Vacuum Forming Design Guidelines

Designing for Vacuum Forming

Vacuum forming is a cost-effective method for producing plastic parts, trays, covers, and enclosures. However, the process has specific design constraints that must be considered from the outset. Designing with these guidelines in mind will ensure your parts form correctly and consistently.

Draft Angles

Draft angles allow the formed part to release cleanly from the mould. A minimum draft angle of 3 degrees is recommended for male (positive) moulds, and 5 degrees for female (negative) moulds. Textured surfaces require additional draft: add 1 degree per 0.025mm of texture depth. Insufficient draft is the most common cause of forming difficulties and part damage during de-moulding.

Wall Thickness & Material Thinning

During vacuum forming, the heated plastic sheet stretches over the mould, causing the material to thin. Corners, deep draws, and sharp features experience the most thinning. As a general rule, the starting sheet thickness should be 3–4 times the minimum required wall thickness in the deepest drawn areas. Keep the draw ratio (depth to width) below 1:1 for consistent wall thickness.

Undercuts & Corner Radii

Avoid undercuts wherever possible, as they prevent the part from releasing from the mould. If undercuts are unavoidable, split moulds or collapsible cores may be required, adding cost and complexity. All internal corners should have a minimum radius equal to the material thickness: sharp corners cause stress concentration and excessive thinning.

Mould Materials

For prototyping and short runs, MDF and timber moulds are cost-effective and quick to produce on our CNC router. For production runs, cast aluminium or machined aluminium moulds offer superior durability, heat transfer, and surface finish. We can advise on the best mould material based on your production volume and part requirements.