Injection Molding DFM Essentials
Draft angles, uniform wall thickness, gate placement, and shrinkage control for moldable plastic parts.
Core DFM rules: draft ≥1°, wall variation <25%, rib thickness ≤0.6× wall, keep gates off cosmetic faces, and plan shrink compensation.
1Draft
Minimum 1° on external walls (no texture); add 0.5° per 0.025 mm texture depth. Internal walls need 0.5–1° more than externals. Deep cavities may need sliders.
2Wall thickness
Typical: ABS 1.5–3 mm, PC 2–4 mm, PP 1–2.5 mm. Adjacent walls should not differ by more than 25% to avoid sink and warp.
3Ribs
Rib thickness 0.5–0.6× outer wall. Height ≤3× wall thickness. Fillet ≥0.25× wall at the base. Spacing ≥2× wall thickness.
4Shrinkage and warp
Semi-crystalline plastics (PP/PA) shrink 1.5–2.5%; amorphous (ABS/PC) 0.4–0.7%. Symmetric designs reduce warp. Validate gate location with mold-flow analysis.
Key points
- External draft ≥ 1°
- Wall thickness change < 25%
- Rib thickness ≤ 0.6× wall
- Keep gates away from appearance surfaces
- Run mold-flow on large parts
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