Rubber molding cost: like injection molding, minus one decisive thing
Costing a molded or vulcanized rubber part. The structure matches injection molding almost exactly, except that the flash cannot be reground — which changes where the money is worth chasing.
The cost structure is close to **injection molding**: multi-cavity tools, cycle time driving machine cost, flash to be trimmed. Read that guide first — everything in it applies, including how to divide machine time by cavity count.
One difference matters enough to change the conclusions.
The waste does not come back
Thermoplastic runners can be granulated and molded again, so in that trade the offcut is a **credit**. Vulcanized rubber cannot: the reaction has already happened and the material does not return to feedstock.
Direct consequence for the sheet: **recovery value is usually zero — and you should enter zero rather than leaving it blank**, so a reader knows it is a conclusion and not an omission.
Which changes the improvement priority
In injection molding, cutting flash is worth something but the material partly comes back. Here every gram of flash is **gone**, so the same improvement is worth more.
- Reduce flash — tighter tooling, more accurate charge weight.
- Reduce rejects — scrapped rubber is unrecoverable too, so it is as expensive as flash.
- Shorten cure time within what the compound allows — it usually dominates the cycle.
The ten categories — three changes from injection molding
| Category | What changes |
|---|---|
| Material | Compound, curatives, fillers, antidegradants — by charge weight divided by cavities, as in injection molding |
| Recovery | Usually zero. Enter zero, do not leave blank |
| Machine time | Cure time typically dominates the cycle, so machine cost carries more weight here than in thermoplastics |
The other seven — labor, tooling, scrap, rework, outside processing, packaging, freight, overhead — follow the injection molding guide without change.
Related guides
- Injection molding cost per part: shot weight, cycle time and cavitation
Costing a molded part across all ten categories. Three numbers dominate everything else — shot weight, cycle time and how many parts come out of each cycle — and getting any of them wrong moves the whole sheet.
- Regrind and recovered material: the only line that subtracts
Runners and rejects go back through the granulator and return as usable material. How to value that recovery honestly, and the double subtraction that quietly flatters the sheet.