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Multiple Extrusion

Two is always better than one. In FFF technology, dual extrusion can print a lot more interesting part than single extrusion. Often first extrusion as printed part while second extrusion as support structure. Dual extrusion was pioneered by Stratasys and implement by default in its big machine for more than 20 years ago until today’s uPrint and Mojo.


Dual extrusion 3d printer commonly seen in the market is having a second extruder mounted next to the single extruder. And both nozzle are sitting at the same height. However they do have problem.


The root cause:

  1. Oozing

Many of the print came out to have color contamination due to plastic material remain in hot molten state, it leak out when it’s idler. Slicer able to temporarily reduce the oozing by generating a Ooze Shield but the root cause is still exist in the extruder hardware.

  1. Print knock off

Slicer software enable second hotend to cold down to minimize oozing, but a bit of plastic still will leak out before plastic being solidify. This causes the second nozzle with a bit of solid plastic on the nozzle tip to scratch on the print surface while first nozzle is printing. Severely, this can knock off the print from build plate.


Instead of printing with dual extrusion, most user just simply treat the second extrusion as spare part. The problem mentioned above are not easy solved by firmware and software. Hence, printer manufacturers and communities are working to redesign a better extruder hardware. Below are some interesting and innovative solution that’s either in beta stage or being used as product.


The solution:

  1. Mechanical tilting

This solution is used in uPrint and Micron3dp. The switching is done by rotating certain degree to allow active nozzle to be parallel against the print bed while idler nozzle tilted away. The rotation is performed when the printhead move to the side to allow sliding bar hit on an obstacle. The hitting linear toggle mechanism of sliding bar then convert it into rotation.

Advantage: 

I. Fully mechanical without need of extra electronic

Ii. Reliable

Disadvantage:

I. Required offset calibration


Image: uPrint SE’s printhead


2. Servo/stepper motor tilting

The mechanism of switching in between extruder is the same as mechanical tilting, instead of sliding bar, it uses servo or mini stepper motor to perform the rotation. Commercial product such as RoboxDualSpiderbot ABSolute and D3D HPX2-MAX



Image: Tilting mechanism with needle valve by RoboxDual


Stratasys has patented a cool solution used in uPrint which is the tilting mechanism to toggle nozzle and at the same time engage the active filament to drive gear. Drive gear just simply reverse direction to drive the filament when switching occur. Single motor dual extruder designed by Sega Liu have similar concept as Stratasys but tilting mechanism is performed by high torque servo motor. Furthermore, the design is improved in Gianni3d version of Dondolo. The plus for these open source version have stopper which stop idler nozzle from oozing. This setup also save one stepper motor’s weight to get the benefit from direct drive. Peter Stoneham full metal version is also look promising and able to perform much more consistent tilting. Eric Sarellana’s version design is quite indifferent and unique. 

Disadvantage: Digital servo motor is not constant and will affect x offset.

3. Mechanical lifting

Mechanical lifting mechanism is made popular with the release of Ultimaker 3.  Genkei T-Lifter also have a similar setup which toggle second hotend while first hotend remain static. Printhead slide across the hook to mechanically toggle the switch. The switch is then lift the second hotend higher than first hotend when printing with first extruder and vice-versa.

Disadvantage: 

Required calibration of x and z offset. 

Need prime tower to clear bit oozing, Prime tower may fall for tall print.

Only bowden setup

Image: Genkei’s T-Lifter (right hotend drop down)


4. Servo revolve lifting


3DGence Industry’s Revolver Hotend using servo motor meshed with gear to do  90° rotation while lift the hot end up and down with CAM mechanism. The design is smart and unique. Digital servo motor is not constant and will affect offset even with high gear ratio but compress spring should be able to resolve the backlash.


Advantage: 

No offset calibration is required


Disadvantage: 

Only for bowden setup, direct drive setup impractical to lift stepper motor up and down

Need to some priming to purge out bit of oozing

Image: One’s Revolver Hotend


5. Magnet

Markus Seidt’s Ultimaker Mark2 is designed to allow Ultimaker 2 user upgrade to dual extrusion as Ultimaker had gave up on dual extruder upgrade. The idea is store the second hot end to the side while not being used. When need to active second extruder, the print head will move to the storage and second hotend will stuck on print head. Three pair of magnets are used to achieve highest repetivity of alignment. The wiring length of second hotend need to have enough strain relief to reduce the frictional force created from wiring.


Advantage: 

Simple upgrade setup

Easier offset calibration


Disadvantage:

Only for bowden setup, high weight of motor on direct drive setup may cause magnet to detach

Switching in between extrusion consume time for big printer

Image: Markus Seidt’s Mark2 upgrade


6. Electromagnet

Electromagnet technique is pretty much same as magnet with a plus of higher suction force. Printhead carriage will move to storage to attach active extruder. Electricity current flow through will generate high magnetic force, hence direct drive with heavy stepper motor is not a problem here. This is part of Lulzbot research project reveal in MRRF 17.

3D-Proto’s dual parking extruder is one of the pioneer that put into practice.

Image: Lulzbot Indepedent Electromagnetic Extruder


Advantage:

Open wide range of possibility to attach variety of nozzle size


Disadvantage:

Switching in between extruder is time consuming for large printer



7. Independent Dual Extrusion System

One of the printer axis have two printhead which drive independently by respective motion system. Each individual printhead has it own endstop to allow machine understand its own path. When is time to print with first printhead, second printhead will move to side storage. After free out the build area space, first printhead then move to the build area to do its job and vise-versa. First printer do this trick was BCN Sigma IDEX System then follow by other manufacturer Leapfrog Bolt and MakergearM3 Independent Dual for better dual printing.

Image: BCN Sigma IDEX system


Advantage: 

Capable ditto mode


Disadvantage:

Offset calibration is tedious

Limited to dual extrusion


8. Switching filament also known as Y-Splitter

All in one out is switching filament in beforehand. A plastic part called Splitter which consists of multiple filament path is mounted on the printhead entrance. Tool change script will call the extruder to retract the idler filament until exit the intersection. And then, the other extruder will extrude the active filament into the hot end melt zone to start the next color. Prometheus System and Atom2.5 have 2 in 1 out while Prusa Dual/Quad upgrad make it further to 4 in 1out.

Image: Prometheus System Y-Splitter’s internal view


Advantage:

No offset calibration is required

Easy upgrade to existing machine

No oozing

Build plate size remained


Disadvantage:

I. Required high torque of extruder motor as melted filament blob has slightly bigger diameter causing friction against hot end path

Ii. Bowden setup only

Iii. Only work with similar temperature range of material

Iv. Waste material, need prime tower


9. Mixing and Blending

All in one out but this time the intersection is at melt zone. RepRap.me’s Diamond hotend with 3 in 1 out and Builder3d with 2 in 1 out started commercialize this product. In this setup, besides you can achieve pure color from extruder one and two but also a range of blending color. So, basically is unlimited color depends on the ratio mixed. Zmorph’s Dual Pro Extruder use Voxelizer’s image mapping with dual color blending make kind of like 3d model with jpg wrap around it. Even much more advanced is gonna be 5 in 1 out which tend to mimic the WCMYK process of inkjet printer. Manufacturer that are working on this solution are Ord Solution Rova4d- 5 colorSomething3d’s Chameleon and Jason Powell.


Image: Jason Powell patented 5 to 1 water-cooled hot end


Advantage:

More color range

No offset calibration


Disadvantage:

Need prime tower

Same range material temperature

Might have color contamination especially changing from darker to lighter color


10. Splice and joint

Plastic has a properties easy to cut and fuse weld joint.  Mosaic Manufacturing’s Palette carry the task automatically through innovative combination of hardware and software. Four stepper motor are used to feed four different color filament respectively into Palette and cut accordingly to length. The filament is arranged in order in one strand and 2 separate filament is then fuse together in heater die. The printer is just operate normally without much of modification.


Advantage

No offset calibration.

Implement to most open sourced printer

No consumption of build plate 


Disadvantage

Not plug and play, required learning curve to dial in color changing calibration

Big prime tower, same range material temperature

Not able to splice flexible and polycarbonate ductility material

Only for same type of material, hence multi-color not multi-material




11. Bonus:

This is so far the most unique dual extrusion that I seen designed by galaxyman7. The goal is to create fully mechanical by enabling hot end nozzle tilted on the stopper while not being used. The design is to translate the rotational motion from one of the extruder motor to filament linear motion. Filament act as bowden cable like in bicycle braking system to control the pivoting on the hot end carriage. While the extruder keep rotating, the magnet wheel allow filament skip the linear motion step while remain the filament position.

Bonus.png

Image: Fully mechanical hot end pivoting extruder


Advantage: 

Easy upgrade, no extra electronic and firmware

Easy offset calibration


Disadvantage:

Annoying clicking sound

Only for bowden setup