Pellet Extruder for 3D Printing

Pellet Extruder

Pellet 3D Printer

Translated version of the project "Extrusor de Pellets para Impresión 3D"

Project Manager

Maker	Photo	Profile
Bustos Fabian (Project Manager)		English .

Introduction

After some years the FDM 3D printing patents and digital fabrication methods were released, the community started to discuss the fact that this industry is getting stuck, that FDM 3D printing is just a hobbie and a method for rapid protyping but not for serious applications in the serial production of products, due to this comments and bad publicity the members and developers of this project found a new way to change this reality, at this point the majority of 3d printing machines have three major problems to analyze and solve.

The first problem is about printing volume, when thinking about printing large objects the major limit is the cost of the material, if a printing session of a large object uses more than 2 rolls of filament the printing method can be discarded due to the cost and replaced by another techniques, this means that the 3D printing community fell into the consumption culture of inkjet printers for example, where the "brands" make more money by selling expensive cartridges of ink and tonners than by selling the actual paper printers.

The second problem is about printing time, due to the large list of coordinate movements that the machine executes to finish one model, the sum of this small portions of material deposed and time makes this FDM technology unsuitable for serial production or could even be seen as non-rapid prototyping method in some cases, analyzing the posibilities for upgrading a printing head to use a diferent technique of deposition, the solution points to increase the amount of plastic deposed versus time.

The third but not final problem depicted here, is the linearity of the materials, it means that if you have only one roll of white PLA plastic, you can only print white PLA models, if you want to make pieces of another color or if you want to make a model of multiple colors, you have to buy the same amount of rolls of plastic, its a good business model for the companies that release this technology for free to the people, but at the same time there is a huge economic interest which works effectively.

FM3D Pellet Extruder (In Spanish)

Project Colaborators

Maker	Photo	Profile
Duran Miguel (Assembly Assistant)		English .
Sebastian Martinez (Assembly and Translation Assistant )		English .

Problem #1: Printing Volume vs Cost

Looking around the social media, we can see that the majority of 3D printing machines are capable to print inside a volume less than 30 x 30 x 30 cm, it's due to the fact that those small volumes are enough to cover the average consumer necessities, because the system is made in that way, but if a new series of big 3d printers become popular and the materials cheaper?, the users would switch automatically to print big scale projects and the consommation of plastic increases. Curiously if you want to make a model that occupies all the volume of your 3D printer, you have to pay a price of plastic even major to the cost of the machine, it's a sad reality if we think about all the plastic we put into the trash every week.

Problem #2: Speed vs Productivity

After some time of using 3D printers the regular user gets certain experience in the usage of the machines, their materials and ll the possiblities to obtain high quality pieces at the highest speed posible, sometimes not even taking care of the price of the tools or materials, the regular DIY 3D printer works with a printing head (extruder) which depose a thin hot filament on a building platform and draws the model layer by layer, with the mindset of quality the usage of small nozzles and deposing small volumes will always get a good result, but when the project becomes bigger and massive quantities of plastic have to be transformed, at this point the amount of spools of filament, the time that it could take to finish, and the delicate process of changing the filaments one spool after another.

Problem #3: Material Versatility

After this lapse of time the user that uses 3D printing to produce prototypes for engineering, toys or even prosthetic hands, it's easy to find around the work place empty spools of plastic with the hope of be rewinded, a box full of at least 5 kilo of failed prints saved as a treasure waiting the moment to be melted and reused, not to talk about a rainbow collection of plastic spools ready to create fantastic creations, every person who works with a 3D printer will always want to have unlimited posibilities of mixing colors and materials, maybe the necessity of generate complex models of materials with special properties to improve mechanical efficiency or high temp performance.

Extruder Design

To solve the problems cited before we propose the development of a Pellet Extruder Printing Head wich works with granulated plastic, the most valuable improvement over filament extruders is the low price per kilo of plastic, this plastic pellet can be found in 25 kilo packets whose costs are less than price of one roll of regular PLA, the industrial method to produce filament in china factories starts with this small balls of plastic, they put some additives and colorants to modify the properties and color of the final product, this generates some uncertainty about what are we melting on our machines, what kind of fumes they produce and the grade of biodegradability this materials really have, the use of a Pellet Extruder on a 3D printer gives total freedom of using your own colorants to match an specfic tone of color, you can add some well known additives to improve the properties of the final models and even make them stronger mixing some carbon fiber chips or steel powder inside, it's the idea of printing composite materials.

There are already very good Pellet Extruders on the market ready to be installed on any xyz cartesian machine, but there is some different on the extruder we have to create, it's a mechanism that shortens the printing time, the system works with a Variable Width Nozzle, instead of using one fixed diameter hole at the output sharp point, we designed a plane metallic cap with a slit of 1x10mm, inside this slit we can find a moving piece that regulates the material output, the initial strategy to make it work faster than Filament Extruders is about using the small opening to mke the perimeters of the model, at the time of printing the infill it opens at the desired width or depending on the software to increase the printing volume and generate layers faster. The operation principle is the same that an industrial type plastic sheet extruder, but simplified to be installed in a moving shafts system.

A regular FDM 3D printer extruder is static and has a fixed diameter output nozzle, this Pellet Extruder generates a variable laminate which has the ability of rotating 360 degrees in order to adapt the orientation of the laminate to the contour of the models, the details of this process can be found in the [Mechanics] and Electronics section of this document.

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  Pellet Printer front

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  Pellet Printer Back

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  Nozzle´s side

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  Nozzle's top

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  Installed Nozzle

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  Installed Nozzle

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  Closed Nozzle

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  50% Nozzle

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  Opened nozzle

Extruder Mechanics

The action strategy of the printing Tip is that when it is making outer perimeters the nozzle closes to let out a 1x1mm filament, that's how we can make the outer layers with good level of detailing, in the moment of filling the piece it opens up to 10mm wide and performs the work at least 6 times faster than a conventional extruder and when it is executing the displacements it closes completely to avoid unwanted extrusions before reaching the work coordinates.

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  Nozzle close

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  Opening for Perimeter

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  Opening for Filling

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  Opening for Perimeter

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  50% Opening

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  75% Opening

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  100% Opening

Extruder Electronics

Machine Firmware Modification

Due to the changes made on the regular Pellet Extruder hardware a correspondent circuit, firmware and software have to be done to make everything work together and in a synchronized way. Since the output Nozzle of the extruder generates a variable width flat filament and is able to twist 180 degrees to adapt itself to the contour of the trajectories, two additional motors have to be configured in the normal printer electronics system and programmed in the firmware. We use for the prototype printer a universal RAMPS board controlled by an Arduino Mega 2560 board, we keep the XYZE cartesian system connections, a secondary extruder driver is installed on the ramps board to control the Nozzle Amplitude.

Note: This is a functional but not definitive firmware modification, posterior reverse engineering has to be done to put the Arduino Mega in charge of the control of all the motors.

The Nozzle Twist motor is controlled by an external driver and an Arduino Nano receiving a PWM signal from the Arduino Mega 2560 through the pin number 4 (Servo 0 Pin in RAMPS), this signal is the result of the firmware calculation of the resulting angle between two received coordinate displacement commands, this means that when the machine receives a displacement command G0 or G1, the firmware takes the angle between the current and the new destination, filter this result to obtain an angle which is mapped in a output PWM signal, this firmware modification can be seen in the image No.1, where we can take a look inside the file Marlin_Main.cpp where exists a function that is executed every time a linear interpolated movement has to be done, this function called gcode_get_destination() takes the incoming coordinate data and refresh the actual state of the position variables, this positions are executed after by the functions found in the file planner.cpp, the atan2() function fed with the old and new pairs of XY coordinates gives us the resultant angle that the nozzle should have to orient the planar filament according to the form of the model, this output raw angle measurement is converted to a scale from 1 to 254 which are the pwm levels on the pin number 4, the external arduino nano will execute this movement and after is completely positioned will send a signal back to the arduino to continue the printing process.

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  1.Angle Calculation to PWM output

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  Marlin Modification for Angle

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  Model for displacement Analisis

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  Raw Angle Reading

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  Full Resolution Angle Calculation

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  PWM Output for External Angle Controller

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  PWM Output Test (Low level)

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  PWM Output Test (High level)

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  External Microcontroller PWM Capture

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  PWM Capture Circuit

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  Stepper PWM Controller Test

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  Motor Swing Control Test

15/01/2020

Due to the fact that the Marlin firware has been designed to support different models of 3D printers and it makes the code harder to modify, a new firmware is in process of modification to achieve the proper combination of movements along the printing session, Sprinter firmware has the basic routines to control a cartesian 3D printer, it was the most used 3d printed controller for ARDUINO/RAMPS boards until 2013.

in the first image we can appreciate the workflow that the program uses to convert gcode commands into coordinate moves sequentially in a 3D printing session, in the second image we can see the modification necessary to make this new method of extrusion work.

At this point we managed to modify the aperture of the nozzle by sending a custom gcode (M93 Ax) to the machine to modify the output width, the twist angle is actually changing depending of the coordinates received at each displacement command and in multiple combinations.

Actual problem: There is a conflict between the timing of the angle change and the displacement blocks received, the program has uses a set of 4 registers for coordinate displacement that change sequentially, during this process the code process the change in the acceleration and speed between movements, sometimes the machine doesn't stop to let the angle change until the final, the nozzle turns and performs extrusion moves at the same time, wich generates a wrong deposition trajectory.

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  Normal Firmware Workflow

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  Firmware Workflow Modification

16/01/2020

A new internal control "st_synchronize()" function was found in the firmware, wich makes the system wait until all the movements are done before processing a new line of gcode, this gives time to the nozzle to adapt the angle before executing the displacement.

Actual problem: The angle changes and the displacements are done in order only for external perimeters, it's still mixing angular and linear movements during infill operation.

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  Firmware Workflow Modification

17/01/2020

The internal control function "st_synchronize()" was set before the angle positioning function, the linear movements are completely executed before the angle positioning of the next destination gcode line.

TODO: Perform a print test on the machine with all the functionalities developed so far, to analize and correct the deposition sequence and generate the first Slic3r profile.

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  Firmware Workflow Modification

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  Cold Extrusion Test

Assembly Manual

Disclaimer

This is a Technical Tutorial for the construction of an Industrial Grade Device which means that only qualified and experienced personnel could execute and obtain the appropiate result without damage, if you dont feel in the capacity to perform the tasks I show in the following steps, dont worry, just find the appropiate place, the appropiate person and the appropiate tools to get it done, keep in mind that the most important thing is your integrity and security, this is not intended as a manual to harm yourself in the process, be careful with the instructions, try to make this work in a good mood and mind clear of alcohol or any other product that could affect your performance, I dont take any responsibility of the use of this information.

Bill of Materials

Quantity	Article	Detail	Material
1	Water pipe Nipple	1/2"(dia) X 3"(Long) double thread	Iron or Bronze
1	Water pipe cap	1/2"(dia) round	Iron or Bronze
1	Floor Flange Fitting	1/2" thread	Iron or Bronze
1	Auger bit	5/8"(dia) X 3"(Long)	Iron
1	Square structural tube	70mm x 70mm X 70mm (Long)	Iron
1	Nema 23 Stepper Motor	with 1:72 Gearbox	N/A
1	Rigid Coupling	5mmdia to 12mmdia (for bit and motor shafts)	Iron or Aluminium
1	Band Resistive Heater	12v 90Watts 28mm(dia) X 30mm(Long)	N/A
1	Thermistor	EPCOS 100K	N/A
1	Kapton Tape	30mm width	Example
1	Teflon Tape	Industrial grade	PTFE
2	Metal Mesh	Square 10x10cm	Iron or Aluminium

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  Materiales

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  Water pipe

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  Water pipe cap

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  Metal Mesh 10x10cm square

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  Square Structural Tube

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  Floor-flange

Electric Tools	Manual Tools
Multimeter	Slot and Philips Screwdrivers
Drill	Pliers
Drill Bits	Pipe Wrench
1" Saw Cup for Metal	Slim-Jaw Adjustable Wrench
Angle Grinder	Allen Key Set
Soldering Iron	Thread Tap M6

Advice

Before we start, there is something that we have to understand, is the fact that we are dealing with high density thermoplastics, those materials need high temperatures and lots of force to manipulate, it means that all the mechanics we are going to build here will be made out of metal, because of this, hard work with "heavy tools" are needed, the material I've succesfully used is iron due to their ideal heath transfer properties for this project, avoid of use alluminum, if it is a problem for you to find iron parts you can use bronze instead which has been proven to give good result.

Step	Description	Tools needed	Image guide
1	Cut 70mm of structural square tube of 70mm by 70mm, this cube will serve as container and the chassis of the extruder, use security glasses and gloves to protect yourself.	Angle grinder with metal cutting disc.	Angle grinder cut
2	Mark down and drill a 1" hole in the center on one surface and the opposite side, use oil or parafine to lubricate the tool frequently, the Auger bit will cross through this two holes, attached to the motor on the top and inside the nipple pipe at the bottom.	Drill with 1" Cup Saw	Cup Saw Cutting Holes
3	Take the measurement of the distance between the holes of the motor and the floor flange, mark down the and drill the holes with the correspondent screw diameters	Drill and Drill bits	Screw Holes Drilling
4	Attach the floor flange with the screws and auto-lock nuts to join the two parts, be aware of the alignement of the big holes to ensure good rotation of the mechanism in the following steps.	Allen Keys or the tool that correspond the screws	Screws in Place
5	Roll some teflon tape around the threads of the nipple pipe and screw the pipe cap on one side and the reservoir on the another, the tape will avoid plastic leaks that could occurr at high temperature.	Teflon tape and pipe wrench	NIpple Pipe and Cap Assembled
6	Example	Example	Screws in Place

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  scheme of the pieces to assemble

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  Pipe and cap with teflon

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  Floor Flange installed

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  Top View

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  Bottom View

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  Auger Installed

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  Mechanical assembly (Front view)

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  Mechanical assembly (Back View)

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  Mechanical assembly

Installing the electrical system

Install the heating element, the heat sensor and motor wiring, this is connected to the machine's controller board.

Mechanical efficiency test

From the computer, send commands to the controller board to verify the correct movement of the pellets inside of the extruder, verify the speed and strength requirements.

Thermal efficiency test

From the computer, send commands to the controller board to verify the heating element performance and define the optimal temperature to melt the plastic and make it flow through the tube.

Material flow test

Heat the extruder to the work temperature obtained before, and define the motor's speed to produce a continuos string of plastic as fast as possible, maintaining the diameter and the material properties. In this step the lenght and material's retraction time are calculated, to get total control of the extrusion during an impression.

3D Printer integration

A cubic 30x30x30cm Kondoro machine chasis has been modified to fit the extruder inside, the mechanical arrangement of the X and Y axis was made temporarily out of wood and plastic ties meanwhile the final adjustments got done and the final 3D design reached the final version, at the end we In order to make this extruder work on a cartesian XYZE system we had to adapt our electronics and modify the Firmware of the microcontroller to add two extra actuators to the extruder to control the output flow and the orientation of the nozzle.

24/06/2019

• We have built a second printer that we will use exclusively for the development of the sheet extruder, it has a print volume of 300x400x300 mm, it was built using recycled materials, a whiskey box for the extruder and motors extracted from a paper printer, we use beer cans and resistive material from an old toaster for the heating element of the extruder.

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  New Pieces Designed

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  Printed parts Assembly

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Calibration and Testing

10/06/2019

Since the first assembly of the extruder, we used a Nema 17 motor of 2,2kg/cm Torque and 1:50 gearbox, which presented printing failures and loss of steps due to overheating, which also affected printing speed, something visible in the quality of the printed pieces, to solve this problem the motor has been replaced with a Nema 23 with 9 kg/cm torque and 1:72 gearbox, after the software adjustments and some tests, the extruder presented a better speed and acceleration control, and an improved print quality.

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  Extruder with Nema motor 17 1:50

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  Extruder with Nema motor 23 1:72

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  Piece Side View

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  Piece Up View

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  Print Test

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  Print test

Reports & TS

Reports & TS in spanish Extrusor de Pellets para Impresión 3D