Our groupmates have a research topic that includes making a plastic pellet. We have to think of an alternative way to produce plastic pellets out of melted HDPE plastic bags since we're still students who couldn't afford buying an expensive pellet maker machine. Does anyone know any cheap alternatives for making a plastic pellet?
You could combine the following two machines:
The Precious Plastic Extrusion machine, an open source, do-it-yourself plastic extruder that is fed with shredded plastic. Use it to create plastic filament in the diameter you need (maybe 3 mm as usual for 3D printers), and collect the filament on a slow-turning spool.
A machine to cut the filament into small pieces as needed for making pellets. Not sure what would be a good basis for this one, though, but it's a pretty simple machine.
It seems preferable to me to separate the process into the two steps above, as creating the pellets from molten plastic in one step could be more difficult to control in a simple machine. You'd likely deform the soft plastic while cutting the part coming out of the extruder, and the heap of fresh pellets might also stick together while it is cooling.