10 DFM Tips That Cut Injection Molding Costs Before Cutting Steel
Published 2026-06-20
Every mold we build starts with a DFM review. After thousands of them, the same findings keep surfacing. Fix these before cutting steel and you'll save weeks and real money.
1. Keep walls uniform — 1.5–3.5 mm
Thick sections sink; abrupt transitions warp. If a rib must be thick, core it out. Wall transitions should taper at 3:1 (runout per step).
2. Draft everything, even "vertical" faces
Minimum 0.5–1° on texture-free faces, 1–2° minimum with VDI texture. Every degree of draft removes polish cost and shortens cycle time.
3. Ribs ≤ 60% of adjoining wall
Rib thickness beyond 60% of the wall guarantees sink on the show face. Coring or multiple thinner ribs beat one chunky rib every time.
4. Move gates before we do
Gate location drives weld lines, sink and cosmetic quality. If a visible face has a weld line the tool cannot avoid, consider gating into a non-cosmetic zone and accepting a slightly longer flow.
5. Undercuts cost money — twice
Sliders and lifters add mold cost and maintenance. Small undercuts (< 0.5 mm on flexible materials) can often "pop" off the core — check with your molder before designing them away entirely.
6. Design text deep, not wide
Engraved text: 0.25–0.4 mm deep, with 2° side draft per letter stroke. Deeper is fine; wider with no draft is not.
7. Threaded holes: inserts or nothing
Molded-in threads in hard plastics crack; metal heat-stake or ultrasonic inserts survive assembly lines. Budget one insert position per critical joint.
8. Tolerance only what matters
Tight-tolerance callouts multiply inspection cost. Apply ±0.05 mm only to functional interfaces; let everything else ride the process default.
9. Think about ejection from day one
Deep-box parts need generous draft plus textured cores to fight vacuum. Ejector marks land somewhere — tell us where they are acceptable, or we'll guess.
10. Tell us the real volumes
Tooling designed for 500K shots differs from one built for 10K (steel grade, hot runner, inserts). Volume honesty is the cheapest cost reduction available.
The earlier we see the CAD, the cheaper each finding is to fix. Upload your drawing for a free DFM review — returned with your quotation.