How do you calculate enclosure molding cost?

Multiply shots by per-shot cost by the good-part rate, then add tool change and startup scrap. For 5,000 shots at $1.85, 97% yield plus $650 startup, total is $9,622.50 and per unit is $1.9245.

What is a good cavity good-part rate for enclosure molding?

Stable enclosure tools typically run 96-99% good parts once dialed in. The 97% in the example is realistic for a mature process; a new or troublesome tool can sit below 90% until the process is optimized.

Why does startup scrap show as a fixed cost?

Tool change and startup scrap happen once per run regardless of volume — you burn resin and cycles bringing the tool up to steady state. Here that $650 is added on top of the variable $8,972.50 for a $9,622.50 total.

How is per-enclosure cost affected by run length?

The fixed $650 startup spreads across all shots, so per-unit cost falls as runs get longer. At 5,000 shots it adds about $0.13 per part; double the run and that fixed adder halves per unit.

Should good-part rate raise or lower total cost here?

In this model the good-part rate scales variable cost — 97% of the raw $9,250 shot cost is $8,972.50 variable — reflecting the yield-adjusted cost basis for the run before the fixed startup adder.

How do I lower per-enclosure molding cost?

Cut cycle time to lower per-shot cost, improve yield to reduce scrap, or lengthen runs to dilute the fixed startup hit. Each lever moves the $1.9245 per-unit figure directly.

Security, Fire & Life Safety Products calculator

Enclosure molding cost Calculator

Enclosure Molding Cost gives the total and per-unit cost of injection-molding plastic enclosures for fire panels, security keypads, and detector housings. Molding and process engineers use it to price a production run, factoring in resin and cycle cost, the cavity yield after scrap, and the fixed hit of a tool change and startup rejects. Enclosures are a high-volume commodity part, so a cent per shot and a point of yield move real money across a run. This calculator ties those variables into one defensible cost so quotes and make-versus-buy decisions hold up.

What this calculator does

Estimate injection molding cost for security and fire device enclosures from resin, cycle time, scrap rate, and one-time mold setup.
A molder running flame-rated housings uses this to price a production lot after accounting for startup scrap and reject rate.
It computes total molding cost as shots times per-shot cost adjusted by good-part rate plus fixed startup cost, and divides by shots for a per-enclosure figure.

Formula used

Total = shots x resin & cycle cost x good-part rate% + tool startup
Per enclosure = Total / enclosures molded

Inputs explained

Enclosures molded:
Resin + cycle cost:
Cavity good-part rate:
Tool change & startup scrap:

How to use the result

Use it when quoting an enclosure run, comparing tools or resins, or building a standard cost for a housing part number.
It treats good-part rate as a simple multiplier on cost rather than modeling scrap regrind value or downstream secondary operations like inserts and painting.

Current U.S. benchmarks

Manufacturing hourly earnings average $30.27 (BLS, Jun 2026), up 4.4% from a year earlier. Median machinist pay is $28.24/hr (OEWS 2025), with state medians on each state page. Manufacturers have 529k open positions nationally (BLS JOLTS).

Common questions

How do you calculate enclosure molding cost? Multiply shots by per-shot cost by the good-part rate, then add tool change and startup scrap. For 5,000 shots at $1.85, 97% yield plus $650 startup, total is $9,622.50 and per unit is $1.9245.
What is a good cavity good-part rate for enclosure molding? Stable enclosure tools typically run 96-99% good parts once dialed in. The 97% in the example is realistic for a mature process; a new or troublesome tool can sit below 90% until the process is optimized.
Why does startup scrap show as a fixed cost? Tool change and startup scrap happen once per run regardless of volume — you burn resin and cycles bringing the tool up to steady state. Here that $650 is added on top of the variable $8,972.50 for a $9,622.50 total.
How is per-enclosure cost affected by run length? The fixed $650 startup spreads across all shots, so per-unit cost falls as runs get longer. At 5,000 shots it adds about $0.13 per part; double the run and that fixed adder halves per unit.
Should good-part rate raise or lower total cost here? In this model the good-part rate scales variable cost — 97% of the raw $9,250 shot cost is $8,972.50 variable — reflecting the yield-adjusted cost basis for the run before the fixed startup adder.

Last reviewed 2026-05-12.