First timer; Vacuum form problem!

Hi there!

I've just started on my first project; making action figures of a character from my Star Wars fan film.

To make the packaging I build a vacuum vormer, but now I ran into a problem;

http://imgur.com/a/7NASE

I can't seem to get the corners right. They always clump up like this. What am I doing wrong? Any tips for me?


Thanks!

Re: First timer; Vacuum vorm problem!

Ok what you seem to have is called "webs". I am not 100% sure but I do belive they are caused by uneven heated plastic, so as it stretches, it clumps rather than pulls down.
Sometimes you get webs by having two or more parts to close together.
The only way to not have these is to pull each part on its own bit of plastic.

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Re: First timer; Vacuum vorm problem!

Thanks! I was afraid that was the problem. Would it be a bad idea to limit the size of the plastic and do one pull at a time? Are there any guidelines to how much room you need along the sides? I don't want to waste too much plastic

Re: First timer; Vacuum vorm problem!

LobsterJohnson said:

Thanks! I was afraid that was the problem. Would it be a bad idea to limit the size of the plastic and do one pull at a time? Are there any guidelines to how much room you need along the sides? I don't want to waste too much plastic

Click to expand...

From what I understand, you should have no less than 40% area of plastic than the area of the part you are making. Then the height of the part also comes into play.

The only way to absolutely rid webs is to do a female tool system. This means that you pull into the shape and not over it. For simple boxes, tooling will not be hard.

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In my experience, webbing comes from the plastic being heated more than it needs to be. When it's being heated, it sags down, increasing the surface area of the plastic. If it sags more than it needs to stretch to wrap around the part, the excess material has to go somewhere. Try pulling it a little sooner, with a little less sag.

You'll also notice that some of the webbing is between the two parts. That's probably about them being a touch too close together, as cavx said. I agree that, because you've got a bit of a tricky pull, you may have better luck going one at a time.

If you don't call joy doing this, I will suggest giving a female tool system a go.

This dome was pulled using nothing more than a section of 100mm PVC pipe with an 80mm hole cut in the end cap. But there is nothing to say that the hole you are pulling into can't be a rectangular prism. This worked upto 5mm Perspex. The dome in the image is 3mm.





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How large is your vacuum form and what are you using for suctioning and heating?

I posted the image of the bench top cooking unit I have and yesterday did a test to see just how hot it can get.

I set the thermostat at 200 degrees C and set the timer at 10 minutes.

As you can see, it gets to the proper temperature and it took just 10 min to do so.

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The webbing is caused by too much material moving too quickly down the side of your tool, and therefore like an ocean wave breaking from two directions at once and meeting in the middle. The excess material at the corners has no where to go, so it forms this "web".

It' not about uneven heating, it's too much heat. The plastic is too soft and is moving too quickly down the sides of the pattern.
Try less heat. This will slow down the material on the sides and pull more material at the corners at the same time as the sides. (I think this will solve your issue)

Adding a separate blocks of wood on the platen (vacuum form machine table) at each corner of the pattern, about an inch away and about half as high as the web. (this distance varies depending on the size of the pattern and height of the web) These blocks of wood will help "use up" the excess material at the corners and allow the plastic to flatten out at the corners, preventing the webbing.

Another way to reduce the webbing is to try and increase the air flow at the corners. This is done by making a slot or cut in each corner, at a 45 degree angle from the bottom surface of the tool up to around halfway up the corner on the side of the pattern. Then drill some large holes in the bottom of the tool, part way into this cut / slot. What you are doing is giving the escaping air (vacuum) more surface area to improve flow at the corner of the tool. Thus pulling the plastic down at the corner fast, to minimize the two "waves" at the sides of the pattern from crashing at the corners. Thus reducing the web.
Another option, is cut a hole, the same shape as your tool, from a piece of MDF or particle board. This hole wants to be about 1/2" to 1-1/2 inches bigger than the tool. This is used to press down over the plastic & pattern as your vacuum is pulling the plastic down. This in effects, "irons - out" the wrinkles or webs before they can form.

Thank you so much, I'm going to take your advice!

Could the power of the vacuum also be a factor in the problem? Too much suction right?

I'll try and post some pictures of the "machine" I build as well

LobsterJohnson said:

Thank you so much, I'm going to take your advice!

Could the power of the vacuum also be a factor in the problem? Too much suction right?

I'll try and post some pictures of the "machine" I build as well

Click to expand...

You can never have too much! No, It is too much plastic, coming down too fast, too easy on the sides and the corners can't keep up. Lower temp makes the plastic stiffer and helps to balance this difference out.

lmgill said:

Another way to reduce the webbing is to try and increase the air flow at the corners. This is done by making a slot or cut in each corner, at a 45 degree angle from the bottom surface of the tool up to around halfway up the corner on the side of the pattern. Then drill some large holes in the bottom of the tool, part way into this cut / slot. What you are doing is giving the escaping air (vacuum) more surface area to improve flow at the corner of the tool. Thus pulling the plastic down at the corner fast, to minimize the two "waves" at the sides of the pattern from crashing at the corners. Thus reducing the web.
Another option, is cut a hole, the same shape as your tool, from a piece of MDF or particle board. This hole wants to be about 1/2" to 1-1/2 inches bigger than the tool. This is used to press down over the plastic & pattern as your vacuum is pulling the plastic down. This in effects, "irons - out" the wrinkles or webs before they can form.

Click to expand...

Three questions for the OP -

1. what are you using for suction? (I am going to assume a vacuum cleaner of sorts?)
2. what are you using to heat? (most DIY guys are using the kitchen oven).
3. what type of plastic and how thick is it?

The suggestion of less heat is good, however there is a fine balance here between what allows the plastic to be soft enough to be formed verses just not quite hot enough.

The frame around the part is a good one. I ended up doing this myself a few years back. My part was taller than it was wide, so needed a little help getting the plastic right down to make the seal.

Check THIS out.

For simple free blown things like those domes, using air pressure instead of vacuum is more common and preferred, since you have no limit on pressure. With a perfect vacuum (at sea level) you have a max of 14.7 psi. Here is an example

lmgill said:

For simple free blown things like those domes, using air pressure instead of vacuum is more common and preferred, since you have no limit on pressure. With a perfect vacuum (at sea level) you have a max of 14.7 psi. Here is an example

Click to expand...

Blowing a dome is much harder than pulling one. And that is not exactly something a DIYer can do at home, is it.

What I am showing is a solution for all the documented problems DIYers face. And you don't even need the chamber I am using.

I must disagree. Having done both, I would say blowing a dome is Much easier than vacuum forming one. No need for a vacuum pump, just a compressor. clamping is pretty easy. You can heat the plastic in a regular oven. I would think a DIYer would go to blow forming long before vacuum forming.
For the shallow domes you were making, you could almost drape form them with enough heat and the right plastic. With no need for vacuum or pressure.

Hey there !
Thanks for all the help. I had to wait for new plastic come in, and a little vacation, but i'e read and applied all your advice.

Right now i'm doing much better! Right now i'm at this:


As you can see I still have a little webbing. But I also don't really have a sharp edge at the bottom. I'm wondering if with less heat I wont love even more of that edge..

My set up is like this:
The oven

The machine itself

My trusty 'r2 unit'


I put my molds on like so:


is there anything you guys could see I could improve on to go less web, more edge?
Thanks, I'm already super happy right now!

LobsterJohnson said:

is there anything you guys could see I could improve on to go less web, more edge?
Thanks, I'm already super happy right now!

Click to expand...

It almost looks like you are making the bubbles for carded action figures.

See if it make a difference removing that white plastic part from the buck (if not glued on) and add some dimes under the wood.