In vacuum forming the piece you use to form the plastic on is called a buck.

The best materials for a form to make nose cones with is solid metal with a smal air hole to aid in removing the part from the buck. The CMR machine used mainly 2 part metal bucks, the nose cone shape and an angled collar that the cone sat on. This made it easier to remove the part from the waste plastic.

I have experimented with urethane casting resin, 3d printed plastic and hardwood for bucks, and the solid metal ones are most desirable from a standpoint of ease f separating the part and less surface prep involved in the form.

kj