Optimal runner design for balanced filling in a multi‐cavity mold using a two‐stage analytical approach

In a multi‐cavity mold, parts from each cavity have consistent properties if the runner system ensures balanced melt‐front advancement. An unbalanced mold, however, narrows the processing window, complicating quality control and making it harder to maintain standards. Molds with an inherently balanced filling, such as the H‐type runner system, are preferred. However, as the number of cavities increases, improvements are needed to address the issues caused by shear heating. Additionally, the material waste in the H‐type runner system is significantly greater than in the fishbone runner system. Based on the rheological concept, a two‐stage analytical approach is established to optimize the fishbone runner system. The diameter of each runner in the fishbone runner system is optimized by controlling pressure drop and remaining time to achieve balanced filling. The impact of these factors is thoroughly examined, as well as why they must be controlled during optimization. The proposed work links the physical situation to its mathematical model, proving highly beneficial for new runner system designs, especially without commercial software assistance.Highlights A new approach to solving unbalanced filling in multi‐cavity molds. Pressure drop and remaining time are key factors for optimization. Two‐stage analytical approach ensures optimization accuracy. The optimal runner system reduces injection pressure for molding. An alternative method for designing fishbone runners without CAE assistance.