Cost
What drives injection molding part cost
Molding cost splits into a large one-time tooling charge and a small per-part charge. Understanding which of your decisions affects which is what makes the number controllable.
The two numbers
A molding quotation always contains a tooling cost paid once and a piece price paid on every part. Bundling them hides which one you are actually paying for, which is why our quotes state them separately along with the lead time.
What drives tooling cost
- Cavitation. Each additional cavity multiplies the most expensive parts of the tool.
- Tool steel and hardness. Aluminum is cheapest and shortest lived; P20 is the production default; H13 and stainless cost more and last longer.
- Part size. Sets the mold base size, and the machine that can run it.
- Undercuts. Every slide, lifter, or unscrewing unit is a mechanism with its own design, machining, and fitting cost.
- Surface finish. A polished or textured cavity costs meaningfully more than a standard machined finish.
- Tolerance. Tight tolerances mean more precise machining, more inspection, and more try-out iterations.
What drives piece price
| Factor | Effect |
|---|---|
| Cycle time | The dominant factor. Driven by wall thickness and cooling design, not by machine speed. |
| Part weight | Sets material consumed per shot, including the runner on a cold runner tool. |
| Resin grade | Commodity resins are inexpensive; PEEK and PEI are orders of magnitude more. |
| Cavitation | Parts per cycle divides machine time across more parts. |
| Machine tonnage | Larger presses cost more per hour. |
| Secondary operations | Pad printing, painting, inserts, assembly, and packing are added per part. |
| Scrap rate | A part with a marginal design pays for its rejects on every run. |
The volume crossover
Because tooling is paid once, unit cost falls steeply with volume at first and then flattens. This is why the same part can be uneconomic at 200 units and very cheap at 200,000, and why the honest first question about any molding inquiry is what the annual volume actually is.
- Below roughly 100 parts, machining or 3D printing is normally cheaper, because no tool is paid for.
- Between roughly 100 and 1,000, a prototype aluminum tool often wins.
- Above roughly 1,000 a year, production tooling usually wins outright and the advantage grows.
Levers that actually reduce cost
- Reduce wall thickness where the function allows. It cuts both material and cycle time.
- Remove undercuts. Each one removed can delete a mechanism from the tool.
- Loosen tolerances on features that do not carry a fit.
- Accept a standard finish on non-cosmetic surfaces.
- Consolidate parts through overmolding or insert molding to delete an assembly step.
- Commit to a realistic volume so cavitation can be chosen correctly rather than defensively.
What does not usually help
Switching to a marginally cheaper resin rarely moves the number much, because material is often a minority of piece price on a small part. Asking for a faster cycle without changing wall thickness or cooling asks the molder to run outside the process window, which raises the scrap rate and costs more in the end.
Machining and printing carry no tooling, so the cost per part barely moves with volume. Molding front-loads the tool and then makes parts for very little, so its cost per part falls steeply. The crossover is the volume at which the tool has paid for itself. Where it sits depends on part size, tool complexity and cycle time, not on a rule of thumb.
Let’s get started on your part
Send your CAD files and target volumes. We come back with a price, a lead time, and any design notes that would reduce either.