A semi‐empirical algorithm for flow balancing in multi‐cavity transfer molding

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Abstract
Multi‐cavity transfer molding is an important process step in several electronic and photonic technologies. In some applications, uniform filling of the cavities of the mold, or mold balancing, is required. A semi‐empirical flow model to predict mold filling patterns was developed. The algorithm is a one‐dimensional network flow simulation that uses experimental pressure drop data to determine the volumetric flow rate through the gates and runners. A comprehensive experimental program was undertaken to determine these hydraulic resistances for different flow rates and mold geometries. A theoretical treatment is also described to compute hydraulic resistance from gate geometry. Uniform gate resistances provide unbalanced filling and higher velocities in the cavities. Balanced filling can significantly reduce the molding compound velocity and the flow induced stresses, but imperfect balancing compromises the benefits. Experimental filling patterns were obtained for two sets of gates. The agreement between the model and the experiments was satisfactory, and the discrepancies were attributed to correctable phenomena.

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