Fused deposition modeling, or FDM for short, is a material extrusion method of additive manufacturing where materials are extruded through a nozzle and joined together to create 3D objects.
In particular, the “standard” FDM process distinguishes itself from other material extrusion techniques, such as concrete and food 3D printing, by using thermoplastics as feedstock materials, usually in the forms of filaments or pellets.
A typical FDM 3D printer, therefore, takes a polymer-based filament and forces it through a heated nozzle, which melts the material and deposits it in 2D layers on the build platform. While still warm, these layers fuse with each other to eventually create a three-dimensional part.
Generally accepted as the simplest way to 3D print stuff, FDM is accessible, reasonably efficient, and widely popular. FDM printers dominate the 3D printing market, being remarkably more straightforward than resin 3D printing and massively cheaper than powder-based methods, such as selective laser sintering (SLS).
In this article, we’ll explore this acclaimed 3D printing process, going into detail about its inner workings, material possibilities, and much more. First, let’s find out how it became so popular among makers and hobbyists.
Background
While FDM is undisputedly the most popular 3D printing method, it can come as a surprise that it was not the first system to be invented. Actually, it’s not even the second.
Scott Crump applied for the first FDM patent in 1989, three years after the patent for Stereolithography (SLA) was filed and one year after selective laser sintering (SLS). Scott and his wife Lisa went on to found one of the leading 3D printing companies, Stratasys.
However, FDM only became popular among non-commercial users later through the RepRap community and under its alternative name, Fused Filament Fabrication (FFF). The RepRap Project started as an academic project in 2005 by Adrian Bowyer at the University of Bath with the primary goal of producing self-replicating devices.
When the FDM patent expired in 2009, several former RepRap volunteers founded MakerBot Industries, one of the first non-industrial companies to commercialize the open-source FDM 3D printers based on the RepRap open-source project. Other 3D printing companies, such as UltiMaker and Prusa Research also started their own journeys from the RepRap movement. Most recently, MakerBot and UltiMaker have joined forces in a merger.
These companies and individuals all paved the way for the vast market of consumer and hobbyist FDM 3D printing we have today.
How It Works
FDM (or FFF) is mainly characterized by the extrusion and selective deposition of thermoplastics into layers that build up to create a three-dimensional object. This may sound a bit vague, so let’s explore the process in more detail.
At its core, the FDM technique is relatively straightforward. Its main functions are performed by two distinct systems: one responsible for the extrusion and deposition and the other for the printhead movement. We’ll discuss both of these systems in the following sections.
Extrusion & Deposition
Broadly speaking, the extrusion and deposition system can be split into two main assemblies: the “cold end” and the “hot end”. The thermoplastics used in FDM 3D printing often come in filament spools, and the cold end is responsible for feeding this material from the spool into the 3D printer. Like such, the cold end also controls the rate at which material is being deposited on the other end, often referred to as “flow”.
The hot end, on the other hand, is responsible for heating the moving plastic material to the point that it’s adequate for being “purged” through a nozzle, hence its name. This step involves different components, including heating cartridges, heatsinks, and of course, nozzles.
The cold and hot ends must work synergistically to extrude just the right amount of material at the required temperature and physical state for properly stacking up layers.
Hardware Setups
When it comes to extrusion, there are many different setups. For instance, the cold end could be located either right next to the moving hot end, in a setup known as direct extrusion, or it could be affixed to the printer’s frame, requiring a linking tube for the filament to be guided into the hot end, often called a Bowden tube.
Hot end assemblies also come in different setups. For example, the so-called “all-metal hot ends” allow for higher temperatures to be reached in the nozzle when compared to the PTFE-lined hot ends that use a short tubing inside to reduce the filament friction. The tubing, however, limits the temperature to a maximum of about 240 °C.
Considering extrusion and deposition together, there are also multi-extrusion systems. These allow multiple materials to be worked with simultaneously.
As with all things, each setup has its pros and cons, and the final choice will come down to the speeds, materials, and applications that the 3D printer will serve.
Printhead Motion
Besides the different extrusion setups FDM 3D printers can have, perhaps the most significant variability in design is found in the frame and the motion system.
The motion system of FDM 3D printers is responsible for moving the hot end assembly in the three-dimensional space to deposit the melted material accordingly. At the smallest level, the components for driving this movement often come from stepper motors, linear guides, leadscrews, and rubber belt systems.
Moving the hot end can be achieved in a variety of ways. To start, let’s characterize the different setups based on their operational coordinate systems. By far, the dominant coordinate system for 3D printers is Cartesian, where the position is given by three linear coordinates (X, Y, and Z). There is, however, a small category of FDM 3D printers that use the polar coordinate system, which uses linear and angular values to describe a physical position.
Cartesian 3D Printer Types
Cartesian machines can be further categorized in terms of their movement system. Delta 3D printers, for example, use vertical rails and three independently controlled arms attached to the hot end, all moving together to position the hot end accordingly. SCARA printers are another sub-category of Cartesian machines, making use of horizontally-moved arms to perform planar movement.
Yet, chances are that if you encounter a 3D printer in the wild, it will be a Cartesian rectilinear-style machine. Here, you have stepper motors directing movement purely along the X-, Y-, and Z-axes using a system of screws, belts, and pulleys. There are several identifiable types falling under this category, with some popular ones being the i3-style Cartesian-XZ-head and the CoreXY printers.
And for another type of FDM printing, belt 3D printers offer continuous 3D printing in the sense that the build platform moves like a conveyor belt in a production line. This allows for uncommonly long parts to be produced or multiple parts being spammed continuously.
How It Compares
FDM offers several advantages over other 3D printing methods, but it also has downsides. Let’s list its pros and cons regarding print performance and overall part quality compared to other popular 3D printing techniques.
Print Performance
Pros
Scalability is one of the most significant advantages of FDM 3D printing. Unlike resin 3D printers, FDM printers can be easily scaled to any size because the only constraint is the movement of each gantry.
One of the more obvious benefits of having an easily-scalable design is the cost-to-size ratio. Due to low part costs and the simple designs involved, FDM printers are continually being made bigger and less expensive.
Speaking of cost, regular FDM filaments are by far the cheapest 3D printing material, especially when compared to other 3D printing methods, such as resin-based printing.
Another advantage regarding materials is flexibility. On any FDM printer, a wide variety of thermoplastic materials and exotic filaments can be printed with relatively few upgrades and modifications, and this cannot be said of other styles where the material must be, for example, a resin.
Finally, the overall experience with FDM printing is more straightforward than resin-based printing. With FDM, there’s no extra cleaning step other than (sometimes) removing supports, as opposed to the mandatory washing and rinsing, support removal, and curing for resin prints.
With FDM, once the printing process is done, the parts are ready to go, with post-processing steps being dependent on the material, printing characteristics, and intended use. Given the versatility of FDM 3D printing, models can pop off the print bed in multiple colors, whereas other productions, like resin prints, will necessitate painting.
Cons
FDM 3D printing, however, is not without its shortcomings. Due to the simplicity and overall cost of its components, FDM printers often require a lot of tweaking and adjusting (namely bed leveling) to reach the level of reliability and quality of other printing methods.
In contrast to resin, FDM relies heavily on physical movement. Because of this, in addition to calibration, many FDM printer components require regular maintenance and attention: belt tension, extruder cleaning, rail lubrication, and even part replacement like hot end nozzles.
Lastly, FDM printing is highly dependent on feedstock material quality. Poor dimensional accuracy in a filament can lead to several extrusion issues, and the chemical composition of the plastics can also make the printing process problematic. In addition, filament spools must be stored appropriately to avoid humidity absorption – which also affects the printing process.
Print Quality
This is a hot topic, as many consider print quality the Achilles heel of FDM 3D printing. While this claim is not unfounded, there are different perspectives to be considered here.
Pros
Print quality is not only about the looks. The mechanical performance also counts here, and FDM offers a great value for producing strong and durable functional parts, especially when compared to fragile resin 3D prints.
FDM 3D printing is also very versatile because the print quality can be sacrificed in favor of speed and even sturdiness, making it an excellent tool for producing both pleasing aesthetic parts and more functional, tough ones.
Having said that, with proper calibration and slicer setting adjustments, FDM 3D printers can achieve a level of print quality that’s amazing considering the cost of the machine and the filament, even when compared to some resin 3D printers. And given the continuous development and open-source nature of the field, with upgrades like input shaping from Klipper or Marlin firmware, aesthetics won’t necessarily be affected by higher speeds.
Though already mentioned, the flexibility and availability of different FDM materials also play an important role here. A single FDM 3D printer can produce parts with entirely different properties and appearances just by changing the type of filament (as we’ll see next).
Cons
Still, if overall aesthetics and surface finish quality is required, FDM can be troublesome. Since the material is extruded in layers with a specific predefined thickness, detailed prints are hard to achieve and often require post-processing to acquire a professional, finished look. Depending on the material, what’s needed might be straightforward sanding or a more involved process, like vapor smoothing.
Small-scale parts are sometimes impossible to be printed with FDM, too. Since the standard nozzle size is 0.4 mm, any finer detail would require a nozzle replacement (down to 0.2 mm), and even so, it simply can’t beat the precision and crispness of resin-based 3D printing.
Another downside of FDM printing is that they create an inherent weak point in the print where each layer is joined. One can argue that this is true for any 3D printing process. While that’s true, this condition is worse for FDM 3D printing, as the bonding strength between layers is lower.
Filament
Throughout this article, we’ve mentioned the feedstock material for FDM 3D printing, which is known by many simply as filament. And that’s precisely what it is: a long strand of polymer-based material rolled up in a spool.
By convention, the diameter of the filament strand is either 1.75 or 2.85 mm, and that’s dependent on the extrusion assembly of the 3D printer. It’s worth noting that a 1.75-mm extruder will only take this filament size.
The most common filaments for FDM are PLA, PETG, and ABS – in this particular order. PLA is perhaps the easiest material to 3D print with FDM, and it’s also biodegradable and odor-free. Its downside is its low heat resistance, softening with temperatures as low as 60 °C.
PETG, on the other hand, offers much better temperature resistance but can be a bit more troublesome to 3D print, as it’s very prone to oozing and stringing. ABS takes the lead in mechanical properties, although it can be tough to 3D print without a printer enclosure. ABS is known to release toxic fumes during the printing process, which is also why an enclosure is needed.
With all that said, the experience with each of these materials may differ with each particular user, equipment, and especially with the filament manufacturer.
As mentioned, one big advantage of FDM 3D printing is the flexibility of materials and its availability in the market. There’s a massive availability of exotic and odd materials, such as metallic-infused filaments, carbon-fiber plastics, glow-in-the-dark materials, and even rubber-like thermoplastics like TPU.
Printer Options
If you feel FDM is a good fit for you or you’re entirely new to 3D printing, maybe it’s time to consider getting a machine to call your own. Let’s assume you’re in the market for a printer: where to start?
The first thing to consider is why you need a 3D printer. Do you want to join the maker movement, learn more about this technology, or use it in some commercial or professional way?
The second thing to think about is what kind of parts you’ll be 3D printing. Are you thinking of decorative, fun-looking parts? Or do you need a printer that can handle high-performance materials for functional parts?
Popular Options
If you’re a beginner or looking for a cheap yet very decent FDM 3D printer, the Ender 3 Series should serve you well. They’re relatively simple and extremely popular, so you’ll be able to find plenty of tutorials and guides.
In case you’re a little more serious about your 3D printing ambitions and have a larger budget, you should definitely take a look at Prusa’s MK4, which has great print performance, automatic bed leveling, and other minor quality of life flourishes.
For users who will be 3D printing professionally or need a new machine for their shop, the UltiMaker S3 will provide great reliability and versatility. It can do nozzle temperatures up to 280 °C and has a closed chamber, both of which allow for a great diversity of materials to be 3D printed. It also supports dual extrusion printing.
Regardless of your goals or budget, there’s definitely a machine that is just right for you. Welcome to the FDM printing world!
License: The text of "What Is FDM 3D Printing? – Simply Explained" by All3DP is licensed under a Creative Commons Attribution 4.0 International License.