Extruder: essential part of a 3D Printer
The 3D extruder is the part of the 3D printer that ejects material in liquid or semi-liquid form in order to deposit it in successive layers within the 3D printing volume. In some cases, the extruder serves only to deposit a bonding agent used to solidify a material that is originally in powder form. Let's discover the function of the 3D printer extruder, a little but essential part, required for some additive manufacturing processes
3D extruder depositing plastic filament on a 3D printing platform
The different 3D printing technologies that require an extruder
Found in 3D FDM or FFF printers, the extruder is also required for proper operation of machines using Binder Jetting or Polyjet technologies, and even 3D Systems' CPX machines. These are additive manufacturing machines that need to deposit material before transforming it either by adding a bonding agent to it (Binder Jetting) or by changing the chemical properties (Polyjet and CPX). These technologies are explained in our guide about the different kinds of 3D printing.
The filament extruder on a FDM printer is the part that extrudes the plastic filament in a liquid form and deposits it on a printing platform by adding successive layers. The printing head is made of many distinct parts including a motor to drive the plastic filament and a nozzle (or extruder) to extrude the plastic.
Some 3D FDM / FFF printers are now equipped with two extruders. This enables you, in particular, to print two materials simultaneously in order to obtain 3D prints in two colours. The presence of two extruders also allows support material to be extruded, which can be removed afterward using a solvent.
To regulate the plastic cooling process, some printers are enclosed. This helps maintain a uniform temperature in the manufacturing chamber, ensuring greater consistency in the print result.
The most common kinds of Binder Jetting printers are probably the Projet printers from 3D Systems. These printers have an extruder that projects a bonding agent (or colour) onto a powder material. It's the action of projecting this bonding agent onto successive layers of powder that creates the object.
Polyjet technology, originally developed by Objet (which is now owned by Stratasys), is also based on the projection of resin in the form of droplets onto the printing platform. Once the droplets are projected, UV polymerises the resin.
Direct or Bowden extruder: Which one to choose?
There is not a single extruder type, your choice will depend on the kind of 3D printer that you have, on the materials that you will use, and on the printing speed and accuracy that you need.
There are two different possibilities: Direct or Bowden extruders. The nature of your projects will determine which extruder you need to use. First, all extruders have motors, but there are also geared extruders to control your print speed. It is not essential, but it can help you to customize your setups in order to improve your print quality.
Direct extruders are directly attached to the hot end, while a Bowden extruder (or remote extruder) has a tube to link the hot end and the extruder body. For direct extruders, the gear rotates by a stepper motor driving directly the filament to the extruder hot end. The filament path is shorter, that is why Direct extruders are better to 3D print flexible materials than Bowden extruders You can totally 3D print flexible filament with a Direct extruder, but it is not really convenient.
With Bowden extruders you can 3D print your projects faster. It is easier to accelerate or decelerate because there is just the printing head to move, not the whole extruder hot end.
They both can have a direct drive system. Indeed, for both of them the filament drive mechanism can be mounted to the motor shaft, directly.
Moreover, keep in mind that there are extruders for all filament thickness, for 3mm filament, 1.75mm filament, etc.
Extruder-related problems in 3D printers
The main problems encountered with 3D printer extruders are the same as with inkjet printers, which is poor maintenance or the use of the wrong materials leading to deterioration or fouling the nozzle that projects the material.
In the particular case of 3D FDM printers, the main problem stems from print nozzles that are blocked by hardened plastic unable to leave the extruder or by slack or space in the plastic extrusion axis, causing discontinuous extrusion.