes a layer, the build platform lowers and the machine begins printing the next layer. In some machine setups, the extrusion head moves up. This process repeats until the part is complete.

What are the printing settings for FDM 3D printers?
For the most part, FDM systems allow for the adjustment of multiple process settings, such as nozzle and build platform temperatures, build speed, layer height, and cooling fan speed. These settings are typically covered by an AM operator, so designers typically do not have to worry about making these adjustments.

However, when designing, it's important to consider factors such as build size and layer height. The standard size for a desktop 3D printer is 200 x 200 x 200 mm, while industrial machines can reach sizes up to 1000 x 1000 x 1000 mm. If you choose to utilize a desktop printer for your project, a large model can be deconstructed into smaller parts and later reconstructed.

FDM printers usually have a layer height that ranges from 50 to 400 microns. Printing shorter layers produces smoother parts and better captures curved geometries, while printing taller layers allows for quicker and more cost-effective part production.

For optimal results, we suggest layer height of 200 microns. For further information, take a look at our article about the influence of layer height on 3D-printed objects.

Is there a distinction between desktop and industrial FDM printers? #

FDM printers can be classified into two main categories: industrial (professional) and prototyping (desktop) machines. Each printer grade has its own specific applications and advantages, though the primary dissimilarity between the two technologies is their production scale.

Industrial FDM 3D printers, such as the Stratasys 3D printer, are pricier compared to their desktop counterparts, which are mainly used for consumer purposes. Therefore, using industrial machines for customized parts will result in higher costs. Because industrial machines are more efficient and powerful than desktop FDM printers, they are frequently utilized for tooling, functional prototypes, and end-use parts.

Furthermore, industrial FDM printers can fulfill larger orders more rapidly than desktop machines. They are engineered for consistent repeatability and reliability, allowing for the creation of identical parts with minimal human intervention. However, desktop FDM printers lack the same durability and robustness. These machines require frequent user maintenance and regular calibration.

In the table below, we break down the main differences between a typical desktop FDM machine and an industrial one.

Property	Industrial FDM	Desktop FDM
Standard accuracy	± 0.15% (lower limit ± 0.2 mm)	± 1% (lower limit: ± 1.0 mm)
Typical layer thickness	0.18 - 0.5 mm	0.10 - 0.25 mm
Minimum wall thickness	1 mm	0.8 - 1 mm
Maximum build envelope	Large (e.g. 900 x 600 x 900 mm)	Medium (e.g. 200 x 200 x 200 mm)
Common materials	ABS, PC, ULTEM	PLA, ABS, PETG
Support material	Water-soluble/Break-away	Same as part (typically)
Production capabilities (per machine)	Low/Medium	Low
Machine cost	$50000+	$500 - $5000

What are the features of FDM 3D printing? #

Although FDM 3D printers differ in their extrusion systems and the quality of parts produced by different machines, common characteristics are present in every FDM printing process.

Warping

Warping is one of the most prevalent defects in FDM. As extruded material cools, its dimensions decrease during solidification. Since different areas of the printed part cool at varying rates, their dimensions also change at different speeds. Differential cooling can cause internal stresses to build up and pull the underlying layer upward, resulting in warping.

To prevent warping, you can closely monitor the temperature of your FDM system, particularly the build platform and chamber. Another mitigation method is to increase adhesion between the part and the build platform.

Additionally, certain design choices can lessen the likelihood of warping. Consider the following examples:

• Large areas with flat surfaces, such as those found on a rectangular box, may be more susceptible to warping. It is best to avoid these types of designs when possible.
• Thin protruding features, like the prongs on a fork, are also prone to warping. To prevent this issue, consider adding extra guiding or stress-relieving material to the edges of thin features, which will increase the surface area that contacts the build platform.
• Additionally, sharp corners tend to warp more than rounded shapes, so we advise including fillets in the design.
• Every material is susceptible to warping to varying degrees. For example, ABS is generally more prone to warping than PLA or PETG.

Layer Adhesion

Secure adhesion between deposited layers is crucial in FDM. When an FDM machine extrudes molten thermoplastic through the nozzle, the material presses against the previously printed layer. The high temperature and pressure cause the layer to re-melt and bond with the previous layer.

This deformation causes the molten material to take an oval shape as it presses against the previously printed layer. This means that parts made with FDM will always have a textured surface, no matter what layer height is used, and small details like holes or threads may need additional processing after printing.

Often, removing support structure

materials can be challenging, so designing parts to reduce the need for support structures is preferable. FDM printers cannot deposit molten thermoplastic over thin air.

Some part geometries require support structures, which are typically printed in the same material as the parts. Support materials that dissolve in liquid are available, but they are generally used in conjunction with higher-end FDM 3D printers. It should be noted that using dissolvable supports will increase the overall cost of a print.

Infill and shell thickness

are typically reduced for FDM printing to save on materials and reduce print time; solid parts are not typically produced. Instead, the machine traces the outer perimeter, known as the shell, in several passes and fills the interior, referred to as the infill, with a low-density structure.

The strength of FDM-printed parts is significantly affected by the thickness of the infill and shell. To achieve quick prints, most desktop FDM printers have a default setting of 20% infill density and a 1mm shell thickness, which offers a suitable balance between strength and speed.

The table below summarizes the main characteristics of FDM 3D printing. 

	FDM
Materials	Thermoplastics (PLA, ABS, PETG, PC, PEI etc)
Dimensional Accuracy	± 0.5% (lower limit ± 0.5 mm) - desktop ± 0.15% (lower limit ± 0.2 mm) - industrial
Typical Build Size	200 x 200 x 200 mm - desktop 900 x 600 x 900 mm - industrial
Common layer thickness	50 to 400 microns
Support	Not always required (dissolvable available)

What materials are typically used in FDM 3D printing? #

One major benefit of FDM technology, both on the desktop and industrial scale, is the wide variety of materials available. These materials include common thermoplastics such as PLA and ABS, engineering materials such as PA, TPU, and PETG, and high-performance thermoplastics like PEEK and PEI.

PLA filament is the most frequently used material in desktop FDM printing due to its ease of use and ability to produce parts with intricate details. When you require increased strength, ductility, and thermal stability, ABS is typically the material of choice. Nonetheless, ABS is more susceptible to warping, particularly if you utilize a machine lacking a heated chamber.

A substitute to consider for desktop FDM printing is PETG, which has a similar composition to ABS and is easy to print with. All three of these materials are suitable for most 3D printing applications, ranging from prototyping to low-volume production of models or functional parts.

Industrial FDM machines primarily use engineering thermoplastics, such as ABS, polycarbonate, and Ultem, for form, fit, and function. These materials often include additives that modify their properties and make them highly valuable for industrial applications such as providing high impact strength, thermal stability, chemical resistance, and biocompatibility.

Printing in different materials will affect your part’s mechanical properties and accuracy, as well as its cost. We compare the most common FDM materials in the table below.

Material	Characteristics
ABS	+ Good strength + Good temperature resistance - More susceptible to warping
PLA	+ Excellent visual quality + Easy to print with - Low impact strength
Nylon (PA)	+ High strength + Excellent wear and chemical resistance - Low humidity resistance
PETG	+ Food Safe* + Good strength + Easy to print with
TPU	+ Very flexible - Difficult to print accurately
PEI	+ Excellent strength to weight + Excellent fire and chemical resistance - High cost

For additional information, refer to this analysis of the key contrasts between PLA and ABS — the two prevalent FDM materials — as well as a comprehensive comparison of all the widespread FDM materials.

Post-processing for FDM 3D printing #

FDM 3D printed parts can be finished to a high standard using methods such as sanding, polishing, priming, painting, cold welding, vapor smoothing, epoxy coating, and metal plating.

If you want to learn more about all the post-processing options available for your next production run of FDM parts, check out our comprehensive guide.

What are the recommended printing practices for FDM? #

FDM can quickly and affordably produce prototypes and functional parts using a variety of materials.

• Most desktop FDM printers have a build size of 200 x 200 x 200mm, while industrial machines have larger build sizes.
• To prevent warping, avoid extensive flat areas while adding fillets to sharp corners.
• It's important to note that FDM inherently possesses anisotropic properties, making it unsuitable for mechanically critical components.
• The minimum feature size of FDM machines is determined by the nozzle diameter and layer thickness.
• Material extrusion prohibits the production of vertical features in the Z direction with smaller geometry than the layer height, typically between 0.1 - 0.2 mm.
• Similarly, planar features on the XY plane cannot be produced by FDM that are smaller than the nozzle diameter, which is between 0.4 - 0.5 mm.
• Walls must be at least two to three times larger than the nozzle diameter, or 0.8 - 1.2 mm.
• If you want to achieve smooth surfaces and fine features, you may require additional post-processing, such as sandblasting and machining. In this scenario, another AM technology, such as SLA, may be a better fit.

Frequently asked questions #