How much does an injection mould cost?

It depends on part size, number of cavities and complexity. Small single-cavity moulds can be modest; multi-cavity or hot-runner moulds for large parts cost much more. Ask moulders to quote the mould and the per-piece price separately.

What is the minimum quantity for injection moulding?

There is no fixed minimum, but because the mould is a one-time cost, moulding becomes worthwhile from a few thousand parts. For a few hundred, machining or 3D printing may be cheaper.

Why do moulded parts warp or show sink marks?

Usually uneven wall thickness, thick sections or cooling problems. Even walls, ribs instead of solid sections, and good mould cooling prevent most of it.

Plastic injection moulding job work: process and cost

Plastic injection moulding makes plastic parts by injecting molten plastic into a steel mould under high pressure, cooling it and ejecting the part. Once the mould is made, parts come out in seconds, very consistently, so it suits medium and large quantities.

Quick facts

Machine: Injection moulding machine, rated in tonnes of clamping force
Common plastics: PP, ABS, nylon (PA6, PA66), POM (Delrin), PC, HDPE
Typical tolerance: About ±0.05–0.2 mm (±0.0020–0.0079 inch), depending on size and plastic
Cycle time: About 10–60 seconds per shot
Mould: Steel (often P20) mould made first; the main one-time cost
Usually priced: Mould cost once, then per piece

What decides the price

The mould: size, number of cavities, side cores, hot runner or not
Part weight and plastic price
Cycle time, which depends mostly on wall thickness
Machine size (tonnage) needed
Secondary work: inserts, printing, assembly, packing

Design rules

Keep walls even, typically about 1.5–3 mm (0.0591–0.118 inch)
Add draft on vertical faces, about 0.5–2°
Use ribs instead of thick walls for strength
Avoid sharp inside corners; give small radii
Allow for shrinkage: each plastic shrinks differently (see the shrinkage calculator)

What to send the moulder

3D model (STEP) and a drawing with critical sizes
Plastic grade and colour (and glass fibre, flame retardant or UV needs)
Yearly quantity, to decide the number of cavities
Who owns the mould and where it stays
Any inserts, logos or textures

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Related job work

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Materials

Questions

How much does an injection mould cost?: It depends on part size, number of cavities and complexity. Small single-cavity moulds can be modest; multi-cavity or hot-runner moulds for large parts cost much more. Ask moulders to quote the mould and the per-piece price separately.
What is the minimum quantity for injection moulding?: There is no fixed minimum, but because the mould is a one-time cost, moulding becomes worthwhile from a few thousand parts. For a few hundred, machining or 3D printing may be cheaper.
Why do moulded parts warp or show sink marks?: Usually uneven wall thickness, thick sections or cooling problems. Even walls, ribs instead of solid sections, and good mould cooling prevent most of it.

The figures on this page are typical values for guidance, written by Diemeco from standard engineering practice. They are not a specification: confirm grades and properties with the relevant standard or the supplier's mill test certificate, and tolerances with your workshop. Last checked 15 October 2026.