Published: June 5, 2026 | By TakumiTech® Design Engineering Team | Reading Time: 12 minutes
Good part design is the foundation of successful injection molding. Design for Manufacturability (DFM) principles ensure that your part can be produced efficiently, consistently, and cost-effectively. This guide covers the essential DFM principles for injection molded parts.
1. Wall Thickness Guidelines
Uniform wall thickness is critical for quality injection molded parts:
- Recommended Range: 1.5mm to 4mm for most materials
- Uniformity: Keep wall thickness within ±10% throughout the part
- Transitions: Use gradual transitions (3:1 ratio) when thickness changes
- Thick Sections: Core out thick areas to prevent sink marks and warpage
- Thin Sections: Avoid walls below 0.5mm (material dependent)
2. Draft Angles
Draft angles are essential for part ejection from the mold:
- Minimum Draft: 0.5° for polished surfaces, 1° for textured surfaces
- Recommended Draft: 1.5° to 2° for most applications
- Deep Draws: Add 1° additional draft for every 25mm depth
- Internal Features: Cores need more draft (2° minimum) than external walls
- Textured Surfaces: Add 1° draft for every 0.025mm texture depth
3. Rib Design
Ribs add strength without increasing wall thickness:
- Rib Thickness: 50-60% of nominal wall thickness
- Rib Height: Maximum 3x rib thickness
- Rib Draft: 0.5° minimum, 1° recommended
- Rib Spacing: Minimum 2x wall thickness between ribs
- Rib Base Radius: 0.25x wall thickness to reduce stress concentration
4. Corner Radii
Generous radii improve material flow and reduce stress concentration:
- Inside Radii: Minimum 0.5x wall thickness, 1x recommended
- Outside Radii: Inside radius + wall thickness
- Sharp Corners: Avoid completely (stress concentration, flow issues)
- Uniform Radii: Use consistent radii throughout the part when possible
5. Boss Design
Bosses provide attachment points for screws and fasteners:
- Boss Diameter: 2x screw diameter for proper strength
- Boss Wall Thickness: 50-60% of nominal wall
- Boss Height: Maximum 3x boss diameter
- Boss Draft: 0.5° minimum
- Boss Gussets: Add for additional strength when needed
6. Undercuts and Side Actions
Undercuts require complex mold actions, increasing cost:
- Avoid When Possible: Redesign to eliminate undercuts
- Minimize Depth: Keep undercut depth as small as possible
- Access for Side Actions: Ensure adequate space for mold action mechanisms
- Cost Impact: Each side action adds $2,000-$10,000 to mold cost
7. Gate Location and Witness Lines
Gate location affects part quality and appearance:
- Gate Placement: At thickest section for proper packing
- Flow Length: Keep flow length under 250mm (material dependent)
- Witness Lines: Locate in non-cosmetic areas
- Multiple Gates: Balance for uniform filling
8. Tolerances
Realistic tolerances prevent manufacturing issues:
- Standard Tolerances: ±0.1mm for dimensions up to 50mm
- Tight Tolerances: ±0.05mm possible but increases cost
- Shrinkage Compensation: Account for material shrinkage in design
- Measurement Method: Specify how dimensions will be measured
9. Surface Finish and Texture
Surface finish affects appearance, function, and moldability:
- SPI Finish Standards: A1 (mirror) to D3 (rough texture)
- Mold Texture: Adds draft, hides flow lines, improves grip
- Parting Line: Specify acceptable location and step
- Ejector Pins: Specify location and acceptable witness
TakumiTech® DFM Services
Our engineering team provides comprehensive DFM analysis:
- Free DFM review for all quotation requests
- Detailed DFM reports with recommendations
- Mold flow analysis and simulation
- Design optimization for cost and quality
- Rapid prototyping for design validation
Have a part design that needs DFM review? Contact TakumiTech® for expert analysis and recommendations.