Defects at sudden wall thickness changes of the product

Bubbles or sink marks appear in the wall thickness transition area. When this defect occurs in products of Process No. 2, it is usually related to a specific process parameter range or equipment status. If it persists, it will directly affect the product qualification rate and production cycle, increasing material loss and rework costs. Timely diagnosis and elimination is a basic requirement to ensure stable production.

1. Reaction process factor: Large reaction exotherm at thick-walled parts generates bubbles, fast curing at thin-walled parts and slow curing at thick-walled parts cause stress, and the flow front is unstable at the transition. 2. Mixing quality factor: 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 that determine the mixing quality. 3. Temperature control factor: The raw material temperature affects the component viscosity and reaction rate, and the mold temperature affects the curing process and product surface quality; both need to be precisely controlled within a narrow window.

1. Process parameter optimization and adjustment: Optimize the wall thickness transition design, control the reaction exotherm, adjust the injection speed, and improve venting. 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, next troubleshoot 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) assessments. For recurring problems, use fishbone diagrams or 5Why analysis to trace the root cause, and solidify countermeasures as PFMEA control points.

This problem is a typical manifestation of defects at sudden wall thickness changes of the product in the RIM process, and the core of the solution lies in ensuring the precise ratio and sufficient 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.