Fused filament fabrication
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.[1] Filament is fed from a large spool through a moving, heated printer extruder head, and is deposited on the growing work. The print head is moved under computer control to define the printed shape. Usually the head 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. The speed of the extruder head may also be controlled to stop and start deposition and form an interrupted plane without stringing or dribbling between sections. "Fused filament fabrication" was coined by the members of the RepRap project to give an acronym (FFF) that would be legally unconstrained in its use.[2]
Fused filament printing is now the most popular process (by number of machines) for hobbyist-grade 3D printing.[3] 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),[4] polylactic acid (PLA), polyethylene terephthalate glycol (PETG), polyethylene terephthalate (PET), high-impact polystyrene (HIPS), thermoplastic polyurethane (TPU) and aliphatic polyamides (nylon).[5]
History
Fused deposition modeling was developed by
Process
This section is missing information about post-processing (solvent smoothing, annealing/remelting, etc.).(December 2020) |
3D printing, also referred to as
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.[14]
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. Changing the nozzle[15] 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.[16]
- 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.[17][18]
- 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[19] or mixtures of thermoplastic binder with powder fillers.[20] 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.
Printing
FFF begins with a software process which processes an STL file, orienting the model for the build process and mathematically slicing the model according to the processing parameters selected. If required, support structures may be generated.[21]
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.[22] Solid layers are generated by following a rasterizing motion where the roads are deposited side by side within an enveloping domain boundary.
Once a layer is completed, the platform is lowered 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
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.[25] 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.[26] EAM is also used in prototyping scaffolds for medical tissue engineering applications.[27] Moreover, EAM with multi extrusion have become very popular to fabricate biomimetic composites.[28] FFF is also applied in manufacturing within other sectors, including aerospace, automotive, construction, electronics, energy, pharmaceuticals, sports, textiles, and toys.[29]
Free applications
There are multiple projects in the open-sourced community aimed at processing post-consumer
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
Because of the FOSH aims of
Development
Customer-driven product customization and demand for cost and time savings have increased interest in agility of manufacturing process. This has led to improvements in rapid prototyping technologies.[37] The development of extruders is going rapidly because of the open source 3-D printer movement caused by products like RepRap. E3D and BondTech are the most known extruder manufacturers currently on the market. Consistent improvements are seen in the form of increased heating temperature of liquefiers, better control and precision of prints, and improved support for a wide variety of materials. Besides the improved hardware, the ability to calibrate the extruder[38] according to the hardware setup has come a long way.
Cost of 3D printer
The cost of 3D printers has decreased dramatically since about 2010, with machines that used to cost US$20,000 now costing less than US$1,000.[39] For instance, as of 2017, several companies and individuals are selling parts to build various RepRap designs, with prices starting at about £99 / US$100.[40]
The open source Fab@Home project[41] has developed printers for general use with anything that can be extruded through a nozzle, from chocolate to silicone sealant and chemical reactants. Printers following the project's designs have been available from suppliers in kits or in pre-assembled form since 2012 at prices in the US$2,000 range.
The
As of September 2018 RepRap style printers are readily available in kit form through online retailers. These kits come complete with all parts needed to make a functioning printer, often including electronic files for test printing as well as a small quantity of PLA filament.
Filaments used for printing with FDM printers are also substantially more cost-effective than their SLA resin counterparts. If we use 3DBenchy as a benchmark for comparing both technologies, it would cost roughly $0.20 to print such a model with an FDM machine, whereas the same object would cost almost $1.00 if created with resin.[43]
Materials
Plastic is the most common material for 3d printing via FFF and other EAM variants. Various polymers
The many different variants of EAM, i.e. of material Extrusion based Additive Manufacturing allow dealing with many additional material types, summarised in the table below. Several material classes can be extruded and 3d printed:
- Thermoplastic polymers, it is the most typical application of FDM;
- Composite materials with polymeric matrix and short or long hard fibers;
- Ceramic slurries and clays, often used in combination with the robocasting technique;
- Green mixtures of ceramic or metal powders and polymeric binders, used in EAM of metals and ceramics;
- Food pastes;
- Biological pastes, used in bioprinting.
Material class | examples | Post-processing requirements | Typical applications |
---|---|---|---|
Thermoplastic polymers | PEEK, recycled plastics[45]
|
support removal | General purpose. These materials have varying physical properties, such as heat resistance, UV resistance, storage requirements, ease of printing, cost, and chemical tolerance. They are available in a variety of formulations to fine tune them to the specific applications (such as ESD material blends, or the addition of flame retardants).
|
Polymer matrix composites | CFRP[46]
|
support removal, curing | Structural applications |
Ceramic slurries and clays | Alumina, Zirconia, Kaolin[47] | support removal, furnace drying and sintering | Insulation, consumers objects, dental applications |
Green ceramic/binder mixture | Zirconia, Calcium phosphate[48] | support removal, debinding, sintering | structural ceramics, piezoelectric components |
Green metal/binder mixture | support removal, debinding, sintering | Tooling, fixtures, mechanical parts | |
Green metal/ceramic/binder mixture | Stainless steel, Iron, tricalciumphosphate, yttria-stabilized zirconia[49] | support removal, debinding, sintering | Mechanical parts, implants |
Food pastes | chocolate, sugar[50] | support removal | |
Biological materials | bioink[51] | bioprinted organs and scaffolds | |
Conductive polymer composites | Composites with Carbon Black, Graphene, Carbon Nano tubes or Copper Nanoparticles[52] | Annealing for lower conductivity | Sensors |
polymer derived ceramics (PDCs) | poly lactic acid (PLA), polycarbonate (PC), nylon alloys, polypropylene (PP), polyethylene terephthalate glycol (PETG), polyethylene terephthalate (PET), and co-polyesters; and flexible materials including: flexible PLA, thermoplastic elastomer and thermoplastic polyurethane filaments | To make SiOC(N) first the printed polymer is dipped in PDC, absorbed then sintered[53] | heat exchangers, heat sinks, scaffoldings for bone tissue growth, chemical/ gas filters and custom scientific hardware |
Print head kinematics
The majority of fused filament printers follow the same basic design. A flat bed is used as the starting point for the print workpiece. A gantry above this carries the moving print head. The gantry design is optimized for movement mostly in the horizontal X & Y directions, with a slow climb in the Z direction as the piece is printed.
Many printers, originally those influenced by the RepRap project, make extensive use of 3D printed components in their own construction. These are typically printed connector blocks with a variety of angled holes, joined by cheap steel threaded rod. This makes a construction that is cheap and easy to assemble, easily allows non-perpendicular framing joints, but does require access to a 3D printer. The notion of 'bootstrapping' 3D printers like this has been something of a dogmatic theme within the RepRap designs. The lack of stiffness in the rod also requires either triangulation, or gives the risk of a gantry structure that flexes and vibrates in service, reducing print quality.
Many machines[specify] now use box-like semi-enclosed frames of either laser-cut plywood, plastic, pressed steel sheet and more recently aluminum extrusions. These are cheap, rigid and can also be used as the basis for an enclosed print volume, allowing temperature control within it to control warping of the print job.
A handful of machines use polar coordinates instead, usually machines optimized to print objects with circular symmetry. These have a radial gantry movement and a rotating bed. Although there are some potential mechanical advantages to this design for printing hollow cylinders, their different geometry and the resulting non-mainstream approach to print planning still keeps them from being popular as yet. Although it is an easy task for a robot's motion planning to convert from Cartesian to polar coordinates, gaining any advantage from this design also requires the print slicing algorithms to be aware of the rotational symmetry from the outset.
Extruder mount to rest of machine
The ways extruders are mounted on the rest of the machine have evolved over time into informal mounting standards. Such factor standards allow new extruder designs to be tested on existing printer frames, and new printer frame designs to use existing extruders. These informal standards include:[14]
Delta robot printers
A different approach is taken with 'Rostock' or 'Kossel' pattern printers, based on a delta robot mechanism.[54][55] These have a large open print volume with a three-armed delta robot mounted at the top. This design of robot is noted for its low inertia and ability for fast movement over a large volume. Stability and freedom from vibration when moving a heavy print head on the end of spindly arms is a technical challenge though. This design has mostly been favored as a means of gaining a large print volume without a large and heavy gantry.
As the print head moves the distance of its filament from storage coil to head also changes, the tension created on the filament is another technical challenge to overcome to avoid affecting the print quality.
See also
- 3D printing
- 3D printer extruder
- Ball bearing
- Direct metal laser sintering
- Fab lab
- Fab@Home
- G-code
- Hyrel 3D
- MakerBot Industries
- Marlin (firmware)
- Methacrylate
- Plastics extrusion
- Printrbot
- Prusa i3
- RAMPS
- Rapid prototyping
- RepRap Project
- Robo 3D
- Selective laser sintering
- Sindoh
- Spindle
- Stepper motor
- Stereolithography
- Thermistor
- Thermocouple
- Ultimaker
- Von Neumann universal constructor
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Further reading
- "Results of Make Magazine's 2015 3D Printer Shootout". Retrieved 1 June 2015.
- "Evaluation Protocol for Make Magazine's 2015 3D Printer Shootout". makezine.com. 2014-11-07. Retrieved 1 June 2015.
- Stephens, Brent; Azimia, Parham; El Orcha, Zeineb; Ramos, Tiffanie (November 2013). "Ultrafine Particle Emissions from Desktop 3D Printers". Atmospheric Environment. 79: 334–339. .
- "How Fused Deposition Modeling Works". THRE3D.com. Archived from the original on February 21, 2014. Retrieved 7 February 2014.
- "3D Printing process and How FDM technology works". homeshop3dprinting.com (Video). Retrieved 4 June 2014.
- "RepRap project's complete list of G-code used by 3D printer's firmware". RepRap.org. Retrieved 26 August 2015.
- "FDM Technology Made Simple". chizel.io. 2018-07-16. Retrieved 10 July 2019.