A misaligned plug enters the cavity off-center, tilted, or at an incorrect relationship to the mold. The resulting part often has one thin wall, a strong witness mark on the opposite side, or recurring damage at one cavity position.
Mechanical play, platen misalignment, incorrect setup, worn guides, thermal expansion, and unequal actuator motion can shift the plug. A thermal gradient can mimic misalignment by allowing the sheet to move away from the plug, so both motion and sheet condition must be measured.
Verification
Clearance should be checked through the full stroke under operating conditions. Static alignment with a cold tool is not enough for large or heated tooling. Witness film, displacement measurement, or controlled low-speed cycling can reveal contact asymmetry.
The mechanical cause should be corrected before heater zoning is used to compensate. A recipe that relies on one hot side to offset a crooked plug will not remain stable across materials and production runs.