The first time you ask a factory for a quote on an injection-molded enclosure, the tooling number lands like a punch: $8,000 for a part that costs $1.20 to mold. The instinct is to think you're being overcharged. Usually you're not — you just don't yet understand what's inside that number, or how it disappears once you spread it over volume.
What actually drives mold cost
A few things move the price far more than part size:
- Number of cavities. A single-cavity mold makes one part per shot. A four-cavity mold makes four. More cavities means more machining, but a lower per-unit cost at volume. For a 200-unit pilot, single-cavity is correct. For 50,000 units a year, multi-cavity pays back fast.
- Steel grade. A P20 pre-hardened steel mold is cheaper and machines faster, good for tens of thousands of shots. Hardened steel (H13, S136) costs more but survives hundreds of thousands of cycles and resists wear on glass-filled or abrasive resins. Choosing hardened steel for a 1,000-unit run is burning money; choosing P20 for a 500,000-unit program is buying a re-cut later.
- Slides and lifters. Every undercut, side hole, snap feature, or threaded boss that isn't aligned with the pull direction needs a slide or lifter — extra mechanism, extra cost. A clean draft-friendly design can be a fraction of the price of one loaded with side-actions.
A realistic cost range
For a typical small electronics enclosure (palm-sized, two-part, a few openings), expect roughly:
- Single-cavity P20 mold: $4,000–10,000
- Multi-cavity or hardened-steel mold: $12,000–30,000+
These are ballpark figures from Shenzhen/Dongguan toolmakers; complex parts with multiple slides push higher.
The unit economics that matter
Tooling is a one-time cost, so the real question is amortization. Say the mold is $8,000 and the molded part costs $1.20:
- At 1,000 units: $8 of tooling per unit. Painful.
- At 10,000 units: $0.80 per unit.
- At 50,000 units: $0.16 per unit — now noise against your BOM.
If your enclosure adds $4 to the retail margin and you're confident in 10,000 units, an $8,000 mold is an easy yes. If you're not sure you'll sell 2,000, don't tool yet — use 3D-printed or CNC enclosures for the pilot and tool once demand is proven.
T1 samples: budget for iteration
No mold runs perfect on the first shot. The first samples — T1 — almost always reveal short shots, flash, sink marks, or warping. Expect 2–3 sample rounds (T1, T2, sometimes T3) before sign-off, and a few weeks between them. Build that into the schedule; a team that promises a perfect first shot is the team that hasn't told you about the second.
Who owns the mold
This is the clause people forget until it bites. The mold is a physical asset, and ownership and transfer rights should be in writing before you pay. If you've paid for the tooling, you should be able to move it to another factory. Get the mold ownership and transfer terms in the contract, not a verbal "of course it's yours."
Where engineering review earns its keep
Most over-priced molds are really under-reviewed designs — an undercut that forced a slide, a wall thickness that warps, a draft angle that wasn't there. A proper DFM (design for manufacturability) review before cutting steel routinely removes side-actions and reshapes the part to mold cleanly.
If you don't have a mechanical engineer reviewing the tool drawings, this is where an engineering-led partner helps. China Sourcing Agents, run by a hardware engineer who does DFM review and tooling on product-development projects, sits between you and the toolmaker so the quote you get reflects a part that's actually designed to mold — not the toolmaker quietly pricing in your mistakes.
The takeaway
Don't tool until your volume justifies it. Match steel grade and cavity count to real demand, get a DFM review before steel is cut, plan for 2–3 T1 iterations, and put mold ownership in the contract. Do that and the scary tooling number becomes the cheapest part of your unit cost.
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