3D Printer: Extruder & Hotend

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 extruder operation is very simple. Drive gear attaches to the motor, idler attaches to the idler arm, a spring pushes the wheel against the teeth and the filament goes in between. Whenever the motor shaft rotates, drive gear should bite into the filament and grab it with its direction. The minimum limit in this operation is failing to grab the filamnet, in this case we need to increase idler wheel pressure against the filament by tightening the spring. The maximum limit is to cut bits of the filament while driving, in this case pressure applied against filament should be decreased.

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.

3D Printer: Basics & Components

Basics of 3D Printers

In this blog, I'll continue writing about the basics of 3D printers & components.

3D printers based on FFF technology will be discussed. RepRap community is the best resource for all design choices which will be discussed in this blog.

Basically, we need a 3-Axis CNC machine with an extra extruder to have a 3D printer.


So, lets do it.



Frame:

We need a frame to hold all axes (X,Y,Z) to be orthogonal to each other & rigid. An extruder (E-Axis) to be added later.

Frames must be rigid & withstand vibrations. Steel, aluminium, acrylic or even wood was used in the reprap community.

One example is a custom designed FFF 3D printer (V-Bot). I used V-Slot aluminum extrusions to assemble the frame which also serves as a linear guide for my motion system using belts, pulleys & V-wheels. Note how the assembled X,Y,Z axes are orthogonal to each other.

V-Bot FFF 3D Printer

Motion:

To have a linear motion, stepper motors are often used in the reprap project. Motion will be transmitted from the motor to a moving carriage using different techniques.

Lead screws, Ball screws & threaded rods are used by attaching the rod to the carriage and the motor. Couplers are used to attach the rod to the motor. By motor rotation, motion will be transmitted to the carriage based on the thread type used.

      Threded Rod                              Lead Screw                       Ball Screw

 Fully Assembled Motion Axis

The other method to transmit motion from motor to a moving carriage is by using timing belts & pulleys. GT2, GT3, MXL are used regularly as a belt.

A pulley is attached to the motor shaft & an idler pulley is fixed at the other end of the axis. The belt will be connected through pulleys to the carriage.

GT2 Pulley               GT2 Belt                     GT2 Idler 

Belt loops around Motor Pulley & Idler

Linear Guides:

Guides are used to direct the carriage movement to one axis direction. It should be stiff & dead straight to guarantee exact straight movement.

Linear bearings (i.e. lm8UU linear bearing) slides into 8mm rod and connected to the moving carriage and fixed to the frame to act as a guide.

Aluminum extrusions (i.e V-Slot) is a linear guide for roller bearings (i.e V-Wheels).

                        V-Slot                                                                      V-Wheel



Machine design & component vary from one to the other to achieve different goals, like speed, rigidity size, ...etc.


Electronics:

Stepper Motor: Wikipedia "A stepper motor or step motor or stepping motor is a brushless DC electric motor that divides a full rotation into a number of equal steps. The motor's position can then be commanded to move and hold at one of these steps without any feedback sensor (an open-loop controller), as long as the motor is carefully sized to the application in respect to torque and speed."

Wikipedia stepper motor operation description:

Animation of a simplified stepper motor (unipolar)
Frame 1: The top electromagnet (1) is turned on, attracting the nearest teeth of the gear-shaped iron rotor. With the teeth aligned to electromagnet 1, they will be slightly offset from right electromagnet (2).
Frame 2: The top electromagnet (1) is turned off, and the right electromagnet (2) is energized, pulling the teeth into alignment with it. This results in a rotation of 3.6° in this example.
Frame 3: The bottom electromagnet (3) is energized; another 3.6° rotation occurs.
Frame 4: The left electromagnet (4) is energized, rotating again by 3.6°. When the top electromagnet (1) is again enabled, the rotor will have rotated by one tooth position; since there are 25 teeth, it will take 100 steps to make a full rotation in this example.


Stepper Motors comes with different sizes NEMA standard or non standard sizes. Geared or non.


Stepper Drivers: are the driver circuits used to control motor stepping speed, direction, power & brake. Famous drivers used are A4988, DRV8825, TMC210 ... etc.

A4988                     DRV8825                  TMC2100

Motherboard: This is the main board that controls the whole printer. Arduino MEGA2560 boards are the most used in the reprap project, however, they are outdated now since the arrival of the smoothieboard & the Duet wifi. The board has many roles to do, therefore it should use appropriate components that helps achieving its goals besides the brain "microcontroller".

We can evaluate motherboards by their capability to run fast motion, drive heated bed, control dual extruders or more, connectivity, price and many more.

MEGA2560 + Ramps 1.4                 Smoothieboard                              Duet



Endstops: endstops are switches used to determine the limit of an axis. Mechanical, Hall Effect, optical switches are all used.

Mechanical Endstop      Hall Effect Endstop         Optical Endstop

Heated Bed: This is used to counteract first layer problems (warping & adhesion) by raising the temperature of the print surface slightly above the glass temperature of the filament used. PCB heated beds, silicone pads, power resistors or whatever source of heat is used. The goal is to have even heat distribution and high energy heat source to raise the bed temperature.

                PCB Heated Bed                       Silicone Pad                     Power Resistors



Bed Surface: Usually, either glass is used for precision levelness or aluminium for better heat conductivity.

Bed Material: This is a material that is applied to the bed surface to ensure better first layer adhesion. Different materials & techniques have been applied in order to find the one solution for all filamnets. Tapes such as Kapton Tape, Blue Tape, PET tape are always used. Glues also played nice with some or hair sprays. Currently, PEI material "Ultem" is one of the best choices that fits most materials. There are some materials like BuildTak, Fleks3D or PRINtTinZ plate ready for printing but I have tried only the BuildTak and had bad results.


Power Supply: DC power supply is used, either LED power supply or computer ATX PSU. I'd say to avoid cheap computer ATX and go for the LED power supply. 12V or 24V whatever the choice, electronics should be able to work with. 250W is what most regular size 3D printers consume.

LED Power Supply                                                                ATX Power Supply

Coolers: Fans are used to cool electronics, motors, hotend & printed part. Not always used & depends on components used & design. Water cooling has been used, but it is a bit overkill for our application.



The de-facto standard in reprap community is the combination:
Aluminuim Frame Prusa I3 style + Threaded rods for frame construction
Double M5 Threaded rod for Z-Axis
GT2 Pulley + Belt + Idler for X & Y axis as motion transmission.
LM8UU Linear bearing guide for X,Y & Z axes.
NEMA17 Motors + Arduino MEGA2560 + RAMPS 1.4 + A4988 Stepper driver + Mechanical Endstops + PCB Bed + 12V Power Supply

This combination gives a 3-axis CNC machine.


Extruder & Hotend are critical choices for 3D printers. That is why the next blog will be dedicated for discussing multiple designs,



Thanks for reading.

Note: My Custom made 3D printer (V-Bot) files will be shared once optimized.

First Blog: Intro To 3D Printing

FFF

(Fused Filament Fabrication)

This is just a basic introduction blog to have an overview of FFF 3D Printing technology developed by Dr. Adrian Bowyer (Special Thanks Doc) & maintained by the RepRap Community. Thanks all.



What is 3D Printing ?

Wikipedia Definition: 3D printing, also known as additive manufacturing (AM), refers to processes used to synthesize a three-dimensional object^[1] in which successive layers of material are formed under computer control to create an object.^[2] Objects can be of almost any shape or geometry and are produced using digital model data from a 3D model or another electronic data source.

Basically, it is the formulation of an existing material into a requested shape by slicing the object into successive layers.

This process uses a 3-axis robot (CNC Machine) commanded to follow specified coordinates (G-Code Commands) while shaping the material into its specified shape to build the 3D object layer by layer (3D file, i.e. .STL File).

Dr. Bowyer presented the 3D printer as a breeding machine that can print itself, which is really a convincing idea, that accelerated the advancements of 3D printing development in consumer market.

there comes the FFF, stands for Fused Filament Fabrication, which uses an extruder head to extrude tiny lines of thermoplastics into a planned path to formulate one layer of the object, and the process repeats for the next layer.

This image shows how the filament is being fed into the extruder then formulated into its shape

So, we have a 3-axis robot that moves in X,Y & Z axes and carry along with it an extruder head. This extruder is being fed by thermoplastic filament to extrude as commanded. That is a 3D Printer ! simple :-)

That is one type & one technology of 3D printers. There are dozens of 3D printing technology & designs, each solves a certain problem or avoid an obstacle.


Note: 3D printer is just a tool to fabricate 3D objects. Keep this in your mind. It is not factory, it is not useful in all scenarios, I have more than 10 3D printers and still make some objects by hand. 3D printers serve a certain purpose that is to fabricate a complex object accurately that is very hard to fabricate by other means. And it is limited in many ways.



In the next blog, I'll write an overview of 3D printers kinematics & components.


Thanks for reading.



CNC Machine: Computer Numerical Controlle Machines
.STL: (Surface Tessellation Language) 3D file formt that describes the surface of an object by meshes
G-Code: command language used to control machines

Adrian Bowyer Page: http://adrianbowyer.com/about.html
RepRap Project: http://reprap.org/