Billow snap-back forming

G. Forming with billow snap-back is recommended for any parts requiring a uniform, controllable wall thickness. 

Billow drape forming consists of a male mold pressed into a sheet prestretched by the billowing process (Fig. 1.74). A similar process is billow vacnnm forming, wherein a female mold is used (Fig. 1.75). In vacuum snap-back forming, vacnnm is nsed to prestretch the sheet, then a male mold is pressed into the sheet, and, finally, pressnre is nsed to force... 

Like the snap back process, billow forming is a sheet pre-stretch process used with a male mold. The sheet is clamped across a pressure chamber and is billow pre-stretched by applying a low magnitude positive air pressure to the chamber. The male mold is then moved into the stretched sheet until the clamp seals on the mold periphery. Contact between the mold and controlling the rate at which the pressure chamber is vented to compensate for the advancing mold can regulate the sheet. 

E. Air-slip forming is similar to vacuum snap-back except that heated sheet is billowed up and mold rises to meet It. 

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