TwinSheet

Twinsheet, or twin-sheet forming, is a plastics manufacturing process in which two sheets of thermoplastic are heated and formed simultaneously in a single forming operation to produce a hollow part with a seam where the sheets meet. The method is related to vacuum forming but uses two forming sheets that are formed in matched dies or cavities and then joined along their edges to create a double-walled or hollow component. The seam can form a continuous bond as the sheets cool and press together, often reducing or eliminating the need for additional fasteners.

In practice, two flat sheets are heated to forming temperature and positioned on opposing dies. The dies come together to form the sheets into the desired cavities, typically using vacuum, air pressure, or mechanical forces. After forming, the sheets are cooled and separated, with the seam area fused or bonded to produce a single, hollow part. Common materials include ABS, polystyrene, acrylic, PETG, polycarbonate, and PVC, with typical thicknesses from about 0.5 to 3 millimeters, depending on part size and stiffness requirements.

Applications span automotive interior components, protective housings, enclosures for electronics, consumer products, and certain packaging parts. The process offers advantages such as lower tooling costs and the ability to create hollow, lightweight parts with smooth exterior surfaces and relatively short lead times. Limitations include visible seams, thickness limitations, and size or geometry constraints tied to sheet forming capabilities.

See also: vacuum forming, thermoforming, sheet forming.