Tool and method for forming contoured composite stringers having reduced wrinkling

A tool for forming a composite charge into a contoured stringer having a desired cross sectional shape, comprising:

• a punch configured to form the composite charge into a formed stringer having the desired cross sectional shape, and to contour the formed stringer along a length of the formed stringer,
• the punch having a first plurality of openings therein, each of the plurality of first openings having a height extending through an entire height of the punch,
• the punch having a second plurality of openings therein into which the composite charge may strain as the formed stringer is being contoured along its length, and
• wherein each of the second plurality of openings having a height less than an entire height of the punch and configured to remain at least partially open during forming the composite charge into the contoured stringer, wherein there is a solid section in the punch immediately above each of the openings that prevents each of the openings from closing completely during the forming.

A tool for forming a composite charge into a contoured composite stringer, comprising:

• a flexible top plate;
• and
• a tool body connected to the flexible top plate,
• the tool body having a plurality of openings extending through an entire height of the tool body, the plurality of openings configured to provide the tool body with flexibility during forming of the contoured composite stringer from the composite charge, and
• the tool body having a plurality of grooves extending through less than the entire height of the tool body, the plurality of grooves configured to remain at least partially open during forming of the contoured composite stringer, wherein there is a solid section in the tool body immediately above each of the plurality of grooves that prevents each of the grooves from closing completely during the forming.