There is no single way to perform 3D printing. There are currently seven standard manufacturing processes recognized by the American Society for Testing and Materials (ASTM) . All of these processes are additive in nature and differ only in the way the layers are arranged. Efforts are being made to innovate new processes beyond additive types, but currently only additive manufacturing processes are applicable to 3D printing. Let's see how the material extrusion process implements 3D printing.
Material Extrusion
Extrusion is a term used to designate a process of creating objects with a fixed cross-sectional profile. In the context of 3D printing, the term “Extrusion” has a more specific meaning and refers to the involvement of a “Hot End” and a “Cold End” in the process. Material extrusion is the most commonly used 3D printing process. Fused Deposition Modeling (FDM) is the most popular material extrusion process, in addition to its open source equivalent Fused Filament Manufacturing (FFF) which only differs in the way it is legally unrestricted.
Fused Deposition Modeling (FDM)
S. Scott Crump is the man behind the development of FDM technology. The technology was developed and patented in the 1980s. Later, Crump founded a company – Stratasys in 1988, which trademarked the term “Fused Deposition Modeling”.
Being an extrusion process, FDM involves a hot end and a cold end. The hot end is an extrusion head to which manufacturing material is supplied by unwinding a plastic filament or metal wire from a spool. The wire or filament is fed to the head nozzle on a worm screw at a controlled rate. As the filament or wire enters the extrusion nozzle, it is heated beyond the glass transition temperature and melts.
When the molten filament or wire leaves the extrusion nozzle exposed to air or an inert gas chamber, it immediately solidifies on a base or on a previous layer. The use of inert gas chambers is on the rise, as it improves the adhesion of layers due to the prevention of oxidation and improves the mechanical characteristics of the created object.
The extrusion nozzle is movable horizontally and/or vertically while the base platform can move along the remaining third plane. The vertical and/or horizontal movement of the nozzle is controlled by a numerical mechanism while its movement along the third plane is determined by a tool path according to computer-aided manufacturing (CAM) software. The nozzle moves from bottom to top, finishing the deposition of each layer, one after the other, or remains stationary in relation to the moving platform. The movement of the nozzle is ultimately rectilinear in an XYZ plane guided by stepper motors. With recent innovations, the deltabot has been successfully tested to move the nozzle end.
Normally in FDM, models are built using several types of thermoplastics and their support structures are generated simultaneously. Support structures are necessary to keep the model in a fixed orientation during the process. The materials used to create support structures are respective soluble materials. There are two types of thermoplastics that are commonly used in FDM – Acrylonitrile Butadiene Styrene (ABS) and Polylactic Acid (PLA). Various other polymers such as polyamide (PA), lignin, polycarbonate (PC), polystyrene (PS), rubber, etc. and some conductive materials are also used.
Fused Filament Manufacturing (FFF)
Fused Filament Fabrication is a term coined by the RepRap project, which is an open source project for developing low-cost and affordable desktop 3D printers. This community-driven project provides free and open source hardware (FOSH) 3D printers. It is the result of successful attempts by the RepRap project that 3D printers that cost no less than $20,000 can now be assembled at an affordable price of $1,000 or less.
The process of manufacturing fused filaments is almost similar to that of fused deposition modeling, except that the terms used to recognize various parts of the 3D printer and the names of the process specifications are different. The extrusion assembly where the feed is melted is referred to as the “Liquefier” and the layer paths deposited are called “Roads”. In most FFF printers, the thermal environment of the chamber is specifically maintained at a temperature only slightly lower than the glass transition temperature of the material.
FFF printers come with several options regarding the mechanical assembly of the extruder. Some of the common mechanical arrangements of extruders in FFF 3D printers are –
Cartesian-XY: The movement of the Liquefier and nozzle is linked to the XY axis and the platform on which the model is built descends (Z axis) as a successfully rasterized layer in the XY plane. The first 3D printer from RepRap – Darwin has the Cartesian-XY type.
Cartesian-XZ: In this configuration, the extruder head moves along the X and Z axis while the platform can move left and right along the Y axis. This way, the platform can support more load. The Mendel is the first Cartesian-XZ type 3D printer from the RepRap project and was built on Arduino. Other popular Cartesian-XZ FFF printers are the RepRap Guru DIY Prusa I3 3D Printer and the Original Prusa i3 3D Printer.
Delta: This is also a Cartesian configuration, but the extruder head is supported by three arms suspended in a triangular configuration. This type of layout allows for greater precision and faster printing. Some affordable Delta 3D printers are Afinibot Micro Delta Kit, Folger Tech Kossel Auto Leveling Delta 3D Printer Kit, He 3D – Mega Delta 3D Printer Kit, Rostock MAX v3 etc.
XY Core: This Cartesian-type extruder head arrangement is an improvement on the traditional XY configuration. Instead of sequential movement in the XY axis, the CoreXY arrangement allows the head to move by a combined effect of x and y coordinates that are manipulated by a parallel system. Some examples of CoreXY 3D printers are RepRap-XY from “jand”, C-bot, AluXY from “Zelogik”, Vulcanus, AXIOM 20 Direct Drive, VSlot-CoreXY and Voron.
SCARA: SCARA is an abbreviation for Selective Compliant Assembly/Articulated Robot Arm. The extruder head moves in Cartesian style in all axes (X, Y and Z)
Cartesian-style FFF printers have three or four stepper motors to move the head in the X, Y, and Z axes, while the Polar printer has only two stepper motors mounted.
Vat photopolymerization is another standard 3D printing process recognized by ASTM. Learn more about Vat Photopolymerization here.
