Part Tearing During Demolding

The surface of the part is torn during demolding. When demolding is difficult, a "hissing" adhesion tearing sound can be heard at the moment of mold opening, whitening or tearing marks appear on the part surface, and obvious ejector whitening or dents occur at the ejector pin positions. In severe mold sticking, part of the material remains in the cavity and requires shutdown for manual cleaning, which not only prolongs the production cycle but may also damage the cavity surface. For multi-cavity molds, sticking in individual cavities can also cause abnormal filling of the remaining cavities.

1. Mold design factors: excessive demolding force, low part strength due to incomplete curing, insufficient demolding draft angle, rough mold surface. 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: extend curing time, increase demolding draft angle, polish the mold surface, improve release agent application. 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.

This problem is a typical manifestation of part tearing during demolding in the RIM process; the core of the solution lies in ensuring the precise ratio and full mixing of the two components, while controlling the reaction temperature and curing conditions within the optimal window. It is recommended to start troubleshooting from the mixing system and metering accuracy.