The Geometry Challenge

In vacuum forming, a "deep draw" refers to a mold where the depth of the part is greater than its width. This stretches the heated plastic sheet to its absolute limits, often resulting in two critical defects: Webbing (folds or wrinkles in the plastic) and Thinning (areas where the plastic stretches so much it loses structural integrity).

Technique 1: Plug Assists

To combat extreme thinning at the base of a deep mold, engineers use a plug assist. This is a mechanical pusher (often made of syntactic foam so it doesn't cool the plastic prematurely) that physically forces the heated sheet into the mold cavity before the vacuum is applied.

• Material Distribution: By pushing the plastic down mechanically, the plug carries material to the bottom of the mold, ensuring the walls and base remain thick and structurally sound.
• Syntactic Foam: Utilizing specialized foam prevents the plug from leaving mark-off lines on the final product.

Technique 2: The Pre-Blow (Bubble) Step

Webbing occurs when there is excess plastic that folds over on itself as it tries to conform to sharp adjacent corners. To fix this, we utilize a pre-blow step.

Before the tool is raised, compressed air is blown beneath the heated sheet, inflating it into a large bubble. This pre-stretches the material evenly in all directions. When the tool is raised into the bubble and the vacuum is pulled, the material wraps around the mold uniformly, completely eliminating wrinkles and webbing.