How Fused Deposition Modeling (FDM) Works
The term "3D printing" refers to building up an object additively. This is accomplished using a number of different methods. Fused Deposition Modeling is one type of 3D printing process.
FDM can easily be understood as drawing with a very precise hot glue gun. FDM (rebranded by the open source community as Fused Filament Fabrication, FFF) works by extruding material through a nozzle to print one cross section of an object, then moving up vertically to repeat the process for a new layer. The printer nozzle contains resistive heaters that melt the plastic as it flows through the tip and forms the layers. The extruded plastic then hardens immediately as it bonds to the layer below it. Repeating this process builds up the object one layer at a time. The quality of prints using this technology depends largely on layer height; the thinner the cross sections, the less noticeable they are, and the smoother the printed objects are. The cross section’s resolution, typically ranges between 75 microns (slightly thinner than a sheet of copy paper) and 300 microns. FDM technology is common in desktop 3D printers and less expensive professional printers.
FDM printers are fed by filament, usually rolled on a spool, and are mainly thermoplastics or thermoplastic/organic-material blends. The most common materials used in FDM printers are ABS, PLA, and polycarbonate (PC). PLA has been a clear winner for home 3D printing because of it’s biodegradability, and because it does not give off unpleasant chemical fumes during the printing process. Dissolvable materials such as PVA are used for scaffolding, and exotic blends containing wood and stone as well as filaments with rubbery characteristics are also becoming popular, as suppliers race to develop new materials. Compared to other 3D printing processes, FDM materials are relatively inexpensive, making them ideal for desktop 3D printing. However, professional FDM printers have the ability to extrude more advanced thermoplastics that demonstrate fire retardancy properties.
How it works
The FDM process begins with software that determines how the filament extruder(s) will draw out each layer to build up the model, preparing it for the building process. Printers with two or more print heads can print out multiple colors and/or use scaffolding materials to support the overhanging parts of complex prints. In either case, FDM printers use only one print head at a time, switching between them for multi-material prints.
The actual printing process works by using a motor to feed the filament through a heating element that melts it at a temperature that typically ranges between 170 and 240 degrees celsius, depending on the type of material being used. The filament emerges molten and quickly hardens to bond with the layer below it. The print head and/or the build platform moves in the X-Y (horizontal) plane before moving in the Z-axis (vertically) once each layer is complete. In this way, the object is built one layer at a time from the bottom upwards. The FDM process uses material for two different purposes, building the object and supporting overhangs in order to avoid extruding material into thin air. Keep in mind that, while FDM is a very flexible printing process, it can have trouble printing sharp angles and overhangs. Choosing an efficient orientation for the model on the printing bed can make a big difference.
If the object was printed using support material or rafts, after the printing process is complete, they are snapped off or dissolved in solvent leaving behind the finished object. Post-processing steps can greatly improve the surface quality of even objects printed at low resolutions. Sanding is a common way to reduce or remove the visibly distinct layers of the model. However, sanding prints can be a time consuming process, and it is sometimes impossible to reach every surface on complex shapes. Sanding might not be effective for certain materials. Another option that works well for select plastics such as ABS is an acetone vapor bath. The vapour creates a cloud when heated and smooths the surface of the object, removing evidence of the distinct layers. Acetone baths leave the part with a glossy shine, similar to glazed ceramics.