Twin sheet thermoforming is the process of brining two sheets of thermoformed sheets together to make one part. This is accomplished by heating two sheets of plastic and pressing them together with two separate molds using platens, thus creating a mechanical bond between the two sheets. here are two methods of accomplishing this, one involves a single station set-up and the second involves using a four station rotary machine. For our discussions here we will cover the second method only.

The process is very similar to thermoforming a single sheet with an added step. The initial sheet is placed into the clamp frames and rotated into a large oven, the sheet is pre-heated in the first oven and then rotated around the second oven to finish bringing it up to the forming temperature, while this is happening the second sheet has entered the first oven and is being heated to almost the forming temperature, at a given point the carousel rotates and the first sheet is brought to one of the molds and is formed onto this tool. Meanwhile the second sheet has entered the second oven and is finished being brought up to forming temperature. At this time the clamp frame releases from the first sheet leaving the sheet on the mold, the carousel rotates and the second sheet is brought around to the second mold on the top platen, the top platen is lowered, takes vacuum, the sheet forms around the mold and then the platens are brought together and locked to create a bond between both sheets.

This process can be used to fulfill a large number of applications, from pallets to trays to consumer goods products.  It is a rather unique process and requires special machines to perform the task, but the outcome can create very unique parts.