Systems and methods are provided for mixing parts of a thermoset resin during impregnation of a composite preform. One embodiment is a method that includes positioning a composite preform at a forming tool, flowing a first part of the thermoset resin into a mixing chamber at the forming tool, flowing a second part of the thermoset resin that is chemically distinct from the first part of the thermoset resin into the mixing chamber, mixing the first part and the second part to form the thermoset resin within the mixing chamber, and infusing the thermoset resin from the mixing chamber into the preform.