garanule extruder design

hey guys,

yesterday i saw a blog post at mendelparts.com regarding the announcement of granule extruder,so i just gave a thought on it and got a few ideas which i would like to share it with the reprap community.

i have uploaded two designs for the extruder.i may not be knowing all the technical terms,so i regret if i have used any wrong terminology in the picture.the design is drawn in a mess(but legible).i hope you guys figure it out.

please post your valuable comments and suggestions.

v1- [www.flickr.com]
v2- [www.flickr.com]

cheers,
shakerobo

Hi,

Looking at the 2nd extruder I would be concerned about how much force is required to suck the molten plastic into the main chamber. Also, it assumes the molten plastic in the feed chambers form a complete seal. If any hole forms then the suction formed by the piston's upwards movement would be severly reduced or removed completely.

Another concern would be that the amount of material is limited by having to move the piston back and forth to feed the plastic in, producing short spurts of plastic rather than one continuous stream. This is where the more common screw, or auger, feed mechanism has the advantage - providing a continuous feed.

You've no doubt already seen the various pages on the wiki of designs others have come up with, but I'll include them in case others find them of interest: [reprap.org], [reprap.org], [forums.reprap.org]

Cheers,
Gary

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garyhodgson.com/reprap | reprap.development-tracker.info | thingtracker.net

thanks for the inputs.the second one was done in hardly an hour.i took the inspiration of a handpump used to draw water from underground.i didnt take the high viscous force of the molten plastic.so it would take up a lot of force to get it in the main chamber,so its a no-no.

Hey gary could explain the problem about the complete seal,i can't get a clear picture of it.

The issue of small sqiurts,could be solved by using multiple heads working alternatively,in a smooth manner.that would ask for a lot of tweaking in the software side and stuff.


I was just so excited and a bit sleepy that i did't do a lot of research on it.anyways,time to do some research and back to finding some new ideas!!!

Cheers,
shakerobo

With regards to the seal problem I would imagine that if the main piston is moving up and drawing in the molten plastic then if there is a gap within the plastic (between it and the walls, for example) then it would simply pull in the air, rather than the plastic.

I'm a big proponent of sharing ideas, at all stages of the development process, as it usually leads to further understanding of the problem and opens up new avenues for exploration! Keep up the research!

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garyhodgson.com/reprap | reprap.development-tracker.info | thingtracker.net

i had searched for granule extruder and got only screw drive based extruders,hence just gave a shot on making a pump based.

thank you for the quick explanation.i have thought of a design by making the heating element slanted and a different mechanism for it's operation.will soon post the developments.

i know the v1 is such a mess that no one could understand it.soon,i will type the written notes in the picture for better understanding.

the auger drive is simple and well designed,i think i may implement it in the designs.

regards,
shakerobo

I really do not wish to offend anyone , i have seen the working granule extruder on youtube made in germany , however if you nitice thier final rendetion (sp?) only shows a heat wrapped thermal head (atleast thats what I assume it is because you cant see any parts)

my main concern with anyof these "granule" units is stamina, what i mean is how much can u actually print at a time before you have to refill?

are you willing to sit there for 5-12 hours loading the granules ?

atleast with the filament you can load 1lb 3lb or even 5 - 10 lbs and just check on it once in a while.

In my personal not (professional) opinion this is a great novelty but impractical for serious usage.

@samberr

well the stamina is an issue but this can can be used as a filament maker,which i hope won't need any need to sit around it and inspect it!!!

as a small formfactor it is a wrong choice but there's a way to solve it.there would be a main feed above the home of the printer and a sensor to detect the amount of granules left in the funnel/hopper.whenever sensor detects less granules is left then,it would pass an interrupt and the print will be paused and then it would home itself.where it would recive the granules from the main feed and continue.this is just an idea!!!

regards,
shakerobo

As mentioned elsewhere...I have an extruder design that is nearly commissioned. It uses a drill press and auger with some custom metalwork and a specially designed microcontroller board with buttons/LCD/thermocouple interfaces/ solid state relays etc

Will post more info when I am happy that it performs "as advertised" and will probably offer various parts for others to make their own machines.

PS it's not only continuous production that's an issue...but also reeling the product...else you will end up with a room full of the output filament!!

well reeling is a problem because i haven't thought much about it.maybe some liquid coolant(saw a youtube video) could be used to cool the hot filament or use many rollers to cool it down gradually.

another issue is regarding the material.i don't know as of yet(because i havn't seen a 3d printer).after seeing some videos of printing by a reprap.i think that the material loses it's elastic properties after being extruded.if i am correct then filament making would become a dream.i was thinking to bringing this reeling issue in another post maybe later,after i get a reprap commissioned.

update-after looking through my v1 design,i found a major flaw in it.so the v1 design is soon going to be upgraded.

it would be great if you post the videos of it's working!!

I like the idea of a power or pellet extruder however the technical issues you have to over come are pretty big.

A big concern of mine (which hasn't been asked) is the weight of the extruder, both loaded and unloaded. At the moment most extruder only carry a fraction of the overall filament weight. ie you can have a 4kg spool feeding the machine but the extruder only holds a few grams of the weight.
With power or pellets you have to have a minimum quantity in the hopper to feed correctly and you either need a large hopper/container with the full content on the extruder or a system of tubing carrying the feed.
Either way its more weigh which means more stress on the frame and stepper motors.

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My Reprap blog

jds-reprap.blogspot.com

... we had some talk regarding the weight issues - best solution seems to be upside-down-printing: the extruder is under the bed and points upward ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

My main concern about the powder/granule extruder as opposite to filament, is how messy the material is.

It's probably ok in a workshop, but that will be an issue for "desktop 3D printers".

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Most of my technical comments should be correct, but is THIS one ?
Anyway, as a rule of thumb, always double check what people write.

would you have to remove all the pellets while still molten so it wont solidify and jam up? wouldnt the soldidified plastic take much longer to remelt if you let it stay in the extruder

Granules aren't particularly messy because they are relatively big, about the size of lentils. They can be a problem to wildlife if they get into the environment, but shouldn't be much problem in a home / office.

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[www.hydraraptor.blogspot.com]

As to keeping the hopper for a granulated plastic extruder filled, that wouldn't seem to be an insurmountable problem.

One example would be to have a smaller hopper on the extruder, and a larger stationary hopper. Position the larger hopper at a corner of your extruders accesible range. When the extruder moves to that position, it taps a paddle and a measured portion of granular pellets is dropped from the large hopper into the extruder hopper. At that point, it is just a matter of inserting gcode to return to the feed coordinates when a particular amount of plastic has been inserted. If you wanted to get fancy, you could always rig a sensor to detect the capacity of your extruder hopper that is filled and adjust the amount the large hopper drops.

Another option would be to have a flexible tube that connects the stationary hopper and your extruder hopper. When a sensor determines that the smaller hopper is below a certain level, it triggers a gravity feed of pellets down the tube until the extruder hopper is filled to a certain level. Obviously you'd have to account for any extra pellets that may be fed between the time the feed is shut down and when the pellets stop coming out of the tube.

There are probably a million and one possible ways of feeding granular pellets from a holding area into the extruder. It would just be a matter of choosing which one to use. To me the greater challenge is in making sure that the granular plastic is fed out from the extruder in a reliable fashion.

karmacappa Wrote:
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> As to keeping the hopper for a granulated plastic
> extruder filled, that wouldn't seem to be an
> insurmountable problem.
>
> One example would be to have a smaller hopper on
> the extruder, and a larger stationary hopper.
> Position the larger hopper at a corner of your
> extruders accesible range. When the extruder
> moves to that position, it taps a paddle and a
> measured portion of granular pellets is dropped
> from the large hopper into the extruder hopper.
> At that point, it is just a matter of inserting
> gcode to return to the feed coordinates when a
> particular amount of plastic has been inserted.
> If you wanted to get fancy, you could always rig a
> sensor to detect the capacity of your extruder
> hopper that is filled and adjust the amount the
> large hopper drops.
>
> Another option would be to have a flexible tube
> that connects the stationary hopper and your
> extruder hopper. When a sensor determines that
> the smaller hopper is below a certain level, it
> triggers a gravity feed of pellets down the tube
> until the extruder hopper is filled to a certain
> level. Obviously you'd have to account for any
> extra pellets that may be fed between the time the
> feed is shut down and when the pellets stop coming
> out of the tube.
>
> There are probably a million and one possible ways
> of feeding granular pellets from a holding area
> into the extruder. It would just be a matter of
> choosing which one to use. To me the greater
> challenge is in making sure that the granular
> plastic is fed out from the extruder in a reliable
> fashion.


Now that seems like a reasonible solution! now where to get the ABS granules ...

Once you get a reliable and cost effective extruder that operates off granules instead of filament, you will find it stocked by the same people that are selling filament to the 3d printing community. You might want to look into it from the injection molding standpoint Samberr. That industry already uses this method.

karmacappa Wrote:
-------------------------------------------------------
>
> Another option would be to have a flexible tube
> that connects the stationary hopper and your
> extruder hopper. When a sensor determines that
> the smaller hopper is below a certain level, it
> triggers a gravity feed of pellets down the tube
> until the extruder hopper is filled to a certain
> level. Obviously you'd have to account for any
> extra pellets that may be fed between the time the
> feed is shut down and when the pellets stop coming
> out of the tube.
>

What about just having a large static hopper above and to the side of the machine, with a flexible tube leading to the extruder. No need for flaps / valves - it can just be a continuous flow device, which continuously replenishes material as it is extruded.

It would take some experimentation to find a tube which has the right diameter and friction characteristics to ensure granules flow freely as the slope of the tube changes (while the print head moves around), but flexible enough to not impede the motion of the print head, even when full of granules. (Too small and the flow will probably "choke"; too big and the column of granules in the tube may become so stiff and compacted that it impedes the motion of the print head.)

However, crack these issues and you can probably create an arbitrarily big continuous feed system - just install a bigger stationary hopper.

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Follow my Mendel Prusa build here: [julianh72.blogspot.com]

i too came to the simmilar idea of julianh for removing the weight issue.

There will be a main storage above the printer which is connected through a flexible pipe and it release the granules into the funnel of the extruder after each stoke of the piston.


Could anyone confirm whether the abs or pla retains its elasticity even after exttusion?

And is there any liquid known as of now which may be used to cool the hot extrusion?

Well Julian, if you did it that way, you'd be forcing your print head to move around the weight of all pellets in the tube. In addition, you would have to work to incorporate an augur into the bottom of the tube. As a third issue, you would have to deal with the full tube possibly being less flexible than the empty tube. It might be simpler just to make some kind of mechanical flow control.

as i said above ,all the granules won't be there in the pipe.
whenever after each stroke,the hopper in the stationary feed will release some of it,which would travel through a pipe to the funnel.thus,there won't be any load on the extruder due to the main stationary feed of granules.

regards,
shakerobo