Extruder & Hotend
Q: What makes CNC machine a 3D printer ?
A: Extruder & Hotend
The Extruder is the core component of the FFF technology used in 3D printing. It has one job to do, extruding filament as commanded. Extruder usually comes bundled with a hotend which do the melting part of the extruding process, while, the extruder does the feeding part of filament to the hotend.
An extruder usually consists of:
Extruder Body: Attaches to the motor and provides mounting solution
Drive Gear: a Gear with teeth to bite & grab into the filamemt
Idler Gear: usually a wheel pressed hardly against the filament
Idler Arm: Carries the idler wheel to provide adjustable wheel tightening.
The drive gear is very important because it is the responsible element for driving the filament. There are many different designs of driving gears differs in tooth profiles, sizes, material & profile width.
Here is a very useful post of testing different drive gears.
https://airtripper.com/1676/3d-printer-extruder-filament-drive-gear-review-benchmark/
Another important part is the Idler wheel. Its simply a roller wheel used to apply constant pressure against the filament. Spring is used to apply adjustable pressure and maintain it due to filament width variation.
Now, we have a working extruder that can feed filament. We need to come up with a way to melt our filament. Here comes the hotend.
Hotend consists of:
Nozzle: The final tip which squirts molten filament.
Heating Block: Acts as a heat tank to hold temperature
Heating Element: Heat source
Sensing Element: Temperature sensor
Heat Break: Breaks heat to prevent heat migration up our hotend
Heat Sink: Sink heat to create a cold zone
Cooling Fan: Cooling the sink to dissipate heat
An example of a full hotend component is the next pic:
The basic objective of the hotend is to melt the incoming filament. Thermodynamics governs the whole process of melting and squirting thermoplastics. Hotend design should heavily rely on thermo analysis to decide all playing factors in the process. Basically we need heat to melt thermoplastics (the amount of heat & the temperature is dependent on used filament) & this heat should be maintained, constrained and conducted to the filament evenly at the right spot.
Heat block acts as a tank to our thermal energy, its size decides its thermal mass, its material decides its thermal conductivity and also it should holds all other components together mechanically. Its place also defines where the hot zone is.
The nozzle will be threaded to the heat block (i.e. M6 thread) and have a good internal geometry design to cancel as much back pressure as it can, and provide a small hole to squirt melted plastics (i.e 0.4mm) which defines printing resolution.
Heat break is very critical to hotend design. It should break thermal transfer upwards while conducting it to filament, the choice between heat insulators (i.e. PTFE as heat break) & poor heat conductors (i.e. Stainless Steel) is both have been considered & widely used.
Heat sinks tries hardly to sink heat in order to create a cold zone to prevent filament from melting too early inside the hotend. Fans are used to direct air over heat sink fins for better cooling. Heat conducting materials are used for best heat sinking (i.e. Aluminium)
That is the hotend ! Very complex indeed.
Capturing energy and preventing it from migrating except in one direction
What else is there ?!
Extruder can be geared to have more torque for pushing filament.
Extruder can also be bowden by inserting a tube (preferably teflon tube) between the extruder & hotend to take the extruder weight out from the moving carriage leaving a light weight hotend only.
Extras:
Titan extruder comes with more torque to push filaments by using gear reduction of 3:1 ratio
http://e3d-online.com/Titan-Extruder
Flexion extruder comes with a self cleaning drive
https://flexionextruder.com/Flex3Drive mix both bowden & direct extruders into one
https://flex3drive.com/flex3drive/
hotend is a critical component, quality parts are preferred here. Many different designs exists. nearly all of them gets the job done. just be careful to the limits.
Some can only goes up to 250'C due to teflon inside (not Full Metal Hotend)
Most are limited to their sensing element (thermistor) up to 270'C (can be easily upgraded)
Some may be limited by their power resistor wattage, can't heat up enough to 300'C (Maybe more:-) )
Nozzles should also be able to squirt incoming filament without being damaged especially when using filled filaments (filled with copper, bronze, stainless steel, Carbon Fibre ... etc). Hardened nozzles or steel nozzles should be used to avoid nozzle wear out or at l,east extend its life.
* I backed a Tungesten nozzle from DDD through kickstarter. It should come in handy one day.
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Now, we are done with all 3D printer components. We can jump next to software side.
Next blog will be about software chain & workflow.
Thanks for reading.
