Twin sheet forming is a type of thermoforming that involves two thermoplastic sheets. SMI employs this process to create double-walled or hollow custom plastics products, such as air ducts, cases, doors, electrical enclosures, fuel tanks, medical enclosures and housings, spine boards, surfboards, table, various transportation and vehicular products, and various marine products.

What is Twin Sheet Forming?

Twin sheet forming is a thermoforming process whereby two sheets of plastic are molded at the same time, creating hollow parts fused together into a structural assembly. Different shapes and contours can be molded on opposite sides of the part, along with differing color, material types or material thickness. By injecting air pressure between the sheets, fine detail on the outer component surface is realized, as with the pressure forming technique

The most commonly-used twin sheet forming technique secures two thermoplastic or acrylic sheets horizontally in an in-line or rotary shuttle machine. The top and bottom sheets are simultaneously pulled by a vacuum process once they’re heated. It is at this point that the molds are brought together and the heated sheets are compressed at designated areas in the custom plastic mold. In the end, both sheets are welded together –– no adhesives necessary.

Advantages of Twin Sheet Forming

When compared with other processes that are designed to create hollow plastic products, such as a blow mold process, for example, twin sheet forming has some distinct advantages:

• Structural integrity
• Enclosed cross-section capability
• Internal reinforcement
• Low cost of tooling
• Structural rigidity

A wide assortment of materials are implemented, including:

• ABS
• Acrylic sheet
• Perspex
• Polycarbonate
• Ultem
• TPOs