Investigation on urea-formaldehyde resin as an in-powder adhesive for the fabrication of Al2O3/borosilicate-glass composite parts by three dimensional printing (3DP)

Using adhesive to bond powdered material is the foundation of three dimensional printing (3DP), which necessitates the need for addressing problems with current 3DP adhesives, such as printhead blockage and complicated material preparation processes. To solve such problems, this paper introduces a novel in-powder adhesive of urea-formaldehyde (UF) resin, which can improve 3DP primarily via its high bonding strength, convenient material preparation and adhesive-free printing liquid. A self-developed 3DP machine tailored for this new adhesive, which features a low-cost commercial piezoelectric printhead, is also presented. A feasibility study was conducted with UF resin as the in-powder adhesive for 3DP fabrication of high-performance alumina/borosilicate-glass composites. Furthermore, the measurements taken throughout fabrication revealed that a double-smoothing (DS) layering method, capable of dispensing intact and thinner powder layers, resulted in better specimen properties. The Al2O3 green specimens obtained maximum tensile strength and flexural strength values of 9.5 MPa and 14.6 MPa, respectively. The green specimens were then sintered and infiltrated with borosilicate glass to form alumina/borosilicate-glass composites, which exhibited maximum values for tensile strength, flexural strength, compressive strength, Young's modulus, Vickers hardness and fracture toughness of 86.7 MPa, 200.7 MPa, 1503.4 MPa, 278.7 GPa, 14.1 GPa and 4.2 MPa m1/2, respectively. The composite also exhibited a low coefficient of thermal expansion (CTE) of 4.6 × 10−6 °C−1. For demonstrational purposes, such composites, as rapid tools and functional parts, were also printed to show the technological potential in engineering applications.