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Injection moulding in China: what you are really buying

You are buying two things with very different lifespans — a steel tool that lasts years, and parts that come out of it. Confusing them is where the money goes.

France → China

Plastic parts look like the simplest thing in a product and behave like the most committing. The part price is low and the tool price is not; once the tool exists, the design is fixed in steel and every change costs real money. Most of the unpleasant surprises in a first hardware project come from this asymmetry being understood too late.

What determines the tool price

  • The number of cavities — how many parts per shot. More cavities cost more upfront and less per part; the right number depends on your real annual volume, not your hoped-for one.
  • The steel grade, which sets how many shots the tool survives. A soft tool is cheaper and right for a first series; a hardened one is right once the design has stopped moving.
  • Undercuts and moving parts. Every feature that prevents the part from simply sliding out adds mechanism, cost and failure points.
  • The finish: texture, polish, where the gate and ejector marks land. Decide this before cutting, not after seeing the first parts.

The ownership question

Who owns the tool decides whether you can ever move production. Paying for it and stating in writing that it is yours, with its physical location named, keeps that option. A tool « offered » by the factory, or amortised into the part price, is cheaper today and makes you dependent. Neither is wrong — but it is a decision, and it should be made deliberately, before the first payment rather than during a dispute.

The sequence that protects you

  1. A design-for-manufacture review before anything is cut. The factory will tell you which features are expensive; listen.
  2. A soft or low-cavity tool for the first series, accepting a higher part price to keep the design movable.
  3. T1 samples — the first parts out of the tool — inspected against the drawing before any production is authorised.
  4. Hardened, multi-cavity tooling only once the product has sold and stopped changing.

A tool sitting in a factory you have left is a hostage. Knowing where yours is, and having the right to collect it in writing, is worth more than the discount you got for not asking.

Keep reading on this.

ShenzhenTooling: the cost people discover too lateUnit price gets all the attention in a first quote. The mould is what actually locks you to a supplier, and it is rarely discussed until it is paid for.ShenzhenFrom working prototype to first production runThe prototype proves the idea. The series proves the drawings, the tooling, the supply chain and the tolerance for variation — four different problems.China sourcingChanging supplier without losing your tooling, your quality or six monthsThe decision is usually made late and executed fast, which is the wrong way round. A transfer prepared over three months costs a fraction of one improvised in three weeks.ShenzhenGetting your product tested and certified while it is still in ChinaTesting at the factory door costs a fraction of testing after a container has crossed the world — and a failure found there is a correction, not a write-off.

If this raised a question about your own project, tell us where you are — the first conversation usually clarifies more than a proposal.

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