Flash

Reaction material overflows at the mold parting line. Flash is distributed along the parting line, the sliding block joint surface, or the edge of the ejector pin hole, appearing as thin sheets or irregular burrs, with the same material as the part but extremely thin thickness. Flash on the assembly surface of the part will seriously affect the fitting accuracy, causing assembly interference or sealing failure; fallen flash fragments may jam moving mechanisms or contaminate the product. Repeated occurrence of flash also wears the mold parting line, causing the mold accuracy to continuously decline, forming a vicious cycle.

1. Process parameter factors: insufficient clamping force, excessive injection pressure, material viscosity too low, mold parting line gap too large. 2. Mixing quality factors: in the RIM process, the mixing uniformity of the two components is the foundation of all quality; the Reynolds number of the mixing head, the impingement mixing energy, and the residence time distribution are the key engineering parameters determining mixing quality. 3. Temperature control factors: raw material temperature affects component viscosity and reaction rate, mold temperature affects the curing process and part surface quality, and both need to be precisely controlled within a narrow window.

1. Process parameter optimization and adjustment: increase clamping force, reduce injection pressure, increase material viscosity, repair the parting line. 2. Systematic troubleshooting method: RIM problem troubleshooting follows the order of "formulation -> mixing -> temperature control -> equipment". First check the two-component ratio and catalyst dosage, then check the mixing head and self-cleaning function, then check the raw material and mold temperature control, and finally check the accuracy of the metering pump and hydraulic system. 3. Preventive management: establish standardized process parameter cards and quality control limits for each mold/product, and regularly conduct process capability index (CPK) evaluation. For recurring problems, use fishbone diagram or 5Why analysis to trace the root cause, and fix the countermeasures as PFMEA control points.

The root cause of flash is that the mold-opening force generated by the cavity internal pressure exceeds the closing force of the clamping system. The logic chain of the solution is: first reduce the cavity pressure peak through process adjustment, then check and repair the clamping system to ensure sufficient closing force, and at the same time repair the parting line to ensure sealing conditions.