Total Cost of Ownership (TCO): Steel Tool Investment vs. Part Unit Savings

Steel pays for itself when unit savings, scrap drop, and labor drop outrun the tool before the product dies.

TCO on a custom silicone program is not “mold quote vs piece price.” It is every dollar that exists because you chose this construction: class, cavitation, finish, scrap, trim, maintenance, freight of the tool, leftover compound, and the recut you already know you will need. Piece price is one term. If you optimize it alone, you will buy an 8-cavity monument for a SKU that lasts a season.

The terms, named so they can be added

Write one line each. Ranges are allowed. Blank lines are not.

T_tool. Construction: aluminum 1-cavity vs Class 104 vs Class 103 vs 102, cavity count, cold runner, vacuum, polish, slides, spare inserts, tryout, FAI. This is the investment people stare at.

T_mod. The first planned geometry change. Soft tools make this small. Hardened steel makes this large. If CAD is not frozen, T_mod is not zero. Put a placeholder.

C_press. Cycle time / cavities × press hour cost × good parts. Cavitation lives here. Cure-dominated LSR parts move little with a faster robot. They move with more cavities *or* with a better thermal design.

C_mat. Mass × grade × (1 + runner waste). Cold-runner design can beat cavitation on this line.

C_labor. Trim, inspect, pack. Flash spec and shutoff live here. A cheap tool that needs a knife on every part can lose TCO to a more expensive land.

C_scrap. Start-up + running yield. Multi-cavity can raise this. Tired aluminum can raise this. Wrong post-cure can raise this.

C_setup. Per batch. Release qty determines how many times you pay it. A beautiful 10,000-piece unit price with 200-piece releases puts C_setup back on the table.

C_pm. Heaters, shutoff refresh, storage, rust. Class 101 assumes you will spend here. Class 105 assumes you will not, because the tool is dead.

C_freight. Tools once (or twice if you dual-source). Parts per release. Dimensional weight on bulky RTV packs vs dense LSR bags.

TCO over a horizon H (12 or 24 months is enough for most custom parts):

T_tool + T_mod + Σ(C_press + C_mat + C_labor + C_scrap + C_setup + C_pm + C_freight)

Unit savings only matter as deltas on the C_ terms when you change construction.

Steel vs the alternatives, as deltas

Stay on RTV vacuum casting. T_tool is small and recurring (jackets die). C_labor is large. C_scrap from scatter is real. C_press is a person. Steel wins when H × labor hours exceed T_tool of a 1- or 2-cavity LSR tool *and* the chemistry must be LSR anyway.

Stay on aluminum 1-cavity LSR. T_tool medium. C_press high per part. C_pm as shutoff roll-over. C_scrap grows with flash. Steel (often 2- or 4-cavity Class 103) wins when press hours plus trim plus a recut of aluminum exceed the steel delta inside H.

Jump to 8-cavity steel. T_tool jumps. C_press drops if yield holds. C_setup and MOQ jump. C_scrap may jump. This wins only when H’s part count keeps that press fed and the product is frozen. Otherwise you bought a low C_press you never use, which is a high TCO.

Never compare T_tool of steel to the *unit price* of aluminum. Compare TCO_H of both.

A crossover sketch (no currency theatre)

Suppose (qualitatively) an aluminum 1-cavity already runs the grade. Steel 4-cavity Class 103 adds a large T_tool. You need:

• Enough parts in H for (press hours saved + trim hours saved + scrap avoided + aluminum PM avoided) > (steel − aluminum) + extra setup if batches get larger + extra runner if any.

If the part is thick (long cure), press hours saved are the story. If the part is flash-prone, trim and scrap are the story. If the part is tiny and already 20 seconds, you need volume or you are buying steel for pride.

Plot two volumes: your *likely* H and your *sales-deck* H. If steel only wins on the deck, do not cut 103 8-cavity. Cut aluminum, or a steel 1-cavity you can still love at the likely volume.

Ways TCO lies

• Amortizing steel across a lifetime the product does not have.
• Ignoring T_mod because “we’ll only change the logo” (you will change the logo).
• Counting 8-cavity yield as 1-cavity yield.
• Forgetting leftover medical LSR pails on small batches.
• Treating freight of a 600 kg tool as zero because it is “NRE.”
• Using a unit price that assumed one giant lot while you will kanban weekly.

What to demand on the quote so TCO is computable

Two constructions, same grade, same flash spec, 12-month qty *and* batch qty:

• Tool (class, cavities, runner, extras)
• Cycle time and whether cure dominates
• Runner waste
• Trim method
• Scrap assumption
• Setup per batch
• Stated PM (shutoff interval)

Then you can add. If they only give unit price at 10,000, you cannot do TCO. You can only do hope.

The test: freeze H, freeze batch size, fill the nine terms for aluminum 1-cavity and steel 4-cavity. The lower sum wins. If you cannot fill C_labor and C_scrap, you are not ready for steel; you are ready for a better tryout on the tool you have.

FAQ

Why not compare steel mold price to aluminum piece price?

TCO is construction plus the first planned geometry change plus press, material, labor, scrap, setup per batch, PM, and freight over a horizon. Piece price is one term. Optimizing it alone buys an 8-cavity monument for a seasonal SKU. Compare TCO of both constructions at the same grade and flash spec.

What is T_mod and why isn't it zero before freeze?

It is the first planned CAD change. Soft tools make it small; hardened steel makes it large. "We'll only change the logo" is still a placeholder. Ignoring it is a classic TCO lie.

When does jumping to 8-cavity steel lose TCO?

When the horizon's part count cannot keep that press fed, batches get larger, yield drops versus 1-cavity, or the product is unfrozen. You bought a low press cost you never use, which is a high TCO. Steel 4-cavity Class 103 wins only if press hours, trim, scrap, and aluminum PM avoided beat the steel delta inside the horizon.

How does weekly kanban lie about a pretty 10,000-piece unit price?

Setup returns every release. Leftover medical pails on small batches, freight of a heavy tool treated as free NRE, and amortizing steel across a lifetime the product does not have also lie. Plot likely volume and sales-deck volume; if steel only wins on the deck, do not cut 103 8-cavity.

What missing numbers mean I am not ready for steel yet?

If you cannot fill trim labor and scrap for the tool you already run, you need a better tryout, not a class jump. Demand cycle (and whether cure dominates), runner waste, trim method, scrap assumption, setup per batch, and shutoff PM interval on both constructions.