thoughts on these three machines?
I am looking for a injection moulding method to make very small (3-5 mm) parts out of polypropylene. Not mass production, I would be happy with one part per min. I can make small moulds of any material (even glass) as I have a tiny precision mill. Tried to mould the ghetto way in the oven, but the plastic oxidizes and crumbles, and as my moulds get more complex it will only get worse.
First, I found these 2 injection machines which were made via a kickstarter project (good). However, the owner does not ship worldwide (I am in the UK), and is not very easy to deal with. One almost feels like he does not want to sell his machines. Has anyone tried these?
Then there are these 400W Chinese desktop “dental fixture” machines all over ebay for $1000-$1500. Of course, the Chinese ship anywhere. Has anyone tried these? A spec search shows 250C melting temps:
if you can use glass you could then use the same process used for metal.
you put a hopper on top of the feeding hole of the mould and you heat up the mould with a halogen lamp.
The transparent mould will allow infrared to melt the plastic without heating up too much the mold, so that it’s gonna be fast in cooling.
in this way the neck of the hopper will not heat up too much either and the hopper will not melt the polymer.
the column of plastic above the mold will feed polimer while air will flow out.
everything works better if you can press pellets, while applying vacuum in order to take air bubble out while tou compensate PP shrinkage also during cooling.
PP shrinks a lot and even if you do not see it from outside it will create cavities inside the part…
a good way for avoiding cavities is to disperse something like baking soda in the melt that by foaming will increase volume elasticity. This elasticity will elastically absorb tensions and reduce deformations.
if something here above is interesting, but not clear, just ask for clarifications!
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