A clamp frame can appear flat when unloaded and bend during heating, clamping, or forming. Large spans, worn supports, insufficient section stiffness, thermal gradients, and uneven actuator force can open local gaps or change the effective sheet boundary.
Deflection should be measured across the frame at operating temperature and representative load. Straightedge checks at room temperature are insufficient. A recurring pull-in or pressure leak that follows one span rather than one cylinder often indicates structural bending.
Supports, hinges, locking points, and frame sections should be restored or reinforced through an engineered modification. Adding local clamp pressure to a flexible frame can increase distortion. Any change must preserve heater clearance, motion safety, and uniform sheet contact.