Here is a short YouTube video showing the vacuum former in action:
What is vacuum forming?
In essence, vacuum forming is the process whereby a sheet of plastic is warmed up until it starts to get soft. Then it is draped over a mould, and a suction force is applied to tightly fit the plastic to the mould. Once the plastic cools, it is removed from the mould and thereafter retains the shape of the mould. Wikipedia has more on this.
It is a useful replication and manufacturing process, alongside sculpting, resin casting and other construction techniques.
Construction of the vacuformer
My vaccum former is essentially a sealed box, with a perforated top plate and a hole on the side where I can attach my vacuum cleaner to. Our vacuum cleaner provides the suction. The mould piece is placed on the perforated top plate, and as the hot plastic is draped over the mould, I switch on the vacuum cleaner and it sucks the plastic tightly around the mould.
The construction of the vacuum former box is pretty simple. It is basically an 8"x8" box made of 3x1 wood pieces, with two 5mm plates of 8x8 plywood stuck on the top and bottom. The top plate has 1/8" holes drilled into it in a regular pattern, about 1" from each side. This part is called the platen.
There is a 3/4" hole cut out of one of the sides. I've attached a PVC cutoff to this hole, which tightly fits my vacuum cleaner hose.
Attached to the platen is an aperture & gasket. The aperture is an 8"x8" piece of plastic with a 4"x4" hole cut out of the center. The aperture is taped to the top of the platen, sealing the edges.
Resting on top of the aperture is a 4"x4" gasket made of rubber silicone.
Separately, I have a frame which holds the plastic, first while it is being softened in the oven and second while it is being stretched over the mould on the vacuum former.
This is made out of two 8"x8" pieces of 5mm plywood with a 4"x4" hole cut out of each, held together by clamps. The 5"x5" piece of plastic is held between these to frames.
The aperture is simply taped to the top of the box, and the gasket sits loosely on top. This setup allows me to swap out a larger (or smaller) set of apertures, gaskets and frames, for when I want to make larger (or smaller) parts.
Doing it this way means I only need one size of vaccum box, but for different sized moulds I can use the right amount of plastic - which minimizes waste and avoids common problems like webbing.
When it is all put together, it looks like this:
Here is my vacuformer box again, showing the aperture and gasket:
Here is the frame, with clamps:
Here is a piece of plastic clamped in the frame:
The frame fits comfortable in my toaster oven:
I made the gasket out of silicone rubber (since I have some lying around ahem). To do this I made a simple double-walled box mould and poured the silicone about 10mm thick in the channel.
This is overkill - I could simply have used weather stripping from the hardware store - but this gives me a bit more room (weather stripping is typically not as thick).
The aperture is cut out of 1mm styrene from a For Sale sign. It is 8"x8" and has a 4"x4" hole cut out of the center. This is taped to the top of the platen, and can be replaced with a larger (or smaller) aperture if I need to.
Once the plastic (held in the frame) has been softened in the oven, the frame is removed from the oven and positioned so that the gasket makes good contact with the frame. This drapes the soft plastic over the mould, and makes a pretty tight seal around the top perforated part of the box.
Then the vacuum cleaner is switched on. This sucks the remaining air between the plastic and the mould & platen out, which tightly wraps the plastic around the mould.
Once the plastic cools, the frame is removed from the box, and the plastic can be removed from the frame. The mould can be removed from the plastic, and the moulded piece of plastic can be cut out and used.
Here is a piece of (transparent) PETG plastic that was just removed from the frame, with the mould (the white car) still embedded in it:
This photo shows the steps I took, from (left to right): initial sketch (in sculpey), monster clay cast that was refined and smoothed out, recast resin mould piece, and the final vacuum formed plastic piece:
- Do I need a large and powerful vacuum cleaner?
Not for the small parts and that I am making and the thin plastic (0.02" to 0.04") that I make them with. We have a pretty generic vacuum cleaner and this does fine.
- What kinds of plastic should I use?
I have thus far succesfully used PETG plastic sheet (transparent) and styrene sheet (opaque), at both 0.02" and 0.04" thickness. I got the PETG from Amazon.
For the styrene I have tested the For Sale signs you can pick up at the hardware store. If you need something in a rush and for pretty cheap, I recommend sanding down a bit of the painted area on the sign: the paint will not stretch nicely, and will make visible lumps on the surface of the part. Sanding it down a bit helps tremendously.
However, the styrene sheets you can get at a hobby shop, from brands like Evergreen and Plastruct, will be much better.
- How much should I heat the plastic?
I go slow on this, and first heat the plastic using the 350 degrees setting on the oven for about 4 minutes, then increase the temperature to 400 degrees F.
The plastic will first start to shrivel a bit, then relax and become smooth, before starting to sag. Once the 4"x4" plastic droops about 1", I know it is ready to go.
- What can I use as a mould?
You want to use something rigid. This is not the place for a silicone mold! I have used polurethane resin casts as molds, but I am sure you can use sculpey or something similar. Keep in mind the mould has to withstand the tension of the air sucking the plastic around it.
The mould does not have to be very heat resistant, as the sucking action seems to lower the temperature of the plastic quite rapidly.
As in all arts and crafts, and especially in DIY manufacturing, please be safe.
- Hot plastic can easily burn. Keep this in mind. Do not leave the area when you have plastic heating up in the oven. No one needs their house on fire.
- Hot plastic, hot metal and even hot wood is hot and does not care about your hands. Wear gloves.
- Hot plastic can produce fumes, and does not care about your lungs. Do this in a well-ventilated area and / or use a respirator.
- Constructing things out of wood can cause injury, keep your fingers attached by using gloves and by using your head.
- Always Use Eye Protection.
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