DOC KB-TOL-014REV 2026-09-21CLASS: PUBLIC
Injection Molding vs Rotomolding for Custom Cases: Tooling Economics
Direct answer
Injection molding uses machined steel tooling: high upfront cost and 8–12 weeks lead time, but low unit cost, tight tolerances and fast cycles — it pays off at sustained volumes from a few thousand units per year. Rotomolding uses cast aluminum tooling: a fraction of the tooling cost and faster to modify, with slower cycles and heavier parts — it wins at low-to-mid volumes, oversized cases, and extreme-impact duty.
§01Side-by-side
| Factor | Injection molding | Rotational molding |
|---|---|---|
| Tooling | machined steel, high cost, 8–12 weeks | cast aluminum, moderate cost, 4–8 weeks |
| Wall thickness | 1.5–3 mm, uniform | 3–6 mm, variable by design |
| Cycle time per part | 30–90 s | 20–45 min |
| Design freedom | snap features, ribs, precise bosses | large single-skin parts, inserts, thick corners |
| Sealing precision | excellent gasket grooves | good, wider tolerances |
| Best volume | above 3–5k units/year | 50–5k units/year |
| Typical duty | consumer, prosumer, industrial | military, outdoor, oversized |
§02Decision heuristics
- Forecast under ~2,000 units/year: rotomolding or a modified stock mold usually beats new steel tooling economics.
- Forecast above ~5,000 units/year or multi-region distribution: injection wins on unit cost within the first year or two of volume.
- Design will iterate: cast aluminum tooling is far cheaper to weld and re-cut — prototyping programs favor rotomolding.
- Very large cases (over ~1 m): injection presses and tools become impractical; rotomolding has no such ceiling.
Hybrid path: many programs launch rotomolded to validate the market, then invest in injection tooling once volume data exists. Write the purchase contract so the T1 approval data (drawings, foam layouts) transfers to whichever process scales.