Make · process

Injection moulding

Molten polymer forced into a steel mould

The dominant process for high-volume plastic parts — everything from bottle caps to car bumpers. Pellets are melted and injected under high pressure into a precision steel mould, cooled and ejected, tens of thousands of times over. The economics are all in the tooling: a mould costs a fortune, but once it exists the parts are nearly free.

Very high (10k–10M+)
Volume
High — steel mould
Tooling
Seconds
Cycle
Tight (±0.05 mm)
Tolerance
How it works
  1. 1
    Feed and melt pellets in a heated barrel with a turning screw.
  2. 2
    Inject the melt at high pressure into a closed steel mould.
  3. 3
    Hold pressure while the part cools and solidifies.
  4. 4
    Open the mould, eject the part, and repeat.
Strengths & limits
Strengths
  • Extremely low cost per part at high volume
  • Complex 3D geometry in a single shot
  • Tight, repeatable tolerances
  • Almost any thermoplastic, and many filled grades
Limits
  • Very high tooling cost — a steel mould
  • Only economic above roughly 10,000 parts
  • Design rules bite: uniform walls, draft angles, no thick sections (they sink and warp)
Typical parts & materials

Typical parts: Caps and closures, housings, connectors, gears, syringes, automotive trim

Commonly run in — open one for its cited properties:

PPABSPA6PA66PCPMMAPEEK

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