Method and Apparatus for Fabricating Variable Gauge, Contoured Composite Stiffeners

A method of fabricating a contoured composite blade stiffener, comprising:

• placing a substantially flat composite charge on a die having a die cavity;
• press forming the flat charge against the die, creating a formed charge, including using a punch to press form the charge into a hat within the die cavity;
• and
• contouring the formed charge by bending the die while the formed charge is in the die.

A method of forming a variable gauge contoured composite blade stringer, comprising:

• providing a substantially flat, multi-ply composite prepreg charge;
• placing a first filler on the charge;
• placing the charge on a die having two opposite die portions and a die cavity between the two opposite die portions;
• heating the charge to a forming temperature;
• using a punch to drive a first portion of the charge and the first filler into the die cavity to form a web portion into a hat;
• using a first plate to compress second portions of the charge against the die to form flange portions of the stringer as the hat is being formed by the punch;
• applying pressure to the web portion after the punch is fully engaged
• releasing the pressure to the web portion and retracting the punch from the die cavity;
• loading a second plate over the flange portions of the stringer;
• holding the flange portions against the die by using the punch to apply pressure to the second plate;
• using a pair of pressurized hoses to respectively apply lateral pressure to the die portions;
• using the die portions, laterally compress the hat between the die portions, creating a formed charge;
• contouring the formed charge by contouring each of the punch and the die along their respective lengths while the web portion is under pressure;
• removing the second plate
• placing a second composite filler in a groove between the flange portions;
• applying an adhesive and a fabric layer over the second filler;
• reloading the second plate over the flange portions, overlying the second filler, the adhesive and the fabric layer;
• using the punch to apply pressure to the second plate and compress the second filler, the adhesive, and the fabric layer;
• retracting the punch after the formed and contoured blade has reached room temperature, making a formed stringer;
• removing the second plate;
• moving the die portions away from each other;
• and
• removing the formed stringer from the die.

An apparatus for forming a composite charge into a contoured blade stringer, comprising:

• an elongate punch flexible along a respective first length;
• an elongate die flexible along a respective second length against which a substantially flat composite charge may be press formed by the punch;
• a first flexible plate backing the punch and a second flexible plate backing the die;
• and
• a contour changing mechanism coupled with the first flexible plate and the second flexible plate for changing a local contour of the punch and the die.

An apparatus for forming a variable gauge contoured composite blade stringer, comprising:

• a first elongate flexible plate spaced apart from a second elongate flexible plate;
• a die mounted on a surface of the first plate facing the second plate, the die including first and second die portions having a die cavity therebetween, each of the first and second die portions being segmented into a plurality of independently movable die blocks slidable on the first plate, the die further including flexible straps coupling the die blocks together;
• a pair of brackets secured to the first plate on opposite sides of the die for laterally retaining the die blocks;
• a pair of hoses respectively between the die blocks and the brackets configured to be coupled with a source of pressurized air for applying a lateral force on the die portions;
• a first tapered shim between each of the die portions and the first plate for transmitting constant force to areas of a charge having thickness variations as the charge is being formed;
• a substantially flat, elongate punch mounted on and extending substantially perpendicular to the second plate for forming a portion of the charge into the die cavity, the punch being segmented into a plurality of independently movable punch portions;
• a second tapered shim on each side of the punch and secured to the second plate for transmitting constant force to areas of the charge having thickness variations as the charge is being formed;
• and
• a plurality of actuators coupled with the first plate and the second plate for forming the punch and the die into a desired contour by bending the first plate and the second plate.