Caul plate system for aircraft fabrication
Methods and apparatus involved in the process of hardening a composite part are disclosed herein. The methods include applying a preform to a mandrel, covering the preform with a caul plate, sealing the caul plate to the mandrel, pushing the caul plate toward the preform and the mandrel and hardening the preform into a composite part while the caul plate is held against the preform. The apparatus include a mandrel, a caul plate which defines a surface of a preform and where the caul plate may include a rigid material and seals disposed between the mandrel and the caul plate. In an additional aspect, the apparatus may include a sealed chamber with a mandrel and a caul plate and a circumferential seal between the mandrel and the caul plate.
1. 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.
2. The method of claim 1 comprising:
evacuating air within a sealed chamber bound by the caul plate, the first circumferential seal, and the mandrel, to allow atmospheric pressure to push the caul plate towards the preform, the stringer preform, and the mandrel.
3. The method of claim 2 further comprising:
sealing an elastomeric flap to the mandrel, wherein the elastomeric flap extends from the caul plate and wherein the first circumferential seal is disposed between the flap and the sealed chamber.
4. The method of claim 2 further comprising:
inserting the bladder into the stringer preform prior to covering the preform with the caul plate.
5. The method of claim 4 further comprising:
sealing the caul plate to the bladder; and
inflating the bladder.
6. The method of claim 5 further comprising:
inflating the bladder by opening the bladder interior to atmospheric pressure when the sealed chamber is evacuated.
7. The method of claim 6 further comprising:
pressurizing and shaping the stringer preform with bladder inflation.
8. The method of claim 5 wherein:
sealing the caul plate to the bladder is performed by screwing a banjo bolt into the inflation port.
9. The method of claim 4 wherein:
the caul plate consolidates the stringer preform against the mandrel.
10. The method of claim 1 wherein indexing the caul plate to the mandrel comprises aligning an indexing feature of the caul plate with an indexing feature of the mandrel.
11. The method of claim 1 , further comprising:
transporting the caul plate with a strongback and wherein indexing the caul plate to the mandrel comprises aligning an indexing feature at the strongback with an indexing feature at the mandrel.
12. The method of claim 1 wherein vacuum sealing the caul plate to the mandrel further comprises:
vacuum sealing the caul plate to the mandrel via a second circumferential seal disposed entirely within the first circumferential seal.
13. The method of claim 12 wherein vacuum sealing the caul plate to the mandrel further comprises:
vacuum sealing the caul plate to the mandrel via a third circumferential seal disposed entirely within the second circumferential seal.
14. The method of claim 13 further comprising:
subdividing a volume between the first circumferential seal and the second circumferential seal into quadrants.
15. The method of claim 13 further comprising:
slipping the mandrel relative to caul plate at one of the first, second, or third circumferential seals.
16. The method of claim 1 wherein:
the caul plate forms an Outer Mold Line (OML) and the mandrel forms an Inner Mold Line (IML) for a section of fuselage.
17. The method of claim 16 wherein:
the section of fuselage is a half barrel section.
18. The method of claim 16 wherein:
the section of fuselage is a full barrel section.
19. The method of claim 1 wherein:
the caul plate forms an Inner Mold Line (IML) and the mandrel forms an Outer Mold Line (OML) for a section of fuselage.
20. The method of claim 1 wherein:
the mandrel further comprises a vacuum system that controllably applies a vacuum via vacuum holes at the mandrel.
21. The method of claim 1 wherein:
the caul plate further comprises a vacuum system that controllably applies a vacuum via vacuum holes at the caul plate.
22. The method of claim 1 wherein:
the inflation port of the bladder is fastened through the opening in the caul plate.
23. The method of claim 1 wherein:
the channel formed in the mandrel has a half-circle cross-section.
24. The method of claim 1 wherein:
the caul plate forms a half barrel shape of half barrel sections for a section of fuselage.