It's been a long time since I posted here, unfortunately no more time to write lengthy articles... Maybe someday.
For those landing here when looking for information on the since long deprecated Bits from Bytes (BfB) Rapman that we used as the 3d printer to bootstrap our first ceramic 3d printers from, here's some info on how to revive those machines. We still use them today since they were included in some of our installations like l'Artisan Électronique from 2010. This installation is still continuously exhibited and now even part of the Centre national des arts plastiques, (CNAP, the national art collection in France).
Since we feel the look of the machine is an integral part of the installation, we keep on maintaining it using original parts. But we also updated one machine to modern electronics and firmware. I've never had the time to do a good writeup of that but fortunately enough, others did. Here's a good blog (still updated) by Alvaro Salgado documenting the process, the most recent post is about replacing the extruder. Most posts also have a Spanish version besides the English posts:
There's also still an OpenBFB Google Group that I setup when BfB pulled the plug on their support forum, not very active but good information is hosted there:
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 3DPrint.com. 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 3dpconsulting@unfold.be
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)
Happy to announce that our book Printing Things,Visions and Essentials for 3D-Printing is finished, off to the printing press and available now for preorder at Gestalten.
We've worked hard over the last several months to compile this book together with Gestalten. Featuring over 100 projects from various artists, designers and makers exploring a new wave of creative 3d printing applications facilitated by the unprecedented lowering of barriers into production. Together with an understandable technical introduction into 3D-printing, we've written eight key essays that delve into the complex topics that these paradigm-shifting technologies bring up: Empowerment, The Right to Copy, Interface and Interact, Body Topology, The Aesthetics of Complexity, Building Blocks, Exploring Machines and Materials & Crafting New Industries.
Thank you Sven and Robert from Gestalten for this great opportunity to work on Printing Things, Sarah for cracking the whip and have the book finished on schedule, Floyd for the design. Thank you Tamar for going beyond 'just' editing all the submitted project texts and adding valuable insights and context. Thank you to our team at Unfold (Hugues & Penny) for assisting in compiling the long list.
You can buy the book atAmazon (or german edition), Gestalten (or german edition) or ask your favorite bookstore.
Update May 2020: RepRap magazine is long gone but here's an archived copy of the magazine: https://www.dropbox.com/s/yjb1ntrv6huz12e/reprap-magazine-3.pdf?dl=0 Update: The issue of RepRap Magazine is live, head over to reprapmagazine.com or download the PDF directly: Download Lo-Res PDF (9MB) Download Hi-Res PDF (25MB)
wow... it's such a long time ago that I have posted something here. Like always, not a lack of fabrication activity, just a lack of spare time (and sometimes incentive...) to document. Hope to get to it again.
Coming up one of these days is the new RepRap Magazine with a cover feature written by yours truly on paste extrusion. It recaps much of the things we've tested and learned and blogged here at Unfold ~fab over the years. The article also includes some new experiments which I will write up a bit more about here when the magazine is out. I really hope that by writing this lengthy article on the state of paste extrusion that more folks will get involved in the development of paste extrusion tool heads.
Looking forward to seeing the rest of the magazine and get into contact if you enjoy getting your hands dirty in extruder development!
ps. Our two person design studio Unfold is currently residing in Fort Collins, Colorado, USA with a Franzen fellowship for Digital Craft at Colorado State University. If you based in that area and interested in discussing paste extrusion, let us know. We'll be there for two more months.
After the previous lengthy post (and the time it represents) the short conclusion was that a paste extruder merely working by pressurizing a syringe full of material in order for the material to extrude is not a reliable method for use in RepRap machines. It's simple, it's straight forward, served us very well but impossible to predict and control the flow rate.
The next episode of chronological brain dumping, an auger valve extruder prototyped and tested in the first halve of 2011.
Convinced that one doesn't need to reinvent the wheel, I started to search for industrial areas and applications where they have similar needs: precise extrusion of paste materials. The field I found the most closely related is the fluid dispensing technology used for the precise deposition of dots or lines of sealant, adhesive, silicone, epoxy, glue, resin, soldering paste etc.
The basic setup of most fluid dispensing implementations looks like this:
There is a material reservoir which holds the material under the necessary conditions (stirring, heating etc). Next there is the feeding system, to transport material from reservoir to dispensing, for low viscosity material this can be gravity feed but higher viscosities need a pressurized syringe or large pressurized container. High viscosity material feeding can be done by using a feed pump (not in drawing). Right before the nozzle is a device called the dispensing valve.
Lets skip the first two for now and jump straight to the dispensing valves, the operating end of this system. I was immediately drawn to them because they sure look like badass extruders!
There is a whole range of valves used in these industrial applications. After researching many suppliers websites and catalogs (with often confusing and contradicting use of terminology), it becomes clear that they fall into only a few categories and most of these devices are, as their name implies, simply valves.
As a non native speaker I had to remind myself what a exactly a valve is, its like a faucet in your kitchen. A device that can switch a flow of material on and off. Nothing more but also nothing less.
Valve a device for controlling the passage of fluid through a pipe or duct.
New Oxford American Dictionary
In this basic valve category we can find fine apparatuses like the Poppet, Needle, Diaphragm, Spool and Pinch Tube valve. They differ in working principle and therefore are better suited for different applications. The Poppet and Spool valve seem the most suitable for high viscosity paste materials, even abrasive and filled pastes (what clay is). They are all operated by air pressure and follow digital logic, open or closed. One can regulate these valves only with set screws which increase or decrease the diameter but this is a fixed setting, not something you control during operation. So it boils down again to two other 'controlling' parameters, time of opening and feed pressure and we know those two from the last episode. This types of valves would make a nice addition to the previously discussed pressurized syringe systems by switching the on/off action to the nozzle side of your system instead of pushing the whole body of material. Think (in faucet analogy) of the pressurized syringe time/pressure system as trying to control your kitchen faucet water flow all the way up at the water tower... No, it makes sense to add the faucet or valve right where you need it, just like a water tower, a syringe is constantly pressurized and will only feed material when there is a demand.
But I was not interested in these 'valves' because while a nice potential improvement for the starting and stopping of your extrusion, there is still no way to predict and control the flow rate. We still have to visually verify how much material is extruded through the nozzle at any given moment or use complicated flow meters and regulating gear.
(To be complete, in many industrial applications previous episode's simple time/pressue syringe is used but I would rather not even call that a valve, and we dismissed this principle for an extruder in that episode)
So first conclusion is that what we're after is not a valve so much but a pump.
There are various other speciality valves that I will look at in later posts like Peristaltic or Progressive Cavity valves. But there was one type at this point in time (feb. 2011) when initially researching industrial dispensing valves that was very different from the simple valves and immediately caught my eye: the Auger Valve. Some promo snippets:
"The XXX series of precision auger valves is suitable for dispensing medium to high viscosity pastes, epoxies, solder pastes and other filled materials."
"The valve uses a feed screw (auger) to dispense fluid with a rotary displacement action, allowing ultra-precise control of the dispensing process."
"The XXX Auger Valve is a precision dispense valve specifically designed for metering controlled deposits of solder pastes, thick sealants and other particle-filled materials."
"Fluids can also be accurately dispensed in continuous beads in widths that range from 0.010” – 0.050” (0.25mm - 1.27mm) at rates up to 4” (102mm) per second."
"The unique design ensures that material is constantly present at the feed screw inlet, while the controlled rotation of the feed screw moves the material from the feed to the discharge point. Discrete control of the forward and reverse rotations of the feed screw controls the amount of material discharged."
"With a feed screw made of Delrin®, the valve is designed for use with two-compound and abrasive materials."
These quotes gathered from the various vendors of auger valves sounded like a sales pitch aimed straight at me:
-high viscosity paste: check
-abrasive filled materials: check
-ultra-precise discrete control and metering: check
-continuous lines: check
Auger valves works like this: The material is fed from a continuously pressurized syringe or external reservoir into the top of the valve. The valve consists of an auger screw fitting perfectly in a cylindrical housing which at the bottom ends in the nozzle. The pressure on the syringe is just enough to feed the material in the valve where it will hit the auger and stops there because of the increased friction caused by the narrower size of the fluid path along the screw thread and ultimately at the even narrower nozzle end. The screw is actuated by a motor and this rotation forces the material down the screw thread out of the nozzle. The flow rate is controlled by the RPM of the motor.
source: dispensingtips.com
These valves are used a lot for precise dispensing of solder paste in SMD electronics and are offered by various brands like Nordson EFD (794 Auger Valve), Nordson Asymtek (DV-7000, DV-8000), Techcon Systems (TS5000, TS5000DMP, TS7000), Fisnar (PDV-1000), IntelliSpense (Auger Valve), GPD Global (HyFlo, MicroDot).
These things are rather expensive (upwards from 2500$) but when you look at them, they consist of a DC motor with optional gears/encoder and on the other end the screw housing with fluid inlet, nozzle end and the screw. If we substitute the motor end with 'standard' RepRap Nema steppers then what we need is only the screw assembly, the extruder's 'business end'. Thats why my attention was immediately drawn to Techcon's TS5000DMP because it has a 'Disposable Material Path' hence the DMP in the name. The DMP is the whole screw assembly in small and affordable delrin plastic package. The cheapest that I have found is around 25€ at dosieren.de (and up to 125€ for the exact same bit, industrial premium prices...).
source: adhesivedispensing.co.uk
source: adhesivedispensing.co.uk
The inlet side has a male luerlock, the nozzle side a female luerlock, the auger is sealed with an o-ring and has a square slot for the motor shaft, you can have the augers with different pitches.
Ordered a couple of the medium 8pitch DMP's and designed a very simple extruder head that mounts on the bfb Rapman for doing the experiments. The extruder is basically two halves that hold the DMP and both bolt together on a stepper with the extruder carriage plate in-between. An new carriage plate was needed because both the syringe and the extruder had to pass through. Its not designed for easy replacement of the DMP, was just to get the job done. The files can be found on Thingiverse: thing:28018
extruder
extruder half open in the middle and custom carriage plate
stepper and DMP parts
Extruder mounted on the Rapman
The first tests with clay were fantastic, this was exactly what we needed. It behaved very much like your standard plastic filament extruder. Turning the stepper on resulted (after priming) in an immediate flow of clay proportional to the speed. So you could easily speed up and down the flow of the clay. Stopping the stepper resulted in an immediate flow stop and no material passed the auger form the continuously pressurized syringe, when that pressure was set just high enough to feed the clay in the auger. We did some initial test with clay, chocolate and potato mash and those looked all promising. The following movie was shot using my original iPhone so looks a bit crap but you get an idea how it prints. This test object has three separate single wall shapes to test the on/off capabilities.
Tests to reduce ooze which is much more annoying in clay because it drags the whole print with it. Prime and reverse were used and jitter to make the point each layer starts at random
But after some further extensive testing with porcelain clay the system became less and less reliable and odd symptoms started to occur: flow rate became unreliable during a print and adjustment was needed, material leaked past the auger when the motor was not turning. Closer inspection of the auger confirmed a suspicion, that the delrin plastic augers were being grinded down by the ceramic material. The auger showed already degradation after a couple of minutes, therefore the auger was less capable at transporting the clay and increasingly the air pressure started feeding the material instead of the degraded screw thread. Vieweg (dosieren.de) conveniently also sells stainless steel augers for use in the DMP, they come at a more hefty 125€ a piece. After installing one of these augers another problem arose, the steel auger and the abrasive clay were eating away the housing. The problem being that it is rather difficult to get the auger to perfectly align with the housing so when it sits at the slightest angle it will grind the housing. I have printed a couple of extruder heads and made adjustments to about every part between stepper and DMP so that the auger would nicely sit in the housing but that proved very hard with RepRapped plastic parts. Maybe one of the reasons that original auger valve was 2500€, precision engineered... I also found complete stainless and even ceramic augers + housings but they were not of the 'disposable' category and cost 600€ and up.
left stainless steel, right delrin plastic (different pitch)
hole in the inner tube, you see the auger through
So the promising DMP part is not really up the task, I also had the feeling that it was underdimensioned for the purpose of extruding continuous and with a rather large flow rate. The stepper was turning at 100-200RPM to get to the speeds needed. But its not because this DMP bit is not up to the task that the whole auger principle is down the drain for our purpose is it?
Imagining that the rapid wear and tear problem would be solvable than there was another observation that was against what we need in a reliable predictable paste extruder. I did a couple of tests to see what happens when you changed the air pressure on the syringe that feeds the material into the auger and, obviously, below a certain point the pressure would drop too low to feed the auger but above that point the output of a fixed speed turning auger would vary in relation to the input pressure. Definitely not as much as when you would use a direct air 'frostruder' system but still more than enough. So that means that after all a change in material viscosity would still result in a changing flow rate at the nozzle and there would be no way to say that at a certain RPM you would get the right width of your extruded line, you would still need to fiddle with the air pressure. DAMN.
I know some people tried building auger valves using drill bits like these guys from Bauhaus University Weimar: GMU:RAPMAN/CLAYSTRUDER Before writing this post I checked if they got any further success with this system but unfortunately not.
While revisiting all my notes bookmarks on the topic I stumbled upon the following pdf: Archimedes Pumps. This is by far the best technical (but very readable) description of how an auger valve works, its operating principles and strong and weak points. In two different paragraphs the relation between viscosity and flow rate (in a previous post I described the relation between viscosity and air pressure, a small change in material viscosity means a change in flow rate under a constant pressure).
"Any changes in material flow characteristics affect the volume of material dispensed"
"Positive displacement implies that a specific volume of material is displaced within a specific mechanical actuation. Positive displacement is not influenced by changes in temperature or viscosity. The Archimedes screw pump is very consistent, but this consistency depends on the viscosity and flow characteristics of the material. Archimedes screws have been marketed as positive displacement pumps, but “viscosity metering pumps” is a better definition."
So the auger pump is not a true positive displacement pump (sometimes referred to as a metering pump) and the conclusion is that that is what we're after!
Positive Displacement Pumps, unlike a Centrifugal or Roto-dynamic Pumps, will produce the same flow at a given speed (RPM) no matter the discharge pressure. Positive Displacement Pumps are "constant flow machines"
Next episode: Positive displacement pumps aka "constant flow machines" (I like that, sounds good)
ps. If there is anyone (or you know someone) with day job experience in the dispensing industry please chime in with your thoughts on these observations.
Some extra links and references:
General descriptions of various valves with pro and contra can be found on several supplier and manufacturer websites:
Around this time summer last year I got an email from an Israeli student who had build a RepStrap and was doing experiments with printing porcelain:
Hello. I'm an industrial design student from Israel (H.I.T institute in Holon). recently I built a 3d printer that prints Porcelain clay (short video).
I must say that your project inspired me in many ways, so thank you!
If I may, I would like to ask you a few questions
1. one of my main problems is that the porcelain collapse after about 4-5 cm (depend on the shape). how do you prevent the clay from collapsing? 2. I am using a 1.2 mm nozzle, i wonder what diameter/type of nozzle do you use? 3. I am trying to build a feeding system that will allow an "endless" feeding material (instead of changing syringes all the time) - do you have any idea or have you guys tried anything like that?
I was thinking of using peristaltic pump, but the "pulses" bother me..
Thank you very much, Best Regards, Eran Gal-Or.
Regularly we get these kinds of emails at Unfold and we always try to help out as much as possible but often these discussions die out after a couple of emails, students loose interest or aimed to high etc. But almost 300 emails later, bouncing off ideas on paste extruders (and lots of him hanging out at #reprap, reading, tinkering, building an Arduino controlled dolly and what else) Eran graduated this june with a fantastic, massive 80x80x80 cm darwin style printer that prints porcelain in a continuous way using a commercial moineau pump and a refilling plunger type extruder he developed. Enjoy the movie! …and the arduino controlled dolly movie pans :)
He's preparing documentation on a blog, I will relay the link when its online and look forward to it.
Congratulations Eran on a job well done!
ps. a lot of the stuff we've been talking about with Eran is also what I am slowly trying to document in this blog. Tomorrow another lengthy post.
Unfoldis looking for a pottery studio or ceramic artist in Istanbul, Turkey(or nearby) who would be interested in participating in a ceramic 3d printing project for the Istanbul Design Biennial2012. Please send us a message or leave it in the comments. Please forward this call to people you know that may help us further. THANKS!
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