Not Really A Prop - female tooled Vacuum Former

are you getting thin spots or a consistent thickness? opcorn

funboy1013xx said:

are you getting thin spots or a consistent thickness? opcorn

Click to expand...

It does vary depending in the type of tooling and how deep it is. That won't matter, regardless of the type of tooling.

So on the body part, which is female tooled, you see it does thin out at the top of the curved part. On the lip, it is virtually the original 4.5mm thickness. At the centre of the bottom on the curve, it is probably about 2mm. Research suggests that if I was to place a piece of machine bar through the middle of the part, it would help even out the thickness as its weight would help draw down the material like a blunger.

If I was to male tool this, it would be about 3.5mm at the top and be as thin at the edges. So it is a bit of a trade off. The reason I went this way was due to problem solving the issues I had when I made my first vacuum forming rig in 2012. Back then, it was all three key elements failing at some point. Most notably, heat and seal. Out of pure frustration, I placed a piece of 3mm perspex on the vacuum chamber, made a seal (the centre bowed in) and then I applied heat. It was a slower method, but I was able to pull a deep dome from the plastic. It them made me think, if the plastic hits shapes on the way down, it would take the shape of the object. As it turns out, it sure does and you can get greater details including raised lettering on the surface of the parts.

The lid and end caps are male tooled, but if the plastic gets too hot, it gets thin as well. So there is a fine balance between just the right about of heat and having enough suction. I have been reducing the amount of suction in fear of breaking the plastic (I ripped a 5mm sheet of Perspex in half because I didn't have enough heat, back when I first built this chamber). I honestly think that once the plastic reaches the point of being pliable, that I really should be upping the suction, not the heat. With the heat box down, there should be enough heat to keep the plastic soft enough for forming.

What I discovered is that because all my tooling is metal, if I over heat plastic, I run the risk of it burning and sticking to the tool. I have been told (and they were joking at first) to use cooking oil (sunflower, not olive) as that stuff can handle 350 degrees C before it burns. It will help lube the parts and like an egg in a pan, it should not stick. You then wash them with warm soapy water.

I am using 4.5mm here because I knew 3mm would not cut it.

I am curious to see how much better (or worse) making the lid in a female tool would be now that I have opened the ends of the tool. It got paper thin with 3mm when I had ends on the tool. Based on what I saw with the body pull is that I would have to move the tool up to the edge so that the handle recess is still thick.

If I can ever get this vacuum forming blacket (propper silicone sheet), the thickness issue is a non point as the plastic simply gets molded by the tool and blanket makes the seal. But at about a $1000, not something I am racing out to buy on a "maybe it works".

A vacuum blanket. Lets see how this goes

cavx said:

https://uploads.tapatalk-cdn.com/20180626/4882d48e086f49d49d55864faa6dd02f.jpg

A vacuum blanket. Lets see how this goes

Click to expand...

It goes good


This vacuum blanket rocks!

My sheets are 2400mm x 1200mm and my rig is 800mm x 800mm, so I only get three 800mm x 800mm sheets from a full sheet with three 800mm x 400mm off cuts that I previously could not use. Now using the blanket, I can have the full sheets cut up into smaller parts and don't have to worry about off cuts.

This is 4.5mm pulled at 20"Hg.


Sent from my CPH1701 using Tapatalk

Too good not to share

From my IG account.

https://www.instagram.com/p/BkyuL16lNTn/?taken-by=cavx01

This vacuum blanket can stretch 250%.

So not only does the blanket stretch to 250 percent, it also handles heat up to 230 degrees C continuous and 250 degrees C short term.

I got brave enough to heat the plastic through the blanket and it is really cool to see it pull down.

This part was heated over a female tool, drawn in and then forced to the final shape under heat and pressure. Not the prettiest part but impressive that it took the mold shape and retained the thickness.

Sent from my CPH1701 using Tapatalk

This is the full set up as it stands now.

The main unit is a vacuum chamber 700mm ID and 150mm deep. The top plate is 800mm x 800mm X 6mm steel. A hinged frame holds the vacuum blanket. The base plate was originally poly plastic, welded to the poly pipe. It had to be replaced with a 6mm steel plate due to warping and breaking of seals.

The vacuum blanket is 3mm thick, high temperature silicone and can stretch 250% and handle up to 250 degrees Celsius. It provides both a seal as well Atmospheric pressure onto the heated plastic. It is actually quite scary when you do the math.

This form is 32" and at full vacuum, there is 14.7 PSI.
32 X 32 X 14.7 = 15052.8 pounds of pressure!
Divide that by 2.2 to convert to metric tonnes and you get 6.842 tonne. No wonder it breaks things that are not supported properly.

I use a gas burner as the heat source and this gets super hot or turned right down to low temp depending on the type of plastic i an forming.

I use a shop vac to as surge to pull the blanket down and make the initial seal. Vacuum cleaners only pull 6"Hg, so I have a change over valve to allow me to use a vacuum pump for deep pulls. The vacuum pump will pull a full vacuum or 30"Hg.

I originally designed this rig for female tooling, but because the blanket can stretch so much, it works perfectly fine with male tools as well, even if they extend past the top of the chamber.

There are 3 main parts to successfully vacuum forming -

1. Heat
2. Seal
3. Suction

This rig has cost me about 5 grand to make but there is nothing I can't make with it. If I was to change anything or start over, I would simply make it bigger.

Sent from my CPH1701 using Tapatalk

I am really loving this vacuum forming blanket. Not only has waste gone to virtually 0, if parts don't pull properly the first time, I can reheat just the area and reform.

And now I have learned that I can really push this hard. The blanket will stretch to its limits and holds and I can heat the plastic through the blanket.

This is a section of handle (for the tube bag) that was not quite round. Is now.

Sent from my CPH1701 using Tapatalk

that's cool! i would LOVE to see if you can make a clean/clear helmet visor?

funboy1013xx said:

that's cool! i would LOVE to see if you can make a clean/clear helmet visor?

Click to expand...

How about a dome pulled into a tool. This is 6mm perspex.
Because it never touched anything, it remained optically clear.
Sent from my CPH1701 using Tapatalk

I was hoping that with your new blanket technique it would be able to maintain the thickness as you showed above. It didn't cross my mind the rubber blanket might "scuff" up the acrylic? maybe not?? :cheers either way this build is damn cool!! :cool

funboy1013xx said:

I was hoping that with your new blanket technique it would be able to maintain the thickness as you showed above. It didn't cross my mind the rubber blanket might "scuff" up the acrylic? maybe not?? :cheers either way this build is damn cool!! :cool

Click to expand...

So there have been quite a few "vacuum forming woes" type threads over the years. This rig is essentially the results of problem solving those issues. It is not perfect, but it allows me to make things that I could not have done prior or do any other way. The best part for me right now is that my waste material has gone to virtually zero.

The blanket creates the seal, so you can use smaller pieces of plastic. When done this way, the plastic keeps it's original thickness. This is fine with solid colour like black, not sure about clear.

When I vacuum formed parts of the first tube bag, upon inspection, you can see how much it thins out as the pull gets deeper. The plastic started at 4.5mm and is 2mm at the far ends of each lid.

Using the blanket and the plastic starts at 4.5mm and finished at 4.5mm. It is now gone from a flat sheet to a shaped sheet. And it is as rigid as any part that was made from injection molding, without the very high cost of tooling.

It is best to think of the blanket as an ever shape changing plug. When you use a male tool, you pull the plastic down over the tool. If you use a femail tool, you pull the plastic in to the tool. Both have limitations due to the stretching of the plastic and sometimes mechanical plugs or frames are used to help shape the plastic over or into the tool and can help reduce the issue of over stretching or even tearing.

Speaking of a tear, if that happens on a tradional vac form, you have lost the seal and therefore have no suction. The plastic could tear under the blanket and because it makes the seal, you can continue to form. I have made parts where the side has torn, but it didn't matter as I was going to cut the sides out during trimming.

When using smaller parts, the plastic tends to pull away from the tool as it cools resulting in deformed shaping of the part. The blanket holds pressure to keep the plastic in the formed shape until it has cooled and can't deform. It is like an infinite number of hands all pushing down at the same time.

The blanket might scuff the plastic in the case of pulling a dome for a visor, but you would certainly have more control on the exact shape using a tool underneath. In most cases, the blanket does not drag across the surface, rather just stretches in the voids as the air is sucked out.

When pulling a dome, you will need a frame to hold the plastic during heating. The blanket would push the plastic down.

Most optical distortions occur due to temp variation between the heated plastic and the cooler temp of the tool. Toolless pulls like that dome are optically clear because the plastic never touched anything during the forming. It was allowed to cool under suction and cooled into the new shape.

My blanket is now getting some "scaring" and these may leave impressions on the surface of really hot plastic. These scars were created from really hot plastic. So at some point, it will need replacing, but it is working for now.

Sent from my CPH1701 using Tapatalk

love it. great info, thanks for sharing. looking forward to your progress and updates! :cheers