Effects of geometry on the tensile strength of extrusion blow molding pinch-off welds

The pinch-off weld is formed when the mold closes on the parison. A strong weld is dependant on the correctly designed pinch-off geometry of the mold. A pinch-off design relies mostly on past experience and trial and error. There are few equations, available to properly design the pinch-off. Material suppliers have provided some guidelines on pinch-off geometry for their materials. The experiments performed in this study show the effect of pinch-off geometry on the tensile load of the weld in extrusion blow molding parts. When the mold closes on the parison and it is squeezed, the geometry affects how the material flows in the pinch-off region. Previous research on pinch-off load was done without an accurate measurement of the parison thickness. The geometry tested was the land-length, first angle, second angle, distance to second angle, and flash pocket. The tensile load of the weld was examined in these experiments by the use of design of experiments.