Caul plate system for aircraft fabrication

A method for hardening a preform of fiber reinforced material, the method comprising:

• applying a preform to a mandrel;
• covering the preform with a caul plate;
• vacuum sealing the caul plate to the mandrel via a first circumferential seal in a clean room environment, the first circumferential seal disposed between the mandrel and the caul plate in a channel formed in the mandrel;
• inserting a bladder into a stringer preform;
• disposing the bladder and the stringer preform between the caul plate and the mandrel;
• two-stage indexing comprising indexing the caul plate to the mandrel to provide initial indexing and indexing an inflation port of the bladder to an opening of the caul plate to provide for fine indexing;
• pushing the caul plate toward the preform, the stringer preform, and the mandrel;
• hardening the preform and the stringer preform into a composite part while the caul plate is held against the preform;
• separating the caul plate from the composite part;
• cleaning the caul plate at a cleaning station outside of the clean room environment;
• and
• returning the caul plate to the clean room environment where it may be re-used with the mandrel for hardening of a second preform.