Pressure forming depends on a sealed volume above the sheet. A damaged gasket, distorted frame, contamination, uneven closure, or inadequate seal compression allows air to escape as pressure rises. The part may lose detail near the leak or form asymmetrically across the tool.
Leak location can be identified by pressure-decay testing at a controlled low pressure, acoustic inspection, or an approved leak-detection method compatible with the machine and material. Seal compression should be checked around the full perimeter at operating temperature because frames and platens can distort under load.
Gaskets must match the temperature, pressure, surface finish, and repeated compression of the process. Increasing regulator pressure to overcome leakage increases air consumption and loading without restoring uniform pressure at the sheet. The sealing surface, alignment, and closure force should be corrected together.