Including a molding function to the extrusion machine

Hello everyone!

I am super new to all of this, but think it is an amazing idea and would like to build some of the machines, but I do not have a lot of space and therefore need to narrow down which machines to build.

The shredder is a must, I will be looking for material or an old shredder that could be upgraded soon. I would also like to start with the extrusion machine but would like to add a function to be able to also attach molds. My idea was to be able to have two types of nozzles (if even necessary) and build some kind of extra apparatus that could hold the mold in place with clamps while the machine pushes the liquid plastic into the mold.

Or in short, one machine that can be used for extrusion and injection molding. Has anyone any good ideas how that could work? or can tell me if I am completely off with that idea?I might not be understanding all this very well!


I’m only familiar with simple shapes being extruded into long strands. If you were to pump hot plastic into a mold a few obstacles come to mind. The pressure to force the plastic into the ends of your mold might exceed what this design can achieve. You would probably want to have a hole in the opposite end from where you inject so the plastic could flow through the mold and not be crammed into a dead end. A restriction would need to be present so the input side would need to be larger than the output. I would start with symmetrical designs to ensure uniform filling.

This is just a very rough guess. I will let you know if or when I get this far.

most low cost plastic molds are not air tight enough to need a air vent.  the bigger issue is that they can freeze up the plastic before it is fully injected unless you pre-heat the mold.  especially for larger volume shots.


Small volume shots the injection molder is less hassle and simpler.  If you need more power  mount a big pneumatic piston or hydraulic

machine of extrusion plus injection is more like industry machine like below, might got some inspiration…

minutes 1:00

thanks everyone for all the suggestions… an exhaust port sounds like the plan! atm we are looking at where to get all the different parts from and it is not all too easy here in Santa Marta, Colombia! Especially with the motor! Will keep you updated! if you have any other ideas on how the machine could work please let us now!

I used to operate and maintain industrial extruders

Our extruders had an exhaust port just after the hopper

If too much pressure built up it would exit via this port but it can create an awful mess

@jamesmeehanhs could it not be a possibility to mount a pressure sensor, and have that de-activate the motor-relay, connect the whole thing to a raspberry pi? That way the system would automatic stop as soon as the mold has been filled…

The extruder builds pressure so closed moulds as used in the injector are not suitable

Excessive pressure build up could lead to and eruption/explosion and injury.
Excessive pressures would also look for a path of relief which may end up filling the hopper with molten plastic. I have seen this in industrial extruders and it makes a mess

Moulds would need an exhaust port for the plastic
When plastic appears at the exhaust port the mould is full

I’ve been researching about moulding and plastic casting. Timmy is right. As bigger your plastic product is, as stronger your mould should be.

For little pieces, maybe you could use High Temperature Silicone to make your mold but for a medium to big size product you should use aluminium or, if bigger, stainless steel (just for a really big product or a high demand production).

Aluminium moulding should be made by a CNC machine or by greensand casting, or a mix of both technics by creating an aluminium solid block with greensand to work in with a CNC milling machine.

There’s hundreds of video tutorials on youtube.