Not Really A Prop - female tooled Vacuum Former

cavx · Jun 26, 2017

The title says it all but I wanted to post it here because of the traffic this part of the forum gets and hopefully the information is useful for others.

I have harped on forever about thermoforming into a female tool instead of vacuum forming over a make tool or buck.

Here is the results of this method using simple DIY parts. The point of this was to make a replacement windshield for the vintage Star Wars Land Speeder. I used 3mm perspex which after the pull came out at about 2mm. I did an earlier version from 5mm.

The heater is a "turbo oven". These can be bought as low as $40.

I happen to own a 9cfm vacuum pump and so I used that for this, but I do think that with enough heat, even a vacuum cleaner could pull the plastic.

The chamber I used today is nothing more than a section of 4 inch PVC pipe with end caps glued into place. A 1/2 inch threaded plug is attached to the side. The top end cap has a big hole cut into it to allow the heated plastic to be pulled into the chamber.

The only thing I did wrong was not to sandwich the plastic between two plates. As a result the plastic warps and breaks the seal.

You could make the tool any shape and it would be best if the tool was placed into the chamber so that the plates holding the plastic get placed over that.

As long as you can get a good seal and have hot plastic, you should be able to make this work. This method is much easier than pulling over a male tool.

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cavx · Jun 27, 2017

The heater is a bench top, fan forced cooking appliance with halogen lighting as the heater.
It has a timer and thermostat.
It seems that the ideal temperature for perspex is 200 degrees C and it takes about 10 minutes to heat 5mm to a plyable state.

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cavx · Jul 10, 2017

bump to update.

cavx · Jul 10, 2017

Update and I have had a win today.

This dome is 300mm wide and 100mm high and made from 6mm Polycarbonate which is way more difficult to thermoform than other plastics like Perspex. The trick is slightly lower temp and today I used 150 degrees C for 10 minutes pre-heat and then continued with that heat during the pull. I also teased up the suction and maxed out at 25"Hg today. It didn't break the seal, just I didn't know how much more it would take in case the plastic cracked.

I have not really tested the limits of this new rig yet, but so far, is looking really promising. Next up is get a tool made up for the inside and pull into that.

You will notice that the cooker is black and that is because this one was replaced with the white one and was to be thrown out as it had stopped working. So the other day, I pulled it apart, gave it a good clean and now it works

The metal ring is part of the new cooker and I think one of the best things they include in the kit. It keeps the heater stable and high enough off the plastic.

I have made two frame from 3mm aluminium, but they actually bent today, so will have to look at 6mm at some point.

cavx · Jul 10, 2017

Reheated the clear dome and got a slightly deeper pull. From 100mm it is now 115mm. I could not get it to seal with the rubber mat so usrd a gasket made of EVA foam and as it pulled, it has blurred the clarity of the polycarbonate.

Looking back to the smaller dome and I don't think I even used a seal as the edge has taken on the shape of the plastic weld.

Then I used that machined ring as a tool and discovered that I don't really have uniform heating at 300mm.

This was looking good for a time but it bulged at would not pull back down.
This is 3mm Perspex.

Fail from uneven heating.

cavx · Jul 10, 2017

Deleted. Edited last post.

cavx · Jul 11, 2017

This is insane.

So I made a tool from 3mm aluminum.

I set it up to be pretty much level with the top of the chamber.
I was 5mm Perspex and had to heat it up to beyond 200 C.
Vacuum pump was almost pulling 30 inches.
It bent the tool!
But the pull came out really cool as was going to have to cut it into this shape anyway.

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cavx · Jul 12, 2017

And all trimmed up. This would be about 1/4 scale I guess.

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cavx · Jul 12, 2017

Made another and it came out the same, so proves this works.

cavx · May 5, 2018

This was an excellent proof of concept, but repeated tests suggest that this was limited to about 250 dia.

It was time to upscale. For those that don't know, this technique is actually used to make spar baths and where they pull up to 20mm thick perspex. So with enough heat and suction, you can make some deep pulls.

I made this rig a couple of years ago but could not get the heat I needed. Suction and seal was great, but with a lack of heat, I watched in horror as a sheet of 5mm Perspex was snapped in half.

I tested many different ways to heat and eventually settled on gas based on successful tests I did on my BBQ's wok burner.

I made a flume from 0.6mm aluminium that I mounted in a MDF box and installed a 3 ring burner at the base. After some tweaks, I was able to get over 200 degrees C out of it. But it was big, hard to move around and set up and didn't allow me to move the plastic fast enough to the platen for forming before the plastic has cooled. I wanted to place the heat above the job like I had been doing on the smaller rig.

My new toy.

This thing is LETHAL! But damn, it can heat the plastic to formable temps in just 2 min.

My vacuum is a 9cfm 2 stage vacuum pump.

The plastic I used here was just 3mm ABS, so not thick enough to do this part properly. But the results are pretty impressive all the same.

More to come soon.

cavx · May 11, 2018

A heat test yesterday proved that I can thermoform 4.5 Perspex on this rig without issue.

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cavx · May 13, 2018

Because that test was not 100 percent, I will have to make interactive tools.

Still not able to find the supplier of the silicone sheet so found a temporary alternative.

If anyone is living in the Atlanta area, please pm, as I have found something there that might be exactly what I want.

So anyway, during the last heat test, I used some off cuts of neoprene rubber as a mold liner and it took the heat well. But because I could not apply suction and seal, the part came out slightly distorted.

So the next step is to create male tools that work with the female tools I already have and the use the new rubber mat as the seal.

I ended up making this mat it's own frame and I did a speed test to see how well it works. So whilst the silicone has amazing stretch, this rubber does not, so the idea here is to use it for the seal and it will apply massive vacuum assisted pressure. Basically atmospheric pressure pushes down on the sheet as I vacate the air from the chamber. If I was not concerned about the sheet ripping, I could take this to a full negative atmosphere. If you do the math, 14.7psi is applied. The surface area is 800mm square. So it is a lot of pressure.

The heat box is attached to the rig with a swing up arm. Once it is clear, I turn on the pump and throw down the framed mat and as you can see in image 1, it works.

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Knightjar · May 14, 2018

Great stuff - thanks for sharing!

cavx · May 14, 2018

Knightjar said:
Great stuff - thanks for sharing!

Your welcome.

I think vacuum forming is one of the best things ever invented, however there are many limitations. It is fun when it works and a nightmare when it fails. Hopefully the things I am sharing here can be duplicated and help others make their own formers.

So apart from being almost a science for the DIYer, some of the limitations are -

1. loss of detail when thick plastic is used
2. inconsistent wall thickness of parts (and this can be from over heating or under heating).
3. lots of waste if using a large form to make small parts.

I want to be able to make thick and even strong plastic parts. I want to use hard plastics like Perspex or Polycarb and not have to make my stuff from 1 or 2mm ABS.

I want sharp details of my parts (when required) and why I turned to female tooling. You can even have raised lettering with this method. I am also incorporating a way to use traditional bucks (male tools) so I have the best of both worlds.

I want to be to use smaller pieces of plastic on my large form to minimize waste and economise on sheeting. This is why I have gone the membrane route. Also by shaping the heated plastic under pressure/vacuum, wall thickness remains the same, part to part, as there is no stretching of the plastic to make a seal. The stretched seal is left up to the membrane.

cavx · May 16, 2018

I have decided that really don't like ABS. It is easy to heat but it cools really fast and as a result, won't form properly.

I wish I know the limits of this rubber sheet. Stretch is amazing but I don't know it's thermal limits. A big part of the problem is the time it takes to get a seal without heat above and the plastic is already starting to cool.

Anyway I had to mod the tools as I was not getting the pull depth I wanted but I decided to the limits and see what happens.

These lids are a complex part and the steep vertical walls of the tool have been a problem so I removed them to open the ends up. It fixed one issue and caused another

Image 2. Whilst it pulled better, it exposed the corner of a piece of angle and the tip was sharp enough to cut the rubber sheet. See blue circle. Even thought I placed a rubber sheet over the tool, there must have been a part that was exposed. It didn't tear, it just made a sound and once I found the hole, I discovered that I could seal it with my finger. Not sure what to seal it with. Maybe a valcanizing patch like used with bike tubes might work.

Image 3 It looks like I can't use that machined part without some modding. I do need to test the inverted option I tested yesterday.

So fail today. Again, great pull into the centre and not so good on the out side. More heat and I burned the plastic.

Image 4. I had bought this large dog bowl ages ago and I decided to test it out and it gave a promising result. I did have to drill a small hole in the centre to vent the air. By taking the suction up to 15"Hg, the rubber sheet hits the bottom of the bowl.

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cavx · May 21, 2018

Seems I didn't update this thread with the good images.

Last week was looking good. But today was really testing. It turned out that there is a really small hole in the bottom of the chamber and that combined with a warped frame for the rubber sheet, and I just could not get it to seal.

On a cool note, I got a look at the silicone matting. Check out the stretch. This one goes to 750 percent before tearing.

It will cost me 900 bucks.

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cavx · May 25, 2018

Woo-hoo this this works like a charm.

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cavx · Jun 8, 2018

Not sure if this video will stick, but check this out. This steel plate is 6mm thick and the aluminium angle is there for a reference.

[video]https://www.facebook.com/cavx1/videos/1681043385318439/?t=0[/video]

Never underestimate the power of atmospheric pressure.

cavx · Jun 9, 2018

Some video to show how this works.

cavx · Jun 9, 2018

Spent a few hours trimming parts and this happened.

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Not Really A Prop - female tooled Vacuum Former

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