Using Pellets Instead of Filament for FDM/FFF

Hi,

I'd read about some upcoming printer called David which has tentatively been announced by a company called Sculptify. They say their printer can accept plastic in the form of pellets instead of filament.

I'd like to know - is there anyone in the RepRap community who has tried coming up with a way to do this?

(On second thought, I suppose that's unlikely, because if anyone had successfully implemented this approach on a RepRap machine, then everybody would be all over it by now.)

I just thought I'd ask.

Also, how much savings could be achieved in materials purchases, if you had a printer that accepted pellets instead of filament?

What might be the likely pro's and cons of using pellets instead of filament, if this were indeed possible?

I think it would be very difficult to come up with an extrusion rate that is as consistent as you get with filament, since there is a slight variation in pellet size, and you might not always get the same number of pellets into each flight of the screw. In filament production, inconsistent pressure in the extruder can be countered by leaving the filament unconstrained so it can speed up or slow down while maintaining diameter, or use a puller whose speed is controlled by on-the-fly measurement of the diameter.

There would need to be some method of measuring and controlling pressure in the melt chamber so you can keep it consistent, and also quickly relieve pressure to prevent oozing since retraction isn't an option.

You could use a "hopper" approach. I considered it before i built my reprap. Frankly i think the filament approach is far superior.. consider with a hopper type system every time you change material or let the "hotend" cool down you need to disassemble EVERYTHING and remove the melted plastic. For a commercial/industrial machine it might be good. But then for that kind of machine all the extra steps/cost etc. and with filament being (relatively) ultracheap theres no real need. Dont get me wrong i love the idea and id definitely consider one and hope they build it and do well commercially but i just dont see an urgent "need" especially when filastruder and open source extruders are around (and are probably the basis on which this machine willbe built anyway)

So far the strategy is to make filament from pellets, then print this filament. Machines for both parts are available as Open Hardware.

If you can create 3mm filament you can undoubtly also produce 0.4mm filament, which means you can print parts with it. Time isn't ripe for this, though.

Edited 1 time(s). Last edit at 07/13/2014 08:37AM by Traumflug.

---

Generation 7 Electronics	Teacup Firmware	RepRap DIY

Oh god, I've had enough nightmare tangles with 1.75mm filament, let alone 0.4 mm. I nearly gave up on home filament extrusion until I built a winder similar to Ian's design.

This idea comes up very regularly both here and on the filastruder forums. I don't think most people understand just how much pressure is required to turn pellets into filament. To put things in perspective, the filastruder comes with a 12 Nm gear motor. This is the holding torque of at least 5 regular stepper motors. Even then, you're still only pushing out 10-14" / min, which is slower than what a printer will be consuming depending on print settings.

Separating the two stages makes a lot of sense, since the constraints are very different.

Quote
jamesshuang
Oh god, I've had enough nightmare tangles with 1.75mm filament, let alone 0.4 mm.

You don't make 0.4 mm filament to coil it up, you put it down right onto the printed part.

Sure, melting and forming pellets requires some torque, but it has been demonstrated to work: [www.youtube.com]

---

Generation 7 Electronics	Teacup Firmware	RepRap DIY