Vacuum forming, is a thermoforming process that creates custom parts by heating a plastic sheet; using air pressure to pull the sheet tightly against a mold corresponding to the desired shape; and allowing the sheet to cool.
Vacuum forming offers a low cost way to mold sheet material. Shapes that can be made by vacuum forming include 3D shapes where the sides are sloped (like a plastic drinking cup) so that the formed part can be removed from the mold. In vacuum forming, features on the side of the shape are very limited as they can prevent release from the mold. Examples of parts made by vacuum forming include trays, enclosures, cups, cup lids, packaging clamshells, auto interior panels, utensil trays, etc.
Vacuum forming is usually applied to plastics, commonly HIPS High Impact Polystyrene, both opaque and transparent. The process requires a custom mold in the shape of the workpiece.
Cost optimization options for vacuum forming include reducing material thickness and shape complexity.
- You can choose positive (male) or negative (female) molding. In positive molds the heated material is stretched over a protruding mold and hence the inner side is more accurate. In negative molds the heated material is pressed into a recessed mold and hence the outer side is more accurate.
- When using vacuum forming you design the mold tooling, not the part. For example, to create a part shaped like a drinking cup you create a mold shaped like a cylinder.
- The thickness of the sheet material will vary at different points on the part due to non-linear stretching that occurs.
- The part shape must not be much higher than it is wide.
- Walls must have draft angles (typically 3 deg) to allow the part to be easily removed from the mold.