A method comprising: by a 3-dimensional, 3D, core design engine of a computing system : identifying , in a computer-aided design, CAD, model , an under-core ply of a composite part and a core footprint on the under-core ply , the under-core ply and core footprint specified for an additive 3D core to be manufactured via additive manufacturing and to be inserted into the composite part; computing a bottom core surface of the additive 3D core from the under-core ply and core footprint by setting a shape of the bottom core surface as a shape of a portion of the under-core ply as outlined by the core footprint ; accessing core design parameters for the additive 3D core, the core design parameters comprising core thickness parameters and core shape parameters that define the additive 3D core; and constructing an additive 3D core design in the CAD model for the additive 3D core based on the computed bottom core surface and the core design parameters; and by a 3D core printing engine of the computing system : storing the additive 3D core design ; providing the additive 3D core design to printing hardware; and manufacturing by the printing hardware, via additive manufacturing, the additive 3D core with the additive 3D core design . by a 3-dimensional, 3D, core design engine of a computing system : identifying , in a computer-aided design, CAD, model , an under-core ply of a composite part and a core footprint on the under-core ply , the under-core ply and core footprint specified for an additive 3D core to be manufactured via additive manufacturing and to be inserted into the composite part; computing a bottom core surface of the additive 3D core from the under-core ply and core footprint by setting a shape of the bottom core surface as a shape of a portion of the under-core ply as outlined by the core footprint ; accessing core design parameters for the additive 3D core, the core design parameters comprising core thickness parameters and core shape parameters that define the additive 3D core; and constructing an additive 3D core design in the CAD model for the additive 3D core based on the computed bottom core surface and the core design parameters; and identifying , in a computer-aided design, CAD, model , an under-core ply of a composite part and a core footprint on the under-core ply , the under-core ply and core footprint specified for an additive 3D core to be manufactured via additive manufacturing and to be inserted into the composite part; computing a bottom core surface of the additive 3D core from the under-core ply and core footprint by setting a shape of the bottom core surface as a shape of a portion of the under-core ply as outlined by the core footprint ; accessing core design parameters for the additive 3D core, the core design parameters comprising core thickness parameters and core shape parameters that define the additive 3D core; and constructing an additive 3D core design in the CAD model for the additive 3D core based on the computed bottom core surface and the core design parameters; and by a 3D core printing engine of the computing system : storing the additive 3D core design ; providing the additive 3D core design to printing hardware; and manufacturing by the printing hardware, via additive manufacturing, the additive 3D core with the additive 3D core design . storing the additive 3D core design ; providing the additive 3D core design to printing hardware; and manufacturing by the printing hardware, via additive manufacturing, the additive 3D core with the additive 3D core design . <EOS>