Injection mold tooling cost is driven by seven decisions, and only one of them is the price of steel. Cavitation, steel grade, complexity, runner type, surface finish, tolerance and lead time make up almost the whole number. Two suppliers quoting the same part at double and half the price are usually describing two different tools, not two different margins. Ask which decisions produced the figure.
Key takeaways
- Tooling cost is a one-time charge; part cost is a running one. Mixing the two is how a cheap tool becomes an expensive programme.
- Machining hours dominate the bill, not material. On a typical production tool, 60–70% of the invoice is machining time on the cavity and core.
- Cavitation scales sub-linearly. Going from one cavity to four does not quadruple the price, and going from four to sixteen does not either. That is what makes high-cavity tooling economic at volume.
- Complexity is the silent multiplier. Every slide, lifter and unscrewing unit is a mechanism that has to be designed, machined, fitted and maintained.
- The cheapest quote is often the one with the most undefined scope. Compare what is included, not just the total.
What “tooling cost” actually covers
A mould invoice is not one number, and reading it as one hides where the money went. It breaks into five parts.
- Design and DFM, including the 3D tool design, the mould flow run and the report you receive.
- Cavity and core machining, the largest line on most tools.
- Mould base, plates, ejector system and standard components, usually bought in from LKM, DME or HASCO, or made in-house where the geometry is unusual.
- Hot runner or runner system, where the part justifies one.
- Trial and verification, including the T1 sample round and the dimensional report.
Everything after that — the machine time, the resin consumed, the labour per part — belongs to part cost and to a different conversation. Our mold cost breakdown itemises where every line lands, and the injection molding cost guide covers the part-cost side.
The seven decisions that move the number
Roughly in order of how much each one moves a quote:
| Decision | What it changes | Usual effect on tooling cost |
|---|---|---|
| Number of cavities | How many parts per shot | Sub-linear: often the biggest single driver, but not proportional |
| Steel grade | Tool life and machinability | Hardened tool steel costs more to buy and considerably more to cut |
| Complexity | Slides, lifters, unscrewing units | Each mechanism adds design and fitting time, and a maintenance item |
| Runner type | Hot runner vs cold runner | A hot runner system is a bought-in assembly and adds to the base cost |
| Surface finish | Polish grade and texture | A mirror finish or a VDI texture is hand work, and hand work is hours |
| Tolerance | How tight the part must hold | Tighter tolerance means more measurement and more rework, not just smaller numbers |
| Lead time | How fast the tool is needed | Compressed schedules are bought with overtime and extra machine capacity |
The table is deliberately qualitative. Any supplier who gives you a fixed percentage for a decision without seeing your part is guessing, and the guess is usually optimistic.
Cavitation: the calculation buyers get wrong
Cavitation is chosen from annual volume and cycle time, not from the price list. The arithmetic is straightforward: divide annual demand by the number of shots you can realistically get per year, and that is the cavity count you need.
A tool running a 30-second cycle for 6,000 hours a year produces about 720,000 shots. If the annual demand is 400,000 parts, a single cavity covers it — but with no margin for a breakdown and no room for a demand spike. Two cavities gives the headroom. Fourteen cavities would be over-buying tooling to save cycle time you do not need.
What makes the decision pay is that cavity count does not scale cost linearly. The mould base grows, the runner and cooling layouts get more complex, and every cavity is another set of inserts to machine, but the design work, the frame and the trial are largely shared. Our multi-cavity mold design guide covers where the economies stop, because they do stop — balance, cooling capacity and press size all impose limits long before the cavity count reaches its theoretical maximum.
Steel grade is a lifespan decision, not a price decision
Steel is where a tooling quote and a tooling lifetime get connected, and the cheapest grade is almost never the cheapest decision.
For high-volume production tools our reference is 1.2344 (H13) and 1.2343 (H11) — hot-work steels hardened to 48–52 HRC. Tool life on those is up to 1,000,000 shots, depending on steel grade and maintenance. A pre-hardened grade such as 1.2738 or P20 machines faster and costs less up front, and it is a perfectly sound choice for a lower-volume tool where the geometry is stable. S136 is the answer for optical and medical parts where corrosion and polish matter more than wear.
Getting this wrong in either direction is expensive. Over-specifying puts money into a tool that will never see the volume. Under-specifying means the tool is scrapped or rebuilt partway through a programme, and a rebuild costs more than the original premium would have. The steel selection guide compares the common grades on wear, polish and corrosion.
Complexity: what slides and lifters really cost
Undercuts are where a comfortable tooling budget becomes a tight one.
A part with no undercuts is a straight pull: cavity and core separate, ejectors push, the part falls. Add one undercut and the tool needs a slide or a lifter, which is a separate mechanism with its own design, its own machining, its own fit-up and its own wear points. Add an internal thread and the tool needs an unscrewing unit, usually driven by a motor, gear train or hydraulic rack.
None of these are unusual, and none of them are unreasonable. What matters is that each one is scoped. A quote that does not mention how many actions the tool needs is a quote that has not finished the design. Our DFM rules reference covers how to spot the features that will require one, and our prototype tooling guide covers the case where you would rather simplify the geometry than pay for the mechanism.
Runner system: hot, cold, or the middle
A cold runner is a plate, a set of channels and a sprue bush. It costs little, it wastes a sprue of material every shot, and it needs someone to cut it off.
A hot runner keeps the melt hot all the way to the gate, so there is no sprue to regrind and no cycle time lost cooling it. It costs more, because it is a bought-in assembly — HRS, Yudo, Husky, Incoe and Mold-Masters are the names you will see quoted — and it adds control channels and maintenance.
The decision follows volume and material value. On a low-volume tool running a commodity resin, a hot runner is a hard sell. On a 16-cavity tool running a glass-filled engineering resin where regrind degrades fibre length, the material saving alone pays for it. Our hot runner vs cold runner comparison works through the crossover point.
Surface finish and texture are hand work
Polish and texture are the two lines on a tooling quote that buyers most often assume are cosmetic, and they are not, because they consume skilled hours.
A part that has to come out of the tool with a specific SPI grade or a VDI roughness is finished by hand, and hand work is the least scalable activity in a tool shop. A mirror finish on a large cavity face can take days. A photo-etched texture adds an outsourced process with its own lead time. Our mould surface finish guide covers the SPI scale, and the VDI roughness guide explains what the numbers mean for the moulded surface.
There is a useful trade here: specifying the finish you can actually see and measure, rather than the finest finish anyone named, moves the number more than most buyers expect.
Tolerance: the least visible driver
Tolerance does not change the shape of the tool, it changes how much work is spent proving the tool holds it.
Our machining tolerance is ±0.005 mm on critical mold dimensions, and the molded part tolerance that tool can then hold is ±0.01 mm on critical dimensions, subject to the resin and the part geometry. Those are two different numbers answering two different questions, and a supplier who quotes a single figure for both has not thought the problem through.
What that costs in tooling terms is inspection and iteration: more CMM time, more measurement on the trial, and more adjustment before the tool is signed off. The tolerances guide covers how to specify a tolerance that is tight where it matters and open everywhere else, which is the version that keeps the tooling budget under control.
T1 is where tooling cost quietly grows
The number in the purchase order is not the final tooling cost, and the gap between them is usually the trial.
Every engineering change that arrives after the tool is cut lands on the steel. A wall thickness change is a cavity and core modification. A moved boss is a new electrode and a weld. A different texture is a re-polish. None of these are unreasonable requests — they are what a trial is for — but they should be budgeted.
Budget at least one or two trials. Molding trials cost $300–$800 each, and a tool that needs three rounds of correction is a tool whose quoted price was optimistic. The discipline that prevents this is front-loading the design: our DFM report returns within 3 working days, at no cost, and every hour spent on it is an hour not spent re-cutting steel.
How to compare two tooling quotes properly
The totals are the least informative part of two quotes. Compare these instead, line by line:
- Cavity count and the volume logic behind it, so you can check it against your own annual demand.
- Steel grade, named, with the hardness and the expected life.
- The action count — how many slides, lifters or unscrewing units the design needs.
- Runner type, and who supplies the hot runner if there is one.
- Specified finish by SPI grade or VDI number, not by adjective.
- What the trial includes: how many rounds, and what documentation comes with the samples.
- What happens after approval — the warranty period, and who pays for a change of scope.
Any quote that answers all seven is comparable. A quote that answers three is a number waiting to be renegotiated. And the deliverable at T1 should be the same either way: samples, trial photos, a trial video and the full process parameter sheet, together with a CMM dimensional report on the critical dimensions, all issued against your mold number.
One more figure belongs in the comparison. We make 20–30 molds a month, with lead time to T1 sample of 35 days on a simple tool, 42 days on a medium one and 50 days on a complex one — and 30 days where the mold drawing is already fixed and the components are in stock. Capacity and schedule are part of what you are buying, and they are the part most often left out of a price comparison. Our seven-step guide to choosing a mold manufacturer covers how to weigh them.
Related guides in this series
- Plastic injection mold cost breakdown — where every dollar on the invoice lands.
- Injection molding cost guide — the part-cost side of the same project.
- Multi-cavity mold design — where the economies of cavity count stop.
- Mold steel selection — P20, NAK80 and S136 compared.
- Hot runner vs cold runner — the crossover point for your volume.
- Mold surface finish guide — SPI grades and what they cost in hours.
Get a tooling quote with the reasoning shown
Send the 3D file, the resin, the annual volume and the tolerance that actually matters on the drawing. We will return the tooling price with the cavity count, the steel grade, the action list and the trial plan written out beside it, so the number can be compared rather than guessed at. Request a tooling quote.