Meaning
Mechanical tension intentionally engineered into mold inserts before production begins prevents mold breathing and core deflection under high injection pressures. Applying tool steel preload involves machining the inserts to be slightly proud of the pocket face. When the mold halves clamp together, this excess height is compressed, creating a tight seal around the cavity boundaries.
Assembly Method
Insets must be machined with extremely precise height tolerances to ensure the correct compression is achieved during clamp-up. When tool steel preload is applied, the insert extends a few hundredths of a millimeter above the pocket floor. This protrusion causes the plate to flex slightly when the clamp tonnage is engaged, ensuring metal-to-metal contact at the parting line.
Flash Prevention
High pressure melt entering the mold cavity exerts massive force that tries to push the insert back into its pocket. In the absence of tool steel preload, this pressure would cause a tiny gap to open between the inserts, letting melt leak out. Preloaded steel remains firmly sealed because the pre-applied clamping force exceeds the melt pressure.
Deflection Control
High mechanical tension prevents the shifting of cores during the filling of asymmetrical part geometries. It ensures that the molding pressure does not move the inserts sideways or backward. This control is critical for maintaining consistent wall thickness and preventing molded part rejection.
