What is Material Extrusion Process?
In 1988 FDM utilizing thermoplastic polymers was commercialized by Scott Crump, a co-founder of Stratasys. This technology now is considered as one of the most widely available and adopted 3D printers worldwide. Noticeably, after the expiration of the patent in 2009, a breakthrough took place in this area that popularized 3D printers for office and home applications.
Despite FDM’s expansion, its applications for manufacturing functional parts are mostly constrained by a limited choice of available materials, low strength, and inconsistency in final products. Prototyping is the broad industrial application of this technology along with biomedical applications.
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Polymer-based AM has recently received more attention from industries, national laboratories, and R&D centers. The reasons for this renaissance include the availability of polymers, flexibility, plasticity, affordability, the large number of companies working with these printers, and advancements in newly improved composite polymers.
The profitability of the polymer-based AM for complex plastic material in small to medium volumes has been proven effective for manufacturing polymers with complex geometry in small batches with the growing list of start-ups and companies employing these technologies, i.e., Voodoo, Shapeways, Makelab, and Fictiv.
Polymers that can be printed with this technology include ABS (acrylonitrile butadiene styrene), investment casting wax, polyamide, and methyl- methacrylate acrylonitrile butadiene styrene, polycarbonate (PC), polyphenylsulfone (PPSF / PPSU), polylactic acid (PLA), and several alloys of above-listed polymers. The list has kept growing to include stiff polymers, i.e., PPS and PEEK, and composite polymers with improved material properties capable of fabricating functional parts.
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The availability and flexibility of thermoplastic polymers, ease of operation, affordability, durability, and modulability promote their application. There are many 3D printers in the market capable of printing various polymers without requiring changes other than in settings and in some cases a nozzle and hot-end. Considering these merits, polymeric 3D printing is gaining ground and growing exponentially worldwide.
Fused Deposition Modeling (FDM)
Desktop 3D printers are salient examples of this type of printer, known as Fused Deposition Modeling (FDM), Fused Filament Fabrication (FFF), or Fused Granular Fabrication (FGF).
Figure 9 shows FDM printers, in which the filament is heated, melted, and extruded through the nozzle that follows the cross-section of the part. The method is similar to other AM technology in terms of the slicing of the part horizontally and depositing sequentially. Its affordability makes it one of the most approachable technologies. FDM has established itself as an indispensable part of prototyping in various industries, and it can be expected to proceed toward manufacturing functional parts shortly.
Fused Deposition Modeling (FDM) technology for manufacturing polymeric parts. The system consists of multiple or single extruders, building platform, firmament feeders, and filaments spools or cartridges
FDM 3D printers consist of three main parts. The first one is a set of extruder heads that heat up the filament or polymer pellets to melting point and push them through nozzles that can be fixed in z-direction and moves in X-Y like a gantry crane or that can be fixed in the X-Y plane and move in the Z direction. The second part is a platform on which the object is built. Based on the available technologies, the platform also can be at a fixed height with X-Y mobility or be fixed in the X-Y plane and move upward or downward. The last part is the firmware and software that accurately sends commands and controls the movement of the heads, the extrusions, temperatures, platform, the enclosure environments if needed, and almost every aspect of the functionality of the printers
Fig. 2. Schematic drawing demonstrates the different part of FDM 3D printers (image from manufacturingguide.com )
In both fixed platform and moving platform, the strategy of the deposition is similar: the cross-section of the components in the X-Y plane is scanned, either by moving the head or platform, while the material is being extruded as needed through the nozzle. These hot and melted polymers join to the previously laid material and coalescence to make solid parts through wetting, welding, healing, and molecular diffusion.
Before starting the printing processes, a slicing software is used for first slicing a solid file, usually STL, into many layers based on printer resolution and rendering the location, motions, feed rate, and other required conditions of the 3D-printed component into understandable code for the machine. The most broadly acceptable machine code is G-code. Although some printers have specially developed codes that are specifically designed for their own printer, the G-code is accepted widely in the FDM 3D printers community.
Vid. 1. In-situ thermography of a 3D printed part with FDM (courtesy of K. Pooladvand)
When the whole section is scanned, and the material is deposited, the platform moves down or the hot-end moves up equal to the thickness of the next layer, and the process repeats until the part is scanned entirely while shaping gradually inside the machine.
The first layer deposited on the heated-bed usually consists of a larger area, which is called a “raft.” This first layer is better and more amenable for the subsequent layers than the smooth glass or metal surface of the bed. It gives better confidence in the quality of the adhesion and guarantees the part is kept attached to the heated-bed during manufacturing. In a large FDM machine, instead of relying on the adhesion between the raft and first layer, vacuum or suction is utilized to satisfy the adhesion requirements.
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To improve quality and to print over-hanged structures, usually a chemically or water-soluble filament is used on a second extruder and is later removed. An effort has been made to manufacture multi-extruder and industrial versions with huge build volumes to manufacture car bodies or objects of similar size.
Additionally, FDM has been used for processing ceramic and metal as well and directly or indirectly demonstrated its application in manufacturing final industrial parts. The technology is flexible, and affordable and keeps increasing its popularity among non-expert consumers. However, several improvements in different directions have to be accomplished for FDM 3D printers to become a reliable method of manufacturing final products. These improvements include but not limited to:
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mechanical properties and strength of products;
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surface finished;
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integrity and consistency of products;
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dimensional discrepancy and tolerances;
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toughness and strength of available materials;
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control over the printer parameters to reduce potential defects;
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new materials.
More information
FDM/FFF Material properties
FDM/FFF Printers' properties
FDM/FFF DoE (Design of Experiment)
FDM/FFF Process Parameters