hey guys,first of all, excuse me if i make any mistypes,but i'm from romania (europe)
i think you can help me, i looks at a lots of pages and forums, but didn't find anything relevant
i want to build a thermoforming table (i mean that with compressed air blown from the top inside somekind of a "bell" instead of beeing vacuumed from the bottom) or a vacuumforming table. i need it to be 150x150 cm (about 60x60 inches).
i want to make custom interior panels for cars, so the detailing is not that precise and the shapes are mainly sloped, without any close edges or corners.and the vertical size isn't bigger than 20 cm (8 inches)
because this is a custom and individual job, i would like to shape the models out of extrudated foam, then cover it in pvc tape, and then form a thin sheed (1-2 milimeter) of pvc or abs (whitch is the better for the job?) to give it some rigidity, and to be easy for the painter that i work with to paint them.
i know some of you would probably tell me to use fiberglass but i hate that crap, it's heavy(a panel with bondo reaches about 4-5 kg), unheathy and it's terible for the painter to get it smooth.
do you think this will melt the foam? i think that if the shape is pretty sloped, i don't have to heat the pvc/abs sheet so much
first of all, if i do a thermoforming table (or whatever that's called what i want to build) what pressure do i need (please in atmospheres)?
second: if i build a vacuumforming table, how big/high must the vacuum be
what kind of compressor/pump do i need?
third: what temperature must i heat the sheets to?
No not really. I think it would be quite useful to be able to mold plastic for the odd project to be able to offer a professional looking product. I have used perspex for a few things but it breaks too easily and would like some other options such as PVC. I understand heating PVC is not a good thing to do, so that was where I thought this thread might go. The saftey issues, tips etc.
Just covers for moving parts. To stop fingers getting caught. Problems come about when I subject sharp corners to stress. Any imperfection will become a fracture point.
Not that I'm looking for help on this. I just thought we might see some of the plastic experts giving some input to your initial questions.
I was looking at pressure for the top but in my case went to vacuum. With pressure what scared me was you need an air tight cover over the system and applying positive pressure I was looking at a bomb. Especially when it gets larger. The guy's can comment on this one as some are more knowledgeable than me.
With pressure I believe you will also cool the material very quick where with vacuum you are taking it out. For molds I make mine from foam but I also cover it with epoxy and glass. The best I find to make a mold is to make a shell and fill it with Polester resin and sand mixed together for weight and strength. The problem with large sizes when using the resin mix is that it will shrink so has to be done a bit at a time.Styro I find will not take much more than 7 or 8 hg before crushing so by itself it is good for making a mold for the other processes.
I made a machine for myself for doing canopies and items for my RC hobby. It will pull down a sheet 24 x 16" and is self contained. After I was given a Di Arco machine that is smaller but has a pump/vacuum compresser with tanks for each side and with a Pyrex heating element that swings over the top.
If I can give any help let us know.
yeah, the positive pressure kept me from doing it to. you need a stirdy build to hold it, especialy when it's big, i don't like working next to a, like you said, bomb.
the other thing that i don't like at this setup is that you have to heat the plate on a rig outside of the "bell", because if you heat it from underneath, it forms like a bubble downwards and melts down on it. and if you heat it outside the bell, you lose temperature while moving it inside.
the thing that made me think about this setup is the cost of tha vacuum pump. if you do a 3 meter by 1,5 meter rig you need a pretty powerfull pump that costs a lot. positive pressure is more easy to make then negative.
if you have an idea of a DIY vacuum pump, that is powerfull enough, please let me know.
I used a shop vac to start with and after picked up 2 vacmotors and mounted them in the bottom. Gives me lots for my size. For a larger one I would go like my Di Arco which has a compressor/vac and has a steel tank for vacuum. It also has a pressure tank separate but I do not use it unless I have to blow the plastic loose. With the tank you can build up lots of vacuum while heating and then when you pull the plastic down throw the lever and instant draw.
Will try to put a couple of pic's on as I drew up a diagram also for another forum.