Injection Moulding?

I had an idea about letting the reprap do injection moulding. It would require that a volume of plastic be pre-liquidized in order to allow for fast injection. So my question is, does the plastic catch fire if it is heated to above its melting pont for a prolonged period of time?

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Jay

Hi Jay,

... it's mostly a wide range between the melting point and ignition, so that's not the problem.

For good forming you should heat the form too a little under the melting point and let cool it down slow after injection.

The main probem is the needed presure - it should be high enough, to press the fluid plastic in all the small edges.

Most plastics are not so low viscouse, even when pressed at much higer temps then melting point, so you need an extreme high prssure for a proper fitting!

Look here: [www.orbi-tech.de]
- this is a 'hand-injection-molding-system', driven with 5 to 10 bar air-pressure, which internally rise the pressure on the molted plastic by 100 to nearly 500 to 1000 bar!

This hand-injector costs nearly 3000 Euros, but the plastic-spools could be a good source for us too

Viktor

Edited 1 time(s). Last edit at 01/13/2008 02:47PM by Viktor Dirks.

Jay,
I find that the HDPE stuck to my nozzle which is at 240C turns black over time. It's nowhere near the point of catching fire but it is decomposing slowly. There is no problem with the extruded filament so short exposure to that temp must be no problem.

Here is a good site for injection molding data although I don't know the meaning of all the figures. [www.ides.com]

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[www.hydraraptor.blogspot.com]

... look at the injection-pressure for HDPE: equals 12400 to 20000 psi / 85.3 to 138 MPa / or 853 to 1380 bar!

I didn't think, we could actually and in near future reprap an injection-head, capable of this forces - maybe with re-forming in metal with lost-cast-molds ...

Viktor

Wow, I didn't realize that there were so many forces acting on an injection mould system. I guess I'll just make the moulded parts by hand with polyurethane moulds, etc.

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Jay

I had an idea when I woke up this morning. What if you make a mould that has nichrome wire embedded in it, and place that mould on a vibrating table? This way, the plastic will keep from being viscous long enough to be able to fill every nook and cranny in the mould.

You could also go the route of making some sort of holder that contains the nicrome wire and th vibration mechanism, which would allow for more moulds that would be cheaper, faster, and less complicated to make.

I don't quite yet know all of the materials that I would use to make this setup, but i figured that you guys could help out with that.

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Jay

As I understand it, plastic is too viscous to settle of its own accord. I think you will need a very hard shake to get it to settle into corners and such as well as expelling air bubbles. Could work though. I'm not sure.

Demented

I think this wouldn't as Demented says too..... viscous we use a vibrating table to help remove air with our resin pours and even this is not 100% and still requires a careful pour and our resin is like milk, I know a local injection moulding company and to inject 700g of polymer they use a 250 Tonne lock (pushing force) I'm not sure over what area etc but how ever you look at it 250T on 700g of plastic is a lot.

I've done a lot of looking in to home brew injection moulding and it seems there are some systems but they only mould very small items think nickels and dimes.

I currently investigating a half way house of injecting resin as this is also good for filling FDM casings see [forums.reprap.org] i get some pumps later this week

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Ian
[www.bitsfrombytes.com]

Here's some info on a homeade injection molding device:
[lindsaybks.com]

The Gingery stuff is generally well written and based on experience, but can be a little hard to follow if you're not shop savvy. Interesting, but I don't see it as a RepRap component either.

Hey,

I spent the past few months looking for a hobby injection molder however they cost a lot and did only a little bit of plastic. I spent some time and money thinking and working on a machine, my freinds thought it was so good they said i should try to sell it. Anyway I am going to be making 20 for the year 2009. I am going to charge 485.00 for them. If you are interested in seeing a picture of it feel free to browse my yahoo group that I set up like a week ago. [groups.yahoo.com] or shoot me an email at xject@yahoo.com or my newly created website and email kevin@backyardengineer.com