Method for preparing a composite product

A method for preparing a composite product, the method comprising:

• forming a core structure having a plurality of layers, each layer being built by an additive manufacturing process;
• wherein the core structure has a shell substantially enclosing an internal chamber of the core structure, wherein the shell is fluid-impermeable, and wherein the outer surface of the shell has a predefined shape, and
• wherein the core structure comprises a plurality of bridging elements arranged for bridging the internal chamber, wherein the bridging elements are arranged inside the internal chamber to connect a part of the shell at one end of the bridging element to another part of the shell at another end of the bridging element;
• introducing a fluid into the chamber of the core structure;
• arranging the core structure and reinforcement fibers in a mould, wherein the mould is arranged to accommodate the core structure including the reinforcement fibers, and wherein the reinforcement fibers and the outer surface of the shell are arranged in contact with each other;
• providing the reinforcement fibers and a resin on the outer surface of the shell of the core structure;
• and
• solidifying the resin to form the composite product inside the mould at a moulding pressure Pm, while controlling the fluid pressure PF of the fluid in the core structure, wherein the core structure comprises a number of internal channels arranged within the core shell for communicating an injection fluid or a vacuum pressure to the outer surface of the shell, and wherein the core structure comprises at least one inlet projecting outside the core shell, wherein the at least one inlet is arranged for connecting the internal chamber and/or the number of internal channels to a fluid pressure device or to a resin injection device.