Mold making

A mould is the tool that gives a plastic or rubber part its shape. A good mould makes the same part, cycle after cycle, for years, so the mould maker's skill in design, machining and finishing shows up in every part you sell.

Mould makers build injection moulds for plastics, compression and transfer moulds for rubber and thermosets, and blow moulds for bottles and containers.

The core and cavity are machined in steel by CNC and EDM, then fitted, polished or textured, and tested on a moulding machine. Cooling channels, gates and ejection are designed so that the part fills, cools evenly and comes out without damage.

Materials commonly used

• P20 and similar pre-hardened steels for medium runs
• H13 and hardened steels for long runs and abrasive plastics
• Stainless steels for corrosive plastics such as PVC
• Aluminium tooling for short runs and prototypes

What to send with your requirement

• A 3D model (STEP) and the drawing with critical dimensions and tolerances
• The plastic or rubber grade and colour, and the shrinkage allowance if you know it
• The expected total quantity and the yearly volume
• The moulding machine you will use: tonnage and platen size
• The surface finish you want: polished, matte or textured

What affects the cost

• Cavity count: more cavities cost more but bring the part price down at volume
• Part size and complexity: undercuts, side actions and thin walls add mould cost
• Steel grade and hardness, decided by the number of parts you expect
• Surface finish, texture and cooling design
• Trials and modifications after the first samples

Common mistakes to avoid

• Choosing the cheapest steel for a mould that has to run for years
• Not agreeing on how many trial rounds are included
• Changing the part design after cutting has begun
• Not sharing the moulding machine details

Frequently asked questions

How many cavities do I need?

It depends on the volume you expect and the budget for the tool. A single cavity is the cheapest tool. More cavities cost more upfront and reduce the cost per part. A mould maker can suggest a sensible number once they know your quantity.

Can a mould maker fix a mould made elsewhere?

Many do repairs, modifications and polishing. Share photos, the part, and what is going wrong, and ask for a quote to inspect first.

What is a fair number of trial rounds?

There is no fixed rule. Agree it before starting: how many trials are included, what counts as a pass, and who pays for changes that come from design revisions.