High-pressure in situ interlayer strengthening process for polyetheretherketone material extrusion

The material extrusion (ME) process enables the integrated fabrication of high-performance polymers like polyetheretherketone (PEEK), driving its use in demanding environments, especially aerospace. However, the layer-by-layer stacking introduces challenges, particularly weak interlayer bonding, which is exacerbated for high-crystalline polymer PEEK prone to warping during processing. This results in anisotropic mechanical properties, limiting PEEK ME's application in high-end manufacturing. This work proposes a high-pressure in situ interlayer strengthening process for PEEK ME. A high-thermal-conductivity front-widening nozzle is designed to enhance melt flow properties and material molecular activity without additional hardware. By progressively optimising stacking-related core process parameters, interlayer pressure and lateral melt flow are improved markedly, facilitating material intermixing at interfaces and mitigating pore defects. The results indicate that the maximum interlayer pressure was enhanced by 152.6% to 96209 Pa compared with the conventional process when doubling the extrusion flow rate. Increased extrusion flow rate enabled dense filling with 0.13% porosity. The interlayer interfacial strength went up by 159.1% to 62.84 MPa. Through dual optimisation of interfacial bonding and compactness, overall interlayer bonding strength improved by 181.4%, reaching 58.65 MPa. Moreover, surface roughness was reduced to within 15.97 μm under high-pressure conditions, thus concurrently improving interlayer mechanical properties and surface-forming quality.