FDM (fused deposition modelling) or FFF (fused filament fabrication) is one of the most common types of 3D printers.
Fig 1: A Prusa i3 MK3S+ printing a Benchy with PLA.
This class of printers melts a thermoplastic by pushing a strand of plastic through a heated metal die. This die is moved in 3D space by a mechanical motion system, often composed of metal shafts, belts, rods, stepper motors, and a microcontroller. The plastic is deposited one layer at a time, building on the previous layer. On the first layer, the plastic is squished onto the print “bed”, where the aim is to keep it stuck onto it for the duration of the print. This bed configuration will vary between each material’s properties, but the most common ones are glass, steel, tape, and a rough plastic.
FDM printers stack plastic on top of each other to create a 3D model. This method is closer to 2.5D, as the printer stacks 2D cross-sections of the model and doesn’t actually deposit material in the Z axis continuously (though some experimental printers do!).
Check out this video for a (very) visual explanation of how FDM printers work.
Here is another video by a very good 3D printing youtuber.
Fig 2: Another shot of a Prusa i3 MK3S+ in its default colours.
Printhead
This part usually contains the assembly for the plastic melting components of the printer. On some printers, the motor that pushes the plastic into the “hotend” (the melting part) is off to the side and is fed through a tube (as with the Ender 3 and Ultimaker printers) resulting in a lighter printhead but a longer travel path. Another configuration is to have the motor right above the hotend, making for a shorter travel path but a heavier printhead.
Hotend
As mentioned previously, the hotend is where the plastic being pushed through is melted. This consists of a few parts:
Fig 3: A cross section view of a PTFE hotend
The filament is fed through a PTFE tube from the top, where it first passes through the Heat Break, surrounded by the Heat Sink. This section ensures that the filament does not melt prematurely, which would cause a blockage. It then passes into the Heat Block, which heats the plastic to a temperature where it could be extruded through the Nozzle. The filament is forced through a very small hole, typically 0.4mm in diametre from its original size of 1.75mm.
In Fig 3. the PTFE tube can be seen going all the way to the nozzle. PTFE (or Teflon) can handle temperatures of up to 250C before it starts to burn. Another style of hotend is an “all-metal hotend” where the PTFE tube stops in the heatbreak. These are typically slightly more expensive than a “PTFE hotend”.
X axis
Fig 4: The stepper motor on the left pulls on a timing belt, which is attached to the printhead on the right.
On bed slingers like in Fig 2, the X-axis has its own stepper motor. The stepper motor can actuate a timing belt sprocket accurately, giving the printhead a precise and way to move. On CoreXY systems, the X and Y motors move the printhead together. The printhead moves along precision railings. Prusa printers use hardened steel rods and bushings, Ender 3’s use V-Rollers on aluminum extrusions, while the Voron uses linear rails and carriages.
Print bed, Y axis
Fig 5: The Y axis motor and belt running underneath the printbed.
Similar to the X axis, the Y axis is controlled by a belt and sprocket, driven by a stepper motor. Attached to the Y axis gantry is the heatbed, a component that heats a flat surface to help adhere plastic onto itself during operation.
Z axis
The X gantry (the hardware responsible for moving the X axis and printhead) sits on top of a lead screw, essentially a long threaded rod. A bushing inside the X gantry threads into the rod, so that it can move along the rod whenever the stepper motor spins the leadscrew. The number of Z axis leadscrews may differ between each printer, but these are largley similar except for a few printer brands.
Control Board
Fig 6: The Prusa Control Board
The control board is responsible for taking a file, processing each commands, then converting those commands into signals to control motors and heaters across the printer. Each printer may have their own style of control board, but the function is very similar.
Display and Button Panel
Fig 7: LCD Panel with click wheel and power reset button
Though it varies between each printer, there will be some sort of interface where the user can control the printer. Some printers can also be controlled through the slicer on a tethered computer.