Vacuum forming plastic parts.
August 14, 2009
Heres a few photos of my home made plastic vacuum former and its maiden test. If you don`t know what vacuum forming is check here, and youtube.
Essentially a sheet of heated plastic is placed over some kind of mould which then has the air sucked out from underneath it. The soft plastic schloops to the shape of the mould and when it cools you have yourself a robot part. It really does sound like schloop if you`re wondering.
I made mine out of a blue box used for holding paint or whatever, a sheet of thin plywood, the top off a bottle, a few screws and lots of hot glue to seal the edges.
I drilled lots of little holes in the plywood which was a waste of time and completely unnecessary. You can get away with having 1 big hole in the center and then laying some kind of metal mesh to cover the top.
I made the mould of kids clay. The clay is actually just paper pulp and calcium plus other stuff. Wrap it in paper overnight to remove the moisture and harden it.
Put the mould in the center of the table with some coins underneath to allow air flow. If you have the single big hole and metal mesh the coins aren`t needed.
The frame I made from some aluminium U channel. You need 2 frames to clamp the plastic in between them.
I made some legs out of wire to hold it up off the bottom of the oven.
The first test is with 1mm thick PP sheet.
I put it in the microwave oven at 140°C for 10 minutes. When the timer went off I pulled it out with some vice clamps and poked the center with some pliers. The center had sagged about 2cm but I didn`t think it was soft enough yet so I put it back in at 160°C for 2 minutes by which time I guessed it was done.
Put it over the mould and hit the vacuums switch! After cooling I cut it roughly from the sheet and tried to get the mould out. DOH. It wouldn`t come out. Not enough taper on the sides. I ended up filling the bottom with water until the clay went soft then dug it out with a spoon. Incidentally I think I can use that clay again.
Once I cut it to fit my robot there will be an update showing it mounted.
- Professional looking moulded plastic parts.
- Equipment is easy to make with simple tools. I used a hacksaw, hand drill and hot glue gun.
- Cheap. PP sheet = $1 for 2 clay = $1 reusable.
- Mould has to be made from something that can withstand heat and pressure.
- Parts are only as professional as your mould is.
- Convex parts only. Some taper on the sides is needed to get the mould out unless you destroy it.
- Limitations on the height of the part.
- A lot of wasted plastic once the part is cut out.
- Figure out a way to make better moulds.
- Try different mould material.
- Try different thermoplastics.