Vacuum Forming

Vacuum forming shapes heated thermoplastic sheet over a tool using vacuum, producing lightweight shells and covers with moderate detail at low tooling cost.

Overview

Vacuum forming is a thermoforming process where a heated plastic sheet is drawn over (or into) a mold by vacuum, then trimmed to final shape. It excels at producing large, thin-walled parts with smooth contours and consistent wall thickness, typically as single-sided “shell” components.

Choose vacuum forming for prototypes through medium-volume production where tooling cost and lead time matter more than tight tolerances or crisp feature definition. It’s common for housings, guards, trays, and cosmetic panels where most geometry can be drafted and radiused.

Tradeoffs: detail on the non-tool side is limited, deep draws thin out material, and tight dimensional control is constrained by sheet thickness variation, cooling shrink, and trim process. Undercuts are difficult without complex tooling, and secondary operations (CNC trim, drilling, inserts, bonding) are often required to finish the part.

Common Materials

  • ABS
  • HIPS
  • PETG
  • Polycarbonate
  • Acrylic (PMMA)
  • HDPE

Tolerances

±0.030 in

Applications

  • Machine guards and safety covers
  • Equipment housings and shrouds
  • Custom packaging trays and dunnage
  • Kiosk and appliance cosmetic panels
  • Medical device enclosures
  • Automotive interior trim panels

When to Choose Vacuum Forming

Vacuum forming fits large-to-medium size plastic parts that can be formed from sheet with draft, radii, and limited fine detail. It’s a strong choice for prototypes, bridge builds, and medium volumes where you want low tooling cost and fast iteration. Plan on trimming and possible secondary ops to add holes, bosses, and attachment features.

vs Pressure Forming

Choose vacuum forming when you don’t need sharp definition, tight cosmetic details, or high feature fidelity on the show surface. Tooling and per-part cost are typically lower, and lead times are faster for large covers and trays. Expect softer corners and less accurate reproduction of textures and small features.

vs Twin Sheet Forming

Choose vacuum forming when the part can be a single shell and doesn’t need an enclosed hollow section or built-in stiffness from a sealed perimeter. Single-sheet tools are simpler and cheaper, and trimming/fixturing is generally easier. If the design needs integral channels, double-wall structure, or trapped air volumes, twin sheet becomes the better fit.

vs Injection Molding

Choose vacuum forming when part size is large, wall thickness can be thin and relatively uniform, and volumes don’t justify high-cost injection tooling. Vacuum forming tolerates design changes and tooling revisions more easily. Expect less precision and fewer integrated features than injection molding.

vs FDM 3D Printing

Choose vacuum forming when you need smooth, thin-wall parts at larger sizes with better surface continuity and faster cycle time per part. Printing is useful for complex internal features and low-quantity one-offs, but becomes slow and expensive as part size and quantity increase. Vacuum forming typically delivers more consistent cosmetic surfaces for panels and covers.

Design Considerations

  • Add 3–5° draft (more for deep draws) on all vertical walls to release from the tool and reduce scuffing
  • Use generous corner radii; small radii thin out first and won’t form consistently
  • Keep draw ratios reasonable and avoid abrupt depth changes to reduce webbing and excessive thinning
  • Define trim strategy early (trim lines, datums, locating features) and specify which edges are functional vs cosmetic
  • Place holes, slots, and sharp cutouts as secondary ops rather than formed features unless the tool is designed for it
  • Call out texture and show-surface requirements explicitly and specify which side is tool-side vs non-tool-side