Fused filament fabrication

Fused deposition modeling was developed by S. Scott Crump, co-founder of Stratasys, in 1988. 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. 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. Recently a German company demonstrated for the first time the technical possibility of processing granular PEEK into filament form and 3D printing parts from the filament material using FFF technology. 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 Model 2 (2009) 3D printer during Mozilla Maker party, Bangalore AW3D v.4 (Prusa) 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. 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 now costing less than . 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 FFF 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 FFF machine, whereas the same object would cost almost $1.00 if created with resin. Materials Plastic is the most common material for 3d printing via FFF and other EAM variants. Various polymers may be used, including acrylonitrile butadiene styrene (ABS), polycarbonate (PC), polylactic acid (PLA), high-density polyethylene (HDPE), PC/ABS, polyethylene terephthalate (PETG), polyphenylsulfone (PPSU) and high impact polystyrene (HIPS). In general, the polymer is in the form of a filament fabricated from virgin resins. Additionally, fluoropolymers such as PTFE tubing are used in the process due to the material's ability to withstand high temperatures. This ability is especially useful in transferring filaments. 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 FFF; • 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. == 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. Stepper motors drive the movement through either leadscrews or toothed belt drives. It is common, owing to the differences in movement speed, to use toothed belts for the X, Y drives and a leadscrew for Z. Some machines also have X axis movement on the gantry, but move the bed (and print job) for Y. As, unlike laser cutters, head movement speeds are low, stepper motors are universally used and there is no need to use servomotors instead. 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, especially commercial machines such as the Bambu X1, Ultimaker S Series and Creality K2, 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: 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. == Ambient temperature ==

Most printers are designed to function optimally at room temperature (approximately 18–25 °C) and preferably with as low humidity as possible, and during printing it is important that the temperature and humidity remain stable and that drafts are avoided to prevent the plastic from warping. Some plastics require a heated chamber. For example, PLA should be printed at room temperature (18-25 celsius), while ABS should have a consistent chamber temperature of around 60-70 celsius. If the printer is to be placed in a chamber, it is important that the printer is designed for such use, for example by having electronics with active cooling, to reduce the risk of fire. == Health ==

Filament printers may have negative effects on health and safety due to dust and harmful emissions, but little research has been published. 3D printers have become popular in businesses, educational institutions 3D printers emit ultrafine particles (in the order of magnitude 1 to 100 nanometers), and research has shown that these are small enough to lodge deep in the respiratory system and be difficult for the body to get rid of. for example by vacuuming more often. Some people place the printer in a cabinet with an exhaust fan through a HEPA filter or activated carbon, but these filters do not remove all particles and exhaust gases. Exhaust to the outdoor air may be beneficial. Lower temperatures in the hotend can produce less emissions, but can also result in poorer print quality. One can choose materials that are less harmful, for example PLA has a reputation for being safer than ABS (but still emits harmful substances). ==See also==