Composite manufacturing method

1. A method of manufacturing a panel, the panel comprising a composite skin and at least one composite stiffener, the method comprising:

forming stiffener portions on each of first and second mandrels;

forming said stiffener by locating said stiffener portions adjacent one another and positioning said first and second mandrels on opposite sides of said stiffener;

transporting said stiffener and said mandrels to a joining station wherein said mandrels support the weight of said stiffener during the transporting step;

joining said stiffener to said skin at the joining station by the steps of laying said skin onto the stiffener at the joining station, the mandrels supporting the weight of the stiffener during the laying step;

positioning first and second compaction tools on opposite sides of the skin; and

compacting the skin between the first and second compaction tools by moving one or both of the compaction tools,

wherein the movement of at least one of the compaction tools causes the first and second mandrels to move towards the stiffener along inclined paths so as to compact the stiffener between the mandrels.

2. The method of claim 1 wherein the mandrels slide against inclined surfaces of one of the compaction tools as they move towards the stiffener.

3. The method of claim 2 wherein the one of the compaction tools has a channel with a base, and first and second walls which are both inclined outwardly from the base; and wherein the mandrels slide against the first and second walls as they move towards the stiffener.

4. The method of claim 1 wherein the panel is an aircraft part.

5. The method of manufacturing a panel according to claim 1 , wherein said stiffener portions are formed on each of said mandrels by the steps of:

placing a stack of plies on each of said mandrels whereby the stack is locally compressed at a seed zone where it engages the mandrel and droops under the action of gravity on two opposite sides of the seed zone, wherein the stack comprises a lower ply and an upper ply, and wherein the lower ply droops more than the upper ply giving a gradually increasing spacing between the plies on the two opposite side of the seed zone; and

deforming the stack of plies to cause the plies to be molded against the mandrel on the two opposite sides of the seed zone, with slippage occurring between the plies as they are molded against the mandrel.

6. The method of claim 5 wherein each mandrel is locally curved where it engages the composite laminate.

7. The method of claim 5 wherein the each mandrel has inclined faces on the two opposite sides of the seed zone.

8. The method of claim 5 , wherein the composite panel is an aircraft part.