Thermoforming: Drape-Forming

A. Description
A simple technique, using a single positive (male) or negative (female) mold, on which a heated PALSUN sheet is placed. The sheet, softened by appropriate thermal processing, sags and conforms to the shape of the mold under its own weight, or by slight mechanical pressure applied by hand. Drape forming is generally used to achieve simple, uniaxial, large curvature thermal forming.

B. The Process
Two main techniques, differing by the position of the mold during the first stage.

1) 1st Method: The sheet (without masking) is placed on top of the mold in its basic, flat state. Both sheet and mold are then slid into a hot-air circulating oven and heated to about 150-155°C (300-312°F). When the sheet (and mold) reaches the required temperature it sags and drapes over the heated mold. Both are then pulled out of the oven and quickly helped, by gloved hands, to conform more precisely to the mold. It is then allowed to cool down.

2) 2nd Method: The sheet is placed into a hot-air circulating oven (without masking), and heated to about 150-155°C (300-312°F). When the sheet reaches the required temperature it is quickly pulled out of the oven and placed on top of the mold. there the sheet sags, aided quickly by the gloved helping hands, and takes the accurate shape of the mold. For better results we recommend pre-heating the mold to about 80-100°C (175-210°F) before putting the heated sheet on top. Then it is, likewise, allowed to cool down.

C. Vacuum Assisted Drape Forming
The technique can be assisted by vacuum and is then very similar in detail to the male (positive) straight vacuum forming.

D. Notes for Consideration (These notes exclude the vacuum assisted drape forming)
1) There is no need for pre-drying in this technique, due to the lower operating temperature it requires.
2) The lower operating temperature leaves the exterior surface harder, helping to keep it mar free, with better optical quality.
3) The emphasis on quick operation during the final finishing touch to the heated sheet derives from the rapid cooling and setting properties of the PALSUN sheet once taken out of the oven.

E. The Molds
1) Regular molds can be made of metal (steel, aluminum or other) or wood, as long as it can stand the
temperature inside the oven without visible distortion. The upper surface is usually covered by heat resistant felt, which will not mar the exterior sheet surface facing the mold face.
2) Premium molds: Finished products requiring premium optical quality (like visors, police shields, vehicles safety glazing etc.) need molds with very smooth, glossy, heat resistant upper surface. They can be made of polished steel, aluminum, glazed ceramics or glass.