What Are the Key Components of Injection Mold Design?

Plastic injection molding design for tooling involves engineering multiple interconnected systems that work together to produce quality parts efficiently.

1. Cavity and Core:

• Cavity (A-side) – Forms external/cosmetic surfaces
• Core (B-side) – Forms internal surfaces, typically where part remains for ejection
• Precision machined from tool steel (P20, H13, S136)
• Surface finish matched to part requirements
• Proper shut-offs and parting line design

2. Runner and Gate System:

• Sprue – Connects nozzle to runner system
• Runners – Channels delivering plastic to gates
• Gates – Entry points into part cavity
• Cold runner vs. hot runner considerations
• Gate type selection (edge, submarine, pin, valve)
• Balanced flow for multi-cavity molds

3. Cooling System:

• Cooling channels throughout cavity and core
• Uniform cooling for dimensional stability
• Baffles, bubblers, and thermal pins for complex areas
• Conformal cooling for optimized performance
• Cooling design directly impacts cycle time

4. Ejection System:

• Ejector pins for part release
• Sleeve ejectors for bosses
• Blade ejectors for ribs
• Stripper plates for deep parts
• Air poppets for vacuum relief
• Ejector pin placement to avoid visible marks

5. Venting:

• Vents at end of fill and weld line locations
• Vent depth sized for material (0.01-0.05mm)
• Prevents burns, short shots, and weld line weakness

6. Side Actions and Lifters:

• Side actions (slides) for external undercuts
• Lifters for internal undercuts
• Cam or hydraulic actuation
• Adds complexity and cost