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Author Topic: moulding HDPE or plexiglass  (Read 6835 times)

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Offline frodoTopic starter

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moulding HDPE or plexiglass
« on: January 06, 2009, 02:52:37 PM »
hi everyone,
i want to build a robot where i have vacuum formed the robots "body". the problem is, when you vacuum form, you end up with wafer thin plastic. was wondering if you guys had any idea how to mould the "body" which still keeping the thickness on the plastic.
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Offline Asellith

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Re: moulding HDPE or plexiglass
« Reply #1 on: January 06, 2009, 02:58:41 PM »
This is a crazy idea but I watch a friend make a custom watch this way. Take thin sheets of either material and make slices. Then glue the slices together and sand smooth. lots of work but if your going for a really cool look on the cheap it might work. Kinda like plywood I guess. Some rapid prototype plastic machines do this. They drop liquid plastic in layers and let it dry but that same concept. Also the plastic doesn't have to be thermoplastic.
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Offline Razor Concepts

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Re: moulding HDPE or plexiglass
« Reply #2 on: January 06, 2009, 04:01:55 PM »
Is there a particular reason why you need it to be thick? Polycarbonate (Lexan) sheets when molded are very strong and wont crack or tear. Hobby grade RC vehicles use lexan as the body material, and they withstand 40+mph crashes.

Offline paulstreats

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Re: moulding HDPE or plexiglass
« Reply #3 on: January 06, 2009, 05:17:55 PM »
My understanding is that when vaccuum forming you can produce any thickness of plastic. The reason its usually so thin is that you try to use the least amount of plastic while keeping a reliable amount of structural integrity. The resultant thickness is likely due to the level of low pressure produced by the vaccuum. so a stronger vaccuum will produce a thinner plastic

Offline pomprocker

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Re: moulding HDPE or plexiglass
« Reply #4 on: January 07, 2009, 01:14:02 AM »
3d printing service

strong enough to stand on the parts once done

Offline frodoTopic starter

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Re: moulding HDPE or plexiglass
« Reply #5 on: January 07, 2009, 05:03:14 AM »
Is there a particular reason why you need it to be thick? Polycarbonate (Lexan) sheets when molded are very strong and wont crack or tear. Hobby grade RC vehicles use lexan as the body material, and they withstand 40+mph crashes.

yes because after being vacuum formed, the plastic that i use cracks really easily.
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Offline Razor Concepts

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Re: moulding HDPE or plexiglass
« Reply #6 on: January 07, 2009, 07:17:06 AM »
Try a sheet of lexan, they don't crack as easily - those unbreakable bowls and cups are made of lexan.

Offline frodoTopic starter

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Re: moulding HDPE or plexiglass
« Reply #7 on: January 07, 2009, 07:37:44 AM »
where can you get lexan from? do you have to buy from the internet?
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Offline Asellith

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Re: moulding HDPE or plexiglass
« Reply #8 on: January 07, 2009, 11:52:19 AM »
Another option is fiberglass. I know a lot of people make full scale R2-D2 models from all fiberglass parts and they tell me if you do it right that it can be strong enough to stand on. You just need to create a mold. So if you use wood or another material that is easy to cut and shape then you can create a mold and make parts that way. Just an idea.
Jonathan Bowen
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Offline frodoTopic starter

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Re: moulding HDPE or plexiglass
« Reply #9 on: January 07, 2009, 11:59:28 AM »
Another option is fiberglass. I know a lot of people make full scale R2-D2 models from all fiberglass parts and they tell me if you do it right that it can be strong enough to stand on. You just need to create a mold. So if you use wood or another material that is easy to cut and shape then you can create a mold and make parts that way. Just an idea.
Isn't fiberglass that yellow stuff you put in attic insulation?
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Offline Razor Concepts

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Re: moulding HDPE or plexiglass
« Reply #10 on: January 07, 2009, 02:36:54 PM »
That's fiberglass insulation, just a bunch of tiny glass threads in a puff ball. Fiberglass is the fibers, but epoxy is applied to create sheets - basically carbon fiber, but cheaper. Look for a Halo-suit tutorial, use the same concept but make the mold for your robot. Halo-suit tutorials usually use card stock molds, which is easy to construct.
« Last Edit: January 07, 2009, 02:38:20 PM by Razor Concepts »

Offline Asellith

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Re: moulding HDPE or plexiglass
« Reply #11 on: January 08, 2009, 08:42:51 AM »
fiberglass is like plastic or wood. It is a type of material. Fiberglass is maybe more complicated because your selection of different materials means a lot. You can put a clear coat or a colored coat on the outside to give it a nice smooth feel. The make up of the fibers you use determines the material properties and the type of epoxy is important. Just find a good tutorial and experiment. Actually might be good thing for me to play with and write a tutorial on. I have all the material just no time to make parts :) I might do that this weekend.
Jonathan Bowen
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Offline rootoftwo

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Re: moulding HDPE or plexiglass
« Reply #12 on: January 16, 2009, 12:37:27 PM »
My favorite material for vacuum forming opaque is ABS (Acrylonitrile Butadiene Styrene). http://en.wikipedia.org/wiki/Acrylonitrile_butadiene_styrene

One of the main advantages is that it dissolves in Acetone. You can mix up a 'slurry' of ABS chips/scrapings in Acetone and make a glue that (if done right) is indistinguishable from the parts you are joining. It also takes paint really well.

If you want transparent parts I would suggest you try PETG - a copolymer of Polyethylene Terephthalate.

When you are vacuum forming, the thickness of the finished part is determined by the amount of 'draw' over your buck or former and the thickness of the material you start with. This will be determined by the size of your machine. I've vacuum formed 0.25" ABS - on a big vacuum former.

http://lh4.ggpht.com/_PYB5xE2EiZk/SXDRKwNojwI/AAAAAAAABtU/C0PWrICqiRU/s144/saucer.jpg

The yellow part is vacuum formed ABS - about 2' across and 0.18" thick. The blue parts are telescoping cylinders made of glass-reinforced plastic (GRP) - fiberglass mat and polyester resin.

Cheers,
John.

Offline colorclocks

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Re: moulding HDPE or plexiglass
« Reply #13 on: January 18, 2009, 03:12:17 PM »
If you're going to vacuum form plexiglass (acrylic), make sure you use extruded acrylic, not cast acrylic.  Cast acrylic has a narrow range of temperature over which it is plastic.

I agree with rootoftwo that PETG is preferable for clear stuff.  It's tougher than acrylic, and cheaper than polycarbonate (lexan).  It also vacuum forms at a lower temperature, and over a wider range of temperature.

In my experience, plastics don't get all that much thinner when vacuum formed, at least as long as you heat them  to the right temperature, and you don't push them too hard.

Offline Admin

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Re: moulding HDPE or plexiglass
« Reply #14 on: January 27, 2009, 12:47:08 AM »
Strength isn't just about thickness. There is strength is the shape too. For example, when you buy toys, they typically come in hard plastic shells that were vacuum formed. Thin plastic, but very strong.

My understanding is that when vaccuum forming you can produce any thickness of plastic. The reason its usually so thin is that you try to use the least amount of plastic while keeping a reliable amount of structural integrity. The resultant thickness is likely due to the level of low pressure produced by the vaccuum. so a stronger vaccuum will produce a thinner plastic
Thinner plastic conforms to the desired shape much easier. Thinner the plastic, the more detail you can get.

Offline frodoTopic starter

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Re: moulding HDPE or plexiglass
« Reply #15 on: January 27, 2009, 12:48:58 PM »
right, i'll bear everything in mind. thanks everyone  ;)
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