The Cause & Solution to Mold Filling Imbalances

This paper presents results of studies which have found that a severe shear and thermal imbalance exists between cavities molded in the industry's traditional “naturally balanced” runner designs. The imbalance has been found to be the major cause of variations in multi-cavity injection molds-limiting product consistency, lower statistical Cpk values and the number of cavities which can be used in molding high precision automotive parts. A new technology developed and patented at Penn State University, provide a simple solution which strategically positions the shear induced melt variations so that a true balance can be achieved. The resultant balance allows for higher cavitation tooling, improved Cpk values, an in increased process window and reduced damp tonnage. This new technology also shows promise in influencing flow of gas in gas-assist injection molding and warpage of molded parts by contolling the position of the higher sheared hot melt in a mold cavity.