Design Specification for Vent Groove Depth of Injection Molds

Vent groove is the core structure of injection molds to discharge cavity air and plastic decomposition gas. Unreasonable vent groove depth is the main cause of product burning, air lines, poor weld lines and insufficient filling. Excessive depth will produce flash and increase trimming cost, while too shallow depth will cause poor exhaust and mass defective products. The vent depth must be designed according to the plastic overflow value, combining material characteristics and product structure to achieve smooth exhaust without glue overflow.

1. Core Design Principles of Vent Groove

The most basic rule is that the cavity side cutting depth must be lower than the material overflow edge value. High-fluidity plastics have strong penetration ability, so the vent depth is strictly limited. Low-fluidity engineering plastics can appropriately relax the tolerance. Visible appearance areas adopt lower limit depth, and non-appearance structural positions can be moderately increased.

Vent grooves are preferentially arranged at melt filling ends and weld line convergence positions. Corrosive and high-temperature decomposed materials need increased exhaust area to accelerate gas discharge. The cutting edge must be flat and neat without rounded corners to avoid increased gap and flash.

2. Standard Vent Depth of Common Materials

High-fluidity materials such as PP, PE and PA have a vent cutting depth of 0.015–0.02mm. Conventional ABS, PS and general hard glue are controlled at 0.02–0.025mm. Engineering plastics such as PC, POM and PBT are 0.025–0.035mm. Glass fiber modified materials have increased viscosity, and the depth can be increased to 0.03–0.04mm. Special high-temperature materials such as LCP and PEEK are strictly controlled within 0.013–0.02mm to prevent high-temperature gas defects.

3. Segmented Vent Groove Structural Standards

The mold adopts a two-stage vent structure. The front cutting section close to the cavity is strictly implemented according to the material depth standard, with a length of 5–8mm and a width of 5–8mm. The rear air guide groove is enlarged to 0.05–0.12mm in depth and 8–12mm in width to reduce gas resistance and quickly discharge gas out of the mold.

Each cavity of multi-cavity molds is independently vented without shared grooves. Vent grooves are arranged at intervals of 20–30mm to ensure uniform exhaust of the entire cavity.

4. Auxiliary Vent Gap Control

In addition to parting surface vents, the matching gaps of inserts, sliders, thimble and sleeve pins are used as auxiliary vents. The unilateral matching gap is stably controlled at 0.01–0.02mm to ensure exhaust while avoiding flash. For deep ribs and dead corners where parting surface cannot be vented, vent inserts are adopted to open gas passages on the back to solve trapped gas.

5. Trial Molding and Daily Maintenance Specifications

During trial molding, poor exhaust priority is solved by widening grooves and increasing vent positions instead of increasing depth randomly. Flash defects are eliminated by fine grinding the cutting edge. In mass production, vent grooves are prone to carbon deposition and blockage, which need regular cleaning and maintenance. Repeated mold polishing will change the vent depth, and regular size calibration is required to ensure long-term stable exhaust effect.

Summary

Vent groove depth design must take the plastic overflow value as the core standard, adopt segmented structural design, and match different depth parameters according to material fluidity and product structure. Standardized processing, trial molding debugging and daily maintenance can effectively avoid exhaust defects and flash problems, ensuring stable product quality and smooth mass production.