Method and systems using independently controlled pallets for fabricating composite stringers
Described herein are methods and systems for manufacturing composite stringers using independently movable pallets with independent vacuum controls. Specifically, a stringer forming system comprises a base plate and a plurality of sets of pallets (e.g., two or more sets of pallets), slidably coupled to the base plate and forming an adjustable cavity. Each pallet comprises a primary vacuum zone, fluidly connected to a separate vacuum port. The system allows for independent application of a reduced pressure to the primary vacuum zone of each pallet. For example, a reduced pressure is applied only to pallets that are already covered with a composite layup and to pallets that are being covered. Any pallets that are exposed are kept at an ambient pressure and decoupled from a vacuum source, thereby reducing the vacuum leakage through the overall system. As the composite layup is being formed over new pallets, these new pallets are subjected to the reduced pressure.
1 . A pallet assembly configured to form a stringer, wherein the pallet assembly comprises:
a first pallet; and
a second pallet, wherein each of the first pallet and the second pallet comprises:
a plurality of interlocking protrusions and a plurality of interlocking openings such that the plurality of interlocking protrusions of the first pallet is configured to slide into the plurality of interlocking openings of the second pallet and such that the plurality of interlocking protrusions of the second pallet is configured to slide into the plurality of interlocking openings of the first pallet thereby forming an adjustable cavity;
a plurality of roller bearings configured to allow each of the first pallet and the second pallet to slide relative to a base plate, along a direction parallel to a processing surface;
a processing surface and a primary vacuum zone on the processing surface; and
a fluid connection to a primary vacuum port, which is independently controlled.
2 . The pallet assembly of claim 1 , wherein each of the first pallet and the second pallet comprises an additional primary vacuum zone, on the processing surface and fluidly connected to an additional primary vacuum port, which is independently controlled.
3 . The pallet assembly of claim 1 , wherein the primary vacuum zone is defined by a plurality of vacuum channels, forming a grid and extending through the processing surface.
4 . The pallet assembly of claim 1 , wherein each of the first pallet and the second pallet comprises an edge vacuum zone, fluidly connected to an edge vacuum port.
5 . The pallet assembly of claim 1 , wherein the plurality of interlocking protrusions forms a side surface of the adjustable cavity and are separated from each other by the plurality of interlocking openings.
6 . The pallet assembly of claim 5 , wherein the side surface of the adjustable cavity extends to, and forms an obtuse angle with, the processing surface.
7 . The pallet assembly of claim 1 , wherein a depth and a cross-section of the adjustable cavity is determined by relative positions of each first and second pallet.
8 . The pallet assembly of claim 4 , wherein the primary vacuum zone is positioned between the edge vacuum zone and the adjustable cavity each.
9 . The pallet assembly of claim 1 , wherein the first and second pallets are offset relative to each other along a direction extending along the adjustable cavity.
10 . The pallet assembly of claim 1 , wherein the primary vacuum port of each first and second pallet is coupled to a same vacuum source.
11 . A method of forming a stringer using a pallet assembly, the method comprising:
interlocking a first plurality of pallets and a second plurality of pallets on a base plate thereby forming an adjustable cavity in between the first plurality of pallets and the second plurality of pallets, wherein the first plurality of pallets and the second plurality of pallets comprise a first interlockable pallet pair and a second interlockable pallet pair, offset relative to the first interlockable pallet pair along the adjustable cavity, and wherein each pallet of the first plurality of pallets and of the second plurality of pallets comprises:
a processing surface and a primary vacuum zone on the processing surface; and
a plurality of roller bearings allowing sliding each of the first plurality of pallets and the second plurality of pallets relative to a base plate, along a direction parallel to the processing surface;
forming a composite layup over the processing surface of each pallet of the first interlockable pallet pair while the primary vacuum zone of each pallet of the first interlockable pallet pair is subjected to a reduced pressure, wherein, while the primary vacuum zone of each pallet of the first interlockable pallet pair is subjected to a reduced pressure, the primary vacuum zone of each pallet of the second interlockable pallet pair is at an ambient pressure and the processing surface of each pallet of the second interlockable pallet pair is free from the composite layup; and
forming the composite layup over the processing surface of each pallet of the second interlockable pallet pair while the primary vacuum zone of each pallet of the second interlockable pallet pair is subjected to the reduced pressure.
12 . The method of claim 11 , wherein, while the primary vacuum zone of each pallet of the second interlockable pallet pair is subjected to the reduced pressure, the primary vacuum zone of each pallet of the first interlockable pallet pair remains at the reduced pressure.
13 . The method of claim 11 , further comprising:
sliding the first plurality of pallets and the second plurality of pallets relative to each on the base plate thereby increasing a depth and a cross-section of the adjustable cavity; and
while sliding the first plurality of pallets and the second plurality of pallets relative to each, protruding a portion of the composite layup into the adjustable cavity thereby forming a hat portion of the stringer.
14 . The method of claim 11 , further comprising, prior to forming the composite layup over the processing surface of each pallet of the first interlockable pallet pair, connecting the primary vacuum zone of each pallet of the first interlockable pallet pair to a corresponding vacuum source using a corresponding one of a plurality of actuators.
15 . The method of claim 14 , wherein connecting the primary vacuum zone of each pallet of the first interlockable pallet pair to the corresponding vacuum source comprises rotating an extendable arm of the corresponding one of the plurality of actuators relative to a shell of the corresponding one of a plurality of actuators.
16 . The method of claim 14 , further comprising sliding the first plurality of pallets and the second plurality of pallets relative to each other using the plurality of actuators.
17 . The method of claim 16 , wherein the first plurality of pallets and the second plurality of pallets are slid relative to each while the primary vacuum zone of each pallet of the second interlockable pallet pair is continuously subjected to a reduced pressure.
18 . The method of claim 14 , wherein:
the base plate comprises a plurality of track openings;
each pallet of the first plurality of pallets and the second plurality of pallets comprises an engaging arm, protruding into one of the plurality of track openings allowing each pallet to slide relative to the base plate, along a direction parallel to the processing surface; and
preventing each pallet to move away from the base plate in a direction perpendicular to the processing surface.
19 . The method of claim 14 , wherein the base plate comprises a plurality of braking mechanisms, each comprising a friction pad, movable in a direction perpendicular to the processing surface and configured to contact one pallet of the first plurality of pallets or the second plurality of pallets to restrict sliding of the one pallet.
20 . The method of claim 19 , wherein each of the plurality of braking mechanisms further comprises a spring, a push pin, and a translation device, and further comprising;
the spring urging the friction pad against the one pallet of the first plurality of pallets or the second plurality of pallets;
moving the push pin in a direction parallel to the processing surface; and
retracting, using the translation device, the friction pad away from the one pallet of the first plurality of pallets or the second plurality of pallets and and compressing the spring in response to the push pin moving in the direction parallel to the processing surface and engaging the translation device.