Gate Location Selection Methods and Key Points for Injection Molds

The gate is the critical channel through which molten plastic flows into the mold cavity, and its positioning directly determines product quality, molding stability, production efficiency and service life of the mold. Reasonable gate layout can effectively eliminate defects such as bubbles, sink marks, weld lines and warpage, while optimizing production efficiency and mold structure.

1. Five Core Principles for Gate Location Selection

Balanced Filling PriorityGates should be placed at the geometric center or symmetrical positions of the product to ensure uniform melt flow. For asymmetric products, multiple gates can be used to balance flow paths and reduce internal stress and warpage.

Avoid Direct ImpactGates shall not directly face cavity walls, cores, inserts or deep ribs. High-speed melt impact may cause deformation, displacement, burn marks and flow lines. Melt should be guided to spread smoothly along the cavity surface.

Smooth VentilationGate position must cooperate with the exhaust system to ensure air and volatiles can be discharged from the end of filling. Improper layout easily leads to trapped gas, short shots and scorching.

Protect Appearance and Assembly SurfacesGates should be hidden on inner surfaces, bottoms or non-decorative areas. Visible surfaces, fitting surfaces and stress-bearing areas must avoid gate marks to maintain appearance and assembly accuracy.

Facilitate Holding Pressure and DemoldingGates should be close to thick sections to ensure effective feeding during the holding stage and prevent shrinkage cavities. Meanwhile, the gate should be easy to remove without affecting ejection.

2. Key Factors for Gate Location Selection

Product Structure

Thin-walled parts require small gates to prevent jetting; thick-walled parts need gates near heavy sections; deep-cavity products are suitable for bottom or side gates; products with inserts should keep gates away from inserts to avoid displacement.

Plastic Material Properties

High-flow materials such as PP and PE allow long flow paths. Poor-flow materials including PC and PMMA require larger gates and shorter flow paths. Heat-sensitive materials must avoid stagnation zones to prevent thermal decomposition.

Mold Structure

Two-plate molds mostly use edge gates; three-plate molds apply pinpoint gates for automatic degating; hot runner molds support flexible gate positions; multi-cavity molds require balanced runners to ensure consistent filling.

3. Common Gate Types and Applications

Direct GateFeatures short flow path and low pressure loss, suitable for large deep-cavity products, but leaves obvious gate marks.

Edge GateWidely used in conventional products, easy to machine and trim, suitable for medium and small plastic parts.

Pinpoint GateLeaves tiny marks and realizes automatic breakage, ideal for high-appearance and precision parts, but with high pressure loss.

Submarine GateHidden under the molding surface, suitable for automatic production and high-appearance parts, with high processing requirements.

4. Common Mistakes to Avoid

Avoid setting gates at the thinnest wall sections, which causes insufficient filling. Do not use single gate for large asymmetric products, leading to warpage. Do not ignore weld line positions and exhaust balance. Avoid excessive pursuit of short flow paths while sacrificing dimensional stability.

Summary

Gate location design must follow fundamental principles and combine product structure, material properties and mold structure. Scientific selection can effectively reduce molding defects, improve product quality and production efficiency, and extend mold service life. Reasonable gate layout is one of the core links to achieve high-quality injection molding.