Friday, December 26, 2014

Road to Better Paste Extrusion, episode 3: Industrial quality 3D printing of paste materials with ViscoTec Moineau Pump

Long overdue update in the Road to Better Paste Extrusion series. As I've hinted at in my Paste Extrusion article in RepRap Magazine, last year an engineering intern -Steffen De Schrijver- spend six months at our design studio Unfold to work on paste extrusion as part of his master thesis. Steffen worked mainly on investigating two pump mechanisms, the Archimedes Auger Screw (again?) and the Moineau Pump, both in a DIY and in an industrial version. In the coming weeks I'll work through all the material, results and observations and write up a few posts. So expect a long one on revisiting the Archimedes Auger Screw as this was the most important part of Steffens research. But I want to jump straight to an industrial Moineau pump we successfully tested as a print head. You might have already seen some of the results of this work announced on your favorite 3d printing blogs last week: 3D Printing Industry and A good impulse to write up my experiences with this system.

Endless Piston Pump (courtesy ViscoTec)
For those who have followed along here, you probably know that I am a big fan of the Moineau pump principle. From the surface this pumps looks pretty much the same as an auger pump but the geometry of the auger (the rotor) and housing (the stator) are a bit more complicated. In a Moineau there is no continued path down the rotor but several sealed cavities between rotor and stator which progress down when the rotor is turned, hence it’s other common name: progressing cavity pump. Think of it as an endless piston pump. Every cavity has a known volume so with each rotation a specific volume is being discharged from one or more cavities. The intricate geometry ensures that the cavities alternate to avoid pulsations in the extrusion.

So as opposed to an Auger, there's close to zero relation between material properties and the volume or flowrate of the extrusion.
Knowing the merits of the Moineau and having fiddled with moderate success with a DIY Moineau designed by Tomi Salo -a little more on this in a later post- I approached ViscoTec, a manufacturer of industrial progressing cavity pumps small enough to be used as an extruder, with the idea to test their dispensing pumps in a 3d printer setup.

We're happy to announce that, together with Unfold, ViscoTec developed a professional solution for continuous 3d printing with a wide range of viscous pastes and gels including those with abrasive and other fillers. As you'll see from our tests, the same pump can dispense both water or viscous clay with the same reliability and without any recalibration associated with the material change. Regardless of the material being extruded, for every rotation of the pump an exact and predictable volume of material is being extruded.

The solution consists of an extruder with dedicated controller that can be integrated in nearly every 3D printer and will be available Q1 2015. Unfortunately this is not a solution for hobbyists but aimed at professional businesses and research institutes developing advanced food applications, high tech ceramics or medical/bio printing to just name a few.

In this movie you see our test setup with one of ViscoTec's existing dispensers from the Preeflow range fitted on a Bits from Bytes 3000 printer (retrofit with Ultimaker Ramps electronics) and printing an espresso cup in porcelain clay. More demo's soon which show the start stop capabilities.

This is ViscoTec's promo video demoing printing with silicone:

When researching the viability of different DIY and professional extruders Steffen performed a couple of bench top tests to check how accurate each system was in consistently extruding the exact same amount of material with varying material properties and inlet pressures (the material is fed into the pump by air pressure). We did this test both with water and porcelain clay each time extruding 1 minute at a fixed speeds and weighing the extruded material on a scale with 0.1 gram precision. We did the same tests with auger based systems.

bench top testing with gravity fed water (left) and pressure fed clay (right)
Below you see the results from just one series of tests at different speeds using clay. The measured values are within the error margin of the scale and the imperfections like air bubbles in our clay mix. This test was performed at both 4 and 5 bar of inlet pressure with the exact same averaged results.

As a progressing cavity pump is truly volumetric, one can calculate the amount of extruded material for each rotation which is a huge benefit and very close to how filament based 3d printers works.

As a bonus, playing with an water drop:

My current setup to control the ViscoTec pump is very much a hack as these pumps uses servo's with  rotary encoders (closed loop) and are controlled using 0-24v set point and start/stop signals as opposed to the somewhat simpler to control stepper motors in typical RepRap based setups. We build an Arduino based controller to convert STEP/DIR signals to something the ViscoTec Preeflow pump controller understands. Our demo system doesn't do retract currently as it was too much work to implement and not immediately necessary. But the final solution offered by ViscoTec will have all those capabilities and be much simpler and compatible with RepRap based and other 3d printers.

If you are interested in employing professional paste extrusion in your business or research and want to employ our expertise in paste extrusion, please contact us at

If you are interested in a 3D printing related job near Munich Germany, ViscoTec has a job open to work on their 3d printing efforts: Business Development Manager 3D-Druck (m/w)

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