Plastic Part Design for Manufacturing — DFM Guidelines for Injection Molding

Design for Manufacturing (DFM) Overview

Design for Manufacturing considers production requirements early in the design phase. For injection molding, DFM prevents costly mold modifications, improves part quality, and reduces production costs.

Wall Thickness Design

Uniform Walls

• Consistent thickness prevents warpage and sink marks
• Target 2-3mm for typical parts
• Transitions should be gradual (3:1 ratio)

Material-Specific Guidelines

Ribs and Bosses

Rib Design

• Thickness: 50-70% of adjacent wall
• Height: Maximum 3× wall thickness
• Draft: 0.5-1° minimum
• Spacing: 2× wall thickness minimum

Boss Design

• Wall thickness: 60-70% of nominal wall
• Core hole depth: 2-3× diameter
• Include radii at base
• Consider draft for ejection

Corners and Radii

Related Reading

Plastic Material Selection  |  Engineering Plastic Cost Factors  |  Moisture Effects on Nylon  |  3D Printing for Prototyping vs Production  |  PEEK vs PEI Compared

• Include radii on all internal corners
• Internal radius: Minimum 0.5× wall thickness
• External radius: Internal radius + wall thickness
• Radii reduce stress concentration
• Improves material flow during filling

Draft Angles

• Standard surfaces: 0.5-1° minimum
• Textured surfaces: 2-5° depending on texture
• Deep features: Increase draft proportionally
• Shrinkage: Account for material shrinkage in draft

Undercuts and Side Actions

Designing Without Undercuts

• Reduces mold complexity
• Lower tooling cost
• Simpler maintenance

When Undercuts Are Necessary

• Use side actions (slides)
• Consider lifters for internal undercuts
• Design for proper release angles

Gating Considerations

• Position gates in non-visible areas
• Consider gate vestige requirements
• Account for weld line locations
• Design for automated degating when possible

Common Design Errors

• Sharp internal corners causing stress
• Insufficient draft causing ejection issues
• Thick sections causing sink marks
• Undercuts without proper mechanisms
• Ignoring shrinkage tolerances

DFM Checklist

• ☐ Uniform wall thickness throughout
• ☐ Adequate draft angles specified
• ☐ Radii on all internal corners
• ☐ Ribs properly proportioned
• ☐ Bosses designed for function
• ☐ Undercuts identified and addressed
• ☐ Gate locations proposed
• ☐ Material shrinkage accounted

結論

DFM for injection molding prevents costly iterations and ensures manufacturable designs. Involve manufacturing engineers early in the design process.

Related Resources

• PEEK vs PEI Comparison
• Flame Retardant Plastics
• Food Grade Plastics Guide
• Nylon Moisture Treatment
• Moisture Effects on Nylon

よくあるご質問

Why is uniform wall thickness important?

Uniform walls ensure even cooling, prevent warpage, and eliminate sink marks in the finished part.

How much draft do I need?

Minimum 0.5-1° for smooth surfaces, 2-5° for textured surfaces, with more draft for deeper features.

What is the ideal rib thickness?

Rib thickness should be 50-70% of the adjacent wall thickness to prevent sink marks.

Should undercuts be avoided?

Minimize undercuts when possible. When necessary, design appropriate side actions or lifters.

When should DFM review occur?

Conduct DFM review early in design, before tooling commitment, to avoid costly mold modifications.