What is Gate Design in Plastic Injection Molding?

Gate design is a crucial element of plastic injection molding design that significantly influences part quality, aesthetics, and manufacturing efficiency.

Common Gate Types:

Edge Gate:

• Located at parting line on part edge
• Easy to machine and modify
• Leaves visible gate vestige
• Good for medium-to-large parts
• Manual or automatic degating

Submarine (Tunnel) Gate:

• Gate below parting line, tunnels into part
• Automatic degating during ejection
• Minimal gate vestige
• Good for small-to-medium parts
• Requires more precise tooling

Pin (Post) Gate:

• Small diameter gate on B-side
• Used with three-plate molds or hot runners
• Minimal vestige, cosmetic location flexible
• Good for multi-cavity molds

Hot Runner Valve Gate:

• Precision controlled gate opening/closing
• Excellent vestige quality
• No runner waste
• Ideal for cosmetic parts
• Higher mold cost, lower piece cost

Fan Gate:

• Wide, thin gate spreads flow
• Reduces stress for flat, thin parts
• Used for optical and low-stress applications

Gate Location Considerations:

• Flow Length: Gate position affects fill distance
• Weld Lines: Gate location determines where weld lines form
• Cosmetics: Gate vestige visibility considerations
• Fiber Orientation: Important for filled materials
• Warpage: Gate location affects shrinkage patterns
• Pack-out: Gate must allow adequate packing

Gate Sizing:

• Too small: High shear, degradation, incomplete fill
• Too large: Long cooling, poor vestige, slow cycle
• Optimal sizing balances fill, pack, and cycle time