Vacuum forming heats a plastic sheet until pliable and pulls it down onto a single sided tool using vacuum. Because only one face of the part is formed by the tool, and because there is no injection pressure to contain, tooling is a small fraction of an injection mould and can be made from materials as simple as machined wood or filled resin.
How the tooling is made
A male or female tool is machined or cast with a pattern of small vent holes so air can be pulled out from between the sheet and the tool. Aluminium tools with drilled vents and integral cooling are the production standard; timber, filled epoxy and printed tools serve for prototypes and low volumes. Temperature control is what separates a production tool from a prototype one.
Male and female tools give different parts
On a male tool the sheet touches the tool on the inside, so the inside surface is accurate and the outside carries the texture of the sheet. On a female tool the reverse is true. Wall thinning also differs: material stretches most over the top of a male tool and into the corners of a female one. Choose the tool type from which surface has to be right.
Wall thickness, draft and radii
The sheet thins as it stretches, so a deep draw is thinnest where it has travelled furthest. Starting sheet thickness is chosen with that in mind. Generous draft is essential because the part shrinks onto a male tool, and generous radii are needed because sharp corners thin dramatically. These three constraints shape every vacuum formed part you have ever handled.
Trimming is a real operation
The formed sheet arrives with a web of excess material that has to be removed, either on a router with a fixture, on a five axis trimmer, or with a trim die. That fixture or die is tooling of its own and is regularly missed from budgets. On low volumes hand routing against a jig is normal; on higher volumes automated trimming quickly pays for itself.
Questions people ask about vacuum forming services
How much does vacuum forming tooling cost?
Far less than an injection mould, because only one face is formed and there is no injection pressure to contain. Prototype tools can be made from timber or filled resin.
Male or female tool?
Whichever face has to be accurate. The sheet reproduces the tool on the side it touches and carries its own surface on the other.
How thin does the wall get?
Thinnest where the sheet has stretched furthest, typically the deepest corners. Starting thickness and draw depth are chosen together.
Is trimming included in a quote?
Not always, and it is a real cost including a fixture or trim die. Ask explicitly what trimming method is assumed and whether its tooling is in the price.