DFM for injection molding
DFM is cheaper before steel is cut. The goal is not to redesign the part; it is to remove the features that will cause scrap, slow cycles or tooling changes.
Checklist
- Draft — enough release angle on walls and ribs.
- Wall thickness — avoid thick sections that sink or warp.
- Radii — reduce stress and improve fill.
- Gate — location affects weld lines, cosmetics and cycle time.
- Ejectors — leave room for ejection without visible marks.
- Tolerances — specify only what the assembly needs.
- Assembly — snap fits, screws and mating parts.
Common issues
| Issue | Why it matters | What to change |
|---|---|---|
| No draft | Part sticks or scratches on ejection | Add 1–2° draft (typical; confirm per part) |
| Thick walls | Sink, voids and long cycles | Core out or reduce wall |
| Sharp corners | Stress and fill problems | Add radii |
| Gate in cosmetic area | Visible mark | Move gate or hide it |
| Over-tight tolerance | Higher tool and inspection cost | Specify assembly requirement |
What to send for a DFM review
3D file, material, quantity, critical dimensions and any cosmetic requirements. A short note on the assembly helps more than a 50-page spec.