Guide to Efficiently Solving Injection Molding Flash

In injection molding production, flash, also known as burrs or overflow, is one of the most common defects that seriously affects production efficiency and product quality. It usually appears at parting surfaces, ejector pin holes, slides, inserts, vent grooves and other locations. Flash not only increases labor and production costs but also causes poor appearance, dimensional deviation, mold damage, and even mass scrap. Many workshops fall into a vicious cycle of temporary adjustments and repeated failures. In fact, flash can be effectively controlled and even completely eliminated by following a systematic approach: process optimization, mold rectification, equipment assurance, material adaptation, and long-term management.

Process Parameter Optimization

Process adjustment is the primary method for on-site flash control, focusing on reducing cavity pressure and controlling melt fluidity to prevent plastic from entering small gaps.Holding pressure and time are the most critical factors. Excessively high holding pressure or long holding time is the main cause of flash. For conventional products, holding pressure should be 30%–50% of injection pressure, and 20%–40% for thin-walled or high-flow materials. Holding time should end when the gate is completely frozen. Injection speed should be controlled in stages, with proper reduction in the late filling stage to avoid sudden pressure spikes.Temperature directly affects melt viscosity. Higher temperatures reduce viscosity and increase flash tendency. Appropriate reductions in barrel and mold temperature can effectively suppress flash without significantly affecting appearance and quality. Injection volume should also be controlled to avoid over-filling.

Mold Structure Rectification

More than 80% of persistent flash is caused by mold defects.Parting surfaces must be clean and flat; contamination or deformation larger than 0.02mm requires re-grinding. Vent depth must be strictly controlled: 0.01–0.02mm for general materials and below 0.015mm for high-flow materials.Clearance of slides, lifters and inserts must be maintained within 0.005–0.01mm. Excessive clearance will inevitably cause flash. Mold positioning and clamping must be checked regularly to avoid misalignment.

Equipment Condition Assurance

Insufficient clamping force is a major hidden cause of flash. Clamping force must exceed the product’s projected area multiplied by cavity pressure, with a safety margin of 10%–15%. Parallelism of platens must be calibrated regularly; deviations exceeding 0.01mm easily cause unilateral flash.

Material Performance Adaptation

High-flow materials such as PA, PP and PE are more prone to flash. For complex and thin-walled products, medium-flow grades are preferred. Excessive recycled material content leads to unstable viscosity and inconsistent flash.

Long-Term Prevention and Control

Stable flash control relies on standardized management: mold cleaning and parameter checking before production, regular inspection during production, and maintenance after production. Only through systematic control can flash be fundamentally eliminated, improving qualification rate, reducing costs and ensuring stable, efficient production.