Injection Moulding

Hi John

I know nothing about the subject in practical terms, but looking at these, I'd say highly feasible

www.mediummachinery.com/
www.injectionmolder.net/
www.lindsaybks.com/dgjp/djgbk/inject/index.html

regards

I know nothing about injection molding except what is available at Wikipedia:
en.wikipedia.org/wiki/Injection_molding
en.wikipedia.org/wiki/Injection_molding_machine

Injection molding requires a large mount of force for two separatebut related reasons. First, you must compress the plastic feed material to about 13,000psi. Next, you must clamp the two pieces of your mold to prevent the plastic from forcing them apart. If the cross-section of the plastic at the interface beween the two mold pieces is one square inch, then you need 13,000 lbs (7.5 tons) of force to keep the two pieces together.
See:
www.moldingmanual.com/
For an excellent explanation. If I were to actually use injection molding, I would send this guy some money just to acknowlege his contrbution.

For high volume, It's clear that the clamping force dominates. But for low volumes. I think that you should be able to use brute-force clamping methoda, such as multip.e nuts and bolts. Sure, thsi meabs that you can only produce 5 parts per hour instead of 20 parts per minute, but this is uirrelevant whe you only need 100 parts.

John, I think you will run into speed issues with hydraulic jacks. The mold should be cold enough to freeze the plastic, and it should be able to do it within a few seconds--certainly less than half a minute.

For reference, a one-oz part on a "real" machine typically has a 45 second cycle time when run slow, and that includes open, eject, close, inject, & hold (freeze).

For home-made stuff, they usually use a mechanical lever to apply pressure, if not an air cylinder. I think speed will be more important that maximum pressure, unless you are trying to eliminate sink from a mediocre design, or you are trying to fill thin deep slots. If you need, you can add a long stroke air cyl to your long lever so you get pressure and consistency.

A long time ago we used to encapsulate relay coils with Polypropylene (PP) using a manually operated toggle link platen and a hand operated spoked wheel (~600mm dia) driving the rack and pinion injection ram (~20mm dia).
Slow going, hard work but it did the job just fine. It would work with PVC too.