Methods for making composite parts from stacked partially cured sublaminate units
A method of forming a composite article. One step involves applying adhesive on surfaces of a plurality of sublaminate units, each ply of each sublaminate unit comprising fibers impregnated with resin which has been initially cured to 30% to 50% of full cure. The initially cured sublaminate units are then arranged in a stack, which stack is pressed against a surface of a forming tool. While pressure is being applied, the stack is heated to an intermediate temperature above a glass transition temperature of the resin for a time interval sufficient to intermediately cure the resin to 50% to 70% of full cure to form a composite laminate having a contour defined by the surface of the forming tool. Then the resin is finally cured at a final temperature higher than the intermediate temperature.
1. A method of forming a composite article, comprising:
(a) applying adhesive on surfaces of a plurality of sublaminate units, each sublaminate unit comprising a multiplicity of plies, each ply comprising fibers impregnated with resin which has been initially cured to an initial cure stage of 30% to 50% of full cure;
(b) arranging the plurality of sublaminate units in a stack;
(c) pressing the stack of sublaminate units against a surface of a forming tool;
(d) heating the stack of sublaminate units to an intermediate temperature above a glass transition temperature of the resin for a time interval sufficient to intermediately cure the resin to an intermediate cure stage of 50% to 70% of full cure while the stack is in contact with the surface of the forming tool to form a composite laminate having a contour defined by the surface of the forming tool; and
(e) finally curing the resin in the composite laminate at a final temperature higher than the intermediate temperature to a final cure stage,
wherein steps (c) and (d) are performed concurrently during a time interval,
further comprising drilling an index hole in each sublaminate unit of the plurality of sublaminate units prior to step (a), wherein step (b) comprises passing a pin through the index hole in each sublaminate unit of the plurality of sublaminate units.
2. The method as recited in claim 1 , wherein step (e) is performed while the composite laminate remains on the forming tool.
3. The method as recited in claim 1 , further comprising:
removing the composite laminate from the forming tool; and
placing the composite laminate inside an oven,
wherein step (e) is performed while the composite laminate is inside the oven.
4. The method as recited in claim 1 , further comprising trimming at least one sublaminate unit of the plurality of sublaminate units prior to step (a).
5. The method as recited in claim 1 , further comprising preparing a surface of at least one sublaminate unit of the plurality of sublaminate units prior to step (a).
6. The method as recited in claim 5 , wherein preparing a surface comprises one of the following processes: sanding, grit blasting, peel-ply removal, or plasma treatment.
7. The method as recited in claim 1 , wherein the pins are made of nylon or polytetrafluoroethylene, further comprising removing the pins from the composite article after step (e).
8. The method as recited in claim 1 , 1 , further comprising enveloping the stack of sublaminate units in a vacuum bag prior to steps (c) and (d).
9. The method as recited in claim 1 , wherein each sublaminate unit of the plurality of sublaminate units is balanced in a sense that for every ply having a +θ ply angle, there is another ply having a −θ ply angle somewhere in the sublaminate unit.
10. The method as recited in claim 1 , wherein each sublaminate unit of the plurality of sublaminate units is symmetric.
11. The method as recited in claim 1 , wherein a first sublaminate unit of the plurality of sublaminate units comprises plies having respective ply angles in accordance with a first configuration, and a second sublaminate unit of the plurality of sublaminate units comprises plies having respective ply angles in accordance with a second configuration different than the first configuration.
12. A method of forming a composite article, comprising:
(a) applying adhesive on surfaces of a plurality of sublaminate units, each sublaminate unit comprising a multiplicity of plies, each ply comprising fibers impregnated with resin which has been initially cured to an initial cure stage of 30% to 50% of full cure;
(b) arranging the plurality of sublaminate units in a stack;
(c) pressing the stack of sublaminate units against a surface of a forming tool;
(d) heating the stack of sublaminate units to an intermediate temperature above a glass transition temperature of the resin for a time interval sufficient to intermediately cure the resin to an intermediate cure stage of 50% to 70% of full cure while the stack is in contact with the surface of the forming tool to form a composite laminate having a contour defined by the surface of the forming tool; and
(e) finally curing the resin in the composite laminate at a final temperature higher than the intermediate temperature to a final cure stage,
wherein steps (c) and (d) are performed concurrently during a time interval,
further comprising:
applying adhesive on a stiffener comprising a multiplicity of plies, each ply comprising fibers impregnated with resin which has been initially cured to an initial cure stage of 30% to 50% of full cure; and
arranging the stiffener on top of the stack of sublaminate units.
13. The method as recited in claim 12 , wherein the sublaminate units are planar and the stiffener is straight.
14. A method of forming a composite article, comprising:
(a) drilling an index hole in each sublaminate unit of a plurality of sublaminate units;
(b) arranging a plurality of sublaminate units in a stack with uncured adhesive between adjacent sublaminate units, each sublaminate unit comprising a multiplicity of plies, each ply comprising fibers impregnated with resin which has been initially cured to an initial cure stage of 30% to 50% of full cure, wherein the arranging comprises passing a pin through the index hole in each sublaminate unit of the plurality of sublaminate units;
(c) heating the stack of sublaminate units to an intermediate temperature above a glass transition temperature of the resin for a time interval sufficient to intermediately cure the resin to an intermediate cure stage of 50% to 70% of full cure;
(d) forming the heated stack of sublaminate units into a composite laminate having a surface defined by a surface of a forming tool; and
(e) finally curing the resin in the composite laminate at a final temperature higher than the intermediate temperature to a final cure stage.
15. The method as recited in claim 14 , wherein the final cure stage is greater than 90% of full cure.
16. The method as recited in claim 14 , wherein the pins are made of nylon or polytetrafluoroethylene.
17. The method as recited in claim 14 , further comprising removing the pins from the composite article after step (e).
18. The method as recited in claim 14 , further comprising:
applying adhesive on a stiffener comprising a multiplicity of plies, each ply comprising fibers impregnated with resin which has been initially cured to an initial cure stage of 30% to 50% of full cure; and
arranging the stiffener on top of the stack of sublaminate units.
19. The method as recited in claim 18 , wherein the sublaminate units are planar and the stiffener is straight.
20. The method as recited in claim 14 , wherein steps (c) and (d) are performed concurrently during a time interval.