Interlayer strengthening method for continuous fiber additive manufacturing based on pressure injected Z-pin-like structures

An interlayer strengthening method for continuous fiber additive manufacturing based on pressure injected Z-pin-like structures, wherein a continuous fiber print head and a thermosetting resin extrusion head are configured for composite printing forming, wherein the continuous fiber print head prints a continuous-fiber-reinforced grid frame in an order of print layers;

• the thermosetting resin extrusion head fills grid holes in the corresponding print layers with a thermosetting resin through pressure injection;
• the grid holes in an overall continuous fiber grid frame are arranged and combined to form interlayer intermittent through spaces in a Z direction, the thermosetting resin filled by extrusion forms continuous longitudinally strengthened Z-pin-like structures across slice layers in the interlayer intermittent through spaces, and the thermosetting resin penetrates and fills pores between the print layers of the overall continuous fiber grid frame under a control of extrusion pressure and without introducing auxiliary energy fields, ultimately achieving an effect of interlayer strengthening for the continuous fiber additive manufacturing, wherein the interlayer strengthening method comprises the following steps:
• step 1:
• setting a thickness t of each of the print layers, a size a×b of each of the grid holes of the overall continuous fiber grid frame, types of the Z-pin-like structures, a base extrusion pressure value p corresponding to a parameter group (t, a*b), and extrusion pressure coefficient groups (k2, k3) corresponding to different types of the Z-pin-like structures and depths of penetration;
• step 2:
• segmenting a target model based on the thickness t of each of the print layers, the size a×b of each of the grid holes of the overall continuous fiber grid frame and the types of the Z-pin-like structures into a continuous fiber frame structure space area model and a Z-pin-like structure space area model, wherein the continuous fiber frame structure space area model and the Z-pin-like structure space area model share a space coordinate system and have a same definition sequence of slice layers;
• step 3:
• for the continuous fiber frame structure space area model, generating a path of the overall continuous fiber grid frame of each horizontal slice layer, to obtain print path information {GF} of each horizontal slice from the continuous fiber print head, wherein ith-layer information is denoted as {GFi};
• step 4:
• for the Z-pin-like structure space area model, processing horizontal slices comprising marking fill areas corresponding to each of the Z-pin-like structures in each of the horizontal slices, to obtain extrusion information {GM} of relevant horizontal slice layers from the thermosetting resin extrusion head by combining the base extrusion pressure value p and the extrusion pressure coefficient groups (k2, k3) of the different types and depths of the Z-pin-like structures, wherein the extrusion information comprises extrusion positions and corresponding extrusion pressure for the pressure injection in each slice layer, and the ith-layer information is denoted as {GMi};
• step 5:
• combining print information from the continuous fiber print head and the extrusion information from the thermosetting resin extrusion head in the relevant horizontal slice layers in an order of the horizontal slice layers from bottom to top, and outputting the print information from the continuous fiber print head and the extrusion information from the thermosetting resin extrusion head {G} corresponding to each horizontal slice print layer, wherein the ith-layer information is denoted as {Gi};
• step 5a:
• during the pressure injection filling of thermosetting resin into grid holes, preforming a mandatory nozzle-wipe protocol after each filling operation, wherein the nozzle is moved along a zig-zag traversal path that avoids crossing unfilled holes, such that any residual resin is wiped against the infill line or the edge of the void, thereby preventing stringing and blockage of the nozzle and ensuring clean deposition for subsequent filling operations;
• and
• step 6:
• performing collaborative printing forming through the continuous fiber print head and the thermosetting resin extrusion head based on respective operation information, and then letting the target model stand for curing.