Key Considerations for Injection Mold Design

1. Part Analysis & Requirements

• Define part specifications:

• Dimensional tolerances (e.g., ±0.05mm), surface finish (glossy/matte), and texture requirements (e.g., EDM etching).

• Material behavior (e.g., PC requires high mold temperature, PP is prone to shrinkage).

• Parting line selection:

• Avoid visible surfaces; place along edges or non-critical areas.

2. Mold Structure Design

(1) Parting Surface Design

• Keep parting lines simple (flat surfaces preferred over complex curves).

• Use lifters or sliders for undercuts and complex geometries.

(2) Gating System

• Gate type selection:

  Gate Type	Best For	Pros & Cons
  Edge Gate	General-purpose parts	Easy machining, but requires trimming
  Pin Gate	Small, precision parts	Auto-degating, but high pressure loss
  Submarine Gate	Aesthetic parts (e.g., phone cases)	No visible marks, but costly

• Runner design:

• Use balanced runners for multi-cavity molds.

• Cold runner vs. hot runner: Hot runners reduce waste but increase mold cost.

(3) Ejection System

• Ejector pin placement:

• Distribute evenly to prevent part deformation.

• Match pin diameter to part thickness (too thin = bending, too thick = marks).

• Additional mechanisms:

• Use lifters, air ejection, or stripper plates for deep ribs or undercuts.

3. Cooling System Design

• Key principles:

• Place cooling channels close to the cavity (≤2x channel diameter).

• Avoid dead zones; use spiral or serial layouts.

• Material considerations:

• High-temp materials (e.g., PC) require more efficient cooling.

4. Mold Material Selection

5. Venting Design

• Problems from poor venting:

• Burn marks, short shots, or bubbles due to trapped air.

• Solutions:

• Venting slots (0.02–0.05mm deep).

• Add vents at parting lines, ejector pins, or inserts.

6. Mold Strength & Durability

• Avoid stress concentration:

• Use fillet radii (R≥1mm) instead of sharp corners.

• Surface treatments:

• Nitriding (hardness), chrome plating (rust prevention), DLC coating (low friction).

7. Tolerances & Fits

• Critical fits:

• Guide pins/bushings: H7/g6 (sliding fit).

• Ejector pins: 0.01–0.02mm clearance.

8. Mold Testing & Optimization

• Trial run checks:

• Balanced filling?

• Smooth ejection?

• Flash or sink marks?

• T0→T1 adjustments:

• Modify gate size, cooling, or ejection layout.

9. Maintenance & Care

• Regular upkeep:

• Clean guide pillars, lubricate ejector pins every 50K cycles.

• Apply rust inhibitor during storage.

10. Cost Control

• Simplify design: Reduce sliders/lifters (each adds ~30% cost).

• Standardize components: Use standard mold bases (e.g., FUTABA, DME).

Common Design Mistakes & Fixes

Conclusion

A well-designed injection mold balances functionality, cost, and longevity:

1. Pre-design analysis: Understand part & material needs.

2. Optimized structure: Smart gating, cooling, and ejection.

3. Process synergy: Align mold design with injection parameters.

Case Study: A car component mold improved cooling, cutting cycle time from 40s → 28s, saving $50K/year!