Injection Mold Cost Factors

Two quotes for the same part can be far apart, and both can be reasonable. A mold's price is mostly design, machining and fitting time, plus steel. These are the things that move them.

Part size

A bigger part needs a bigger mold base, more steel, longer machining and a bigger press to run it. Size sets the floor for the whole quote.

Number of cavities

A four-cavity mold costs more than a single-cavity one, but it makes four parts per shot, so the part price drops. At low volumes one cavity usually wins. At high volumes the extra cavities pay for themselves.

Steel and mold class

Aluminum and soft steel are quicker to cut and cheaper. Hardened steel lasts much longer and costs more to build. The SPI mold class on the quote tells you how many cycles the tool is built for. We went through this in detail in aluminum vs steel injection molds.

Side actions

Slides, lifters and unscrewing cores are mechanisms inside the mold that move to release undercuts. Each one adds design, machining, fitting and maintenance. Removing an undercut at the design stage is often the single biggest saving available.

Surface finish

Finishes are usually called out on the SPI scale from A-1, a mirror polish for lenses and clear parts, down to D-3, a coarse blasted finish. Mirror polishing is hours of hand work. Textures add their own step. Specify the finish each face needs.

Tolerances

Tight tolerances mean more trial rounds: shoot parts, measure them, adjust the steel, repeat. Hold the tight numbers where they matter and let the rest relax.

Runner system

A cold runner is simpler and cheaper to build, but the runner is scrap or regrind on every shot. A hot runner costs more up front and saves material and cycle time, which makes sense at higher volumes.

Sampling and paperwork

First shots (often called T0 or T1), dimensional reports, and for automotive work a PPAP submission all take time. They are worth doing, and they belong in the quote rather than on a later invoice.

Changes after steel is cut

Design changes after machining starts are expensive, and some are impossible without welding. Freeze the design before you release the tool, or ask for the areas likely to change to be built steel safe.

How to compare quotes

Ask each supplier to list the mold class and steel, cavities, runner type, side actions, surface finish, number of sampling rounds, and who owns and maintains the mold. Once those line up, the prices usually make sense. If they don't, the cheaper quote has usually left something out.

We quote tooling with those details spelled out. To make your first quote faster, see what to send and injection molding design rules that keep tooling costs down.