Flash, also called burrs or overflow, is a common defect in injection molding where molten plastic escapes from the parting line, ejector pins, inserts, or vents. Flash not only increases trimming labor and cost but also damages mold precision and shortens service life. Severe flash causes dimensional deviation, poor assembly, and appearance failure. The formation of flash involves mold design, manufacturing precision, processing parameters, material properties, and equipment condition. This article provides complete and practical solutions from mold, process, and material perspectives.
Mold-related Causes and SolutionsThe most fundamental cause of flash is poor mold matching and insufficient rigidity. The parting line must be flat, smooth, and closely fitted, with surface roughness Ra ≤ 0.8μm. Wear, deformation, or poor machining creates gaps where melt can penetrate. For large or long-term molds, supporting pillars should be added to prevent expansion under high pressure. Venting depth is critical: normally 0.01–0.02mm, too deep causes flash while too shallow causes burning and short shots. Worn inserts, ejector pins, and sliding components must be replaced or repaired promptly. Regular maintenance includes grinding parting lines, matching gaps, and cleaning residues. Proper mold design with reasonable gate location, balanced flow, and uniform pressure distribution also reduces flash risk.
Process Parameter Adjustment to Reduce FlashFrom the processing perspective, flash is often caused by excessive injection speed, pressure, temperature, or insufficient clamping force. Clamping force must be higher than the cavity expansion force calculated from projected area. Increasing clamping pressure properly helps suppress flash. Excessively high barrel temperature reduces viscosity and increases overflow tendency; therefore, temperature should be lowered appropriately. Injection speed and pressure should be gradually optimized to avoid over-packing. Holding pressure and time should be reduced if flash occurs near the end of filling. Mold temperature also affects flowability; excessive temperature increases flash risk. Most temporary flash problems can be improved by parameter adjustment, but long-term issues require mold modification.
Material Factors and Improvement MethodsMaterials with high flowability such as PP, PE, and nylon are more likely to produce flash due to low viscosity. Increasing molecular weight or adding modifiers can improve viscosity. The use of excessive recycled material reduces viscosity and should be limited. Moisture-absorbing materials must be adequately dried to prevent degradation and fluidity changes. For difficult materials, lower temperature and moderate speed help reduce flash. In mass production, stable raw material quality is essential to avoid fluctuations causing frequent defects.
Comprehensive Prevention and Control StrategyFlash control requires combination of mold design, precision manufacturing, reasonable parameters, and stable materials. Regular inspection and maintenance prevent mold wear. Operators should monitor product quality and adjust parameters in a timely manner. Establishing standard operating procedures reduces human error. Through comprehensive control, flash can be effectively eliminated, improving product qualification rate and reducing production cost.
