building a vacuum /thermoforming machine

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    Question building a vacuum /thermoforming machine

    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?

    thanks

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    This is something I have been thinking about too.
    I would imagine there will be a lot of interest in this thread if we get some good info.
    Paul



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    paulC do yo have a specific procedure in mind?



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    Quote Originally Posted by drifter
    paulC do yo have a specific procedure in mind?
    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.
    Paul



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    what did you use it for, how big were the loads on the parts?



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    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.
    Paul



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    maybe ?

    Attached Thumbnails Attached Thumbnails building a vacuum /thermoforming machine-pressure-forming-bmp  


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    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.
    John



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    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.



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    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.
    John

    Attached Thumbnails Attached Thumbnails building a vacuum /thermoforming machine-vacformer-jpg  


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    could you please give me any specs on the vac motor/pump, and the diagram for the vaccum tank?



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    I will take a look to refresh myself on the system and then draw something up. Never did learn cad and getting to old to be proficient anymore.
    John



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    Drifter,

    150x150 cm or 60x60 inches?

    Do you have access to sheet this large? Auto interiors are often an injected poly type of plastic, which does not thermal form well do to its memory charcteristics. A fire retardent ABS would be your best bet. The size is a bit questionable since 48x96 or 48x120 would be a stock size.

    Secondarily you would need a massive machine and die to keep the pressure sealed inside. If a perfect vacuum is 0psi or 29 inches of mercury or one atmosphere. To convert that to pressure would be roughly 15psi acting on 60x60" or......around 54000lbs of force.

    I've done pressure forming, but only about a 30cm square. To get as much detail out of the die as would be in a vacuum , I think it was around 60-80 PSI or 4-7 atmospheres. My time in the trade was 11-12 years ago, so I'm a bit lost on the old memory cells myself!

    The material would need to be around 370 degrees and the droop once at forming temp would be around 20-30% of the width. The softer it gets, the easier it forms.

    The oven and support frame would be on the order of 2 meters larger in each direction of the blank. If you expect to form 150x150 you will need something for clamping so figure 160x160cm blanks? The cycle time could be short, but to heat soak that large of a sheet with even distribution is going to take some planning.

    Tank and pump capacity for 450,000 cubic cm(150x150x20 box) would take about 150 US gallon or 98UK gallon tanks. The pump size would depend on the cycle time you expect. 15-20cfm should be adequate, but that may still be on the conservative side. A screw type vac pump would be the only way to go for a quick cycle. It is not like you need the full vacuum instantly. It will take time to pull the material down, but you do need to keep it going before it chills off quickly.

    What you propose is no simple task. Nothing a lot of time and money won't solve. It just sounds large for pressure forming as I recall it. I used to build seal ring dies for parts near this large(48x60"). The seal ring came down on the material just outside the trim area. The sheets were much smaller which benefited the overall time and cost.

    DC



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    ello'

    i have done quite alot of vacuum forming on both hommeade and manual model-shop style machines..

    the user 'one of many' brings up a very good point about sheet sizes... in all my time working with the stuff(5 years maybe), i havent seen sheets larger than 48x96"... i hate to quess what it would cost for a sheet larger... the desired product, car interior panels seem entirely doable on a 48x48 machine..

    i must warn you - a positive pressure machine, which i have no experience with, will requires signifigant effort to get perfect, i would think. also, without a large system to mechanize the cover and sheet frame, the whole thing will be cumbersome... a site i saw once comes to mind - it was basically big, temporary vacuum forming machines... it took a whole 48x96" sheet in a frame hooked to hinges on the floor. this could pivot up to heating elements mounted on the wall, and then pivot down to a 48x96" vacuum forming surface. this will be the only economical way to approach this idea. the pro equipment to form sheet that big must cost at least 10,000 used - unless you get lucky with someones old junk....

    another thing to keep in mind, you will not have good luck heating a sheet that big without very good and accurate heat sources... quartz\ir heaters to heat that area would cost at least $25 sq/ft.... the power required to heat this if electric would be probably 3-phase and expensive transformers... an alternative is to use gas heating elements - again, costly and dangerous... your cost of gas would not be insignifigant.. many larger industrail machines use gas, but the process is controlled to save time.. it really will get expensive...

    however, your project is totaly possible... im not certain a vertical heating position will work well for a sheet that big depeding on molding requirements and sheet thickness. it will heat more in some places and be very difficult to control.. it will have a similar effect to the much-less liquid window-glass, which actually flows over the years and old windows are thicker at the bottom than the top(or so i have been told! never looked into it)....

    i put up some simplified pages here (in download section i think) describing a 'nice' homebuilt machine.. also, i beleive the web site with the large-sheet former was showing a machine used to make stuff for theatre or tv\movie sets..

    give more information for a better answer. what are your facilities like? ventillation! is there gas or 3-phase available? budget? plastic thickness, most often used stock sheet size... etc. a person deciding on this sort of thing for a factory would carefully consider all of this - DO A GOOGLE SEARCH.. reading even 8 or 10 pages will really give you a much better idea about this...

    i also agree that positive pressure sounds like a bomb! you should probably not follow that route, especially when vacuum forming is far more common and probably easier.. also, some machines use both, with a much weaker positive pressure....

    just my nonsense experience....



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    i found 300x150 cm pvc sheets, that are thermoformable, up to 2 mm thickness, but i would want to use 1 mm.
    gas is available, good ventilations could be obtained(i'm planning to get a bigger shop)
    the forms i'm looking for are pretty fluent, with out negative corners.
    i'm also considering vacuum forming.
    i don't want the cost to be very high, say 1000 bucks.
    i think i am going to build a smaller one first, abou 20-25 inches square.
    would apreciate plans and specs for that sizes
    thanks guys



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    Hi I saw this and I thought I'd put in my 2cents. I have built a 2'x4' thermo former and it works well. I am planning to modify the plans and build a 4x4 next. I built it from the plans I bought from these guys here http://www.build-stuff.com/1002plans.htm

    They were at the Toledo Ohio hobby show and I bought the plans there. I would not try pressure forming at a budget of only $1000. My machine cost me $3000 and I thought that was pretty cheap. They say it can be built for $1800 but it seems low.

    All my molds are made of ½” thick fiberglass. They have reinforcements inside also to prevent implosions. (I learnt that the hard way) My first mold imploded the back cover that sealed the mold off. Talk about almost S***ing my pants. It was loud!! It even bent the ¼” plate that was clamping the mold down. I build all my patterns with there own vacuum boxes.

    Drifter, If you would like to use foam to design the molds, that would work but I would be making fiberglass patterns from them and going the vacuforming route. It will be cheaper and is a heck of a lot less dangerous. I build my molds thick but you can get away with thinner molds if you reinforce them properly. The foam by itself will just crush. I use a small pump that evacuates the air out of a tank. The tank I have is overkill for my setup but I planned on having more than 1 machine. Right now it takes 5 minutes to evacuate the tank. After a cycle it only drops 1 inch of mercury and only takes 1 minute to get it back to 26 which is the max that my pump will pull. I form 1/8” thick abs and it is working well for me.

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    If you want to build a fairly large (2 x 2, 2 x 3, or even 4 x 4) vacuum forming machine cheaply, your best bet is probably Thurston James's plans in his book "The Prop Builder's Molding and Casting Handbook."

    The web site http://www.tk560.com has articles on building a vacuum former like that, for a very few hundred dollars, with a few cost-saving substitutions. A number of people have built such machines, either straight or with significant variations.

    There is also a discussion board with a vacuum forming forum, where people discuss design alternatives (over & under machines, different kinds of heating elements, vacuum source alternatives, etc.)

    http://www.tk560.com/phpBB2/viewforum.php?f=1

    That's the most useful site I've found for discussing vacuum formers. There's also a vacuum forming forum on hobbymolding.com, but it's less active.



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    Recently I completed a 4' x 4' vacuform machine. I used a turkey burner unit for the oven. I have a 4' 6" square oven that has a 1/4" steel plate over the burner, with the addition of a flue pipe fan to circulate air. I can heat a .040 sheet of styrene in about 5 minutes. I made a flip frame that is hinged between the oven and the vacuum table. The table top is made with a MDF base, 1/4 spacers and finally 1/8" peg board.

    The vacuum is then created with a air compressor that i converted. I use the air filter input as the pump system. This is hooked up to 2-80 gallon hot water tanks. I stripped the tanks of all components as well as the insulation and outer shell (this was done to shrink the over all size). The two tanks are connected together to the pump system with a series of pipes and valves. I also installed a filter and check valve inline. Using this system I can heat and create my needed vacuum in about the same time period. I have found that if I am not as caring about the quality of the finished piece I can pull a new mold about every 7 minutes.



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    Cool. Could you post pictures?

    Paul



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    Wow guys, this is an awesome forum. I've learned a lot just reading the last two pages.

    I once tried to build a garage thermoform using plaster of paris for the mold and heating the LDPE held in an angle iron frame using my oven broiler(I was a single man then). I had poor surface finish and some bubbles. So, I gave up and worked on other projects. Maybe now is a good time to try again.



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