Fused filament fabrication (FFF), also known as fused deposition modeling (with the trademarked acronym FDM), or filament freeform fabrication, is a 3D printing process that uses a continuous filament of a thermoplastic material. Filament is fed from a large spool through a moving, heated printer extruder head, and is deposited on the growing work. The toolhead, also known as printhead with the heated nozzle is controlled by a computer executing g-code files that are generated by a slicer which generates movements to match a 3D file. In one common design, the toolhead moves in two dimensions to deposit one horizontal plane, or layer, at a time; the work or the print head is then moved vertically by a small amount to begin a new layer. "Fused filament fabrication" was coined by the members of the RepRap project to give an acronym (FFF) that would be legally unconstrained in use.
Fused filament printing has in the 2010s–2020s been the most popular process (by number of machines) for hobbyist-grade 3D printing because of its relatively low cost and ease of use. Other techniques such as photopolymerisation and powder sintering may offer better results, but they are much more costly.
The 3D printer head or 3D printer extruder is a part in material extrusion additive manufacturing responsible for raw material melting or softening and forming it into a continuous profile. A wide variety of filament materials are extruded, including thermoplastics such as acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), polyethylene terephthalate glycol (PETG), polyethylene terephthalate (PET), high-impact polystyrene (HIPS), thermoplastic polyurethane (TPU) and aliphatic polyamides (nylon), and acrylonitrile styrene acrylate (ASA).
History and spread
Fused deposition modeling was developed by S. Scott Crump, co-founder of Stratasys, in 1988.
The patent on FDM technology expired in 2009, so people could use this type of printing without asking or paying Stratasys for the right to do so. Soon after, a large industry of commercial FFF-based 3D printers could flourish. Additionally, there would be a litany of DIY and open-source 3D printer designs popular with amateurs and institutions, including designs produced by RepRap. The expiry of the patent has been credited for enabling a two-orders-of-magnitude price drop since this technology's creation.
As with Chevron's Techron, Stratasys still owns the trademark on the term "FDM," leading to the adoption of the alternative name FFF by RepRap and others.
Process
3D printing, also referred to as additive manufacturing (AM), involves manufacturing a part by depositing material layer by layer. There is a wide array of different AM technologies that can do this, including material extrusion, binder jetting, material jetting and directed energy deposition. These processes have varied types of extruders and extrude different materials to achieve the final product.
Material extrusion
Fused filament fabrication uses material extrusion to print items, where a feedstock material is pushed through an extruder. In most fused filament fabrication 3D printing machines, the feedstock material comes in the form of a filament wound onto a spool.
The 3D printer liquefier is the component predominantly used in this type of printing. Extruders for these printers have a cold end and a hot end. The cold end pulls material from the spool, using gear- or roller-based torque to the material and controlling the feed rate by means of a stepper motor. The cold end pushes feedstock into the hot end. The hot end consists of a heating chamber and a nozzle. The heating chamber hosts the liquefier, which melts the feedstock to transform it into a liquid. It allows the molten material to exit from the small nozzle to form a thin, tacky bead of plastic that will adhere to the material it is laid on. The nozzle will usually have a diameter of between 0.3 mm and 1.0 mm.
Different types of nozzles and heating methods are used depending upon the material to be printed. Brass nozzles are sufficient for soft plastics like PLA, while hardened steel nozzles are needed for more abrasive and tougher materials or plastics with additives (like for example PLA with added wood or carbon fiber). Different types of nozzles have different ways of replacing them. The most common used nozzles are the V6 nozzles made popular by E3D and MK8 nozzles, which both have standard M6×1 metric threads. Changing the nozzle must be done while hot, to avoid plastic leaks.
Variants of the process
Hot extrusion of rods - In these types of 3d printing machines, the feedstock is in form of a rod instead of a filament. Since the rod is thicker than the filament, it can be pushed towards the hot end by means of a piston or rollers, applying a greater force and/or velocity compared to conventional FFF. Cold extrusion of slurries - In these types of 3D printing machines, the feedstock comes in form of a slurry, a paste or a clay—all of which are viscous suspension of solid powder particles in a liquid medium, which is dried after deposition. In this case, the material is generally pushed towards the nozzle by the action of a piston, and the nozzle is not heated. Paste-like materials such as ceramics and chocolate can be extruded using the fused filament process and a specialized paste extruder. Hot extrusion of pellets - In these types of 3d printing machines the feedstock comes in form of pellets, i.e. small granules of thermoplastic material or mixtures of thermoplastic binder with powder fillers. The material is pushed towards the nozzle by the action of a piston or a rotating screw, which are contained by an extrusion barrel. In this case the whole extrusion barrel is heated, along with the nozzle. The adhesion strength of the layers of the parts depend on the printing temperature and other printing parameter.
The nozzle can be moved in both horizontal and vertical directions, and is mounted to a mechanical stage, which can be moved in the xy plane.
As the nozzle is moved over the table in a prescribed geometry, it deposits a thin bead of extruded plastic, called a road which solidifies quickly upon contact with the substrate and/or roads deposited earlier. Solid layers are generated by following a rasterizing motion where the roads are deposited side by side within an enveloping domain boundary.
Stepper motors or servo motors are typically employed to move the extrusion head. The mechanism used is often an X-Y-Z rectilinear design, although other mechanical designs such as deltabot have been employed.
Once a layer is completed, the platform is lowered (or the extruder is raised) in the z direction in order to start the next layer. This process continues until the fabrication of the object is completed.
For successful bonding of the roads in the process, thermal control of the deposited material is necessary. The system can be kept inside a chamber, maintained at a temperature below the melting point of the material being deposited.
Although as a printing technology FFF is very flexible, and it is capable of dealing with small overhangs by the support from lower layers, FFF generally has some restrictions on the slope of the overhang, and cannot produce unsupported stalactites.
Myriad materials are available, such as acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), polycarbonate (PC), polyamide (PA), polystyrene (PS), lignin, rubber, among many others, with different trade-offs between strength and temperature properties. In addition, even the color of a given thermoplastic material may affect the strength of the printed object.
During FFF, the hot molten polymer is exposed to air. Operating the FFF process within an inert gas atmosphere such as nitrogen or argon can significantly increase the layer adhesion and leads to improved mechanical properties of the 3D printed objects. An inert gas is routinely used to prevent oxidation during selective laser sintering.
Physics of the process
During extrusion the thermoplastic filament is introduced by mechanical pressure from rollers, into the liquefier (or hotend), where it melts and is then extruded. Flow geometry of the extruder, heating method and the melt flow behavior of a non-Newtonian fluid are of main consideration in the part. The rollers are the only drive mechanism in the material delivery system, therefore filament is under tensile stress upstream to the roller and under compression at the downstream side acting as a plunger. Therefore, compressive stress is the driving force behind the extrusion process.
The force required to extrude the melt must be sufficient to overcome the pressure drop across the system, which strictly depends on the viscous properties of the melted material and the flow geometry of the liquefier and nozzle. The melted material is subjected to shear deformation during the flow. Shear thinning behavior is observed in most of the materials used in this type of 3-D printing. This is modeled using power law for generalized Newtonian fluids.
The temperature is regulated by heat input from electrical coil heaters. The system continuously adjusts the power supplied to the coils according to the temperature difference between the desired value and the value detected by the thermocouple, forming a negative feedback loop. This is similar to ambient heating of a room.
Applications
Commercial applications FFF and the other technologies of additive manufacturing by material extrusion (EAM) techniques are commonly used for prototyping and rapid manufacturing. Rapid prototyping facilitates iterative testing, and for very short runs, rapid manufacturing can be a relatively inexpensive alternative. EAM is also used in prototyping scaffolds for medical tissue engineering applications. Moreover, EAM with multi extrusion have become very popular to fabricate biomimetic composites. FFF is also applied in manufacturing within other sectors, including aerospace, automotive, construction, electronics, energy, pharmaceuticals, sports, textiles, and toys.
Free applications
There are multiple projects in the open-sourced community aimed at processing post-consumer plastic waste into filament. These involve machines used to shred and extrude the plastic material into filament such as recyclebots.
Several projects and companies are making efforts to develop affordable 3D printers for home desktop use. Much of this work has been driven by and targeted at DIY/enthusiast/early adopter communities, with additional ties to the academic and hacker communities.
RepRap is one of the longest running projects in the desktop category. The RepRap project aims to produce a free and open source hardware (FOSH) 3D printer, whose full specifications are released under the GNU General Public License, and which is capable of replicating itself by printing many of its own (plastic) parts to create more machines. RepRaps have already been shown to be able to print circuit boards and metal parts. Fab@Home is the other opensource hardware project for DIY 3D printers.
Because of the FOSH aims of RepRap, many related projects have used their design for inspiration, creating an ecosystem of related or derivative 3D printers, most of which are also open source designs. The availability of these open source designs means that variants of 3D printers are easy to invent. The quality and complexity of printer designs, however, as well as the quality of kit or finished products, varies greatly from project to project. This rapid development of open source 3D printers is gaining interest in many spheres as it enables hyper-customization and the use of public domain designs to fabricate open source appropriate technology. This technology can also assist initiatives in sustainable development since technologies are easily and economically made from resources available to local communities.
Development