Still in the planning stage and never have vacuum formed anything. Looks relatively simple.
I plan to make a large dome shaped item. I was going to use .060 styrene sheets my friend has. I am guessing that the finished product would be a little flimsy. I need the item to be stiff to the touch.
I was wondering if I vacuum form the styrene to the mold, then vacuum form another piece over the first styrene piece (on the mold). Would the two pieces melt together, forming a thicker whole, or would I end up with a mess?
Or can I match up two sheets(double up) in the form, heat that up and mold.
You may get away with forming another part on top the previous part. Once the first part is cooled, drill vac holes in the trim area. Preferably where the mold meets the flat surface and if any corners in the part itself that can trap air. Basically porting vacuum through the first sheet. Styrene heats and cools quickly, so getting your timing right is going to take some trials.
Some formers may use a talc powder to help the second material move against each other as the second layer forms. Another option is to dash on a few dabs of PVC cement near the trim line(leaving air gaps) to prevent seperation or delamination.
One shop I know of uses this technique to form the skeletal part, then forms a cloth backed naugahyde(fake leather) similar to what used to be called softouch on top of the previously formed part still on the mold. Softouch is not available in the color the customer chose and it didn't form reliably over deep draws. The worst part is the fumes from the glue applied on the warm plastic surface.
Learn cause and effect through experience. Mastering those relationships is the "Common Sense" ability within the art of any trade.