Manufacturing services · Chapter B · Method 09

Plastic injection moulding

Core TCI route

Molten thermoplastic is injected into a steel or aluminium tool, cooled and ejected. The lowest-cost route per part at scale.

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Production injection moulding machine. Representative process photo · Bricetofly · CC0 · Wikimedia Commons

How it works

Plastic injection moulding, step by step.

A labelled schematic of the process (not to scale), and the four steps every job goes through.

Labelled diagram showing how plastic injection moulding works — Schematic · not to scale. Drawn by TCI Group.

STEP 01

Tool

Design and cut the tool; sample and groom critical features.

STEP 02

Melt

Granules are heated and plasticised by the screw.

STEP 03

Inject & pack

Melt fills the cavity and is packed as it cools.

STEP 04

Eject

The tool opens and ejector pins release the part.

Reference figures

What to expect.

Typical industry values to help you plan. We agree the figures for your part on the drawing.

Tool Tolerance±0.13 mm + 0.002 mm/mmIncluding shrink

Repeatability±0.10 mm or lessPart to part

Wall1.5–2.5 mmTypical guidance

Volume1,000s – millionsPer tool

Materials	PP, PE, ABS, PC, PC/ABS, nylon (PA6, PA66), POM, PBT, TPE/TPU and filled engineering grades.
Finishes	SPI A–D polish classes, VDI 3400 EDM textures and etched textures; colour matching is close, not perfect.
Design guidance	Add draft (1–2° typical, more for texture). Keep walls even; use ribs instead of thickness. Agree gate, ejector and parting-line positions.
Best suited to	Enclosures, clips, housings, closures and any plastic part needed in volume.
Watch-outs	Tool cost and lead time are front-loaded; design changes after tooling are expensive.

Other methods in Plastics & polyurethane

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Next step

Not sure this is the right route?

Send a sketch, photo, sample or CAD file with your quantity and target date. We will recommend the most sensible route and explain the trade-offs before quoting.

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Reference figures are typical published industry values for planning, not a guarantee; final tolerances, materials and finishes are agreed in writing for each project.