Induction heating cells with cauls over mandrels methods of using thereof
Disclosed herein are induction heating cells and methods of using these cells for processing. An induction heating cell may be used for processing (e.g., consolidating and/or curing a composite layup having a non-planar portion. The induction heating cell comprises a caul, configured to position over and conform to this non-planar portion. Furthermore, the cell comprises a mandrel, configured to position over the caul and force the caul again the surface of the feature. The CTE of the caul may be closer to the CTE of the composite layup than to the CTE of the mandrel. As such, the caul isolates the composite layup from the dimensional changes of the mandrel, driven by temperature fluctuations. At the same time, the caul may conform to the surface of the mandrel, which can be used to define the shape and transfer pressure to the non-planar portion.
1. A method comprising:
a step of positioning a composite layup over a die, wherein:
the composite layup comprises a planar portion and a non-planar portion, extending away from the planar portion in a direction away from the die, and
a step of positioning a caul over the non-planar portion of the composite layup, wherein:
the caul is configured to conform to a surface of the non-planar portion;
a step of positioning a mandrel over the caul, wherein:
the caul is disposed between the mandrel and the non-planar portion, and
a difference between a coefficient of thermal expansion (CTE) of the caul and a CTE of the composite layup is less than a difference between the CTE of the mandrel and the CTE of the caul;
a step of positioning a bladder over the mandrel and over the planar portion of the composite layup;
a step of heating the composite layup using an induction heater; and
a step of applying pressure using the bladder onto the mandrel and the planar portion of the composite layup.
2. The method according to claim 1 , wherein the step of heating the composite layup using the induction heater comprises a step of inductively heating the caul using a magnetic field generated by the induction heater.
3. The method according to claim 2 , wherein the caul directly interfaces the non-planar portion of the composite layup.
4. The method according to claim 1 , wherein the step of heating the composite layup using the induction heater comprising a step of inductively heating a susceptor of the induction heater using a magnetic field generated by the induction heater.
5. The method according to claim 4 , wherein the composite layup is disposed between the susceptor and the caul.
6. The method according to claim 5 , wherein the composite layup is at least partially permeable to the magnetic field generated by the induction heater.
7. The method according to claim 1 , wherein the step of heating the composite ayup and the step of applying pressure using the bladder overlap in time.
8. The method according to claim 1 , wherein:
the mandrel comprises thermal expansion slots,
the thermal expansion slots change widths during the step of heating the composite layup, and
the caul extends over at least one of the thermal expansion slots.
9. The method according to claim 8 , wherein the caul is a continuous sheet extending substantially an entire length of the mandrel and over all of the thermal expansion slots.
10. The method according to claim 1 , wherein the mandrel does not directly interface the composite layup.
11. The method according to claim 1 , wherein the mandrel comprises aluminum.
12. The according to claim 1 , wherein the caul is formed from an alloy comprising an iron.
13. The method according to claim 12 , wherein the alloy further comprises nickel.
14. The method according to claim 13 , wherein a concentration of nickel in the alloy is between about 30% atomic and 47% atomic.
15. The method according to claim 13 , wherein the alloy further comprises cobalt.
16. The method according to claim 15 , wherein:
a concentration of nickel in the alloy is between about 20% atomic and 40% atomic, and
a concentration of cobalt in the alloy is between about 10% atomic and 20% atomic.
17. The method according to claim 1 , wherein the caul has a thickness of between about 0.3 millimeters and 0.7 millimeter.
18. The method according to claim 1 , wherein the caul has a non-planar shape.
19. The method according to claim 1 , wherein the step of heating the composite layup and the step of applying the pressure using the bladder forms a composite part from the composite layup.
20. An induction heating cell for processing a composite layup comprising a planar portion and a non-planar portion, extending away from the planar portion, the induction heating cell comprising:
a die, configured to receive the composite layup;
an induction heater, configured to inductively heat the composite layup;
a caul, configured to position over and conform to the non-planar portion of the composite layup;
a mandrel, configured to position over the caul, wherein a difference between a coefficient of thermal expansion (CTE) of the caul and a CTE of the composite layup is less than a difference between the CTE of the mandrel and the CTE of the caul; and
a bladder, configured to position over the mandrel and the planar portion of the composite layup.