A one-sentence summary: Injection molding quotes fail when they ignore the direct link between mold steel selection, expected cavity life, and per-part tooling amortization—especially with abrasive or corrosive resins.

Most mold engineers know that quoting an injection molded part isn’t just summing material and cycle time. But the real trap sits in the amortization math tied to mold life. Take a standard ABS housing: a tool built with P20 or 718H, hardened to HRC 28–32, and designed for 500,000 shots gives a per-part tooling cost of total mold price divided by 500,000. That’s straightforward. However, when the customer specifies a glass-filled compound like PA66+30% GF, the game changes completely. The same P20 cavity will wear rapidly at the gate and along flow paths, causing flash and dimensional drift within 50,000–80,000 cycles. You’ll be pulling the tool for weld repairs, nickel plating, or even cavity replacement—each downtime event erasing your margin.

To survive glass-filled or chemically aggressive resins, the mold must be upgraded to SKD61 or S136, typically hardened to HRC 48–52. That means higher material cost, more complex heat treatment, and often additional surface coating (e.g., TiAlN or CrN) to resist abrasive wear. The tool price can easily double—say from $18,000 to $36,000 for a medium-size cavity—yet the guaranteed shot count may drop to 200,000 due to fatigue or corrosion limits. Now your amortization per part jumps from $0.036 to $0.18, a fivefold increase that many quoters miss when they only compare resin price per kilogram. Worse, if you quote the lower amortization and the tool fails early, you absorb the rework cost or face a claim.

So the correct approach is to model the full tribological picture before sending a quote. Check the resin’s abrasiveness (glass content, mineral fillers), its chemical byproducts (e.g., acetal or PVC releasing corrosive gases), and the required surface finish. For unfilled ABS or PP, P20 with a nitrided surface is fine. For PA66+GF30 or PBT+30% GF, go straight to S136 or a powder metallurgy grade like Vanadis 4 Extra, and budget for a minimum of 300,000–500,000 shots only if you design the cooling and venting correctly. Also factor in a spare insert for the gate area—it’s cheaper than a full rebuild. That’s the kind of practical logic that keeps your shop profitable. For more mold sourcing and costing insights, visit MoldWorld at www.moldw.com.