Vacuum forming is an industrial process where a sheet of thermoplastic is heated to a forming temperature dependent on its thickness.
Once heated the plastic will be stretched over a mould .It is a cost effective process.
The stretching of the material is possible because of the application of a vacuum created between the mould surface and the plastic sheet.
Problems with vacuum forming:
Sheet does not pull down over the mould:
Air may be trapped between the mould and the sheet.
Check that you have enough evacuation holes
The sheet may not be hot enough increase heating time
The clamp frame may need replacing
The vacuum pump filter may need cleaning
The sheet may be cast acrylic which is not vest for vacuum forming
Sheet burns or blisters:
The sheet has become too hot
The sheet may be hygroscopic and moisture in it causes blisters
If sheet is over 5mm it will need more time for the heat to soak all the way through
Reduce power and increase heating time
Sheet pulls out of clamp frame when raising the platen and mould:
The sheet is not positioned correctly
The sheet is not hot enough increase the heating time
The material may not be vacuum formable
The mould may be too large or the edges too close to the perimeter of the forming
aperture. Modify the mould design
Webbing occurs on the finished forming:
The sheet is too hot and it has sagged during heating. Reduce heating time
The design of the mould may need to be modified
Forming will not release from the mould:
There may be undercuts on the mould which are holding the forming in place
The forming may have srunk onto the mould start the blow cycle early
The mould material may have bonded with the forming material
Put a thin coating of silicone oil on the mould before forming
The mould is too hot, turn the machine off and wait for the mould to cool off
before attempting another forming
The mould surface is too rough, make sure there is an even finish on the mould before