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mold and unmold

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This topic contains 7 replies, has 4 voices, and was last updated by  HAHATAY SON RISAS DE GANDIOL 6 months ago.


mold and unmold

02/12/2019 at 00:47

Hello everybody,
Is there any of you that had any problems with the plastic injected into molds when it comes to unmold the object? We cannot figure out what we do wrong. It becomes quite difficult to unmold them. We are even thinking that maybe we should add some products to the mold or maybe look for some special paint. Any idea?
team defaratt

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In reply to: mold and unmold

03/12/2019 at 19:13

Hello @defarat
There are a couple things you can do to easily remove your plastic parts from the moulds:

#1: Make sure that the internal walls of your mould are as smooth as possible. If your mould has any type of texture, the molten plastic will adhere to them.

#2: Use a mould release agent: You can buy mould release in spray cans, or make your own with cooking oil. Here are some examples:




In reply to: mold and unmold

03/12/2019 at 21:07

Do you have a picture of your mold or design?

In reply to: mold and unmold

04/12/2019 at 12:01

@defarat, You can also drill a few ejector holes and punch it out with some pins – or make a thread and screw it out.
However, the walls need a slight angle to address exactly this problem. Also have a look at the more popular video about injection molding – explaining a little this problem.



In reply to: mold and unmold

15/12/2019 at 23:54

Please find attached some pics.
I am very sorry about the delay of my answer, but we got some problems with the extrusion and the compression machines, which took us lots of time and energy.


In reply to: mold and unmold

16/12/2019 at 00:04

@xxxolivierxxx, thanks for the feedback, but I do not see that we can use any of those solutions with metallic molds or at least this is what I could understand from the videos and info you have shared.

Thanks for the idea of the ejection pins, we may be trying them if we get a go to an aluminum mold which we are thinking of.

For what concern the pics I have just posted it is clear that one of the problems is due to the fact that the surface is not smooth enough. Lately we got some tests done very well ( with the new square mold): even if we have some difficulties to reach correct temperature in the tube, it seems that if we are able to fill the mold in one go and not to heat the mold itself too much the object comes out quite well (see last pics) and it gets unmold nicely.


In reply to: mold and unmold

16/12/2019 at 03:43

From your first and second picture it looks like you are injecting through a small hole so your part is trapped in the top piece. Are you doing that to help remove the part from the bottom pieces? You could add some jack screws in the perimeter frame to help separate the stack.

Yeah, a little more grind and polish to smooth the surface would help as well.

In reply to: mold and unmold

17/12/2019 at 10:48

@s2019, the small hole for injecting through has been made as it is with no special cause. Right now we made it a bit wider. I think we will test the jack screes for the perimeters, it sounds to me a very good idea. Thanks a lot

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