Not sure which way you're going with this question...but yes, people have made their own vacforming machines for sheet plastic
(I have, HowmetTX and several others here have), and yes, people have used vacformed plastic shells as molds for resin bodies.
Does that help?
Vacuums are sometimes used in resin casting and in injection moulding - otherwise the material simply would not make it into some areas of the more intricate moulds due to pressure from trapped air. Remove all or most of the air and there is nothing to block the path of the resin/plastic.
It's great in theory but probably tricky in practice.
I would be interested in how it is done on a DIY scale.
Biggest problem I can see is that the vacuum could potentially distort silicone moulds (because of tiny air bubbles in them) so they would need to be formed in the same level of vacuum or be well reinforced.
Obviously if you are using a metal mould then no problem BUT this would need a very carefully crafted shape or you would never get the casting out!
Thin bodies can also be formed by slush casting - that involves putting a small amount of resin into a mould (preferably a sealed hollow mould) and rotating the mould constantly and in all directions to spread the resin thinly. It's a very similar process to making chocolate Easter eggs. Once set the excess material is cut away. You can also do it with an open mould - you just need to be a bit more careful with how you move the mould about to evenly distribute the resin. The problem with this method is creating body mounting posts accurately - these are probably best added in afterwards.
There is also a variation on slush casting where resin is brushed into the mould to make sure all detail is created. After curing a second layer of resin is slushed about until it sets. Body posts can be added this way by using thickened resin as "glue" to fix them into the shell. The main issue with this is de-lamination (where the multiple layers of resin don't fully bond to each other for whatever reason).
Well that's the theory. Me - I make an open mould, carefully mix and then pour in the gunk, vibrate the table if I remember, and cross my fingers
apologies for my first response...a dialectical misunderstanding? Over here, that would be a "vacuum pump" *grin*
Now that I understand...I'm wondering if you're interested in easy alternatives to pressurization. Pressure's great, especially if
you're planning a production run, but not necessary IMO for hobby casting a body or two. The easiest way around this is simply
to brush thin layers of liquid resin into the mold until you have a nice uniform outer surface and then slush cast the rest. You can
also go with a two-part mold if you want a very consistent thickness...and again, start with brushing and voids won't be an issue.
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