Make · process

Rotational moulding

Powder tumbled and melted in a rotating mould

Powder is loaded into a hollow mould that rotates on two axes inside an oven, so the melting polymer coats the walls evenly — making large, seamless, stress-free hollow parts at very low tooling cost. The trade is speed: a cycle takes minutes to hours, not seconds.

Low–moderate
Volume
Low
Tooling
Minutes–hours
Cycle
Loose
Tolerance
How it works
  1. 1
    Load polymer powder into a hollow mould.
  2. 2
    Rotate it on two axes inside an oven.
  3. 3
    The powder melts and evenly coats the inner walls.
  4. 4
    Cool while still rotating, then unload the part.
Strengths & limits
Strengths
  • Large, seamless, one-piece hollow parts
  • Low tooling cost (cast aluminium)
  • Uniform wall, very low residual stress
  • Double walls and complex hollow shapes
Limits
  • Long cycle times (minutes to hours)
  • Low to moderate volumes
  • Narrow material range — mostly polyethylene
  • Tight tolerances are hard
Typical parts & materials

Typical parts: Water and chemical tanks, kayaks and canoes, playground equipment, ducting

Commonly run in — open one for its cited properties:

HDPEPPPVCPA6

Part of the Make map of manufacturing processes. Browse the cited database, or see where these parts end up in the application domains.