Vacuum timing determines where the sheet contacts first and how material is distributed before it freezes against the tool. Applied too early, vacuum can drag the sheet into uncontrolled contact, create webbing, or chill material before a plug completes its stroke. Applied too late, it allows sag, heat loss, or loss of forming pressure.
Evaluate the full sequence
The timing reference should be a confirmed machine event, not an assumed timer value. Tool closure, pressure-box sealing, plug position, sheet transfer, and valve response all contain mechanical delays. A command shown on the HMI may occur well before pressure changes at the mold.
High-speed pressure logging or video can reveal the actual relationship between motion and airflow. The sequence should then be adjusted to establish the intended first-contact pattern. In plug-assisted forming, vacuum often needs to begin in a controlled relationship to plug engagement rather than at one universal position.
Timing changes should be validated against wall thickness, detail, webbing, and cycle repeatability. A part that looks complete can still have an unacceptable thickness shift caused by a few tenths of a second in the wrong sequence.